Sunday, November 2, 2014

Glenosphere offset in reverse total shoulder - how to get it and does it matter?

Does bony increased-offset reverse shoulder arthroplasty decrease scapular notching?

A principle of the Grammont-style reverse shoulder is that the hemispherical glenosphere would be placed directly on the prepared face of the bony glenoid. The rationale was that the medial placement of the center of rotation would maximize the deltoid lever arm and minimize the loosening moment on the glenoid fixation.

Subsequently there has been interest in having a lateral offset center of rotation for the glenosphere. The rationale is to minimize notching and to increase stability by East-West tensioning. Offset can be achieved either by using glenosphere components with a neck

 or by placing a bone graft between the glenosphere and the glenoid bone (bony increased-offset reverse shoulder arthroplasty, or BIO-RSA).

These authors compared scapular notching rates, range of motion, and functional outcomes between 20 patients who underwent a standard Grammont-style reverse shoulder arthroplasty and 20 similar patients who underwent bony increased-offset reverse shoulder arthroplasty.

The range of motion and outcome scores were not significantly different between the two groups. However, the frequency of scapular notching was significantly higher in the standard reverse total shoulder cohort than in the BIO-RSA cohort: 75% versus 40%.

Comment: At an average followup of just under 3 years, the use of BIO-RSA lessened the notching rate. The 3 year clinical outcomes were not significantly different. The long term effects of notching have yet to be determined, but contact between the lateral scapula and the humeral polyethylene cannot be a good thing. Intuitively, it makes sense to avoid undesired contact between the humeral component and the scapula in reverse total shoulder. Notching has to be important. We've previously posted on the effects of a lateral offset (see this link). 

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