Effect of glenosphere size on reverse shoulder arthroplasty revision rate: an analysis from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR).

Abstract

Modularity is an integral element of reverse total shoulder arthroplasty (RTSA). Glenosphere diameter is a key component, but its effect on revision rate is unknown. The aim of this study was to investigate the relationship between glenosphere size and revision rates in RTSA procedures. Data from a large national arthroplasty registry were analyzed for the period April 2004 to 31 December 2019. The study population included all primary RTSA procedures using glenosphere sizes <38 mm, 38-40 mm, and >40 mm. A subanalysis of glenosphere sizes for each of the 3 most commonly implanted prostheses and further analyses by patient age and gender were also performed. The rate of revision was determined by Kaplan-Meier estimates, with comparisons by Cox proportional hazard models. There were 28,817 primary RTSA procedures. Glenosphere sizes <38 mm had a higher revision rate compared to 38-40-mm glenospheres (hazard ratio [HR] 1.28, 95% confidence interval [CI] 1.11, 1.48, P < .001) and >40-mm sizes (HR 1.35, 95% CI 1.15, 1.59, P < .001). Males with <38-mm and 38-40-mm glenospheres had significantly higher revision rates compared to >40-mm glenospheres (HR 1.49, 95% CI 1.21, 1.83, P < .001; and HR 1.28, 95% CI 1.03, 1.58, P = .025, respectively). Females with <38-mm and >40-mm glenospheres had higher revision rates compared to females with 38-40-mm glenospheres (HR 1.38, 95% CI 1.14, 1.68, P < .001; and HR 1.41, 95% CI 1.06, 1.88, P = .019, respectively). For patients aged 65-74 years, glenospheres >40 mm had a significantly lower revision rate than both the <38-mm glenospheres (entire period: HR 0.59, 95% CI 0.45, 0.76, P < .001) and 38-40-mm glenospheres (entire period: HR 0.72, 95% CI 0.54, 0.94, P = .017). For patients aged ≥75 years (n = 14,622), <38-mm glenospheres had a significantly higher rate of revision compared with 38-40-mm glenospheres after 3 months (HR  1.43, 95% CI 1.09, 1.86, P = .009). Analysis comparing glenosphere sizes within each of the 3 most commonly implanted prostheses found that the Delta Xtend with 38-40-mm glenospheres had higher revision rates compared with >40-mm glenospheres (HR 1.49, 95% CI 1.14, 1.92, P = .003). The SMR L1 (Lima) 38-40-mm glenospheres had a lower rate of revision compared with the <38-mm (HR 0.50, 95% CI 0.37, 0.67, P < .001) and >40-mm glenospheres (HR 0.60, 95% CI 0.43, 0.85, P = .004). Glenospheres <38 mm can be expected to increase revision rates in primary RTSAs. The optimum size of glenospheres is gender, age, and prosthesis specific, with revision rates lower for females with 38-40-mm glenospheres and lower for males with >40-mm glenospheres.