The effect of adjusting the baseplate size to the glenoid on primary fixation stability in reverse total shoulder arthroplasty: a finite element analysis

BACKGROUND: The optimal baseplate size for reverse shoulder arthroplasty in patients with varying glenoid dimensions remains controversial. In this study, we evaluated the biomechanical effects of adjusting baseplate size to different glenoid dimensions on primary fixation stability and analyzed the structural relationship between the baseplate and glenoid. METHODS: We evaluated the primary fixation stability and structural relationship of glenoid components with two circular baseplate sizes (25 mm vs. 29 mm) in different glenoid sizes (small vs. large) using finite element analysis. Three-dimensional finite element models were constructed from 14 cadaveric scapulae and glenoid components with 25‑ and 29‑mm baseplates. The relative micromotion of the bone-baseplate interface at measurement points 1-4, bone stress distribution under the baseplate and around the screws, contact surface area between bone and the baseplate back surface, contact surface area between bone and screws, and length of supporting bone stock (LSBS) for screws were analyzed. RESULTS: In small glenoids, relative micromotion and maximum bone stress were significantly greater with the 29‑mm baseplate than with the 25‑mm baseplate. Bone-screw contact surface and LSBS for anterior and posterior screws were significantly greater with the 25‑mm baseplate. In large glenoids, there were no significant differences between baseplate sizes. CONCLUSIONS: Compared with the 29‑mm baseplate, the 25‑mm baseplate improved primary fixation stability in small glenoids through increased bone-screw contact and LSBS of the anterior and posterior screws. In the large glenoid, baseplate size did not significantly affect the primary fixation stability of the glenoid component. In the small glenoid, adjusting the baseplate size using a small baseplate matching the anatomical size may improve primary fixation stability of the glenoid component. Optimizing bone-screw contact and LSBS is critical for baseplate stability in the small glenoid. However, adjusting the baseplate size to the glenoid does not affect the primary fixation stability in the large glenoid with sufficient bone stock. Baseplate size can be selected with greater flexibility in the large glenoid without compromising primary fixation stability.