Risk factors for acromial stress fractures following primary reverse total shoulder arthroplasty: the impact of prior acromioplasty and radiographic parameters.

HYPOTHESIS/

BACKGROUND

Acromial scapular stress fractures (ASFs) are a complication after primary reverse total shoulder arthroplasty (rTSA), often causing functional impairment. The role of acromioplasty and radiographic predictors in ASF is unclear. Prior acromioplasty, acromial thickness (AT), deltoid tuberosity index (DTI), and changes in critical shoulder angle (ΔCSA) may influence ASF development.

METHODS

A retrospective analysis of 698 patients who underwent primary rTSA from 2017 to 2022 with a minimum 2-year follow-up was carried out. ASF were confirmed by CT and classified according to Levy et al. Demographic, surgical, and radiographic data-AT, DTI, critical shoulder angle, ΔCSA, lateralization shoulder angle, and distalization shoulder angle-were collected. Data were analyzed using Firths penalized logistic regression.

RESULTS

ASF occurred in 36 patients (5.2%), (52.8% Type I, 41.6% Type II, and 5.6% Type III). Prior acromioplasty was more frequent in ASF patients (30.6% vs. 15%, P = .014). ASF patients had lower AT (6.5 ± 1.6 vs. 7.7 ± 1.6 mm, P < .001), lower DTI (1.29 ± 0.09 vs. 1.38 ± 0.13, P < .001), and higher ΔCSA (4.7 ± 6.9° vs. 1.0 ± 4.9°, P = .001). Regression identified lower DTI (odds ratio 0.61, 95% confidence interval 0.45-0.80, P < .001) and higher ΔCSA (odds ratio 1.14, 95% confidence interval 1.06-1.22, P < .001) as independent predictors, while AT and prior acromioplasty were not significant.

CONCLUSION

Reduced DTI and greater ΔCSA are significant independent predictors of ASF after primary rTSA. Preoperative assessment DTI and careful management of critical shoulder angle may help identify high-risk patients and mitigate the incidence of ASF.