Tuesday, January 1, 2013

Ream conservatively in shoulder arthroplasty

Glenoid morphology after reaming in computer-simulated total shoulder arthroplasty.

These authors open their article by stating "The most common cause of TSA failure is loosening of the glenoid component." They point out that posterior bone loss and retroversion are common features of glenohumeral osteoarthritis and that these characteristics complicate the secure and durable placement of a glenoid component. They indicate that preservation of glenoid bone stock, correction of glenoid version and maximization of glenoid component-glenoid bone contact may be competing priorities

This paper emphasizes the hazards of zealous attempts to normalize glenoid version by reaming. They used computer models from computed tomography scans of patients with advanced osteoarthritis. Computer-simulated reaming was performed to study the effect of  reaming depth, reamer placement, and version correction. They found that reamed surface area significantly increased with larger depths of reaming and smaller amounts of initial glenoid retroversion. Bone volume removed was related to reaming depth. They concluded that smaller amounts of initial glenoid retroversion allow for greater implant-bone surface contact.

Glenoid retroversion is common in patients needing shoulder arthroplasty. As we've pointed out in previous posts and as shown in the figure below, are also concerned about the amount of bone removed in trying to 'correct' a retroverted glenoid (upper two figures). For that reason we often choose to ream in retroversion to preserve glenoid bone stock (lower two figures), finding that preserving bone stock and achieving good component-bone contact produce a stable reconstruction.  Paradoxically, shoulders managed this way have greater glenohumeral stability than those in which version is 'corrected'.


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