Monday, February 2, 2015

Posteriorly augmented glenoid components - computing how much bone is lost on insertion

Augmented glenoid component designs for type B2 erosions: a computational comparison by volume of bone removal and quality of remaining bone

These authors used a computational modeling was to compare the volume of glenoid bone that would need to be removed in the implantation of three different designs of posteriorly augmented glenoid components in the management of B2 genoid erosion. They 'virtually implanted' a full-wedge, a posterior-wedge, and a posterior-step in 3-D reconstructions of 16 patients with B2 glenoids, correcting retroversion to 0° and 10°.

Importantly the amount of bone removed with these implants ranged from 1500 to 3000 cubic millimeters. When correcting to 0°, the posterior-wedge implant removed less bone than the posterior-step and the full-wedge. 

The residual glenoid bone density with the posterior-wedge was significantly greater than with the posterior-step.

Comment: This is an interesting study, suggesting that bone removal is necessary for fitting posteriorly augmented glenoids to the pathoanatomy encountered in glenohumeral arthritis. 

Their implant fitting was virtual and not actual: implants could be manipulated to rotate (clockwise/ counterclockwise and superoinferior) and to translate (anteroposterior and superoinferior). The instrumentation for fitting the glenoid bone to the back of the glenoid component would seem to be quite complex. While the authors suggest that it would be best to use computerized
preoperative planning software making use of 3D CT-based models of the glenoid with properly sized implants, the problem of developing instrumentation to implement the plan remains.

While the authors conclude that " Augmented components can provide a bone-preserving option for B2 glenoid management." that statement is only correct if B2 glenoid management involves correction of retroversion. Our approach is manage the B2 glenoid by conservatively reaming only enough to convert the biconcavity to a single concavity without attempting to change version. See also this related article. this one, and this one as well.

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