Risk of acromial fractures after reverse total shoulder arthroplasty - what can we control?

Acromial fractures are an important cause of poor outcome after reverse total shoulder arthroplasty (RSA). These fractures can cause pain, deltoid weakness because of loss of a secure muscle origin, and restricted range of motion due to unwanted contact between the inferiorly displaced lateral acromion and the humeral tuberosity. They can be associated with scapular notching, which may further compromise shoulder comfort and function.

These fractures are of the "stress" or "fatigue" type, meaning that they result from the repeated application of loads that were unknown to the acromion prior to the reverse total shoulder arthroplasty. This change in loading occurs abruptly - immediately post op -  without the bone having time to remodel. As suggested by the direction of the deformity, repeated downward loading of the lateral acromion from the pull of the acromion is a likely culprit. Conversely, upward loading from contact between the tuberosity and the undersurface of the acromion may also be a contributing factor. 

The risk of acromial fractures is increased by a number of factors that cannot be modified by the surgeon, such as advanced age, female sex,  higher ASA score, poor nutritional status, osteoporosis/osteopenia, inflammatory arthropathy (e.g. rheumatoid arthritis), corticosteroid medication, diabetes, smoking, thinning of the acromion from wear, a diagnosis of cuff tear arthropathy (CTA), diagnosis of massive irreparable cuff tear, prior trauma, prior surgery on the acromion, and prior sectioning of the coracoacromial ligament. 

While the surgeon does determine the implant selection, sizing, positioning, insertion, fixation, distalization, and lateralization, the optimal reverse total shoulder technique remains to be determined because of the myriad of other variables that affect the risk of fracture; analysis of the importance of surgeon-determined variables requires that the study controls for many important variables such as those identified in the previous paragraph.

Here are a few recent articles that are of interest regarding these fractures.

Risk factors of acromial and scapular spine stress fractures differ by indication: a study by the ASES Complications of Reverse Shoulder Arthroplasty Multicenter Research Group found that 1 in 25 patients having RSA sustained an acromial fracture at a minimum of 3 months after surgery. For patients with osteoarthritis the rate was 1 out of 50; for patients with CTA or massive cuff tears that rate was 1 out of 20. While inflammatory arthritis, female sex, and osteoporosis increased the risk, these authors did not identify surgeon-controlled risk factors for acromial fracture.

Acromial Bony Adaptations in Rotator Cuff Tear Arthropathy Facilitates Acromial Stress Fracture Following Reverse Total Shoulder Arthroplasty suggests that (1) cuff tear arthropathy results in adaptive changes in the acromion and (2) the change in acromial loading is more radical when a reverse total shoulder is performed for cuff tear arthropathy than when a RSA is performed for osteoarthritis.

Up to 8mm of Glenoid-Sided Lateralization Does Not Increase the Risk of Acromial or Scapular Spine Stress Fracture Following Reverse Shoulder Arthroplasty With a 135° Inlay Humeral Component looked for surgeon controlled risk fractures for acromial/spine fractures after RSA, which occurred in just over 1 of 20 cases. For the 135 degree inlay component used, glenoid-sided lateralization was not associated with fracture risk. In contrast too other studies, these authors found no relationship between patient age, sex, preoperative acromial thinning, or diagnosis and risk of fracture. They did note that greater preoperative to postoperative change in acromiohumeral distance increased the fracture risk: for every centimeter increase, there was a 121% increased risk for fracture.

See also Acromial stress fracture after reverse total shoulder - does component geometry matter?

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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).

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