Tuesday, July 12, 2016

Reverse total shoulder -- a review what's been published

Current Controversies in Reverse Total Shoulder Arthroplasty

These authors conducted a review of the literature in search of guidance on optimizing the application of reverse total shoulder arthroplasty.

They concluded that 
(1) glenospheres with a Grammont-style prosthesis (medialized center of rotation) have historically decreased glenosphere loosening but increase scapular notching. 

Components with  lateralized center of rotation decrease notching and improve range of motion but historically have resulted in increased baseplate failure. 

(2) inferior placement of the glenosphere increases internal rotation, external rotation, abduction, and adduction while reducing notching. Superior baseplate positioning and tilt are correlated with baseplate failure. In the example below, as a result of superior angulation of the baseplate the inferior screw was not placed in bone, resulting in baseplate failure as pointed out in this link: "the screw nearest the point of load application made the largest contribution. Load to failure was less when the load was colinear with a line through the nonlocking holes in the base plate compared to colinear with a line through the locking holes. In performing a reverse total shoulder, surgeons should emphasize secure intraosseous placement of the fixation screws in the best quality bone available. The placement of the inferior screw appears to be the most critical".

(3) humeral prostheses with a  humerosocket inclination angle of 135° (below right) appear to have a lower rate of scapular notching than the Grammont-style 155° humerosocket inclination angle (below left).  

They point to the risk of glenosphere dissociation from the base plate.
They mention the use of bone graft to achieve glenosphere offset with a Grammont-style prosthesis

However the advantage of bone graft over a prosthesis with built in offset (see below) is unclear.

Our approach to reverse total shoulder arthroplasty is shown in this link. Our goal, whenever possible, is a cementless impaction grafted humeral stem with a 135 degree angle and a laterally offset glenopshere securely fixed with screws in the high quality bone at the base of the subscapularis fossa with minimal inferior placement to avoid excess tension on the acromion and the brachial plexus.


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