These authors compared two augmented glenoid implants (wedge and step) using finite element analysis (FEA) under maximum physiological loading.
Models of the implants were virtually implanted in a scapula model to correct 20° of retroversion. Simulation of shoulder abduction was performed using the FEA shoulder model.
The force ratio was 0.56 for the wedge design and 0.87 for the step design. Micromotion (com- bination of distraction, translation, and compression) was greater for the step design than the wedge design. Distraction measured 0.05 mm for the wedge design and 0.14 mm for the step component. Both implants showed a similar pattern for translation; however, compression was almost 3 times greater for the step component. Both implants showed high stress levels on the cement mantle. At the glenoid vault and on the implants, the stress levels were 1.65 MPa and 6.62 MPa, respectively, for the wedge design and 3.78 MPa and 13.25 MPa, respectively, for the step design.
The authors concluded that the augmented wedge design provides better implant fixation and stress profiles with less micromotion.
Comment: While this model did show differences in load characteristics between the two components, we cannot be sure how these results relate to the clinical situation or, more importantly, how these load characteristics compare to those of non-augmented components. It is of note that both designs require extra polyethylene to provide the restraint to translation that is normally provided in vivo by soft tissues, muscle forces, and glenoid anatomy. The clinical benefit and survivorship of these implants in comparison to standard implants has yet to be determined.
For some types of implant there is a concern about the amount of bone that is removed during insertion (see below).
In viewing the example of an "average type B2 glenoid" shown in this article (see below), this pathology is typical of what we routinely manage with a standard (non-augmented) glenoid component.
In the introduction, the article states, "Augmented glenoid implants are available to help restore the biomechanics of the glenohumeral joint with excessive retroversion". Do the images above show a shoulder with "excessive retroversion"?
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