Reverse total shoulder: avoiding notching

 Clinical and radiological outcomes of eccentric glenosphere versus concentric glenosphere in reverse shoulder arthroplasty

Scapular notching is an important complication of reverse total shoulder arthroplasty

It results from unwanted contact between the humeral polyethylene and the neck of the scapula

These authors conducted a retrospective analysis of 49 reverse total shoulders with an inferiorly eccentric glenoid (EG) and 49 RSAs with a concentric glenoid (CG) at a minimum 60 months. Notching was observed 2.7 times more often in the CG group (p=0.040). However the notching severity was not statistically relevant between the groups.

 Compared to a CG, an EG did not increase the percentage of radiolucent lines around the screws,

As pointed out be the authors, the eccentric glenosphere reduces the risk of notching by moving the humerus further distally away from the scapular neck.

Moving the humerus distally can result in a relatively un-anatomic reconstruction with increase tension on the deltoid, acromion and brachial plexus.

   

An alternative method for minimizing the risk of notching is to use a glenosphere with an extended neck  that moves the humeral component laterally (rather than inferiorly) away form the the scapular neck resulting in a more anatomic reconstruction.

Some designs of RSA create a major disruption of the normal anatomic relationships of the shoulder while others do not (see this link).  One way to look at this is to consider the arch created by the medial aspect of the humerus and the lateral aspect of the scapula. This arch can be referred to as "Bani's line", described in 1981 (Bandi W Die Läsion der Rotatorenmanschette. Helv Chir Acta 48:537-549). 

 

Some approaches create minimal disruption of the arch (i.e. a more "anatomic" reverse)

While other approaches create greater disruption of the normal relationships as indicated by the break in the arch.

If the arch is disrupted, several things happen: (1) increased stress is put on the acromion and scapular spine leading to an increased risk of acromial and scapular spine fractures, (2) increase stress is placed on the brachial plexus, and (3) the normal alignment of residual infraspinus and subscapularis is disrupted.

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