Sunday, June 17, 2018

What is the optimal position of a reverse total shoulder?

The lateralization and distalization shoulder angles are important determinants of clinical outcomes in reverse shoulder arthroplasty. 

These authors sought to determine the effect of reverse total shoulder (RSA) lateralization and distalization on final functional outcomes.

They measured the “distalization shoulder angle” (DSA)

 and the  “lateralization shoulder angle” (LSA).

in 46 patients who underwent RSA. Functional outcome and radiographs were evaluated at a minimum of 2 years postoperatively.

LSA values between 75° and 95° were correlated with better active external rotation. Postoperative active anterior elevation, Constant, and Activities of Daily Living Requiring External Rotation scores had a positive correlation with the LSA.

DSA between 40° and 65° resulted in better active anterior elevation and abduction.

However there was a lot of scatter in the data

They looked at four groups of prosthetic techniques

With the exception of the low active external rotation in Group I, there were no discernible differences in outcome among the groups.

Comment: The position of the humerus relative to the scapula after reverse total shoulder arthroplasty is determined by the prosthesis selected and the position in which it is inserted. The classical Grammont approach emphasized medialization and distalization. As shown in the diagrams below by Steve Lippitt, medialization (middle figure below) can slacken the rotators resulting in the loss of active external rotation noted in this study.

More modern approaches emphasize a more anatomic reconstruction with less distalization and more lateralization as shown below.

While the two angles described in this study are of interest, we find it simpler to measure distalization directly as shown here
 and lateralization directly as shown here

Finally, since instability is one of the most common complications of reverse total shoulder arthroplasty,    it is important to prioritize the component geometry and the component position that optimizes the stability for each patient.

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