Characteristics associated with re-revision of primary inlay and onlay reverse shoulder arthroplasty. Analysis from the Australian Orthopaedic Association National Joint Replacement Registry.

INTRODUCTION Two designs of primary reverse total shoulder arthroplasty (rTSA), inlay (in-rTSA) and onlay (on-rTSA) that had undergone an aseptic revision were compared to determine differences in the rate of re-revision. MATERIALS AND METHODS In this comparative observational national registry study between 1 Jan 2012 and 31 December 2021 all rTSA utilizing either a modular inlay or onlay metaphyseal humeral component that had been revised for aseptic reasons formed two cohort groups. The cumulative percentage re-revision (2nd CPR) was determined using Kaplan-Meier estimates of survivorship and hazard ratios (HR) from Cox proportional hazard models adjusted for age and sex. A minor category revision involved exchange of parts not fixed to bone whilst major revisions did. The primary and revision diagnoses, surgeon primary volume experience, and revision category were compared. SMR/SMR L1 or L2 combination (Lima Corporate, San Daniele del Friuli, Italy) was excluded at sub-analysis. RESULTS The 2nd CPR at 3 years was 20.4%(95% confidence interval (CI)17.1, 24.1) for in-rTSA (n=571) and 16.1%(11.6, 22.2) for on-rTSA (n=249). The risk of re-revision was not different between the two cohort groups. Primary diagnosis fracture was associated with an increased risk of re-revision for on-rTSA (entire period on-rTSA HR = 3.16(1.50, 6.68),p=0.002), and in-rTSA at sub-analysis (entire period on-rTSA HR = 2.91(1.33, 6.33),p=0.007). 59.9% of in-rTSA and 24.1% of on-rTSA aseptic revisions were minor. If the revision was major or minor, or the surgical experience of rTSA, and the revision diagnosis did not change the rate of re-revision. The most common reason for both in-rTSA (50%) and (43.2%) on-rTSA re-revision was instability/dislocation. DISCUSSION Re-revision rates of in-rTSA and on-rTSA after aseptic revision are high. The primary rather the revision diagnosis changed re-revision rates in contemporary rTSA surgery. Minor revisions did not reduce re-revision rates for in-rTSA or on-rTSA compared to Humeral/glenoid revision. Increased surgical experience of primary rTSA did not change the rate of re-revision of in-rTSA or on-rTSA.