Acromial (ASF) and scapular spine (SSF) stress fractures are clinically important complications of reverse total shoulder arthroplasty (RSA) occurring in as many as 15% of patients having this procedure. The risk of these complications depends on characteristics of the patient, the shoulder, the prosthesis and the procedure. In an attempt to evaluate the non-modifiable and modifiable risk factors the authors of Implant-Positioning and Patient Factors Associated with Acromial and Scapular Spine Fractures After Reverse Shoulder Arthroplasty: A Study by the ASES Complications of RSA Multicenter Research Group conducted a multicenter study of 6,320 patients having a minimum 3-month follow-up (recognizing that a substantial number of these stress fractures occur later than three months post RSA).
Radiographic data, including the lateralization shoulder angle, distalization shoulder angle, glenoid offset, and lateral humeral offset were collected in a 2:1 control-to-fracture ratio and analyzed to evaluate their association with ASFs/SSFs.
The overall stress fracture rate was 3.8% (180 ASFs [2.8%] and 59 SSFs [0.9%]).
Unmodifiable patient risk factors for acromial fractures included inflammatory arthritis (odds ratio [OR] = 2.29, p < 0.001), osteoporosis (OR = 2.00, p < 0.001), female sex (OR = 1.74, p = 0.003), and older age (OR = 1.02, p = 0.018)
Unmodifiable shoulder risk factors included a massive rotator cuff tear (OR = 2.05, p = 0.010), , prior shoulder surgery (OR = 1.82, p < 0.001), and cuff tear arthropathy (OR = 1.76, p = 0.002)
Modifiable procedure risk factors were less important (greater glenoid lateral offset (OR = 1.06, p = 0.025)).
Unmodifiable patient risk factors for scapular spine fractures included female sex (OR = 2.45, p = 0.009), osteoporosis (OR = 2.18, p = 0.009), and inflammatory arthritis (OR = 2.04, p = 0.024).
Unmodifiable shoulder risk factors for scapular spine fractures included rotator cuff disease (OR = 2.36, p = 0.003)
No modifiable procedure risk factors for scapular spine fractures (including glenoid lateral offset) were identified.
On multivariable analysis, increased humeral lateralization was found to be associated with lower fracture rates whereas excessive glenoid-sided and global lateralization were associated with higher fracture rates.
Comment: Reverse total shoulder arthroplasty is being increasingly used to treat osteoarthritis with an intact rotator cuff as an alternative to anatomic total shoulder arthroplasty (ATSA). Patients with osteoarthritis and an intact rotator cuff are less at risk for stress fractures than those patients for which ATSA is not an option (rotator cuff tear arthropathy, massive rotator cuff tear). Currently about 50% of RSAs are performed for osteoarthritis with intact cuff (see this link).
Yet patients having RSA for osteoarthritis with intact cuff comprise only 10% of patients with stress fractures (see this link).
Because of the indication drift towards RSA for patients with osteoarthritis and an intact rotator cuff, the overall rate of stress fractures after RSA is decreasing, because more RSAs are being done on patients at low risk.
It is not known if the rate of stress fractures in high risk patients is changing.
RSA dramatically changes the loading of the acromion and scapular spine. As is the case with runners and stress fractures, some patients and some bones can tolerate the loading changes better than others. Perhaps we would be advised to consider patients having RSA in two groups:
Patients and shoulders with unmodifiable factors (female sex, advanced age, osteoporosis, inflammatory arthritis, prior surgery, cuff disease) remain at risk and deserve a separate study to identify potential risk-lowering surgical strategies, such as glenoid-sided medialization.
On the other hand patients without these risk factors may be better served by investigating factors that optimize function rather than focusing on further lowering stress fracture risk. For example in such patients glenoid-sided lateralization may safely improve shoulder rotation while lowering rates of scapular notching and impingement.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
