Monday, June 17, 2013

Fixation of the glenoid component - preserve cortical bone!

Glenoid implant orientation and cement failure in total shoulder arthroplasty: a finite element analysis.

The authors propose that the risk glenoid implant loosening is minimized by correction to neutral version, complete implant-bone contact, and bone stock preservation. While the second and third of these make good sense, the value of correction of glenoid version to neutral has yet to be proven in robust clinical studies. 

The authors created computer models for homogeneous cortical bone and for heterogeneous cortical-trabecular bone model. They predicted the risk of cement mantle fracture when a 750-N load was applied.

Basically the question here is how to manage a retroverted glenoid. Does one place the glenoid component on the cortical bone without attempting to 'correct' the version:

Or does one 'correct' the version by reaming the anterior bone into the cancellous bone:

In the heterogeneous bone model (which most closely represents what we see clinically), complete correction resulted in the highest risk of failure. A positive correlation was found between the risk of cement failure and amount of exposed trabecular bone.

So the lesson from this model seems to be 'preserve cortical bone'.
There may be another lesson as well. Since the model measured failure by the stress in the cement mantle beneath the face of the component (shown in red above), it seems preferable to avoid cement between the plastic and the bone and, instead, achieve bone-prosthesis contact by careful reaming to fit the back of the component. Our method is shown here.

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