Friday, October 19, 2012

Glenoid bone loss in primary total shoulder arthroplasty: evaluation and management. JAAOS

Glenoid bone loss in primary total shoulder arthroplasty: evaluation and management. This article, published recently in the JAAOS, nicely describes the various types of glenoid pathoanatomy encounted when we perform shoulder arthroplasty. Again, the authors point out that the #1 complication of total shoulder arthroplasty is glenoid component failure, and suggest that altered glenoid joint reaction forces, glenoid component malposition, and insufficient bone support are contributing factors to this complication. The use the Walch classification to describe glenoid anatomy.

In cases of glenoid retroversion (Walch C) or biconcavity (Walch B2) the conventional wisdom is to 'correct' the version in hopes of stabilizing the humeral head in the glenoid with a 'normalized' orientation. Various authors have used (1) reaming of the anterior glenoid (eccentric reaming), (2) posterior bone grafting, or (3) special glenoid components with a built up posterior segment to help manage these situations, which are commonly encountered in shoulders with osteoarthritis or capsulorrhaphy arthropathy. However, each of these approaches has a downside. Eccentric reaming removes precious glenoid bone. Posterior bone grafting is technically difficult and runs the risk of graft resorption, leaving the component unsupported. Glenoid components with thickened posterior aspects run the risk of cold flow as they attempt to support posteriorly directed humeral joint reaction forces. Furthermore, and perhaps most importantly, as pointed out in an article reviewed in our Sept 26 post, "Glenoid morphology rather than version predicts humeral subluxation: a different perspective on the glenoid in total shoulder arthroplasty".  As we pointed out then, the reason that retroversion is not necessarily associated with subluxation lies in the concavity compression mechanism of glenohumeral stability. As long as the ball is pressed into a suitable concavity, the shoulder is stable. With the biconcave glenoid, however, the humeral head is pressed into the posterior concavity and remains there unless the biconcavity is corrected. 

Apparently some authors have recently advocated using a Reverse Total Shoulder Arthroplasty for Primary Glenohumeral Osteoarthritis with Biconcave Glenoid, but, due to the limitations on physical activity after a reverse shoulder, this would not seem the preferred option for those individuals seeking active use of their shoulder after surgery.

In selected cases, we have taken a different approach. Rather than 'correcting' the retroversion, we have converted the biconcavity to a single concavity through reaming and have stabilized the humeral head prosthesis using soft tissue balancing and possibly eccentric humeral components. Our approach to the correction of posterior humeral subluxation and biconcavity with a ream and run is shown in this post. This technique minimizes the amount of bone removed by reaming and avoids the risks of glenoid bone grafting and glenoid component failure and avoids the activity limitations associated with a reverse total shoulder. 

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