Posterior augmented glenoid implants require less bone removal and generate lower stresses: a finite element analysis.

Hypothesis: Glenoid retroversion can be corrected with standard glenoid implants after anterior-side asymmetric reaming or by using posterior augmented glenoid implants with built-in corrections. The purpose of this study was to compare 2 augmented glenoid designs with a standard glenoid design, measure the amount of bone removed, and compute the stresses generated in the cement and bone.

Methods: Finite element models of 3 arthritic scapulae with varying severities of posterior glenoid wear were each implanted with 4 different implant configurations: standard glenoid implant in neutral alignment with asymmetric reaming, standard glenoid implant in retroversion, glenoid implant augmented with a posterior wedge in neutral alignment, and glenoid implant augmented with a posterior step in neutral alignment. The volume of cortical and cancellous bone removed and the percentage of implant back surface supported by cortical bone were measured. Stresses and strains in the implant, cement, and glenoid bone were computed.

Results: Asymmetric reaming for the standard implant in neutral version required the most bone removal, resulted in the lowest percentage of back surface supported by cortical bone, and generated strain levels that risked damage to the most bone volume. The wedged implant removed less bone, had a significantly greater percentage of the back surface supported by cortical bone, and generated strain levels that risked damage to significantly less bone volume.

Conclusions: The wedged glenoid implants appear to have various advantages over the standard implant for the correction of retroversion.

Level Of Evidence: Basic Science Study; Computer Modeling.