Stemless reverse humeral component neck-shaft angle has an influence on initial fixation

• Published in: Journal of shoulder and elbow surgery Vol. 33; no. 1; pp. 164 - 171
• Main Authors: Cunningham, David E, Spangenberg, Gregory W, Langohr, G Daniel G, Athwal, George S, Johnson, James A
• Format: Journal Article
• Language: English
• Published: United States 01.01.2024
• Subjects: Activities of Daily Living; Arthroplasty, Replacement; Arthroplasty, Replacement, Shoulder; Humans; Humeral Head - surgery; Prosthesis Design; Shoulder Joint - diagnostic imaging; Shoulder Joint - surgery; neck shaft angle; Stemless; reverse shoulder arthroplasty; finite element; arthroplasty; cuff tear arthropathy; implant design
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2023.06.035

Stemless anatomic humeral components are commonly used and are an accepted alternative to traditional stemmed implants in patients with good bone quality. Presently, little literature exists on the design and implantation parameters that influence primary time-zero fixation of stemless reverse humeral implants. Accordingly, this finite element analysis study assessed the surgical implantation variable of neck-shaft angle, and its effect on the primary time-zero fixation of reversed stemless humeral implants. Eight computed tomography-derived humeral finite element models were used to examine a generic stemless humeral implant at varying neck-shaft angles of 130°, 135°, 140°, 145°, and 150°. Four loading scenarios (30° shoulder abduction with neutral forearm rotation, 30° shoulder abduction with forearm supination, a head-height lifting motion, and a single-handed steering motion) were employed. Implantation inclinations were compared based on the maximum bone-implant interface distraction detected after loading. The implant-bone distraction was greatest in the 130° neck-shaft angle implantation cases. All implant loading scenarios elicited significantly lower micromotion magnitudes when neck-shaft angle was increased (P = .0001). With every 5° increase in neck-shaft angle, there was an average 17% reduction in bone-implant distraction. The neck-shaft angle of implantation for a stemless reverse humeral component is a modifiable parameter that appears to influence time-zero implant stability. Lower, more varus, neck-shaft angles increase bone-implant distractions with simulated activities of daily living. It is therefore suggested that humeral head osteotomies at a higher neck-shaft angle may be beneficial to maximize stemless humeral component stability.