Bone density and its relation to the development of acromial stress fracture following reverse total shoulder arthroplasty.

Background: Postoperative acromial stress fracture is a troublesome postoperative complication after reverse shoulder arthroplasty. Our study aims to utilize routinely performed preoperative computed tomography scans to identify differences in the material properties of the acromion in patients who did and did not develop a postoperative acromial stress fracture.
Methods: Treatment records and computed tomography scans for 99 reverse shoulder arthroplasties were collected. Scans were calibrated using a phantom and transferred for post-processing where the acromion, full scapula, and humeral head were isolated. The final segmented model was used to assess acromial volume and volumetric bone mineral density for each region of interest.
Results: There was no association between age and volumetric bone mineral density in any region of interest (all R 2 ≤ 0.048, all p > 0.082). Patients who developed an acromial stress fracture were not significantly different from those who did not in terms of age, acromial volume, or acromial volumetric bone mineral density (all p > 0.559). Patients with known osteoporosis or osteopenia had slightly lower volumetric bone mineral density, but the differences were not significant (all p ≥ 0.072).
Conclusion: Postoperative acromial fractures following reverse shoulder arthroplasty cannot be predicted by computed tomography-derived volumetric bone mineral density or volume. These mechanical characteristics also do not predictably decrease with age or osteoporosis diagnosis.