Monday, July 22, 2013

The effect of lateral offset and glenosphere size on notching in reverse total shoulder

Evaluation of the role of glenosphere design and humeral component retroversion in avoiding scapular notching during reverse shoulder arthroplasty

The others observe that scapular notching has been noted in 60% of reverse total shoulders at 2 years after surgery. The stated purpose of this study was to evaluate the effect of Aequalis Reversed Shoulder Prosthesis (Tornier) glenosphere design and humeral component retroversion on inferior scapular impingement in 40 cadaver shoulders.

8 different combinations were tested: 36-mm glenosphere: centered (standard), eccentric, with an inferior tilt, or with the center of rotation (COR) lateralized by 5 or 7 mm; and 42-mm centered glenosphere: used alone or with the COR lateralized by 7 or 10 mm.

In comparison to to a 36-mm centered glenosphere, a 42-mm glenosphere, especially when it was lateralized by 10 mm resulted in greater degrees of adduction before contact between the humeral component and the scapula occurred. Positioning of the humeral component in 10° or 20° of retroversion or in anatomical retroversion was also effective at avoiding inferior impingement.

However, the authors point out that the patient suffering from cuff tear arthropathy is often a woman of small stature so that the use of a large-diameter glenosphere may difficult because of its excessive volume.

They conclude that glenoid combinations with a 7- or 10-mm-thick lateralization and a 42-mm glenosphere were most effective at reducing the risk of scapular notching.

While some have advocated lateralization of the glenosphere with a bone graft, the risk of glenoid component loosening is also greater because of higher loads at the glenoid base plate–bone interface and because of the potential for graft failure - especially if it is harvested from an osteoporotic humeral head. 

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