Lateralization and distalization shoulder angles do not predict outcomes in reverse shoulder arthroplasty for cuff tear arthropathy

Abstract

In reverse shoulder arthroplasty (RSA), there is a plethora of measurements regarding implant lateralization and distalization to optimize the center of rotation. Two specific measurements known as the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) have been the recent focus of studies to assess their association with RSA and postoperative function. The aim of this study was to evaluate the prognostic clinical value of the LSA and DSA in a large cohort of patients with cuff tear arthropathy (CTA) who were treated with different RSA systems. Two local shoulder arthroplasty registries were reviewed for all RSA patients documented with a radiological assessment and complete 2-year follow-up examination. The main inclusion criterion was primary RSA for patients with CTA. Any patients with either a complete teres minor tear, os acromiale or acromial stress fractures reported between the time of surgery and the 24-month follow-up were excluded. Five different RSA implant systems with four different neck-shaft angles were assessed. The Constant Score (CS), Subjective Shoulder Value (SSV) and range of motion (ROM) at two years were correlated with both LSA and DSA assessed on 6-month anteroposterior radiographs. Linear and parabolic univariable regressions were calculated for both shoulder angles, for each prosthesis system and for the entire patient cohort. Between May 2006 and November 2019, there were a total of 630 CTA patients who had undergone primary RSA. Of this large cohort, 270 were treated with the Promos Reverse (neck-shaft angle [NSA], 155°), 44 with the Aequalis Reversed II (NSA, 155°), 62 with the Lima SMR Reverse (150°), 25 with the Aequalis Ascend Flex (145°) and 229 with the Univers Revers (135°) prosthesis systems. The mean (standard deviation [SD]) LSA was 78° (10; range, 6-107) and the mean DSA was 51° (10; range, 7-91). The average CS at 24 months follow-up was 68.1 (SD: 13; 13-96) points. Neither the linear nor parabolic regression calculations for LSA or DSA revealed significant associations with any of the clinical outcomes. Different patients may achieve different clinical outcomes despite having identical LSA and DSA values. There is no association between angular radiographic measurements and 2-year functional outcome.