Aims. Reverse total shoulder arthroplasty (rTSA) can be used in complex cases when the glenoid requires reconstruction. In this study, a baseplate with composite bone autograft and a central trabecular titanium peg was implanted, and its migration was assessed for two years postoperatively using radiostereometric analysis (RSA). Methods. A total of 14 patients who underwent a rTSA with an autograft consented to participate. Of these, 11 had a primary rTSA using humeral head autograft and three had a revision rTSA with autograft harvested from the iliac crest. The mean age of the patients was 66 years (39 to 81). Tantalum beads were implanted in the scapula around the glenoid. RSA imaging (stereographic radiographs) was undertaken immediately postoperatively and at three, six, 12, and 24 months. Analysis was completed using model-based RSA software. Outcomes were collected preoperatively and at two years postoperatively, including the Oxford Shoulder Score, the American Shoulder and Elbow Score, and a visual analogue score for pain. A Constant score was also obtained for the assessment of strength and range of motion. Results. RSA analysis showed a small increase in all translation and rotational values up to six months postoperatively, consistent with settling of the implant. The mean values plateaued by 12 months, with no evidence of further migration. In four patients, there was significant variation outside the mean, which corresponded to postoperative complications. There was a significant improvement in the clinical and patient-reported outcomes from the preoperative values to those at two years postoperatively (p < 0.001). Conclusion. These findings show, using RSA, that a glenoid baseplate composite of a trabecular titanium peg with autograft stabilizes within the glenoid about 12 months after surgery, and reinforce findings from a previous study of this implant/graft with CT scans at two years postoperatively, indicating that this type of structural composite results in sound early fixation. Cite this article: Bone Joint J 2023;105-B(8):912–919

Aims. The aim of this study was to compare a bicruciate-retaining (BCR) total knee arthroplasty (TKA) with a posterior cruciate-retaining (CR) TKA design in terms of kinematics, measured using fluoroscopy and stability as micromotion using radiostereometric analysis (RSA). Methods. A total of 40 patients with end-stage osteoarthritis were included in this randomized controlled trial. All patients performed a step-up and lunge task in front of a monoplane fluoroscope one year postoperatively. Femorotibial contact point (CP) locations were determined at every flexion angle and compared between the groups. RSA images were taken at baseline, six weeks, three, six, 12, and 24 months postoperatively. Clinical and functional outcomes were compared postoperatively for two years. Results. The BCR-TKA demonstrated a kinematic pattern comparable to the natural knee’s screw-home mechanism in the step-up task. In the lunge task, the medial CP of the BCR-TKA was more anterior in the early flexion phase, while laterally the CP was more posterior during the entire movement cycle. The BCR-TKA group showed higher tibial migration. No differences were found for the clinical and functional outcomes. Conclusion. The BCR-TKA shows a different kinematic pattern in early flexion/late extension compared to the CR-TKA. The difference between both implants is mostly visible in the flexion phase in which the anterior cruciate ligament is effective; however, both designs fail to fully replicate the motion of a natural knee. The higher migration of the BCR-TKA was concerning and highlights the importance of longer follow-up. Cite this article: Bone Joint J 2023;105-B(1):35–46

Aims. Our intention was to investigate if the highly porous biological fixation surfaces of a new 3D-printed total knee arthroplasty (TKA) achieved adequate fixation of the tibial and patellar components to the underlying bone. Patients and Methods. A total of 29 patients undergoing primary TKA consented to participate in this prospective cohort study. All patients received a highly porous tibial baseplate and metal-backed patella. Patient-reported outcomes measures were recorded and implant migration was assessed using radiostereometric analysis. Results. Patient function significantly improved by three months postoperatively (p < 0.001). Mean difference in maximum total point motion between 12 and 24 months was 0.021 mm (-0.265 to 0.572) for the tibial implant and 0.089 mm (-0.337 to 0.758) for the patellar implant. The rate of tibial and patellar migration was largest over the first six postoperative weeks, with no changes in mean tibia migration occurring after six months, and no changes in mean patellar migration occurring after six weeks. One patellar component showed a rapid rate of migration between 12 and 24 months. Conclusion. Biological fixation appears to occur reliably on the highly porous implant surface of the tibial baseplate and metal-backed patellar component. Rapid migration after 12 months was measured for one patellar component. Further investigation is required to assess the long-term stability of the 3D-printed components and to determine if the high-migrating components achieve fixation. Cite this article: Bone Joint J 2019;101-B(7 Supple C):40–47

Aims. Conflicting clinical results are reported for the ATTUNE Total Knee Arthroplasty (TKA). This randomized controlled trial (RCT) evaluated five-year follow-up results comparing cemented ATTUNE and PFC-Sigma cruciate retaining TKAs, analyzing component migration as measured by radiostereometric analysis (RSA), clinical outcomes, patient-reported outcome measures (PROMs), and radiological outcomes. Methods. A total of 74 primary TKAs were included in this single-blind RCT. RSA examinations were performed, and PROMs and clinical outcomes were collected immediate postoperatively, and at three, six, 12, 24, and 60 months’ follow-up. Radiolucent lines (RLLs) were measured in standard anteroposterior radiographs at six weeks, and 12 and 60 months postoperatively. Results. At five-year follow-up, RSA data from 61 patients were available and the mean maximum total point motion (MTPM) of the femoral components were: ATTUNE: 0.96 mm (95% confidence interval (CI) 0.79 to 1.14) and PFC-Sigma 1.37 mm (95% CI 1.18 to 1.59) (p < 0.001). The PFC-Sigma femoral component migrated more in the first postoperative year, but stabilized thereafter. MPTM of the tibial components were comparable at five-year follow-up: ATTUNE 1.12 mm (95% CI 0.95 to 1.31) and PFC-Sigma 1.25 mm (95% CI 1.07 to 1.44) (p = 0.438). RLL at the medial tibial implant-cement interface remained more prevalent for the ATTUNE at five-year follow-up compared to the PFC-Sigma (20% vs 3%). RLL did not progress over time, and varied between patients at different timepoints for both TKA systems. Clinical outcomes and PROMs improved compared with preoperative scores, and were not different between groups. Conclusion. MTPM migration at five-year follow-up of the femoral and tibial component of the ATTUNE were similar and as low as that of the PFC-Sigma. MTPM migration of both knee implants did not significantly change from one year post-surgery, indicating stable fixation. Long-term ATTUNE performance may be expected to be comparable to the clinically well-performing PFC-Sigma. We have not found evidence of increased tibial component migration as measured by RSA to support concerns about cement debonding and a higher risk of aseptic loosening with the ATTUNE TKA. Cite this article: Bone Joint J 2023;105-B(11):1168–1176

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. Cite this article: Bone Joint J 2024;106-B(2):136–143

Objectives. Static radiostereometric analysis (RSA) using implanted markers is considered the most accurate system for the evaluation of prosthesis migration. By using CT bone models instead of markers, combined with a dynamic RSA system, a non-invasive measurement of joint movement is enabled. This method is more accurate than current 3D skin marker-based tracking systems. The purpose of this study was to evaluate the accuracy of the CT model method for measuring knee joint kinematics in static and dynamic RSA using the marker method as the benchmark. Methods. Bone models were created from CT scans, and tantalum beads were implanted into the tibia and femur of eight human cadaver knees. Each specimen was secured in a fixture, static and dynamic stereoradiographs were recorded, and the bone models and marker models were fitted to the stereoradiographs. Results. Results showed a mean difference between the two methods in all six degrees of freedom for static RSA to be within -0.10 mm/° and 0.08 mm/° with a 95% limit of agreement (LoA) ranging from ± 0.49 to 1.26. Dynamic RSA had a slightly larger range in mean difference of -0.23 mm/° to 0.16 mm/° with LoA ranging from ± 0.75 to 1.50. Conclusions. In a laboratory-controlled setting, the CT model method combined with dynamic RSA may be an alternative to previous marker-based methods for kinematic analyses. Cite this article: K. Stentz-Olesen, E. T. Nielsen, S. De Raedt, P. B. Jørgensen, O. G. Sørensen, B. L. Kaptein, M. S. Andersen, M. Stilling. Validation of static and dynamic radiostereometric analysis of the knee joint using bone models from CT data. Bone Joint Res 2017;6:376–384. DOI: 10.1302/2046-3758.66.BJR-2016-0113.R3

Aims. The primary objective of this study was to compare the five-year tibial component migration and wear between highly crosslinked polyethylene (HXLPE) inserts and conventional polyethylene (PE) inserts of the uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary objectives included clinical outcomes and patient-reported outcome measures (PROMs). Methods. A double-blinded, randomized study was conducted including 96 TKAs. Tibial component migration and insert wear were measured with radiostereometric analysis (RSA) at three, six, 12, 24, and 60 months postoperatively. PROMS were collected preoperatively and at all follow-up timepoints. Results. There was no clinically relevant difference in terms of tibial component migration, insert wear, and PROMs between the HXLPE and PE groups. The mean difference in tibial component migration (maximal total point migration (MTPM)) was 0.02 mm (95% confidence interval (CI) -0.07 to 0.11), which is below the value of 0.2 mm considered to be clinically relevant. Wear after five years for HXLPE was 0.16 mm (95% CI 0.05 to 0.27), and for PE was 0.23 mm (95% CI 0.12 to 0.35). The mean difference in wear rate was 0.01 mm/year (95% CI -0.02 to 0.05) in favour of the HXLPE group. Wear is mainly present on the medial side of the insert. Conclusion. There is no clinically relevant difference in tibial component migration and insert wear for up to five years between the HXLPE conventional PE inserts. For the implant studied, the potential advantages of a HXLPE insert remain to be proven under clinical conditions at longer-term follow-up. Cite this article: Bone Joint J 2023;105-B(5):518–525

Aims. The introduction of a novel design of total knee arthroplasty (TKA) must achieve outcomes at least as good as existing designs. A novel design of TKA with a reducing radius of the femoral component and a modified cam-post articulation has been released and requires assessment of the fixation to bone. Radiostereometric analysis (RSA) of the components within the first two postoperative years has been shown to be predictive of medium- to long-term fixation. The aim of this study was to assess the stability of the tibial component of this system during this period of time using RSA. Patients and Methods. A cohort of 30 patients underwent primary, cemented TKA using the novel posterior stabilized fixed-bearing (ATTUNE) design. There was an even distribution of men and women (15:15). The mean age of the patients was 64 years (sd 8) at the time of surgery; their mean body mass index (BMI) was 35.4 kg/m2 (sd 7.9). RSA was used to assess the stability of the tibial component at 6, 12, and 24 months compared with a six-week baseline examination. Patient-reported outcome measures were also assessed. Results. The mean maximum total point motion (MTPM) of the tibial component between 12 and 24 months postoperatively was 0.08 mm (sd 0.08), which is well below the published threshold of 0.2 mm (p < 0.001). Patient-reported outcome measures consistently improved. Conclusion. The tibial component of this novel design of TKA showed stability between assessment 12 and 24 months postoperatively, suggesting an acceptably low risk of medium- to long-term failure due to aseptic loosening

Aims. Although bone cement is the primary mode of fixation in total knee arthroplasty (TKA), cementless fixation is gaining interest as it has the potential of achieving lasting biological fixation. By 3D printing an implant, highly porous structures can be manufactured, promoting osseointegration into the implant to prevent aseptic loosening. This study compares the migration of cementless, 3D-printed TKA to cemented TKA of a similar design up to two years of follow-up using radiostereometric analysis (RSA) known for its ability to predict aseptic loosening. Methods. A total of 72 patients were randomized to either cementless 3D-printed or a cemented cruciate retaining TKA. RSA and clinical scores were evaluated at baseline and postoperatively at three, 12, and 24 months. A mixed model was used to analyze the repeated measurements. Results. The mean maximum total point motion (MTPM) at three, 12, and 24 months was 0.33 mm (95% confidence interval (CI) 0.25 to 0.42), 0.42 mm (95% CI 0.33 to 0.51), and 0.47 mm (95% CI 0.38 to 0.57) respectively in the cemented group, versus 0.52 mm (95% CI 0.43 to 0.63), 0.62 mm (95% CI 0.52 to 0.73), and 0.64 mm (95% CI 0.53 to 0.75) in the cementless group (p = 0.003). However, using three months as baseline, no difference in mean migration between groups was found (p = 0.497). Three implants in the cemented group showed a > 0.2 mm increase in MTPM between one and two years of follow-up. In the cementless group, one implant was revised due to pain and progressive migration, and one patient had a liner-exchange due to a deep infection. Conclusion. The cementless TKA migrated more than the cemented TKA in the first two-year period. This difference was mainly due to a higher initial migration of the cementless TKA in the first three postoperative months after which stabilization was observed in all but one malaligned and early revised TKA. Whether the biological fixation of the cementless implants will result in an increased long-term survivorship requires a longer follow-up. Cite this article: Bone Joint J 2020;102-B(8):1016–1024

Aims. Vitamin E-diffused, highly crosslinked polyethylene (VEPE) and porous titanium-coated (PTC) shells were introduced in total hip arthroplasty (THA) to reduce the risk of aseptic loosening. The purpose of this study was: 1) to compare the wear properties of VEPE to moderately crosslinked polyethylene; 2) to assess the stability of PTC shells; and 3) to report their clinical outcomes at seven years. Patients and Methods. A total of 89 patients were enrolled into a prospective study. All patients received a PTC shell and were randomized to receive a VEPE liner (n = 44) or a moderately crosslinked polyethylene (ModXLPE) liner (n = 45). Radiostereometric analysis (RSA) was used to measure polyethylene wear and component migration. Differences in wear were assessed while adjusting for body mass index, activity level, acetabular inclination, anteversion, and head size. Plain radiographs were assessed for radiolucency and patient-reported outcome measures (PROMs) were administered at each follow-up. Results. In total, 73 patients (82%) completed the seven-year visit. Mean seven-year linear proximal penetration was -0.07 mm (. sd. 0.16) and 0.00 mm (. sd. 0.22) for the VEPE and ModXLPE cohorts, respectively (p = 0.116). PROMs (p = 0.310 to 0.807) and radiolucency incidence (p = 0.330) were not different between the polyethylene cohorts. The mean proximal shell migration rate was 0.04 mm per year (. sd. 0.09). At seven years, patients with radiolucency (34%) demonstrated greater migration (mean difference: 0.6 mm (. sd. 0.2); p < 0.001). PROMs were lower for patients with radiolucency and greater proximal migration (p = 0.009 to p = 0.045). No implants were revised for aseptic loosening. Conclusion. This is the first randomized controlled trial to report seven-year RSA results for VEPE. All wear rates were below the previously reported osteolysis threshold (0.1 mm per year). PTC shells demonstrated acceptable primary stability through seven years, as indicated by low migration and lack of aseptic loosening. However, patients with acetabular radiolucency were associated with higher shell migration and lower PROM scores. Cite this article: Bone Joint J 2019;101-B:760–767

Aims. Instability is a common cause of failure after total hip arthroplasty. A novel reverse total hip has been developed, with a femoral cup and acetabular ball, creating enhanced mechanical stability. The purpose of this study was to assess the implant fixation using radiostereometric analysis (RSA), and the clinical safety and efficacy of this novel design. Methods. Patients with end-stage osteoarthritis were enrolled in a prospective cohort at a single centre. The cohort consisted of 11 females and 11 males with mean age of 70.6 years (SD 3.5) and BMI of 31.0 kg/m. 2. (SD 5.7). Implant fixation was evaluated using RSA as well as Western Ontario and McMaster Universities Osteoarthritis Index, Harris Hip Score, Oxford Hip Score, Hip disability and Osteoarthritis Outcome Score, 38-item Short Form survey, and EuroQol five-dimension health questionnaire scores at two-year follow-up. At least one acetabular screw was used in all cases. RSA markers were inserted into the innominate bone and proximal femur with imaging at six weeks (baseline) and six, 12, and 24 months. Independent-samples t-tests were used to compare to published thresholds. Results. Mean acetabular subsidence from baseline to 24 months was 0.087 mm (SD 0.152), below the critical threshold of 0.2 mm (p = 0.005). Mean femoral subsidence from baseline to 24 months was -0.002 mm (SD 0.194), below the published reference of 0.5 mm (p < 0.001). There was significant improvement in patient-reported outcome measures at 24 months with good to excellent results. Conclusion. RSA analysis demonstrates excellent fixation with a predicted low risk of revision at ten years of this novel reverse total hip system. Clinical outcomes were consistent with safe and effective hip replacement prostheses. Cite this article: Bone Jt Open 2023;4(5):385–392

Aims. The primary aim of this trial was to compare the subsidence of two similar hydroxyapatite-coated titanium femoral components from different manufacturers. Secondary aims were to compare rotational migration (anteversion/retroversion and varus/valgus tilt) and patient-reported outcome measures between both femoral components. Methods. Patients were randomized to receive one of the two femoral components (Avenir or Corail) during their primary total hip arthroplasty between August 2018 and September 2020. Radiostereometric analysis examinations at six, 12, and 24 months were used to assess the migration of each implanted femoral component compared to a baseline assessment. Patient-reported outcome measures were also recorded for these same timepoints. Overall, 50 patients were enrolled (62% male (n = 31), with a mean age of 65.7 years (SD 7.3), and mean BMI of 30.2 kg/m. 2. (SD 5.2)). Results. The two-year subsidence was similar for Avenir (-0.018 mm (95% confidence interval (CI) -0.053 to 0.018) and Corail (0.000 mm (95% CI -0.027 to 0.026; p = 0.428). Both anteversion/retroversion (Avenir 0.139° (95% CI -0.204 to 0.481°); Corail -0.196° (95% CI -0.445 to 0.053°; p = 0.110) and varus/valgus tilt (Avenir -0.024° (95% CI -0.077 to 0.028); Corail -0.049° (95% CI -0.098 to 0.000°; p = 0.473) were not statistically significantly different. After two years, patients reported similar improvements in EuroQol five-dimension five-level health questionnaire (Avenir 0.22 (SD 0.2); Corail 0.22 (SD 0.18); p = 0.965) and other outcomes scores. Patient satisfaction on a five-point Likert scale was also similar between both groups after two years (Avenir 1.38 (SD 0.88); Corail 1.33 (SD 0.57); p = 0.846). Conclusion. The performance of both femoral components was similar in terms of stability and patient outcomes. Cite this article: Bone Joint J 2023;105-B(10):1045–1051

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. Cite this article: Bone Joint J 2024;106-B(8):826–833

Over the last decade stemless shoulder arthroplasty has become increasingly popular. However, stability of metaphyseal loading humeral components remains a concern. This study aimed to assess the stability of the Affinis stemless humeral component using Radiostereometric analysis (RSA). Patients underwent total shoulder arthroplasty via a standardised technique with a press-fit stemless humeral component and a cemented pegged glenoid. Tantalum beads were inserted into the humerus at the time of operation. RSA of the relaxed shoulder was completed at weeks 1, 6, 13, 26, 52 and 104 post-operatively. Stressed RSA with 12 newtons of abduction force was completed from week 13 onwards. ABRSA 5.0 software (Downing Imaging Limited, Aberdeen) was used to calculate humeral component migration and induced movement. 15 patients were recruited. Precision was: 0.041, 0.034, 0.086 and 0.101 mm for Superior, Medial, Posterior and Total Point Motion (TPM) respectively. The mean TPM over 2 years was 0.24 (0.30) mm, (Mean (Standard deviation)). The mean rate of migration per 3 month time period decreased from 0.45 (0.31) to 0.02 (0.01) mm over 2 years. Mean inducible movement TPM peaked at 26 weeks at 0.1 (0.08) mm, which reduced to 0.07 (0.06) mm by 104 weeks when only 3 patients had measurable inducible motion. There was no clear trend in direction of induced movement. There were no adverse events or revisions required. We conclude migration of the humeral component was low with little inducible movement in the majority of patients implying initial and 2 year stability of the stemless humeral component

Femoral impaction bone grafting (IBG) may be used to restore bone stock in revision total hip arthroplasty (THA) and allow use of a shorter, than otherwise, length prosthesis. This is most beneficial in young patients who are more likely to require further revision surgery. This study aimed to assess the results of femoral IBG for staged revision THA for infection. A prospective cohort of 29 patients who underwent staged revision THA for infection with femoral IBG and a cemented polished double-tapered (CPDT) stem at the final reconstruction was investigated. The minimum follow-up was two years (2 – 10 years, median 6 years). Stem subsidence was measured with radiostereometric analysis. Clinical outcomes were assessed with the Harris Hip, Harris Pain, and and Société Internationale de Chirurgie Orthopédique et de Traumatologie Activity (SICOT) Scores. The original infection was eradicated in 28 patients. One patient required a repeat staged revision due to re-infection with the same organism. At two-year follow-up, the median subsidence at the stem-bone interface was −1.70 mm (−0.31 to −4.98mm). The median Harris Hip Score improved from 51 pre-operatively to 80 at two years (p=0.000), the Harris Pain Score from 20 to 44 (p=0.000) and the SICOT Score from 2.5 to 3 (p=0.003). As successful eradication of infection was achieved in the majority of patients and the stem migration was similar to that of a primary CPDT stem, this study supports the use of femoral IBG during the final reconstruction of the femur after staged revision THA for infection

Dual mobility hip arthroplasty utilizes a freely rotating polyethylene liner to protect against dislocation. As liner motion has not been confirmed in vivo, we investigated the liner kinematics in vivo using dynamic radiostereometry. 16 patients with Anatomical Dual Mobility acetabular components were included. Markers were implanted in the liners using a drill guide. Static RSA recordings and patient reported outcome measures were obtained at post-op and 1-year follow-up. Dynamic RSA recordings were obtained at 1-year follow-up during a passive hip movement: abduction/external rotation, adduction/internal rotation (modified FABER-FADIR), to end-range and at 45° hip flexion. Liner- and neck movements were described as anteversion, inclination and rotation. Liner movement during modified FABER-FADIR was detected in 12 of 16 patients. Median (range) absolute liner movements were: anteversion 10° (5–20), inclination 6° (2–12), and rotation 11° (5–48) relative to the cup. Median absolute changes in the resulting liner/neck angle (small articulation) was 28° (12–46) and liner/cup angle (larger articulation) was 6° (4–21). Static RSA showed changes in median (range) liner anteversion from 7° (-12–23) postoperatively to 10° (-3–16) at 1-year follow-up and inclination from 42 (35–66) postoperatively to 59 (46–80) at 1-year follow-up. Liner/neck contact was associated with high initial liner anteversion (p=0.01). The polyethylene liner moves over time. One year after surgery the liner can move with or without liner/neck contact. The majority of movement is in the smaller articulation between head and liner

Radiostereometric analysis (RSA) allows for precise measurement of interbody distances on X-ray images, such as movement between a joint replacement implant and the bone. The low radiation biplanar EOS imager (EOS imaging, France) scans patients in a weight-bearing position, provides calibrated three-dimensional information on bony anatomy, and could limit the radiation during serial RSA studies. Following the ISO-16087 standard, 15 double exams were conducted to determine the RSA precision of total knee arthroplasty (TKA) patients in the EOS imager, compared to the standard instantaneous, cone-beam, uniplanar digital X-ray set-up. At a mean of 5 years post-surgery, 15 TKA participants (mean 67 years, 12 female, 3 male) were imaged twice in the biplanar imager. To reduce motion during the scan, a support for the foot was added and the scan speed was increased. The voltage was also increased compared to standard settings for better marker visibility over the implant. A small calibration object was included to remove any remaining sway in post-processing. The 95% confidence interval precision was 0.11, 0.04, and 0.15 mm in the x, y, and z planes, respectively and 0.15, 0.20, and 0.14° in Rx, Ry, and Rz. Two participants had motion artifacts successfully removed during post-processing using the small calibration object. With faster speeds and stabilization support, this study found an in vivo RSA precision of ≤ 0.15 mm and ≤ 0.20° for TKA exams, which is within published uniplanar values for arthroplasty RSA. The biplanar imager also adds the benefits of weight bearing imaging, 3D alignment measurements, a lower radiation dose, and does not require a reference object due to known system geometry and automatic image registration

Background. Short bone-conserving femoral stem implants were developed to achieve more physiological, proximal bone loading than conventional femoral stems. Concerns have arisen, however, that improved loading may be offset by lower primary stability because of the reduced potential area for bony contact. Aims. The aim of this study was to determine the primary stability of a novel short femoral stem compared with a conventional femoral stem following cementless total hip arthroplasty (THA), in a prospective, blinded, randomised, controlled trial using radiostereometric analysis. Methods. Fifty-three patients were randomised to receive cementless THA with either a short femoral stem or a conventional femoral stem. The CONSORT diagram is shown (Figure I). Surgery was performed at one institution by three surgeons. 26 patients received the short stem and 23 received the conventional stem. Complete follow-up was available on 40 patients (82%). All patients received the same cementless acetabular component. The primary outcomes were dynamically inducible micromotion and migration of the femoral stems at two years. Both were measured using radiostereometric analysis. Radiographs for radiostereometric analysis were taken post-operatively and at three, six, 12, 18 and 24 months. Validated geometric algorithms were used to determine the relative three-dimensional position of the prosthetic stem and host bone. Results. At two years, there was significantly less subsidence (inferior migration) of the short femoral stem (head: 0.28mm; 95% confidence interval [CI] +/−0.17; SD 0.38; tip: 0.10mm; 95% CI +/− 0.18; SD 0.41) compared with the conventional stem (head: 0.61mm, 95% CI +/−0.26, SD 0.55, P=0.03; tip: 0.44mm, 95% CI +/−0.21, SD 0.43, P=0.02) (Figure II). There was no significant difference in dynamically inducible micromotion. Conclusion. This study demonstrates that the short femoral stem has a stable and predictable migration. However, longer-term survival analysis remains important. For any figures and tables, please contact the authors directly

Aims. Vitamin E-infused highly crosslinked polyethylene (VEPE) has been introduced into total hip arthroplasty (THA) with the aim of further improving the wear characteristics of moderately and highly crosslinked polyethylenes (ModXLPE and HXLPE). There are few studies analyzing the outcomes of vitamin E-infused components in cemented arthroplasty, though early acetabular component migration has been reported. The aim of this study was to measure five-year polyethylene wear and acetabular component stability of a cemented VEPE acetabular component compared with a ModXLPE cemented acetabular component. Methods. In a prospective randomized controlled trial (RCT), we assessed polyethylene wear and acetabular component stability (primary outcome) with radiostereometric analysis (RSA) in 68 patients with reverse hybrid THA at five years follow-up. Patients were randomized to either a VEPE or a ModXLPE cemented acetabular component. Results. Mean polyethylene wear in the proximal direction was 0.17 mm (SD 0.15) for the VEPE group and 0.20 mm (SD 0.09) for the ModXLPE group (p = 0.005) at five years. Annual proximal wear rates were 0.03 mm/year (VEPE) and 0.04 mm/year (ModXLPE). Total 3D wear was 0.21 mm (SD 0.26) and 0.23 mm (SD 0.10) for the VEPE and ModXLPE groups, respectively (p = 0.009). Total 3D cup translation was 0.72 mm (SD 0.70) (VEPE) and 0.50 mm (SD 0.44) (ModXLPE) (p = 0.409). Conclusion. At five years, there was less polyethylene wear in the VEPE group than in the ModXLPE group. Both VEPE and ModXLPE cemented components showed low annual wear rates. Component stability was similar in the two groups and remained constant up to five years. Whether these results will equate to a lower long-term revision rate is still unknown. Cite this article: Bone Joint J 2020;102-B(12):1646–1653

Introduction. Total hip arthroplasty (THA) is a highly successful procedure achieving excellent clinical outcomes beyond 10 years post-surgery. With exception of periprosthetic infection, dislocation is the most common cause of failure in THA. A novel reverse total hip (RTH) replacement has been developed to address dislocation through reversal of the typical THA articulation in which a femoral cup and acetabular ball interlock at the extremes of motion to enhance mechanical stability in all planes. The purpose of this study was to assess the safety and efficacy of this novel RTH in a series of 22 patients and to monitor implant fixation using radiostereometric analysis (RSA). Methods. Twenty two patients with end-stage osteoarthritis of the hip were enrolled between 2017 and 2019 at a single center. All surgeries were performed by a group of four high-volume fellowship-trained arthroplasty surgeons. All patients received at least 1 acetabular cup screw and RSA markers inserted into the acetabulum and proximal femur. Follow-up time points were 6 weeks, 6, 12 and 24 months and included patient reported outcome measures (HOOS, Oxford-12, Harris Hip Score, SF-36 and Satisfaction) as well as RSA assessment. Results. The patient cohort consisted of 11 females and 11 males with mean age of 70.8 years and body mass index 31.3 kg/m. 2. At the time of writing, 21, 15 and 3 patients had completed their 6-month, 1- and 2-year clinical follow-ups, respectively. There was a significant improvement in function and pain with the RTH between pre-operative and six and twelve month follow up as collected by the HOOS, Oxfrod-12, HHS, WOMAC, EQ-5D and SF-36 PCS with p<0.001 for all. The sole exception was the SF-36 MCS which had a non-statistical improvement. Eighteen of 20 patients were satisfied or very satisfied with the outcome of surgery. Average vertical migration of the acetabular cup at 6 and 12 months was 0.082 mm and 0.110 mm, respectively. Average distal migration of the femoral stem at 6 and 12 months was 0.015 mm and 0.035 mm, respectively. Conclusions. Early results indicate acceptable safety and efficacy of this novel RTH for treating osteoarthritis of the hip. The femoral and acetabular components both appear well fixed at near-term follow-up, as assessed with RSA. Further follow-up will determine if these results are maintained at 24 months post-surgery. Additional patient enrollment will assess acetabular cup fixation without the use of screws. For any figures or tables, please contact authors directly

Percutaneous physiodesis is an established technique for treating mild leg-length discrepancy and problems of expected extreme height. Angular deformities resulting from incomplete physeal arrest have been reported, and little is known about the time interval from percutaneous physiodesis to actual physeal arrest. This procedure was carried out in ten children, six with leg-length discrepancy and four with expected extreme height. Radiostereometric analysis was used to determine the three-dimensional dynamics of growth retardation. Errors of measurement of translation were less than 0.05 mm and of rotation less than 0.06°. Physeal arrest was obtained in all but one child within 12 weeks after physiodesis and no clinically-relevant angular deformities occurred. This is a suitable method for following up patients after percutaneous physiodesis. Incomplete physeal arrest can be detected at an early stage and the procedure repeated before corrective osteotomy is required

Introduction. This research determines the feasibility of radiostereometric analysis (RSA) as a diagnostic tool for assessing fusion following spinal arthrodesis. Further, to estimate clinical thresholds for precision and accuracy of the proposed method in the cervical and lumbar spine. Methods. Two-level lumbo-sacral and three-level cervical posterior arthrodesis procedures were performed on an artificial spine model and a cadaveric spine (Figure 1). Using a spring-loaded inserter, RSA marker beads were placed within each of the L4-S1 and C3-C6 vertebrae, then analyzed for optimal bead distribution and detection. RSA imaging consisted of 12 double exams (24 exams) of the cervical and lumbar regions for both the Sawbones and cadaveric spine to assess precision of measurement under zero-displacement conditions, defined as the 95% confidence interval of error. Accuracy assessment was performed on the Sawbones model in which the middle vertebrae (L5 and C4-C5) were moved relative to the superior (L4 and C3) and inferior (S1 and C6) vertebrae by known, incremental displacements (Figure 2). RSA images were obtained at each displacement (Figure 3). Accuracy was defined as the mean difference between known and measured displacements. Results. Median RSA bead detection was 100% in cervical vertebrae and >75% in lumbar vertebrae in the artificial and cadaveric models. Translational RSA precision for both spine models was better than 0.25mm and 0.82mm for the lumbar and cervical regions, respectively. Rotational precision was better than 0.4° and 1.9° for the lumbar and cervical regions, respectively. RSA accuracy for the artificial spine overall demonstrated less than 0.11 mm translational bias (margin < ±0.02 mm) and less than 0.22° rotational bias (margin < ±0.15°). Discussion and Conclusion. This study demonstrates that RSA achieves sufficient precision and accuracy to detect intervertebral micromotion for the purpose of assessing arthrodesis. Well dispersed bead placement is critical to achieving sufficient accuracy and avoiding occlusion by metal hardware. The results of this work will aid in the development of a clinical study to assess arthrodesis in patients. For any figures or tables, please contact the authors directly

The purpose of this research was to determine the feasibility of radiostereometric analysis (RSA) as a diagnostic tool for assessing non-union following spinal arthrodesis procedures. Further, to estimate clinical thresholds for precision and accuracy of the proposed method in the cervical and lumbar spine. A three-level lumbo-sacral and a four-level cervical posterior arthrodesis procedures were performed on an artificial spine model (Sawbones, WA). Using a spring loaded inserter (RSA Biomedical, Sweden), eight to ten RSA markers were placed within each of the L4 and L5 segments in the spinous process (L4 only), lamina, transverse processes, posterior and anterior (down the pedicle) wall of the vertebral body. Eight to ten markers were placed within the proximal sacrum (S1) at the medial and lateral crests, tuberosity, and within the sacral canal wall. Four to eight RSA markers were placed into the C3-C6 lateral masses. Titanium screws and rods were applied to the spinal segments. Identical procedures were then performed on a cadaveric spine using similar bead placement and hardware. RSA imaging consisted of 12 double exams (24 exams) of the cervical and lumbar regions for both the Sawbones and cadaveric spine to assess precision of measurement under zero-displacement conditions. The most distal vertebrae were considered the datum against which the movement of all other vertebrae was compared. The artificial spine was then dismantled for accuracy assessment in which the middle vertebrae (L5 and C4-C5) were moved relative to the superior (L4 and C3) and inferior (S1 and C6) vertebrae by known, incremental displacements on an imaging phantom device. Displacements occurred along the superior-inferior, anterior-posterior, and flexion-extension (rotational) axes of motion. RSA images were obtained at each displacement. Image analysis was performed using model-based software (RSACore v3.41, Leiden, Netherlands) to visualize implanted RSA beads in 3-D space. Precision was defined as the 95% confidence interval of error in measuring zero-displacement. Accuracy was defined as the mean difference (with 95% confidence interval) between the known and measured displacement. The rate of RSA bead detection was high with 5–8 implanted beads being visible in both the lumbar and cervical regions of the artificial and cadaveric spines. Translational RSA precision for both spines was better than 0.25 mm and 0.82 mm for the lumbar and cervical regions, respectively. Rotational precision was better than 0.40° and 1.9° for the lumbar and cervical regions, respectively. RSA accuracy for the artificial spine overall demonstrated less than 0.11 mm translational bias (margin < ±0.02 mm) and less than 0.22° rotational bias (margin < ±0.15°). This study demonstrates that RSA achieves sufficient precision and accuracy to detect intervertebral micromotion for the purpose of assessing arthrodesis. Well dispersed RSA bead placement is critical to achieving sufficient accuracy as well as avoiding occlusion by metal hardware. Cervical bead implantation is particularly sensitive to bead clustering due to small vertebrae size and proximity to critical structures. The results of this work will aid in the development of a clinical study to assess arthrodesis in patients

Abstract. Introduction. Cementless fixation of Oxford Unicompartmental Knee Replacements (UKRs) is an alternative to cemented fixation, however, it is unknown whether cementless fixation is as good long-term. This study aimed to compare primary and long-term fixation of cemented and cementless Oxford UKRs using radiostereometric analysis (RSA). Methodology. Twenty-nine patients were randomised to receive cemented or cementless Oxford UKRs and followed for ten years. Differences in primary fixation and long-term fixation of the tibial components (inferred from 0/3/6-month and 6-month/1-year/2-year/5-year/10-year migration, respectively) were analysed using RSA and radiolucencies were assessed on radiographs. Migration rates were determined by linear regression and clinical outcomes measured using the Oxford Knee Score (OKS). Results. Preliminary analysis of Maximum Total Point Motion (MTPM) indicated cementless tibial components undergo significantly more migration than cemented components during the first 6 months (1.6mm/year, SD=0.92 versus 1.3mm/year, SD=1.1, p<0.001). Cementless migration was predominantly subsidence inferiorly (Mean=0.51mm/year, SD=0.29, p<0.001) and posteriorly (0.13mm/year, SD=0.21, p=0.03). Contrastingly, from 6 months to 10 years cemented components migrated significantly (MTPM=0.039mm/year, SD=0.11, p=0.04) whereas cementless components did not (MTPM=0.002mm/year, SD=0.02, p=0.744). Radiolucent lines occurred more frequently below cemented (10/13) than cementless (4/16) tibial components, but radiolucencies did not correlate with differences in migration or OKS. There was no significant difference in OKS between cemented and cementless. Conclusion. These results suggest that cementless tibial components migrate more than cemented before achieving primary fixation. However, long-term fixation of cementless tibial components appears to be as good, if not better, than cemented with the benefit of fewer radiolucent lines

Purpose: To measure any observed migration and rotation of humeral and ulnar components using radiostereometric analysis. Methods: From 2002–2004 in a prospective study, twelve elbows in patients treated with either a linked(3) or unlinked(9) Acclaim total elbow prosthesis were included in a radiostereometry study. Six tantalum markers were introduced into the humerus another 3 markers were located on a humeral component. Four markers were placed in to ulna and three markers located on the ulnar component. RSA radiographs were taken postoperatively, six, twelve and twenty-four months. The radiographs were digitised and analysed using UmRSA software. The relative movement of the humeral and ulnar implants with respect to the bone was measured. Results: At twelve months, the largest rotation of the humeral component was anteversion/retroversion with a mean of 20, anterior tilt had a mean of 1.10 and varus/valgus tilt was minimal mean 0.60. Mean difference between twelve and 24 months segment rotation was no more than 0.50. Rotation in unlinked humeral implants reached a plateau at 12 months this did not occur in linked implants. Paired t-tests between twelve and 24 months segment translation data showed the mean differences to be no more than 0.04mm. In contrast, humeral tip motion produced a mean of 1.3mm at 12 months dominated by movement in the horizontal plane with a mean difference at 24 months of 0.2mm. Mean micro-motion of the ulna implant tip was 0.32mm at 12 months with a mean difference at 24 months of 0.1mm. Conclusions: Early micromotion of the Acclaim humeral implant occurs mostly by rotation about the vertical axis accompanied by anterior tilt. In unlinked implants this motion reaches a plateau at 12 months after operation but does occur in linked implants

We performed a three-year radiostereometric analysis (RSA) study of the Elite Plus femoral component on 25 patients undergoing primary total hip replacement. Additional assessments and measurements from standard radiographs were also made. Subsidence of the stem occurred at the cement-stem interface. At 36 months the subsidence of the stem centroid was a mean of 0.30 mm (0.02 to 1.28), and was continuing at a slow rate. At the same time point, internal rotation and posterior migration of the femoral head had ceased. One stem migrated excessively and additional assessments suggested that this was probably due to high patient demand. The failure rate of 4% in our study is consistent with data from arthroplasty registers but contrasts with poor results from another RSA study, and from some clinical studies. We believe that the surgical technique, particularly the use of high-viscosity cement, may have been an important factor contributing to our results

Introduction & aims. The magnitude and pattern of acceptable migration in clinically successful cementless stems is not well understood. Radiostereometric analysis (RSA) is a well-recognised method of assessing implant migration. Previous studies have reported long term RSA results for cemented stems. The aim of this study was to assess the long-term migration characteristics of the Corail hydroxyapatite-coated cementless stem at 10 years using RSA. Method. A prospective cohort of 30 patients undergoing primary total hip arthroplasty for primary hip osteoarthritis were enrolled into a study to characterise the migration behaviour of a cementless stem. Tantalum markers were attached to the stem and placed in the bone intraoperatively, allowing for RSA measurements to be taken in vivo. Previous 5-year results have been presented. A total of 14 patients (total 15 hips, one bilateral) with mean age 82 years (range, 69–92 years) underwent repeat long-term RSA radiographs at minimum 10 years post op. The mean time to follow up was 13.9 years (range, 13.3–14.4 years). The RSA radiographs were analysed to assess for implant rotation and translation. Results. None of the 14 patients (15 hips) followed up have been revised. The migration (rotation and translation) at 6 months, 1 year, 2 years, and 6 years has been described previously. No stems had additional subsidence of more than 0.25 mm between 6 months and 6 years. The resultant mean subsidence between 2 years and 6 years was 0.03 mm, which is below the limit measurable by RSA. The long-term, 10-year results, on implant rotation and translation will be presented. Conclusions. The Corail stem exhibited variable subsidence within the first 6 months after which there is persistent stabilisation through to 6 years. 10-year results on long-term migration show no further migration. These results can be used as a gold standard for other uncemented stems

Objectives. Lengthening osteotomies of the calcaneus in children are in general grafted with bone from the iliac crest. Artificial bone grafts have been introduced, however, their structural and clinical durability has not been documented. Radiostereometric analysis (RSA) is a very accurate and precise method for measurements of rigid body movements including the evaluation of joint implant and fracture stability, however, RSA has not previously been used in clinical studies of calcaneal osteotomies. We assessed the precision of RSA as a measurement tool in a lateral calcaneal lengthening osteotomy (LCLO). Methods. LCLO was performed in six fixed adult cadaver feet. Tantalum markers were inserted on each side of the osteotomy and in the cuboideum. Lengthening was done with a plexiglas wedge. A total of 24 radiological double examinations were obtained. Two feet were excluded due to loose and poorly dispersed markers. Precision was assessed as systematic bias and 95% repeatability limits. Results. Systematic bias was generally below 0.10 mm for translations. Precision of migration measurements was below 0.2 mm for translations in the osteotomy. Conclusion. RSA is a precise tool for the evaluation of stability in LCLO. Cite this article: Bone Joint Res 2015;4:78–83

Aims. The primary aim of this study was to compare the migration of the femoral and tibial components of the cementless rotating platform Attune and Low Contact Stress (LCS) total knee arthroplasty (TKA) designs, two years postoperatively, using radiostereometric analysis (RSA) in order to assess the risk of the development of aseptic loosening. A secondary aim was to compare clinical and patient-reported outcome measures (PROMs) between the designs. Methods. A total of 61 TKAs were analyzed in this randomized clinical RSA trial. RSA examinations were performed one day and three, six, 12, and 24 months postoperatively. The maximal total point motion (MPTM), translations, and rotations of the components were analyzed. PROMs and clinical data were collected preoperatively and at six weeks and three, six, 12, and 24 months postoperatively. Linear mixed effect modelling was used for statistical analyses. Results. The mean MTPM two years postoperatively (95% confidence interval (CI)) of the Attune femoral component (0.92 mm (0.75 to 1.11)) differed significantly from that of the LCS TKA (1.72 mm (1.47 to 2.00), p < 0.001). The Attune femoral component subsided, tilted (anteroposteriorly), and rotated (internal-external) significantly less. The mean tibial MTPM two years postoperatively did not differ significantly, being 1.11 mm (0.94 to 1.30) and 1.17 mm (0.99 to 1.36, p = 0.447) for the Attune and LCS components, respectively. The rate of migration in the second postoperative year was negligible for the femoral and tibial components of both designs. The mean pain-at-rest (numerical rating scale (NRS)-rest) in the Attune group was significantly less compared with that in the LCS group during the entire follow-up period. At three months postoperatively, the Knee injury and Osteoarthritis Outcome Physical Function Shortform score, the Oxford Knee Score, and the NRS-activity scores were significantly better in the Attune group. Conclusion. The mean MTPM of the femoral components of the cementless rotating platform Attune was significantly less compared with that of the LCS design. This was reflected mainly in significantly less subsidence, posterior tilting, and internal rotation. The mean tibial MTPMs were not significantly different. During the second postoperative year, the components of both designs stabilized and low risks for the development of aseptic loosening are expected. Cite this article: Bone Joint J 2023;105-B(2):148–157

Aims. The Exeter short stem was designed for patients with Dorr type A femora and short-term results are promising. The aim of this study was to evaluate the minimum five-year stem migration pattern of Exeter short stems in comparison with Exeter standard stems. Methods. In this case-control study, 25 patients (22 female) at mean age of 78 years (70 to 89) received cemented Exeter short stem (case group). Cases were selected based on Dorr type A femora and matched first by Dorr type A and then age to a control cohort of 21 patients (11 female) at mean age of 74 years (70 to 89) who received with cemented Exeter standard stems (control group). Preoperatively, all patients had primary hip osteoarthritis and no osteoporosis as confirmed by dual X-ray absorptiometry scanning. Patients were followed with radiostereometry for evaluation of stem migration (primary endpoint), evaluation of cement quality, and Oxford Hip Score. Measurements were taken preoperatively, and at three, 12, and 24 months and a minimum five-year follow-up. Results. At three months, subsidence of the short stem -0.87 mm (95% confidence interval (CI) -1.07 to -0.67) was lower compared to the standard stem -1.59 mm (95% CI -1.82 to -1.36; p < 0.001). Both stems continued a similar pattern of subsidence until five-year follow-up. At five-year follow-up, the short stem had subsided mean -1.67 mm (95% CI -1.98 to -1.36) compared to mean -2.67 mm (95% CI -3.03 to -2.32) for the standard stem (p < 0.001). Subsidence was not influenced by preoperative bone quality (osteopenia vs normal) or cement mantle thickness. Conclusion. The standard Exeter stem had more early subsidence compared with the short Exeter stem in patients with Dorr type A femora, but thereafter a similar migration pattern of subsidence until minimum five years follow-up. Both the standard and the short Exeter stems subside. The standard stem subsides more compared to the short stem in Dorr type A femurs. Subsidence of the Exeter stems was not affected by cement mantle thickness. Cite this article: Bone Jt Open 2023;4(7):507–515

Aims. Both the femoral and tibial component are usually cemented at revision total knee arthroplasty (rTKA), while stems can be added with either cemented or press-fit (hybrid) fixation. The aim of this study was to compare the long-term stability of rTKA with cemented and press-fitted stems, using radiostereometric analysis (RSA). Methods. This is a follow-up of a randomized controlled trial, initially involving 32 patients, of whom 19 (nine cemented, ten hybrid) were available for follow-up ten years postoperatively, when further RSA measurements were made. Micromotion of the femoral and tibial components was assessed using model-based RSA software (RSAcore). The clinical outcome was evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), and visual analogue scale (pain and satisfaction). Results. The median total femoral translation and rotation at ten years were 0.39 mm (interquartile range (IQR) 0.20 to 0.54) and 0.59° (IQR 0.46° to 0.73°) for the cemented group and 0.70 mm (IQR 0.15 to 0.77) and 0.78° (IQR 0.47° to 1.43°) for the hybrid group. For the tibial components this was 0.38 mm (IQR 0.33 to 0.85) and 0.98° (IQR 0.38° to 1.34°) for the cemented group and 0.42 mm (IQR 0.30 to 0.52) and 0.72° (IQR 0.62° to 0.82°) for the hybrid group. None of these values were significantly different between the two groups and there were no significant differences between the clinical scores in the two groups at this time. There was only one re-revision, in the hybrid group, for infection and not for aseptic loosening. Conclusion. These results show good long-term fixation with no difference in micromotion and clinical outcome between fully cemented and hybrid fixation in rTKA, which builds on earlier short- to mid-term results. The patients all had type I or II osseous defects, which may in part explain the good results. Cite this article: Bone Joint J 2022;104-B(7):875–883

Introduction: In the past, surgeons have found impaction bone grafting technically difficult leading to its limited use. This paper reviews the long term results and developments in instrumentation and techniques aimed at simplifying femoral impaction grafting at revision hip replacement. The expanded indications for this procedure are reviewed and recent results of stem fixation using radiostereometric analysis (RSA) are reported. Methods: The impaction bone grafting procedure, using a cemented collarless polished double taper stem, has been used in 66 hips (median patient age 63yrs) since 1993. The technique has undergone numerous developments. Modular tamps have been used in the last 29 hips and in the last seven hips, a pneumatic mechanical vibration device has been used in place of manual impaction. Stem subsidence at both the prosthesis-cement and cement-graft/bone interfaces was measured, more recently using radiostereometric analysis. Results: There was a high early incidence of failure in the initial cases but there have been no further revisions for mechanical failure at up to 15 years. Technique developments have resulted in dramatic improvements in stem fixation achieved. In the modular tamp cases, the mean stem subsidence at the cement-bone interface at 12 months was 0.07mm (0 to 0.7mm) at 12 months. The stem subsidence in the hips where the mechanical vibration device was used was 0.05mm (0 to 0.06mm). Femoral impaction grafting offers special advantages in younger patients include standard femoral stem revision and at the second stage of two stage revision for infection. Discussion and Conclusion: A stable cement-bone interface is achieved using advanced techniques of femoral impaction grafting that includes the use of modular impaction instruments. Early results of mechanical vibration impaction are encouraging. Femoral impaction grafting restores bone and new techniques simplify the femoral revision procedure

Aims. The aim of this study was to compare the mid-term patient-reported outcome, bone remodelling, and migration of a short stem (Collum Femoris Preserving; CFP) with a conventional uncemented stem (Corail). Methods. Of 81 patients who were initially enrolled, 71 were available at five years’ follow-up. The outcomes at two years have previously been reported. The primary outcome measure was the clinical result assessed using the Oxford Hip Score (OHS). Secondary outcomes were the migration of the stem, measured using radiostereometric analysis (RSA), change of bone mineral density (BMD) around the stem, the development of radiolucent lines, and additional patient-reported outcome measures (PROMs). Results. There were no statistically significant differences between the groups regarding PROMs (median OHS (CFP 45 (interquartile range (IQR) 35 to 48); Corail 45 (IQR 40 to 48); p = 0.568). RSA showed stable stems in both groups, with little or no further subsidence between two and five years. Resorption of the femoral neck was evident in nine patients in the CFP group and in none of the 15 Corail stems with a collar that could be studied. Dual X-ray absorbiometry showed a significantly higher loss of BMD in the proximal Gruen zones in the CFP group (mean changes in BMD: Gruen zone 1, CFP -9.5 (95% confidence interval (CI) -14.8 to -4.2), Corail 1.0 (95% CI 3.4 to 5.4); Gruen zone 7, CFP -23.0 (95% CI -29.4 to -16.6), Corail -7.2 (95% CI -15.9 to 1.4). Two CFP stems were revised before two years’ follow-up due to loosening, and one Corail stem was revised after two years due to chronic infection. Conclusion. The CFP stem has a similar clinical outcome and subsidence pattern when compared with the Corail stem. More pronounced proximal stress-shielding was seen with the CFP stem, suggesting diaphyseal fixation, and questioning its femoral neck-sparing properties in the long term. Cite this article: Bone Joint J 2022;104-B(5):581–588

Introduction. Surgeons performing a total knee replacement (TKR) have two techniques to assist them achieve proper bone resections and ligament tension – gap balancing (GB) and measured resection (MR). GB relies on balancing ligaments prior to bony resections, whereas bony resections are made based on anatomical landmarks in MR. Many studies have been done to compare the implant migration and kinematics between the two techniques, but the results have been varied. However, these studies have not been done on modern anatomically designed prostheses using radiostereometric analysis (RSA). Anatomical designs attempt to mimic the normal knee joint structure to return more natural kinematics to the joint, with emphasis on eliminating both paradoxical anterior motion and reduced posterior femoral rollback. Given the major design differences between anatomical and non-anatomical prostheses, it is important to investigate whether one surgical technique may have advantages another. We hypothesize that there would be no difference between GB and MR techniques in implant migration, but that GB might provide better knee kinematics. Methods. Patients were recruited to receive an anatomically designed prosthesis and randomized to groups where the GB or MR technique is used. For all patients in the study, RSA images were acquired at a 2 week baseline, as well as at 6 weeks, 3 months, and 6 months post-operatively. These images were used to collect the maximum total point motion (MTPM) of the tibial and femoral implant components relative to the bone using a model-based RSA software. A series of RSA images were also acquired at 3-months post-operatively at different knee flexion angles, ranging in 20° increments from 0° to 100°. Model-based RSA software was used to obtain the 3D positions and orientations of the femoral and tibial components, which were used to obtain the anterior-posterior (AP) contact locations for each condyle. Results. Results from 47 patients (27 GB, 20 MR) were analyzed. No significant differences were present between the two surgical techniques for tibial component MTPM at 6 weeks (mean difference=0.02 mm, p=0.61), 3 months (mean difference=0.01 mm, p=0.92), and 6 months (mean difference=0.01 mm, p=0.93) post-operatively. No significant differences were present between the two surgical techniques for femoral component MTPM at 6 weeks (mean difference=0.12 mm, p=0.08), 3 months (mean difference=0.05 mm, p=0.54), and 6 months (mean difference=0.13 mm, p=0.05) post-operatively. On the medial condyle, no significant differences in AP contact location were found at all angles between 0° and 80° of flexion (p-values from 0.28 to 0.95). There was a significant difference medially between the AP contact location of the two surgical techniques at 100° of flexion (p=0.01), indicating more posterior rollback on the medial condyle in the GB technique. On the lateral condyle, no significant differences in AP contact location were found at all angles of flexion (p-values from 0.13 to 0.62). On the medial condyle of the GB group, the AP contact location moved posteriorly 5.83 mm from 0° to 20°, anteriorly 2.60 mm from 20° to 60°, and posteriorly 7.40 mm from 60° to 100°. On the medial condyle of the MR group, the AP contact location moved posteriorly 5.36 mm from 0° to 20°, anteriorly 2.87 mm from 20° to 60°, and posteriorly 3.65 mm from 60° to 100°. On the lateral condyle of the GB group, the AP contact location moved posteriorly 6.87 mm from 0° to 20°, 0.30 mm from 20° to 60°, and 3.61 mm from 60° to 100°. On the lateral condyle of the MR group, the AP contact location moved posteriorly 6.86 mm from 0° to 20°, anteriorly 0.02 mm from 20° to 60°, and posteriorly 3.56 mm from 60° to 100°. Conclusions. The GB and MR techniques are very similar in terms of implant migration and overall kinematics when an anatomical prosthesis design is used for TKR. This study suggests that surgeon preference should be used when deciding which technique to use for implanting this anatomically designed knee replacement. For figures, tables, or references, please contact authors directly

Aims. Although the Fitmore Hip Stem has been on the market for almost 15 years, it is still not well documented in randomized controlled trials. This study compares the Fitmore stem with the CementLeSs (CLS) in several different clinical and radiological aspects. The hypothesis is that there will be no difference in outcome between stems. Methods. In total, 44 patients with bilateral hip osteoarthritis were recruited from the outpatient clinic at a single tertiary orthopaedic centre. The patients were operated with bilateral one-stage total hip arthroplasty. The most painful hip was randomized to either Fitmore or CLS femoral component; the second hip was operated with the femoral component not used on the first side. Patients were evaluated at three and six months and at one, two, and five years postoperatively with patient-reported outcome measures, radiostereometric analysis, dual-energy X-ray absorptiometry, and conventional radiography. A total of 39 patients attended the follow-up visit at two years (primary outcome) and 35 patients at five years. The primary outcome was which hip the patient considered to have the best function at two years. Results. At two and five years, more patients considered the hip with the CLS femoral component as superior but without a statistically significant difference. There were no differences in clinical outcome, magnitude of femoral component migration, or change of bone mineral density at five years. At three months, the Fitmore femoral component had subsided a median -0.71 mm (interquartile range (IQR) -1.67 to -0.20) and the CLS femoral component -0.70 mm (IQR -1.53 to -0.17; p = 0.742). In both groups the femoral head centre had migrated posteriorly (Fitmore -0.17 mm (IQR -0.98 to -0.04) and CLS -0.23 mm (IQR -0.87 to 0.07; p = 0.936)). After three months neither of the femoral components showed much further migration. During the first postoperative year, one Fitmore femoral component was revised due to aseptic loosening. Conclusion. Up to five years, we found no statistically significant difference in outcomes between the Fitmore and the CLS femoral components. The slightly worse outcomes, including one revised hip because of loosening, speaks against the hypothesis that the Fitmore femoral component should be advantageous compared to the CLS if more patients had been recruited to this study. Cite this article: Bone Jt Open 2023;4(5):306–314

Aims. Stemless humeral implants have been developed to overcome stem-related complications in total shoulder arthroplasty (TSA). However, stemless implant designs may hypothetically result in less stable initial fixation, potentially affecting long-term survival. The aim of this study is to investigate early fixation and migration patterns of the stemless humeral component of the Simpliciti Shoulder System and to evaluate clinical outcomes. Methods. In this prospective cohort study, radiostereometric analysis (RSA) radiographs were obtained in 24 patients at one day, six weeks, six months, one year, and two years postoperatively. Migration was calculated using model-based RSA. Clinical outcomes were evaluated using the visual analogue scale (VAS), the Oxford Shoulder Score (OSS), the Constant-Murley Score (CMS), and the Disabilities of the Arm, Shoulder and Hand (DASH) score. Results. At two years, median translation along the x-, y-, and z-axis was -0.12 mm (interquartile range (IQR) -0.18 to 0.02), -0.17 mm (IQR -0.27 to -0.09), and 0.09 mm (IQR 0.02 to 0.31). Median rotation around the x-, y-, and z-axis was 0.12° (IQR -0.50 to 0.57), -0.98° (IQR -1.83 to 1.23), and 0.09° (IQR -0.76 to 0.30). Overall, 20 prostheses stabilized within 12 months postoperatively. Four prostheses showed continuous migration between 12 and 24 months. At two-year follow-up, with the exception of one revised prosthesis, all clinical scores improved significantly (median VAS difference at rest: -3.0 (IQR -1.5 to -6.0); OSS 22.0 (IQR 15.0 to 25.0); CMS 29.5 (IQR 15.0 to 35.75); and DASH -30.0 (IQR -20.6 to -41.67) (all p < 0.001)) with the exception of one revised prosthesis. Conclusion. In conclusion, we found that 20 out of 24 implants stabilized within 12 months postoperatively. The significance of continuous migration in four implants is unclear and future research on the predictive value of early migration for future loosening in TSA is required. Clinical results revealed a clinically relevant improvement. Cite this article: Bone Joint J 2022;104-B(1):76–82

This was a randomised controlled trial studying the safety of a new short metaphyseal fixation (SMF) stem. We hypothesised that it would have similar early clinical results and micromovement to those of a standard-length tapered Synergy metaphyseal fixation stem. Using radiostereometric analysis (RSA) we compared the two stems in 43 patients. A short metaphyseal fixation stem was used in 22 patients and a Synergy stem in 21 patients. No difference was found in the clinical outcomes pre- or post-operatively between groups. RSA showed no significant differences two years post-operatively in mean micromovement between the two stems (except for varus/valgus tilt at p = 0.05) (subsidence 0.94 mm (. sd.  1.71) vs 0.32 mm (. sd. 0.45), p = 0.66; rotation 0.96° (. sd. 1.49) vs 1.41° (. sd. 2.95), p = 0.88; and total migration 1.09 mm (. sd. 1.74) vs 0.73 mm (. sd. 0.72), p = 0.51). A few stems (four SMF and three Synergy) had initial migration > 1.0 mm but stabilised by three to six months, with the exception of one SMF stem which required revision three years post-operatively. For most stems, total micromovement was very low at two years (subsidence < 0.5 mm, rotation < 1.0°, total migration < 0.5 mm), which was consistent with osseous ingrowth. The small sample makes it difficult to confirm the universal applicability of or elucidate the potential contraindications to the use of this particular new design of stem. Cite this article: Bone Joint J 2015; 97-B:595–602

Background. Patient specific instrumentation (PSI) for total knee replacement (TKR) has demonstrated mixed success in simplifying the operation, reducing its costs, and improving limb alignment. Evaluation of PSI with tools such as radiostereometric analysis (RSA) has been limited, especially for cut-through style guides providing mechanical alignment. The primary goal of the present study was to compare implant migration following TKR using conventional and PSI surgical techniques, with secondary goals to examine whether the use of PSI reduces operative time, instrumentation, and surgical waste. Methods. The study was designed as a prospective, randomized controlled trial of 50 patients, with 25 patients each in the PSI and conventional groups, powered for the RSA analysis. Patients in the PSI group received an MRI and standing 3-foot x-rays to construct patient-specific cut-through surgical guides for the femur and tibia with a mechanical alignment. All patients received the same posterior-stabilized implant, with marker beads inserted in the bone around the implants to enable RSA imaging. Intraoperative variables such as time, number of instrumentation trays used, and mass of surgical waste were recorded. Patients underwent supine RSA exams at multiple time points (2&6 weeks, 3&6 months and yearly) with 6 months data currently available. Migration of the tibial and femoral components was calculated using model-based RSA software. WOMAC, SF-12, EQ5D, and UCLA outcome measures were recorded pre-operatively and post-operatively. Results. There were no demographic differences between groups. One patient in the PSI group was revised for infection, and three patients required manipulation, with no revisions or manipulations in the conventional group. There was no difference in maximum total point motion between groups for the tibia (mean 0.50 vs. 0.50 mm, p = 0.98) or femur (mean 0.46 vs. 0.48 mm, p = 0.87). The PSI group displayed greater tibial posterior tilt (p = 0.048, Fig. 1) and greater femoral anterior tilt (p = 0.01) and valgus rotation (p = 0.04, Fig. 2) than the conventional group, but there were no other differences in migrations. The PSI group required less instrument trays than the conventional group (mean 4.8 vs. 8.1 trays, p < 0.0001), but procedure time was equivalent (mean 79 vs. 74 min, p = 0.06). The PSI group produced less recyclable waste (mean 0.3 vs. 1.4 kg, p < 0.001), but total waste (Fig. 3) was equivalent between groups (mean 10.1 vs. 10.6 kg, p = 0.32). At 6 months there was no difference between groups for SF-12, WOMAC, EQ5D, or UCLA scores. Discussion. At early RSA follow-up, the two groups were broadly similar in implant fixation except for small rotational changes in the tibial and femoral components. The PSI group provided minimal or no advantage over the conventional group for operative time, instrumentation used, or surgical waste produced. The observed increase in manipulations in the PSI group is concerning, and requires additional investigation. Further radiographic and economic analysis is underway to determine if there is any benefit to the use of PSI for TKR during the perioperative and early follow-up period. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aims. The objective of this study was to compare the two-year migration pattern and clinical outcomes of a total knee arthroplasty (TKA) with an asymmetrical tibial design (Persona PS) and a well-proven TKA with a symmetrical tibial design (NexGen LPS). Methods. A randomized controlled radiostereometric analysis (RSA) trial was conducted including 75 cemented posterior-stabilized TKAs. Implant migration was measured with RSA. Maximum total point motion (MTPM), translations, rotations, clinical outcomes, and patient-reported outcome measures (PROMs) were assessed at one week postoperatively and at three, six, 12, and 24 months postoperatively. Results. A linear mixed-effect model using RSA data of 31 asymmetrical and 38 symmetrical TKAs did not show a difference in mean MTPM migration pattern of the tibial or femoral components. Mean tibial component MTPM at two years postoperative of the asymmetrical TKA design was 0.93 mm and 1.00 mm for the symmetrical design. For the femoral component these values were 1.04 mm and 1.14 mm, respectively. No significant differences were observed in other migration parameters or in clinical and PROM measurements. Conclusion. The TKA design with an asymmetrical tibial component has comparable component migration with the proven TKA with a symmetrical tibial component. This suggests the risk of long-term aseptic loosening of the two designs is comparable. Cite this article: Bone Joint J 2021;103-B(5):855–863

Aims. Thresholds of acceptable early migration of the components in total knee arthroplasty (TKA) have traditionally ignored the effects of patient and implant factors that may influence migration. The aim of this study was to determine which of these factors are associated with overall longitudinal migration of well-fixed tibial components following TKA. Methods. Radiostereometric analysis (RSA) data over a two-year period were available for 419 successful primary TKAs (267 cemented and 152 uncemented in 257 female and 162 male patients). Longitudinal analysis of data using marginal models was performed to examine the associations of patient factors (age, sex, BMI, smoking status) and implant factors (cemented or uncemented, the size of the implant) with maximum total point motion (MTPM) migration. Analyses were also performed on subgroups based on sex and fixation. Results. In the overall group, only fixation was significantly associated with migration (p < 0.001). For uncemented tibial components in males, smoking was significantly associated with lower migration (p = 0.030) and BMI approached significance (p = 0.061). For females with uncemented components, smoking (p = 0.081) and age (p = 0.063) approached significance and were both associated with increased migration. The small number of self-reported smokers in this study warrants cautious interpretation and further investigation. For cemented components in females, larger sizes of tibial component were significantly associated with increased migration (p = 0.004). No factors were significant for cemented components in males. Conclusion. The migration of uncemented tibial components was more sensitive to patient factors than cemented implants. These differences were not consistent by sex, suggesting that it may be of value to evaluate female and male patients separately following TKA. Cite this article: Bone Joint J 2022;104-B(4):444–451

Introduction. The effectiveness of patient specific instrumentation (PSI) to perform total knee arthroplasty (TKA) remains controversial. Multiple studies have been published that reveal conflicting results on the effectiveness of PSI, but no study has analyzed the contact kinematics within knee joints replaced with the use of PSI. Since a departure from normal kinematics can lead to eccentric loading, premature wear, and component loosening, studying the kinematics in patients who have undergone TKA with PSI can provide valuable insight on the ability of PSI to improve functionality and increase longevity. The goal of the present study was to compare femoral and tibial component migration (predictive of long-term loosening and revision) and contact kinematics following TKA using conventional instruments (CI) and PSI based surgical techniques. Methods. The study was designed as a prospective, randomized controlled trial of 50 patients, with 25 patients each in the PSI and CI groups, powered for radiostereometric analysis (RSA). Patients in the PSI group received an MRI and standing 3-foot x-rays to construct patient-specific cut-through surgical guides for the femur and tibia with a mechanical limb alignment. All patients received the same posterior-stabilized implant with marker beads inserted in the bone around the implants to enable RSA imaging. Patients underwent supine RSA exams at multiple time points (two and six weeks, three and six months, and one and two years). At 2 years post-op, a series of RSA radiographs were acquired at different knee flexion angles, ranging in 20° increments from 0° to 120°, to measure the tibiofemoral contact kinematics. Migrations of the femoral and tibial components were calculated using model-based RSA software. Kinematics were measured for each condyle for magnitude of excursion, contact location, and stability. Results. There were no differences (p > 0.05) between the PSI and CI groups for demographics or pre- and post-operative patient reported outcome scores. Three patients in the PSI group and seven patients in the CI group (p = 0.28) had a post-operative limb alignment outside of the neutral target (>3° varus or valgus). There was no difference in the change of tibial slope from pre- to post-operation between groups (p = 0.49). There were no differences (p > 0.05) in translations or rotations in any individual plane across all time points for either the tibial or femoral components. Maximum total point motion (MTPM) at 6 months for the tibial component was 0.54 ± 0.25 mm in the CI group and 0.51 ± 0.22 mm in the PSI group (p = 0.77), placing both groups at the low end of the “at risk” category for predicted loosening. Change in MTPM from 6 months to 1 year and again from 1 year to 2 years was <0.2 mm, indicating both groups of implants had stable fixation. Femoral component MTPM was also not different (p > 0.05) between groups. There was no significant difference between PSI and CI groups with respect to magnitude of excursion on both medial (p = 0.54) and lateral (p = 0.81) condyles. There was also no difference in contact locations on both the medial and lateral condyles (p = 0.28 to 0.91) for all angles of flexion. There was no significant difference present between PSI and CI groups when comparing the stability for both the medial (p = 0.06) and lateral (= 0.85) condyles. Condylar separation was present in 3/20 CI patients and 0/16 PSI patients (p = 0.24). Conclusion. Using the latest RSA criteria for predicting failure from early migration, the use of PSI does not provide an advantage over CI for preventing aseptic loosening. Moreover, PSI did not provide any substantial advantage over CI for TKA surgery with respect to contact kinematics

Summary. Application of RSA in supine and standing positions allows pelvic fracture stability to be measured more accurately than current techniques. RSA may enable a better understanding of these injuries. Introduction. The in vivo stability of the pelvic ring after fracture stabilisation remains unknown. Plain radiographs have a low accuracy in diagnosing loss of fracture reduction over time. Radiostereometric analysis (RSA) is an accurate imaging measurement method that has previously been applied to measure the healing of other fractures. This pilot study investigated the potential application of RSA in supine and standing positions to measure pelvic fracture stability over time and under weightbearing load. Methods. Five patients with a similar type C pelvic ring disruption who were all operated on using the same surgical technique and had RSA markers inserted at the time of surgery. All five patients had a unilateral comminuted sacral fracture lateral to the sacral foramina treated with posterior plating and pubic rami fractures stabilised by external fixation for six weeks. All patients were mobilised partial weight bearing after regaining leg control. RSA examinations at 2, 4, 12, 26 and 52 weeks included three radiographic pairs taken in supine, standing and supine positions at each time point. Two additional RSA examinations were performed the day prior and post pin removal at 6 weeks. Results. All patients ambulated before the 2 week follow-up and progressed uneventfully. At latest follow-up, there were no complications. Minimal displacements (translations less than 0.3mm and rotations less than 0.5°) were recorded between the supine exams pre and post standing at 2 weeks. Hence, the supine examination was found to be a reliable position to measure the migration of the ilium over time. No loss of reduction was identifiable on plain radiographs over time. At 52 weeks, in contrast to plain radiographic results, RSA measurements revealed that one patient had a fracture migration greater than 4mm. Such large displacements could result in sacral nerve root transection, leading to devastating consequences, such as incontinence, for patients whose sacral fractures are through or medial to the sacral foramina. In one patient, the migration recorded for the apparent uninjured posterior complex side exceeded the migration of the injured side suggesting an unrecognised bilateral injury. Comparative RSA examinations pre and post external fixator removal demonstrated that in three patients the injured hemipelvis migrated greater than 2mm after the removal of the external fixator, which may be indicative that the fixator was removed prematurely. Discussion and Conclusion. The application of RSA allows accurate measurement of pelvic fracture stability which is difficult, if not impossible, to identify and quantify with any other imaging techniques. Hence, RSA has the capacity to enable a better understanding of pelvic ring injuries and optimise their treatment

Purpose. The purpose of this study was to assess the clinical outcomes over two years for total ankle arthroplasty (TAA) using Short Form-36, Foot Function Index and Ankle Osteoarthritis Scores, and to compare these with radiostereometric analysis longitudinal migration and inducible displacement results. Method. Twenty patients undergoing TAA implanting the Mobility Total Ankle System (DePuy, Warsaw IN) were assessed at 3mth, 6mth, 1yr and 2yr followup periods by model-based radiostereometric analysis, MBRSA 3.2 (Medis specials, Leiden, The Netherlands), for longitudinal migration (LM) and inducible displacement (ID). The same subjects completed clinical outcome questionnaires at these followup periods for Short Form-36 (SF-36; Physical Component Scores (PCS) and Mental Component Scores (MCS)), Foot Function Index (FFI) and Ankle Osteoarthritis Scores (AOS). Descriptive statistics and Pearson correlations (alpha = 0.05) were calculated using Minitab 15 (Minitab Inc., State College PA). Results. For the PCS of SF-36, FFI and AOS the scores were significantly different at 2 year followup when compared to preoperative values; p = 0.005, 0.0002 and 0.0003 respectively. The PCS on average increased with respect to pre-operative by 10 points (SD = +/−13), while the MCS on average did not change with respect to pre-operative (SD = +/− 12). The FFI on average decreased by 25 points with respect to pre-operative (SD = +/− 18) and AOS on average decreased by 23 points with respect to pre-operative (SD = +/− 21). There were several correlations for the 2 yr results: AOS to FFI of r = 0.92 (p = 0.000); AOS to PCS of r = −0.67 (p = 0.005); AOS to MCS of r = −0.51 (p = 0.046); AOS to talar component ID of r = 0.70 (p = 0.004); AOS to the talar component LM of r = 0.62 (p = 0.046). PCS related better than MCS to both AOS and FFI. The LM of the talar component and tibial component were not significantly correlated, r = 0.18 (p = 0.62). The ID of the talar component and tibial component were not significantly correlated, r = 0.48 (p = 0.07). The latter result may be too underpowered to determine a significant difference; due to the small sample size. Conclusion. The outcome scores of AOS, FFI, SF-36 (PCS) and SF-36 (MCS) were correlated to each other. The strongest outcome score relationships were AOS to FFI, followed by AOS to SF-36 (PCS). The correlation of AOS to the talar component LM and ID suggests that the implant performance may be related to the stability of the talar component

Introduction. Uncemented highly porous titanium implants have been shown to promote osseointegration, and may result in a durable construct for total knee arthroplasty (TKA). Given the mixed results of uncemented TKA, it is important to evaluate the early stability for this product. The objective of the following study was to use radiostereometric analysis (RSA) to assess early fixation of a highly porous tibial baseplate and metal backed patella. Methods. Twenty-seven patients (mean age 64 years, 30% female) undergoing primary TKA consented to participate in this prospective cohort study. All patients received a highly porous tibial baseplate, a metal backed patella and tantalum RSA bone markers. Implant migration was assessed using model-based RSA at 1.5, 3, 6, 12 and 24 months post-operative. Patient reported outcome measures were captured using the same follow-up schedule, and compared to pre-operative measures. Results. There were no adverse events affecting implant fixation, and no revisions. Patient function significantly improved by 3 months post-operation (p < 0.001). The highest rate of tibia and patellar component migration occurred over the first six post-operative weeks, with minimal migration thereafter. Mean maximum total point motion (MTPM) at 24 months was 0.72 (SD 0.34) mm for the tibia, and 0.44 (SD 0.25) mm for the patella. Three tibia baseplates migrated more than 1 standard deviation greater than the mean at 24 months, and also had continuous migration (> 0.2mm of MTPM) in the second post-operative year. One patellar component showed a rapid rate of migration between 6 and 24 months, whereas all other patellar components appeared to stabilize. Conclusions. Osseointegration appears to occur on the highly porous implant surface of the tibia baseplate and metal backed patella, as evidenced by implant stability. Further follow-up is required to determine if clinical loosening will manifest in the continuously migrating implants

Background. Migration analysis after total joint arthroplasty are performed using EBRA analysis (Krismer et al., 1997) or - more accurate but also much more cost-intensive and time-consuming – via radiostereometric analysis (RSA). For the latter, additional radiographs from two inclined perspectives are needed in regular intervals in order to define the position of the implant relative to tantalum bone markers which have been implanted during surgery of the artificial joint (Fig. 1). Modern analysis software promises a migration precision along the stem axis of a hip implant of less than 100 μm (Witvoet-Brahm et al., 2007). However, as the analysis is performed semi-automatically, the results are still dependent on the subjective evaluation of the X-rays by the observer. Thus, the present phantom study aims at evaluating the inter- and intra-observer reliability, the repeatability as well as the precision and gives insight into the potential and limits of the RSA method. Materials and Methods. Considering published models, an RSA phantom model has been developed which allows a continuous and exact positioning of the prostheses in all six degrees of freedom (Fig. 2). The position sensitivities of the translative and rotative positioning components are 1 μm and 5 to 24, respectively. The roentgen setup and Model-Based RSA software (3.3, Medis specials bv, Leiden, Netherlands) was evaluated using the SL-PLUS® standard hip stem (size 7, Smith & Nephew, Baar, Switzerland). The inter-observer (10 repetitions) and intra-observer (3 observers) reliability have been considered. Additionally, the influences of the model repositioning and inclination as well as the precision after migration and rotation along the stem axis are investigated. Results and Discussion. Precision along the stem axis was determined to 161 μm (± 230 μm), in the lateral plane 100 μm (± 85 μm) and maximal rotations to 0.524° (± 1.268°). High reproducibility (intra-observer reliability) is reported with relevant influences of the inclination of the implant on the radiograph, in particular for the first clinical scene which serves as a reference. Deviations after translations along the stem axis are 0.37 ± 1.92% and −3.28 ± 6.62% after rotations. In conclusion, the precision given by the software producer of less than 100 μm could not be verified. Beside the limitations from the software, potential sources of errors are the subjective analysis by the observer, a small number of bone markers and the positioning of the implant (patient) during X-ray examination. Though, Model-Based RSA largely outmatches the EBRA approach in terms of measuring implant migration. However, standardization of the X-rays and RSA analysis is recommended

Adequate fixation of implant components is an important goal for all arthroplasty procedures. Aseptic loosening is one of the leading causes of revision surgery in total knee arthroplasty. Radiostereometric analysis (RSA) is an imaging technique to measure implant migration, with established migration thresholds for well-fixed, at risk, and unacceptably migrating components. The purpose of the present study was to examine the long-term fixation of a cemented titanium fixed bearing polished tibial baseplate. Patients enrolled in a previous two-year prospective trial were recalled at ten years. All patients received a cemented, posterior-stabilised total knee replacement of the same design implanted by one of three surgeons. Of the original 35 patients, 16 were available for long-term follow-up, with one patient lost to follow-up, nine patients deceased, and a further nine patients unwilling to return to the clinic. Each patient underwent RSA imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes as well as maximum total point motion (MTPM) was compared between all time points (baseline, six weeks, three months, six months, one year, two years) up to the ten year follow-up visits. Outcome scores including the Knee Society Score (KSS), WOMAC, SF-12, and UCLA Activity Score were recorded. At ten years, the mean migrations of the tibial component were less than 0.1 mm and 0.1 degree in all planes relative to the post-operative RSA exam. There was no significant difference in tibial component migration between time points. However, MTPM increased significantly over time (p = 0.002), from 0.23 ± 0.18 mm at six weeks to 0.42 ± 0.20 mm at ten years. At one year, 13 patients had an acceptable MTPM level, three patients had an ‘at risk’ level, and no patient had an ‘unacceptable’ level. No patients were revised at ten years. WOMAC and KSS were significantly improved (p < 0.0001) at the latest follow-up compared to pre-operatively, but there was no difference in SF-12. The median UCLA Activity Score at latest follow-up was six (range, two to eight). The tibial baseplate demonstrated solid fixation at ten years. No patients had an unacceptable MTPM level at one year and no patients were revised at ten years, supporting the use of RSA to predict long-term loosening risk. The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries

Aims. The aim of this prospective cohort study was to evaluate the early migration of the TriFit cementless proximally coated tapered femoral stem using radiostereometric analysis (RSA). Methods. A total of 21 patients (eight men and 13 women) undergoing primary total hip arthroplasty (THA) for osteoarthritis of the hip were recruited in this study and followed up for two years. Two patients were lost to follow-up. All patients received a TriFit stem and Trinity Cup with a vitamin E-infused highly cross-linked ultra-high molecular weight polyethylene liner. Radiographs for RSA were taken postoperatively and then at three, 12, and 24 months. Oxford Hip Score (OHS), EuroQol five-dimension questionnaire (EQ-5D), and adverse events were reported. Results. At two years, the mean subsidence of the head and tip for the TriFit stem was 0.38 mm (SD 0.32) and 0.52 mm (SD 0.36), respectively. The total migration of the head and tip was 0.55 mm (SD 0.32) and 0.71 mm (SD 0.38), respectively. There were no statistically significant differences between the three to 12 months' migration (p = 0.105) and 12 to 24 months' migration (p = 0.694). The OHS and EQ-5D showed significant improvements at two years. Conclusion. The results of this study suggest that the TriFit femoral stem achieves initial stability and is likely to be stable in the mid and long term. A long-term outcome study is required to assess late mechanisms of failure and the effects of bone mineral density (BMD) related changes. Cite this article: Bone Joint J 2021;103-B(4):644–649

We obtained simultaneous measurements of sagittal knee laxity in 12 consecutive patients after reconstruction of the anterior cruciate ligament (ACL), using the Stryker laxity tester and radiostereometric analysis (RSA). The mean anteroposterior (AP) displacement when a 90 N load was applied in both directions was 5.3 ± 2.7 mm with RSA and 9.8 ± 1.6 mm with the external device (p < 0.001). The corresponding measurements at a load of 180 N were 5.7 ± 2.4 mm and 13.8 ± 3.7 mm, respectively (p < 0.001). More than 50% of the sagittal knee movement, as measured by the external device at a load of 180 N, was not true femorotibial displacement of the joint but was due to soft-tissue deformation

This study used model-based radiostereometric analysis (MBRSA) to compare migration of a recently introduced cementless hip stem to an established hip stem of similar design. Novel design features of the newer hip stem included a greater thickness of hydroxyapatite coating and a blended compaction extraction femoral broach.

Fifty-seven patients requiring primary total hip arthroplasty (THA) were enrolled at a single centre. Patients were randomized to receive either an Avenir collarless stem and Trilogy IT cup (ZimmerBiomet) or a Corail collarless stem and Pinnacle cup (DePuy Synthes) via a posterior or lateral approach. Both stems are broach-only femoral bone preparation. RSA beads (Halifax Biomedical) were inserted into the proximal femur during surgery. Patients underwent supine RSA imaging a 6 weeks (baseline), 6, 12, and 24 months following surgery. The primary study outcome was total subsidence of the hip stem from baseline to 24 months as well as progression of subsidence between 12 and 24 months. These values were compared against published migration thresholds for well-performing hip stems (0.5mm). The detection limit, or precision, of MBRSA was calculated based on duplicate examinations taken at baseline. Patient reported outcome measures were collected throughout the study and included the Oxford-12 Hip Score (OHS), EuroQoL EQ-5D-5L, Hip Osteoarthritis Score (HOOS) as well as visual analogue scales (VAS) for thigh pain and satisfaction. Analysis comprised of paired and unpaired t-tests with significance set at p≤0.05.

Forty-eight patients (30 males) were included for analysis; 7 patients received a non-study hip stem intra-operatively, 1 patient suffered a traumatic dislocation within three weeks of surgery, and 1 patient died within 12 months post-surgery. RSA data was obtained for 45 patients as three patients did not receive RSA beads intra-operatively. Our patient cohort had a mean age of 65.9 years (±;7.2) at the time of surgery and body mass index of 30.5 kg/m2 (±;5.2). No statistical difference in total stem migration was found between the Avenir and Corail stems at 12 months (p=0.045, 95%CI: −0.046 to 0.088) and 24 months (p=0.936, 95% CI: −0.098 to 0.090). Progression of subsidence from 12-24 months was 0.011mm and 0.034mm for the Avenir and Corail groups which were not statistically different (p=0.163, 95%CI: −0.100 to 0.008) between groups and significantly less than the 0.5mm threshold (pNo statistically significant differences existed between study groups for any pre-operative function scores (p>0.05). All patients showed significant functional improvement from pre- to post-surgery and no outcome measures were different between study groups with exception of EQ-5D-5L health visual analogue scale at 12 months which showed marginally superior (p=0.036) scores in the Avenir group. This study was not powered to detect differences in clinical outcomes.

This study has demonstrated no statistical difference in subsidence or patient-reported outcomes between the Corail hip stem and the more recently introduced Avenir hip stem. This result is predictable as both stems are of a triple-tapered design, are coated with hydroxyapatite, and utilize a broach-only bone preparation technique. Both stem designs demonstrate migration below 0.5mm suggesting both are low-risk for aseptic loosening in the long-term.

Aims. For many designs of total knee arthroplasty (TKA) it remains unclear whether cemented or uncemented fixation provides optimal long-term survival. The main limitation in most studies is a retrospective or non-comparative study design. The same is true for comparative trials looking only at the survival rate as extensive sample sizes are needed to detect true differences in fixation and durability. Studies using radiostereometric analysis (RSA) techniques have shown to be highly predictive in detecting late occurring aseptic loosening at an early stage. To investigate the difference in predicted long-term survival between cemented, uncemented, and hybrid fixation of TKA, we performed a randomized controlled trial using RSA. Methods. A total of 105 patients were randomized into three groups (cemented, uncemented, and hybrid fixation of the ACS Mobile Bearing (ACS MB) knee system, implantcast). RSA examinations were performed on the first day after surgery and at scheduled follow-up visits at three months, six months, one year, and two years postoperatively. Patient-reported outcome measures (PROMs) were obtained preoperatively and after two years follow-up. Patients and follow-up investigators were blinded for the result of randomization. Results. RSA secondary stabilization did not show a significant difference between the three types of fixation. A maximum total point motion of less than 0.2 mm in the second postoperative year was shown in each group, which suggests stabilization of the implant. At 24 months after surgery, PROMs significantly improved compared to baseline in all treatment groups. No significant difference was observed between the three groups. Conclusion. Secondary stabilization measurements in this study demonstrated no significant difference between the groups. In all groups migration stabilized after initial settling of the implant. For this implant the long-term outcome is not expected to be influenced by the type of fixation to the bone. Cite this article: Bone Joint J 2021;103-B(1):98–104

Background. Radiostereometric Analysis (RSA) is an accurate measure of implant migration following total joint replacement surgery. Early implant migration predicts later loosening and implant failure, with RSA a proven short-term predictor of long-term survivorship. The proximal migration of an acetabular cup has been demonstrated to be a surrogate measure of component loosening and the associated risk of revision. RSA was used to assess migration of the R3 acetabular component which utilises an enhanced porous ingrowth surface. Migration of the R3 acetabular component was also assessed when comparing the fixation technique of the femoral stems implanted. Methods. Twenty patients undergoing primary total hip arthroplasty were implanted with the R3 acetabular cup. The median age was 70 years (range, 53–87 years). During surgery tantalum markers were inserted into the acetabulum and the outer rim of the polyliner. RSA examinations were performed postoperatively at 4 to 5 days, 6, 12 and 24 months. Data was analysed for fourteen patients to determine the migration of the acetabular cup relative to the acetabulum. Of these fourteen patients, six were implanted with a cementless femoral stem and eight with a cemented femoral stem. Patients were clinically assessed using the Harris Hip Score (HHS) and Hip Disability and Osteoarthritis Outcome Score (HOOS) preoperatively and at 6, 12 and 24 months postoperatively. Results. RSA revealed no significant acetabular cup migration in all planes of translation and rotation with mean translations below 0.40 mm and mean rotations below 1 deg at 24 months. The data suggests that acetabular migration occurred primarily in the first 6 months postoperatively. We observed mean translations at 24 months of 0.36 mm (x-axis), 0.39 mm (y-axis) and 0.35 mm (z-axis). Mean rotations of 0.68 deg (x-axis), 0.99 deg (y-axis) and 0.77 deg (z-axis) were also observed at 24 months. Micromotion along the proximal-distal translation (y-axis) plane represented proximal migration of the acetabular component (Figure 1). On investigation of the femoral stems (cementless and cemented) implanted with the R3 acetabular cup, the mean proximal migration of the acetabular cup for both was 0.39 mm (CI 0.19–0.58). For cementless femoral stems a mean proximal migration of 0.45 mm (CI 0.09–0.98) and for cemented femoral stems a mean proximal migration of 0.35 mm (CI 0.24–0.45) were observed (Figure 1). A significant difference in the clinical assessment of patients when comparing pre-operative with 6, 12 and 24 months were also observed (p < 0.0001). All clinical assessments demonstrated equivalent results when comparing the post-operative follow-up time points and the R3 acetabular cup and stem combinations. Conclusions. Mean translations and rotations were higher than previously reported for acetabular components with the enhanced porous ingrowth surface. The magnitude of proximal migration 24 months postoperatively was within published ‘acceptable’ levels, albeit within the ‘at risk’ range of 0.2–1.0 mm. Comparison of the proximal migration for cementless and cemented femoral stems expressed similar outcomes, a trend also observed with the clinical assessments. These findings support further investigation and analysis of the R3 acetabular component

Osteolysis secondary to ultra-high molecular weight polyethylene (UHMWPE) wear is a leading cause of late-term implant failure via aseptic loosening in patients treated with total hip arthroplasty (THA). Radiation crosslinking of UHMWPE has been shown to decrease wear. However, the resulting polymer (crosslinked-PE) has a high free radical content. Two different methods that have been used to reduce the remaining free radicals are mechanical annealing and chemical stabilization using Vitamin E, a free radical scavenger. The primary purpose of the current study was to evaluate and compare the wear properties of vitamin E-doped crosslinked-PE (VEPE) and one formulation of mechanically annealed crosslinked-PE using radiostereometric analysis (RSA) in patients five years after primary THA. We also sought to understand the association between polyethylene wear and patient-reported outcome measures (PROMs). Three-hundred and five patients from six international centers were enrolled. Seventy-six percent were treated with highly-crosslinked (95 kGy) VEPE liners, and the rest received moderately-crosslinked (50 kGy) (ModXL), mechanically annealed liners. Data was collected prospectively at one-, two-, and five-year intervals. At the 5-year follow-up, proximal femoral head penetration into the VEPE liners (median = 0.05mm (range, −0.03–1.20)) was significantly lower than the penetration into the ModXL liners (median = 0.15mm (range, −0.22–1.04)) (p<0.001). In the VEPE cohort the median proximal penetration did not increase from one- to five-year follow-up (p=0.209). In contrast, there was a significant increase in femoral head penetration for the ModXL group (p<0.001) during that same time. Multivariable regression showed that the only variable predictive of increased wear was ModXL liner type (B=0.12, p<0.001). There were no differences in PROMs between the liner groups, and there was no correlation between polyethylene wear and PROMs for the cohort as a whole. The current study is the largest analysis of polyethylene wear at five-year follow-up using the RSA technique. We observed similar bedding in through the two-year interval between the two liner types, however, there was significantly more wear in the ModXL cohort at five-years. Currently, the wear rates for both liner groups are below the osteolysis threshold and have not led to any implant failures via aseptic loosening. Continued follow-up will provide a better understanding of the association between wear rate and clinical outcomes

Radiostereometric analysis (RSA) has become the gold standard technique for measuring implant migration and wear following joint replacement due to its high measurement precision and accuracy. However, RSA is conventionally performed using two oblique radiographic views with the presence of a calibration cage. Thus, a second set of radiographs must be acquired for clinical interpretation, for example anterior-posterior and cross-table lateral views following total hip arthroplasty (THA). We propose a modification to the RSA setup for examining THA, in which RSA measurements are performed from anterior-posterior and lateral views, with the calibration cage images acquired separately from the patient images. The objective of the current study was to compare the accuracy and precision of the novel technique to the conventional technique using a phantom. X-ray cassette holders were developed to enable simultaneous acquisition of anterior-posterior and cross-table lateral radiographs with the patient in a supine position in the RSA suite. A Sawbones phantom with total hip implant components was attached to a micrometer-driven stage. The femoral component was translated known distances relative to the acetabular cup in all planes, mimicking head penetration due to wear. Double RSA examinations were acquired for each increment using the traditional and novel radiograph orientations. Translations were measured from the radiographic images using RSA software. For both techniques, accuracy was calculated by comparing the measured translations to the known translation from the micrometer, and reported as the 95% confidence interval. Precision was measured by comparing the measured translations between the double exams, and reported as the standard deviation. Accuracy was greater for the conventional technique in the inferior-superior axis (p = 0.03), greater for the novel technique in the anterior-posterior axis (p = 0.01), and equivalent in the medial-lateral axis (p = 0.06). Overall accuracy for both the conventional and novel techniques was identical at ±0.022 mm. Precision was equivalent between both techniques for the medial-lateral (p = 0.68), inferior-superior (p = 0.14), and anterior-posterior axes (p = 0.86). Overall precision for the conventional technique was ±0.127 mm and for the novel technique was ±0.095 mm. Utilising standard clinical radiograph view angles within an RSA exam had no detrimental effect on wear measurement accuracy or precision. This reduces the barriers to implementing RSA imaging in routine follow-up of arthroplasty patients, potentially greatly increasing the numbers of patients that can have quantitative data on implant performance. Future applications can involve applying more clinically relevant radiograph view angles to RSA exams of the knee and shoulder

Background and purpose. At the Ganz periacetabular osteotomy the osteotomized acetabular fragment is reoriented in an adducted, extended and rotated position. Two screws fixate the acetabular fragment and the patients are allowed 30 kg weight bearing immediately after surgery. We were interested in examining the stability of the reoriented acetabulum after the Ganz osteotomy and accordingly the migration of the acetabular fragment was assessed by radiostereometry. Methods. Thirty two dysplastic patients (thirty two hips), twenty seven females and five males were included in the study. Median age was 39 (20–57) years. Radio-stereometric examinations were done at one week, four weeks, 8 weeks and six months. Data are presented as mean with 95% CI. Results. Six months postoperatively, the acetabular fragment had migrated 0.7mm (0.4–1.0mm) medially, and 0.7mm (0.5–0.9 mm) cranially. Mean rotation in valgus direction was 0.5° (−0.1–1.0°). In other directions, migration was below 0.4. There was no statistical difference between migration 8 weeks and 24 weeks postoperative in translation or rotation. Interpretation. This is the first paper dealing with radio-stereometric analysis in Ganz osteotomy. Due to the very limited migration, we find our postoperative partial weight-bearing regime safe

A recurrence of objectively measured knee laxity after anterior cruciate ligament (ACL) reconstruction has previously been reported in various papers; the purpose of this study was to accurately measure in vivo knee laxity after both bone-tendon-bone (BTB) and hamstring reconstruction using radiostereometric analysis (RSA), and to differentiate between graft fixation slippage and graft stretching and their relative contributions to any increase in laxity. Twenty patients were studied prospectively after ACL reconstruction. Ten had been operated on using BTB grafts, and ten using hamstring (four-stranded semitendinosus/gracilis) grafts. Tantalum markers were inserted in the distal femur, proximal tibia and into the graft itself. (RSA) was used to measure sagittal laxity, graft stretching and fixation slippage early post-operatively, and then at intervals up to 1 year. A steady increase in total anteroposterior laxity was found in both groups over the year. For the BTB group, total mean slippage of the bone plugs increased to 1.28 mm at 1 year. For the hamstring group, the tunnel attachments had slipped by a total of 6.82 mm. More stretching was found for the hamstrings grafts than for the BTB grafts and the amount of stretching increased significantly with time post-surgery. The hamstring grafts stretched by a mean of 4.18%, the BTB grafts by 1.18%. This is believed to be the most detailed application of RSA in analysing the performance of the two commonly used grafts in ACL reconstruction. Details such as graft stretching and fixation slippage have not been available previously; the data obtained in this study may have implications for clinical practice

The healing index, external fixation time divided by length gain, is commonly used as an outcome measure in distraction osteogenesis. This can be imprecise, and experimentally, regenerate stiffness is the accepted measure, but this can be difficult to measure clinically. The aim of this study was to investigate whether radiostereometric analysis (RSA) may be used to determine stiffness of new bone. Two Ilizarov frames of differing stiffness were constructed around Sawbones tibiae. Known loads were applied to the frames and RSA was used to analyse the movement that occurred at the distraction gap. The axial stiffness of the frames was calculated. The distraction gap was filled with materials with a range of stiffnesses, representative of regenerate at different stages of consolidation. Loads were applied and RSA was used to measure the stiffness of the construct. A simple load share model was then used to estimate stiffness of the materials, and these values compared with those obtained from a materials testing machine. The measured stiffnesses of the frames were 94N/mm and 55N/mm. RSA tended to underestimate the material properties of the ‘regenerate’, and this effect became greater at higher stiffness. There was also a 30% difference in estimated stiffness of the ‘regenerate’ when comparing the two fixators. RSA is a very precise non-invasive method for measuring regenerate displacement. However, simple models to estimate stiffness tend to underestimate the true value, and assumptions made in basic engineering models are not valid when the stiffness of the regenerate approaches that of surrounding bone

Aims. Interest in soft tissue Radiostereometric Analysis (RSA) is rising. Previous authors have tried, with varying levels of success, to use this technique to analyse the intra-substance portion of anterior cruciate ligament (ACL) graft constructs. These methods were either prone to large amounts of marker migration, deemed unsuitable for in-vivo use or, where alternative markers such as stainless steel sutures were used, lost the inherent accuracy that made RSA an attractive tool in the first place. We describe a modification of tantalum marker balls that allows for a new method of secure fixation to soft tissue in order to accurately analyse stretch, displacement and, potentially, dynamic movement using RSA. Methods. 1.5 mm tantalum tendon markers were predrilled with 0.3 mm holes, allowing them to be sutured directly to soft tissue. Using a previously described ACL graft model, the amount of marker ball migration was then analysed using RSA after cyclical loading between 20 N and 170 N at 25 Hz for 225,000 cycles. Results. None of 40 balls loosened or became detached from the tendon grafts after 225,000 cycles. Mean migration of the tendon attached marker balls was < 0.1 mm. The maximum imprecision in determining the distance between two markers as assessed by intra- and inter-observer variability was 0.082 mm. Analysis of elastic stretch, plastic stretch, stiffness and localisation of stretch within the graft model was possible due to the low migration levels. Conclusions. This method of attachment of marker beads to soft tissue is simple, reliable and mechanically sound. This technique could potentially be used not only for the post-operative assessment of ACL reconstruction, but in all areas where soft tissue RSA is of interest

Aims. The direct anterior (DA) approach has been associated with rapid patient recovery after total hip arthroplasty (THA) but may be associated with more frequent femoral complications including implant loosening. The objective of this study was to determine whether the addition of a collar to the femoral stem affects implant migration, patient activity, and patient function following primary THA using the DA approach. Methods. Patients were randomized to either a collared (n = 23) or collarless (n = 26) cementless femoral stem implanted using the DA approach. Canal fill ratio (CFR) was measured on the first postoperative radiographs. Patients underwent a supine radiostereometric analysis (RSA) exam postoperatively on the day of surgery and at two, four, six, 12, 26, and 52 weeks postoperatively. Patient-reported outcome measures (Western Ontario and McMaster Universities Osteoarthritis (WOMAC) Index, the 12-item Short Form Health Survey Mental and Physical Score, and University of California, Los Angeles (UCLA) Activity Score) were measured preoperatively and at each post-surgery clinic visit. Activity and function were also measured as the weekly average step count recorded by an activity tracker, and an instrumented timed up-and-go (TUG) test in clinic, respectively. Results. Comparing the RSA between the day of surgery baseline exam to two weeks postoperatively, subsidence was significantly lower (mean difference 2.23 mm (SD 0.71), p = 0.023) with collared stems, though these patients had a greater CFR (p = 0.048). There was no difference (p = 0.426) in subsidence between stems from a two-week baseline through to one year postoperatively. There were no clinically relevant differences in PROMs; and there was no difference in the change in activity (p = 0.078) or the change in functional capacity (p = 0.664) between the collared stem group and the collarless stem group at any timepoint. Conclusion. Presence of a collar on the femoral stem resulted in reduced subsidence during the first two postoperative weeks following primary THA using the DA approach. However, the clinical implications are unclear, and larger studies examining patient activity and outcomes are required. Cite this article: Bone Joint J 2020;102-B(12):1654–1661

Background. Safety and efficacy of novel prostheses relies on the determination of early implant migration and subsequent risk of loosening. Radiostereometric Analysis (RSA) has been used to evaluate the clinical failure risks of femoral stems by reporting distal migration, a measure of stem subsidence, when examining early migration characteristics. The migratory patterns of femoral stems, 24 months postoperatively, have provided a surrogate outcome measure to determine implant stabilisation and predict long-term performance and survivorship. RSA assessed femoral stem migration and provided comparison of the early migration characteristics with published data of a clinically established counterpart. Methods. Twenty five patients undergoing primary total hip arthroplasty were implanted with a hydroxyapatite-coated femoral stem. The median age was 65 years (range, 43–75 years). During surgery tantalum markers were attached onto the distal tip and shoulder of the stem. Eight tantalum markers were inserted into the femur, four placed in each of the greater and lesser trochanter. RSA examinations were performed postoperatively at 4 to 5 days, 6, 12 and 24 months. Eleven patients who had complete RSA follow-up as well as the valid data from five patients were analysed to determine the movement of the femoral stem relative to the femur and were compared to the published data of a clinically established counterpart. Results. At 24 months the magnitude of migration of the femoral stem translations for the y axis of movement was 0.32 mm (range, 0.00 to 2.04 mm) (Figure 1). The data demonstrates that this migration of the femoral stem occurred primarily in the first 6 months postoperatively and that the migration characteristics exhibit a pattern of implant stabilisation between 6 and 24 months. At 24 months the magnitude of migration of the femoral stem rotations for the longitudinal y axis of movement was 0.60. o. (range, 0.08 to 2.08. o. ). The data demonstrates continuing migration of the femoral stem at 12 months postoperatively with early indications of implant stabilisation between 12 and 24 months. At 24 months the mean subsidence/distal migration of the femoral stem was 0.20 mm (range, −2.04 to 0.32 mm) (Figure 2). At 6 months, two patients (12.5%) exhibited subsidence greater than 0.50 mm with one demonstrating a mean subsidence of 2.00 mm. Between 6 and 24 months these two patients exhibited no more than 0.04 mm of subsidence (Figure 3). The mean retroversion rotation of the stem was 0.10. o. (range, −0.99 to 2.08. o. ). One patient rotated more than 2.00. o. into retroversion at 12 and 24 months postoperatively. Conclusions. In comparison the data demonstrates less stem subsidence and retroversion rotation than published data for a cementless hydroxyapatite-coated femoral stem when observing early migration characteristics. The magnitude and pattern of migration exhibited is indicative of good clinical outcomes and is comparable with a clinically established counterpart after short-term follow-up with RSA. These findings and comparisons highlight the early migration characteristics of a hydroxyapatite-coated femoral stem, however the analysis and comparison of the migratory pattern and characteristics over the mid-term follow-up will confirm implant stabilisation

Aims. To compare the in vivo long-term fixation achieved by two acetabular components with different porous ingrowth surfaces using radiostereometric analysis (RSA). Methods. This was a minimum ten-year follow-up of a prospective randomized trial of 62 hips with two different porous ingrowth acetabular components. RSA exams had previously been acquired through two years of follow-up. Patients returned for RSA examination at a minimum of ten years. In addition, radiological appearance of these acetabular components was analyzed, and patient-reported outcome measures (PROMs) obtained. Results. In all, 15 hips were available at ten years. There was no statistically significant difference in PROMS between the two groups; PROMs were improved at ten years compared to preoperative scores. Conventional radiological assessment revealed well-fixed components. There was minimal movement for both porous surfaces in translation (X, Y, Z, 3D translation in mm (median and interquartile range (IQR)), StikTite (Smith and Nephew, Memphis, Tennessee, USA): 0.03 (1.08), 0.12 (0.7), 0.003 (2.3), 0.37 (0.30), and Roughcoat (Smith and Nephew): -0.6 (0.59),–0.1 (0.49), 0.1 (1.12), 0.48 (0.38)), and rotation (X, Y, Z rotation in degrees (median and IQR), (Stiktite: -0.4 (3), 0.28 (2), -0.2 (1), and Roughcoat: - 0.4 (1),–0.1 (1), 0.2 (2)). There was no statistically significant difference between the two cohorts (p-value for X, Y, Z, 3D translation - 0.54, 0.46, 0.87, 0.55 and for X, Y, Z rotation - 0.41, 0.23, 0.23 respectively) at ten years. There was significant correlation between two years and ten years 3D translation for all components (r = 0.81(p =< 0.001)). Conclusion. Both porous ingrowth surfaces demonstrated excellent fixation on plain radiographs and with RSA at ten years. Short-term RSA data are good predictors for long-term migration data

Purpose. The foam metal backed Advance BioFoam Knee Arthroplasty components utilize a porous titanium coating on the underside of the tibial baseplate, intended to promote bone in-growth and provide a more robust bone-implant interface without cement. There is also a version of the Biofoam Advance that incorporates screwed fixation that allows for augmented fixation with up to four titanium screws; however, it is not clear that this augmentation is necessary. The purpose of this study was to employ radiostereometric analysis (RSA) to compare implant migration in a randomized controlled trial of this implant design with or without screw fixation. Method. Fifty-one patients were randomized to receive a BioFoam total knee replacement (Wright Medical Technologies) with or without screw fixaiton. During surgery, eight tantalum markers, one millimetre in diameter, were inserted into the proximal tibia. Using a calibration box, stereo RSA radiographs were taken post-operatively and then again at six weeks and three, six and 12 months following surgery. Model Based RSA was used with 3D models of the tibial component to measure migration. Health status and functional outcome measures were recorded to quantify functional status of subjects before surgery and at each follow-up interval. Results. The migration results at one year, calculated as maximum total point motion (MTPM) were 1.751.93 mm for with screw fixation and 1.431.41 mm without screw fixation (p value =0.575). The clinical precision of the MTPM metric is 0.33 mm, calculated as the standard deviation of measurements made from double exams of all patients. There were no significant differences between groups for all other outcomes. Conclusion. The migration results at one year indicate that the addition of screws does not impact implant fixation in the short term. Longer term monitoring of the migration of these two implant groups will continue. Although higher than the migration seen with cemented tibial components, the amount of migration is comparable to other uncemented designs

Purpose of the study: Several authors have focused attention on the kinematics of total knee arthroplasty. In vitro studies have shown the influence of prosthetic kinematics on wear of the tibial insert. In vivo, investigations are limited for this important parameter. We propose computer algorithm which gives a linear assessment of femur penetration into the tibial insert. The purpose of this work was to test this measurement by radiostereometric analysis (RSA) on pre-worn prosthesis models. Material and methods: A resin plateau was manufactured with four Triatlhon posterior stabilized inserts. Three of these inserts were pre-worn on the medial glenoid; wear varied from 0.8 to 1.2 mm. The wear pattern was controlled by a computer program in order to localize it on a posteromedial gliding band posteriorly to the posterior stabilization implant. A femoral component was implanted on dry bone and loaded on a simulator. RSA images were obtained for each of the plateau. Five series of images were obtained from 0 to 40° flexion. The measurement method consisted in defined a perfect middle plane based on the analysis of tantalum beads embedded in the resin plateau, the to define the point the closest to this plane belonging to the medial condyle. The norm of the normal vector for this plane passing through the lowest point of the femur was the reference. The difference of the norms of the vectors constructed from the healthy plateau and the worn plateaus was defined as penetration of the femur into the tibia insert. The rood mean square (RMS) method was used to measure intraobserver variability and the interclass coefficient of correlation (ICC) was determined. Results and Discussion: Our results were encouraging. 0.8/to 1.12 mm wear was detected with very good accuracy. The data spread was however wide, irrespective of the wear value. The images in flexion of this model provided the most reliable readings. This study is the first offering an approach to wear measurement in vivo. The data spread should be improved by fine tuning the experimental model and the pre-wear pattern. Conclusion: In vivo measurement of TKA wear remains a challenge in clinical medicine. Our work demonstrate the feasibility of using RSA

Aims: To study prospectively the characteristic migration of four different cemented femoral stems using Radiostereometry. Methods: 96 patients undergoing cemented femoral hip replacement for osteoarthritis were randomised to receive an Exeter (Howmedica Stryker), Ultima Tapered Polished Stem [TPS], Ultima straight stem [USS] (Johnson and Johnson) or Charnley Elite (Depuy/Johnson and Johnson) stem. RSA migration measurements were performed at postoperatively and at 6,12,18 and 24 months post surgery using the UMRSA system enhanced with locally developed software. Results: Two significantly distinct patterns of distal migration in the y direction (subsidence) were seen compatible with previous studies. Tapered stems subsided rapidly by six months Exeter 0.85mm (+/−0.15) UTPS 0.85mm (+/−0.15) stabilising by 2 years Exeter 1.3mm(+/−0.35), UTPS 1.2mm(+/−0.25). The USS and Elite designs showed lower migrations of 0.1mm (+/−0.1) and 0.15 (+/−0.15) mm at six and 0.25mm(+/−0.15) and 0.35mm (+/−0.15) 24 months. For migrations and rotations in other directions differences were seen between prostheses with the same design concept. Whilst both the UTPS and Exeter exhibited posterior migration of the head, by 24 months this was expressed as a rotation about the transverse axis for the TPS and the axial axis for the Exeter. The Elite and USS differed in rates of posterior migration and varus tilt. Conclusions: Patterns of migration for stems with the same design concept may vary due to subtle differences in prosthesis shape. These variations produce a distinct migration “signature” for each stem

Purpose of the study: The concept introduced by Gilles Bousquet is an effective arm against dislocation of total hip arthroplasty (THA), as has been demonstrated in clinical series with a long follow-up. There remain certain questions concerning wear of dual mobility cups. We propose a radiostereometrical analysis (RSA) of femoral head migration in this type of implant. Our objective was to establish an accurate measurement and determine the intra- and interobserver variabilities. Material and methods: A THA model was implanted and loaded with a simulator. Penetration of the implants was measured using a specially designed polyethylene insert with increasingly concentric wear (from 0, 0.25, 0.5 to 0.75 mm). Three investigators analysed (7 times in a double-blind protocol) the RSA images of these four inserts. The investigators were an expert (I), well-trained (II), naive (III). The accuracy of the measurement as well as the intra- and interobserver variabilities were determined using the root mean square (RMS) method, the interclass coefficient of correlation (ICC), the Bland and Altman analyses, and weighted Kappa analysis. Results: Regarding accuracy, the RMS was 0.0388 [CI95: 0.02266–0.05564]. The mean error for preworn inserts was respectively 0.022mm (for 0.25mm prewear), 0.59mm (for 0.5mm), and 0.022mm (for 0.75mm). The intra-observer ICC was 0.9714 [0.9028–0.9918] for investigator I. The interobserver ICCs between investigators I and II and between I and III were respectively 0.943 and 0.968. The weighted kappa coefficients between I and II and between I and III were 0.827 and 0.849. The Bland and Altman analysis confirmed these results. Discussion: Several RSA protocols could be designed to measure wear of the dual mobility cup. We chose detection of the wear pattern instead of the tantalum beads method. Our protocol, using a simple geometric model and not the manufacturers CAD files, showed an accuracy comparable with manufacturing tolerances with low variability. Conclusion: This study validated our measurement method, a prerequisite for a randomized multicentric study which has been initiated to compare, by RSA, penetration of the head into the double mobility insert versus a fixed insert

Introduction. The number of revisions of total knee replacements (TKR) increases annually. Because of reduced bone stock, stable fixation of the implant is important. The femoral and tibial components are usually cemented whereas stems can be placed either cemented or press-fit (hybrid construct). To assess the stability of revision TKR with either cemented or hybrid places implants a randomized controlled trial (RCT) was executed, by using radiostereometric analysis (RSA). The short-term results of this RCT showed no differences between the two groups in stability and clinical outcomes. Although there were no clinical or radiological signs of loosening, both groups showed implants micromotion > 1 mm or degree. These findings might indicate the possibility of loosening later in time; therefore, the current study investigated the stability of cemented versus hybrid-placed revision TKR 6.5 years after surgery. Additionally, clinical results were evaluated. Methods. Of the 32 patients in the original RCT, 23 (12 cement, 11 press-fit) were available for mid-term follow-up measures. RSA images taken at baseline, 6 weeks, 3, 6, 12 and 24 months postoperatively were used from the previous study. New RSA images were taken at median 6.5 years (range 5.4–7.3) postoperatively. Stability of the femoral and tibial implants was assessed by using model-based RSA software (RSAcore, Leiden, The Netherlands) to determine micromotion. Clinical results were evaluated using the Knee Society Score (KSS), the Knee injury and Osteoarthritis Outcome Score (KOOS), active flexion, and VAS pain and satisfaction. Stability and clinical outcome were compared between the two groups using independent t-tests or Mann-Whitney U tests when applicable. Results. The median total translation at 6.5 years was 0.37 (0.13–1.96) mm and median total rotation 0.62 (0.11 – 2.81)° for the femoral component. For the tibia component the median total translation was 0.41 (0.10 – 1.04) mm and the median total rotation 0.61 (0.09 – 1.99)°. There were no differences in total translation and total rotation of the femoral and tibial component between the two groups. Additionally, none of the clinical scores differed between the groups. Interestingly, in the group with cemented stems five tibia implants showed > 1 mm or degree migration compared to zero in the hybrid group (p=0.02; Figure 1). Conclusion. There was no difference in stability and clinical outcome between fully cemented and hybrid-placed revision TKR 6.5 years postoperatively. Until now micromotion >1 mm or degree in the tibial components of the cemented group has not yet resulted in re- revisions. The patients will be followed to examine the consequences of these amounts of micromotion in this type of implant in the long-term. Figure 1. Scatter plot of total translation (x-axis) and total rotation (y-axis) for the tibia component at 6.5 years follow-up for fully cemented and hybrid-placed revision TKA

Purpose. To compare Radiostereometric Analysis (RSA) and subjective outcomes of Total Knee Arthroplasty (TKA) and Total Ankle Arthroplasty (TAA). Method. Twenty-five patients were recruited to receive TKA (Zimmer, NexGen LPS Trabecular Metal Monoblock) and 20 patients were recruited to receive TAA (DePuy, Mobility). The tibial component of the TKA and the tibial component of the TAA were followed for two years with RSA with exams postoperatively at six, 12 and 24 months. At two years, inducible displacement RSA at the knee and ankle was also performed. RSA outcomes measured were translations in the anterior-posterior, medial-lateral and distal-proximal directions of both implants. SF-36 outcome questionnaires were completed preoperatively and at each RSA follow-up with the outcome being the mental component score (MCS) and physical component score (PCS). Analysis of variance statistical testing was used to compare RSA outcomes and subjective outcomes. Results. Preoperatively there were no differences in age, BMI, SF-36 MCS or SF-36 PCS between the TKA and TAA patients. At six, 12 and 24 months the TKA group had significantly higher SF-36 PCS scores (p=0.006, p=0.002 and p=0.004 respectively. There were no differences at any time point in SF-36 MCS. Longitudinal RSA results showed that the TAA tibial component moved further into the bone at all follow-ups (p=0.000 at all time points). The TAA also migrated more anteriorly compared with the TKA, although this only became significant at 12 and 24 months (p=0.013, p=0.05). RSA inducible displacement showed that the TAA had greater inducible displacement into the bone than the TKA (p=0.015). Conclusion. The subjective data show that TAA and TKA both improve the symptoms of patients. However, the subjective results of the TAA have not achieved the high standard set by TKA. The RSA data suggest that the TAA is stabilizing within the bone. However, the higher longitudinal migrations and inducible displacements seen in the TAA suggest that the interface may not be as robust as in the TKA. This may partially be explained by the much smaller surface area available to distribute the loads at the ankle resulting in higher stresses and migrations. The 3rd generation of TAA has recently been reintroduced as a treatment option for severe arthritis of the ankle. Previous generations of TAA have been unsuccessful with high failure rates. It is unclear if the current generation of TAA will be more successful in the long term. Comparisons between these arthroplasty procedures with high precision measures such as RSA can provide insight into whether TAA has achieved the same level of success as TKA. Although there are no comparable migration thresholds for TAA as TKA, this study suggests that TAA may not achieve as robust an interface with the bone as TKA. The results of the current generation of TAA are promising. However, TAA still has room for improvement to achieve the same outstanding results as TKA

Introduction: Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary displacements under measured weightbearing and joint movement. We have used this technique to prospectively monitor tibial plateau fractures and present the results of the first nine patients with six month follow up. Method: Nine 41-B3 fractures were treated with open reduction internal fixation by one surgeon. At operation, RSA beads were inserted in the depressed osteochondral fragment and the adjacent non-fractured metaphysis. Postoperative weightbearing was restricted to 20kg and knee flexion to 60° for the first six weeks. Follow up included clinical and radiological examinations and patient reported outcome scores (Lysholm, KOOS). DLRSA examinations included RSA radiographs in 60° flexion and under measured weightbearing at six weekly intervals up to six months postoperatively. Significant interfragmentary displacement was defined as translations greater than 0.5mm and/or rotations greater than 1.5°. Results: No postoperative displacement was identified on plain radiographs, except in one patient who fell two weeks postoperatively. RSA: Longitudinal Results: In all patients, the osteo-chondral fragment continued to migrate up to six months, with one exception that stabilised at three months. At six months, the osteochondral fragment translated between 0.02 and 4.15 mm and rotated between 0.2 and 7.2° (> 0.5mm and/or > 1.5° in five cases). DLRSA: Flexion Results: During 60° of flexion, translations exceeding 0.5mm were recorded in only one patient (0.7 mm at 2 weeks). Rotations exceeding 1.5° were recorded in three patients (1.6°, 2° and 2.1° all at six months). DLRSA: Weightbearing Results: Translations exceeding 0.5mm were recorded in four patients whilst full weightbearing (0.7mm in two patients at three months, and 0.6mm and 0.8 mm at 18 weeks). Rotations exceeding 1.5° were recorded in two patients. One patient recorded 2.3° under full weightbearing at three months. Another recorded 2.3° under 20kg of weight at two weeks and 1.8° under full weightbearing at 18 weeks. Patient reported outcomes improved progressively. At six months, five patients reported excellent results, two good and two fair. The two patients reporting fair results recorded low interfragmentary displacements. Discussion: Tibial plateau fractures continue to migrate up to six months after treatment. Active range of motion, partial weightbearing to six weeks and weightbearing up to one body weight after six weeks was proven a safe postoperative regimen. Greater displacements recorded over time may be attributed to loading of more than one body weight, for example, the patient that fell recorded the largest amount of migration over time

Aims Intro: Radiostereometry (RSA) is a powerful tool for assessment of prosthesis migration in total hip replacement. Typically marker beads are inserted into the bone and into turrets inserted into the prosthesis. Where the prosthesis can not be beaded valuable information may be lost. We present two methods that determine the three-dimensional prosthesis position using geometric models. Method: The þrst method approximates the stem of the prosthesis to an axially symmetric cylinder and spherical head. The method is fast but may lead to errors due to the cylinder approximation. The second uses accurate three-dimensional surface models of each implant model. Clinical precision was determined from repeat same day RSA examinations. Results: Given as 99% precision limit rotation ranged from 0.4 degrees (sagittal) to 2.5 degrees (axial) for the cylinder method (n = 38), compared to 0.2 degrees (sagittal) to 0.6 degrees (axial) for the 3d model (n = 6). Translations were similar ranging from 0.2mm axial to 0.7mm sagittal. Conclusion: Model based RSA can give useful results where beads can not be implanted into the prosthesis. Although the primary method gives good results these are less precise than that for beaded RSA. Simulations infer a potential accuracy for the method of a few microns, however this is currently limited by the closeness of correspondence of an individual stem to its model. The method here is applicable to any implant type. Accurate 3D models are required, however for new designs these should be available

The direction of penetration of the femoral head following total hip replacement has been shown at revision to be superomedial, superior or superolateral. However, it is important to study well functioning components to describe normal patterns of wear. The aim of this study was to characterise the 3D direction of penetration in standard and HXLPE. A prospective double blind randomised control trial was conducted using Radiostereometric Analysis (RSA). Fifty-four subjects were randomised to receive hip replacements with either UHMWPE liners or HXLPE liners. All subjects received a cemented CPT stem and uncemented Trilogy acetabular component (Zimmer, Warsaw, IN, USA). The 3D penetration of the head into the socket was determined to a minimum of 7 years. The direction of penetration between one and seven years was in a superior and lateral direction for both groups. In the HXLPE group there was no significant penetration in the coronal or sagittal planes (superiorly 0.009 mm/yr, 95% confidence interval, ±0.045, p1 = 0.68, laterally 0.003mm/yr, CI 0.031, p1 = 0.85). In the UHMWPE group there was significant penetration 0.059 mm/yr superiorly (CI 0.042, p1 = 0.01) and 0.049 mm/yr laterally (CI 0.044, p1 = 0.03). The anterior-posterior steady state penetration was not significant in either group (HXLPE p1 = 0.39, UHMWPE p1 = 0.37). We have previously demonstrated that the penetration in the first year is creep-dominated and is in the proximal direction. From one year onwards the superolateral direction of penetration is probably due to wear. The steady-state wear direction is the same in both bearings types. It is likely that creep occurs in the direction of the Joint Reaction Force i.e. superomedial, whereas wear is perpendicular to the axis of rotation and therefore superolateral. This work may enable us to develop more accurate models for predicting wear in total hip arthroplasty

Introduction: C-stem is a triple taper polished femoral stem. The rationale for this design is to achieve an evenly distributed proximal loading of the cement mantle. This design is thought to enhance stability of the stem inside the mantle and lead to bone remodelling medially. There is to our knowledge no randomized trial comparing this stem to a well documented stem. We chose to compare it to the best documented stem in the Norwegian arthroplasty register, the Charnley monoblock. Methods: 70 patients scheduled for total hip replacement were randomized to either C-stem or Charnley monoblock. All received a 22 mm stainless steel head, OGGEE cup and Palacos Cement with Gentamycin. We used a transgluteal approach in all cases. Harris and Oxford hip scores were measured preoperatively and after two years. Standard X-rays were taken postoperatively and after two years. Radiostereometry (RSA) was done postoperatively and after 3,6,12 and 24 months. Results: There was no significant difference in Harris or Oxford hip scores after two years. RSA after two years: (table deleted). Discussion: Polished tapered stems are designed to sink inside the mantle. Our results confirm this theory for the C-stem. The subsidence is comparable to other collarless tapered stems with good long-term survival. For all other migrations/rotations the C-stem is as stable as the Charnley monoblock. This predicts good long-term results for this stem

Introduction: Spondylolysis in skeletally immature individuals is common but only a small proportion of cases develop pain and spondylolisthesis. The pattern of instability and pathologic consequences of surgically created spondylolytic defects have not previously been described. An animal model of lumbar spondylolysis was created using skeletally immature sheep with the aim of observing the intervertebral mobility and pathologic consequences of creating a spondylolytic segment. Methods: Bilateral spondylolytic defects were created in the fifth lumbar vertebrae of fourteen sheep aged approximately 16 weeks using a posterior surgical approach. Using tantalum markers that were placed in the lumbar spine segments in the vicinity of the lesion, three dimensional translations and rotations in flexion and extension were recorded under general anaesthetic using Radiostereometric Analysis (RSA) at the time of surgery. A novel method of ovine spine manipulation was developed. Briefly, with the animal in a lateral decubitus position spinal extension was achieved by fixing the shoulders and hips in full extension. Similarly, the limbs were brought into apposition to achieve spinal flexion. A control group of seven sheep had tantalum markers only in the same lumbar spine segments. The animals were re-tested under general anaesthetic at six weeks and six months following surgery. After six months the animals were sacrificed and their spines examined using CT and microscopic analysis. Results: Bilateral spondylolytic defects did not result in significant transverse (x-axis) translation. RSA showed significant differences between the spondylolytic group (mean 1.22°, range 0.30–3.74) and controls (mean 0.28°, range 0.03–0.77)) for rotation in the axial plane (y-axis, p< 0.0025) immediately after surgery. The spines radiologically stabilised over six months. Discussion: Surgically induced bilateral spondylolytic defects in this immature ovine model result in increased rotation in the axial plane but do not create transverse translation (spondylolisthesis)

Aims. Early implant migration measured with radiostereometric analysis (RSA) has been proposed as a useful predictor of long-term fixation of tibial components in total knee arthroplasty. Evaluation of actual long-term fixation is of interest for cemented components, as well as for cementless fixation, which may offer long-term advantages once osseointegration has occurred. The objective of this study was to compare the long-term migration with one- and two-year migration to evaluate the predictive ability of short-term migration data and to compare migration and inducible displacement between cemented and cementless (porous metal monoblock) components at least ten years postoperatively. Patients and Methods. Patients who had participated in RSA migration studies with two-year follow-up were recruited to return for a long-term follow-up, at least ten years from surgery. Two cemented tibial designs from two manufacturers and one porous metal monoblock cementless tibial design were studied. At the long-term follow-up, patients had supine RSA examinations to determine migration and loaded examinations (single leg stance) to determine inducible displacement. In total, 79 patients (54 female) returned, with mean time since surgery of 12 years (10 to 14). There were 58 cemented and 21 cementless tibial components. Results. Migration at one year and two years was significantly correlated with long-term migration (p < 0.001). Median migration at the long-term follow-up was 0.6 mm (maximum total point motion; interquartile range (IQR) 0.4 to 0.9) for the cemented group and 0.6 mm. (IQR 0.3 to 1.1) for the cementless group with no difference between groups (p = 0.99). Inducible displacement was significantly lower for the cementless components (p < 0.001). Conclusion. Long-term migration was strongly correlated with two-year migration. Although long-term migration was not different for cemented or cementless tibial components, inducible displacement at the long-term visit was significantly lower for these cementless components, suggesting superior fixation. These findings support the predictive value of short-term migration in determining long-term fixation. Cite this article: Bone Joint J 2019;101-B(7 Supple C):55–60

Introduction: In a pioneer study Oonishi et al (1988) found reduced socket wear with the use of polyethylene subjected to high radiation doses. This observation has stimulated the development of a new generation polyethylene. In addition to high radiation doses the plastic is also subjected to various types of heat treatment to reduce the amount of free radicals. The purpose of the present study is to evaluate one of the new highly cross-linked polyethylenes in a randomized controlled study of cemented THA. The hypothesis is that the improved wear resistance will reduce the prevalence of osteolytic lesions with long-term follow-up. Methods and materials: Patients in clinical and radiographic need of a THR with non-inflammatory osteoarthritis of the hip were randomized in two groups. Group 1 received a cemented Weber cup (Sulzer®, Switzerland) made of highly cross-linked (WIAM) polyethylene, group 2 got a conventional cup. All patients received a cemented Spectron (Smith & Nephew, USA) with a 28mm cobalt-chromium head. So far 15 patients, (6 male and 9 females) with a median age of 55 years (range 42–62) have been evaluated in group 1 and 14 (9 male and 5 females) with a median age of 55 years (range 45–70) in group 2. The penetration of the femoral heads has so far been measured postoperatively (all hips supine), after 3 month (17 hips supine and standing) and after 6 month (11 hips supine and standing) using radiostereometry. Results: The median proximal and three-dimensional (3-D) penetration (total wear) 0–6 month (supine position) was almost equal in the two groups. Group 1 had a proximal penetration of 0.08 mm (range 0.00–0.17) and a total penetration of 0.11 mm (range 0.06–0.14). The corresponding values for group 2 were 0,10 mm (0.05–0.21) for proximal penetration and 0.13 mm (0.10–0.16) for total penetration. Between 3 and 6 month the penetration (median values) was 0.04 mm/0.10 mm (proximal/3-D) for group 1 and 0.07 mm/0.12 mm for group 2. With the patients standing we found a proximally migration of the socket (0–6 month) in group 1 of 0,08 mm (−0.07 – 0.21) and 0.12 mm (0.1–0.13) in group 2. Discussion: Use of a highly cross-linked polyethylene in the socket did not influence the early penetration rate after THR. Early creep of the material is possible explanation. 1-year follow-up on approximately 50% of the patients will be presented at the meeting

Introduction: The C-stem (DePuy, Leeds, UK) is triple tapered, polished and collarless. These features can facilitate distal stem migration within the cement mantle, a phenomenon first noticed on radiographs and later confirmed by radiostrereometric analysis (RSA) for the double tapered polished Exeter stem (Stryker, Mahwah, NJ). Low revision rates are reported for the Exeter stem and the view that early migration predicts later failure has not been confirmed with double tapered designs. If a triple tapered stem has any advantages is however not known. Patients and methods: 33 primary hip arthroplasties with a median age of 66 (46–74) years were followed for 2 years with radiostereometric analysis (RSA) at 3 months, 6 months, 1, 2 and 3 years. The diagnosis was primary osteoarthrosis in all hips. Both migration and rotation were studied. Results: All the stems migrated distally and posteriorly within the cement mantle. The median distal migration was 1.47 mm at 3 years and the median posterior migration was 1.56 mm at 3 years. All the stems rotated towards retroversion and median rotation at 3 years was 2.0°. For all the other directions the prosthesis was stable up to 3 years. Discussion: The C-stem migrates and rotates more than cemented prostheses of other designs. Compared with other tapered prostheses the distal migration is at the same level but posterior rotation is higher and furthermore it migrates posteriorly, which the other tapered stems do not. If this migration/rotation pattern is tolerable without risk of prosthetic failure needs to be studied further, but at present there is no indication from the available clinical results for the C-Stem that this pattern is deleterious

Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary translations and rotations under measured amounts of weight bearing. The aim of this paper was to measure the mechanical stiffness of distal femoral fractures during healing. Six patients with a 33A2, 33A3, 33B2 and 33C2 fracture were treated with open reduction, internal fixation using a long bridging plate. All patients had a DLRSA examination at 6, 12, 18 and 26 weeks postoperatively. Each DLRSA examination consisted of RSA radiographs taken without load (pre-load), under different increments of load, and finally, without load (post-load). The direction and magnitude of the interfragmentary displacements in six degrees of freedom were recorded at each examination. DLRSA examinations were able to monitor the inter-fragmentary displacements of the distal femoral fragment relative to the femoral shaft. The interfragmentary displacement recorded, progressively increased as more load was applied in all patients, at all follow-up time points. The two dimensional (2D) translations under maximum tolerated load, progressively decreased over time in three patients. The 2D translations recorded under 60 kg of load at 26 weeks for these patients was 0.18, 0.21 and 0.27mm. The 2D translations of two patients did not decrease progressively between 6 and 18 weeks but did decrease at 26 weeks to 0.47 and 0.75mm. One patient recorded 2D translations of 4.11, 3.48 and 4.53mm under 30kg at 12, 18 and 26 weeks respectively. In the majority of examinations, post-load radiographs enabled the interfragmentary displacements under load to be identified as elastic in nature. The DLRSA stiffness data confirmed that at 26 weeks three patients had united; two were delayed but improving; and one was a clear non-union without progression. DLRSA examinations may be used as a clinical research tool. to monitor in vivo the stiffness of healing femoral fractures fixed with “relative stability”

Anterior lumbar inter-body fusion (ALIF) is a surgical procedure that is available to chronic lower back pain patients who fail to respond to conservative treatments. Failure to achieve fusion may result in persistence of pain. Fusion of the lumber vertebral segment is more accurately assessed using fine-cut helical Computed tomography (CT) scans (0.25 mm thickness slices). Unfortunately this technique exposes the body to high radiation dose with hazard of increase risk of late malignancy. An alternative imaging tool is radiostereometry (RSA) which developed as a means to determine the magnitude of relative motion between two rigid bodies. In this study we used RSA to detect movement at the fused lumbar segment (ALIF site) during flexion and extension and compare the results obtained with fine-cut helical CT scan using histopathology as final gold standard assessment tool. ALIF of three levels of lumbar spine (L1-L2, L3-L4, and L5-L6) was done in 9 sheep. The sheep divided into three groups (3sheep each). The first group had RSA assessment immediately, 3, and 6 months after surgery. The second group had RSA immediately, 3, 6, 9 months after surgery. The third group had an RSA immediately, 3, 6, 9, 12 months after surgery All the animals were humanly killed immediately after having the last scheduled RSA (group1, group2, and group 3 sheep were killed 6 month, 9month and 12 months after surgery respectively). This followed by in vitro fine cut CT and histopathology after the animals are scarified. Micro CT scan has been also used to identify the area where histopathology slide should be made to pick up fusion. Fine cut CT scan assessment for all sheep were done. The CT scan has been reported by two independent radiologists. Histopathology has been started and will finish in 2 weeks. RSA showed there was significant increasing stiffness of the spine though the fused segments as the time pass on compare to immediate postoperative assessment. CT scan were done and showed variable fusion though out the spinal segments. Histopathology of all sheep has been started and the results will be available in 2 weeks which will be followed by statistical assessment to decide how accurate RSA compare to CT scan in assessment of fusion

Objectives. To validate the precision of digitally reconstructed radiograph (DRR) radiostereometric analysis (RSA) and the model-based method (MBM) RSA with respect to benchmark marker-based (MM) RSA for evaluation of kinematics in the native hip joint. Methods. Seven human cadaveric hemipelves were CT scanned and bone models were segmented. Tantalum beads were placed in the pelvis and proximal femoral bone. RSA recordings of the hips were performed during flexion, adduction and internal rotation. Stereoradiographic recordings were all analyzed with DRR, MBM and MM. Migration results for the MBM and DRR with respect to MM were compared. Precision was assessed as systematic bias (mean difference) and random variation (Pitman’s test for equal variance). Results. A total of 288 dynamic RSA images were analyzed. Systematic bias for DRR and MBM with respect to MM in translations (p < 0.018 mm) and rotations (p < 0.009°) were approximately 0. Pitman’s test showed lower random variation in all degrees of freedom for DRR compared with MBM (p < 0.001). Conclusion. Systematic error was approximately 0 for both DRR or MBM. However, precision of DRR was statistically significantly better than MBM. Since DRR does not require marker insertion it can be used for investigation of preoperative hip kinematics in comparison with the postoperative results after joint preserving hip surgery. . Cite this article: L. Hansen, S. De Raedt, P. B. Jørgensen, B. Mygind-Klavsen, B. Kaptein, M. Stilling. Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study. Bone Joint Res 2018;7:379–387. DOI: 10.1302/2046-3758.76.BJR-2017-0268.R1

Aims. Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement. Patients and Methods. A total of 47 patients due to undergo TKA were randomized to KA+PSI (n = 24) or MA+CAS (n = 23). In the KA+PSI group, there were 16 female and eight male patients with a mean age of 64 years (. sd. 8). In the MA+CAS group, there were 17 female and six male patients with a mean age of 63 years (. sd. 7). Surgery was performed using cemented, cruciate-retaining Triathlon total knees with patellar resurfacing, and patients were followed up for two years. The effect of alignment on tibial component migration and inducible displacement was analyzed irrespective of study group. Results. There was no difference over two years in longitudinal migration of the tibial component between the KA+PSI and MA+CAS groups (reaching median maximum total point motion migration at two years of 0.40 mm for the KA+PSI group and 0.37 mm for the MA+CAS group, p = 0.82; p = 0.68 adjusted for age, sex, and body mass index (BMI) for all follow-ups). Both groups had mean migrations below acceptable thresholds. There was no difference in inducible displacement (p = 0.34) or PROMS (p = 0.61 for the Oxford Knee Score) between groups. There was no correlation between alignment and tibial component migration or alignment and inducible displacement. These findings support non-neutral alignment as a viable option with this component, with no evidence that it compromises fixation. Conclusion. Kinematic alignment using patient-specific instrumentation in TKA was associated with acceptable tibial component migration, indicating stable fixation. These results are supportive of future investigations of kinematic alignment. Cite this article: Bone Joint J 2019;101-B:929–940

Introduction. Radiostereometric Analysis (RSA) is an imaging method that is increasingly being utilized for monitoring fixation of orthopaedic implants in randomized clinical trials. Extensive RSA research has been conducted over the last 35+ years using standard clinical x-ray acquisition modalities that irradiate screen/film media or Computed Radiography (CR) plates. The precision of RSA can depend on a number of factors including modality image quality. Objective. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Methods. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 8 times at 100, 125 kV at 2.5 mAs. For DR additional test were performed at 150 kV, and again at 100 kV at 0.5 mAs. At the time of abstract submission CR results at these settings were not available. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. Standard deviations of the inter-bead distances measured in the pedicle screw were 44.4 and 32.1 μm (N=8) respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 109.0, 55.8 μm for CR [Fig. 1]. The distances between the bone implanted beads provided standard deviations of 24.4 and 22.7 μm respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 33.1 and 33.0 μm with the CR system. Further increasing the photon energy to 150 kV with the DR system reduces the precision error to 22.4 μm in the pedicle screw and remains approximately the same at 21.0 μm in bone. Lowering the mAs while maintaining 100 kV increases the precision error in the pedicle screw (64 μm) and showed no significant difference in bone (24.4 μm). Conclusion. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a considerable reduction in precision error when using DR compared to CR imaging equipment for RSA analysis. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. This approach may be useful in assessing the in vivo position of spine or other titanium implants

Aims. The primary aim of this study was to compare the wear properties of vitamin E-diffused, highly crosslinked polyethylene (VEPE) and one formulation of moderately crosslinked and mechanically annealed ultra-high molecular weight polyethylene (ModXLPE) in patients five years after primary total hip arthroplasty (THA). The secondary aim was to assess the clinical results of patients treated with VEPE by evaluating patient-reported outcome measures (PROMs), radiological evidence of fixation, and the incidence of mechanical failure. Patients and Methods. A total of 208 patients (221 THAs) from four international centres were recruited into a prospective study involving radiostereometric analysis (RSA) and the assessment of clinical outcomes. A total of 193 hips (87%) were reviewed at the five-year follow-up. Of these, 136 (70%) received VEPE (vs ModXLPE) liners and 68 (35%) received ceramic (vs metal) femoral heads. PROMs and radiographs were collected preoperatively and at one, two, and five years postoperatively. In addition, RSA images were collected to measure PE wear postoperatively and at one, two, and five years after surgery. Results. We observed similar bedding in one year postoperatively and wear two years postoperatively between the two types of liner. However, there was significantly more penetration of the femoral head in the ModXLPE cohort compared with the VEPE cohort five years postoperatively (p < 0.001). The only variables independently predictive of increased wear were ModXLPE (vs VEPE) liner type (β = 0.22, p = 0.010) and metal (vs ceramic) femoral head (β = 0.21, p = 0.013). There was no association between increased wear and the development of radiolucency (p = 0.866) or PROMs. No patient had evidence of osteolysis. Conclusion. Five years postoperatively, patients with VEPE (vs ModXLPE) and ceramic (vs metal) femoral heads had decreased wear. The rates of wear for both liners were very low and have not led to any osteolysis or implant failure due to aseptic loosening

Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary translations and rotations under measured weight bearing and joint movement. We have recently introduced this technique to monitor tibial plateau fracture healing. This paper presents our preliminary results. Twelve patients with a 41 B2, B3, C2, or C3 fracture were followed for a minimum of three months. RSA beads were inserted in the largest osteochondral fragment and the adjacent metaphysis. Knee flexion was restricted to 60° for 6 weeks. After partial weight bearing (20kg) between 2 and 6 weeks, patients progressed to full weight bearing. Follow up included clinical and radiological examinations and patient reported outcome scores (Lysholm, KOOS). DLRSA examinations included RSA radiographs in 60° flexion and under measured weight bearing. Significant interfragmentary displacement was defined as translations greater than 0.5mm and/or rotations greater than 1.5°. There was no loss to follow-up. Longitudinal RSA follow-up: Follow-up RSA radiographs were compared to postoperative examinations. Osteochondral fragment depression was less than 0.5mm in seven patients and between 2 and 4mm in the remaining five patients. Significant interfragmentary displacement after three months was recorded in three patients. DLRSA flexion results: Under 60° of flexion, translations over 0.5mm were recorded in five patients (one postoperatively; one at 2 weeks; two at 6 weeks; and one postoperatively, at 2 weeks and at 3 months). Rotations over 1.5° were recorded in six patients (one postoperatively; two at 2 weeks; one at 6 weeks; one at 2 weeks, 3 months and 4.5 months; and one postoperatively, at 2 weeks, 3 months and 6 months). DLRSA weight bearing results: Under partial weight bearing at two weeks, two patients recorded significant translations, one involving a significant rotation. Under weight bearing as tolerated, three patients recorded significant translations (one at 6 weeks; and two at 18 weeks) and four patients recorded significant rotations (one at 6 weeks; one at 18 weeks; and two at 12 and 18 weeks). Patient Reported Outcomes: Both the Lysholm and KOOS scores improved between 6 weeks and 3 months. DLRSA provides new insight and perspective in tibial plateau fractures. Some fractures take more than three months to heal. Our current rehabilitation protocol was safe in most patients, however significant interfragmentary displacement was encountered in 17% at the 2 week followup, raising questions about the quality of the initial stability

In a previous report from a randomised study we reported excellent fixation and less proximal periprosthetic bone mineral loss around the Epoch design at 2 years follow-up when compared with a solid stem of similar design. We now present the 7 years follow-up. Forty consecutive patients (20 men, 10 women, mean age 57, 41–74) with non-inflammatory osteoarthritis were randomised to receive either a cementless porous-coated composite stem with reduced stiffness (Epoch) or a cementless stiff stem with a porous coating (Anatomic). Patients were followed for 7 years with repeated evaluations using radiostereometry, DXA, conventional radiography and Harris Hip Score (HHS). At 7 years 1 stem had been revised (Anatomic) due to late infection. Subsidence and stem rotations were close to zero without any difference between the two groups (p> 0,12). Median wear rates were lower than expected (0.4mm up to 7 years) for both stem designs. At 2 years loss bone mineral density was less in Gruen regions 1, 2, 6 and 7 for the Epoch stems (p< 0.04), but this difference tended to disappear with time. At 7 years only the calcar region (Gruen region 7) had significantly denser bone in the Epoch group (p< 0.001). The HHS scores did not differ (median 98, 51–100). No stem was radiographically loose. The Epoch stem achieved excellent fixation. Wear rates were low despite use of conventionally gamma-sterilised polyethylene. This low modulus stem had positive effects on early proximal bone remodeling, but this effect decreased with time

Purpose. Radiostereometric Analysis (RSA) is a well developed imaging technique used to estimate implant fixation of orthopaedic implants in randomized clinical trials. The precision of RSA depends on a number of factors including image quality related to the individual modality properties. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Method. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment – superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 15 times at 100, 125 kV at 2.5 mAs. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. The precision error (PE), defined as the standard deviation of the 3D Bone Marker marker locations for CR is 35.5 m for 100kV at 0.5 mAs setting and 42.2, 39.4, and 26.7 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However, for DR, the PE is 27.5 m for 100kV at 0.5 mAs setting and 25.7, 25.1, and 20.1 m for the 2.5 mAs at 100, 125, and 150 kV settings. The PE for Screw Marker 3D locations, for CR is 38.2 m for the 100kV at 0.5 mAs setting and 55.2, 47.3, and 37.1 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However for DR, the PE is 40.3 m for 100kV at 0.5 mAs setting and 33.2, 24.9, and 17.0 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. The PE for all Bone Marker and Screw Marker 3D locations were significantly lower (P<0.05) for the DR technology than the CR technology except at the 100kV at 0.5 mAs exposure of the Screw Marker, P = 0.589. Conclusion. The PE decreases for increasing kV, especially in the case of screw markers where the error goes from 33 micron (100kV) to 17 micron (150 kV). Increasing the mAs reduces the error for the DR, but increases the error for CR. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a gain in precision when using DR compared to CR imaging equipment for RSA analysis

Aims. Post-operative migration of cemented acetabular components as measured by radiostereometric analysis (RSA) has a strong predictive power for late, aseptic loosening. Also, radiolucent lines predict late loosening. Migration has been reduced by systemic bisphosphonate treatment in randomised trials of hip and knee arthroplasty. Used as a local treatment, a higher local dose of bisphosphonate can be achieved without systemic exposure. We wished to see if this principle could be applied usefully in total hip arthroplasty (THA). Patients and Methods. In this randomised placebo-controlled, double-blinded trial with 60 participants, we compressed gauze soaked in bisphosphonate solution (ibandronate) or saline against the acetabular bone bed immediately before cementing the acetabular component. RSA, classification of radiolucent lines, the Harris Hip Score (HHS) and the Western Ontario McMasters Universities Osteoarthritis Index (WOMAC) were carried out at three-, six-, 12-, and 24-month follow-up. Results. Migration of the cemented acetabular component relative to the pelvis was reduced by movement almost half in the ibandronate group, when measured as maximum total point or as movement of the femoral head (p = 0.001 and 0.004, respectively). Radiolucent lines after one year were classified as absent, partial or complete, and correlated with treatment (rho 0.37; p = 0.004). Only three of 30 patients in the ibandronate group had complete lines, compared with 13 of 28 in the placebo group (p = 0.002). There were no significant effects on HHS or WOMAC score. Conclusion. Considering the power of RSA to predict loosening of cemented acetabular components, and the likelihood that radiolucent lines indicate risk of loosening, these data suggest that local treatment with a bisphosphonate can reduce the risk of late aseptic loosening. Cite this article: Bone Joint J 2017;99-B:317–24

Aims. The aim of this study was to evaluate the long-term inducible displacement of cemented tibial components ten years after total knee arthroplasty (TKA). Patients and Methods. A total of 15 patients from a previously reported prospective trial of fixation using radiostereometric analysis (RSA) were examined at a mean of 11 years (10 to 11) postoperatively. Longitudinal supine RSA examinations were acquired at one week, one year, and two years postoperatively and at final follow-up. Weight-bearing RSA examinations were also undertaken with the operated lower limb in neutral and in maximum internal rotation positions. Maximum total point motion (MTPM) was calculated for the longitudinal and inducible displacement examinations (supine versus standing, standing versus internal rotation, and supine versus standing with internal rotation). Results. All patients showed some inducible displacement. Two patients with radiolucent lines had greater mean standing-supine MTPM displacement (1.35; . sd. 0.38) compared with the remaining patients (0.68; . sd. 0.36). These two patients also had a greater mean longitudinal MTPM at ten years (0.64; . sd. 0.50) compared with the remaining patients (0.39; . sd. 0.13 mm). Conclusion. Small inducible displacements in well-fixed cemented tibial components were seen ten years postoperatively, of a similar magnitude to that which has been reported for well-fixed components one to two years postoperatively. Greater displacements were found in components with radiolucent lines. Cite this article: Bone Joint J 2018;100-B:170–5

Aims. The optimal method of tibial component fixation remains uncertain in total knee arthroplasty (TKA). Hydroxyapatite coatings have been applied to improve bone ingrowth in uncemented designs, but may only coat the directly accessible surface. As peri-apatite (PA) is solution deposited, this may increase the coverage of the implant surface and thereby fixation. We assessed the tibial component fixation of uncemented PA-coated TKAs versus cemented TKAs. Patients and Methods. Patients were randomised to PA-coated or cemented TKAs. In 60 patients (30 in each group), radiostereometric analysis of tibial component migration was evaluated as the primary outcome at baseline, three months post-operatively and at one, two and five years. A linear mixed-effects model was used to analyse the repeated measurements. Results. After five years of follow-up, one (cemented) component was revised due to ligament instability. Overall, uncemented PA-coated tibial components migrated significantly more (p = 0.003), with the mean maximum total point motion (MTPM) at five years being 0.62 mm (95% confidence intervals (CI) 0.49 to 0.76) for cemented tibial components and 0.97 mm (95% CI 0.81 to 1.15) for PA-coated tibial components in TKA. However, between three months and five years the cemented TKAs migrated significantly more (p = 0.02), displaying a MTPM of 0.27 mm (95% CI, 0.19 to 0.36) versus 0.13 mm (95% CI, 0.01 to 0.25) for PA-coated tibial components. One implant in each group was considered at risk for aseptic loosening due to continuous migration after five years of follow-up, albeit with different migration patterns for each group (i.e. higher initial migration but diminishing over time for the PA-coated component versus gradually increasing migration for the cemented component). Conclusion. The tibial components of PA-coated TKAs showed more overall migration compared with the tibial components of cemented TKAs. However, post hoc analysis showed that this difference was caused by higher migration of PA-coated components in the first three months, after which a stable migration pattern was observed. Clinically, there was no significant difference in outcome between the groups. Cite this article: Bone Joint J 2017;99-B:1467–76

The metal on metal implants was introduced without the proper stepwise introduction. The ASR resurfacing hip arthroplasty (RHA) withdrawn due to high clinical failure rates and the large diameter head THA (LDH-THA) are also widely abandoned. Early (2 year) radiostereometry studies does not support early instability as cause of failure but more likely metal wear products. A possible advantage may be maintenance of bone mineral density (BMD). We present 5 year prospective follow up from a randomized series, aiming to report changes from baseline and to investigate links between implant micromotion, Cr & Co ions and BMD. Patients eligible for an artificial hip were randomized to RHA, Biomet LDH-THA or standard Biometric THA. 19, 17 and 15 patients completed 5 year follow-up. All followed with BMD of the femur, acetabulum and for RHA the collum. RHA and THA with whole blood Co and Co. LDH-THA only at 5 year. RHA had marker based RSA of both components, cup only for LDH-THA. Translations were compiled to total translation (TT= √(x. 2. +y. 2. +z. 2. )). Data were collected at baseline, 8 weeks, 6 months, 1, 2 and 5 years. Statistical tests: ANCOVA for TT movement, Spearman's correlation for BMD, Cr, Co and BMI to TT at 5 years. RSA: The 5 year median (25%to75%) RHA cup translations were X=-0.00(−0.49 to 0.19) Y=0.15(−0.03 to 0.20), z=0.24(−0.42 to 0.37) and TT 0.58 (0.16 to 1.82) mm. For the LDH-THA X=−0.33(−0.90 to 0.20) Y=0.28(0.02 to 0.54), z=0.43(−1.12 to −0.19) and TT 1.06 (0.97 to 1.72) mm. The TT was statistically different (p<0.05) for the two cups. The RHA femoral component moved X=0.37(0.21 to 0.56) Y=0.02(−0.07 to 0.11), z=-0.01(−0.07 to 0.26) and TT 0.48 (0.29 to 0.60) mm at 5 years. There was no TT movement from year 2. The mean (SD) acetabular BMD was diminished to 93(90–97)% for RHA and 97(93–99.9)% for THA, but LDH-THA maintained 99(95–103)%. Overall femoral BMD was unchanged at 5 years for all interventions, but both stemmed implants lost 17% at the calcar. Median (25%to75%) whole-blood Cr peaked in the LDH-THA group with 1.7 (0.9 to 3.1) followed by RHA 1.2 (0.8 to 5.0) and THA with 0.5 (0.4 to 0.7)ppb. For Co the highest levels were found in RHA with 1.6(0.8 to 4.7) followed by LDH-THA 1.2 (0.7–1.7) and THA 0.2 (0.2 to 0.6) ppb. The only correlations above +/−0.3 for TT were the RHA femoral component with a correlation of 0.47 to BMI, 0.30 to Co and Cr. The ASR cup conversely had a negative correlation of −0.60 to BMI and again, the LDH-THA cup had a negative correlation of −0.37 to Cr. In contrast to registered revision rates, we found significantly larger movement for the Biomet cup than the ASR cup. The metal ion levels were similar. The LDH-THA cup maintained the acetabular BMD best at 5 years, but the difference was small, we are limited by small numbers and the correlations between TT and the covariates showed no clear pattern

The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery.

Model-based RSA radiographs were collected for 106 patients who underwent primary TKR at a single institution. Supine RSA radiographs were obtained post-operatively and at 6-, 12-, and 24-months. Standing (weight-bearing) RSA radiographs were obtained at 12-months (n=45) and 24-months (n=48). All patients received the same knee design with a fixed, conventional PE insert of either a cruciate retaining or posterior stabilized design. Ethics approval for this study was obtained.

In order to assess in vivo wear, a highly accurate 3-dimensional virtual model of each in vivo TKA was developed. Coordinate data from RSA radiographs (mbRSA v3.41, RSACore) were applied to digital implant models to reconstruct each patient's replaced knee joint in a virtual environment (Geomagic Studio, 3D Systems). Wear was assessed volumetrically (digital model overlap) on medial and lateral condyles separately, across each follow-up. Annual rate of wear was calculated for each patient as the slope of the linear best fit between wear and time-point. The influence of weight-bearing was assessed as the difference in annual wear rate between standing and supine exams. Age, BMI, and Oxford-12 knee improvement were measured against wear rates to determine correlations.

Weight bearing wear measurement was most consistent and prevalent in the medial condyle with 35% negative wear rates for the lateral condyle. For the medial condyle, standing exams revealed higher mean wear rates at 1 and 2 years, supine, 16.3 mm3/yr (SD: 27.8) and 11.2 mm3/yr (SD: 18.5) versus standing, 51.3 mm3/yr (SD: 55.9) and 32.7 mm3/yr (SD: 31.7). The addition of weight-bearing increased the measured volume of wear for 78% of patients at 1 year (Avg: 32.4 mm3/yr) and 71% of patients at 2 years (Avg: 48.9 mm3/yr). There were no significant (95% CI) correlations between patient demographics and wear rates.

Volumetric, weight-bearing wear measurement of TKR using model-based RSA determined an average of 33 mm3/yr at 2 years post-surgery for a modern, non-cross-linked polyethylene bearing. This value is comparable to wear rates obtained from retrieved TKRs. Weight-bearing exams produced better wear data with fewer negative wear rates and reduced variance. Limitations of this study include: supine patient imaging performed at post-op, no knee flexion performed, unknown patient activity level, and inability to distinguish wear from plastic creep or deformation under load. Strengths of this study include: large sample size of a single TKR system, linear regression of wear measurements and no requirement for implanted RSA beads with this method. Based on these results, in vivo volumetric wear of total knee replacement polyethylene can be reliably measured using model-based RSA and weight-bearing examinations in the short- to mid–term. Further work is needed to validate the accuracy of the measurements in vivo.

Aims. The objective of this five-year prospective, blinded, randomised controlled trial (RCT) was to compare femoral head penetration into a vitamin E diffused highly cross-linked polyethylene (HXLPE) liner with penetration into a medium cross-linked polyethylene control liner using radiostereometric analysis. . Patients and Methods. Patients scheduled for total hip arthroplasty (THA) were randomised to receive either the study E1 (32 patients) or the control ArComXL polyethylene (35 patients). The median age (range) of the overall cohort was 66 years (40 to 76). Results. The five-year median (interquartile range) proximal femoral head penetration into the E1 was -0.05 mm (-0.13 to -0.02) and 0.07 mm (-0.03 to 0.16) for ArComXL. At three and five years, the penetration was significantly greater in the ArComXL group compared with the E1 group (p = 0.029 and p = 0.019, respectively). All patient-reported outcomes (PROs) improved significantly from the pre-operative interval compared with those at one year, and remained favourable at five years. There were no differences between the two groups at any interval. Conclusion. The five-year results showed that E1 polyethylene does not wear more than the control, ArComXL. This is the longest-term RCT comparing the wear performance and clinical outcome of vitamin E diffused HXLPE with a previous generation of medium cross-linked polyethylene. Cite this article: Bone Joint J 2017;99-B:577–84.

Aims. The increased in vivo resistance to wear of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA) has led to an increased use of larger articulations which have been shown to reduce the incidence of early dislocation. To date, there are few reports of the wear of larger articulations using second generation HXLPE liners. Our prospective cohort study measured the bedding-in and early wear of large (36 mm and 40 mm diameter) articulations involving a second generation X3 HXLPE liner and compared our findings with previous clinical and in vitro studies of the same material. Patients and Methods. The proximal penetration of the femoral head five years post-operatively was measured for 15 patients using radiostereometric analysis (RSA). Results. The median proximal bedding-in within the first post-operative year was 0.022 mm (interquartile range (IQR) -0.050 to 0.091). The median proximal rate of wear between one and five years was -0.004 mm/year (IQR -0.021 to 0.022). The rates of proximal, medial, 2D or 3D wear between one and five years post-operatively of the X3 HXLPE liner did not increase with larger articulations compared with our previous study of 32 mm articulations. Conclusion. Although reassuring, the use of larger articulations requires continued monitoring to determine whether the low wear observed in the short-term continues to the mid- to long-term. Cite this article: Bone Joint J 2016;98-B:1604–10

Aims

The primary outcome was investigating differences in wear, as measured by femoral head penetration, between cross-linked vitamin E-diffused polyethylene (vE-PE) and cross-linked polyethylene (XLPE) acetabular component liners and between 32 and 36 mm head sizes at the ten-year follow-up. Secondary outcomes included acetabular component migration and patient-reported outcome measures (PROMs) such as the EuroQol five-dimension questionnaire, 36-Item Short-Form Health Survey, Harris Hip Score, and University of California, Los Angeles Activity Scale (UCLA).

Articulation of the polyethylene (PE) insert between the metal femoral and tibial components in total knee replacements (TKR) results in wear of the insert which can necessitate revision surgery. Continuous PE advancements have improved wear resistance and durability increasing implant longevity. Keeping up with these material advancements, this study utilises model-based radiostereometric analysis (mbRSA) as a tool to measure in vivo short-term linear PE wear to thus predict long-term wear of the insert.

Radiographic data was collected from the QEII Health Sciences Centre in Halifax, NS. Data consisted of follow-up RSA examinations at post-operative, six-, 12-, and 24-month time periods for 72 patients who received a TKR. Implanted in all patients were Stryker Triathlon TKRs with a fixed, conventional PE bearing of either a cruciate retaining or posterior stabilised design. Computer-aided design (CAD) implant models were either provided by the manufacturer or obtained from 3D scanned retrieved implants. Tibial and femoral CAD models were used in mbRSA to capture pose data in the form of Cartesian coordinates at all follow-ups for each patient. Coordinate data was manually entered into a 3D modeling software (Geomagic Studio) to position the implant components in virtual space as presented in the RSA examinations. PE wear was measured over successive follow-ups as the linear change in joint space, defined as the shortest distance between the tibial baseplate and femoral component, independently for medial and lateral sides. A linear best-fit was applied to each patient's wear data; the slope of this line determined the annual wear rate per individual patient. Wear rates were averaged to provide a mean rate of in vivo wear for the Triathlon PE bearing.

Mean linear wear per annum across all 72 patients was 0.088mm/yr (SD: 0.271 mm/yr) for the medial condyle and 0.032 mm/yr (SD: 0.230 mm/yr) for the lateral condyle. Cumulative linear wear at the 2-year follow-up interval was 0.207mm (SD: 0.565mm) and 0.068mm (SD: 0.484mm) for the medial and lateral condyles, respectively.

Linear PE wear measurements using mbRSA and Geomagic Studio resulted in 0.056mm/yr additional wear on the medial condyle than the lateral condyle. Large standard deviations for yearly wear rates and cumulative measurements demonstrate this method does not yet exhibit the accuracy needed to provide short-term in vivo wear measurement. Inter-patient variability from RSA examinations is likely a source of error when dealing with such small units of measure. Further analysis on patient age and body mass index may eliminate some variability in the data to improve accuracy. Despite high standard deviations, the results from this research are in proximity to previously reported linear wear measurements 0.052mm/yr and 0.054mm/yr. Linear wear analysis will continue upon completion of >100 patients, in addition to volumetric PE wear over the entire articulating surface.

The Exeter femoral stem is a double-tapered highly polished collarless cemented implant with good long-term clinical results. In order to determine why the stem functions well we have undertaken a long-term radiostereometric analysis (RSA) study. A total of 20 patients undergoing primary Exeter total hip replacement for osteoarthritis using the Hardinge approach were recruited and followed with RSA for ten years. The stems progressively subsided and internally rotated with posterior head migration. The mean subsidence was 0.7 mm (95% confidence interval (CI) 0.5 to 0.9) at two years and 1.3 mm (95% CI 1.0 to 1.6) at ten years. The mean posterior migration of the head was 0.7 mm (95% CI 0.5 to 0.9) at two years and 1.2 mm (95% CI 1.0 to 1.4) at ten years. There was no significant cement restrictor migration. The Exeter stem continues to subside slowly into the cement mantle in the long term. This appears to compress the cement and the cement bone interface, contributing to secure fixation in the long term. Cite this article: Bone Joint J 2013;95-B:605–8

Introduction: Highly cross-linked polyethylene acetabular cups and Oxinium femoral heads were developed to reduce wear debris induced osteolysis. Laboratory tests have shown less wear with these new materials. This RSA-study was performed to compare these new materials in vivo with conventional bearing materials used in total hip arthroplasty. Methods:150 patients were randomized to 5 groups. The patients received either a cemented Charnley mono-block stainless steel femoral stem with a 22.2 mm head or a cemented Spectron EF femoral stem with a 28 mm head. The Charnley stem articulated with a cemented Charnley Ogee acetabular cup. The Spectron EF stem was used with either cemented Reflection All-Poly EtO-sterilized ultra-high molecular weight polyethylene (UHMWPE) acetabular cups or cemented Reflection highly cross-linked polyethylene (XLPE) acetabular cups, combined with either Cobalt Chrome or Oxinium 28 mm femoral heads. Patients were followed up with repeated radiostereometric analysis (RSA) for two years to assess the rate of penetration of the femoral head into the cup (MTPM). Results: At 2 years follow-up the mean MTPM (95 % CI) for Charnley Ogee (n=25) was 0.20 mm (0.11–0.29). For the Spectron EF femoral stem used with Reflection All-Poly UHMWPE acetabular cups the mean MTPM (CI) at 2 years was 0.40 mm (0.23–0.57) when combined with Cobalt Chrome femoral head (n=23) and 0.50 mm (0.29–0.71) when combined with Oxinium femoral head (n=16). When using the Spectron EF femoral stem with Reflection XLPE combined with Cobalt Chrome (n=27) or Oxinium (n=24) femoral head the mean MTPM (CI) at 2 years was 0.19 mm (0.10–0.28) and 0.18 mm (0.07–0.29), respectively. There were no differences in penetration between the Charnley/Ogee, XLPE/CoCr and XLPE/Oxinium groups (student t-test, p=0.5–0.8). There was no statistically significant difference between the two Reflection All-Poly UHMWPE groups (p=0.09). The groups with Reflection All-Poly cups had a statistically significant higher penetration than the three groups mentioned above (p< 0.001). Discussion: The use of Reflection XLPE cups instead of Reflection All-Poly cups reduced femoral head penetration at 2 years. We used the Charnley Ogee cup as a reference due to a long clinical record. This cup was superior to Reflection All-Poly, but not Reflection XLPE, regarding femoral head penetration. Because the femoral head of Charnley Ogee is smaller than the Oxinium/Cobalt Chrome head it might be more clinical relevant to measure volumetric wear. The groups with Oxinium heads did not have less wear than the groups with Cobalt Chrome heads after 2 years follow-up. Further follow-up is needed to evaluate the benefits, if any, of Oxinium femoral heads in the clinical setting

Femoral bone preservation is an important consideration in total hip replacement for those patients expected to outlive the success of their primary procedure. A clinical study was initiated to assess the performance of a new, ultra-short, cementless femoral implant that is sited in the region of the femoral neck. This two-centre study, conducted in Australia and Germany, was approved by the ethics committees and regulatory authorities in both countries. Patients aged between 25 and 65 with non-inflammatory arthritis were included subject to review against the detailed study selection criteria and the provision of written informed consent. Patients were assessed pre-operatively using the Harris Hip Score and Oxford Hip Score. These scores were repeated and standard radiographs taken at 3, 6, 12 and 24 months follow-up. Radiostereometric analysis (RSA) was employed to monitor the in-vivo femoral implant stability. The Oxford Hip was additionally collected at 36 and 48 months. Forty-one patients, 23 males and 18 females, received the SILENT. ™. femoral implant in primary total hip replacement surgery between January and November 2003. The mean age was 50.4 years (range 26–65) with an average BMI of 26.6 (Range 19–37). The diagnoses included osteoarthritis (68%), AVN (15%), DDH (7%), post-infection osteoarthritis (5%) and others (5%). The average Harris Hip Score increased from 54.3 (Range 26–80) pre-operatively to 95.0 (Range 46–100) at 24 months. This improvement was supported by the patient’s view with the mean Oxford Hip Score data changing from a pre-operative level of 38.9 (Range 19–52) to a 4-year average of 13.2 (Range 12–27). The radiographic performance is also positive with only one patient having evidence of a radiolucent line on the latest x-rays at 24 months however this is non-progressive and has been present since 6 months post-op. RSA data shows the mean values for the translations of the implant and distal tip in any of the three axes to be low out to 2 years follow-up indicating a high degree of stability in this critical post-operative period. No revisions of the SILENT. ™. implant have been undertaken to date. Early prosthetic stability is acknowledged as a critical success criterion for any new femoral implant being introduced into clinical practice. This has been demonstrated for a new, ultra-short, femoral implant thereby presenting a new solution for patients who could benefit from healthy bone preservation at the time of primary surgery

We evaluated an anatomical uncemented stem, SP-CL, (Static Physiologicus – CementLess) designed to facilitate insertion and to avoid stress concentration at solitary contact points in a randomized controlled trial, with use of the Corail stem as control. The SPÅ-Cl stem has been on the market since 2014 but is still not well documented.

79 patients (80 hips) were primarily recruited and 71 patients (72 hips, 36 SP-CL, 36 Corail) attended the last follow up at 2 years. The clinical evaluation included several types of PROMs with Oxford Hip Score (OHS) as primary outcome. In addition, repeated measurements of stem migration, changes in bone mineral density and development of radiolucencies were studied with RSA, DXA and conventional radiography.

At two years the Oxford Hip Score did not differ between the SP-CL and Corail stem (estimated mean difference: −0.70 (95% CI: −4.28 – 2.89). In both groups Oxford hip score had almost doubled at 3 months, continued to increase up to 6 months and was about equal at 2 years (SP-CL; median 46 (17–48), Corail; median 47 (19–48)). At 2 years the SP-CL stems showed a median distal migration of −0.23 (−5.2 – 0.1) and the Corail stems of − 0.11 (−4.4 – 0.4). The SP-CL stems showed slightly more loss of bone mineral density in Gruen region 7 (p = 0.003).

We found no difference in clinical results with use of either of the two stems. Bone mineral density loss tended to be higher with use of the SP-CL stem and the early subsidence tended to be more pronounced, which turned out to be compatible with about the same stem stability reached between 1 and 2 years. As a next step we think that the SP-CL stem should be studied in a multi-center setting, before accepted for general use.

The primary purpose of the current study was to evaluate and compare the wear properties of vitamin E-doped, highly-crosslinked PE (VEPE) and one formulation of moderately cross-linked and mechanically-annealed ultra-high molecular weight PE (ModXLPE) in patients five years after primary THA. We also sought to understand whether polyethylene wear is associated with radiographic evidence of bone resorption or with deterioration in patient-reported outcome measures (PROMs).

A total of 221 patients from four international centers were recruited into a prospective RSA and clinical outcomes study. Seventy percent (76%) of patients received VEPE (vs. ModXLPE) liners, and 36% received ceramic (vs. metal) femoral heads. PROMs and radiographs were collected preoperatively and at one, two, and five years postoperatively. In addition, RSA radiographs were collected to measure PE wear.

We observed similar bedding in through the one-year interval and wear through the two-year interval between the two liner types. However, there was significantly more femoral head penetration in the ModXLPE cohort compared to the VEPE cohort at the five-year follow-up (p<0.001). The only variables independently predictive of increased wear were ModXLPE (vs VEPE) liner type (β=0.22, p=0.010) and metal (vs. ceramic) femoral head type (β=0.21, p=0.013). There was no association between increased wear and radiolucency development (p=0.866) or PROMs. No patients were found to have evidence of osteolysis.

At five-years postoperatively, patients treated with VEPE (vs. ModXLPE) and ceramic (vs. metal) femoral heads demonstrated decreased wear. At the longest follow-up (five years postoperatively), the wear rates for both liner groups were very low and have not led to any osteolysis or implant failures via aseptic loosening.

Studies that have previously examined the relationship between inclination angle and polyethylene wear have shown increased wear of conventional polyethylene with high inclination angles. To date, there have been no long term in vivo studies examining the correlation between cup position and polyethylene wear with highly crosslinked polyethylene.

An institutional arthroplasty database was used to identify patients who had metal-on-highly crosslinked polyethylene primary total hip arthroplasty (THA) using the same component design with a minimum follow up of 10 years ago. A modified RSA examination setup was utilised, recreating standard anteroposterior (AP) and cross-table lateral exams in a single biplane RSA acquisition. Three dimensional head penetration was measured using the centre index method. The same radiographs were used to measure inclination angle and anteversion. Spearman correlation was used to show an association between the parameters of acetabular position and wear rate.

A total of 43 hips were included for analysis in this study. Average follow-up was 12.3 ± 1.2 years. The average linear wear rate was calculated to be 0.066 ± 0.066 mm/year. Inclination angle was not correlated with polyethylene wear rate (p=0.82). Anteversion was also not correlated with polyethylene wear rate (p=0.11). There was no statistical difference between wear rates of hips within Lewinnek's “safe zone” and those outside this “safe zone” (p=0.11). Males had a higher wear rate of 0.094 ± 0.089 mm/year compared to females with a wear rate of 0.046 ± 0.032 mm/year (p=0.045).

At long term follow up of greater than 10 years, highly cross linked polyethylene has very low wear rates. This excellent tribology is independent of acetabular position, but gender did impact wear rates. Due to the low wear rates, follow-up of even longer term is suggested to examine variables affecting wear.