Wednesday, April 24, 2013

Reverse total shoulder glenoid fixation

Initial glenoid fixation using two different reverse shoulder designs with an equivalent center of rotation in a low-density and high-density bone substitute

Four of the authors of this paper are employed by Exactech Inc. and a fifth receives royalties from the company that makes the reverse total shoulder design associated with better results in this study.

This study sets out to evaluate initial reverse shoulder glenoid baseplate fixation in 2 reverse shoulder designs having an equivalent center of rotation in low-density and high-density bone substitute materials. There were many differences between the baseplates of the two systems tested (glenoid plate profile, contour of back of baseplate, number of screws, shape of peg, etc).

 The Zimmer design (circularporous reverse shoulder) was associated with approximately twice the micromotion per equivalent test than the Exactech design (oblong-grit-blasted reverse shoulder). Additionally, 6 of the 7 circular-porous reverse shoulders failed catastrophically in the low-density bone model. None of the oblong-gritblasted designs failed in the low-or high-density bone models and none of the circular-porous designs failed in the high-density bone models after 10,000 cycles of loading.

Comment: Perhaps the most important finding in this study is that bone quality is a factor in fixation of the glenoid component in reverse total shoulder leading us to the conclusion that reaming of the precious glenoid bone stock needs to be minimized to preserve as much of the quality bone as possible.  A second observation is that both of the designs tested here depend on bone ingrowth for a substantial part of the fixation - however, bone ingrowth could not be tested in this model system; instead, the study focused on initial glenoid fixation as indicated by 'micromotion' and 'catastrophic failure'.

We have no fiscal interest in an implant system. The system we prefer (shown here) does not depend on ingrowth (which under the best of circumstances takes some time), but rather provides excellent initial fixation from compression of the base plate against the prepared glenoid bone - especially if the glenoid subchondral plate is preserved.


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