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

Abstract

Background: 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.

Methods: 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.

Results: 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).

Conclusions: 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.

Keywords: Glenosphere size; glenosphere diameter; reverse total shoulder arthroplasty; revision.