BACKGROUND AND PURPOSE:The primary objective was to compare subsidence and retroversion in the first 2 postoperative years of 2 uncemented hip stem designs in primary minimally invasive anterior-supine surgical (MIS-ASI) total hip arthroplasty: a shortened hip stem (Microplasty) and a standard-length stem with reduced distal width (Reduced Distal). Secondary objectives were to compare migration patterns, patient-reported outcome measures (PROMs), clinical and radiological scores, and the occurrence of (serious) adverse events up to 2 years postoperatively. METHODS:50 patients were randomized in this non-blinded, single-surgeon, industry-funded, radiostereometric analysis study (RSA) (ClinicalTrials.gov NCT03409666). Stem migration was measured relative to directly postoperative at 6 weeks, 1 year, and 2 years postoperatively, using model-based RSA. Linear mixed-effect modelling was used to compare migration. Primary outcomes were subsidence and retroversion at 2 years postoperatively. Secondary outcomes were migration, PROM questionnaires, clinical and radiological scores, and the presence of adverse events in the first 2 postoperative years. RESULTS:Migration of 15 Microplasty and 20 Reduced Distal stems showed comparable initial migration between direct and 6 weeks postoperative RSA, stabilizing thereafter. Predominant migration directions were subsidence and retroversion with mean values at 2 years of 1.47 mm (95% confidence interval [CI] 0.32-2.61) and 2.57° (CI 1.64-3.50) for the Microplasty stem and 2.35 mm (CI 1.36-3.34) and 1.59° (CI 0.79-2.39) for the Reduced Distal stem. At 6 weeks postoperatively, posterior tilt about the medial-lateral axis was different between stem designs, with 0.07° (CI -0.27 to 0.40) for the Microplasty and 0.48° (CI 0.19-0.77) for the Reduced Distal designs. Secondary outcomes were not clinically different between the stem designs. CONCLUSION:We showed that initial subsidence and retroversion for both stem designs in MIS-ASI surgery was present, although likely not clinically relevant. There was no statistically significant difference in subsidence and retroversion between the stem designs. Although initial migration varied substantially between patients and the Reduced Distal design showed more posterior tilting, both designs maintained a stable position from 6 weeks to 2 years postoperatively.

BACKGROUND AND PURPOSE:Radiostereometric analysis (RSA) of total knee arthroplasty (TKA) is used as an early safeguard during the phased evidence-based introduction of new implants. The goal of our study was to compare the long-term revision risk between RSA-tested implants and non-RSA-tested implants in the Netherlands using patient-level data. METHODS:All primary TKAs between 2007 and 2016 from the Dutch Arthroplasty Register were included, and procedures with an RSA-tested implant were identified. Both all-cause major revision risk and revision risk because of loosening were calculated at 5 and 10 years postoperatively using Kaplan-Meier analyses. Sensitivity analyses were performed with stricter definitions of implant characteristics to classify procedures as RSA-tested, to avoid camouflage of different subdesigns within the same brand implant portfolio. RESULTS:83,638 RSA-tested and 104,105 non-RSA-tested TKAs were included. Cumulative all-cause major revision percentages for the RSA-tested group at 5 and 10 years were 2.2% (95% confidence interval [CI] 2.1-2.3) and 3.6% (CI 3.4-3.7), respectively, compared with 2.5% (CI 2.4-2.6) and 3.3% (CI 3.2-3.4) for the non-RSA-tested group. RSA-tested TKAs showed higher 10-year revision risks because of loosening than non-RSA-tested procedures (1.8%, CI 1.7-1.9 vs 1.4%, CI 1.3-1.4, respectively). Comparable results were found after stratification by various patient characteristics and with stricter classification approaches. CONCLUSION:Regarding all-cause revision risk, RSA-tested TKAs had a slightly lower risk at 5 years. However, at 10 years the RSA-tested TKAs had a higher all-cause revision risk and higher revision risk because of loosening compared with the non-RSA-tested TKAs.

Aims The primary objective of this study was to evaluate the influence of postoperative slope on the five-year tibial component migration and wear following uncemented cruciate-retaining condylar-stabilized total knee arthroplasty (TKA). Secondary objectives included the association between postoperative slope and clinical and functional outcomes. Methods This observational study was a secondary analysis of a randomized controlled trial of 93 TKAs on insert materials. Tibial component migration and insert wear were measured across three postoperative slope groups (small (≤ 5°), intermediate (6° to 9°), and large (≥ 10°)) using radiostereometric analysis at three, six, 12, 24, and 60 months postoperatively. Patient-reported outcome measures were collected preoperatively and at all follow-up timepoints. Results There was an association between tibial component migration and postoperative tibial slope: the group with the largest postoperative tibial slope showed the largest posterior tilting. At five years, there was no difference in insert wear between the small, intermediate, and large slope groups. There was also no association between postoperative slope and functional or patient-reported outcomes. Conclusion TKA implanted with more than 10° of slope showed increased tibial component migration and posterior tilting, independent of the native slope. At five years, there was no influence of slope on wear or functional outcomes. Cite this article: Bone Joint J 2026;108-B(5):634–642.

Aims:The primary objective of this study was to evaluate the influence of postoperative slope on the five-year tibial component migration and wear following uncemented cruciate-retaining condylar-stabilized total knee arthroplasty (TKA). Secondary objectives included the association between postoperative slope and clinical and functional outcomes. Methods:This observational study was a secondary analysis of a randomized controlled trial of 93 TKAs on insert materials. Tibial component migration and insert wear were measured across three postoperative slope groups (small (≤ 5°), intermediate (6° to 9°), and large (≥ 10°)) using radiostereometric analysis at three, six, 12, 24, and 60 months postoperatively. Patient-reported outcome measures were collected preoperatively and at all follow-up timepoints. Results:There was an association between tibial component migration and postoperative tibial slope: the group with the largest postoperative tibial slope showed the largest posterior tilting. At five years, there was no difference in insert wear between the small, intermediate, and large slope groups. There was also no association between postoperative slope and functional or patient-reported outcomes. Conclusion:TKA implanted with more than 10° of slope showed increased tibial component migration and posterior tilting, independent of the native slope. At five years, there was no influence of slope on wear or functional outcomes.

Background and purpose: We conducted a systematic review and meta-analysis of radiostereometric analysis studies of primary uncemented femoral stems to investigate their subsidence and retroversion patterns and the migration patterns according to implant, patient, and study characteristics. Methods: A systematic search of PubMed, Web of Science, Cochrane, and Embase databases to identify all radiostereometric analysis studies on femoral stem migration following primary uncemented total hip replacement was performed. Clinical studies with 2 or more postoperative radiostereometric measurements within 2 years were included. Subsidence and retroversion at 6 weeks, 3 and 6 months, 1, 2, 5, and 10 years were included for analysis. Extracted implant characteristics included implant design, coating, and surgical approach. Data was analyzed using a random effects model. Results: 73 studies on 120 cohorts and 2,970 uncemented stems were included. 119 cohorts reported on subsidence and 91 on retroversion. The pooled subsidence at 3 months was 0.29 mm (95% confidence interval [CI] 0.19–0.39) and 0.32 mm (CI 0.21–0.43) at 2 years. The pooled retroversion at 3 months was 0.51° (CI 0.33–0.70) and 0.70° (CI 0.48–0.93) at 2 years. Hydroxyapatite-coated stems showed the least migration (subsidence 0.26 mm; CI 0.13–0.40; retroversion 0.51°; CI 0.22–0.80) among different coating types. The anterior approach showed more migration (subsidence 1.04 mm, CI 0.53–1.55; retroversion 1.52°, CI 1.08–1.95) than other surgical approaches. Conclusion: Our study shows that most subsidence and retroversion of uncemented femoral stems occurs during the first 3 months. Stabilization of subsidence occurred after 3 months, and retroversion stabilized after 2 years. Migration patterns differ based on stem type, coating, surgical approach, the time period when inclusion started, and timing of baseline measurement.

BACKGROUND AND PURPOSE:Early migration of the uncemented cruciate-sacrificing rotating platform ATTUNE and Low Contact Stress (LCS) tibial components was classified as at-risk for aseptic loosening rates exceeding 6.5% at 15 years based on recent fixation-specific migration thresholds. In this secondary report of a randomized controlled trial (RCT) we aimed to evaluate whether the 5-year migration, inducible displacement, and the clinical outcome of the ATTUNE components were comparable to those of the LCS. METHODS:Patients from the initial 2-year radiostereometric analysis (RSA) RCT were recruited for a 5-year follow-up. At 5 years, participants underwent 2 supine and 1 loaded RSA examination, clinical assessments, and questionnaires. Migration was analyzed using maximum total point motion (MTPM), translations, and rotations, focusing on 5-year migration, continuous migration (> 0.10 mm/year), and inducible displacement. Revisions, along with clinical and functional outcomes, were also evaluated. RESULTS:At 5 years, 24 ATTUNE and 24 LCS implants were analyzed. The mean MTPM was similar for tibial components (ATTUNE 1.13mm [confidence interval (CI) 0.94-1.33]; LCS 1.24 mm [CI 1.05-1.46]) but significantly lower for the ATTUNE femoral component (1.14 mm [CI 0.92-1.39]) than LCS 1.87 mm [CI 1.57-2.21]). 2-to-5-year migration rates were comparable, but 11 ATTUNE and 7 LCS exceeded 0.10 mm MTPM/year, indicating a higher risk of loosening. Inducible displacement was similar, although 1 patient with a tibial ATTUNE showed excessive displacement (3.34 mm MTPM) with focal osteolysis but no symptoms. 1 revision 10 days post-surgery was performed for an ATTUNE insert spinout, resolved with an isolated insert exchange. Clinical and functional outcomes were comparable. CONCLUSION:At the 5-year follow-up, ATTUNE tibial components showed similar migration, while the femoral component migrated significantly less than the LCS, which mainly occurred during the first 2 years. 2-to-5-year migration rates, inducible displacement, and clinical and functional outcomes were comparable. These findings suggest a comparable long-term risk of aseptic loosening between the uncemented ATTUNE and LCS knee systems.

Acetabular defects pose significant challenges in orthopedic surgery, particularly in revision total hip arthroplasty (THA). Here, we design, additively manufacture, and evaluate shape-morphing porous implants with kinematic structures to address these defects. Three defect types were examined using synthetic hemipelvis models: posterior wall, cranial-posterior combination, and central-posterior defects. The implants were secured with screws and bone cement, and their surface conformity was assessed through micro computed tomography (µCT). Biomechanical performance was evaluated under quasi-static compression and cyclic loading conditions. Results demonstrated high surface conformity of the flexible mesh across all defect types, with minimal differences from healthy acetabula (< 10 mm). The mesh implants exhibited strong load-bearing capacity, with failures occurring only in the pubic region of the hemipelvis, while both the implants and mesh-cement interfaces remained intact. The implants withstood cyclic loading simulating half the body weight of a 80 kg patient for >1000,000 loading cycles with no evidence of fatigue failure, further confirming their durability. These findings suggest that the flexible mesh implant provides a potential solution for complex acetabular defects, offering anatomical conformity and mechanical stability, even in cases where conventional mesh grafts might be inadequate. Future studies, including cadaveric testing and clinical trials, are necessary to further validate these results in (pre-)clinical settings. STATEMENT OF SIGNIFICANCE: This study addresses the need for adaptable solutions to complex acetabular defects in revision total hip arthroplasty (THA). Traditional implants struggle to conform to severe bone loss and irregular geometries, risking suboptimal fit, and implant migration. We introduce a 3D-printed, shape-morphing porous implant with kinematic structures, offering high anatomical conformity, mechanical robustness, and support for bone graft integration. Combining the adaptability of patient-specific implants with the efficiency of standard designs, this implant reduces lead times while enabling a tailored fit. This innovative approach provides a reliable solution for managing complex defects, addressing limitations of conventional implants, and improving outcomes in orthopedic reconstruction.

Background The risk of early revision of total hip arthroplasty (THA) for polyethylene wear is now low, but there remains a need to perform wear measurements in patients for clinical surveillance. The gold standard of wear measurements has been radiostereometric analysis (RSA), which has limited availability. The use of computed tomography (CT) to perform THA wear measurement was described a decade ago and found to have acceptable accuracy and precision, but high radiation dose was a concern. Additionally, the use of larger femoral head sizes and ceramic femoral heads has risen in the past decade. The objectives of the study were to determine the effect of femoral head size, femoral head material, and lowered radiation dose on femoral head penetration measurement repeatability. Methods A cadaveric hip was implanted with a cementless THA implant system. CT scans were acquired at a conventional radiation dose and at a reduced dose and repeated for a 32 mm and 36 mm cobalt-chromium femoral heads and a 32 mm ceramic femoral head. Apparent translation of the femoral head versus the acetabular cup was measured between the repeated scans using a CT-RSA software, where deviations from zero indicated measurement precision. Results The mean and standard deviation of translations in all planes was <0.200 mm. There was no effect for 3D translation of increasing cobalt-chromium head size (p = 0.2252). Cobalt-chromium heads had superior repeatability compared to ceramic heads at reduced dose (p = 0.022), but not at conventional dose (p = 0.1265). Further, superior repeatability was achieved with the reduced dose scan for the cobalt-chromium head (p = 0.0058), however there was no difference between doses for the ceramic head (p = 0.8148). Discussion CT-based wear measurement repeatability is excellent and consistent with prior literature even when implementing a larger femoral head, a ceramic femoral head, or reducing radiation dose to 25% of a conventional clinical scan.

Background and purpose: Standardized reporting on methodology and results in clinical RSA research papers facilitates evaluation of quality and interpretation of results. We aimed to assess the extent to which radiostereometric analysis (RSA) and computed tomography-based RSA (CT-RSA) studies adhered to the items of the new RSA reporting guideline from 2024. Methods: A systematic literature search was performed to identify all clinical RSA studies published between January 2012 and February 2024. Studies were eligible for inclusion if prosthesis migration over time was assessed. The adherence of studies to each applicable guideline item (full, partial, or no) was assessed. Results: 285 studies were included, most of which assessed prosthesis migration in the hip (n = 161) or knee (n = 99). No study reported on all guideline items. The mean (full or partial) adherence of studies to all (applicable) items was 61% (standard deviation [SD] 11). Large variation between the reporting of items was found, ranging from being reported in 1% of the studies to 100%. The least reported items in studies were the mean number and SD of days between surgery and baseline RSA examination (8% of studies), mean number and SD of days between surgery and primary endpoint RSA examination (1%), and consistent- or all-marker method for RSA analysis (3%). Conclusion: Current studies on average reported only 61% of the items from the updated RSA guidelines. Adherence to the guidelines in clinical RSA studies on prosthesis migration should be improved, in order to improve the quality of studies and the interpretation of outcomes on implant migration.

BACKGROUND AND PURPOSE:Computed tomography-based radiostereometric analysis (CT-RSA) is an alternative to conventional radiostereometric analysis (RSA) in measuring implant migration, circumventing the need for operative insertion of tantalum markers. The accuracy and precision of different CT-RSA techniques in various joints are still unclear, and the effective radiation dose (ED) of CT-RSA is usually higher than RSA. In this systematic literature review, we aimed to provide an overview of the accuracy, precision, clinical precision, and ED of CT-RSA techniques. METHODS:We performed a systematic search in PubMed, Cochrane, and Embase databases. Main search items were "arthroplasty" AND "migration" AND "computed tomography." We included full-text English papers, using CT for migration analysis (CT-RSA) in human, animal, or synthetic models with arthroplasties, reporting accuracy and/or precision. Eligible studies were screened and reviewed by 2 authors independently. Main outcomes were accuracy, precision, and clinical precision of CT-RSA in 6 degrees of freedom. Secondary outcome was the mean ED. A meta-analysis on (clinical) precision of CT-RSA was performed. RESULTS:23 studies were included involving 163 patients, 20 human cadaveric, 3 porcine cadaveric, and 7 synthetic models. 6 different CT-RSA techniques were used to study 6 different joint components in cervical disc replacement and shoulder, hip, and knee arthroplasty. CT-RSA accuracy ranged between 0.02 and 0.71 mm and 0.03° and 1.00°. CT-RSA precision ranged between 0.00 and 0.47 mm and 0.00° and 1.09°. Mean precision was 0.15 mm (95% confidence interval [CI] 0.05-0.25) in the acetabulum, 0.13 mm (CI 0.00-0.28) and 0.24° (CI 0.00-0.51) in the proximal femur, and 0.04 mm (CI 0.00-0.08) and 0.07° (CI 0.00-0.15) in the proximal tibia. CT-RSA clinical precision ranged between 0.03 and 1.36 mm and 0.06° and 2.25°. Mean clinical precision was 0.13 mm (CI 0.11-0.16) and 0.26° (CI 0.20-0.32) in the acetabulum. The mean ED of CT-RSA ranged between 0.02 and 5.80 mSv. CONCLUSION:CT-RSA shows comparable accuracy and precision to standard RSA. CT-RSA seems to be a promising alternative to RSA.

Objective During cruciate-retaining total knee arthroplasty (CR-TKA) the contact point (CP) of the femur on the tibia is determined by balancing the posterior cruciate ligament (PCL). This can be done with the spacer technique. The aim of this secondary analysis was to analyze the position, of the medial and lateral CP in CR-TKA and to assess the association of CP with clinical outcome. Methods 23 patients received CR-TKA with intraoperative PCL balancing performed with the spacer technique. At 3, 12, and 24 months postoperative, a pair of standing radiographs was made of the flexed knee using a radiostereometric analysis (RSA) setup. The 3D positions of femur and tibia components were used to calculate the medial and lateral CPs, defined as the point with the smallest distance between femoral condyle and tibia plateau. Positions of CPs and tibial slope were compared between patients with/without flexion limitation. Results Patients with flexion limitation (n=6) showed a more posterior medial CP and higher tibial slope, compared with patients with no flexion complaints (p=0.022, and p=0.027, respectively). Besides less flexion, patients with flexion limitation reported more pain, less function and less satisfaction. Conclusion The medial CP seems to relate to clinical outcome; patients with flexion limitation had a more posterior medial CP. This might be an indication for a too tightly balanced PCL, resulting from a suboptimally functioning spacer technique for this implant.

Background and purpose: To address the limitations of radiostereometric imaging and to eliminate the need for intraoperative marker placement, CT-based radiostereometric analysis (CT-RSA) software systems have been developed. We aimed to evaluate the precision of a novel CT-RSA software system, V3MA, against an established CT-RSA software system, CTMA, while also examining the impact of CT scanner model on precision. Methods: 7 CT scans per scanner (Siemens SOMATOM Force and GE Revolution) of a porcine cadaver with a knee implant were used for pairwise comparisons. By aligning paired CT scans, the translation (mm), rotation (°), and maximum total point motion (MTPM, mm) of the tibial implant with respect to the bone were computed. V3MA aligned the scans using the voxel gray values of the bone and implant, whereas CTMA aligned the surface points of the bone and implant. The precision of both software systems and the effect of both scanner models were investigated using paired data in a linear mixed model. Results: Both software systems resulted in a similar MTPM (contrast V3MA–CTMA –0.002 mm, 95% confidence interval [CI] –0.015 to 0.011; V3MA: 0.09 mm; CTMA: 0.10 mm), indicating comparable precision using a minimal important difference of 0.10 mm. Using Siemens scanner data resulted in a higher estimated MTPM than using GE scanner data (contrast Siemens–GE 0.046 mm, CI 0.024–0.067; Siemens: 0.12 mm; GE: 0.072 mm). Conclusion: The precision of the new CT-RSA software system, V3MA, is comparable to that of CTMA under zero-motion assumptions. Minor, clinically irrelevant, inter-scanner differences in CT-RSA precision exist for both software systems.

BACKGROUND:Aseptic loosening is a significant cause of implant revision in total knee arthroplasty, and radiostereometric analysis has been used to predict loosening by measuring implant migration over time relative to its position at the time of the index surgery. Studies have suggested that analyzing specific migration patterns may improve prediction of loosening, compared to using measures of the Maximum Total Point Motion alone. Therefore, the objective of this study was to determine whether patients monitored using radiostereometric analysis who experienced either aseptic loosening or revision exhibited distinctive tibial implant migration patterns. METHODS:Extending a previous study using radiostereometric analysis, we calculated the 6-degree-of-freedom tibial implant migration patterns for seven patients with cemented mechanically aligned total knee arthroplasty implants who either developed aseptic loosening or were candidates for revision. We used simple linear regression to identify trends over time. FINDINGS:We observed two trends that achieved statistical significance: negative rotation in the coronal plane (medial tilting) of the tibial implant (b = 0.260/month, p < 0.001) and anterior translation (b = 0.67 mm/month, p = 0.005). INTERPRETATION:Our study showed two statistically detectable migration trends associated with tibial component aseptic loosening. Although we were unable to assess in this study whether focusing on migration patterns in these directions provides greater predictive value than using Maximum Total Point Motion, the results suggest that certain migration mechanisms are more prevalent than others, which could motivate further research into the causes of such migration patterns.

Opening remarks: These guidelines are the result of discussions within a diverse group of RSA researchers. They were approved in December 2023 by the board and selected members of the International Radiostereometry Society to update the guidelines by Valstar et al. [1]. By adhering to these guidelines, RSA studies will become more transparent and consistent in execution, presentation, reporting, and interpretation. Both authors and reviewers of scientific papers using RSA may use these guidelines, summarized in the Checklist, as a reference. Deviations from these guidelines should have the underlying rationale stated.

Aims:The aim of this study was to compare the migration of the femoral component, five years postoperatively, between patients with a highly cross-linked polyethylene (HXLPE) insert and those with a conventional polyethylene (PE) insert in an uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary aims included clinical outcomes and patient-reported outcome measures (PROMs). We have previously reported the migration and outcome of the tibial components in these patients. Methods:A double-blinded randomized controlled trial was conducted including 96 TKAs. The migration of the femoral component was measured with radiostereometry (RSA) at three and six months and one, two, and five years postoperatively. PROMs were collected preoperatively and at all periods of follow-up. Results:There was no clinically relevant difference in terms of migration of the femoral component or PROMs between the HXLPE and PE groups. The mean difference in migration (maximum total point motion), five years postopeatively, was 0.04 mm (95% CI -0.06 to 0.16) in favour of the PE group. Conclusion:There was no clinically relevant difference in migration of the femoral component, for up to five years between the two groups. These findings will help to establish a benchmark for future studies on migration of femoral components in TKA.

Model-based Roentgen Stereophotogrammetric Analysis (RSA) is able to measure the migration of metallic prostheses with submillimeter accuracy through contour-detection and 3D surface model matching techniques. However, contour-detection is only possible if the prosthesis is clearly visible in the radiograph; consequently Model-based RSA cannot be directly used for polymeric materials due to their limited X-ray attenuation; this is especially clinically relevant for all-polyethylene implants. In this study the radiopacity of unicompartmental Ultra-High Molecular Weight Polyethylene (UHMWPE) knee bearings was increased by diffusing an oil-based contrast agent into the surface to create three different levels of surface radiopacity. Model-based RSA was performed on the bearings alone, the bearings alongside a metallic component held in position using a phantom, the bearings cemented into a Sawbone tibia, and the bearings at different distances from the femoral component. For each condition the precision and accuracy of zero motion of Model-based RSA were assessed. The radiopaque bearings could be located in the stereo-radiographs using Model-based RSA an accuracy comparable to metallic parts for translational movements (0.03 mm to 0.50 mm). For rotational movements, the accuracy was lower (0.1∘ to 3.0∘). The measurement accuracy was compared for all the radiopacity levels and no significant difference was found (p=0.08). This study demonstrates that contrast enhanced radiopaque polyethylene can be used for Model-based RSA studies and has equivalent translational measurement precision to metallic parts in the superior-inferior direction.

Aims The objective of this study was to compare the two- year migration and clinical outcomes of a new cementless hydroxyapatite (HA)- coated titanium acetabular shell with its previous version, which shared the same geometrical design but a different manufacturing process for applying the titanium surface. Methods Overall, 87 patients undergoing total hip arthroplasty (THA) were randomized to either a Trident II HA or Trident HA shell, each cementless with clusterholes and HA- coating. All components were used in combination with a cemented Exeter V40 femoral stem. Implant migration was measured using radiostereometric analysis (RSA), with radiographs taken within two days of surgery (baseline), and at three, 12, and 24 months postoperatively. Proximal acetabular component migration was the primary outcome measure. Clinical scores and patient- reported outcome measures (PROMs) were collected at each follow- up. Results Mean proximal migrations at three, 12, and 24 months were 0.08 mm (95% confidence interval (CI) 0.03 to 0.14), 0.11 mm (95% CI 0.06 to 0.16), and 0.14 mm (95% CI 0.09 to 0.20), respectively, in the Trident II HA group, versus 0.11 mm (95% CI 0.06 to 0.16), 0.12 mm (95% CI 0.07 to 0.17), and 0.14 mm (95% CI 0.09 to 0.19) in the Trident HA group (p = 0.875). No significant differences in translations or rotations between the two designs were found in any other direction. Clinical scores and PROMs were comparable between groups, except for an initially greater postoperative improvement in Hip disability and Osteoarthritis Outcome Symptoms score in the Trident HA group (p = 0.033). Conclusion The Trident II clusterhole HA shell has comparable migration with its predecessor, the Trident hemispherical HA cluster shell, suggesting a similar risk of long - term aseptic loosening.

Background and purpose - Different marker -selection methods are applied to represent implant and tibial segments in radiostereometric analysis (RSA) studies of total knee arthroplasty (TKA). Either a consistent set of markers throughout subsequent RSA examinations ("consistentmarker method") is used or all available markers at each follow-up ("all -marker method"). The aim of this secondary analysis was to compare marker -selection methods on individual and group level TKA migration results. Methods - Data from a randomized RSA study with 72 patients was included. Tibial baseplate migration was evaluated at 3 months, 1, 2, and 5 years postoperatively with both marker -selection methods. Additionally, migration was calculated using 5 fictive points, either plotted based on the consistent set of markers or all available markers. Results - Migration could be calculated with both markerselection methods for 248 examinations. The same prosthesis and bone markers (n = 136), different prosthesis markers (n = 71), different bone markers (n = 21), or different prosthesis and bone markers (n = 20) were used. The mean difference in maximum total point motion (MTPM) between all examinations was 0.02 mm, 95% confidence interval -0.26 to 0.31 mm. 5 implants were classified as continuously migrating with the consistent -marker method versus 6 implants (same 5 plus one additional implant) with the all -marker method. Using fictive points, fewer implants were classified as continuously migrating in both marker -selection methods. Differences between TKA groups in mean MTPM were comparable with both marker -selection methods, also when fictive points were used. Conclusion - Estimated group differences in mean MTPM were similar between marker -selection methods, but individual migration results differed. The latter has implications when classifying implants for estimated risk of future loosening.

Background and purpose: The low-dose EOS Imaging System is an emerging tool for 3-dimensional measurements in orthopedics. The clinical feasibility for measuring total hip arthroplasty (THA) liner wear has not yet been investigated. We aimed to evaluate the feasibility of using EOS to measure THA liner wear by examining the experimental accuracy using a THA phantom and clinical precision of patients with THA, considering a clinically relevant precision at the 95% repeatability limit to be 0.2 mm. Methods: An experimental THA phantom with movable stem and a fixed cup with a plastic liner was constructed to simulate progressive 3D liner wear. Series of 11 pairs of radiographs with 50 μm femoral movement in between were obtained for each 3D axis in EOS. 30 patients with a THA were scanned twice using EOS to assess precision. Model-based radiostereometric analysis (RSA) was used for wear measurement. Results: The mean difference (true minus simulated wear) with standard deviation (SD) and 95% limits of agreement for experimental THA wear were 0.005 (0.037) and [–0.069 to 0.079] mm for the vertical (y) axis. The mean (SD) and 95% repeatability limit for precision for clinical measurement were –0.029 (0.105) and 0.218 mm. Conclusion: Experimental THA liner wear using EOS was within clinically relevant tolerances and without bias. The clinical precision was just outside our defined clinically relevant precision. Compared with conventional RSA, EOS is less accurate and precise but may still be of value for certain clinical applications, provided larger sample size or longer follow-up are available.

Purpose: This clinical fluoroscopy study investigated knee kinematics of two different cemented fixed-bearing, posterior-stabilised (PS) total knee arthroplasty (TKA) designs: an asymmetric tibial component including an asymmetric insert designed to optimise personalised balance and fit and its precursor symmetrical design with symmetric insert. Methods: A consecutive series of patients (16 TKAs from each treatment group) participating in a randomised controlled trial comparing TKA migration was included. The exclusion criterion was the use of walking aids. Flat-panel fluoroscopic recordings of step-up and lunge motions were acquired 1-year postoperatively. Medial and lateral contact points (CPs) were determined to calculate CP displacement, femoral axial rotation and pivot position. Using linear mixed-effects modelling techniques, kinematics between TKA designs were compared. Results: During knee extension between 20 degrees flexion and full extension, the CPs moved anteriorly combined with a small internal femoral rotation (a screw-home mechanism). Whereas CP movement was reversed: femoral rollback, external femoral rotation while flexing the knee between full extension and 20 degrees knee flexion, At larger flexion angles, femoral axial rotation (FAR) occurred around a lateral pivot point both during step-up and lunge. The symmetric design had a 2.3 degrees larger range of FAR compared to the asymmetric design during lunge (p = 0.02). All other kinematics were comparable. Conclusion: Despite the differences in design, this study showed that the asymmetric and symmetric PS TKA designs had mostly comparable knee kinematics during step-up and lunge motions. It is therefore expected that the functionality of the successor TKA design is similar to that of its precursor design.