Acromial and spine fractures after reverse arthroplasty: Prevalence and risk factors

Abstract Background Stress fractures of the acromion and spine of the scapula are a known complication after reverse shoulder arthroplasty (RSA). Most reports on these fractures include single implants and relatively small numbers. Controversy remains regarding risk factors and optimal management for these fractures. The purpose of this study was to assess the prevalence and risk factors for periprosthetic scapular acromion and spine fractures in a large series of consecutive primary RSA. Methods Between 2004 and 2016, 2,172 primary RSAs were performed at a single tertiary referral center using various implants over time. Medical records were reviewed to identify all shoulders (n = 36) that sustained a postoperative fracture of the scapular spine or acromion. Univariate and multivariable-adjusted logistic regression analyses were used to determine whether any of the following were significant risk factors for fracture: age, gender, BMI, diagnosis, prior acromioplasty, prior cuff repair, and implant type. Results There were 34 acromial and 2 scapular spine stress fractures, resulting in a prevalence rate of 2%. The mean interval between the index arthroplasty and the diagnosis of fracture was 12 months. The majority of the fractures (89%) were treated non-operatively with shoulder immobilization for 6 weeks. The remaining four fractures (11%) were treated open reduction internal fixation (ORIF). In the multivariate regression analysis, there was a trend towards increased risk of fracture for females (HR = 1.71, p = 0.09) and those with a prior acromioplasty (HR = 2.55, p = 0.07). No significant associations were found with age (HR = 0.84, p = 0.26), BMI (HR = 1.01, p = 0.62), previous rotator cuff repair (HR = 1.47, p = 0.25), diagnosis (HR = 1.03, p = 0.97), medialized (HR = 1.30, p = 0.44), or lateralized center of rotation (HR = 0.77, p = 0.44). Conclusions Postoperative stress fractures of the acromion or spine of the scapula complicated the course of 1.6% of all primary RSAs included in this study. Female gender and a prior acromioplasty may predispose to these fractures. The majority of the fractures involve the acromion, with much less frequent involvement of the spine of the scapula. With the numbers available, no associations were found with age, BMI, diagnosis and various implant features. Level of Evidence Level III; Retrospective comparative study; Treatment study.