Advisor(s)

Alan Eberhardt

Committee Member(s)

David Littlefield
Eugene Brabston

Document Type

Thesis

Date of Award

6-1-2026

Degree Name

Master of Science in Biomedical Engineering (MSBME)

School

Joint Health Sciences (Interdisciplinary)

Department

Biomedical Engineering

Abstract

This study compared a standard‑post baseplate with a threaded‑post baseplate in reverse total shoulder arthroplasty (rTSA) to determine whether threaded central fixation improves micromotion and stress distribution. A finite element model of a left scapula with a commercially available rTSA system was created; the two designs differed only by the central post (standard press‑fit versus threaded). A 756 N physiological load was applied at 60°, 90°, and 120° of abduction. Outcomes included total and directional relative micromotion at the bone–implant interface and von Mises stress in the glenoid and baseplate. Total micromotion remained below the 150 µm osseointegration threshold for both designs. At 60° and 120°, the threaded-post significantly reduced mean total micromotion (60°: 13.80 µm versus 18.37 µm, p < 0.001; 120°: 15.41 µm versus 16.46 µm, p < 0.001). Directional displacements were also lower with the threaded-post, especially lateral pull‑away (60°: 1.62 µm versus 7.2 µm; 120°: 0.53 µm versus 9.5 µm). Stress in the glenoid and baseplate was consistently lower and more uniformly distributed with the threaded design. At 90°, no significant differences were observed. The threaded‑post baseplate provided superior fixation under shear‑dominant loading, reducing micromotion and stress while maintaining more uniform load distribution. These findings support the use of a threaded central post to enhance initial stability and potentially improve long‑term osseointegration in rTSA; however, the threaded post may be best reserved for patients with high functional demands, poor bone quality, or when revision arthroplasty is anticipated, as the added operative time and technical precision required for rotational alignment may outweigh its biomechanical benefits in lower‑risk patients.

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