Effect of Bone Density and Lesser Tuberosity Osteotomy on Stemmed and Stemless Shoulder Arthroplasty Stability: A Biomechanical Study.

Abstract

Stemless anatomic total shoulder arthroplasty (aTSA) is a popular option for glenohumeral arthritis. There is a minimal literature addressing how bone mineral density (BMD) or performing a lesser tuberosity osteotomy (LTO) during the surgical exposure affects stemless aTSA micromotion. There is concern that performing an LTO compromises stemless implant fixation in patients with low BMD. The purpose of this study is to assess if performing an LTO in patients with lower BMD compromises stemless aTSA stability. Three different implants were included: a 130-mm stemmed implant, Stemless-A, and Stemless-B. Eighteen matched cadaveric humeral samples (36 total) stripped of all soft-tissue attachments were randomized to one of three implant cohorts (6 pairs, 12 total samples per cohort), with one sample of each pair undergoing an LTO versus no LTO (control). Dual-energy x-ray absorptiometry was used to determine BMD. To assess for micromotion, implants were placed onto a biaxial biomechanical testing device, loaded to 220, 520, and 820-Newton forces, and then underwent torsional stress to failure. There were no differences in baseline demographics. Increased micromotion at 820 N axial load (p < 0.001) and reduced torsional stability (p < 0.001) was seen in stemless versus stemmed implants. Performing an LTO did not incur increased micromotion regardless of implant type. Regression analysis demonstrated that decreased BMD led to increased instability amongst all implants regardless of age, gender, or LTO (p < 0.001). Our findings demonstrate that an LTO can be performed safely regardless of implant choice, with BMD remaining the principal factor in implant selection.