The authors performed a prospective study in 42 patients with rotator cuff deficiency to determine whether BIO-RSA would avoid the problems caused by humeral medialization. At a minimum follow-up of 2 years (average, 28 months), 39 of 42 patients (93%) were satisfied or very satisfied with its functional results; 32 of the 42 patients (76%) had good or excellent adjusted Constant-Murley scores. There were no cases of loosening of the glenoid component of the prosthesis. The graft bone used with the prosthesis was observed to have healed to the glenoid in 41 of the 42 patients (98%) on follow-up examination with radiography and CT scanning. Scapular notching occurred in 19% (8 of 42) of the patients. There were no instances of instability of the prosthesis and no instances of reoperation.
Comment: In the early days of the reverse, surgeons avoided lateral offset because of concerns about the loosening moments applied to the glenosphere and a desire to optimize the deltoid moment arm. However, medial placement of the glenosphere is now recognized to risk contact between the medial aspect of the humeral component and the inferior glenoid which can lead to notching and instability. As a result, surgeons are using one of two methods for lateralizing the center of rotation:
(1) the bony increased-offset reverse shoulder arthroplasty described in this article
and (2) glenoid components with a built-in lateral offset.
In both instances, the lateralized center of rotation places additional demands on the fixation of the glenoid component to the scapula. Our preference is for glenoid components with a built-in lateral offset as described here and here because (a) the fixation does not depend on healing of a bone graft, (b) the quality of bone available for a bone graft is variable in patients having primary reverse total shoulders, (c) bone graft from the humeral head is not available in revision arthroplasty, (d) the operative time and special instruments for bone graft harvest are eliminated and (e) the central screw can be tightened to compress the glenoid component on the bone of the glenoid without worry of crushing the graft.
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