Superior glenoid inclination in shoulder arthroplasty: a comparison of standard to superiorly augmented glenoid implants.

BACKGROUND

The success of anatomic total shoulder arthroplasty depends on glenoid component stability, with loosening responsible for nearly half of revision surgeries. Superior glenoid inclination exacerbates component loosening by promoting unbalanced loading by the humeral head. This study investigates a novel superiorly augmented glenoid component designed to correct excessive superior inclination. We hypothesized that increasing augmentation would limit superior humeral head migration and asymmetric loading, thereby increasing compressive rather than tensile stresses at the implant-bone interface.

METHODS

Finite element models of 8 scapulae with glenohumeral osteoarthritis were fitted with a standard 4-peg component and 3 superiorly augmented components (5°, 10°, and 15° augment angles). Loads angled 25° inferiorly to 25° superiorly were applied. Outcomes included superior-inferior humeral head position and implant-bone interface stresses.

RESULTS

For every 5° increase in augmentation, the humeral head translated inferiorly by 0.4 ± 0.1 mm for the 15° native inclination group, 0.3 ± 0.1 mm for 10°, and 0.2 ± 0.1 mm for 5°. Translations ranged between 0.2 mm and 1.0 mm, consistent with previous findings. The humeral head position in the fully corrected state differed significantly from uncorrected states in each native inclination group (P < .01). The percentage of implant-bone interface area in compression increased by 4.3 ± 0.6% per 5° correction for the 15° native inclination group, 2.6 ± 0.6% for 10°, and 1.8 ± 1.9% for 5°.

DISCUSSION: Superior augmentation restored humeral head centralization and increased the proportion of the implant-bone interface in compression, decreasing liftoff potential and reducing mechanical risk factors for loosening in patients with excessive superior inclination.