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.