Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

Abstract

Background During the last 5 years, there has been an increase in the use of unicompartmental knee arthroplasty (UKA) to treat knee osteoarthritis in Australia, and these account for almost 6% of annual knee replacement procedures. However, there is debate as to whether a fixed bearing or a mobile bearing design is best for decreasing revision for loosening and disease progression as well as improving survivorship. Small sample sizes and possible confounding in the studies on the topic may have masked differences between fixed and mobile bearing designs. Questions/purposes Using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), we selected the four contemporary designs of medial compartment UKA: mobile bearing, fixed modular, all-polyethylene, and fixed molded metal-backed used for the treatment of osteoarthritis to ask: (1) How do the different designs of unicompartmental knees compare with survivorship as measured by cumulative percentage revision (CPR)? (2) Is there a difference in the revision rate between designs as a function of patient sex or age? (3) Do the reasons for revision differ, and what types of revision procedures are performed when these UKA are revised? Methods The AOANJRR longitudinally maintains data on all primary and revision joint arthroplasties, with nearly 100% capture. The study population included all UKA procedures undertaken for osteoarthritis between September 1999 and December 2018. Of 56,628 unicompartmental knees recorded during the study period, 50,380 medial UKA procedures undertaken for osteoarthritis were included in the analysis after exclusion of procedures with unknown bearing types (31 of 56,628), lateral or patellofemoral compartment UKA procedures (5657 of 56,628), and those performed for a primary diagnosis other than osteoarthritis (560 of 56,628). There were 50,380 UKA procedures available for analysis. The study group consisted of 40% (20,208 of 50,380) mobile bearing UKA, 35% (17,822 of 50,380) fixed modular UKA, 23% (11,461 of 50,380) all-polyethylene UKA, and 2% (889 of 50,380) fixed molded metal-backed UKA. There were similar sex proportions and age distributions for each bearing group. The overall mean age of patients was 65 ± 9.4 years, and 55% (27,496 of 50,380) of patients were males. The outcome measure was the CPR, which was defined using Kaplan-Meier estimates of survivorship to describe the time to the first revision. Hazard ratios from Cox proportional hazards models, adjusted for sex and age, were performed to compare the revision rates among groups. The cohort was stratified into age groups of younger than 65 years and 65 years and older to compare revision rates as a function of age. Differences among bearing groups for the major causes and modes of revision were assessed using hazard ratios. Results At 15 years, fixed modular UKA had a CPR of 16% (95% CI 15% to 17%). In comparison, the CPR was 23% (95% CI 22% to 24%) for mobile bearing UKA, 26% (95% CI 24% to 27%) for all-polyethylene UKA, and 20% (95% CI 16% to 24%) for fixed molded metal-backed UKA. The lower revision rate for fixed modular UKA was seen through the entire period compared with mobile bearing UKA (hazard ratio 1.5 [95% CI 1.4 to 1.6]; p < 0.001) and fixed molded metal-backed UKA (HR 1.3 [95% CI 1.1 to 1.6]; p = 0.003), but it varied with time compared with all-polyethylene UKA. The findings were consistent when stratified by sex or age. Although all-polyethylene UKA had the highest revision rate overall and for patients younger than 65 years, for patients aged 65 years and older, there was no difference between all-polyethylene and mobile bearing UKA. When compared with fixed modular UKA, a higher revision risk for loosening was shown in both mobile bearing UKA (HR 1.7 [95% CI 1.5 to 1.9]; p < 0.001) and all-polyethylene UKA (HR 2.4 [95% CI 2.1 to 2.7]; p < 0.001). The revision risk for disease progression was higher for all-polyethylene UKA at all time points (HR 1.4 [95% CI 1.3 to 1.6]; p < 0.001) and for mobile bearing UKA after 8 years when each were compared with fixed modular UKA (8 to 12 years: HR 1.4 [95% CI 1.2 to 1.7]; p < 0.001; 12 or more years: HR 1.9 [95% CI 1.5 to 2.3]; p < 0.001). The risk of revision to TKA was higher for mobile bearing UKA compared with fixed modular UKA (HR 1.4 [95% CI 1.3 to 1.5]; p < 0.001). Conclusion If UKA is to be considered for the treatment of isolated medial compartment osteoarthritis, the fixed modular UKA bearing has the best survivorship of the current UKA designs. Level of Evidence Level III, therapeutic study.

Mid-term survivorship of fixed bearing unicondylar knee arthroplasty with no exclusion of early PFJ arthritis or ACL deficiency: Analysis of clinical and radiological predictors

“…The expected survivorship of 94.65% in 8.3 years using such criteria and surgical technique was comparable with latest registry data (91.7–93.6% in 10 years), 1,2 large cohort study 17,18 and metaanalysis. 3,4 However, selection criteria were heterogeneous in registries and meta-analysis such that their survivorship results could not differentiate between those with different selection criteria. de Grave 17 reported the estimated survival of a 460 cohort to be 97.2% and 94.2% at 5 and 10 years but selection criteria excluded cases with pre-existing PFJ OA and clinical ACL deficiency.…”

“…Comparing with MB UKA, superior 15 years' survivorship has been demonstrated in FB UKA even with conventional technique. 3,4 There are other good reasons to stick to conventional technique. The first is higher cost and time associated with robotic surgery, second is the higher infection rate.…”

“…1 It has consistently produced the longest survivorship according to the latest registries with revision rate of 3.6–4.8% in 5 years and 6.4–8.3% in 10 years. 3,4 Several factors might have contributed to the gaining popularity of MB UKA; the first is the wider selection criteria which does not preclude patients with patellofemoral joint (PFJ) arthritis 5 ; the second is the use of non-navigated, non-robotic instrument 6 which could save time and cost; the third is the presence of robust clinical studies in MB UKA suggesting the benign nature of various postoperative conditions which could have affected survivorship such as tibial tray overhang, 7 periprosthetic radiolucency or radiosclerosis 8 and anteromedial knee pain. 9 On the other hand, the integrity of anterior cruciate ligament (ACL) is of larger concern in UKA and could be an advantage for FB UKA in terms of patient selection and survivorship.…”

Presence of a Lateral Trochlear Osteophyte Predicts Medial Unicompartmental Arthroplasty Failure at Midterm Follow-up

“…The Oxford UKA is a commonly used medial UKA implant [ 4 , [13] , [14] , [15] , [16] ]. Described failure modes of medial UKA at midterm follow-up include progression of lateral or patellofemoral joint OA and aseptic loosening [ 13 , [15] , [16] , [17] , [18] ].…”

CORR Insights®: Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

“…In the current study, Kannan et al [3] use the Australian Orthopaedic Association National Joint Replacement Registry to determine whether fixed or mobile bearing implants have better survivorship in medial UKA. The authors found that a fixed modular UKA has the best survivorship among the modern implant designs examined in their study [3]. This finding is a critical component in advising our patients regarding the outcomes of UKA.…”