Progressive Wear Divergence Beyond 10 Years in Ceramic- vs. Metal-on-Polyethylene Bearings: The 25- Year Impact of Zirconia Degradation in Total Hip Arthroplasty

Progressive Wear Divergence Beyond 10 Years in Ceramic- vs. Metal-on-Polyethylene Bearings: The 25- Year Impact of Zirconia Degradation in Total Hip Arthroplasty | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Progressive Wear Divergence Beyond 10 Years in Ceramic- vs. Metal-on-Polyethylene Bearings: The 25- Year Impact of Zirconia Degradation in Total Hip Arthroplasty Tsunehito Ishida, Yasuhito Takahashi, Toshiyuki Tateiwa, Toshinori Masaoka, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8152731/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Jan, 2026 Read the published version in Journal of Orthopaedic Surgery and Research → Version 1 posted 14 You are reading this latest preprint version Abstract Background This study aimed to compare the long-term implant survivorship and polyethylene wear in total hip arthroplasty (THA) using ceramic-on-polyethylene (CoP) bearings with zirconia femoral heads versus metal-on-polyethylene (MoP) bearings with cobalt-chromium heads. A secondary objective was to assess the in vivo impact of zirconia low-temperature degradation (LTD) on polyethylene wear. Methods Sixty-two hips were assigned to two demographically matched cohorts receiving crosslinked polyethylene liners paired with either 28-mm zirconia or cobalt-chromium heads. All patients received the same implant design and were followed for a minimum of 20 years. Implant survivorship and linear head penetration were evaluated over a 25-year period. A zirconia head retrieved after 25 years was analyzed via Raman spectroscopy to investigate phase transformation and residual stress. Results During the first 10 years post-THA, no significant differences were observed in cumulative polyethylene wear or linear wear rates between the MoP and CoP groups. However, beyond 10 years, these groups demonstrated differing wear patterns, with wear tending to increase in the CoP group and decrease in the MoP group. Between 10 and 25 years, the wear rate in the CoP group was approximately 2.4 times higher than that in the MoP group. Analysis of the retrieved zirconia head revealed extensive monoclinic phase transformation (92.3%), high compressive residual stress (–1.9 GPa), and notable grain uplift, correlating with an elevated wear rate of 0.212 mm/year during the second decade. Conclusions MoP and CoP bearings demonstrated similar polyethylene wear characteristics during the first decade after THA. However, a marked divergence emerged in the second decade, with significantly higher wear rates observed in the CoP group, likely attributable to the accelerated progression of zirconia LTD. These findings highlight the long-term implications of ceramic degradation and emphasize the need for careful evaluation of zirconia-based components in THA regarding their durability over time. Total hip arthroplasty Ceramic-on-polyethylene Metal-on-polyethylene Polyethylene Wear Zirconia low-temperature degradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Ultra-high molecular weight polyethylene (UHMWPE, hereafter referred to as polyethylene) wear debris is a well-established cause of periprosthetic osteolysis and implant loosening in total hip arthroplasty (THA) [ 1 , 2 ]. In addition to submicron- and micron-sized particles, the generation of large polyethylene wear particles (> 100 µm) has been implicated in the formation of pseudotumors, which can result in pain, soft tissue damage, and ultimately, the need for revision surgery [ 3 , 4 ]. Consequently, long-term polyethylene wear remains a key factor limiting the survivorship of THA implants. The introduction of crosslinked polyethylene has substantially reduced wear rates and the incidence of osteolysis, thereby improving long-term clinical outcomes [ 5 , 6 ]. Nontheless, polyethylene wear is influenced not only by the properties of the liner but also by other factors, including the material and diameter of the femoral head. Zirconia ceramic heads were developed as an alternative to alumina ceramics, offering superior fracture toughness and mechanical strength [ 7 , 8 ]. Owing to their low surface roughness, zirconia heads have been reported in some studies to generate less polyethylene wear than metal heads [ 9 – 11 ]. Despite these advantages, concerns remain regarding the long-term phase stability of zirconia. Zirconia ceramics are known to exist in a metastable tetragonal phase and may undergo low-temperature degradation (LTD), characterized by a tetragonal-to-monoclinic transformation induced by the combined effects of the aqueous biological environment and mechanical stress (e.g., frictional wear, weight-bearing, and impingement) [ 7 , 8 ]. This transformation is associated with volume expansion, increased surface roughness, and the development of residual stresses, potentially accelerating polyethylene wear and increasing the risk of microcracking or catastrophic head fracture [ 7 , 12 – 14 ]. Although several mid-term studies with follow-up periods of up to 10 years have suggested that LTD-related surface changes exert minimal clinical influence on polyethylene wear [ 9 – 11 ], the long-term in vivo tribological behavior of zirconia femoral heads beyond 20 years remains insufficiently understood. Therefore, the objectives of this study were twofold: (1) to compare long-term implant survivorship and polyethylene wear in patients undergoing ceramic-on-polyethylene (CoP) THA using zirconia femoral heads and metal-on-polyethylene (MoP) THA using the same implant design, with a minimum follow-up of 20 years; and (2) to evaluate the potential long-term effects of zirconia LTD on polyethylene wear in vivo. The strengths of this study include its extended follow-up period, the homogeneity of implant size and design, the consistency of surgical technique, and the use of the same cross-linked polyethylene liner in both groups. These factors permit a more isolated assessment of the influence of femoral head material on wear and implant survivorship. In addition, detailed analysis of a zirconia head retrieved after 25 years in vivo provides supplemental insight into long-term surface alterations associated with LTD. To our knowledge, this represents the first study to report over 20 years of comparative clinical and radiographic outcomes of THA using zirconia and metal heads within the same implant system. Materials and methods Patients This study was approved by our institutional review board. We retrospectively reviewed the medical records of 92 patients (108 hips) who underwent cementless THA using either MoP or CoP bearing surfaces at our institution between April 1997 and December 2003 (Fig. 1 ). The femoral head material was randomly selected by the operating surgeons, and all heads were 28 mm in diameter. Of these, 10 patients (12 hips) died from causes unrelated to THA, and 28 patients (34 hips) had incomplete follow-up data beyond 20 years postoperatively. The remaining 54 patients (62 hips; 59%) were included in the final analysis, each with a minimum follow-up of 20 years. The MoP group comprised 31 hips in 26 patients (28 hips in 23 women and 3 hips in 3 men), with a mean (± standard deviation, SD) age at primary THA of 55.9 ± 8.4 years. The CoP group consisted of 31 hips in 28 patients (26 hips in 23 women and 5 hips in 5 men), with a mean age at surgery of 55.1 ± 6.6 years. The mean follow-up periods were 22.3 ± 1.8 years for the MoP group and 24.2 ± 2.4 years for the CoP group. Detailed patient demographics and clinical characteristics are summarized in Table 1 . Table 1 Baseline demographics for the patient groups implanted either with MoP or CoP bearings Variable MoP CoP P-v alue Number of THAs/ patients 31/ 26 31/ 28 Age at THA (year) † 55.9 ± 8.4 55.1 ± 6.6 0.698 Gender (female: male) 28: 3 26: 5 0.707 Diagnosis (OA: ION: RA) 29: 2: 0 28: 2: 1 0.601 BMI (kg/m 2 ) † 22.9 ± 3.4 23.6 ± 3.3 0.412 Cup outer diameter (mm) † 51.5 ± 2.7 50.5 ± 2.0 0.141 Liner thickness (mm) † 7.1 ± 1.5 6.5 ± 1.1 0.081 Cup inclination (°) † 44.3 ± 4.2 43.0 ± 5.4 0.333 Cup anteversion (°) † 15.2 ± 8.0 16.4 ± 8.7 0.586 Preoperative HHS (points) † 49.6 ± 2.2 47.4 ± 4.3 0.378 Postoperative HHS (points) † 88.6 ± 5.8 85.4 ± 6.7 0.479 Incidence of acetabular osteolysis 4 (13%) 11 (35%) 0.073 Incidence of femoral osteolysis 5 (16%) 10 (32%) 0.235 Follow-up duration (years) † 22.3 ± 1.8 24.2 ± 2.4 MoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene; THA, total hip arthroplasty; OA, osteoarthritis; ION, idiopathic osteonecrosis of the femoral head; RA, rheumatoid arthritis; BMI, body mass index; HHS, Harris hip score. † Values are presented as the mean ± standard deviation (SD). Implants and Surgical Procedure All patients received a cementless, plasma-sprayed, porous-coated RingLoc® acetabular cup with a 33-kGy crosslinked ArCom® polyethylene liner and a proximally hydroxyapatite-coated Bi-Metric® femoral stem, all manufactured by Zimmer-Biomet (Warsaw, IN, USA). The femoral heads used were 28-mm in diameter and made of either cobalt-chromium (CoCr) or 3 mol % yttria-stabilized zirconia (3Y-TZP) ceramic (Prozyr®, Saint-Gobain Céramiques Avancées Desmarquest, Evreux, France). All surgeries were performed under general anesthesia via a posterolateral approach by one of three surgeons (MT, ST, or YK). Clinical and Radiographic Evaluation Demographic data, clinical scores, and complications were assessed retrospectively using medical records. Clinical outcomes were evaluated using the Harris Hip Score (HHS) before surgery and at follow-up visits. Standardized anteroposterior (AP) and lateral radiographs of the hip were obtained annually to assess periprosthetic osteolysis and aseptic loosening of both the femoral stem and the acetabular cup. Radiographic assessments were performed using the seven Gruen zones for the femur [ 15 ] and the three DeLee and Charnley zones for the acetabulum [ 16 ]. Periprosthetic osteolysis was defined, following the method of Zicat et al. [ 17 ], as a localized area of bone resorption greater than 2 mm in width that was not present on immediate postoperative radiographs. Loosening of the acetabular component was defined as progressive migration exceeding 3 mm. Polyethylene Creep and Wear Analysis Polyethylene creep deformation and wear were quantitatively evaluated using serial radiographic measurements of femoral head penetration into the liner. Standardized AP pelvic radiographs in the supine position, with both hips in neutral rotation, were obtained at 4 weeks and at 1, 5, 10, 15, 20, and 25 years postoperatively. Two-dimensional assessments of femoral head penetration, as well as measurements of acetabular cup inclination and anteversion angles, were performed using Martell’s Hip Analysis Suite software (version 8.0.4.5; University of Chicago, IL). This software employs validated edge detection algorithms to identify the centers of the femoral head and acetabular component, enabling precise calculation of linear polyethylene creep and wear in millimeters [ 18 ]. Given that polyethylene creep (bedding-in) predominantly occurs during the early postoperative period [ 18 , 19 ], the 1-year postoperative radiograph was used as the reference baseline to minimize the confounding effect of creep when calculating wear. Head penetration into the liner was expressed as a magnitude (mm) and a rate (mm/year). Plots of linear wear vs. time were created, and wear rates were determined as a linear regression with 95% confidence bands. Zirconia Phase Transformation and Residual Stress Analysis of a Retrieved Head Phase transformation from the tetragonal to the monoclinic crystal structure, as well as residual stress in a zirconia femoral head retrieval, were analyzed using Raman microprobe spectroscopy. Raman spectra were acquired using a 488 nm argon-ion laser (30 mW; GLG3103, Showa Optronics, Japan) focused through a 100× Olympus LMPlanFLN objective lens (numerical aperture = 0.8), producing an approximate spot size of 1 µm. Confocal detection was achieved using a 100 µm pinhole. All spectra were recorded at room temperature (25 ± 1°C) using a spectrometer (MS3504i, SOL Instruments, Belarus) equipped with a thermoelectrically cooled charge-coupled device (CCD) camera (iDus DU-420A-BR-DD, Andor Technology, UK) and a 2400 lines/mm holographic grating. Each spectrum was acquired with a 10-second integration time, and the final spectrum at each point was calculated by averaging three consecutive measurements. Raman mapping was performed on a 200 × 200 µm² wear zone located at the polar region of the femoral head. Spectra were collected at approximately 15 µm step intervals, resulting in 196 measurement points and a total of 588 spectra per area. Spectral deconvolution was conducted using a mixed Gaussian/Lorentzian fitting model to extract peak positions and intensities. The monoclinic phase volume fraction was estimated using the Raman bands at 150, 180, and 190 cm⁻¹, based on the Katagiri equation [ 20 ]. Residual stresses in the tetragonal and monoclinic phases were calculated from the shifts in peak positions at 260 and 460 cm⁻¹, respectively. Overall equilibrium stress was then derived by incorporating the phase-specific stress contributions [ 21 ]. Statistical Analysis Comparative analyses between the MoP and CoP groups were performed for categorical variables (gender distribution, preoperative diagnosis, and incidence of cup and stem osteolysis) using the chi-square test. Implant survivorship was evaluated using the Kaplan–Meier method, with intergroup differences assessed via the log-rank test. Continuous variables, including age, body mass index (BMI), cup outer diameter, liner thickness, cup alignment, preoperative and postoperative HHS, and follow-up duration were compared using Student’s t-test. Unpaired Welch’s t test was employed for linear head penetration between groups. Zar’s t test was applied to compared wear rates (regression slopes) between groups. All statistical analyses were conducted using GraphPad Prism software (version 8.4.1; GraphPad Software Inc., San Diego, CA, USA). A P-value < 0.05 was considered indicative of statistical significance. Results Clinical and radiographic outcomes No significant differences between the MoP and CoP groups were noted in age at operation, gender, preoperative diagnosis, BMI, cup outer diameter, liner thickness, cup alignment (inclination and anteversion), and pre-/post-operative HHS although the study groups were not randomized (Table 1 ). Therefore, the two matched subgroups of 62 hips for each were compared in this study. The mean HHS improved significantly in both groups from 49.6 ± 2.2 preoperatively to 88.6 ± 5.8 at final follow-up in the MoP group (P < 0.001), and from 47.4 ± 4.3 to 85.4 ± 6.7 in the CoP group (P < 0.001). The incidence of acetabular osteolysis was 13% in the MoP group (zone 1: 2 hips; zone 2: 2 hips) and 35% in the CoP group (zone 1: 5 hips; zone 2: 4 hips; zone 3: 2 hips), though the difference did not reach statistical significance (P = 0.073). Femoral osteolysis was observed in 5 hips (16%) in the MoP group (zone 1 only) and in 10 hips (32%) in the CoP group (zone 1: 6 hips; zone 2: 1 hip; zone 3: 3 hips) (P = 0.235). No cases of definite loosening were observed in either group. Implant Survivorship Kaplan–Meier survival analysis, using revision for any reason as the endpoint, demonstrated 10-, 15-, 20-, and 25-year survival rates of 96.8%, 87.1%, 87.1%, and 83.1% for the MoP group, and 96.8%, 93.5%, 83.9%, and 73.8% for the CoP group, respectively (Fig. 2 ). No statistically significant difference in survivorship was observed at 25 years (P = 0.799; hazard ratio, 0.864; 95% confidence interval, 0.277–2.692). Details of all revision surgeries are summarized in Table 2 . In the MoP group, all five patients (M_1–5) underwent revision due to polyethylene liner wear approximately 10 years after the index surgery, and three of them (M_1, M_2, and M_4) developed symptomatic pseudotumors. In contrast, the CoP group included seven revision cases, with indications including recurrent dislocation, ceramic head fracture, and polyethylene wear. One patient in the CoP group (C_2) experienced an atraumatic ceramic head fracture 14 years postoperatively (Fig. 3 A). All revision THAs in the CoP group performed more than 15 years after the index surgery (C_3–7) were attributed to polyethylene wear. Notably, patient C_7 underwent both MoP and CoP THAs in the right and left hips 26 and 25 years ago, respectively. In contrast to the right MoP hip, the left CoP hip demonstrated substantial migration of the zirconia head into the polyethylene liner (Fig. 3 B). Table 2 Demographic data on patients who underwent revision surgery Case Age/ Gender Diagnosis Bearing Reason for revision Time in-vivo (years) M_1 52/ F OA MoP PE wear, Symptomatic pseudotumor 10 M_2 39/ M ION MoP PE wear, Symptomatic pseudotumor 11 M_3 43/ F OA MoP PE wear 13 M_4 39/ M ION MoP PE wear, Symptomatic pseudotumor 15 M_5 63/ F OA MoP PE wear 21 C_1 65/ F OA CoP Recurrent dislocation 9 C_2 59/ F OA CoP Femoral head fracture 14 C_3 33/ M OA CoP PE wear 17 C_4 50/ M OA CoP PE wear 19 C_5 53/ F OA CoP PE wear 20 C_6 58/ F OA CoP PE wear, dislocation 23 C_7 53/ F OA CoP PE wear, Symptomatic pseudotumor 25 F, female; M, male; OA, osteoarthritis; ION, idiopathic osteonecrosis of the femoral head; MoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene; PE, polyethylene Polyethylene Creep and Wear Behavior Figure 4 A illustrates the polyethylene liner head penetration in the MoP and CoP groups over a 25-year postoperative period. This time-dependent profile reveals distinct changes in the penetration rate corresponding to the duration since surgery, allowing the penetration process to be classified into three phases: the initial creep phase (0–1 year), the stable wear phase (1–10 years), and the late wear phase (10–25 years). During the initial creep phase (first postoperative year), linear head penetration did not differ significantly between the two groups, with values of 0.49 ± 0.30 mm in the MoP group and 0.54 ± 0.28 mm in the CoP group (P = 0.475; Table 3 ). Similarly, during the stable wear phase (1–10 years), there was no significant difference in cumulative wear or linear wear rate between the groups, indicating comparable wear behavior. The slopes of the regression lines for mean linear penetration vs. time were 0.069 ± 0.021 mm/year for the MoP group and 0.071 ± 0.016 mm/year for the CoP group, representing steady-state wear rates within the 95% confidence interval (Fig. 4 B). This difference was not statistically significant according to Zar’s t-test (P = 0.865). Table 3 Mean (standard deviation, SD) linear head penetration into polyethylene liners associated with creep and wear at different time intervals in the patients implanted either with MoP or CoP bearings MoP CoP P -value Mean SD / CI Mean SD / CI Creep deformation (mm) † 0–1 year 0.49 0.30 0.54 0.28 0.475 Cumulative wear (mm) † 1–5 years 0.29 0.25 0.29 0.25 0.892 1–10 years 0.62 0.53 0.64 0.35 0.901 1–15 years 0.74 0.44 1.00 0.42 0.032 1–20 years 1.02 0.57 1.50 0.53 0.005 1–25 years 1.06 0.48 1.76 0.79 0.016 Wear rate (mm/year) †† 1–10 years 0.069 0.021 0.071 0.016 0.865 10–25 years 0.032 0.016 0.077 0.017 0.0002 1–25 years 0.044 0.078 0.075 0.082 < 0.0001 MoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene † Values are presented as the mean ± standard deviation (SD). †† Values are presented as the mean ± 95% confidence interval (CI). Numbers in bold are statistically significant. However, beyond the 10-year mark, divergent wear trends were observed: the wear rate in the CoP group increased, while that in the MoP group decreased. Consequently, at 15 years postoperatively, cumulative wear was significantly greater in the CoP group compared to the MoP group (1.00 ± 0.42 mm vs. 0.74 ± 0.44 mm, respectively; P = 0.032). During the late wear phase (10–25 years), the CoP group also exhibited significantly higher wear rates than the MoP group (0.077 ± 0.017 mm/year vs. 0.032 ± 0.016 mm/year; P = 0.0002), indicating a progressively widening difference in wear performance over time (Fig. 4 C). Over the entire observation period from 1 to 25 years postoperatively, total linear polyethylene wear was significantly higher in the CoP group than in the MoP group (1.76 ± 0.79 mm vs. 1.06 ± 0.48 mm, respectively; P = 0.016). The corresponding steady-state wear rates were 0.075 ± 0.082 mm/year in the CoP group and 0.045 ± 0.078 mm/year in the MoP group, again indicating a significantly higher wear rate in the CoP group (P < 0.0001) (Fig. 4 D). Zirconia Retrieval Analysis Figures 5 A–E illustrate the surface degradation of a zirconia femoral head retrieved after 25 years of implantation—the longest implantation duration among the retrievals (C_7 in Table 2 ). Figure 5 B shows pronounced surface roughening and grain uplift, consistent with volumetric expansion due to phase transformation. Raman spectral analysis (Fig. 5 C) revealed characteristic tetragonal zirconia peaks (150, 260, 320, 465, 605, and 640 cm⁻¹) in the unused head, whereas the retrieved head displayed dominant monoclinic peaks (180, 190, 220, 300, 330, 345, 380, 475, 535, 560, 615, and 630 cm⁻¹), indicating extensive in vivo tetragonal-to-monoclinic transformation. Quantitative Raman mapping showed a monoclinic phase volume fraction of 92.3 ± 3.1% (Fig. 5 D). This transformation was accompanied by substantial compressive residual stress, measured at − 1.9 ± 0.1 GPa, which is attributed to transformation-induced volume expansion (Fig. 5 E). Figure 5 F presents the polyethylene liner head penetration in the patient C7 over the 25-year postoperative period. Notably, a sharp increase in the wear rate was observed starting around the 10-year mark. The slopes of the regression lines for the stable and late wear phases were 0.037 ± 0.079 mm/year and 0.212 ± 0.078 mm/year, respectively (Fig. 5 G and 5 H). This indicates that wear progressed approximately 5.7 times faster in the late wear phase compared to the stable wear phase, likely due to the onset of significant phase transformation in the zirconia head surface. The total cumulative wear over the 25 years was 3.98 mm. Discussion Several in vivo and retrieval studies have reported favorable early wear characteristics of zirconia femoral heads, including lower surface roughness and superior wear resistance compared with CoCr heads within the first decade following THA [ 9 – 11 ]. For example, Kim et al. [ 9 ] observed a mean annual linear polyethylene wear rate of 0.17 mm/year with 28-mm metal heads, compared with 0.08 mm/year with zirconia heads after a mean follow-up of 7 years. Fukui et al. [ 10 ] reported an increased monoclinic phase fraction in zirconia heads retrieved after an average of 8.6 years; however, scanning electron microscopy did not reveal substantial surface roughening. Additionally, Morrison et al. [ 11 ] demonstrated nearly equivalent wear rates at 10 years for CoCr and zirconia heads (0.07 vs. 0.06 mm/year). Based on these studies, most of which had follow-up periods of 10 years or less, zirconia LTD was previously considered to have minimal clinical impact on polyethylene wear. An ASTM-standardized simulation study conducted at our institution predicted that the volume fraction of phase-transformed zirconia in Prozyr heads would remain below 12% during the first 10 years postoperatively [ 14 ], a level not expected to compromise the mechanical integrity or clinical performance of the implant [ 22 ]. Consistent with this expectation, Stewart et al. [ 23 ] reported monoclinic contents of 4.48–7.75% after 1.6–4 years in vivo, while Chevalier [ 24 ] observed approximately 10% transformation after 8 years. Notably, however, the same ASTM simulation also predicted an exponential acceleration of phase transformation between 10 and 15 years, potentially reaching 12–41 vol% [ 14 ], leading to volumetric expansion and increased surface roughness. In our current study, the observed increase in polyethylene wear after 10 years (Fig. 4 A and 5 F) aligns with these predictions and supports the hypothesis that progressive zirconia LTD may significantly contribute to polyethylene wear through surface morphological degradation. Consistent with this mechanistic interpretation, Boyer et al. [ 22 ] analyzed 45 retrieved zirconia heads, including cases with over 10 years in vivo, and found monoclinic phase fractions exceeding 19.5% in all specimens, irrespective of the indication for revision. Higher transformation levels were associated with increased surface roughness and greater rates of aseptic loosening, particularly when the monoclinic content surpassed the critical threshold of 24.5%. Similarly, Hernigou and Bahrami [ 12 ] reported monoclinic contents of 25% and 30% after 10 and 11 years in vivo, respectively, both exceeding this threshold. In our Raman spectroscopic analysis, a zirconia head retrieved after 25 years exhibited a monoclinic content of 92.3% (Fig. 5 B–D), accompanied by severe polyethylene wear (3.98 mm total) and a maximal wear rate of 0.212 mm/year during the late wear phase (Fig. 5 F–H). Registry data also reflect potential long-term concerns. The Norwegian Arthroplasty Registry [ 25 ] reported a 12-year implant survival rate of 74.8% for zirconia heads, compared with 88.1% for CoCr heads. In our cohort, implant survival at 15 years was higher in the CoP group than in the MoP group (93.5% vs. 87.1%). However, by 20 years, survival in the MoP group remained unchanged at 87.1%, whereas it declined to 83.9% in the CoP group (Fig. 2 ). By 25 years, survivorship in the CoP group further declined to 73.8%, while the MoP group maintained a rate of 83.1%. Although these differences were not statistically significant, it is noteworthy that all revisions for severe polyethylene wear in the CoP group occurred after 15 years (Table 2 ), corresponding to the predicted period of accelerated zirconia degradation. The divergence in wear behavior between groups became particularly evident after 10 years, with the wear rate in the CoP group exceeding that of the MoP group by a factor of 2.4 during the late wear phase (10–25 years) (Fig. 4 C). In the MoP group, the reduced wear rate observed during the late wear phase (Fig. 4 A) may reflect improved articular conformity and optimized clearance resulting from early creep and wear, which decrease contact stresses and frictional forces [ 26 , 27 ]. Although a similar benefit might reasonably be expected in the CoP group, this effect appears to have been offset by progressive surface roughening due to zirconia LTD, leading to increased polyethylene wear (Fig. 4 A and 5 F). In the individual case of a 25-year implantation (C_7), the wear rate increased 5.7-fold, from 0.037 ± 0.079 mm/year to 0.212 ± 0.078 mm/year, during this phase (Fig. 5 F–H). Collectively, these findings provide important long-term insights into the tribological performance of zirconia femoral heads. Unlike CoCr heads, which demonstrated stable wear behavior when paired with cross-linked polyethylene, zirconia heads appear to undergo progressive surface degradation over time, often accompanied by increased penetration into the liner, as illustrated radiographically in Fig. 3 B. These results suggest that periodic radiographic surveillance is warranted beyond 15 years for patients with CoP bearings. From a materials engineering perspective, the present study underscores the need for continued advancements in zirconia ceramic processing to mitigate LTD and maintain long-term surface integrity. This study has several limitations. First, it was a retrospective analysis involving relatively small, non-randomized cohorts. Nonetheless, no significant differences were found between groups with respect to wear-related factors, including age, sex distribution, preoperative diagnosis, BMI, femoral head and cup sizes, cup alignment, or pre- and postoperative HHS. Second, polyethylene wear was assessed using two-dimensional measurements of femoral head penetration from supine anteroposterior pelvic radiographs, analyzed with the Martell Hip Analysis Suite™. While this method is less precise than radiostereometric analysis (RSA), which captures three-dimensional migration, Bragdon et al. [ 28 ] reported reasonable agreement between Martell and RSA wear rates, particularly during the steady-state phase, despite overestimation of absolute penetration by the Martell method. Third, all radiographs were obtained in the supine position. However, we employed the protocol described by Moore et al. [ 29 ], in which patients' lower limbs are internally rotated during imaging. Their findings indicated that head penetration measurements did not differ substantially between weight-bearing and supine positions when internal rotation was applied, likely due to adequate soft tissue tension maintaining joint congruency across loading conditions. Conclusions MoP and CoP bearings demonstrated similar polyethylene wear performance during the first decade following THA. However, a progressive divergence emerged thereafter, with the CoP group exhibiting significantly higher wear rates, potentially due to accelerated zirconia LTD during the second decade. These findings highlight the importance of long-term surveillance and raise concerns about the durability of zirconia-based ceramic components over extended periods. Abbreviations THA: Total hip arthroplasty CoP: Ceramic-on-polyethylene MoP: Metal-on-polyethylene LTD: low-temperature degradation UHMWPE: Ultra-high molecular weight polyethylene CoCr: Cobalt chromium 3Y-ZTP: 3 mol % yttria-stabilized zirconia HHS: Harris hip score AP: Anteroposterior CCD: Charge-coupled device BMI: Body mass index RSA: Radiostereometric analysis Declarations Authors’ contributions All authors made substantial contributions to this study. The design of the research objectives and concepts was undertaken by Tsunehito Ishida and Yasuhito Takahashi. Data collection was performed by Tsunehito Ishida, Yasuhito Takahashi, Toshiyuki Tateiwa, Toshinori Masaoka, Takaaki Shishido, and Takeshi Seki. Data analysis was conducted by Tsunehito Ishida and Yasuhito Takahashi. The initial draft of the manuscript was written by Tsunehito Ishida, and Yasuhito Takahashi revised the manuscript and finalized the submission version. Kengo Yamamoto was responsible for project supervision. All authors engaged in critical discussions and approved the final version of the manuscript. Acknowledgements We extend our sincere gratitude to the colleagues who contributed to this research. Funding No external funding has been received for conducting the study. Availability of data and materials The datasets used and/or analyzed during the current study are available from the corresponding authors upon reasonable request. Ethics approval and consent to participate All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Institutional Review Board of Tokyo Medical University (Approval No. T2020-0154). The requirement for individual informed consent was waived by the Ethics Committee of Tokyo Medical University because this study used anonymized retrospective data. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. References Dowd JE, Sychterz CJ, Young AM, et al. Characterization of long-term femoral- head-penetration rates. Association with and prediction of osteolysis. J Bone Joint Surg Am. 2000;82–A(8):1102. Dumbleton JH, Manley MT, Edidin AA. A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty. 2002;17(5):649. Ishida T, Tateiwa T, Takahashi Y et al. Do Polyethylene Supra-Macroparticles Lead to Pseudotumor Formation in Metal-on-Polyethylene Total Hip Arthroplasty? Arthroplast Today. 2020; 23;6(3):526–531. Ishida T, Tateiwa T, Takahashi Y et al. Do polyethylene wear particles affect the development of pseudotumor in total hip arthroplasty? 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Yanagida, editors, Science and technology of zirconia III (Advances in Ceramics, Vol. 24), Columbus, Am. Ceram. Soc. 1988:537–544. Pezzotti G, Porporati AA. Raman spectroscopic analysis of phase-transformation and stress patterns in zirconia hip joints. J Biomed Opt. 2004;9:372–84. Boyer B, Uribe J, Launay M, et al. Zirconia ageing is related to total hip arthroplasty aseptic loosening. A study of 45 retrieved zirconia heads. Orthop Traumatol Surg Res. 2024;110(8):103991. Stewart T, Flemming N, Wroblewski M et al. February. Thestability and durability of zirconia femoral heads. Proceedings of the 51st Annual Meeting of the Orthopaedic Research Society, Posterno.1167, Washington, DC, USA, 2005. Chevalier J. What future for zirconia as a biomaterial? Biomaterials. 2006;27(4):535–43. Kadar T, Dybvik E, Hallan G, et al. Head material influences survival of a cemented total hip prosthesis in the Norwegian Arthroplasty Register. Clin Orthop Relat Res. 2012;470(11):3007–13. Takahashi Y, Sugano N, Zhu W, et al. Wear degradation of long-term in vivo exposed alumina-on-alumina hip joints: linking nanometer-scale phenomena to macroscopic joint design. J Mater Sci Mater Med. 2012;23(2):591–603. Tateiwa T, Affatato S, Takahashi Y, et al. To what extent could the acetabular liner thickness be reduced yet remaining tribologically acceptable in metal-on-vitamin E-diffused crosslinked polyethylene hip arthroplasty? J Biomed Mater Res B Appl Biomater. 2022;110(10):2299–309. Bragdon CR, Martell JM, Greene ME, et al. Comparison of femoral head penetration using RSA and the Martell method. Clin Orthop Relat Res. 2006;448:52–7. Moore KD, Barrack RL, Sychterz CJ, et al. The effect of weight-bearing on the radiographic measurement of the position of the femoral head after total hip arthroplasty. J Bone Joint Surg Am. 2000;82(1):62–9. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 29 Jan, 2026 Read the published version in Journal of Orthopaedic Surgery and Research → Version 1 posted Editorial decision: Revision requested 21 Dec, 2025 Reviews received at journal 15 Dec, 2025 Reviews received at journal 15 Dec, 2025 Reviews received at journal 08 Dec, 2025 Reviewers agreed at journal 08 Dec, 2025 Reviewers agreed at journal 05 Dec, 2025 Reviews received at journal 05 Dec, 2025 Reviewers agreed at journal 05 Dec, 2025 Reviewers agreed at journal 05 Dec, 2025 Reviewers agreed at journal 04 Dec, 2025 Reviewers invited by journal 03 Dec, 2025 Editor assigned by journal 27 Nov, 2025 Submission checks completed at journal 26 Nov, 2025 First submitted to journal 25 Nov, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8152731","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":555475295,"identity":"74d1fbc3-ff19-40f6-ab6b-6c630ab3ff88","order_by":0,"name":"Tsunehito 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10:57:51","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":110729,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/4ae81cca4220f8d7a74a1120.html"},{"id":97691037,"identity":"bf71bd54-dbd1-4ae8-9821-fbfa9de8ff68","added_by":"auto","created_at":"2025-12-08 10:57:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":359162,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart illustrating patient inclusion and exclusion criteria, along with reasons for non-participation in the minimum 20-year follow-up.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/99bbcc36efe5508b16985255.png"},{"id":97691038,"identity":"cc0c9512-7204-4558-a636-777c75c9da5a","added_by":"auto","created_at":"2025-12-08 10:57:51","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":300549,"visible":true,"origin":"","legend":"\u003cp\u003eKaplan–Meier survival curves comparing the MoP and CoP groups, with any revision as the endpoint. Dotted lines represent 95% confidence intervals (CIs).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/a620247975ee6798e5a09225.png"},{"id":97893608,"identity":"8d7ac140-28fa-4732-befc-6161ce79f68a","added_by":"auto","created_at":"2025-12-10 15:30:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4223683,"visible":true,"origin":"","legend":"\u003cp\u003e(A) AP radiograph of the right hip showing an atraumatic fracture of the zirconia femoral head 14 years postoperatively in patient C_2; (B) AP radiograph of the right and left hips in patient C_7, taken 26 and 25 years after the initial MoP and CoP THAs, respectively. In contrast to the right hip, the left hip demonstrates substantial migration of the zirconia head into the polyethylene liner.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/728fb0aca54b5d9282292275.png"},{"id":97893461,"identity":"65c4c208-b3c7-4b9e-80dd-836217cd9153","added_by":"auto","created_at":"2025-12-10 15:30:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1015109,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Comparison of mean femoral head penetration (± SD) into polyethylene liners over a 25-year postoperative period in patients with metal-on-polyethylene (MoP) and ceramic-on-polyethylene (CoP) bearings; (B) Linear wear in the MoP and CoP groups during the 1–10-year postoperative period, measured using the Martell 2D method. Solid lines represent regression; dotted curves indicate 95% CIs. The linear wear rates were 0.069 ± 0.021 mm/year for the MoP group and 0.071 ± 0.016 mm/year for the CoP group (values represent means ± 95% CI); (C) Linear wear in the MoP and CoP groups during the 10–25-year postoperative period, assessed using the Martell 2D method. Solid lines represent regression; dotted curves indicate 95% CIs. The linear wear rates were 0.032 ± 0.016 mm/year for the MoP group and 0.077 ± 0.017 mm/year for the CoP group (means ± 95% CI); (D) Linear wear in the MoP and CoP groups over the entire 1–25-year postoperative period, determined using the Martell 2D method. Solid lines represent regression; dotted curves indicate 95% CIs. The linear wear rates were 0.044 ± 0.078 mm/year for the MoP group and 0.075 ± 0.082 mm/year for the CoP group (means ± 95% CI).\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/441742579693930f72371c6e.png"},{"id":97691043,"identity":"1f73c7ee-574f-470c-adf0-be484d598ec3","added_by":"auto","created_at":"2025-12-08 10:57:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":3842287,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Photograph of a zirconia femoral head retrieved after 25 years of implantation in patient C_7; (B) Optical micrograph of the worn surface, showing pronounced roughening and marked grain uplift; (C) Raman spectra comparing the unused (gray dashed line) and retrieved (red solid line) femoral head surfaces, revealing extensive tetragonal-to-monoclinic phase transformation after 25 years in vivo; (D) Raman mapping of the transformed phase content, indicating a widespread monoclinic fraction across the surface (average: 92.3%); (E) Distribution map of surface residual equilibrium stress, showing substantial compressive stress due to transformation-induced volume expansion (average: –1.9 GPa); (F) Femoral head penetration into the polyethylene liner over a 25-year postoperative period in patient C_7. (G) Linear wear in patient C_7 during the 1–10-year postoperative period, measured using the Martell 2D method. Solid line represent regression; dotted curves indicate 95% CIs. The linear wear rate was 0.037 ± 0.079 mm/year (mean ± 95% CI). (H) Linear wear in patient C_7 during the 10–25-year postoperative period, measured using the Martell 2D method. Solid line represent regression; dotted curves indicate 95% CIs. The linear wear rate was 0.212 ± 0.078 mm/year (mean ± 95% CI).\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/ab33245b5057dae8c6806488.png"},{"id":101691900,"identity":"926fd196-6129-4511-bc5d-14124968acb0","added_by":"auto","created_at":"2026-02-02 16:16:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":10358653,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8152731/v1/18719c8a-14a6-428c-963c-97dbf70e2036.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Progressive Wear Divergence Beyond 10 Years in Ceramic- vs. Metal-on-Polyethylene Bearings: The 25- Year Impact of Zirconia Degradation in Total Hip Arthroplasty","fulltext":[{"header":"Introduction","content":"\u003cp\u003eUltra-high molecular weight polyethylene (UHMWPE, hereafter referred to as polyethylene) wear debris is a well-established cause of periprosthetic osteolysis and implant loosening in total hip arthroplasty (THA) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In addition to submicron- and micron-sized particles, the generation of large polyethylene wear particles (\u0026gt;\u0026thinsp;100 \u0026micro;m) has been implicated in the formation of pseudotumors, which can result in pain, soft tissue damage, and ultimately, the need for revision surgery [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Consequently, long-term polyethylene wear remains a key factor limiting the survivorship of THA implants.\u003c/p\u003e\u003cp\u003eThe introduction of crosslinked polyethylene has substantially reduced wear rates and the incidence of osteolysis, thereby improving long-term clinical outcomes [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Nontheless, polyethylene wear is influenced not only by the properties of the liner but also by other factors, including the material and diameter of the femoral head. Zirconia ceramic heads were developed as an alternative to alumina ceramics, offering superior fracture toughness and mechanical strength [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Owing to their low surface roughness, zirconia heads have been reported in some studies to generate less polyethylene wear than metal heads [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDespite these advantages, concerns remain regarding the long-term phase stability of zirconia. Zirconia ceramics are known to exist in a metastable tetragonal phase and may undergo low-temperature degradation (LTD), characterized by a tetragonal-to-monoclinic transformation induced by the combined effects of the aqueous biological environment and mechanical stress (e.g., frictional wear, weight-bearing, and impingement) [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This transformation is associated with volume expansion, increased surface roughness, and the development of residual stresses, potentially accelerating polyethylene wear and increasing the risk of microcracking or catastrophic head fracture [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Although several mid-term studies with follow-up periods of up to 10 years have suggested that LTD-related surface changes exert minimal clinical influence on polyethylene wear [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], the long-term in vivo tribological behavior of zirconia femoral heads beyond 20 years remains insufficiently understood.\u003c/p\u003e\u003cp\u003eTherefore, the objectives of this study were twofold: (1) to compare long-term implant survivorship and polyethylene wear in patients undergoing ceramic-on-polyethylene (CoP) THA using zirconia femoral heads and metal-on-polyethylene (MoP) THA using the same implant design, with a minimum follow-up of 20 years; and (2) to evaluate the potential long-term effects of zirconia LTD on polyethylene wear in vivo.\u003c/p\u003e\u003cp\u003eThe strengths of this study include its extended follow-up period, the homogeneity of implant size and design, the consistency of surgical technique, and the use of the same cross-linked polyethylene liner in both groups. These factors permit a more isolated assessment of the influence of femoral head material on wear and implant survivorship. In addition, detailed analysis of a zirconia head retrieved after 25 years in vivo provides supplemental insight into long-term surface alterations associated with LTD. To our knowledge, this represents the first study to report over 20 years of comparative clinical and radiographic outcomes of THA using zirconia and metal heads within the same implant system.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePatients\u003c/h2\u003e\u003cp\u003e This study was approved by our institutional review board. We retrospectively reviewed the medical records of 92 patients (108 hips) who underwent cementless THA using either MoP or CoP bearing surfaces at our institution between April 1997 and December 2003 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The femoral head material was randomly selected by the operating surgeons, and all heads were 28 mm in diameter.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eOf these, 10 patients (12 hips) died from causes unrelated to THA, and 28 patients (34 hips) had incomplete follow-up data beyond 20 years postoperatively. The remaining 54 patients (62 hips; 59%) were included in the final analysis, each with a minimum follow-up of 20 years. The MoP group comprised 31 hips in 26 patients (28 hips in 23 women and 3 hips in 3 men), with a mean (\u0026plusmn;\u0026thinsp;standard deviation, SD) age at primary THA of 55.9\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4 years. The CoP group consisted of 31 hips in 28 patients (26 hips in 23 women and 5 hips in 5 men), with a mean age at surgery of 55.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6 years. The mean follow-up periods were 22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8 years for the MoP group and 24.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4 years for the CoP group. Detailed patient demographics and clinical characteristics are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eBaseline demographics for the patient groups implanted either with MoP or CoP bearings\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eP-v\u003c/em\u003ealue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of THAs/ patients\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e31/ 26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e31/ 28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge at THA (year) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e55.9\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e55.1\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.698\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGender (female: male)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e28: 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e26: 5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.707\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiagnosis (OA: ION: RA)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e29: 2: 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e28: 2: 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.601\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e22.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.412\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCup outer diameter (mm) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e51.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e50.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.141\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLiner thickness (mm) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.081\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCup inclination (\u0026deg;) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e44.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e43.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.333\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCup anteversion (\u0026deg;) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e16.4\u0026thinsp;\u0026plusmn;\u0026thinsp;8.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.586\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePreoperative HHS (points) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e47.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.378\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePostoperative HHS (points) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e88.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e85.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.479\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIncidence of acetabular osteolysis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4 (13%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e11 (35%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.073\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIncidence of femoral osteolysis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5 (16%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10 (32%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.235\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFollow-up duration (years) \u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e24.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"4\"\u003eMoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene; THA, total hip arthroplasty; OA, osteoarthritis; ION, idiopathic osteonecrosis of the femoral head; RA, rheumatoid arthritis; BMI, body mass index; HHS, Harris hip score.\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003csup\u003e\u0026dagger;\u003c/sup\u003e Values are presented as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD).\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eImplants and Surgical Procedure\u003c/h3\u003e\n\u003cp\u003eAll patients received a cementless, plasma-sprayed, porous-coated RingLoc\u0026reg; acetabular cup with a 33-kGy crosslinked ArCom\u0026reg; polyethylene liner and a proximally hydroxyapatite-coated Bi-Metric\u0026reg; femoral stem, all manufactured by Zimmer-Biomet (Warsaw, IN, USA). The femoral heads used were 28-mm in diameter and made of either cobalt-chromium (CoCr) or 3 mol % yttria-stabilized zirconia (3Y-TZP) ceramic (Prozyr\u0026reg;, Saint-Gobain C\u0026eacute;ramiques Avanc\u0026eacute;es Desmarquest, Evreux, France). All surgeries were performed under general anesthesia via a posterolateral approach by one of three surgeons (MT, ST, or YK).\u003c/p\u003e\n\u003ch3\u003eClinical and Radiographic Evaluation\u003c/h3\u003e\n\u003cp\u003eDemographic data, clinical scores, and complications were assessed retrospectively using medical records. Clinical outcomes were evaluated using the Harris Hip Score (HHS) before surgery and at follow-up visits. Standardized anteroposterior (AP) and lateral radiographs of the hip were obtained annually to assess periprosthetic osteolysis and aseptic loosening of both the femoral stem and the acetabular cup. Radiographic assessments were performed using the seven Gruen zones for the femur [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] and the three DeLee and Charnley zones for the acetabulum [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Periprosthetic osteolysis was defined, following the method of Zicat et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], as a localized area of bone resorption greater than 2 mm in width that was not present on immediate postoperative radiographs. Loosening of the acetabular component was defined as progressive migration exceeding 3 mm.\u003c/p\u003e\n\u003ch3\u003ePolyethylene Creep and Wear Analysis\u003c/h3\u003e\n\u003cp\u003ePolyethylene creep deformation and wear were quantitatively evaluated using serial radiographic measurements of femoral head penetration into the liner. Standardized AP pelvic radiographs in the supine position, with both hips in neutral rotation, were obtained at 4 weeks and at 1, 5, 10, 15, 20, and 25 years postoperatively. Two-dimensional assessments of femoral head penetration, as well as measurements of acetabular cup inclination and anteversion angles, were performed using Martell\u0026rsquo;s Hip Analysis Suite software (version 8.0.4.5; University of Chicago, IL). This software employs validated edge detection algorithms to identify the centers of the femoral head and acetabular component, enabling precise calculation of linear polyethylene creep and wear in millimeters [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Given that polyethylene creep (bedding-in) predominantly occurs during the early postoperative period [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], the 1-year postoperative radiograph was used as the reference baseline to minimize the confounding effect of creep when calculating wear. Head penetration into the liner was expressed as a magnitude (mm) and a rate (mm/year). Plots of linear wear vs. time were created, and wear rates were determined as a linear regression with 95% confidence bands.\u003c/p\u003e\n\u003ch3\u003eZirconia Phase Transformation and Residual Stress Analysis of a Retrieved Head\u003c/h3\u003e\n\u003cp\u003ePhase transformation from the tetragonal to the monoclinic crystal structure, as well as residual stress in a zirconia femoral head retrieval, were analyzed using Raman microprobe spectroscopy. Raman spectra were acquired using a 488 nm argon-ion laser (30 mW; GLG3103, Showa Optronics, Japan) focused through a 100\u0026times; Olympus LMPlanFLN objective lens (numerical aperture\u0026thinsp;=\u0026thinsp;0.8), producing an approximate spot size of 1 \u0026micro;m. Confocal detection was achieved using a 100 \u0026micro;m pinhole. All spectra were recorded at room temperature (25\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C) using a spectrometer (MS3504i, SOL Instruments, Belarus) equipped with a thermoelectrically cooled charge-coupled device (CCD) camera (iDus DU-420A-BR-DD, Andor Technology, UK) and a 2400 lines/mm holographic grating. Each spectrum was acquired with a 10-second integration time, and the final spectrum at each point was calculated by averaging three consecutive measurements.\u003c/p\u003e\u003cp\u003eRaman mapping was performed on a 200 \u0026times; 200 \u0026micro;m\u0026sup2; wear zone located at the polar region of the femoral head. Spectra were collected at approximately 15 \u0026micro;m step intervals, resulting in 196 measurement points and a total of 588 spectra per area. Spectral deconvolution was conducted using a mixed Gaussian/Lorentzian fitting model to extract peak positions and intensities. The monoclinic phase volume fraction was estimated using the Raman bands at 150, 180, and 190 cm⁻\u0026sup1;, based on the Katagiri equation [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Residual stresses in the tetragonal and monoclinic phases were calculated from the shifts in peak positions at 260 and 460 cm⁻\u0026sup1;, respectively. Overall equilibrium stress was then derived by incorporating the phase-specific stress contributions [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eComparative analyses between the MoP and CoP groups were performed for categorical variables (gender distribution, preoperative diagnosis, and incidence of cup and stem osteolysis) using the chi-square test. Implant survivorship was evaluated using the Kaplan\u0026ndash;Meier method, with intergroup differences assessed via the log-rank test. Continuous variables, including age, body mass index (BMI), cup outer diameter, liner thickness, cup alignment, preoperative and postoperative HHS, and follow-up duration were compared using Student\u0026rsquo;s t-test. Unpaired Welch\u0026rsquo;s t test was employed for linear head penetration between groups. Zar\u0026rsquo;s t test was applied to compared wear rates (regression slopes) between groups.\u003c/p\u003e\u003cp\u003eAll statistical analyses were conducted using GraphPad Prism software (version 8.4.1; GraphPad Software Inc., San Diego, CA, USA). A P-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered indicative of statistical significance.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eClinical and radiographic outcomes\u003c/h2\u003e\u003cp\u003eNo significant differences between the MoP and CoP groups were noted in age at operation, gender, preoperative diagnosis, BMI, cup outer diameter, liner thickness, cup alignment (inclination and anteversion), and pre-/post-operative HHS although the study groups were not randomized (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Therefore, the two matched subgroups of 62 hips for each were compared in this study. The mean HHS improved significantly in both groups from 49.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2 preoperatively to 88.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8 at final follow-up in the MoP group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and from 47.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3 to 85.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7 in the CoP group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The incidence of acetabular osteolysis was 13% in the MoP group (zone 1: 2 hips; zone 2: 2 hips) and 35% in the CoP group (zone 1: 5 hips; zone 2: 4 hips; zone 3: 2 hips), though the difference did not reach statistical significance (P\u0026thinsp;=\u0026thinsp;0.073). Femoral osteolysis was observed in 5 hips (16%) in the MoP group (zone 1 only) and in 10 hips (32%) in the CoP group (zone 1: 6 hips; zone 2: 1 hip; zone 3: 3 hips) (P\u0026thinsp;=\u0026thinsp;0.235). No cases of definite loosening were observed in either group.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eImplant Survivorship\u003c/h2\u003e\u003cp\u003eKaplan\u0026ndash;Meier survival analysis, using revision for any reason as the endpoint, demonstrated 10-, 15-, 20-, and 25-year survival rates of 96.8%, 87.1%, 87.1%, and 83.1% for the MoP group, and 96.8%, 93.5%, 83.9%, and 73.8% for the CoP group, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). No statistically significant difference in survivorship was observed at 25 years (P\u0026thinsp;=\u0026thinsp;0.799; hazard ratio, 0.864; 95% confidence interval, 0.277\u0026ndash;2.692).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eDetails of all revision surgeries are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In the MoP group, all five patients (M_1\u0026ndash;5) underwent revision due to polyethylene liner wear approximately 10 years after the index surgery, and three of them (M_1, M_2, and M_4) developed symptomatic pseudotumors. In contrast, the CoP group included seven revision cases, with indications including recurrent dislocation, ceramic head fracture, and polyethylene wear. One patient in the CoP group (C_2) experienced an atraumatic ceramic head fracture 14 years postoperatively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). All revision THAs in the CoP group performed more than 15 years after the index surgery (C_3\u0026ndash;7) were attributed to polyethylene wear. Notably, patient C_7 underwent both MoP and CoP THAs in the right and left hips 26 and 25 years ago, respectively. In contrast to the right MoP hip, the left CoP hip demonstrated substantial migration of the zirconia head into the polyethylene liner (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDemographic data on patients who underwent revision surgery\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAge/ Gender\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDiagnosis\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eBearing\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eReason for revision\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eTime \u003cem\u003ein-vivo\u003c/em\u003e (years)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eM_1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e52/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear, Symptomatic pseudotumor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eM_2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e39/ M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eION\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear, Symptomatic pseudotumor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eM_3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eM_4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e39/ M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eION\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear, Symptomatic pseudotumor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eM_5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e63/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e65/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRecurrent dislocation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eFemoral head fracture\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e33/ M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50/ M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e53/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e58/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear, dislocation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC_7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e53/ F\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003ePE wear, Symptomatic pseudotumor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003eF, female; M, male; OA, osteoarthritis; ION, idiopathic osteonecrosis of the femoral head; MoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene; PE, polyethylene\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003ePolyethylene Creep and Wear Behavior\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA illustrates the polyethylene liner head penetration in the MoP and CoP groups over a 25-year postoperative period. This time-dependent profile reveals distinct changes in the penetration rate corresponding to the duration since surgery, allowing the penetration process to be classified into three phases: the initial creep phase (0\u0026ndash;1 year), the stable wear phase (1\u0026ndash;10 years), and the late wear phase (10\u0026ndash;25 years). During the initial creep phase (first postoperative year), linear head penetration did not differ significantly between the two groups, with values of 0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30 mm in the MoP group and 0.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 mm in the CoP group (P\u0026thinsp;=\u0026thinsp;0.475; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Similarly, during the stable wear phase (1\u0026ndash;10 years), there was no significant difference in cumulative wear or linear wear rate between the groups, indicating comparable wear behavior. The slopes of the regression lines for mean linear penetration vs. time were 0.069\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021 mm/year for the MoP group and 0.071\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016 mm/year for the CoP group, representing steady-state wear rates within the 95% confidence interval (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). This difference was not statistically significant according to Zar\u0026rsquo;s t-test (P\u0026thinsp;=\u0026thinsp;0.865).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMean (standard deviation, SD) linear head penetration into polyethylene liners associated with creep and wear at different time intervals in the patients implanted either with MoP or CoP bearings\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eMoP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003eCoP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSD / CI\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSD / CI\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCreep deformation (mm)\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0\u0026ndash;1 year\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.49\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.475\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCumulative wear (mm)\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;5 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.892\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;10 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.901\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;15 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.032\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;20 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.005\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;25 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.016\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWear rate (mm/year)\u003csup\u003e\u0026dagger;\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;10 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.069\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.021\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.071\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.016\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.865\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u0026ndash;25 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.032\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.016\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.077\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e0.0002\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u0026ndash;25 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.044\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.078\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.075\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.082\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003eMoP, metal-on-polyethylene; CoP, ceramic-on-polyethylene\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003csup\u003e\u0026dagger;\u003c/sup\u003e Values are presented as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD).\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003csup\u003e\u0026dagger;\u0026dagger;\u003c/sup\u003e Values are presented as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;95% confidence interval (CI).\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd colspan=\"6\"\u003eNumbers in bold are statistically significant.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eHowever, beyond the 10-year mark, divergent wear trends were observed: the wear rate in the CoP group increased, while that in the MoP group decreased. Consequently, at 15 years postoperatively, cumulative wear was significantly greater in the CoP group compared to the MoP group (1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42 mm vs. 0.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44 mm, respectively; P\u0026thinsp;=\u0026thinsp;0.032). During the late wear phase (10\u0026ndash;25 years), the CoP group also exhibited significantly higher wear rates than the MoP group (0.077\u0026thinsp;\u0026plusmn;\u0026thinsp;0.017 mm/year vs. 0.032\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016 mm/year; P\u0026thinsp;=\u0026thinsp;0.0002), indicating a progressively widening difference in wear performance over time (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003eOver the entire observation period from 1 to 25 years postoperatively, total linear polyethylene wear was significantly higher in the CoP group than in the MoP group (1.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.79 mm vs. 1.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48 mm, respectively; P\u0026thinsp;=\u0026thinsp;0.016). The corresponding steady-state wear rates were 0.075\u0026thinsp;\u0026plusmn;\u0026thinsp;0.082 mm/year in the CoP group and 0.045\u0026thinsp;\u0026plusmn;\u0026thinsp;0.078 mm/year in the MoP group, again indicating a significantly higher wear rate in the CoP group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eZirconia Retrieval Analysis\u003c/h2\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA\u0026ndash;E illustrate the surface degradation of a zirconia femoral head retrieved after 25 years of implantation\u0026mdash;the longest implantation duration among the retrievals (C_7 in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB shows pronounced surface roughening and grain uplift, consistent with volumetric expansion due to phase transformation. Raman spectral analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC) revealed characteristic tetragonal zirconia peaks (150, 260, 320, 465, 605, and 640 cm⁻\u0026sup1;) in the unused head, whereas the retrieved head displayed dominant monoclinic peaks (180, 190, 220, 300, 330, 345, 380, 475, 535, 560, 615, and 630 cm⁻\u0026sup1;), indicating extensive in vivo tetragonal-to-monoclinic transformation. Quantitative Raman mapping showed a monoclinic phase volume fraction of 92.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1% (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD). This transformation was accompanied by substantial compressive residual stress, measured at \u0026minus;\u0026thinsp;1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 GPa, which is attributed to transformation-induced volume expansion (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eE).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF presents the polyethylene liner head penetration in the patient C7 over the 25-year postoperative period. Notably, a sharp increase in the wear rate was observed starting around the 10-year mark. The slopes of the regression lines for the stable and late wear phases were 0.037\u0026thinsp;\u0026plusmn;\u0026thinsp;0.079 mm/year and 0.212\u0026thinsp;\u0026plusmn;\u0026thinsp;0.078 mm/year, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eG and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eH). This indicates that wear progressed approximately 5.7 times faster in the late wear phase compared to the stable wear phase, likely due to the onset of significant phase transformation in the zirconia head surface. The total cumulative wear over the 25 years was 3.98 mm.\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eSeveral in vivo and retrieval studies have reported favorable early wear characteristics of zirconia femoral heads, including lower surface roughness and superior wear resistance compared with CoCr heads within the first decade following THA [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. For example, Kim et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] observed a mean annual linear polyethylene wear rate of 0.17 mm/year with 28-mm metal heads, compared with 0.08 mm/year with zirconia heads after a mean follow-up of 7 years. Fukui et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] reported an increased monoclinic phase fraction in zirconia heads retrieved after an average of 8.6 years; however, scanning electron microscopy did not reveal substantial surface roughening. Additionally, Morrison et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] demonstrated nearly equivalent wear rates at 10 years for CoCr and zirconia heads (0.07 vs. 0.06 mm/year). Based on these studies, most of which had follow-up periods of 10 years or less, zirconia LTD was previously considered to have minimal clinical impact on polyethylene wear.\u003c/p\u003e\u003cp\u003eAn ASTM-standardized simulation study conducted at our institution predicted that the volume fraction of phase-transformed zirconia in Prozyr heads would remain below 12% during the first 10 years postoperatively [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], a level not expected to compromise the mechanical integrity or clinical performance of the implant [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Consistent with this expectation, Stewart et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] reported monoclinic contents of 4.48\u0026ndash;7.75% after 1.6\u0026ndash;4 years in vivo, while Chevalier [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] observed approximately 10% transformation after 8 years. Notably, however, the same ASTM simulation also predicted an exponential acceleration of phase transformation between 10 and 15 years, potentially reaching 12\u0026ndash;41 vol% [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], leading to volumetric expansion and increased surface roughness. In our current study, the observed increase in polyethylene wear after 10 years (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF) aligns with these predictions and supports the hypothesis that progressive zirconia LTD may significantly contribute to polyethylene wear through surface morphological degradation.\u003c/p\u003e\u003cp\u003eConsistent with this mechanistic interpretation, Boyer et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] analyzed 45 retrieved zirconia heads, including cases with over 10 years in vivo, and found monoclinic phase fractions exceeding 19.5% in all specimens, irrespective of the indication for revision. Higher transformation levels were associated with increased surface roughness and greater rates of aseptic loosening, particularly when the monoclinic content surpassed the critical threshold of 24.5%. Similarly, Hernigou and Bahrami [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] reported monoclinic contents of 25% and 30% after 10 and 11 years in vivo, respectively, both exceeding this threshold. In our Raman spectroscopic analysis, a zirconia head retrieved after 25 years exhibited a monoclinic content of 92.3% (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB\u0026ndash;D), accompanied by severe polyethylene wear (3.98 mm total) and a maximal wear rate of 0.212 mm/year during the late wear phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF\u0026ndash;H).\u003c/p\u003e\u003cp\u003eRegistry data also reflect potential long-term concerns. The Norwegian Arthroplasty Registry [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] reported a 12-year implant survival rate of 74.8% for zirconia heads, compared with 88.1% for CoCr heads. In our cohort, implant survival at 15 years was higher in the CoP group than in the MoP group (93.5% vs. 87.1%). However, by 20 years, survival in the MoP group remained unchanged at 87.1%, whereas it declined to 83.9% in the CoP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). By 25 years, survivorship in the CoP group further declined to 73.8%, while the MoP group maintained a rate of 83.1%. Although these differences were not statistically significant, it is noteworthy that all revisions for severe polyethylene wear in the CoP group occurred after 15 years (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), corresponding to the predicted period of accelerated zirconia degradation.\u003c/p\u003e\u003cp\u003eThe divergence in wear behavior between groups became particularly evident after 10 years, with the wear rate in the CoP group exceeding that of the MoP group by a factor of 2.4 during the late wear phase (10\u0026ndash;25 years) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). In the MoP group, the reduced wear rate observed during the late wear phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA) may reflect improved articular conformity and optimized clearance resulting from early creep and wear, which decrease contact stresses and frictional forces [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Although a similar benefit might reasonably be expected in the CoP group, this effect appears to have been offset by progressive surface roughening due to zirconia LTD, leading to increased polyethylene wear (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF). In the individual case of a 25-year implantation (C_7), the wear rate increased 5.7-fold, from 0.037\u0026thinsp;\u0026plusmn;\u0026thinsp;0.079 mm/year to 0.212\u0026thinsp;\u0026plusmn;\u0026thinsp;0.078 mm/year, during this phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF\u0026ndash;H).\u003c/p\u003e\u003cp\u003eCollectively, these findings provide important long-term insights into the tribological performance of zirconia femoral heads. Unlike CoCr heads, which demonstrated stable wear behavior when paired with cross-linked polyethylene, zirconia heads appear to undergo progressive surface degradation over time, often accompanied by increased penetration into the liner, as illustrated radiographically in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB. These results suggest that periodic radiographic surveillance is warranted beyond 15 years for patients with CoP bearings. From a materials engineering perspective, the present study underscores the need for continued advancements in zirconia ceramic processing to mitigate LTD and maintain long-term surface integrity.\u003c/p\u003e\u003cp\u003eThis study has several limitations. First, it was a retrospective analysis involving relatively small, non-randomized cohorts. Nonetheless, no significant differences were found between groups with respect to wear-related factors, including age, sex distribution, preoperative diagnosis, BMI, femoral head and cup sizes, cup alignment, or pre- and postoperative HHS. Second, polyethylene wear was assessed using two-dimensional measurements of femoral head penetration from supine anteroposterior pelvic radiographs, analyzed with the Martell Hip Analysis Suite\u0026trade;. While this method is less precise than radiostereometric analysis (RSA), which captures three-dimensional migration, Bragdon et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] reported reasonable agreement between Martell and RSA wear rates, particularly during the steady-state phase, despite overestimation of absolute penetration by the Martell method. Third, all radiographs were obtained in the supine position. However, we employed the protocol described by Moore et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], in which patients' lower limbs are internally rotated during imaging. Their findings indicated that head penetration measurements did not differ substantially between weight-bearing and supine positions when internal rotation was applied, likely due to adequate soft tissue tension maintaining joint congruency across loading conditions.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eMoP and CoP bearings demonstrated similar polyethylene wear performance during the first decade following THA. However, a progressive divergence emerged thereafter, with the CoP group exhibiting significantly higher wear rates, potentially due to accelerated zirconia LTD during the second decade. These findings highlight the importance of long-term surveillance and raise concerns about the durability of zirconia-based ceramic components over extended periods.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eTHA: Total hip arthroplasty\u003c/p\u003e\n\u003cp\u003eCoP: Ceramic-on-polyethylene\u003c/p\u003e\n\u003cp\u003eMoP: Metal-on-polyethylene\u003c/p\u003e\n\u003cp\u003eLTD: low-temperature degradation\u003c/p\u003e\n\u003cp\u003eUHMWPE: Ultra-high molecular weight polyethylene\u003c/p\u003e\n\u003cp\u003eCoCr: Cobalt chromium\u003c/p\u003e\n\u003cp\u003e3Y-ZTP: 3 mol % yttria-stabilized zirconia\u003c/p\u003e\n\u003cp\u003eHHS: Harris hip score\u003c/p\u003e\n\u003cp\u003eAP: Anteroposterior\u003c/p\u003e\n\u003cp\u003eCCD: Charge-coupled device\u003c/p\u003e\n\u003cp\u003eBMI: Body mass index\u003c/p\u003e\n\u003cp\u003eRSA: Radiostereometric analysis\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors made substantial contributions to this study. The design of the research objectives and concepts was undertaken by Tsunehito Ishida and Yasuhito Takahashi. Data collection was performed by Tsunehito Ishida, Yasuhito Takahashi, Toshiyuki Tateiwa, Toshinori Masaoka, Takaaki Shishido, and Takeshi Seki. Data analysis was conducted by Tsunehito Ishida and Yasuhito Takahashi. The initial draft of the manuscript was written by Tsunehito Ishida, and Yasuhito Takahashi revised the manuscript and finalized the submission version. Kengo Yamamoto was responsible for project supervision. All authors engaged in critical discussions and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe extend our sincere gratitude to the colleagues who contributed to this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo external funding has been received for conducting the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analyzed during the current study are available from the corresponding authors upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the Institutional Review Board of Tokyo Medical University (Approval No. T2020-0154). The requirement for individual informed consent was waived by the Ethics Committee of Tokyo Medical University because this study used anonymized retrospective data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDowd JE, Sychterz CJ, Young AM, et al. Characterization of long-term femoral- head-penetration rates. Association with and prediction of osteolysis. J Bone Joint Surg Am. 2000;82\u0026ndash;A(8):1102.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDumbleton JH, Manley MT, Edidin AA. A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty. 2002;17(5):649.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIshida T, Tateiwa T, Takahashi Y et al. Do Polyethylene Supra-Macroparticles Lead to Pseudotumor Formation in Metal-on-Polyethylene Total Hip Arthroplasty? Arthroplast Today. 2020; 23;6(3):526\u0026ndash;531.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIshida T, Tateiwa T, Takahashi Y et al. Do polyethylene wear particles affect the development of pseudotumor in total hip arthroplasty? A minimum 15-year follow-up. J Orthop Surg Res. 2023; 28;18(1):147.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKurtz SM, Gawel HA, Patel JD. History and systematic review of wear and osteolysis outcomes for first-generation highly crosslinked polyethylene. Clin Orthop Relat Res. 2011;469:2262\u0026ndash;77.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHopper RH Jr, Ho H, Sritulanondha S, et al. Otto Aufranc Award: Crosslinking Reduces THA Wear, Osteolysis, and Revision Rates at 15-year Followup Compared With Noncrosslinked Polyethylene. Clin Orthop Relat Res. 2018;476(2):279\u0026ndash;90.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eClarke IC, Manaka M, Green DD, et al. Current status of zirconia used in total hip implants. J Bone Joint Surg Am. 2003;85\u0026ndash;A(Suppl 4):73\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePiconi C, Maccauro G. Zirconia as a ceramic biomaterial. Biomaterials. 1999;20(1):1\u0026ndash;25.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKim YH. Comparison of polyethylene wear associated with cobalt-chromium and zirconia heads after total hip replacement. A prospective, randomized study. J Bone Joint Surg Am. 2005;87(8):1769\u0026ndash;76.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFukui K, Kaneuji A, Sugimori T, et al. Retrieval analysis of new-generation yttria-stabilized zirconia femoral heads after total hip arthroplasty. Eur J Orthop Surg Traumatol. 2013;24:1197\u0026ndash;202.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMorrison TA, Moore RD, Meng J, et al. No Difference in Conventional Polyethylene Wear Between Yttria-stabilized Zirconia and Cobalt-chromium-molybdenum Femoral Heads at 10 Years. HSS J. 2018;14(1):60\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHernigou P, Bahrami T. Zirconia and alumina ceramics in comparison with stainless-steel heads. Polyethylene wear after a minimum ten-year follow-up. J Bone Joint Surg Br. 2003;85(4):504\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMasonis JL, Bourne RB, Ries MD, et al. Zirconia femoral head fractures: a clinical and retrieval analysis. J Arthroplasty. 2004;19(7):898\u0026ndash;905.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArita M, Takahashi Y, Pezzotti G, et al. Environmental Stability and Residual Stresses in Zirconia Femoral Head for Total Hip Arthroplasty: In Vitro Aging versus Retrieval Studies. Biomed Res Int. 2015;2015:638502.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGruen TA, McNeice GM, Amstutz HC. Modes of failure of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res. 1979;141:17\u0026ndash;27.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDe Lee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res. 1976:20\u0026ndash;32.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZicat B, Engh CA, Gokcen E. Patterns of osteolysis around total hip components inserted with and without cement. J Bone Jt Surg Am. 1995;77:432\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMatsuoka T, Takahashi Y, Ishida T, et al. In vivo creep and wear performance of vitamin-E-diffused highly crosslinked polyethylene in total hip arthroplasty. Arch Orthop Trauma Surg. 2023;143(12):7195\u0026ndash;203.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eManning DW, Chiang PP, Martell JM, et al. In vivo comparative wear study of traditional and highly cross- linked polyethylene in total hip arthroplasty. J Arthroplasty. 2005;20:880\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKatagiri G, Ishida H, Ishitani A et al. Direct determination by a Raman microprobe of transformation zone size in Y2O3-containing tetragonal ZrO2 polycrystals. In: S. Somiya, N. Yamamoto, and H. Yanagida, editors, Science and technology of zirconia III (Advances in Ceramics, Vol. 24), Columbus, Am. Ceram. Soc. 1988:537\u0026ndash;544.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePezzotti G, Porporati AA. Raman spectroscopic analysis of phase-transformation and stress patterns in zirconia hip joints. J Biomed Opt. 2004;9:372\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBoyer B, Uribe J, Launay M, et al. Zirconia ageing is related to total hip arthroplasty aseptic loosening. A study of 45 retrieved zirconia heads. Orthop Traumatol Surg Res. 2024;110(8):103991.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStewart T, Flemming N, Wroblewski M et al. February. Thestability and durability of zirconia femoral heads. Proceedings of the 51st Annual Meeting of the Orthopaedic Research Society, Posterno.1167, Washington, DC, USA, 2005.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChevalier J. What future for zirconia as a biomaterial? Biomaterials. 2006;27(4):535\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKadar T, Dybvik E, Hallan G, et al. Head material influences survival of a cemented total hip prosthesis in the Norwegian Arthroplasty Register. Clin Orthop Relat Res. 2012;470(11):3007\u0026ndash;13.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTakahashi Y, Sugano N, Zhu W, et al. Wear degradation of long-term in vivo exposed alumina-on-alumina hip joints: linking nanometer-scale phenomena to macroscopic joint design. J Mater Sci Mater Med. 2012;23(2):591\u0026ndash;603.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTateiwa T, Affatato S, Takahashi Y, et al. To what extent could the acetabular liner thickness be reduced yet remaining tribologically acceptable in metal-on-vitamin E-diffused crosslinked polyethylene hip arthroplasty? J Biomed Mater Res B Appl Biomater. 2022;110(10):2299\u0026ndash;309.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBragdon CR, Martell JM, Greene ME, et al. Comparison of femoral head penetration using RSA and the Martell method. Clin Orthop Relat Res. 2006;448:52\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoore KD, Barrack RL, Sychterz CJ, et al. The effect of weight-bearing on the radiographic measurement of the position of the femoral head after total hip arthroplasty. J Bone Joint Surg Am. 2000;82(1):62\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Total hip arthroplasty, Ceramic-on-polyethylene, Metal-on-polyethylene, Polyethylene Wear, Zirconia low-temperature degradation","lastPublishedDoi":"10.21203/rs.3.rs-8152731/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8152731/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eThis study aimed to compare the long-term implant survivorship and polyethylene wear in total hip arthroplasty (THA) using ceramic-on-polyethylene (CoP) bearings with zirconia femoral heads versus metal-on-polyethylene (MoP) bearings with cobalt-chromium heads. A secondary objective was to assess the in vivo impact of zirconia low-temperature degradation (LTD) on polyethylene wear.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eSixty-two hips were assigned to two demographically matched cohorts receiving crosslinked polyethylene liners paired with either 28-mm zirconia or cobalt-chromium heads. All patients received the same implant design and were followed for a minimum of 20 years. Implant survivorship and linear head penetration were evaluated over a 25-year period. A zirconia head retrieved after 25 years was analyzed via Raman spectroscopy to investigate phase transformation and residual stress.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eDuring the first 10 years post-THA, no significant differences were observed in cumulative polyethylene wear or linear wear rates between the MoP and CoP groups. However, beyond 10 years, these groups demonstrated differing wear patterns, with wear tending to increase in the CoP group and decrease in the MoP group. Between 10 and 25 years, the wear rate in the CoP group was approximately 2.4 times higher than that in the MoP group. Analysis of the retrieved zirconia head revealed extensive monoclinic phase transformation (92.3%), high compressive residual stress (\u0026ndash;1.9 GPa), and notable grain uplift, correlating with an elevated wear rate of 0.212 mm/year during the second decade.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eMoP and CoP bearings demonstrated similar polyethylene wear characteristics during the first decade after THA. However, a marked divergence emerged in the second decade, with significantly higher wear rates observed in the CoP group, likely attributable to the accelerated progression of zirconia LTD. These findings highlight the long-term implications of ceramic degradation and emphasize the need for careful evaluation of zirconia-based components in THA regarding their durability over time.\u003c/p\u003e","manuscriptTitle":"Progressive Wear Divergence Beyond 10 Years in Ceramic- vs. Metal-on-Polyethylene Bearings: The 25- Year Impact of Zirconia Degradation in Total Hip Arthroplasty","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-08 10:57:46","doi":"10.21203/rs.3.rs-8152731/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-21T15:55:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-15T11:54:24+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-15T11:11:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-08T10:12:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"253959168429406769756640272940472719149","date":"2025-12-08T09:35:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"60253143892887268505232824872772174982","date":"2025-12-05T23:00:21+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-05T19:12:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"204607835825944535286978950014591587405","date":"2025-12-05T18:43:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"114422596981509921516016911344884191963","date":"2025-12-05T12:52:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"213609243150986086364423640643355522530","date":"2025-12-04T21:25:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-03T22:21:20+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-27T12:22:56+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-26T12:09:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Orthopaedic Surgery and Research","date":"2025-11-25T10:06:08+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"95dbd204-c52c-414c-a866-8d28e0bbd9fb","owner":[],"postedDate":"December 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-02T16:12:42+00:00","versionOfRecord":{"articleIdentity":"rs-8152731","link":"https://doi.org/10.1186/s13018-026-06681-y","journal":{"identity":"journal-of-orthopaedic-surgery-and-research","isVorOnly":false,"title":"Journal of Orthopaedic Surgery and Research"},"publishedOn":"2026-01-29 15:59:23","publishedOnDateReadable":"January 29th, 2026"},"versionCreatedAt":"2025-12-08 10:57:46","video":"","vorDoi":"10.1186/s13018-026-06681-y","vorDoiUrl":"https://doi.org/10.1186/s13018-026-06681-y","workflowStages":[]},"version":"v1","identity":"rs-8152731","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8152731","identity":"rs-8152731","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}