21 members of the American Shoulder and Elbow Surgeons (ASES) from 15 institutions sought to determine the incidence of acromial (ASF) and scapular spine (SSF) stress fractures after reverse shoulder arthroplasty (RSA) and to identify preoperative patient characteristics associated with their occurrence. They followed 6755 RSAs with an average follow-up of 19.8 months (range, 3-94).
Only symptomatic ASF/SSF diagnosed by radiograph or computed tomography were considered.
The total stress fracture incidence rate was 3.9%; 3.0% were ASF and 0.9% were SSF.
Fractures occurred at an average 8.2 months (0-64) following RSA with 21.2% following a trauma.
Patient-related factors independently predictive of ASF were chronic dislocation (odds ratio [OR] 3.67, massive rotator cuff tear without arthritis (OR 2.51), rotator cuff arthropathy (OR 2.14), self-reported osteoporosis (OR 2.21), inflammatory arthritis (OR 2.18), female sex (OR 1.51), and older age (OR 1.02 per 1-year increase).
Factors independently associated with the development of SSF included osteoporosis (OR 2.63), female sex (OR 2.34), rotator cuff arthropathy (OR 2.12), and inflammatory arthritis (OR 2.05).
The authors concluded that about 1 in 26 patients undergoing RSA will develop a symptomatic ASF or SSF, more frequently within the first year of surgery and that severe rotator cuff disease may play an important role in the occurrence of stress fractures following RSA.
Comment: The incidence of ASF and SSF fractures is likely to be greater than that reported in this study: the minimum length of followup in the study was 3 months, whereas the average time from arthroplasty to fracture was 8.2 months with some occurring as long as 64 months after RSA.
It is of interest that the most common indication for RSA was cuff tear arthropathy (37% of all cases); this diagnosis accounted for over half of the cases of acromial and spine fractures.
Unfortunately, the risk factors identified in this study are non modifiable. The study did not assess modifiable risk factors such as RSA prosthesis design, implant position, humerus distalization, and acromial abutment by the greater tuberosity.
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