Sunday, July 26, 2015

Reverse total shoulder - lateral offset of the glenoid component - is bone graft best?

Bony Increased-Offset Reverse Shoulder Arthroplasty

In the abstract of this article, the authors state "Reverse shoulder arthroplasty has proven useful in numerous pathologic conditions, such as that of pseudoparalytic shoulder with severe rotator cuff deficiency with or without collapse (so-called cuff-tear arthropathy), rheumatoid arthritis, dislocations and sequelae of proximal humerus fractures, and revision shoulder arthroplasty. Despite the advances beyond the constrained reverse prostheses of the 1970s resulting from Grammont’s principles, problems remain with current systems, with high rates of scapular notching and prosthetic instability. Lateralization of the center of rotation of the shoulder joint has been viewed as a potential solution to these persistent problems, and is included in the procedure known as bony increased-offset reverse shoulder arthroplasty. This article presents our surgical technique for this procedure and promising early results of its use." The article itself is elegantly presented by the highly experienced shoulder surgeon who has exhibited mastery of this method.

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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