Accuracy, efficiency, and clinical outcomes of a pinless CT-Free, robotic arm-assisted total hip replacement system

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The purpose of this study was to investigate the accuracy, efficiency, and early post-operative clinical outcomes of a pinless, fluoroscopic-based raTHA system. Methods A retrospective review of a single surgeon’s first 50 raTHA cases using the direct anterior approach (DAA) was conducted. Accuracy of acetabular component placement was determined by analysing the final planned target and post‐operative supine anteroposterior (AP) pelvic radiographs. Mean absolute differences (MAD) between target and post-operative radiographs were computed for cup inclination and anteversion, and the percentage of cases within the Lewinnek Safe Zone was calculated. To assess efficiencies in adoption, cumulative summation (CUSUM) analysis was performed using operative times and robotic timestamps to compare between learning and proficiency phases. Hip Disability and Osteoarthritis Outcome Score-12 (HOOS-12) and Oxford Hip Score (OHS) were collected pre-operatively and up to one-year post-operative. Results There were no significant (p=0.419) differences between targeted and radiographic cup inclination (41.8±1.5 vs. 42.3± 4)) or anteversion (15.9±1.3 vs. 15.2±3.0, p = 0.121). The raTHA MAD for inclination and anteversion were 3.6±2.7° and 2.4±1.8° respectively, and the percentage of cases within the Lewinnek Safe Zone was 96% (48/50). CUSUM analysis revealed an initial learning curve of 25 cases, with significantly shorter operative times in the proficiency compared to learning phase (65.6±7.9 vs. 72.4±12.7 min, p=0.028), and without significant differences in accuracy between phases. Both HOOS-12 and OHS significantly (p<0.0001) improved between pre-operative and one-year post-operative. Conclusion The results of this study demonstrate that use of a pinless, fluoroscopic-based raTHA system for DAA THA demonstrates high accuracy and reproducibility of acetabular cup placement with an initial learning curve of 25 cases. Accuracy Clinical outcomes Direct anterior approach Learning curve Total hip arthroplasty Robotic Figures Figure 1 Figure 2 Figure 3 Figure 4 Background Total hip arthroplasty (THA) is one of the most commonly performed orthopedic procedures [1, 2], and is considered the gold standard of care for treating end-stage osteoarthritis [3] by significantly improving function, pain [4-7], and health-related quality of life [8, 9]. THAs have increased in volume by approximately 14% in the United States and Europe from 2009 to 2015 [2, 10], and this is expected to increase by approximately 29% between 2020 and 2025 in the United States [11] and 66% by 2040 in Australia [12]. Revision THA increased by over 28% during the same time period in the United States and Europe [2, 13] and is similarly expected to increase by over 9% between 2020 and 2025 in the United States [14]. Dislocation and instability, alongside infection, are the leading causes of revision in the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR: Figure HT6) [15]. Malpositioning of the acetabular cup has been associated with accelerated component wear, instability, dislocation, poor patient reported outcome measures (PROMs), reduced range of motion (ROM), and revision [16-21]. Technological advancements, such as computer and robotic assistance, have been developed to improve the precision of THA. Recent meta-analyses report robotic-assisted THA (raTHA) has shown greater accuracy in placing the acetabular cup within the Lewinnek Safe Zone compared to manual THA (mTHA) [22, 23]. However, the gains from increased accuracy of robotic systems may be offset by increased surgical times. For example, robotic systems that rely on pre-operative computed tomography (CT) imaging for planning, and the intra-operative placement of navigation pins for anatomical landmarking and cup positioning, affect surgical scheduling and surgical workflow, resulting in prolonged operative times along with the introduction of additional radiation exposure [23-25]. Recent developments include a pinless fluoroscopy-based robotic system that offers advantages over CT-based systems, such as reduced radiation exposure [26] and shorter operating times with less variance, while removing the risk of pin-site complications [27]. Preliminary research indicates fluoroscopy-based raTHA may provide superior accuracy and reproducibility in cup placement compared to mTHA [28-31], with an initial learning curve of 12 cases [32]. To the best of our knowledge, clinical outcomes comparing pinless fluoroscopy-based raTHA to mTHA are presently limited to three studies. Buchan et al. [33] reported lower pain scores at two-weeks post-operative, a shorter hospital length of stay, and a lower rate of complications through 90-days post-operative, and less in-hospital and post-operative narcotic usage with raTHA [34]. At one-year post-operative, the same group reported greater improvements in Hip Disability and Osteoarthritis Outcome (HOOS) pain, physical function, and joint replacement scores [35]. Despite the positive findings from the aforementioned studies, more research is necessary to confirm the reports of high accuracy and clinical outcomes, and to study the learning curve and surgical efficiency associated with fluoroscopy-based raTHA in different settings. The purpose of this study was therefore to investigate the initial accuracy, reproducibility, efficiency, and short-term clinical outcomes of a pinless, CT-free, raTHA system. Methods This was a retrospective cohort analysis of a single surgeon’s first 50 fluoroscopy-based raTHA cases performed between August 2023 and February 2024. Patients over 18 years of age undergoing direct anterior approach (DAA) THA due to osteoarthritis were included in this study (Table 1). Ethics approval was obtained prior to study participation with a waiver of authorization and consent (Ethics approval #30625 from University of Tasmania, 2024). Table 1 Patient demographics Female Sex 27 (54%) Age 70.0 ± 7.9 BMI 29.0 ± 5.0 ASA Score I II III 16 (32%) 30 (60%) 4 (8%) Laterality (right) 28 (56%) All patients were implanted with a G7 Acetabular cup combined with Taperloc Femoral stem (Zimmer Biomet, Warsaw, IN). Patients received DAA THA with the assistance of a pinless fluoroscopic-based robotic arm orthopedic surgical assistance device (ROSA ® Total Hip System, Zimmer Biomet, Montreal, Quebec, Canada). The surgical procedure has been described in detail previously [25, 26, 36]. In brief, a fluoroscopic image of the leveled pelvis is acquired in the supine position and transferred to the robotic system for automatic identification of landmarks, which the surgeon reviews to match pelvic orientation to the pre-operative standing anteroposterior radiograph. Manual techniques are used for femoral head resection and reaming. The cup is then secured to the Robotic Arm and positioned semi-autonomously in collaboration with the surgeon for impaction to achieve the planned cup placement angles. Additional fluoroscopic images are taken during the verification stage and after the final femoral component is inserted to confirm proper alignment (Trial and Validation). Inclination and anteversion were initially targeted at 40° and 15°, respectively. In cases where the surgeon modified the target angles intra-operatively, these were recorded as the final planned target using the raTHA system and prior to impaction. The primary outcome of this study was acetabular component placement accuracy, defined as the mean difference between the final planned and post-operative radiographic inclination and version angles. Acetabular cup orientation was measured from four to twelve-week post-operative from supine radiographs with Ein-Bild-Roentgen-analyse (EBRA)-Cup (Universität Innsbruck, Innsbruck, Austria) [37]. The outliers of accurate acetabular cup placement were defined as an absolute difference in either inclination or anteversion of more than 5° from the final planned angle and the overall success rate was calculated based on the percentage of participants who were within the range of the Lewinnek Safe Zone [38]. There were two cases missing raTHA logs that were included in the safe zone analysis, but excluded from the mean absolute difference calculations, resulting in 48 cases available for accuracy analysis. Inclination and anteversion readings were performed three times by two independent readers and the reported values represent the averages of the two readings. Intra- and inter-rater reliability were assessed across all cases. The amount of agreement for ICC was classified as poor, < 0.5; moderate, 0.5 to < 0.75; good 0.75 to 0.9 [39]. Intra-rater reliability for inclination was ICC = 0.996 and 0.992 for rater 1 and rater 2, respectively. Intra-rater reliability was ICC = 0.99, 0.985 for anteversion for rater 1 and rater 2, respectively. Inter-rater reliability for inclination and anteversion were ICC = 0.994 and 0.94 for inclination and anteversion, respectively. Secondary outcomes included operative time (first incision to closure), the learning curve with respect to operative time, and PROMs. The Hip Disability and Osteoarthritis Outcome Score-12 (HOOS-12) and Oxford Hip Score (OHS) were collected pre-operatively, and at three, six, and 12-months post-operative from the AOANJRR. PROMs data was available for 29 patients. The minimal clinically important difference (MCID) for the HOOS-12 [40] and OHS [41] are 10.1 and 4.1, respectively. Statistical Analysis Descriptive statistics for patient demographics and surgical time are reported as means and standard deviations (SD) for continuous variables, and frequencies and percents for categorical variables. After confirming data normality, continuous variables were assessed with paired samples t -tests with the Tukey HSD correction for multiple comparisons, when appropriate. Statistical significance was set at p<0.05 a priori. Assessment of learning curve associated with adoption of the ROSA Hip system was conducted by generating Cumulative Sum Charts (CUSUM) with respect to operative time. The number of cases preceding the first downward inflection on the CUSUM chart trendline was accepted as the learning curve, with the number of cases prior to the downward inflection representing the learning phase and the number of cases following representing the proficiency phase. Results There was no significant difference between the final raTHA target and post-operative radiographic measure for inclination and anteversion (Table 2). Table 2 The mean inclination and anteversion measurements between final planned targets and post-operative radiographic measurements, including the mean absolute difference Final raTHA Target Radiographic Reading Mean Absolute Difference P -value Inclination 41.8 ± 1.5 42.3 ± 4 3.4 ± 2.6 0.419 Anteversion 15.9 ± 1.3 15.2 ± 3 2.7 ± 2.2 0.121 P-value between final target and radiographic reading The rate of raTHA outliers was 27.1% (13/48) for inclination and 10.4% (5/48) for anteversion. For the inclination outliers, eight were at least 5° greater than the final planned target angles while six were at least 5° less than the final planned target. All anteversion outliers were at least 5° less than the final planned target. The rate of cases within the Lewinnek Safe Zone was 96% (48/50) (Fig. 1). Fig. 1 Scatter plot of post-operative radiograph measures within the Lewinnek Safe Zone Operative time was 68.9 ± 11.4 minutes. A downward trend (R 2 =0.048) for operative times was observed over the first 50 cases (Fig. 2). Analysis of the CUSUM plot illustrates the first clear downward inflection occurring following the 25 th case, suggestive of a 25-case learning curve associated with the fluoroscopic-based raTHA system investigated (Fig. 3) to develop operative time efficiency with the system. The mean operative time was significantly (p=0.0277) greater in the learning (72.4±12.7 minutes) compared to the proficiency phase (65.6±7.9 minutes). Fig. 4 illustrates the times of the five steps in the raTHA workflow. Though most steps showed improved efficiency, there were no significant differences between the learning and proficiency phases. Mean absolute cup inclination and anteversion differences were not significantly different between the learning and proficiency phase (Table 3). There were no significant differences in the rate of outliers between the proficiency and learning phase for inclination (8/25 (32%) vs. 5/23 (21.7%), p=0.243) or anteversion (2/25 (8%) vs. 3/23 (13%), p=568). Fig. 2 Operative time (skin to skin) scatterplot of first 50 raTHA cases. Fig. 3 Operative time (skin-to-skin) CUSUM analysis of raTHA cases with dashed line representing the transition from the learning to the proficiency phase Fig. 4 Robotic workflow time components during the learning and proficiency phase Table 3 Mean absolute differences for the learning and proficiency phases Learning Phase Proficiency Phase P -value Inclination 3.3 ± 2.5 4.0 ± 2.9 0.374 Anteversion 2.1 ± 1.5 2.6 ± 2.1 0.322 HOOS-12 (Table 4) and OHS (Table 5) significantly improved from pre-operative at each follow-up time point. Mean changes in HOOS-12 and OHS exceeded their respective MCIDs at each post-operative follow-up, and 20 of 22 patients (90.9%) achieved MCID at final follow-up for HOOS-12 and OHS. There were no incidents of post-operative complications through one-year follow-up. Table 4 Hip Disability and Osteoarthritis Outcome Score-12 Follow-up Time HOOS-12 Change from Pre-Operative t -test P -value* Pre-op 43.1 ± 16.3, 95%CI (36.9, 49.3) N/A N/A 3 Months 82.4 ± 14.7, 95%CI (76.3, 88.5) 38 ± 22, 95%CI (28.7, 47.3) <0.001 6 Months 87.7 ± 12.2, 95%CI (82.9, 92.5) 43.4 ± 19, 95%CI (35.7, 51.1) <0.001 12 Months 88.6 ± 13.8, 95%CI (82.6, 94.6) 44.1 ± 21.2, 95%CI (34.7, 53.5) <0.0001 *Versus pre-operative Table 5 Oxford Hip Score Follow-up Time OHS Change from Pre-Operative t -test P -value* Pre-op 23.9 ± 10, 95%CI (20.1, 27.7) N/A N/A 3 Months 40.5 ± 7.3, 95%CI (37.5, 43.5) 15.7 ± 11, 95%CI (11.1, 20.3) <0.001 6 Months 43.3 ± 5.6, 95%CI (41, 45.5) 19 ± 9.9, 95%CI (15, 23) <0.001 12 Months 43.6 ± 6.2, 95%CI (40.9, 46.3) 18.5 ± 10.6, 95%CI (13.8, 23.1) <0.001 *Versus pre-operative Discussion This study evaluated the accuracy and reliability of DAA THA using a novel fluoroscopy-based raTHA system. The main findings indicated that the system allows for precise control of the cup position, with no significant difference between planned and achieved cup inclination and anteversion, and 96% of cups placed within the Lewinnek Safe Zone. The initial learning curve for this single-surgeon study was 25 cases with proficiency improving over time. There were no differences in accuracy between the learning and proficiency phases. Appropriate positioning of the acetabular component is linked to a lower risk of hip instability, dislocation, impingement, component wear, and limitations in range of motion (ROM) [16-21, 38, 42]. By minimizing human error, robotics may allow a surgeon to execute a THA surgical plan with higher levels of accuracy and reproducibility than with manual instrumentation [22, 23]. Robotic assistance may provide further benefit to the direct anterior surgical approach, as odds of cup malposition are twice as high with the DAA compared to the posterior approach with manual placement [42]. To the best of our knowledge, only two other studies have reported mean absolute differences associated with this fluoroscopic-based raTHA system. Ong et al. [30] reported mean absolute differences of 5.99° and 5.15° for inclination and 4.72° and 4.78° for anteversion in obese and non-obese patients, respectively. Similar to the present study, Liu et al. [43] reported inclination and anteversion mean absolute errors of 3.8° and 2.9°. The findings of previous DAA with CT-based raTHA are comparable to the mean absolute differences reported in the present study. Domb et al. [44] reported differences between pre-operative target and post-operative radiographs of 4.88° for inclination and 4.81° for anteversion, Redmond et al. [45] reported mean absolute difference of 3.9° for inclination and 3.5° for anteversion, and Stewart et al. [46] reported mean absolute errors of 3.8° and 3.64° for inclination and anteversion, respectively. Although the accuracy of Lewinnek Safe Zone for predicting dislocations has come under recent scrutiny [47, 48], historically it has been a benchmark for acetabular cup positioning and remains a common metric [49]. In the present study, 96% of raTHA cups were placed within the Lewinnek Safe Zone. These results are comparable to CT-based raTHA whereby the frequency of cups placed within the Safe Zone with the DAA has been reported between 87 to 100% [50-52]. To the best of our knowledge, only one other study has evaluated the learning curve associated with this fluoroscopic-based raTHA system. Buchan et al. [32] reported an initial learning curve of 12 cases, a difference between learning and proficiency phases of approximately 6 minutes, and no difference in inclination or anteversion accuracy. Although the initial learning curve in the present study was greater than that of Buchan et al., the difference in operative time between learning and proficiency phases and lack of difference in accuracy between phases were similar. The operative times in the learning (72.2 min) and proficiency phases (65.6 min) of the present study were also longer than the learning (44.3 minutes) and proficiency phase (38.0) minutes reported previous by Buchan et al. [32]. This may be due to the variability of the operative workflow between these institutions. Other studies from the same surgeons and authors have reported operative times of 38.7 min [27] and 39 min [28], while Liu et al. reported an operative time of 76.4 and 112.6 min for two surgeons. Nonetheless, the operative times recorded in the present study were considerably less than those reported for CT-based raTHA, ranging from 96.6 to 162.3 min [45, 53, 54]. Although a direct comparison cannot be made across investigations, these differences in operative times agree with a recent study that reported significantly shorter operative times with fluoroscopic- compared to CT-based raTHA [27]. At twelve-months post-operative, 92% of patients had achieved MCID in the HOOS-12 and OHS. The mean HOOS-12 and OHS scores at 12-months post-operative in the present study (87.7 and 43.6, respectively) are similar to Liu et al. [43] (91.4 and 44.3, respectively), and comparable to those reported for CT-based raTHA systems [55, 56]. Given there were no reported complications, these results are suggestive of excellent short-term outcomes. Limitations must be considered when interpreting this study. First, pelvic tilt and X-ray offset are reported to affect inclination and anteversion on radiographs [57-61]. While several corrective methods have been developed to minimize pelvic tilt and X-ray offset bias, high variability and significant inconsistency between the corrective algorithms and CT scans have been reported [61] such that 5° is suggested as an acceptable measurement deviation [62]. Thus, the inability to control for pelvic tilt or X-ray offset may bias the accuracy measurements in the present study. Second, we did not include a control group of manual THA cases, limiting the ability to compare accuracy and outcomes to the current standard of care. Third, as PROMs were obtained from the AOANJRR, we were unable to ensure compliance with follow-up, leading to a limited data set, thus potentially biasing the PROMs findings. Conclusions The results of this study are suggestive of high accuracy and precision for acetabular cup placement with a fluoroscopy-based, pinless, robotic system for direct anterior approach THA. CUSUM analysis of operative times suggests a short initial learning curve, with small efficiency gains as the user becomes more familiar with the system over time, but no effect on acetabular cup placement accuracy, and satisfactory short-term clinical outcomes. Further studies are necessary to investigate the association between improved acetabular cup placement accuracy and clinical outcomes. List of Abbreviations AOANJRR Australian Orthopaedic Association National Joint Replacement Registry AP Anteroposterior CT Computed Tomography CUSUM Cumulative Summation DAA Direct Anterior Approach EBRA Ein-Bild-Roentgen-analyse HOOS-12 Hip Disability and Osteoarthritis Outcome Score-12 HOOS Hip Disability and Osteoarthritis Outcome Score ICC Intraclass Correlation Coefficient MAD Mean Absolute Difference MCID Minimally Clinically Important Difference mTHA Manual Total Hip Arthroplasty OHS Oxford Hip Score PROM Patient-Reported Outcome Measure raTHA Robotic-assisted Total Hip Arthroplasty ROM Range of Motion SD Standard Deviation THA Total Hip Arthroplasty Declarations Ethics approval and consent to participate University of Tasmania Human Research Ethics Committee, Project ID: 30625. A waiver of authorization and informed consent was granted by the Committee in accordance with the National Statement on Ethical Conduct in Human Research. Consent for publication The manuscript and any part of its contents are currently not under consideration, nor have they been published in another journal. The manuscript is wholly original; all authors have contributed to this research and have provided consent to publication of the manuscript. Availability of data and materials The datasets analysed during the current study are available from the corresponding author on reasonable request. Competing interests J.P is a paid consultant of, and has received research support from Zimmer Biomet. M.A and J.C are paid employees of Zimmer Biomet. N.M and MT declare that they have no competing interests. Funding No monetary funding was received. Support was provided by Zimmer Biomet for the project leading to publication. Authors’ Contributions Conception: JP, MA; Methodology: JP, MA; Data acquisition: JP, NS, MT; Formal analysis: MA; Writing – Original draft: JC; Writing – Review and Editing: JP, NS, MT, MA, JC. Acknowledgements The authors would like to acknowledge Sabine Montenegro for assistance in the synthesis of study data and preparation of the manuscript. Authors’ information 1 Department of Orthopaedics, Calvary Hospital, 49 Augusta Rd, Lenah Valley 7008, Australia 2 Department of Orthopaedics, Royal Hobart Hospital, 48 Liverpool St, Hobart 7000, Australia 3 Zimmer Biomet, Belrose 2085, Australia 4 Petterwood Orthopaedics, Calvary Hospital, 49 Augusta Rd, Lenah Valley 7008, Australia 5 Zimmer Biomet, Warsaw, IN 46580, USA References Pabinger C, Geissler A. Utilization rates of hip arthroplasty in OECD countries. Osteoarthritis and Cartilage. 2014; 22(6): 734-741. Patel I, Nham F, Zalikha AK, El-Othmani MM. Epidemiology of total hip arthroplasty: demographics, comorbidities and outcomes. Arthroplasty. 2023; 5(1): 2. Knight SR, Aujla R, Biswas SP. Total Hip Arthroplasty - over 100 years of operative history. Orthop Rev (Pavia). 2011; 3(2): e16. Bota NC, Nistor DV, Caterev S, Todor A. 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Use of a fluoroscopy-based robotic-assisted total hip arthroplasty system produced greater improvements in patient-reported outcomes at one year compared to manual, fluoroscopic-assisted technique. Arch Orthop Trauma Surg. 2024; 144(4): 1843-1850. Kamath AF, Durbhakula SM, Pickering T, Cafferky NL, Murray TG, Wind MA, Jr., Methot S. Improved accuracy and fewer outliers with a novel CT-free robotic THA system in matched-pair analysis with manual THA. J Robot Surg. 2022; 16(4): 905-913. Ilchmann T, Mjöberg B, Wingstrand H. Measurement accuracy in acetabular cup wear. Three retrospective methods compared with Roentgen stereophotogrammetry. J Arthroplasty. 1995; 10(5): 636-642. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978; 60(2): 217-220. Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016; 15(2): 155-163. Ayers D, Yousef M, Zheng H, Yang W, Franklin P. Do Patient Outcomes Vary by Patient Age Following Primary Total Hip Arthroplasty? J Arthroplasty. 2022; 37(7S): S510-S516. Sabah SA, Alvand A, Beard DJ, Price AJ. Minimal important changes and differences were estimated for Oxford hip and knee scores following primary and revision arthroplasty. J Clin Epidemiol. 2022; 143: 159-168. Callanan MC, Jarrett B, Bragdon CR, Zurakowski D, Rubash HE, Freiberg AA, Malchau H. The John Charnley Award: risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res. 2011; 469(2): 319-329. Liu D, Kamath AF, Cholewa J, Stoenica L, Anderson MB, Lennox H. Cup accuracy and early-term clinical outcomes of a novel, pinless, robotic-assisted total hip arthroplasty system: A first-in-human pilot study. Arthroplasty. 2025; 7(1): 20. Domb BG, Redmond JM, Louis SS, Alden KJ, Daley RJ, LaReau JM, Petrakos AE, Gui C, Suarez-Ahedo C. Accuracy of Component Positioning in 1980 Total Hip Arthroplasties: A Comparative Analysis by Surgical Technique and Mode of Guidance. J Arthroplasty. 2015; 30(12): 2208-2218. Redmond JM, Gupta A, Hammarstedt JE, Petrakos A, Stake CE, Domb BG. Accuracy of Component Placement in Robotic-Assisted Total Hip Arthroplasty. Orthopedics. 2016; 39(3): 193-199. Stewart NJ, Stewart JL, Brisbin A. A Comparison of Component Positioning Between Fluoroscopy-Assisted and Robotic-Assisted Total Hip Arthroplasty. J Arthroplasty. 2022; 37(8): 1602-1605. Abdel MP, von Roth P, Jennings MT, Hanssen AD, Pagnano MW. What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position. Clin Orthop Relat Res. 2016; 474(2): 386-391. Murphy WS, Yun HH, Hayden B, Kowal JH, Murphy SB. The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA. Clin Orthop Relat Res. 2018; 476(2): 325-335. Burapachaisri A, Elbuluk A, Abotsi E, Pierrepont J, Jerabek SA, Buckland AJ, Vigdorchik JM. Lewinnek Safe Zone References are Frequently Misquoted. Arthroplast Today. 2020; 6(4): 945-953. Domb BG, Chen JW, Lall AC, Perets I, Maldonado DR. Minimum 5-Year Outcomes of Robotic-assisted Primary Total Hip Arthroplasty With a Nested Comparison Against Manual Primary Total Hip Arthroplasty: A Propensity Score-Matched Study. J Am Acad Orthop Surg. 2020; 28(20): 847-856. Xu S, Bernardo LIC, Andy KS, Pang HN. Robotic-Arm Assisted Direct Anterior Total Hip Arthroplasty; Improving Implant Accuracy. Surg Technol Int. 2020; 38: 347-352. Perets I, Walsh JP, Mu BH, Mansor Y, Rosinsky PJ, Maldonado DR, Lall AC, Domb BG. Short-term Clinical Outcomes of Robotic-Arm Assisted Total Hip Arthroplasty: A Pair-Matched Controlled Study. Orthopedics. 2021; 44(2): e236-e242. Domb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014; 472(1): 329-336. Kamara E, Robinson J, Bas MA, Rodriguez JA, Hepinstall MS. Adoption of Robotic vs Fluoroscopic Guidance in Total Hip Arthroplasty: Is Acetabular Positioning Improved in the Learning Curve? J Arthroplasty. 2017; 32(1): 125-130. Coulomb R, Cascales V, Haignere V, Bauzou F, Kouyoumdjian P. Does acetabular robotic-assisted total hip arthroplasty with femoral navigation improve clinical outcomes at 1-year post-operative? A case-matched propensity score study comparing 98 robotic-assisted versus 98 manual implantation hip arthroplasties. Orthop Traumatol Surg Res. 2023; 109(1): 103477. Singh V, Realyvasquez J, Simcox T, Rozell JC, Schwarzkopf R, Davidovitch RI. Robotics Versus Navigation Versus Conventional Total Hip Arthroplasty: Does the Use of Technology Yield Superior Outcomes? J Arthroplasty. 2021; 36(8): 2801-2807. Anda S, Svenningsen S, Grontvedt T, Benum P. Pelvic inclination and spatial orientation of the acetabulum. A radiographic, computed tomographic and clinical investigation. Acta Radiol. 1990; 31(4): 389-394. Buckland AJ, Vigdorchik J, Schwab FJ, Errico TJ, Lafage R, Ames C, Bess S, Smith J, Mundis GM, Lafage V. Acetabular Anteversion Changes Due to Spinal Deformity Correction: Bridging the Gap Between Hip and Spine Surgeons. J Bone Joint Surg Am. 2015; 97(23): 1913-1920. Maratt JD, Esposito CI, McLawhorn AS, Jerabek SA, Padgett DE, Mayman DJ. Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter? J Arthroplasty. 2014; 30(3): 387-391. Zhao JX, Su XY, Zhao Z, Xiao RX, Sun GF, Zhang LC, Tang PF. The synergetic effect of pelvic rotation and X-ray offset on radiographic angles of the acetabular cup. Med Biol Eng Comput. 2019; 57(11): 2359-2371. Zhao JX, Su XY, Zhao Z, Xiao RX, Zhang LC, Tang PF. Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review. Ann Transl Med. 2020; 8(4): 130. Delagrammaticas DE, Alvi HM, Kaat AJ, Sullivan RR, Stover MD, Manning DW. Quantitative Effect of Pelvic Position on Radiographic Assessment of Acetabular Component Position. J Arthroplasty. 2018; 33(2): 608-614. Additional Declarations Competing interest reported. J.P is a paid consultant of, and has received research support from Zimmer Biomet. M.A and J.C are paid employees of Zimmer Biomet. N.M and MT declare that they have no competing interests. Cite Share Download PDF Status: Posted Version 1 posted 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. 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12:50:17","extension":"json","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":7330,"visible":true,"origin":"","legend":"","description":"","filename":"72972f4436404076bb95a279582c57f8.json","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/73f59cc548b8eef6d26e115c.json"},{"id":95227307,"identity":"383886a7-9c25-4eb6-b252-39f35a963470","added_by":"auto","created_at":"2025-11-05 16:32:22","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":65038,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScatter plot of post-operative radiograph measures within the Lewinnek Safe Zone\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/4ff2e694252bc3aec89f6fdd.jpg"},{"id":95227777,"identity":"3afa8a23-3788-4ad8-80b5-564c071f6cf4","added_by":"auto","created_at":"2025-11-05 16:32:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":201727,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOperative time (skin to skin) scatterplot of first 50 raTHA cases.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/15f5132da84f457bb78bbf81.jpg"},{"id":95203371,"identity":"c1449473-a9bc-47f7-a14d-69f3adfb3d9a","added_by":"auto","created_at":"2025-11-05 12:50:17","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":188114,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOperative time (skin-to-skin) CUSUM analysis of raTHA cases with dashed line representing the transition from the learning to the proficiency phase\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/ce1ce83c303dfdb3e7e7fcf7.jpg"},{"id":95203375,"identity":"6ae22712-74ce-4193-a1b2-d7133e22999b","added_by":"auto","created_at":"2025-11-05 12:50:17","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":59524,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRobotic workflow time components during the learning and proficiency phase\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/125cb1df9d189f59ba646241.jpg"},{"id":96915905,"identity":"2e6ca71a-b9fb-4049-a20c-8b4c3d12efc4","added_by":"auto","created_at":"2025-11-27 14:07:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1456283,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7796241/v1/dee0b676-5517-41ba-b643-355b7536d2c3.pdf"}],"financialInterests":"Competing interest reported. J.P is a paid consultant of, and has received research support from Zimmer Biomet. M.A and J.C are paid employees of Zimmer Biomet. N.M and MT declare that they have no competing interests.","formattedTitle":"Accuracy, efficiency, and clinical outcomes of a pinless CT-Free, robotic arm-assisted total hip replacement system","fulltext":[{"header":"Background","content":"\u003cp\u003eTotal hip arthroplasty (THA) is one of the most commonly performed orthopedic procedures [1, 2], and is considered the gold standard of care for treating end-stage osteoarthritis [3] by significantly improving function, pain [4-7], and health-related quality of life [8, 9]. THAs have increased in volume by approximately 14% in the United States and Europe from 2009 to 2015 [2, 10], and this is expected to increase by approximately 29% between 2020 and 2025 in the United States [11] and 66% by 2040 in Australia [12]. Revision THA increased by over 28% during the same time period in the United States and Europe [2, 13] and is similarly expected to increase by over 9% between 2020 and 2025 in the United States [14].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDislocation and instability, alongside infection, are the leading causes of revision in the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR: Figure HT6) [15]. Malpositioning of the acetabular cup has been associated with accelerated component wear, instability, dislocation, poor patient reported outcome measures (PROMs), reduced range of motion (ROM), and revision [16-21]. Technological advancements, such as computer and robotic assistance, have been developed to improve the precision of THA. Recent meta-analyses report robotic-assisted THA (raTHA) has shown greater accuracy in placing the acetabular cup within the Lewinnek Safe Zone compared to manual THA (mTHA) [22, 23]. \u0026nbsp;However, the gains from increased accuracy of robotic systems may be offset by increased surgical times. For example, robotic systems that rely on pre-operative computed tomography (CT) imaging for planning, and the intra-operative placement of navigation pins for anatomical landmarking and cup positioning, affect surgical scheduling and surgical workflow, resulting in prolonged operative times along with the introduction of additional radiation exposure [23-25].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRecent developments include a pinless fluoroscopy-based robotic system that offers advantages over CT-based systems, such as reduced radiation exposure [26] and shorter operating times with less variance, while removing the risk of pin-site complications [27]. Preliminary research indicates fluoroscopy-based raTHA may provide superior accuracy and reproducibility in cup placement compared to mTHA [28-31], with an initial learning curve of 12 cases [32]. To the best of our knowledge, clinical outcomes comparing pinless fluoroscopy-based raTHA to mTHA are presently limited to three studies. Buchan et al.\u0026nbsp;[33] reported lower pain scores at two-weeks post-operative, a shorter hospital length of stay, and a lower rate of complications through 90-days post-operative, and less in-hospital and post-operative narcotic usage with raTHA [34]. At one-year post-operative, the same group reported greater improvements in Hip Disability and Osteoarthritis Outcome (HOOS) pain, physical function, and joint replacement scores [35].\u003c/p\u003e\n\u003cp\u003eDespite the positive findings from the aforementioned studies, more research is necessary to confirm the reports of high accuracy and clinical outcomes, and to study the learning curve and surgical efficiency associated with fluoroscopy-based raTHA in different settings. The purpose of this study was therefore to investigate the initial accuracy, reproducibility, efficiency, and short-term clinical outcomes of a pinless, CT-free, raTHA system.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis was a retrospective cohort analysis of a single surgeon\u0026rsquo;s first 50 fluoroscopy-based raTHA cases performed between August 2023 and February 2024. Patients over 18 years of age undergoing direct anterior approach (DAA) THA due to osteoarthritis were included in this study (Table 1). Ethics approval was obtained prior to study participation with a waiver of authorization and consent (Ethics approval #30625 from University of Tasmania, 2024).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Patient demographics\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 208px;\"\u003e\n \u003cp\u003eFemale Sex\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e27 (54%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 208px;\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e70.0 \u0026plusmn; 7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 208px;\"\u003e\n \u003cp\u003eBMI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e29.0 \u0026plusmn; 5.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 208px;\"\u003e\n \u003cp\u003eASA Score\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;I\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;II\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;III\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e16 (32%)\u003c/p\u003e\n \u003cp\u003e30 (60%)\u003c/p\u003e\n \u003cp\u003e4 (8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 208px;\"\u003e\n \u003cp\u003eLaterality (right)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 170px;\"\u003e\n \u003cp\u003e28 (56%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll patients were implanted with a G7 Acetabular cup combined with Taperloc Femoral stem (Zimmer Biomet, Warsaw, IN). Patients received DAA THA with the assistance of a pinless fluoroscopic-based robotic arm orthopedic surgical assistance device (ROSA\u003csup\u003e\u0026reg;\u003c/sup\u003e Total Hip System, Zimmer Biomet, Montreal, Quebec, Canada). The surgical procedure has been described in detail previously [25, 26, 36]. In brief, a fluoroscopic image of the leveled pelvis is acquired in the supine position and transferred to the robotic system for automatic identification of landmarks, which the surgeon reviews to match pelvic orientation to the pre-operative standing anteroposterior radiograph. Manual techniques are used for femoral head resection and reaming. The cup is then secured to the Robotic Arm and positioned semi-autonomously in collaboration with the surgeon for impaction to achieve the planned cup placement angles. Additional fluoroscopic images are taken during the verification stage and after the final femoral component is inserted to confirm proper alignment (Trial and Validation). Inclination and anteversion were initially targeted at 40\u0026deg; and 15\u0026deg;, respectively. In cases where the surgeon modified the target angles intra-operatively, these were recorded as the final planned target using the raTHA system and prior to impaction.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe primary outcome of this study was acetabular component placement accuracy, defined as the mean difference between the final planned and post-operative radiographic inclination and version angles. Acetabular cup orientation was measured from four to twelve-week post-operative from supine radiographs with Ein-Bild-Roentgen-analyse (EBRA)-Cup (Universit\u0026auml;t Innsbruck, Innsbruck, Austria) [37]. The outliers of accurate acetabular cup placement were defined as an absolute difference in either inclination or anteversion of more than 5\u0026deg; from the final planned angle and the overall success rate was calculated based on the percentage of participants who were within the range of the Lewinnek Safe Zone [38]. There were two cases missing raTHA logs that were included in the safe zone analysis, but excluded from the mean absolute difference calculations, resulting in 48 cases available for accuracy analysis.\u003c/p\u003e\n\u003cp\u003eInclination and anteversion readings were performed three times by two independent readers and the reported values represent the averages of the two readings. Intra- and inter-rater reliability were assessed across all cases. The amount of agreement for ICC was classified as poor, \u0026lt; 0.5; moderate, 0.5 to \u0026lt; 0.75; good 0.75 to \u0026lt; 0.9; and excellent reliability, \u0026gt; 0.9 [39]. Intra-rater reliability for inclination was ICC = 0.996 and 0.992 for rater 1 and rater 2, respectively. Intra-rater reliability was ICC = 0.99, 0.985 for anteversion for rater 1 and rater 2, respectively. Inter-rater reliability for inclination and anteversion were ICC = 0.994 and 0.94 for inclination and anteversion, respectively.\u003c/p\u003e\n\u003cp\u003eSecondary outcomes included operative time (first incision to closure), the learning curve with respect to operative time, and PROMs. The Hip Disability and Osteoarthritis Outcome Score-12 (HOOS-12) and Oxford Hip Score (OHS) were collected pre-operatively, and at three, six, and 12-months post-operative from the AOANJRR. PROMs data was available for 29 patients. The minimal clinically important difference (MCID) for the HOOS-12 [40] and OHS [41] are 10.1 and 4.1, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical Analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDescriptive statistics for patient demographics and surgical time are reported as means and standard deviations (SD) for continuous variables, and frequencies and percents for categorical variables. After confirming data normality, continuous variables were assessed with paired samples \u003cem\u003et\u003c/em\u003e-tests with the Tukey HSD correction for multiple comparisons, when appropriate. Statistical significance was set at p\u0026lt;0.05 a priori.\u003c/p\u003e\n\u003cp\u003eAssessment of learning curve associated with adoption of the ROSA Hip system was conducted by generating Cumulative Sum Charts (CUSUM) with respect to operative time. The number of cases preceding the first downward inflection on the CUSUM chart trendline was accepted as the learning curve, with the number of cases prior to the downward inflection representing the learning phase and the number of cases following representing the proficiency phase. \u0026nbsp;\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThere was no significant difference between the final raTHA target and post-operative radiographic measure for inclination and anteversion (Table 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e The mean inclination and anteversion measurements between final planned targets and post-operative radiographic measurements, including the mean absolute difference\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 125px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 125px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFinal raTHA Target\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 125px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRadiographic Reading\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 136px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMean Absolute Difference\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eP\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003eInclination\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e41.8 \u0026plusmn; 1.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e42.3 \u0026plusmn; 4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 136px;\"\u003e\n \u003cp\u003e3.4 \u0026plusmn; 2.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.419\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003eAnteversion\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e15.9 \u0026plusmn; 1.3\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 125px;\"\u003e\n \u003cp\u003e15.2 \u0026plusmn; 3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 136px;\"\u003e\n \u003cp\u003e2.7 \u0026plusmn; 2.2\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.121\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003eP-value between final target and radiographic reading\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe rate of raTHA outliers was 27.1% (13/48) for inclination and 10.4% (5/48) for anteversion. For the inclination outliers, eight were at least 5\u0026deg; greater than the final planned target angles while six were at least 5\u0026deg; less than the final planned target. All anteversion outliers were at least 5\u0026deg; less than the final planned target. The rate of cases within the Lewinnek Safe Zone was 96% (48/50) (Fig. 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 1 Scatter plot of post-operative radiograph measures within the Lewinnek Safe Zone\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOperative time was 68.9 \u0026plusmn; 11.4 minutes. \u0026nbsp;A downward trend (R\u003csup\u003e2\u003c/sup\u003e=0.048) for operative times was observed over the first 50 cases (Fig. 2). Analysis of the CUSUM plot illustrates the first clear downward inflection occurring following the 25\u003csup\u003eth\u003c/sup\u003e case, suggestive of a 25-case learning curve associated with the fluoroscopic-based raTHA system investigated (Fig. 3) to develop operative time efficiency with the system. The mean operative time was significantly (p=0.0277) greater in the learning (72.4\u0026plusmn;12.7 minutes) compared to the proficiency phase (65.6\u0026plusmn;7.9 minutes). Fig. 4 illustrates the times of the five steps in the raTHA workflow. Though most steps showed improved efficiency, there were no significant differences between the learning and proficiency phases. Mean absolute cup inclination and anteversion differences were not significantly different between the learning and proficiency phase (Table 3). There were no significant differences in the rate of outliers between the proficiency and learning phase for inclination (8/25 (32%) vs. 5/23 (21.7%), p=0.243) or anteversion (2/25 (8%) vs. 3/23 (13%), p=568).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 2 Operative time (skin to skin) scatterplot of first 50 raTHA cases.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 3\u003c/strong\u003e \u003cstrong\u003eOperative time (skin-to-skin) CUSUM analysis of raTHA cases with dashed line representing the transition from the learning to the proficiency phase\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 4\u003c/strong\u003e \u003cstrong\u003eRobotic workflow time components during the learning and proficiency phase\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e Mean absolute differences for the learning and proficiency phases\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 151px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLearning Phase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 161px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eProficiency Phase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eP\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 142px;\"\u003e\n \u003cp\u003eInclination\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e3.3 \u0026plusmn; 2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 161px;\"\u003e\n \u003cp\u003e4.0 \u0026plusmn; 2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e0.374\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 142px;\"\u003e\n \u003cp\u003eAnteversion\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003e2.1 \u0026plusmn; 1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 161px;\"\u003e\n \u003cp\u003e2.6 \u0026plusmn; 2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 95px;\"\u003e\n \u003cp\u003e0.322\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eHOOS-12 (Table 4) and OHS (Table 5) significantly improved from pre-operative at each follow-up time point. Mean changes in HOOS-12 and OHS exceeded their respective MCIDs at each post-operative follow-up, and 20 of 22 patients (90.9%) achieved MCID at final follow-up for HOOS-12 and OHS. There were no incidents of post-operative complications through one-year follow-up.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u003c/strong\u003e Hip Disability and Osteoarthritis Outcome Score-12\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"748\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFollow-up Time\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 246px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHOOS-12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 246px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChange from Pre-Operative\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003et\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e-test \u003cem\u003eP\u003c/em\u003e-value*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003ePre-op\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e43.1 \u0026plusmn; 16.3, 95%CI (36.9, 49.3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e3 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e82.4 \u0026plusmn; 14.7, 95%CI (76.3, 88.5)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e38 \u0026plusmn; 22, 95%CI (28.7, 47.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e6 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e87.7 \u0026plusmn; 12.2, 95%CI (82.9, 92.5)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e43.4 \u0026plusmn; 19, 95%CI (35.7, 51.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e12 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e88.6 \u0026plusmn; 13.8, 95%CI (82.6, 94.6)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e44.1 \u0026plusmn; 21.2, 95%CI (34.7, 53.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.0001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003e*Versus pre-operative\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5\u003c/strong\u003e Oxford Hip Score\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"748\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFollow-up Time\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 246px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOHS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 246px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eChange from Pre-Operative\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 128px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003et\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e-test \u003cem\u003eP\u003c/em\u003e-value*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003ePre-op\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e23.9 \u0026plusmn; 10, 95%CI (20.1, 27.7)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e3 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e40.5 \u0026plusmn; 7.3, 95%CI (37.5, 43.5)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e15.7 \u0026plusmn; 11, 95%CI (11.1, 20.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e6 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e43.3 \u0026plusmn; 5.6, 95%CI (41, 45.5)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e19 \u0026plusmn; 9.9, 95%CI (15, 23)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e12 Months\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e43.6 \u0026plusmn; 6.2, 95%CI (40.9, 46.3)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 246px;\"\u003e\n \u003cp\u003e18.5 \u0026plusmn; 10.6, 95%CI (13.8, 23.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 128px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003e*Versus pre-operative\u003c/em\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis study evaluated the accuracy and reliability of DAA THA using a novel fluoroscopy-based raTHA system. The main findings indicated that the system allows for precise control of the cup position, with no significant difference between planned and achieved cup inclination and anteversion, and 96% of cups placed within the Lewinnek Safe Zone. The initial learning curve for this single-surgeon study was 25 cases with proficiency improving over time. There were no differences in accuracy between the learning and proficiency phases.\u003c/p\u003e\n\u003cp\u003eAppropriate positioning of the acetabular component is linked to a lower risk of hip instability, dislocation, impingement, component wear, and limitations in range of motion (ROM) [16-21, 38, 42]. By minimizing human error, robotics may allow a surgeon to execute a THA surgical plan with higher levels of accuracy and reproducibility than with manual instrumentation [22, 23]. Robotic assistance may provide further benefit to the direct anterior surgical approach, as odds of cup malposition are twice as high with the DAA compared to the posterior approach with manual placement [42]. To the best of our knowledge, only two other studies have reported mean absolute differences associated with this fluoroscopic-based raTHA system. Ong et al. [30] reported mean absolute differences of 5.99° and 5.15° for inclination and 4.72° and 4.78° for anteversion in obese and non-obese patients, respectively. Similar to the present study, Liu et al. [43] reported inclination and anteversion mean absolute errors of 3.8° and 2.9°. The findings of previous DAA with CT-based raTHA are comparable to the mean absolute differences reported in the present study. Domb et al. [44] reported differences between pre-operative target and post-operative radiographs of 4.88° for inclination and 4.81° for anteversion, Redmond et al. [45] reported mean absolute difference of 3.9° for inclination and 3.5° for anteversion, and Stewart et al. [46] reported mean absolute errors of 3.8° and 3.64° for inclination and anteversion, respectively. Although the accuracy of Lewinnek Safe Zone for predicting dislocations has come under recent scrutiny [47, 48], historically it has been a benchmark for acetabular cup positioning and remains a common metric [49]. In the present study, 96% of raTHA cups were placed within the Lewinnek Safe Zone. These results are comparable to CT-based raTHA whereby the frequency of cups placed within the Safe Zone with the DAA has been reported between 87 to 100% [50-52].\u003c/p\u003e\n\u003cp\u003eTo the best of our knowledge, only one other study has evaluated the learning curve associated with this fluoroscopic-based raTHA system. Buchan et al. [32] reported an initial learning curve of 12 cases, a difference between learning and proficiency phases of approximately 6 minutes, and no difference in inclination or anteversion accuracy. Although the initial learning curve in the present study was greater than that of Buchan et al., the difference in operative time between learning and proficiency phases and lack of difference in accuracy between phases were similar. The operative times in the learning (72.2 min) and proficiency phases (65.6 min) of the present study were also longer than the learning (44.3 minutes) and proficiency phase (38.0) minutes reported previous by Buchan et al. [32]. This may be due to the variability of the operative workflow between these institutions. Other studies from the same surgeons and authors have reported operative times of 38.7 min [27] and 39 min [28], while Liu et al. reported an operative time of 76.4 and 112.6 min for two surgeons. Nonetheless, the operative times recorded in the present study were considerably less than those reported for CT-based raTHA, ranging from 96.6 to 162.3 min [45, 53, 54]. Although a direct comparison cannot be made across investigations, these differences in operative times agree with a recent study that reported significantly shorter operative times with fluoroscopic- compared to CT-based raTHA [27].\u003c/p\u003e\n\u003cp\u003eAt twelve-months post-operative, 92% of patients had achieved MCID in the HOOS-12 and OHS. The mean HOOS-12 and OHS scores at 12-months post-operative in the present study (87.7 and 43.6, respectively) are similar to Liu et al. [43] (91.4 and 44.3, respectively), and comparable to those reported for CT-based raTHA systems [55, 56]. Given there were no reported complications, these results are suggestive of excellent short-term outcomes.\u003c/p\u003e\n\u003cp\u003eLimitations must be considered when interpreting this study. First, pelvic tilt and X-ray offset are reported to affect inclination and anteversion on radiographs [57-61]. While several corrective methods have been developed to minimize pelvic tilt and X-ray offset bias, high variability and significant inconsistency between the corrective algorithms and CT scans have been reported [61] such that 5° is suggested as an acceptable measurement deviation [62]. Thus, the inability to control for pelvic tilt or X-ray offset may bias the accuracy measurements in the present study. Second, we did not include a control group of manual THA cases, limiting the ability to compare accuracy and outcomes to the current standard of care. Third, as PROMs were obtained from the AOANJRR, we were unable to ensure compliance with follow-up, leading to a limited data set, thus potentially biasing the PROMs findings.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe results of this study are suggestive of high accuracy and precision for acetabular cup placement with a fluoroscopy-based, pinless, robotic system for direct anterior approach THA. CUSUM analysis of operative times suggests a short initial learning curve, with small efficiency gains as the user becomes more familiar with the system over time, but no effect on acetabular cup placement accuracy, and satisfactory short-term clinical outcomes. Further studies are necessary to investigate the association between improved acetabular cup placement accuracy and clinical outcomes.\u0026nbsp;\u003c/p\u003e"},{"header":"List of Abbreviations","content":"\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eAOANJRR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eAustralian Orthopaedic Association National Joint Replacement Registry\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eAP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eAnteroposterior\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eCT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eComputed Tomography\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eCUSUM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eCumulative Summation\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eDAA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eDirect Anterior Approach\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eEBRA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eEin-Bild-Roentgen-analyse\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eHOOS-12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eHip Disability and Osteoarthritis Outcome Score-12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eHOOS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eHip Disability and Osteoarthritis Outcome Score\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eICC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eIntraclass Correlation Coefficient\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMAD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eMean Absolute Difference\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eMCID\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eMinimally Clinically Important Difference\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003emTHA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eManual Total Hip Arthroplasty\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eOHS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eOxford Hip Score\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003ePROM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003ePatient-Reported Outcome Measure\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eraTHA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eRobotic-assisted Total Hip Arthroplasty\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eROM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eRange of Motion\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eSD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eStandard Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 94px;\"\u003e\n \u003cp\u003eTHA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 529px;\"\u003e\n \u003cp\u003eTotal Hip Arthroplasty\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUniversity of Tasmania Human Research Ethics Committee, Project ID: 30625.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA waiver of authorization and informed consent was granted by the Committee in accordance with the National Statement on Ethical Conduct in Human Research.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe manuscript and any part of its contents are currently not under consideration, nor have they been published in another journal. The manuscript is wholly original; all authors have contributed to this research and have provided consent to publication of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ.P is a paid consultant of, and has received research support from Zimmer Biomet. M.A and J.C are paid employees of Zimmer Biomet. N.M and MT declare that they have no competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo monetary funding was received. Support was provided by Zimmer Biomet for the project leading to publication.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConception: JP, MA; Methodology: JP, MA; Data acquisition: JP, NS, MT; Formal analysis: MA; Writing \u0026ndash; Original draft: JC; Writing \u0026ndash; Review and Editing: JP, NS, MT, MA, JC.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to acknowledge Sabine Montenegro for assistance in the synthesis of study data and preparation of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eDepartment of Orthopaedics, Calvary Hospital, 49 Augusta Rd, Lenah Valley 7008, Australia\u003cbr\u003e\u003csup\u003e2\u003c/sup\u003eDepartment of Orthopaedics, Royal Hobart Hospital, 48 Liverpool St, Hobart 7000, Australia\u003cbr\u003e\u003csup\u003e3\u003c/sup\u003eZimmer Biomet, Belrose 2085, Australia\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e4\u003c/sup\u003ePetterwood Orthopaedics, Calvary Hospital, 49 Augusta Rd, Lenah Valley 7008, Australia\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e5\u003c/sup\u003eZimmer Biomet, Warsaw, IN 46580, USA\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePabinger C, Geissler A. 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Robotic-arm assisted versus manual total hip arthroplasty: Systematic review and meta-analysis of radiographic accuracy. Int J Med Robot. 2021; 17(6): e2332.\u003c/li\u003e\n\u003cli\u003eKumar V, Patel S, Baburaj V, Rajnish RK, Aggarwal S. Does robotic-assisted surgery improve outcomes of total hip arthroplasty compared to manual technique? A systematic review and meta-analysis. Postgrad Med J. 2021; 99(1171): 375-383.\u003c/li\u003e\n\u003cli\u003ePerazzini P, Trevisan M, Sembenini P, Alberton F, Laterza M, Marangon A, Magnan B. The Mako robotic arm-assisted total hip arthroplasty using direct anterior approach: surgical technique, skills and pitfals. Acta Biomed 91. 2020; (4-S): 21-30.\u003c/li\u003e\n\u003cli\u003eBullock EKC, Brown MJ, Clark G, Plant JGA, Blakeney WG. Robotics in Total Hip Arthroplasty: Current Concepts. J Clin Med. 2022; 11(22): 6674.\u003c/li\u003e\n\u003cli\u003eBuchan G, Ong C, Hecht C, Tanous TJ, Peterson B, Hasegawa A, Kamath AF. Equivalent radiation exposure with robotic total hip replacement using a novel, fluoroscopic-guided (CT-free) system: case-control study versus manual technique. J Robot Surg. 2023; 17(4): 1561-1567.\u003c/li\u003e\n\u003cli\u003eOng CB, Buchan GBJ, Hecht II CJ, Lawrie CM, DeCook CA, Sculco PK, Kamath AF. Robotic-assisted total hip arthroplasty utilizing a fluoroscopy-guided system resulted in improved intra-operative efficiency relative to a computerized tomography-based platform. J Robot Surg. 2023; 17(6): 2841-2847.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Hecht II CJ, Liu D, Mokete L, Kendoff D, Kamath AF. Improved accuracy of a novel fluoroscopy-based robotically assisted THA system compared to manual THA. J Robot Surg. 2023; 17(5): 2073-2079.\u003c/li\u003e\n\u003cli\u003eOng CB, Buchan GBJ, Hecht II CJ, Homma Y, Harmon DJ, Kendoff DO, Petterwood J, Kamath AF. Fluoroscopy-based robotics in total hip arthroplasty mitigates laterality-based differences in acetabular cup placement when compared to the manual, fluoroscopic- assisted technique. Technol Health Care. 2024; 32(5): 3693-3701.\u003c/li\u003e\n\u003cli\u003eOng CB, Buchan GBJ, Hecht II CJ, Kendoff DO, Homma Y, Kamath AF. Fluoroscopy-based robotic assistance for total hip arthroplasty improves acetabular cup placement accuracy for obese patients compared to the manual, fluoroscopic- assisted technique. Technol Health Care. 2024; 32(5): 3703-3712.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Hecht II CJ, Nugent M, Heckmann ND, Kanaji A, Kamath AF. Efficacy of a novel, fluoroscopy-based robotic-assisted total hip arthroplasty system in restoring limb length and offset. Arch Orthop Trauma Surg. 2025; 145(1): 175.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Hecht II CJ, Lawrie CM, Sculco PK, Kamath AF. The learning curve for a novel, fluoroscopy-based robotic-assisted total hip arthroplasty system. Int J Med Robot. 2023; e2518.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Hecht II CJ, Sculco PK, Chen JB, Kamath AF. Improved short-term outcomes for a novel, fluoroscopy-based robotic-assisted total hip arthroplasty system compared to manual technique with fluoroscopic assistance. Arch Orthop Trauma Surg. 2024; 144(1): 501-508.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Bernhard Z, Hecht CJ, Davis GA, Pickering T, Kamath AF. Improved perioperative narcotic usage patterns in patients undergoing robotic-assisted compared to manual total hip arthroplasty. Arthroplasty. 2023; 5(1): 56.\u003c/li\u003e\n\u003cli\u003eBuchan GBJ, Ong CB, Hecht II CJ, DeCook CA, Spencer-Gardner LS, Kamath AF. Use of a fluoroscopy-based robotic-assisted total hip arthroplasty system produced greater improvements in patient-reported outcomes at one year compared to manual, fluoroscopic-assisted technique. Arch Orthop Trauma Surg. 2024; 144(4): 1843-1850.\u003c/li\u003e\n\u003cli\u003eKamath AF, Durbhakula SM, Pickering T, Cafferky NL, Murray TG, Wind MA, Jr., Methot S. Improved accuracy and fewer outliers with a novel CT-free robotic THA system in matched-pair analysis with manual THA. J Robot Surg. 2022; 16(4): 905-913.\u003c/li\u003e\n\u003cli\u003eIlchmann T, Mj\u0026ouml;berg B, Wingstrand H. Measurement accuracy in acetabular cup wear. Three retrospective methods compared with Roentgen stereophotogrammetry. J Arthroplasty. 1995; 10(5): 636-642.\u003c/li\u003e\n\u003cli\u003eLewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978; 60(2): 217-220.\u003c/li\u003e\n\u003cli\u003eKoo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016; 15(2): 155-163.\u003c/li\u003e\n\u003cli\u003eAyers D, Yousef M, Zheng H, Yang W, Franklin P. Do Patient Outcomes Vary by Patient Age Following Primary Total Hip Arthroplasty? J Arthroplasty. 2022; 37(7S): S510-S516.\u003c/li\u003e\n\u003cli\u003eSabah SA, Alvand A, Beard DJ, Price AJ. Minimal important changes and differences were estimated for Oxford hip and knee scores following primary and revision arthroplasty. J Clin Epidemiol. 2022; 143: 159-168.\u003c/li\u003e\n\u003cli\u003eCallanan MC, Jarrett B, Bragdon CR, Zurakowski D, Rubash HE, Freiberg AA, Malchau H. The John Charnley Award: risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res. 2011; 469(2): 319-329.\u003c/li\u003e\n\u003cli\u003eLiu D, Kamath AF, Cholewa J, Stoenica L, Anderson MB, Lennox H. 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What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position. Clin Orthop Relat Res. 2016; 474(2): 386-391.\u003c/li\u003e\n\u003cli\u003eMurphy WS, Yun HH, Hayden B, Kowal JH, Murphy SB. The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA. Clin Orthop Relat Res. 2018; 476(2): 325-335.\u003c/li\u003e\n\u003cli\u003eBurapachaisri A, Elbuluk A, Abotsi E, Pierrepont J, Jerabek SA, Buckland AJ, Vigdorchik JM. Lewinnek Safe Zone References are Frequently Misquoted. Arthroplast Today. 2020; 6(4): 945-953.\u003c/li\u003e\n\u003cli\u003eDomb BG, Chen JW, Lall AC, Perets I, Maldonado DR. Minimum 5-Year Outcomes of Robotic-assisted Primary Total Hip Arthroplasty With a Nested Comparison Against Manual Primary Total Hip Arthroplasty: A Propensity Score-Matched Study. J Am Acad Orthop Surg. 2020; 28(20): 847-856.\u003c/li\u003e\n\u003cli\u003eXu S, Bernardo LIC, Andy KS, Pang HN. Robotic-Arm Assisted Direct Anterior Total Hip Arthroplasty; Improving Implant Accuracy. Surg Technol Int. 2020; 38: 347-352.\u003c/li\u003e\n\u003cli\u003ePerets I, Walsh JP, Mu BH, Mansor Y, Rosinsky PJ, Maldonado DR, Lall AC, Domb BG. Short-term Clinical Outcomes of Robotic-Arm Assisted Total Hip Arthroplasty: A Pair-Matched Controlled Study. Orthopedics. 2021; 44(2): e236-e242.\u003c/li\u003e\n\u003cli\u003eDomb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014; 472(1): 329-336.\u003c/li\u003e\n\u003cli\u003eKamara E, Robinson J, Bas MA, Rodriguez JA, Hepinstall MS. Adoption of Robotic vs Fluoroscopic Guidance in Total Hip Arthroplasty: Is Acetabular Positioning Improved in the Learning Curve? J Arthroplasty. 2017; 32(1): 125-130.\u003c/li\u003e\n\u003cli\u003eCoulomb R, Cascales V, Haignere V, Bauzou F, Kouyoumdjian P. Does acetabular robotic-assisted total hip arthroplasty with femoral navigation improve clinical outcomes at 1-year post-operative? A case-matched propensity score study comparing 98 robotic-assisted versus 98 manual implantation hip arthroplasties. Orthop Traumatol Surg Res. 2023; 109(1): 103477.\u003c/li\u003e\n\u003cli\u003eSingh V, Realyvasquez J, Simcox T, Rozell JC, Schwarzkopf R, Davidovitch RI. Robotics Versus Navigation Versus Conventional Total Hip Arthroplasty: Does the Use of Technology Yield Superior Outcomes? J Arthroplasty. 2021; 36(8): 2801-2807.\u003c/li\u003e\n\u003cli\u003eAnda S, Svenningsen S, Grontvedt T, Benum P. Pelvic inclination and spatial orientation of the acetabulum. A radiographic, computed tomographic and clinical investigation. Acta Radiol. 1990; 31(4): 389-394.\u003c/li\u003e\n\u003cli\u003eBuckland AJ, Vigdorchik J, Schwab FJ, Errico TJ, Lafage R, Ames C, Bess S, Smith J, Mundis GM, Lafage V. Acetabular Anteversion Changes Due to Spinal Deformity Correction: Bridging the Gap Between Hip and Spine Surgeons. J Bone Joint Surg Am. 2015; 97(23): 1913-1920.\u003c/li\u003e\n\u003cli\u003eMaratt JD, Esposito CI, McLawhorn AS, Jerabek SA, Padgett DE, Mayman DJ. Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter? J Arthroplasty. 2014; 30(3): 387-391.\u003c/li\u003e\n\u003cli\u003eZhao JX, Su XY, Zhao Z, Xiao RX, Sun GF, Zhang LC, Tang PF. The synergetic effect of pelvic rotation and X-ray offset on radiographic angles of the acetabular cup. Med Biol Eng Comput. 2019; 57(11): 2359-2371.\u003c/li\u003e\n\u003cli\u003eZhao JX, Su XY, Zhao Z, Xiao RX, Zhang LC, Tang PF. Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review. Ann Transl Med. 2020; 8(4): 130.\u003c/li\u003e\n\u003cli\u003eDelagrammaticas DE, Alvi HM, Kaat AJ, Sullivan RR, Stover MD, Manning DW. 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J Arthroplasty. 2018; 33(2): 608-614.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Accuracy, Clinical outcomes, Direct anterior approach, Learning curve, Total hip arthroplasty, Robotic","lastPublishedDoi":"10.21203/rs.3.rs-7796241/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7796241/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground \u003c/strong\u003eFluoroscopic-based robotic-assisted total hip arthroplasty (raTHA) platforms expose patients to less radiation than CT-based raTHA, however, the accuracy of these novel raTHA systems requires further investigation. The purpose of this study was to investigate the accuracy, efficiency, and early post-operative clinical outcomes of a pinless, fluoroscopic-based raTHA system.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods \u003c/strong\u003eA retrospective review of a single surgeon’s first 50 raTHA cases using the direct anterior approach (DAA) was conducted. Accuracy of acetabular component placement was determined by analysing the final planned target and post‐operative supine anteroposterior (AP) pelvic radiographs. Mean absolute differences (MAD) between target and post-operative radiographs were computed for cup inclination and anteversion, and the percentage of cases within the Lewinnek Safe Zone was calculated. To assess efficiencies in adoption, cumulative summation (CUSUM) analysis was performed using operative times and robotic timestamps to compare between learning and proficiency phases. Hip Disability and Osteoarthritis Outcome Score-12 (HOOS-12) and Oxford Hip Score (OHS) were collected pre-operatively and up to one-year post-operative.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults \u003c/strong\u003eThere were no significant (p=0.419) differences between targeted and radiographic cup inclination (41.8±1.5 vs. 42.3± 4)) or anteversion (15.9±1.3 vs. 15.2±3.0, p = 0.121). The raTHA MAD for inclination and anteversion were 3.6±2.7° and 2.4±1.8° respectively, and the percentage of cases within the Lewinnek Safe Zone was 96% (48/50). CUSUM analysis revealed an initial learning curve of 25 cases, with significantly shorter operative times in the proficiency compared to learning phase (65.6±7.9 vs. 72.4±12.7 min, p=0.028), and without significant differences in accuracy between phases. Both HOOS-12 and OHS significantly (p\u0026lt;0.0001) improved between pre-operative and one-year post-operative.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion \u003c/strong\u003eThe results of this study demonstrate that use of a pinless, fluoroscopic-based raTHA system for DAA THA demonstrates high accuracy and reproducibility of acetabular cup placement with an initial learning curve of 25 cases.\u003c/p\u003e","manuscriptTitle":"Accuracy, efficiency, and clinical outcomes of a pinless CT-Free, robotic arm-assisted total hip replacement system","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-05 12:50:13","doi":"10.21203/rs.3.rs-7796241/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bcd27a76-8710-4051-8516-f32b67b4483d","owner":[],"postedDate":"November 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-26T02:39:03+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-05 12:50:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7796241","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7796241","identity":"rs-7796241","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}