Primary inlay reverse shoulder arthroplasty has a higher rate of revision than onlay reverse shoulder arthroplasty: Analysis from the Australian Orthopaedic Association National Joint Replacement Registry

Background: Two classes of primary reverse total shoulder arthroplasty (rTSA), inlay (in-rTSA), and onlay (on-rTSA) were compared to determine differences in rates of revision. Methods: Between 1 January 2012 and 31 December 2020, all primary in-rTSA or on-rTSA procedures were compared from a large national arthroplasty registry by cumulative percentage revision (CPR). Kaplan–Meier estimates of survivorship and hazard ratios from Cox proportional hazard models adjusted for age, gender, glenosphere size, and humeral fixation determined any associations to the risk of revision. Results: Of the 14,807 in-rTSA and 6590 on-rTSA procedures, the CPR at seven years was 4.9%. There was an increased risk of revision for in-rTSA vs on-rTSA (p = 0.039) when adjusted for age, gender, glenosphere size, and humeral fixation. Glenosphere size <38 mm adjusted for age and gender (p = 0.016) increased the revision risk. Revision for instability/dislocation occurred more often for in-rTSA vs on-rTSA (p < 0.001) in the first three months. Males had a higher rate of revision than females for in-rTSA (3months+, p = 0.001) and for on-rTSA (p < 0.001). Discussion: Care should be taken when considering in-rTSA particularly in males, and if preoperative planning suggests a small (<38 mm) glenosphere. Level of evidence: Level III, therapeutic study. Original article.