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

Background: Two designs of primary reverse total shoulder arthroplasty (rTSA), inlay reverse total shoulder arthroplasty (in-rTSA) and onlay reverse total shoulder arthroplasty (on-rTSA) that had undergone an aseptic revision were compared to determine differences in the rate of rerevision. Methods: In this comparative observational national registry study between January 1, 2012, and December 31, 2021, all rTSA utilizing either a modular inlay or onlay metaphyseal humeral component that had been revised for aseptic reasons formed 2 cohort groups. The cumulative percentage rerevision (2^nd CPR) was determined using Kaplan-Meier estimates of survivorship and hazard ratios (HRs) 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. Shoulder Modular Replacement (SMR)/SMR L1 or L2 combination (Lima Corporate, San Daniele del Friuli, Italy) was excluded at subanalysis. Results: The 2^nd CPR at 3 years was 20.4% (95% confidence interval 17.1, 24.1) for in-rTSA (n = 571) and 16.1%(11.6, 22.2) for on-rTSA (n = 249). The risk of rerevision was not different between the 2 cohort groups. Primary diagnosis fracture was associated with an increased risk of rerevision for on-rTSA (entire period on-rTSA HR = 3.16(1.50, 6.68), P = .002), and in-rTSA at subanalysis (entire period on-rTSA HR = 2.91(1.33, 6.33), P = .007). 59.9% of in-rTSA and 24.1% of on-rTSA aseptic revisions were minor. The revision diagnosis, the surgical experience of rTSA and if the revision was major or minor did not change the rate of rerevision. The most common reason for both in-rTSA (50%) and (43.2%) on-rTSA rerevision was instability/dislocation. Discussion: Rerevision rates of in-rTSA and on-rTSA after aseptic revision are high. The primary rather the revision diagnosis changed rerevision rates in contemporary rTSA surgery. Minor revisions did not reduce rerevision rates for in-rTSA or on-rTSA compared to humeral/glenoid revision. Increased surgical experience of primary rTSA did not change the rate of rerevision of in-rTSA or on-rTSA.