In vivo volumetric and linear wear measurement of reverse shoulder arthroplasty at minimum 5-year follow-up

Abstract

Reverse shoulder arthroplasty is quickly becoming the most frequently performed glenohumeral joint replacement. The purpose of this study was to evaluate the volumetric and linear wear rates of ultrahigh-molecular-weight polyethylene humeral liners invivo at a minimum 5-year follow-up. Radiostereometric analysis was used to image 15 patients at terminal range of motion in forward flexion, abduction, external rotation, and internal rotationand with the arm at the side. The relative position and orientation of the glenosphere and polyethylene were identified for each arm position. The apparent intersection of the glenosphere into the polyethylene was recorded as wear. Mean volumetric and linear wear rates were recorded, and Pearsoncorrelation coefficients were applied to the 36-mm liners to assess the relationship between the wear rate and term of service. The mean reverse shoulder arthroplasty term of service at the time of imaging was 8 ± 1 years (range, 6-11 years). The mean volumetric and linear wear rates for the 36-mm liners (n = 13) were 42 ± 22 mm3/yr (r = 0.688, P = .009)and 0.11 ± 0.03 mm/yr (r = 0.767, P = .002), respectively. The mean volumetric and linear wear rates for the 42-mm liners (n = 2) were 114 ± 44 mm3/yr and 0.17 ± 0.01 mm/yr, respectively. No single arm position was able to capture all recorded wear individually. This study showed volumetric and linear wear rates of approximately 40 mm3/yr and 0.1 mm/yr, respectively, for the 36-mm polyethylene liners. The 42-mm liners showed higher wear rates, although a greater number of subjects is required for conclusive results. Invivo wear of reverse total shoulder arthroplasty is multidirectional and perceptible.