Monday, June 11, 2018

When is the acromion likely to break after a reverse total shoulder?

Acromial Fractures in Reverse Shoulder Arthroplasty: A Clinical and Radiographic Analysis

The authors reviewed 12 patients diagnosed with a postoperative acromial stress fracture after a reverse total shoulder and compared them to a case matched control group of 48 shoulders having reverse total shoulders but no fracture.  The rate of acromial fracture in this series was 1.11%. Compared to controls, patients with fractures were less satisfied with their outcome.

Only 1 of the 12 fractures had a history of direct trauma, while the 11 others were considered stress fractures. The mean time from surgery to fracture diagnosis was 9 months (range, 2–38 months). Five (42%) occurred less than 3 months after surgery, 3 (25%) from 3 to 6 months after surgery, 1 (8%) from 6 to 12 months, 1 (8%) between 1 and 2 years, and 2 (17%) occurred greater than 2 years postoperatively. 

 Four (33%) of the fractures were displaced.

Osteoporosis,  smaller lateral offset of the greater tuberosity, greater arm lengthening, and a thinner acromion were more common in the fracture group.

The authors concluded that the combination of a thin acromion and superior migration of the humeral head increase the risk of acromial fracture.
Comment: It is apparent that the quality of the acromial bone prior to a reverse total shoulder is likely to be diminished by wear, disuse local osteopenia, and systemic osteoporosis.  A reverse total shoulder dramatically increases the loads on the acromion by restoring use and by increasing the static and dynamic tension on the deltoid origin. Indeed it is surprising that these stress fractures are not recognized more often.

The observations in article suggest that surgeons performing reverse total shoulders should warn their patients of this possible event and it should be suspected with the onset of posterior scapular or acromial area complaints of pain. Surgeons may also wish to avoid excessive deltoid tension when implanting a reverse total shoulder, especially in patients at increased risk.
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