Less wear in deep‐dished mobile compared to fixed bearing total knee arthroplasty of the same design at 5‐year follow‐up: a randomised controlled model‐based Roentgen stereophotogrammetric analysis trial

Abstract

AbstractPurposeThe aim of this prospective randomised controlled study was to compare wear characteristics and functional outcome between deep‐dished mobile bearing (MB) and fixed bearing (FB) cemented total knee arthroplasty (TKA). We hypothesised that deep‐dished MB reduces polyethylene wear and improves patient‐reported outcome measures.MethodsA total of 50 patients were randomised to receive a MB or FB tibia component of the same cemented TKA design. Patients were evaluated over a 5‐year follow‐up period. Medial and lateral wear were assessed using model‐based Roentgen Stereophotogrammetric Analysis (RSA) and compared with the direct postoperative minimal joint space measurement. Functional outcome was assessed by the clinician‐derived KSS and OKS, WOMAC, LEAS, and FJS‐12. All data were derived using a general linear mixed model.ResultsAt 5‐year follow‐up, decreased wear in the MB compared to the FB group was observed on the lateral side (0.07 ± 0.17 mm, p = 0.026), but not on the medial side (0.31 ± 0.055 mm, p = 0.665). Functional outcomes improved with a statistical significant effect over time, with no significant differences between groups (all p > 0.17).ConclusionThis model‐based RSA study with 5‐year follow‐up showed that cemented deep‐dished MB reduced lateral polyethylene wear as compared to FB in a single TKA system, whilst clinical outcomes were comparable. Longer follow‐up is needed to establish clinical implications of these altered wear patterns and determine type of wear.Level of evidenceLevel 1 randomised controlled trial.