Biomechanical comparison of 2 augmented glenoid designs: an integrated kinematic finite element analysis.

BACKGROUND

Augmented glenoid implants are available to help restore the biomechanics of the glenohumeral joint with excessive retroversion. It is imperative to understand their behavior to make a knowledgeable preoperative decision. Therefore, our goal was to identify an optimal augmented glenoid design based on finite element analysis (FEA) under maximum physiological loading.

METHODS

FEA models of 2 augmented glenoid designs-wedge and step-were created per the manufacturers' specifications and virtually implanted in a scapula model to correct 20° of retroversion. Simulation of shoulder abduction was performed using the FEA shoulder model. The glenohumeral force ratio, relative micromotion, and stress levels on the cement mantle, glenoid vault, and backside of the implants were compared between the 2 designs.

RESULTS

The force ratio was 0.56 for the wedge design and 0.87 for the step design. Micromotion (combination 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.

CONCLUSION

Implant design slightly affects joint stability; however, it plays a major role regarding long-term survival. Overall, the augmented wedge design provides better implant fixation and stress profiles with less micromotion.