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. 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

Background. In recent years, the use of modern cementless implants in total knee arthroplasty has been increasing in popularity. These implants take advantage of new technologies such as additive manufacturing and potentially provide a promising alternative to cemented implant designs. The purpose of this study was to compare implant migration and tibiofemoral contact kinematics of a cementless primary total knee arthroplasty (TKA) implanted using either a gap balancing (GB) or measured resection (MR) surgical technique. Methods. Thirty-nine patients undergoing unilateral TKA were recruited and assigned based on surgeon referral to an arthroplasty surgeon who utilizes either a GB (n = 19) or a MR (n = 20) surgical technique. All patients received an identical fixed-bearing, cruciate-retaining beaded peri-apatite coated cementless femoral component and a pegged highly porous cementless tibial baseplate with a condylar stabilizing tibial insert. Patients underwent a baseline radiostereometric analysis (RSA) exam at two weeks post-operation, with follow-up visits at six weeks, three months, six months, and one year post-operation. Migration including maximum total point motion (MTPM) of the femoral and tibial components was calculated over time. At the one year visit patients also underwent a kinematic exam using the RSA system. Results. Mean MTPM of the tibial component at one year post-operation was not different (mean difference = 0.09 mm, p = 0.980) between the GB group (0.85 ± 0.37 mm) and the MR group (0.94 ± 0.41 mm). Femoral component MTPM at one year post-operation was also not different (mean difference = 0.27 mm, p = 0.463) between the GB group (0.62 ± 0.34 mm) and the MR group (0.89 ± 0.44 mm). Both groups displayed a lateral pivot pattern with similar frequencies of condylar separation. Conclusion. There was no difference in implant migration and kinematics of a single-radius, cruciate retaining cementless TKA performed using a GB or MR surgical technique. The magnitude of migration suggests there is no risk of early loosening. The results provide support for the use of a cementless TKA as a viable alternative to cemented fixation

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

Introduction. A total knee arthroplasty (TKA) is the standard of care treatment for end-stage osteoarthritis (OA) of the knee. Over the last decade, we have observed a change in TKA patient population to include younger patients. This cohort tends to be more active and thus places more stress on the implanted prothesis. Bone cement has historically been used to establish fixation between the implant and host bone, resulting in two interfaces where loosening may occur. Uncemented fixation methods provide a promising alternative to cemented fixation. While vulnerable during the early post-operative period, cementless implants may be better suited to long-term stability in younger patient cohorts. It is currently unknown whether the surgical technique used to implant the cementless prostheses impacts the longevity of the implant. Two different surgical techniques are commonly used by surgeons and may result in different load distribution across the joint, which will affect bone ingrowth. The overall objective of the study is to assess implant migration and in vivo kinematics following cementless TKA. Methods. Thirty-nine patients undergoing a primary unilateral TKA as a result of OA were recruited prior to surgery and randomized to a surgical technique based on surgeon referral. In the gap balancing surgical technique (GB) soft tissues releases are made to restore neutral limb alignment followed by bone cuts (resection) to balance the joint space in flexion and extension. In the measured resection surgical technique (MR) bone cuts are first made based on anatomical landmarks and soft tissue releases are subsequently conducted with implant components in-situ. Patients returned 2 weeks, 6 weeks, 12 weeks, 24 weeks, and 52 weeks following surgery for radiographic evaluation. Kinematics were assessed 52 weeks post-operatively. Results. No significant difference was observed between groups in maximum total point motion (MTPM) at any time point during the first post-operative year. MTPM of both the tibial and femoral component did not significantly change between the six month and one year follow up visits for both the GB (6 mths=0.67 ±0.34mm, 1 yr=0.65 ±0.52, p=0.71) and MR (6 mths= 0.79 ±0.53mm, 1 yr= 0.82 ±0.43mm, p=0.56) cohorts. MTPM for both components over the follow up period is displayed in Figure 1. No significant difference was observed in contact location or pattern on the medial condyle during deep flexion (Figure 2A). A significant difference (p=0.01) was observed, however, between surgical techniques in the lateral contact location at full extension (Figure 2B). No significant difference was observed in the magnitude of AP excursion for both the medial and lateral condyles within and between groups. Conclusion. Surgical technique did not impact the MTPM of an uncemented TKA design during the first post-operative year. By the six month post-operative period tibial and femoral MTPM plateaus indicating that osseointegration between the host bone and implanted components has occurred. Kinematic evaluation indicates contact locations anterior to the midline of the sagittal plane, paradoxical anterior translation, and a lateral pivot point, regardless of surgical technique

Early migration of the acetabular and femoral component after total hip replacement has shown to be a good predictor of implant failure. The only current technique available for this measurement is RSA. An entirely new technique for the measurement of component migration and polyethylene wear has been developed. Required are a single CT of the patients’ pelvis and femur, and routine serial postoperative antero-posterior (AP) and lateral radiographs. A CT scan of the patients pelvis and proximal femur is performed either pre or post-operatively. This CT is used to build a solid model of the patients’ bony anatomy. CAD models of the femoral and acetabular component are obtained from the manufacturer and all four solid models are imported into custom software. Ray tracer (RT) technology is the computer generation of images of a solid model placed between a camera and a screen. It has been adapted to reproduce the radiological setup used to take clinical AP and lateral radiographs. The four solid models (pelvis, acetabular component, femoral component, femoral shaft) are each placed in the RT. Manipulation of each solid model is performed (6 degrees of freedom, x, y, z translation, and rotation about the x, y, z axis) using Artificial Intelligence, until an outline of the solid model generated by the ray tracer is identical to the outline of the AP and lateral radiograph of that patient. Change in relative positions of each solid model over time (pelvis acetabular component represents acetabular migration, acetabular component femoral stem represents polyethylene wear, and femoral stem femur represents femoral migration) are recorded. Validation to measure accuracy of the technique has been performed using computer models, and femoral and acetabular prostheses implanted into a cadaver. Despite significant variations in the position of the pelvis and leg during the obtaining of post-operative radiographs, this new technique was able to measure polyethylene wear and component migration with accuracy similar to that of RSA (0.25 mm in the AP plane). Further testing and validation is required, but this technique offers promise for the future in being able to retrospectively measure component migration and poly-ethylene wear, using a single CT scan and routine clinical postoperative radiographs

Introduction. The dual mobility design concept for acetabular liners is intended to reduce the risk of dislocation and increase range of motion, but the wear pattern of this design is unclear and may have implications in implant fixation. Additionally, the solid back cups do not have the option for supplementary screw fixation, providing an additional smooth articulating surface for the liner to move against. The objective of this study was to assess cup fixation by measuring implant migration. A secondary objective was to evaluate the mobile bearing motion after rotating the hip. Methods. Thirty subjects were recruited in a consecutive series prospective study and received Anatomic Dual Mobility (Stryker Orthopedics) uncemented acetabular components with mobile bearing polyethylene liners through a direct lateral approach. Femoral stems were cemented (Exeter) or uncemented (Accolade, Stryker Orthopedics). The femur, acetabulum, and non-articulating surface of the polyethylene liner were marked with tantalum beads. Radiostereometric analysis (RSA) exams were performed post-operatively and at 6 weeks, 3, 6, months, and at 1 year. At the 1 year exam, a frog leg RSA exam was performed to assess the mobility of the cup compared to its position during a supine exam. Results. Proximal translation of the cup was 0.16 ± 0.28 mm (range −0.18 to 0.92 mm) and sagittal rotation was 0.08 ± 0.86 degrees (range −1.81 to 2.18 degrees) at 1 year. Analysis of the motion of the mobile bearing liner during the frog leg RSA exam showed total motions of between 0.10 to 5.58 mm (maximum total point motion). Discussion & Conclusions. The migration of the cup has a low group average and is on track to be in the “acceptable” range as defined by Pijls et al. [1] of less than 0.2 mm of subsidence at 2 years. The combination of low subsidence and low sagittal rotations of the cup are favorable predictors of good long-term performance [2]. The wide range of motions of the mobile bearing suggest that in some patients the liner is moving freely, while in a subset of subjects there is no motion. The implications of this in terms of the generation of wear particles and affect on implant migration will be monitored to 3 years

Introduction. Debate over appropriate alignment in total knee arthroplasty has become a topical subject as technology allows planned alignments that differ from a neutral mechanical axis. These surgical techniques employ patient-specific cutting blocks derived from 3D reconstructions of pre-operative imaging, commonly MRI or CT. The patient-specific OtisMed system uses a detailed MRI scan of the knee for 3D reconstruction to estimate the kinematic axis, dictating the cutting planes in the custom-fit cutting blocks machined for each patient [1, 2]. The purpose of this study was to evaluate the correlation between post-operative limb alignment and implant migration in subjects receiving shape match derived kinematic alignment. Methods. In a randomized controlled trial comparing patient-specific cutting blocks to navigated surgery, seventeen subjects in the patient specific group had complete 1 year data. They received cruciate retaining cemented total knee replacements (Triathlon, Stryker) using patient-specific cutting blocks (OtisMed custom-fit blocks, Stryker). Intra-operatively, 6–8 tantalum markers (1 mm diameter) were inserted in the proximal tibia. Radiostereometric analysis (RSA) [3, 4] exams were performed with subjects supine on post-operative day 1 and at 6 week, 3, 6, and 12 month follow-ups with dual overhead tubes (Rad 92, Varian Medical Systems, Inc., Palo Alto, CA, USA), digital detectors (CXDI-55C, Canon Inc., Tokyo, Japan), and a uniplanar calibration box (Halifax Biomedical Inc., Mabou, NS, Canada). RSA exams were analyzed in Model-based RSA (Version 3.32, RSAcore, Leiden, The Netherlands. Post-operative limb alignment was evaluated from weight-bearing long-leg films. Results. Post-operative limb alignments ranged from 5 degrees of varus to 5 degrees of valgus. Comparing implant migration to post-operative alignment did not demonstrate a relationship between deviation from neutral mechanical alignment and increased migration (Pearson correlation coefficient = 0.25, P = 0.33) (Figure 1). Conclusions. Previous studies have suggested that alignment of greater than 3 degrees from neutral may have adverse effects on implant survivorship [5], but this early data does not suggest increased migration with non-neutral alignment. Continued evaluation with RSA to 2 years will be performed to monitor these subjects over the longer term

Factors that allow the generation or ingression of wear particles at the implant-host interface after total hip arthroplasty (THA) may include early migration and periprosthetic bone loss. We have previously shown that a single 90mg dose of the bisphosphonate pamidronate prevents bone loss over 6 months after THA. In this 2 year randomised trial extension study we assessed the longer term effects of this intervention on bone loss and implant migration. Twenty-two patients received 90mg of pamidronate and 22 received placebo at randomisation 5 days after surgery. Femoral and pelvic bone mineral density (BMD) was measured by dual energy x-ray absorptiometry (DXA) and implant migration was measured using the EBRA-Digital method over a 104 week period. In the placebo group rapid periprosthetic bone loss occurred over the first 6 months. After this period a partial recovery in bone mass occurred in most regions. Patients in the pamidronate group had significantly less femoral, but not pelvic, bone loss than those give placebo (ANOVA P=0.02). Pamidronate was most effective in preventing bone loss in Gruen zones 6 and 7 (ANOVA P=0.004, and P=0.014, respectively). At week 104 the mean total stem migration was 1.77mm±0.27 and 1.62mm±0.37 for the placebo and pamidronate groups, respectively (P> 0.05). Total cup migration was 0.75mm±0.26 and 0.76mm±0.14, respectively (P> 0.05). Age at surgery accounted for 26% (linear regression r=−0.65, P=0.02) and 38% (r=−0.51, P=0.007) of the variability in stem and cup migration at week 104, with younger subjects experiencing greater migration. Stem migration at week 104 was also inversely related to the Barrack cement mantle grade (r=−0.66, r. 2. 41%, P=0.0003). Implant migration was not significantly related to changes in periprosthetic bone mass. Pamidronate therapy has a significant effect on bone mass, but not implant stability, after THA.Our findings suggest that the major determinants of early migration after THA are young patient age and poor cementing technique

Aims

Radiostereometric analysis (RSA) is considered the gold standard for in vivo migration analysis, but CT-based alternatives show comparable results in the shoulder and hip. We have previously validated a CT-based migration analysis method (CTMA) in a knee phantom compared to RSA. In this study, we validated the method in patients undergoing total knee arthroplasty (TKA). Our primary outcome measure was the difference in maximum total point motion (MTPM) between the differing methods.

Purpose: Although femoral neck fractures remain a concern in terms of short term failures for hip resurfacing, acetabular component position and fixation are increasingly being recognized as causes of mid term failures for hip resurfacing. The purpose of our study was to evaluate the migration pattern of a cementless acetabular component for a metal on metal hip resurfacing. Method: Between January 2006 and June 2007, 130 patients underwent metal on metal hip resurfacing; 66 hips in 60 patients were included in this analysis. Forty-eight patients were male and 12 were female, with a mean age of 50 (range, 32–66). Ninety-five percent of the surgeries were performed for osteoarthritis. All surgeries were performed by two surgeons using the Conserve Plus (Wright Medical Technology, Memphis, TN) hip resurfacing system. The acetabular component is a monoblock cobalt chrome with a porous beaded surface for osteointegration. In all cases acetabular migration was measured both vertically and horizontally, on serial radiographs using the computer-assisted Ein Bild Röntgen Analyse (EBRA) method. A minimum of three comparable radiographs is necessary for calculating the migration curves. We scored medial migration as negative horizontal movement. Results: At a mean follow up 25.3 months (range, 24–36 months), each hip had an average of 5.1 radiographs for analysis. The software excluded two cases for poor comparability ending finally with 64 cases for the analysis. Eighty-seven point five per cent of the cups showed less than 1 mm migration in the medium-lateral axis and 54.7% less than 1 mm in the vertical axis. Seventy-seven percent of the cups showed a combined migration of less than 2 mm in the observation period, without radiolucencies, leaving 23% of the acetabular components with 2 mm or greater of component migration. One of these cases required revision for aseptic loosening at 34 months. Conclusion: In our study the majority of the acetabular components were stable with some of the migration observed secondary to lack of complete initial seating due to the rigidity of the shell. Krismer et al did report on the migration of the PCA shell (also a porous beaded cobalt-chrome shell) using EBRA, with 27.5% of the shells demonstrating > 1 mm of migration. Although hip resurfacing has only mid term followup, results have been good to excellent. Caution should still be maintained since the higher frictional torque generated by the larger femoral head size as well as the nanometer size particles could negatively affect long term fixation of the acetabular component

Introduction and Aims: The purpose of this study was to validate in a clinical series a method to measure femoral component migration in surface arthroplasty based on the principles of EBRA-FCA. Method: The first 400 hybrid MMSA in 355 patients have an average of 3.5 years follow-up (range two to six years). The average age was 48 years, 73% were men and 35% had secondary osteoarthritis. All patients were evaluated prospectively at three months and then yearly. We reviewed the x-rays of 26 hips that had undergone metal-on-metal resurfacing using EBRA-FCA. Minimum follow-up was 3.5 years. Group 1was free of any clinical or radiographic signs of loosening (17 hips); group 2 had failed from femoral component aseptic loosening (nine hips). Mean age for the whole group was 50.7 years (28–67). Sixty-six percent were male and 63% were operated for osteoarthritis. We recorded migrations of 2mm or greater and the time to initiation of migration. Results: Group 2 showed significantly greater migration than group 1, respectively: 4.57 mm versus 1.62mm for centre of the head (p=0.005), 4.51mm versus 1.05mm for stem tip (p=0.001). Initial migration was significantly sooner in group 2 versus group 1: 19 months versus 29.2 months (p=0.030). In group 2, the average time to first migration detected with EBRA-FCA was significantly less than time to first clinical symptoms: 19 months versus 29.5 months (p=0.003). More importantly, the time to detection of significant migration was shorter than the time to detection of the first metaphyseal stem radiolucency: 19 months versus 24.3 months (p=0.028). Conclusion: EBRA-FCA represents a reliable tool to measure migration of femoral component, which may become essential in the assessment of the clinical performance of MMSA. It is best used in large clinical series with standardised x-ray technique and limiting the number of observers

Introduction: Long-term, aseptic loosening is the central problem for total hip replacements (THR). 1. Several studies have suggested the possibility of predicting long-term loosening of femoral components (after about 7 years) by assessment of the short-term migration pattern (1 – 2 years) using radiostereometric analysis (RSA). 2. During the past 2 years, we have been conducting an RSA study of the Elite Plus (DePuy) femoral component migration in 25 (8M, 17F) primary THR patients (mean age 61 years). Results: The Table below shows the mean and SD of the stem centroid migrations after 12 months. The mean subsidence rate of 0.71 mm/year (15 patients) during the first month reduced to 0.16 mm/year, (22 patients) during the following two months. By the latter half of the first postoperative year, the mean rate had reduced to 0.13 mm/year. Subsidence. 0.20 ± 0.12 mm (15). Internal Rotation. 0.89 ± 0.52 deg (14). Lateral. 0.13 ± 0.09 mm (8). External Rotation. 0.16 deg (1). Medial. 0.11 ± 0.09 mm (7). Valgus Rotation. 0.09 ± 0.06 deg (5). Posterior. 0.17 ± 0.12 mm (11). Varus Rotation. 0.23 ± 0.14 deg (10). Anterior. 0.08 ± 0.08 mm (4). Flexion. 0.28 ± 0.15 deg (7). Extension. 0.15 ± 0.09 deg (8). Discussion: A study by the Oxford group (Alfaro-Adrian et al. 3. ) compared the migration of 19 Elite Plus stems with 32 Exeter (Howmedica) stems over a two year period. After 1 year, there is a remarkable similarity in the subsidence, lateral migration and internal rotation between the two groups. However, combining the posterior and anterior migrations in the present study, the mean posterior migration was 0.15 mm. This is about half of that measured by the Oxford group (0.28 mm). Furthermore, the present study shows that varus rotation is predominant – compared to valgus rotation in the Oxford group’s study

Aims: The aim of this study was to measure implant migration and bone remodelling of the proximal femur two years after insertion of a customized or a standard femoral stem. Materials and methods: In a prospective, randomized study 26 hips (26 patients) have been examined postoperatively and after 3, 6, 12 and 24 months using radiostereometry (RSA) and DEXA. Thirteen hips received a customized femoral stem (Unique, SCP as) and 13 hips received a standard uncemented femoral stem (ABG¨, Stryker-Howmedica). An uncemented acetabular cup (Duraloc¨, DePuy) was used in all hips. The mean age of the patients was 55 (24–67) years. Results: The median displacement of the custom/ standard femoral stems was 0.04/0.01 mm along the - medial-lateral axis, 0.08/0.02 mm along the proximal-distal axis and 0.03/0.08 mm along the anterior-posterior axis, respectively. Statistically, there was no difference between the two groups. One custom stem subsided 5.2 mm at one year, but showed no further migration at two years. The mean decrease in bone mineral density (BMD) in all Gruen zones was 6% in the Custom-group and 7% in the ABG-group. The most pronounced bone loss was seen in Zone 7 and was 21% and 25% for the two groups, respectively. Discussion: We found no statistically signiþcant difference in short-term stem migration comparing a customized and a standard, uncemented femoral stem. Furthermore, the changes in bone mineral density were almost equal in femurs with either type of prosthesis

Background

Surgeons generally perform total knee replacement using either a gap balancing or measured resection approach. In gap balancing, ligamentous releases are performed first to create an equal joint space before any bony resections are performed. In measured resection, bony resections are performed first to match anatomical landmarks, and soft tissue releases are subsequently performed to balance the joint space. Previous studies have found a greater rate of coronal instability and femoral component lift-off using the measured resection technique, but it is unknown how potential differences in loading translate into component stability and fixation.

Background

There is increasing impetus to use rapid recovery care pathways when treating patients undergoing total hip arthroplasty (THA). The direct anterior (DA) approach is a muscle sparing technique that is believed to support these new pathways. Implants designed for these approaches are available in both collared and collarless variations and understanding the impact each has is important for providing the best treatment to patients.

Purpose: The goal of this study was to investigate if musculoskeletal activation patterns measured with electromyography (EMG) are predictive of migration of total knee replacements (TKR) measured with radiostereometric analysis (RSA).

Method: 37 TKR patients who were part of a larger randomized controlled RSA trial were recruited to this study. Study participants had been randomized to receive the Nexgen LPS Trabecular Metal tibial monoblock component (n = 19), or the cemented NexGen Option Stemmed tibial component (n = 18) (Zimmer, Warsaw IN). Ethics approval was received from the institutional review board. In the week prior to their surgery, the patients went to the dynamics of human motion laboratory and underwent EMG data collection. Surface electrodes were placed over the vastus lateralis, vastus medialis, rectus femoris, the lateral and medial hamstrings, and the lateral and medial gastrocnemius using standardized placements (Hubley-Kozey et al., 2006). The variability in subject EMG patterns was captured with a set of discrete scores that represented weightings on objectively-extracted features of the gait waveform data using principal component analysis (PCA). Within four days of surgery and at six months post-operatively, patients had bi-planar knee x-rays taken. RSA analysis was performed with MB-RSA (MEDIS, Leiden). RSA results were reported as maximum total point motion (MTPM), and six degrees of freedom translations and rotations at six months.

Results: A correlation was found between the third principle component of the lateral gastrocnemius muscle (representing high gastrocnemius activation in late stance) and the anterior migration of the component (R2=0.247 P=0.002). A correlation was found between the vastus medialis principle component three (representing low vastus medialis activation in late stance) and the anterior migration of the component (R2= 0.338, P=0.000). A stepwise regression model was developed for anterior migration of the tibial component. To reduce the number of terms in the model only the two EMG variables that were correlated with anterior migration, implant type and BMI were entered leaving four possible terms. The stepwise regression eliminated all variables but the lateral gastrocnemius and the vastus medialis. The regression equation was Anterior-Posterior Migration = 0.01 +0.12*Vastus Medialis PC3 + 0.074*Lateral Gastrocnemius PC3 (R2=0.487, R2 Adj=0.457, P< 0.0001)

Conclusion: It has previously been shown that anterior shear on the tibial component of TKR is temporally localized to the last third of stance phase of gait. Both the gastrocnemius and vastus muscle groups have the ability to produce large anterior posterior shear on an the knee during late stance. This result shows that variables which capture the temporal activation patterns of these muscles preoperatively are related to the migration of the tibial component of TKR postoperatively. This may have implications for rehabilitation of these patients.

Introduction

Although femoral neck fractures remain a concern in short term failures for hip resurfacing, acetabular component position and fixation are increasingly being recognized as causes of mid term failures for hip resurfacing. This study aimed to evaluate the migration pattern of a cobalt chrome, beaded acetabular component for a metal on metal hip resurfacing.

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