Baseplate coverage in reverse total shoulder arthroplasty: a systematic review.

Background: The aim of this systematic review is to produce a qualitative review of the current literature describing the biomechanical and clinical implications regarding the degree of contact surface area between the glenoid baseplate and the glenoid bone in reverse total shoulder arthroplasty (rTSA). Methods: A comprehensive systematic review of the existing literature was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed, EMBASE, and Cochrane library databases were accessed in June 2024, using relevant keywords. All biomechanical and clinical studies investigating varying amounts of contact between the glenoid baseplate and glenoid bone, as well as clinical studies which discuss a decision on surgical technique based on the amount of baseplate coverage were included. Results: The search yielded 692 titles, and 555 titles remained after duplicate records were removed. A total of 8 studies were found to meet the inclusion criteria, including 6 biomechanical studies and 2 level IV case series. Twenty-one studies included a statement on the impact of rTSA baseplate coverage on surgical management, citing that less than 50%-80% of baseplate coverage necessitates further augmentation to achieve stability. The biomechanical studies reported varying results, with statistically significant baseplate instability seen at coverage levels anywhere from 25% to 60%, when defined by micromotion or displacement. Conclusion: A firmly defined minimum baseplate coverage has yet to be established, however, 75% or greater baseplate coverage allows for adequate time zero fixation across all included biomechanical studies, with coverage as low as 67% potentially providing adequate fixation.