Reverse total shoulder: does prior acromioplasty increase the risk of acromial fracture?

 Incidence and risk factors of acromial fracture following reverse total shoulder arthroplasty

These authors sought to determine the incidence and risk factors for acromial fractures after reverse total shoulder (RTSA), comparing 29 patients with acromial fracture and 758 without this complication (3.7% incidence).

Acromial fractures were detected at a mean of 10.0 months (range 1-66) postoperatively. The occurrence of an acromial fracture was associated with a previous operation, deltoid lengthening, and low bone mineral density.

Eleven cases with postoperative acromial fractures had a history of a shoulder operation (rotator cuff repair with acromioplasty in 8, infection control surgery for pyogenic arthritis in 2, and total shoulder arthroplasty in 1).

Acromioplasty thins the acromion, making it more susceptible to fracture. Secondly, acromioplasty involves transection of the coracoacromial ligament, which, as shown in the article below, increases strain on the scapular spine.

Scapular Ring Preservation: Coracoacromial Ligament Transection Increases Scapular Spine Strains Following Reverse Total Shoulder Arthroplasty

Stating that the coracoacromial ligament (CAL) is often transacted during surgical exposure for reverse total shoulder arthroplasty (RSA), these authors hypothesized that the CAL contributes to the structural integrity of the “scapular ring” and that the transection of this ligament during RSA alters the scapular strain patterns in a way that may contribute to scapular fractures following this procedure.

They performed RSA on 8 cadaveric specimens and measured strains at the acromion and scapular spine before and after CAL section while a shoulder simulator positioned the joint in 0, 30, and 60 of glenohumeral abduction.

With the CAL intact, there was no significant difference between strain experienced by the acromion and scapular spine at 0, 30, and 60 of glenohumeral abduction. 

CAL transection generated significantly increased strain in the scapular spine at all abduction angles compared with an intact CAL. 

They concluded that the  CAL is an important structure that completes the “scapular ring” and therefore serves to help distribute strain in a more normalized fashion. 

In his 1934 book, E. A. Codman wrote prophetically, "The coracoacromial ligament has an important duty and should not be thoughtlessly divided at any operation."

We have not found it necessary to divide the CAL "at any operation." Not only is it a halyard stabilizing the scapular spine and acromion to the robust coracoid process, as suggest by this study, but it is also an essential element of the stabilizing coracoacromial arch.

which, when sacrificed, risks anterosuperior escape

which, in turn, is one of the reasons for performing a reverse total shoulder. 

So, we agree with Codman, "The coracoacromial ligament has an important duty and should not be thoughtlessly divided at any operation."

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