Finite element analysis of mechanical stress in a cementless tapered-wedge short stem in the varus position

Finite element analysis of mechanical stress in a cementless tapered-wedge short stem in the varus position | 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 Finite element analysis of mechanical stress in a cementless tapered-wedge short stem in the varus position Takahiro Maeda, Osamu Obayashi, Muneaki Ishijima, Taichi Sato, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4236152/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jul, 2024 Read the published version in Journal of Orthopaedic Surgery and Research → Version 1 posted 10 You are reading this latest preprint version Abstract Background: In recent years, the use of tapered-wedge short stems has increased because of their ability to preserve bones and tendons. Surgical techniques occasionally result in a varus position of the stem, which is particularly pronounced in short stems. Although the varus position is not clinically problematic, there are reports of an increased incidence of stress shielding and cortical hypertrophy. Thus, we evaluated and examined the acceptable range of varus angles using finite element analysis. Methods: We selected patients diagnosed with osteoarthritis of the hip joint who had undergone arthroplasty and were classified into three types [champagne-flute (type A), intermediate (type B), and stovepipe (type C)]. Finite element analysis was performed using Mechanical Finder. The model was created using a Taperloc microplasty stem with the varus angle increased by 1° from 0° to 5° from the bone axis and classified into seven zones based on Gruen’s zone classification under loading conditions in a one-leg standing position. The volume of interest was set, the mean equivalent stress for each zone was calculated, and the mean value of the equivalent stress in each zone was calculated. Results: A significant decrease in stress was observed in zone 2, and increased stress was observed in zones 3 and 4, suggesting the emergence of a distal periosteal reaction, similar to the results of previous studies. In zone 2, there was a significant decrease in stress in all groups at a varus angle ≥3°. In zone 3, stress increased from ≥3° in type B and ≥4° in type C. In zone 4, there was a significant increase in stress at varus angles of ≥2° in types A and B and at ≥3° in type C. Conclusion: In zone 2, the varus angle at which stress shielding above Engh classification grade 3 may appear is expected to be ≥3°. Distal cortical hypertrophy may appear in zones 3 and 4; the narrower the medullary cavity shape, the smaller the allowable angle of internal recession, and the wider the medullary cavity shape, the wider the allowable range. Long-term follow-up is required in patients with varus angles >3°. mechanical stress varus position malalignment finite element analysis stress shielding cortical hypertrophy total hip arthroplasty tapered-wedge stem short stems Gruen’s zone Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Background Various types of implants are used in total hip arthroplasty (THA). The use of short-stem implants has increased in recent years. The reasons for this include greater bone preservation, better proximal load transfer, less invasive surgery, and ease of use of the anterior approach [ 1 – 3 ]. The postoperative stress distribution in the femur changes significantly after stem placement because the load is transmitted to the femur through the stem. Bone density in the proximal femur decreases in the early postoperative period after THA, and remodeling occurs to accommodate the new load. Stresses in the proximal femur are low, and bone atrophy occurs; in the long term, bone atrophy may lead to peri-implant fractures and stem instability [ 4 – 6 ]. Short stems transmit stress more easily proximally than standard stems, and many surgeons have reported good results with short stems [ 7 , 8 ]. A disadvantage of short stems is that they tend to be inserted during misalignment. The stem should be inserted horizontally along the bony axis. However, depending on the skill of the surgeon, implant design, and approach technique, the stem may be in the varus or valgus position [ 9 ]. Short stems, in particular, are prone to the varus position, and peri-stem bone reactions due to the varus position have been reported [ 10 ]. We used finite element analysis to investigate how stress transfer changes with the degree of varus position, especially for short stems that are prone to the varus position. This study aimed to evaluate the stresses on the femur as the varus angle increases and to investigate the varus angle at which peri-stem bony reactions can occur. Therefore, in this study, we used preoperative computed tomography (CT) images of patients undergoing surgery to examine the change in stress when the stem was tilted in increments of 1° varus angle. Methods This study included cases of hip osteoarthritis that underwent joint replacement surgery at Juntendo University Shizuoka Hospital between April 1, 2018, and March 31, 2021. The patients who underwent preoperative CT were classified into three femoral types based on Noble’s Canal Flare Index (CFI), with CFI < 4.7 being the champagne-flute type (type A), CFI < 3 being the stovepipe type (type C), and CFI between the two being intermediate type (type B). Because 10 cases with the champagne-flute type were indicated, 10 cases of types B and C were also randomly selected [ 11 ]. Since only two male patients were included in type A and the other patients were female, we excluded the male patients to ensure homogeneity, as being male has been identified as a risk factor for proximal stress shielding in previous studies, and other reports have consistently focused on female patients [ 9 , 12 , 13 ] (Table 1 .) Table 1 Patient demographics Age (years) Sex Side (right/left) CFI Type A 63 ± 9.9 Female 4 / 4 5.19 ± 0.35 Type B 71 ± 11.9 Female 8 / 2 3.56 ± 0.26 Type C 73 ± 14.6 Female 5 / 5 2.49 ± 0.14 *Values are mean Type A (champagne-flute), Type B (intermediate), Type C (stovepipe) CFI, canal flare index; Side femoral affected side Finite element analysis was performed using Mechanical Finder ver. 10.0 (Research Center for Computational Mechanics, Japan). CT DICOM data (Discovery CT750 HD; GE Medical Systems, Milwaukee, WI, USA) were used to create a finite element model. One millimeter slice thickness of the affected femur was obtained from the preoperative CT of the extracted case. The femur contour was extracted, and a 3-D finite element model was created using tetrahedral elements. The stems were subjected to Taperloc microplasty (Zimmer Biomet Holdings Inc., Indiana, USA). This stem is a cementless, tapered-wedge stem that is shorter than a standard stem. Stem contours were captured using a 3D scanner (ATOS Core Education, GOM, Germany). The contours and coordinate axes were corrected, converted to stereolithography data, and imported into Mechanical Finder. The femoral model was osteotomized approximately 10 mm proximal to the lesser trochanter. The stem was placed through the proximal metaphyseal bone axis, and stem anteversion was performed in the direction of the femoral neck bone axis [ 14 ] (Fig. 1 ). The stem was placed by the same examiner, and the appropriate size was determined to be a proximal metaphyseal fit, with the medial and lateral sides of the stem fitted into the bone cortex [ 15 ]. A total of 168 bone models were created: 48 (with 8 examples) for type A, 60 (with 10 examples) for type B, and 60 (with 10 examples) for type C.; the varus angle increased by 1° from 0° to 5° from the bone axis. Load restraint conditions were set assuming a one-leg standing position, with a joint reactive force of 2400 N exerted by the weight of the body on the femoral head or prosthetic head at an angle of 15° proximal medial relative to the femoral axis, and a 1200 N force generated by the abductor muscles exerted at an angle of 20° distal lateral relative to the greater trochanter [ 16 , 17 ] (Fig. 2 ). Young’s modulus based on CT values (Hounsfield units) was set for each element using the conversion formula of Keyak et al. for femoral material properties to reflect the differences in bone density in each case. The Poisson’s ratio of the femoral material was set to 0.40, and the stem was made of titanium (Ti-6Al-4V) with a Poisson’s ratio of 0.28 [ 18 ]. The stem and femur were assumed to share a nodal point and completely adhere to each other. Seven zones were classified based on Gruen’s zone classification, the volume of interest was set, and the mean value of the equivalent stress for each zone was calculated [ 19 ] (Fig. 3 ). EZR software (version 4.2.2) was used for the statistical analysis [ 20 ]. Multiway analysis of variance (ANOVA) was applied for between-group comparisons, and repeated-measures analysis of variance, and multiple comparisons (Bonferroni method) were applied for within-county comparisons at a significance level of 5%. Results First, a comparative study of the average stress in each zone with increasing internal warping angle was conducted. In zone 2, all femur types showed a significant decrease in stress from a varus angle of 3°, whereas in zone 3, femur types B and C showed significant increases in stress from varus angles of 3° and 4°, respectively. In zone 4, there was a significant increase in stress from a varus angle of 2° in femurs A and B and from a varus angle of 3° in type C (Table 2 , Fig. 4 ). Table 2 Varus angles at which a significant increase or decrease in von Mises stress began to occur in the Gruen zone. Zone Von Mises stress Type A Type B Type C Varus angle (°) Zone 2 Decrease 3°≤ (P = 0.001) 3°≤ (P = 0.046) 3°≤ (P = 0.007) Zone 3 Increase (P = 0.077) 3°≤ (P = 0.003) 4°≤ (P = 0.002) Zone 4 Increase 2°≤ (P = 0.017) 2°≤ (P = 0.004) 3°≤ (P = 0.001) Second, because the quality of each bone was different, we examined the rate of change instead of the stress value. In zone 2, there was a significant decrease in stress in femur types A and C from a varus angle of 3°, a significant increase in stress in femur type B from a varus angle of 3°, and a significant increase in stress in femur types A and C from a varus angle of 4°. In zone 4, there was a significant increase in stress in femur type B from an angle of 4 ° and in femur type C from a varus angle of 5° (Table 3 , Fig. 5 ). Table 3 Change in von Mises stress ratio with respect to the 0° varus angle in Gruen’s zone with increasing varus angle. Zone Von Mises stress Type A Type B Type C Varus angle (°) Zone 2 Decrease 3°≤ (P = 0.026) 4°≤ (P = 0.022) 3°≤ (P = 0.002) Zone 3 Increase (P = 0.118) 3°≤ (P = 0.027) 4°≤ (P = 0.034) Zone 4 Increase (P = 0.483) 4°≤ (P < 0.001) 5°≤ (P = 0.012) We also examined whether there was a significant difference in stress between the femurs in each zone at each angle. The stress was highest in zones 3 and 4 for all femur types, with type A having the highest stress, followed by types B and C (Table 3 and Fig. 5 ). There was no significant difference in the stress in the zones owing to the change in the angle between the femur types (Figs. 6 and 7 ). Discussion Recently, the use of tapered-wedge short stems has increased because of their ability to preserve bone and tendon. Barrington et al. compared the postoperative results of the Taperloc standard stem and microplasty and found that both had good results, with low revision rates of 0.9%/1.0%. Molli et al. reported a lower intraoperative fracture risk of 3.1%/0.4% with Taperloc microplasty, indicating that the short stem is useful [ 1 , 2 ]. Depending on the surgical technique, implant design, and surgeon’s skill, the stem may be placed in the varus position. This is particularly true for short stems, which are not inserted into the distal medullary cavity but only into the proximal medullary cavity, thus increasing the degrees of freedom [ 10 , 21 , 22 ]. Although it has been reported that the varus position is not clinically problematic [ 10 ], Vresiovic et al. evaluated stem fixation and radiographic images at the time of surgery in patients who underwent THA revision for pain and found that 83% of the varus position cases had instability and a high revision rate, which was associated with clinical symptoms [ 23 ]. It has been reported that short stems have less stress loading around the stem than standard stems and that the proximal loss of bone density caused by stem insertion is significantly less with short stems because force transmission is shifted more proximally [ 7 , 8 ]. However, there are few reports of peri-stem bony reactions in short stems, although there are no comprehensive reports on such reactions. Evola et al. reported an increased risk of femoral cortical hypertrophy and pain associated with varus insertion [ 24 ]. Crawford et al. found distal femoral cortical hypertrophy in 74% of cases in Gruen zone 3 and 56% in zone 5, and Innmann et al. found cortical hypertrophy in 56% of cases, mostly in zones 3 and 5 [ 25 , 26 ]. In the present study, there was a significant decrease in stress in zone 2 and increased stress in zones 3 and 4, suggesting the appearance of a distal periosteal reaction, similar to the results of previous studies. In the comparison of mean stress values, zone 2 showed a significant decrease in all groups at a 3° varus angle, and the acceptable varus angle for the appearance of SS above Engh classification grade 3 was expected to be 3° [ 27 ]. In zone 3, there was an increase from a 3° varus angle in type B and from a 4° varus angle in type C. In zone 4, there was a significant increase in stress from a 2° varus angle in types A and B and a 3° varus angle in type C. This suggests the appearance of cortical hypertrophy distally, with a narrower medullary lumen shape indicating a narrower tolerance range and a wider medullary lumen shape indicating a wider tolerance range. Considering the differences in the bone quality of each patient, we also analyzed the rate of change in stress with increasing varus angle from 0° as a reference point. In zone 2, we observed a significant decrease in stress in all groups at a varus angle of ≥ 3°. In zone 3, the stress increased significantly from 3° for type B to 4° for type C, whereas in zone 4, the stress increased significantly from 4° for type B to 5° for type C. As mentioned above, the tolerance range increased with the medial cavity geometry. Oba et al. compared the stress distribution in the Accolade TMZF stem (tapered-wedge cementless stem) with different luminal geometries (cases with stem alignment < 3°) and analyzed three luminal types (champagne-flute, intermediate, and stovepipe). The authors reported that the stovepipe type tended to have a larger stem size, a stem contacting the cortex distally, and a decrease in stress proximally and that bone mineral density decreased in zone 2, although there was no significant difference in stress in Gruen’s zone 6 [ 12 ]. Cooper et al. also studied the postoperative radiographic osteointegration of Accolade TMZF stems and reported that the risk of proximal stress shielding and proximal osteointegration failure was associated with a small CFI (stovepipe type) and a large stem size [ 13 ]. Ishi et al. reported that osteointegration failure was more common in patients with a large CFI (champagne-flute type), which they attributed to distal fixation due to the narrow femoral marrow cavity in Asians, and concluded that both stovepipe and champagne-flute types should be treated with caution [ 28 ]. In the present study, there was no change in the stress distribution in each medullary cavity when the insertion was parallel to the bone axis (0° varus angle), and there was no significant difference between the groups. However, the highest stresses were found in zone 4, and there was no change in the stress distribution from zones 2 and 6 distally. The reason for the lack of change in stress distribution due to the difference in the medullary cavity is that, unlike the stems used by Oba et al., Cooper et al., and Ishi et al., the stem shape is a reduced structure to avoid distal fixation, and the stem is not distally fixed, which is thought to be because it adapts to various medullary cavity configurations and transmits stress (Fig. 8 ). Because an appropriate stem size was used in this study, it was thought that Taperloc microplasty could accommodate any luminal configuration and transmit stress firmly distally, at least if the proper size was selected in preoperative planning and the stem alignment was neutral. However, as in the studies by Oba et al. and Ishi et al., this study was limited to women only, and Cooper et al. found the male sex to be a risk factor. Therefore, the results of this study conducted on women may not be applicable to men, and caution is required when treating men. Further analysis of male patients is required. A narrow medullary space of this type showed a significant increase in distal stress with a 2° varus angle. Therefore, stem insertion should be performed more carefully in patients with a narrow medullary space. The main limitation of this study is that in setting the boundary conditions, the stem and femur were analyzed with a shared contact point and complete adherence between the stem and femur. The stems were proximally porous and distally smooth. To construct a realistic model, different friction coefficients must be set for each stem surface. Although Oba et al. also mentioned this as a limitation of their study, they considered that assuming successful fixation of the cementless stem, finite element analysis may show characteristic stress distributions, even with a simplified finite element model [ 12 ]. Second, no comparison with actual cases or bone density evaluation was performed. Third, stem insertion in fragile bones, such in as femoral neck fractures, should be considered separately. Finally, it should be noted that the results of this study may not apply to all cases, as no analysis was performed on male patients. Additional studies on stem flexion/extension, valgus, anterior/posterior insertion, and male patients will further clarify the advantages and disadvantages of short stems. Conclusion Most of the articles we reviewed only evaluated a group of cases of stem varus malalignment with periosteal reactions in imaging studies, and none of the articles investigated the stem varus angle. In the present study, stress decreased with increasing varus angle in zone 2 of the Gruen classification when the varus angle was ≥ 3°, suggesting the appearance of a grade 3 Engh classification of stress shielding and the appearance of cortical hypertrophy in zones 3 and 4. In the champagne-flute type (type A) with a narrow medullary cavity, a significant increase in distal stress was observed at a 2° varus angle, and careful stem insertion was necessary. Taperloc microplasty provided good distal load transfer in all femoral medullary configurations when the stem was neutrally inserted. List of Abbreviations CFI, Canal Flare Index CT, computed tomography THA, total hip arthroplasty VMS, von Mises stress Declarations Ethics approval and consent to participate The research protocol was approved by the Research Ethics Committee of the Faculty of Medicine, Juntendo University (research project number E21-0191), and research permission was obtained from Toho University Medical Center Ohashi Hospital (control NumberC_H21009). Consent for publication Informed consent was obtained from all participants included in the study. Competing interests The authors declare that they have no competing interests. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Author Contribution OO, MI, and TS elaborated on the plan and arranged for the experiment at Juntendo University Shizuoka Hospital. YM performed most of the laboratory work. HI was a major contributor to the writing of the manuscript. All authors have read and approved the final manuscript. Acknowledgement We would like to thank Dr. Kanda and Dr. Morohashi of Juntendo University Shizuoka Hospital for their invaluable advice and for providing us with the patient’s femoral CT data. Availability of data and materials Data supporting the findings of this study are available from the corresponding author upon reasonable request. References [ References] Barrington JW, Emerson RH. The short and shorter of it: >1750 tapered titanium stems at 6- to 88-month follow-up. J Arthroplasty. 2013;28:38–40. Molli RG, Lombardi AV, Berend KR, Adams JB, Sneller MA. A short tapered stem reduces intraoperative complications in primary total hip arthroplasty. Clin Orthop Relat Res. 2012;470:450–61. Morrey BF. Short-stemmed uncemented femoral component for primary hip arthroplasty. Clin Orthop Relat Res. 1989:(249):169–75. Engh CA, McGovern TF, Bobyn JD, Harris WH. A quantitative evaluation of periprosthetic bone-remodeling after cementless total hip arthroplasty. J Bone Joint Surg Am. 1992;74:1009–20. Engh CA, Hooten JP Jr, Zettl-Schaffer KF, Ghaffarpour M, McGovern TF, Bobyn JD. Porous-coated total hip replacement. Clin Orthop Relat Res. 1994;298:89–96. Engh CA, Bobyn JD. The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty. Clin Orthop Relat Res. 1988;(231):7–28. Kaku N, Pramudita JA, Yamamoto K, Hosoyama T, Tsumura H. Stress distributions of the short stem and the tapered wedge stem at different alignments: a finite element analysis study. J Orthop Surg Res. 2022;17:530. Roth A, Richartz G, Sander K, Sachse A, Fuhrmann R, Wagner A, et al. [Periprosthetic bone loss after total hip endoprosthesis. Dependence on the type of prosthesis and preoperative bone configuration]. Orthopade. 2005;34:334–44. Bernasek TL, Lee WS, Lee HJ, Lee JS, Kim KH, Yang JJ. Minimally invasive primary THA: anterolateral intermuscular approach versus lateral transmuscular approach. Arch Orthop Trauma Surg. 2010;130:1349–54. Nishioka ST, Andrews SN, Mathews K, Nakasone CK. Varus malalignment of short femoral stem not associated with post-hip arthroplasty fracture. Arch Orthop Trauma Surg. 2022;142:3533–8. Noble PC, Alexander JW, Lindahl LJ, Yew DT, Granberry WM, Tullos HS. The anatomic basis of femoral component design. Clin Orthop Relat Res. 1988;(235):148–65. Oba M, Inaba Y, Kobayashi N, Ike H, Tezuka T, Saito T. Effect of femoral canal shape on mechanical stress distribution and adaptive bone remodelling around a cementless tapered-wedge stem. Bone Joint Res. 2016;5:362–9. Cooper HJ, Jacob AP, Rodriguez JA. Distal fixation of proximally coated tapered stems may predispose to a failure of osteointegration. J Arthroplasty. 2011;26:78–83. Abe H, Sakai T, Takao M, Nishii T, Nakamura N, Sugano N. Difference in stem alignment between the direct anterior approach and the posterolateral approach in total hip arthroplasty. J Arthroplasty. 2015;30:1761–6. Khanuja HS, Banerjee S, Jain D, Pivec R, Mont MA. Short bone-conserving stems in cementless hip arthroplasty. J Bone Joint Surg Am. 2014;96:1742–52. Herrera A, Panisello JJ, Ibarz E, Cegoñino J, Puértolas JA, Gracia L. Long-term study of bone remodelling after femoral stem: a comparison between dexa and finite element simulation. J Biomech. 2007;40:3615–25. Ike H, Inaba Y, Kobayashi N, Hirata Y, Yukizawa Y, Aoki C, et al. Comparison between mechanical stress and bone mineral density in the femur after total hip arthroplasty by using subject-specific finite element analyses. Comput Methods Biomech Biomed Engin. 2015;18:1056–65. Keyak JH, Rossi SA, Jones KA, Skinner HB. Prediction of femoral fracture load using automated finite element modeling. J Biomech. 1998;31:125–33. Gruen 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):17–27. Kanda Y. Investigation of the freely available easy-to-use software ‘EZR’ for medical statistics. Bone Marrow Transpl. 2013;48:452–8. Gustke K. Short stems for total hip arthroplasty: initial experience with the Fitmore stem. J Bone Joint Surg Br. 2012;94:47–51. Jacquel A, Le Viguelloux A, Valluy J, Saffarini M, Bonin N. A shortened uncemented stem offers comparable positioning and increased metaphyseal fill compared to a standard uncemented stem. J Exp Orthop. 2019;6:28. Vresilovic EJ, Hozack WJ, Rothman RH. Radiographic assessment of cementless femoral components. Correlation with intraoperative mechanical stability. J Arthroplasty. 1994;9:137–41. Evola FR, Evola G, Graceffa A, Sessa A, Pavone V, Costarella L, et al. Performance of the CLS Spotorno uncemented stem in the third decade after implantation. Bone Joint J. 2014;96–B:455–61. Crawford DA, Adams JB, Morris MJ, Berend KR, Lombardi AV. Distal femoral cortical hypertrophy not associated with thigh pain using a short stem femoral implant. Hip Int. 2021;31:722–8. Innmann MM, Weishorn J, Bruckner T, Streit MR, Walker T, Gotterbarm T, et al. Fifty-six percent of proximal femoral cortical hypertrophies 6 to 10 years after total hip arthroplasty with a short cementless curved hip stem - a cause for concern. BMC Musculoskelet Disord. 2019;20:261. Engh CA, Bobyn JD, Glassman AH. Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results. J Bone Joint Surg Br. 1987;69:45–55. Ishii S, Homma Y, Baba T, Ozaki Y, Matsumoto M, Kaneko K. Does the canal fill ratio and femoral morphology of Asian females influence early radiographic outcomes of total hip arthroplasty with an uncemented proximally coated, tapered-wedge stem. J Arthroplasty. 2016;31:1524–8. [Figure Legends]. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 01 Jul, 2024 Read the published version in Journal of Orthopaedic Surgery and Research → Version 1 posted Editorial decision: Revision requested 29 Apr, 2024 Reviews received at journal 23 Apr, 2024 Reviews received at journal 23 Apr, 2024 Reviewers agreed at journal 15 Apr, 2024 Reviewers agreed at journal 15 Apr, 2024 Reviewers agreed at journal 14 Apr, 2024 Reviewers invited by journal 12 Apr, 2024 Editor assigned by journal 11 Apr, 2024 Submission checks completed at journal 10 Apr, 2024 First submitted to journal 08 Apr, 2024 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4236152","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":291026613,"identity":"9b1b458e-b0ae-4b0f-9974-553d9644f20f","order_by":0,"name":"Takahiro Maeda","email":"","orcid":"","institution":"Toho University Graduate School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Takahiro","middleName":"","lastName":"Maeda","suffix":""},{"id":291026614,"identity":"6733ffde-d578-4215-acde-bbb6ab9b1182","order_by":1,"name":"Osamu Obayashi","email":"","orcid":"","institution":"Juntendo Shizuoka Hospital","correspondingAuthor":false,"prefix":"","firstName":"Osamu","middleName":"","lastName":"Obayashi","suffix":""},{"id":291026615,"identity":"b3166148-7adf-497f-b12f-e132a809453a","order_by":2,"name":"Muneaki Ishijima","email":"","orcid":"","institution":"Juntendo University Hospital","correspondingAuthor":false,"prefix":"","firstName":"Muneaki","middleName":"","lastName":"Ishijima","suffix":""},{"id":291026618,"identity":"3afc090d-0d45-4634-9976-67040e051ac8","order_by":3,"name":"Taichi Sato","email":"","orcid":"","institution":"Tokyo Denki University","correspondingAuthor":false,"prefix":"","firstName":"Taichi","middleName":"","lastName":"Sato","suffix":""},{"id":291026619,"identity":"11d1aef0-7e4f-4e1f-88f2-7928b0ec207e","order_by":4,"name":"Yoshiro Musha","email":"","orcid":"","institution":"Toho University Ohashi Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Yoshiro","middleName":"","lastName":"Musha","suffix":""},{"id":291026621,"identity":"71fe884f-8fb7-47f8-b6fe-de4856abf992","order_by":5,"name":"Hiroyasu Ikegami","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABP0lEQVRIie2RP0vEMBTAUwPpktK1R+t36BG4P1D0q7QUOh0quJYSEOoid7McfgddnCuBrG5ykEGLawcPjlIQDxu9nrQ9dRXsD5I8XvjxXvIA6Oj4g9iwiiD6OLBebka53O3Fr0qPSsX9QfkK0SaTNJQmQ1VLn3EYeVRFXroKby3ywO4WSuEc6QDboAiBOqwr4zOVEMyZRyFixOICD0Tgj4AbnPYotpULDuCY1htjCJkYJaWixqaBpDIZlI0x7/oxs4FGAZSttpR1JJXzV2MtMJkf559KUlZ5+0bRYigb48oyFtg2J2irwN1VYP9qykgMkW8qU4ENEZCRGwTeJUUnzOJG6y33XHnK8mh/pvP+ssjFoT7308WL43gzAG/SLHT8xo9J9vBmKhBXqWoocka+3VaUohnUONihdHR0dPwr3gG02mr/JcwZJAAAAABJRU5ErkJggg==","orcid":"","institution":"Toho University Ohashi Medical Center","correspondingAuthor":true,"prefix":"","firstName":"Hiroyasu","middleName":"","lastName":"Ikegami","suffix":""}],"badges":[],"createdAt":"2024-04-08 11:42:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4236152/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4236152/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s13018-024-04856-z","type":"published","date":"2024-07-01T15:03:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54929300,"identity":"276a6d66-496a-4f88-9e96-9250c42af627","added_by":"auto","created_at":"2024-04-18 17:48:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":167528,"visible":true,"origin":"","legend":"\u003cp\u003e3D bone model\u003c/p\u003e\n\u003cp\u003eThe DICOM data of the preoperative femur CT were read to extract the contour of the femur and create a 3D bone model using tetrahedral elements. The femur was osteotomized approximately 10 mm from the lesser trochanter.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/bea32fd5d054dd85b8ba7df6.png"},{"id":54928823,"identity":"b904802f-d75c-4069-aba1-3b81cff29be7","added_by":"auto","created_at":"2024-04-18 17:40:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":50087,"visible":true,"origin":"","legend":"\u003cp\u003eAnalysis conditions\u003c/p\u003e\n\u003cp\u003eThe load restraint conditions were set assuming a one-leg standing posture, with 2,400 N at the stem head from 15° proximal medial to the femoral axis and 1,200 N at the abductor pollicis brevis from 20° distal lateral to the femoral axis.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/52c96fcaa2b39e1c915c2bee.png"},{"id":54928826,"identity":"7eaf89a0-57c2-4286-9a6c-c289314ad83f","added_by":"auto","created_at":"2024-04-18 17:40:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":283065,"visible":true,"origin":"","legend":"\u003cp\u003eSegmentation of the finite element models of the femur according to Gruen’s zones.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/55dc296dc2d3cda27b3eeb44.png"},{"id":54928822,"identity":"c835f002-85a9-426b-ac79-a44db017a916","added_by":"auto","created_at":"2024-04-18 17:40:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":82833,"visible":true,"origin":"","legend":"\u003cp\u003eChange in von Mises stress values in Gruen’s zone with increasing varus angle.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/e1aaca10ae89d8a718ea0e1d.png"},{"id":54928829,"identity":"70e12821-8ecb-4a64-ba2c-9b150b2e9d4a","added_by":"auto","created_at":"2024-04-18 17:40:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":48662,"visible":true,"origin":"","legend":"\u003cp\u003eChange in the von Mises stress ratio in Gruen’s zone with increasing varus angle.\u003c/p\u003e\n\u003cp\u003evon Mises stress ratio; von Mises stress values of varus angle 1°, 2°, 3°, 4°, 5° / von Mises stress values of varus angle 0°\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/dd4a6d5d1d8dd4a70ba0357f.png"},{"id":54928830,"identity":"f00b6392-d6a3-457c-9f72-6116d372645e","added_by":"auto","created_at":"2024-04-18 17:40:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":302593,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution diagram when the stem is neutrally inserted\u003c/p\u003e\n\u003cp\u003eGood load transfer occurred distally from Gruen zones 2 and 6.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/bb64eb02e1cff89192f790d1.png"},{"id":54929302,"identity":"b9241055-cb19-4b10-b8a7-afcc0f7861d7","added_by":"auto","created_at":"2024-04-18 17:48:24","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":13306,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of stresses between femur types\u003c/p\u003e\n\u003cp\u003eThe mean VMS values per zone for each angle are shown. Zone 4 shows the highest stress for all types, and type A (champagne-flute) shows the highest stress value.\u003c/p\u003e\n\u003cp\u003eVMS: von Mises stress\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/8cb50653182dc4d9adb31064.png"},{"id":54929556,"identity":"e38dcc0f-48f7-41e2-8af1-49df2e9c851b","added_by":"auto","created_at":"2024-04-18 17:56:24","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":81012,"visible":true,"origin":"","legend":"\u003cp\u003eTaperloc stem (Zimmer Biomet Holdings, Inc., Indiana, USA). (a) Standard stem and (b) short stem (35 mm shorter than the standard stem)\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/58a8c4522d7f47dce412d0a0.png"},{"id":61427251,"identity":"2484d47c-a32e-440d-95d3-95b9e8eda5bf","added_by":"auto","created_at":"2024-07-30 15:03:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1552866,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4236152/v1/a188c9c0-523f-4ced-9e3e-ba40510afb7d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Finite element analysis of mechanical stress in a cementless tapered-wedge short stem in the varus position","fulltext":[{"header":"Background","content":"\u003cp\u003eVarious types of implants are used in total hip arthroplasty (THA). The use of short-stem implants has increased in recent years. The reasons for this include greater bone preservation, better proximal load transfer, less invasive surgery, and ease of use of the anterior approach [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The postoperative stress distribution in the femur changes significantly after stem placement because the load is transmitted to the femur through the stem. Bone density in the proximal femur decreases in the early postoperative period after THA, and remodeling occurs to accommodate the new load. Stresses in the proximal femur are low, and bone atrophy occurs; in the long term, bone atrophy may lead to peri-implant fractures and stem instability [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eShort stems transmit stress more easily proximally than standard stems, and many surgeons have reported good results with short stems [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. A disadvantage of short stems is that they tend to be inserted during misalignment. The stem should be inserted horizontally along the bony axis. However, depending on the skill of the surgeon, implant design, and approach technique, the stem may be in the varus or valgus position [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Short stems, in particular, are prone to the varus position, and peri-stem bone reactions due to the varus position have been reported [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWe used finite element analysis to investigate how stress transfer changes with the degree of varus position, especially for short stems that are prone to the varus position. This study aimed to evaluate the stresses on the femur as the varus angle increases and to investigate the varus angle at which peri-stem bony reactions can occur.\u003c/p\u003e \u003cp\u003eTherefore, in this study, we used preoperative computed tomography (CT) images of patients undergoing surgery to examine the change in stress when the stem was tilted in increments of 1\u0026deg; varus angle.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis study included cases of hip osteoarthritis that underwent joint replacement surgery at Juntendo University Shizuoka Hospital between April 1, 2018, and March 31, 2021. The patients who underwent preoperative CT were classified into three femoral types based on Noble\u0026rsquo;s Canal Flare Index (CFI), with CFI\u0026thinsp;\u0026lt;\u0026thinsp;4.7 being the champagne-flute type (type A), CFI\u0026thinsp;\u0026lt;\u0026thinsp;3 being the stovepipe type (type C), and CFI between the two being intermediate type (type B). Because 10 cases with the champagne-flute type were indicated, 10 cases of types B and C were also randomly selected [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSince only two male patients were included in type A and the other patients were female, we excluded the male patients to ensure homogeneity, as being male has been identified as a risk factor for proximal stress shielding in previous studies, and other reports have consistently focused on female patients [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] (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\u003ePatient demographics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" 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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSide (right/left)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCFI\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e63\u0026thinsp;\u0026plusmn;\u0026thinsp;9.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4 / 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e5.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType B\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e71\u0026thinsp;\u0026plusmn;\u0026thinsp;11.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 / 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e3.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e73\u0026thinsp;\u0026plusmn;\u0026thinsp;14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFemale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5 / 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e2.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e*Values are mean\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eType A (champagne-flute), Type B (intermediate), Type C (stovepipe)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eCFI, canal flare index; Side femoral affected side\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFinite element analysis was performed using Mechanical Finder ver. 10.0 (Research Center for Computational Mechanics, Japan).\u003c/p\u003e \u003cp\u003eCT DICOM data (Discovery CT750 HD; GE Medical Systems, Milwaukee, WI, USA) were used to create a finite element model. One millimeter slice thickness of the affected femur was obtained from the preoperative CT of the extracted case. The femur contour was extracted, and a 3-D finite element model was created using tetrahedral elements. The stems were subjected to Taperloc microplasty (Zimmer Biomet Holdings Inc., Indiana, USA). This stem is a cementless, tapered-wedge stem that is shorter than a standard stem. Stem contours were captured using a 3D scanner (ATOS Core Education, GOM, Germany). The contours and coordinate axes were corrected, converted to stereolithography data, and imported into Mechanical Finder. The femoral model was osteotomized approximately 10 mm proximal to the lesser trochanter. The stem was placed through the proximal metaphyseal bone axis, and stem anteversion was performed in the direction of the femoral neck bone axis [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe stem was placed by the same examiner, and the appropriate size was determined to be a proximal metaphyseal fit, with the medial and lateral sides of the stem fitted into the bone cortex [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA total of 168 bone models were created: 48 (with 8 examples) for type A, 60 (with 10 examples) for type B, and 60 (with 10 examples) for type C.; the varus angle increased by 1\u0026deg; from 0\u0026deg; to 5\u0026deg; from the bone axis.\u003c/p\u003e \u003cp\u003eLoad restraint conditions were set assuming a one-leg standing position, with a joint reactive force of 2400 N exerted by the weight of the body on the femoral head or prosthetic head at an angle of 15\u0026deg; proximal medial relative to the femoral axis, and a 1200 N force generated by the abductor muscles exerted at an angle of 20\u0026deg; distal lateral relative to the greater trochanter [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eYoung\u0026rsquo;s modulus based on CT values (Hounsfield units) was set for each element using the conversion formula of Keyak et al. for femoral material properties to reflect the differences in bone density in each case. The Poisson\u0026rsquo;s ratio of the femoral material was set to 0.40, and the stem was made of titanium (Ti-6Al-4V) with a Poisson\u0026rsquo;s ratio of 0.28 [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The stem and femur were assumed to share a nodal point and completely adhere to each other. Seven zones were classified based on Gruen\u0026rsquo;s zone classification, the volume of interest was set, and the mean value of the equivalent stress for each zone was calculated [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEZR software (version 4.2.2) was used for the statistical analysis [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Multiway analysis of variance (ANOVA) was applied for between-group comparisons, and repeated-measures analysis of variance, and multiple comparisons (Bonferroni method) were applied for within-county comparisons at a significance level of 5%.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eFirst, a comparative study of the average stress in each zone with increasing internal warping angle was conducted. In zone 2, all femur types showed a significant decrease in stress from a varus angle of 3\u0026deg;, whereas in zone 3, femur types B and C showed significant increases in stress from varus angles of 3\u0026deg; and 4\u0026deg;, respectively. In zone 4, there was a significant increase in stress from a varus angle of 2\u0026deg; in femurs A and B and from a varus angle of 3\u0026deg; in type C (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\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\u003eVarus angles at which a significant increase or decrease in von Mises stress began to occur in the Gruen zone.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVon Mises stress\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eType A\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eType B\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eType C\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eVarus angle (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDecrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.001)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.046)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.007)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.077)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.003)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.002)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.017)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.004)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.001)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eSecond, because the quality of each bone was different, we examined the rate of change instead of the stress value. In zone 2, there was a significant decrease in stress in femur types A and C from a varus angle of 3\u0026deg;, a significant increase in stress in femur type B from a varus angle of 3\u0026deg;, and a significant increase in stress in femur types A and C from a varus angle of 4\u0026deg;. In zone 4, there was a significant increase in stress in femur type B from an angle of 4 \u0026deg; and in femur type C from a varus angle of 5\u0026deg; (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\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\u003eChange in von Mises stress ratio with respect to the 0\u0026deg; varus angle in Gruen\u0026rsquo;s zone with increasing varus angle.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVon Mises stress\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eType A\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eType B\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eType C\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eVarus angle (\u0026deg;)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDecrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.026)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.002)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.118)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.027)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.034)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZone 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncrease\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.483)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;\u0026lt;\u0026thinsp;0.001)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5\u0026deg;\u0026le;\u003c/p\u003e \u003cp\u003e(P\u0026thinsp;=\u0026thinsp;0.012)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWe also examined whether there was a significant difference in stress between the femurs in each zone at each angle. The stress was highest in zones 3 and 4 for all femur types, with type A having the highest stress, followed by types B and C (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). There was no significant difference in the stress in the zones owing to the change in the angle between the femur types (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eRecently, the use of tapered-wedge short stems has increased because of their ability to preserve bone and tendon. Barrington et al. compared the postoperative results of the Taperloc standard stem and microplasty and found that both had good results, with low revision rates of 0.9%/1.0%. Molli et al. reported a lower intraoperative fracture risk of 3.1%/0.4% with Taperloc microplasty, indicating that the short stem is useful [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDepending on the surgical technique, implant design, and surgeon\u0026rsquo;s skill, the stem may be placed in the varus position. This is particularly true for short stems, which are not inserted into the distal medullary cavity but only into the proximal medullary cavity, thus increasing the degrees of freedom [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlthough it has been reported that the varus position is not clinically problematic [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], Vresiovic et al. evaluated stem fixation and radiographic images at the time of surgery in patients who underwent THA revision for pain and found that 83% of the varus position cases had instability and a high revision rate, which was associated with clinical symptoms [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt has been reported that short stems have less stress loading around the stem than standard stems and that the proximal loss of bone density caused by stem insertion is significantly less with short stems because force transmission is shifted more proximally [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, there are few reports of peri-stem bony reactions in short stems, although there are no comprehensive reports on such reactions. Evola et al. reported an increased risk of femoral cortical hypertrophy and pain associated with varus insertion [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Crawford et al. found distal femoral cortical hypertrophy in 74% of cases in Gruen zone 3 and 56% in zone 5, and Innmann et al. found cortical hypertrophy in 56% of cases, mostly in zones 3 and 5 [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the present study, there was a significant decrease in stress in zone 2 and increased stress in zones 3 and 4, suggesting the appearance of a distal periosteal reaction, similar to the results of previous studies. In the comparison of mean stress values, zone 2 showed a significant decrease in all groups at a 3\u0026deg; varus angle, and the acceptable varus angle for the appearance of SS above Engh classification grade 3 was expected to be 3\u0026deg; [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn zone 3, there was an increase from a 3\u0026deg; varus angle in type B and from a 4\u0026deg; varus angle in type C. In zone 4, there was a significant increase in stress from a 2\u0026deg; varus angle in types A and B and a 3\u0026deg; varus angle in type C. This suggests the appearance of cortical hypertrophy distally, with a narrower medullary lumen shape indicating a narrower tolerance range and a wider medullary lumen shape indicating a wider tolerance range.\u003c/p\u003e \u003cp\u003eConsidering the differences in the bone quality of each patient, we also analyzed the rate of change in stress with increasing varus angle from 0\u0026deg; as a reference point. In zone 2, we observed a significant decrease in stress in all groups at a varus angle of \u0026ge;\u0026thinsp;3\u0026deg;. In zone 3, the stress increased significantly from 3\u0026deg; for type B to 4\u0026deg; for type C, whereas in zone 4, the stress increased significantly from 4\u0026deg; for type B to 5\u0026deg; for type C. As mentioned above, the tolerance range increased with the medial cavity geometry.\u003c/p\u003e \u003cp\u003eOba et al. compared the stress distribution in the Accolade TMZF stem (tapered-wedge cementless stem) with different luminal geometries (cases with stem alignment\u0026thinsp;\u0026lt;\u0026thinsp;3\u0026deg;) and analyzed three luminal types (champagne-flute, intermediate, and stovepipe). The authors reported that the stovepipe type tended to have a larger stem size, a stem contacting the cortex distally, and a decrease in stress proximally and that bone mineral density decreased in zone 2, although there was no significant difference in stress in Gruen\u0026rsquo;s zone 6 [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Cooper et al. also studied the postoperative radiographic osteointegration of Accolade TMZF stems and reported that the risk of proximal stress shielding and proximal osteointegration failure was associated with a small CFI (stovepipe type) and a large stem size [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Ishi et al. reported that osteointegration failure was more common in patients with a large CFI (champagne-flute type), which they attributed to distal fixation due to the narrow femoral marrow cavity in Asians, and concluded that both stovepipe and champagne-flute types should be treated with caution [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the present study, there was no change in the stress distribution in each medullary cavity when the insertion was parallel to the bone axis (0\u0026deg; varus angle), and there was no significant difference between the groups. However, the highest stresses were found in zone 4, and there was no change in the stress distribution from zones 2 and 6 distally. The reason for the lack of change in stress distribution due to the difference in the medullary cavity is that, unlike the stems used by Oba et al., Cooper et al., and Ishi et al., the stem shape is a reduced structure to avoid distal fixation, and the stem is not distally fixed, which is thought to be because it adapts to various medullary cavity configurations and transmits stress (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBecause an appropriate stem size was used in this study, it was thought that Taperloc microplasty could accommodate any luminal configuration and transmit stress firmly distally, at least if the proper size was selected in preoperative planning and the stem alignment was neutral. However, as in the studies by Oba et al. and Ishi et al., this study was limited to women only, and Cooper et al. found the male sex to be a risk factor. Therefore, the results of this study conducted on women may not be applicable to men, and caution is required when treating men. Further analysis of male patients is required. A narrow medullary space of this type showed a significant increase in distal stress with a 2\u0026deg; varus angle. Therefore, stem insertion should be performed more carefully in patients with a narrow medullary space.\u003c/p\u003e \u003cp\u003eThe main limitation of this study is that in setting the boundary conditions, the stem and femur were analyzed with a shared contact point and complete adherence between the stem and femur. The stems were proximally porous and distally smooth. To construct a realistic model, different friction coefficients must be set for each stem surface. Although Oba et al. also mentioned this as a limitation of their study, they considered that assuming successful fixation of the cementless stem, finite element analysis may show characteristic stress distributions, even with a simplified finite element model [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Second, no comparison with actual cases or bone density evaluation was performed. Third, stem insertion in fragile bones, such in as femoral neck fractures, should be considered separately. Finally, it should be noted that the results of this study may not apply to all cases, as no analysis was performed on male patients.\u003c/p\u003e \u003cp\u003eAdditional studies on stem flexion/extension, valgus, anterior/posterior insertion, and male patients will further clarify the advantages and disadvantages of short stems.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eMost of the articles we reviewed only evaluated a group of cases of stem varus malalignment with periosteal reactions in imaging studies, and none of the articles investigated the stem varus angle. In the present study, stress decreased with increasing varus angle in zone 2 of the Gruen classification when the varus angle was \u0026ge;\u0026thinsp;3\u0026deg;, suggesting the appearance of a grade 3 Engh classification of stress shielding and the appearance of cortical hypertrophy in zones 3 and 4. In the champagne-flute type (type A) with a narrow medullary cavity, a significant increase in distal stress was observed at a 2\u0026deg; varus angle, and careful stem insertion was necessary. Taperloc microplasty provided good distal load transfer in all femoral medullary configurations when the stem was neutrally inserted.\u003c/p\u003e"},{"header":"List of Abbreviations","content":"\u003cp\u003eCFI, Canal Flare Index\u003c/p\u003e \u003cp\u003eCT, computed tomography\u003c/p\u003e \u003cp\u003eTHA, total hip arthroplasty\u003c/p\u003e \u003cp\u003eVMS, von Mises stress\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthics approval and consent to participate\u003c/h2\u003e \u003cp\u003e The research protocol was approved by the Research Ethics Committee of the Faculty of Medicine, Juntendo University (research project number E21-0191), and research permission was obtained from Toho University Medical Center Ohashi Hospital (control NumberC_H21009).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication\u003c/strong\u003e \u003cp\u003e Informed consent was obtained from all participants included in the study.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eOO, MI, and TS elaborated on the plan and arranged for the experiment at Juntendo University Shizuoka Hospital. YM performed most of the laboratory work. HI was a major contributor to the writing of the manuscript. All authors have read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe would like to thank Dr. Kanda and Dr. Morohashi of Juntendo University Shizuoka Hospital for their invaluable advice and for providing us with the patient\u0026rsquo;s femoral CT data.\u003c/p\u003e\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e \u003cp\u003eData supporting the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cdiv class=\"Heading\"\u003e[\u003cb\u003eReferences]\u003c/b\u003e\u003c/div\u003e \u003cli\u003e\u003cspan\u003eBarrington JW, Emerson RH. The short and shorter of it: \u0026gt;1750 tapered titanium stems at 6- to 88-month follow-up. J Arthroplasty. 2013;28:38\u0026ndash;40.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMolli RG, Lombardi AV, Berend KR, Adams JB, Sneller MA. A short tapered stem reduces intraoperative complications in primary total hip arthroplasty. Clin Orthop Relat Res. 2012;470:450\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMorrey BF. Short-stemmed uncemented femoral component for primary hip arthroplasty. Clin Orthop Relat Res. 1989:(249):169\u0026ndash;75.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEngh CA, McGovern TF, Bobyn JD, Harris WH. A quantitative evaluation of periprosthetic bone-remodeling after cementless total hip arthroplasty. J Bone Joint Surg Am. 1992;74:1009\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEngh CA, Hooten JP Jr, Zettl-Schaffer KF, Ghaffarpour M, McGovern TF, Bobyn JD. Porous-coated total hip replacement. Clin Orthop Relat Res. 1994;298:89\u0026ndash;96.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEngh CA, Bobyn JD. The influence of stem size and extent of porous coating on femoral bone resorption after primary cementless hip arthroplasty. Clin Orthop Relat Res. 1988;(231):7\u0026ndash;28.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaku N, Pramudita JA, Yamamoto K, Hosoyama T, Tsumura H. Stress distributions of the short stem and the tapered wedge stem at different alignments: a finite element analysis study. J Orthop Surg Res. 2022;17:530.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoth A, Richartz G, Sander K, Sachse A, Fuhrmann R, Wagner A, et al. [Periprosthetic bone loss after total hip endoprosthesis. Dependence on the type of prosthesis and preoperative bone configuration]. Orthopade. 2005;34:334\u0026ndash;44.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBernasek TL, Lee WS, Lee HJ, Lee JS, Kim KH, Yang JJ. Minimally invasive primary THA: anterolateral intermuscular approach versus lateral transmuscular approach. Arch Orthop Trauma Surg. 2010;130:1349\u0026ndash;54.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNishioka ST, Andrews SN, Mathews K, Nakasone CK. Varus malalignment of short femoral stem not associated with post-hip arthroplasty fracture. Arch Orthop Trauma Surg. 2022;142:3533\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNoble PC, Alexander JW, Lindahl LJ, Yew DT, Granberry WM, Tullos HS. The anatomic basis of femoral component design. Clin Orthop Relat Res. 1988;(235):148\u0026ndash;65.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOba M, Inaba Y, Kobayashi N, Ike H, Tezuka T, Saito T. Effect of femoral canal shape on mechanical stress distribution and adaptive bone remodelling around a cementless tapered-wedge stem. Bone Joint Res. 2016;5:362\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCooper HJ, Jacob AP, Rodriguez JA. Distal fixation of proximally coated tapered stems may predispose to a failure of osteointegration. J Arthroplasty. 2011;26:78\u0026ndash;83.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbe H, Sakai T, Takao M, Nishii T, Nakamura N, Sugano N. Difference in stem alignment between the direct anterior approach and the posterolateral approach in total hip arthroplasty. J Arthroplasty. 2015;30:1761\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhanuja HS, Banerjee S, Jain D, Pivec R, Mont MA. Short bone-conserving stems in cementless hip arthroplasty. J Bone Joint Surg Am. 2014;96:1742\u0026ndash;52.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHerrera A, Panisello JJ, Ibarz E, Cego\u0026ntilde;ino J, Pu\u0026eacute;rtolas JA, Gracia L. Long-term study of bone remodelling after femoral stem: a comparison between dexa and finite element simulation. J Biomech. 2007;40:3615\u0026ndash;25.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIke H, Inaba Y, Kobayashi N, Hirata Y, Yukizawa Y, Aoki C, et al. Comparison between mechanical stress and bone mineral density in the femur after total hip arthroplasty by using subject-specific finite element analyses. Comput Methods Biomech Biomed Engin. 2015;18:1056\u0026ndash;65.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKeyak JH, Rossi SA, Jones KA, Skinner HB. Prediction of femoral fracture load using automated finite element modeling. J Biomech. 1998;31:125\u0026ndash;33.\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\u003eKanda Y. Investigation of the freely available easy-to-use software \u0026lsquo;EZR\u0026rsquo; for medical statistics. Bone Marrow Transpl. 2013;48:452\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGustke K. Short stems for total hip arthroplasty: initial experience with the Fitmore stem. J Bone Joint Surg Br. 2012;94:47\u0026ndash;51.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJacquel A, Le Viguelloux A, Valluy J, Saffarini M, Bonin N. A shortened uncemented stem offers comparable positioning and increased metaphyseal fill compared to a standard uncemented stem. J Exp Orthop. 2019;6:28.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVresilovic EJ, Hozack WJ, Rothman RH. Radiographic assessment of cementless femoral components. Correlation with intraoperative mechanical stability. J Arthroplasty. 1994;9:137\u0026ndash;41.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEvola FR, Evola G, Graceffa A, Sessa A, Pavone V, Costarella L, et al. Performance of the CLS Spotorno uncemented stem in the third decade after implantation. Bone Joint J. 2014;96\u0026ndash;B:455\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCrawford DA, Adams JB, Morris MJ, Berend KR, Lombardi AV. Distal femoral cortical hypertrophy not associated with thigh pain using a short stem femoral implant. Hip Int. 2021;31:722\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInnmann MM, Weishorn J, Bruckner T, Streit MR, Walker T, Gotterbarm T, et al. Fifty-six percent of proximal femoral cortical hypertrophies 6 to 10 years after total hip arthroplasty with a short cementless curved hip stem - a cause for concern. BMC Musculoskelet Disord. 2019;20:261.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEngh CA, Bobyn JD, Glassman AH. Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results. J Bone Joint Surg Br. 1987;69:45\u0026ndash;55.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIshii S, Homma Y, Baba T, Ozaki Y, Matsumoto M, Kaneko K. Does the canal fill ratio and femoral morphology of Asian females influence early radiographic outcomes of total hip arthroplasty with an uncemented proximally coated, tapered-wedge stem. J Arthroplasty. 2016;31:1524\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e[Figure Legends].\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":"mechanical stress, varus position, malalignment, finite element analysis, stress shielding, cortical hypertrophy, total hip arthroplasty, tapered-wedge stem, short stems, Gruen’s zone","lastPublishedDoi":"10.21203/rs.3.rs-4236152/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4236152/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e In recent years, the use of tapered-wedge short stems has increased because of their ability to preserve bones and tendons. Surgical techniques occasionally result in a varus position of the stem, which is particularly pronounced in short stems. Although the varus position is not clinically problematic, there are reports of an increased incidence of stress shielding and cortical hypertrophy. Thus, we evaluated and examined the acceptable range of varus angles using finite element analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods:\u003c/strong\u003e We selected patients diagnosed with osteoarthritis of the hip joint who had undergone arthroplasty and were classified into three types [champagne-flute (type A), intermediate (type B), and stovepipe (type C)]. Finite element analysis was performed using Mechanical Finder. The model was created using a Taperloc microplasty stem with the varus angle increased by 1° from 0° to 5° from the bone axis and classified into seven zones based on Gruen’s zone classification under loading conditions in a one-leg standing position. The volume of interest was set, the mean equivalent stress for each zone was calculated, and the mean value of the equivalent stress in each zone was calculated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eA significant decrease in stress was observed in zone 2, and increased stress was observed in zones 3 and 4, suggesting the emergence of a distal periosteal reaction, similar to the results of previous studies. In zone 2, there was a significant decrease in stress in all groups at a varus angle ≥3°. In zone 3, stress increased from ≥3° in type B and ≥4° in type C. In zone 4, there was a significant increase in stress at varus angles of ≥2° in types A and B and at ≥3° in type C.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e In zone 2, the varus angle at which stress shielding above Engh classification grade 3 may appear is expected to be ≥3°. Distal cortical hypertrophy may appear in zones 3 and 4; the narrower the medullary cavity shape, the smaller the allowable angle of internal recession, and the wider the medullary cavity shape, the wider the allowable range. Long-term follow-up is required in patients with varus angles \u0026gt;3°.\u003c/p\u003e","manuscriptTitle":"Finite element analysis of mechanical stress in a cementless tapered-wedge short stem in the varus position","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-18 17:40:19","doi":"10.21203/rs.3.rs-4236152/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-04-30T02:41:49+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-23T23:36:10+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-23T15:12:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"0cb3dbc8-3a5b-4d57-bd93-58c3acc242ed","date":"2024-04-15T05:56:01+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"26d47871-dd06-4f44-b716-babc9ee7cfc5","date":"2024-04-15T05:05:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"61959893-8695-42ac-a214-1292988c2fef","date":"2024-04-14T15:06:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-13T03:49:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-11T05:28:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-10T07:51:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Orthopaedic Surgery and Research","date":"2024-04-08T11:40:50+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":"d6c0eafe-535b-41d0-81dd-8f341ffb3acd","owner":[],"postedDate":"April 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-07-30T15:03:13+00:00","versionOfRecord":{"articleIdentity":"rs-4236152","link":"https://doi.org/10.1186/s13018-024-04856-z","journal":{"identity":"journal-of-orthopaedic-surgery-and-research","isVorOnly":false,"title":"Journal of Orthopaedic Surgery and Research"},"publishedOn":"2024-07-01 15:03:13","publishedOnDateReadable":"July 1st, 2024"},"versionCreatedAt":"2024-04-18 17:40:19","video":"","vorDoi":"10.1186/s13018-024-04856-z","vorDoiUrl":"https://doi.org/10.1186/s13018-024-04856-z","workflowStages":[]},"version":"v1","identity":"rs-4236152","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4236152","identity":"rs-4236152","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}