David R Walker1, Allison L Kinney2, Thomas W Wright3, Scott A Banks1. 1. Department of Mechanical Engineering, University of Florida, Gainesville, FL, USA. 2. Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA. 3. Orthopaedics and Sports Medicine Institute, University of Florida, Gainesville, FL, USA. Electronic address: wrightw@ortho.ufl.edu.
Abstract
BACKGROUND: Reverse total shoulder arthroplasty commonly treats cuff-deficient or osteoarthritic shoulders not amenable to rotator cuff repair. This study investigates deltoid moment arm sensitivity to variations in the joint center and humeral offset of 3 representative reverse total shoulder arthroplasty subjects. We hypothesized that a superior joint implant placement may exist, indicated by muscle moment arms, compared with the current actual surgical implant configuration. METHODS: Moment arms for the anterior, lateral, and posterior aspects of the deltoid muscle were determined for 1521 perturbations of the humeral offset location away from the surgical placement in a subject-specific musculoskeletal model with motion defined by subject-specific in vivo abduction kinematics. The humeral offset was varied from its surgical position ±4 mm in the anterior/posterior direction, ±12 mm in the medial/lateral direction, and -10 to 14 mm in the superior/inferior direction. RESULTS: The anterior deltoid moment arm varied in humeral offset and center of rotation up to 20 mm, primarily in the medial/lateral and superior/inferior directions. The lateral deltoid moment arm varied in humeral offset up to 20 mm, primarily in the medial/lateral and anterior/posterior directions. The posterior deltoid moment arm varied up to 15 mm, primarily in early abduction, and was most sensitive to humeral offset changes in the superior/inferior direction. DISCUSSION: High variations in muscle moment arms were found for all 3 deltoid components, presenting an opportunity to dramatically change the deltoid moment arms through surgical placement of the reverse shoulder components and by varying the overall offset of the humerus. LEVEL OF EVIDENCE: Basic Science Study; Computer Modeling.
BACKGROUND: Reverse total shoulder arthroplasty commonly treats cuff-deficient or osteoarthritic shoulders not amenable to rotator cuff repair. This study investigates deltoid moment arm sensitivity to variations in the joint center and humeral offset of 3 representative reverse total shoulder arthroplasty subjects. We hypothesized that a superior joint implant placement may exist, indicated by muscle moment arms, compared with the current actual surgical implant configuration. METHODS: Moment arms for the anterior, lateral, and posterior aspects of the deltoid muscle were determined for 1521 perturbations of the humeral offset location away from the surgical placement in a subject-specific musculoskeletal model with motion defined by subject-specific in vivo abduction kinematics. The humeral offset was varied from its surgical position ±4 mm in the anterior/posterior direction, ±12 mm in the medial/lateral direction, and -10 to 14 mm in the superior/inferior direction. RESULTS: The anterior deltoid moment arm varied in humeral offset and center of rotation up to 20 mm, primarily in the medial/lateral and superior/inferior directions. The lateral deltoid moment arm varied in humeral offset up to 20 mm, primarily in the medial/lateral and anterior/posterior directions. The posterior deltoid moment arm varied up to 15 mm, primarily in early abduction, and was most sensitive to humeral offset changes in the superior/inferior direction. DISCUSSION: High variations in muscle moment arms were found for all 3 deltoid components, presenting an opportunity to dramatically change the deltoid moment arms through surgical placement of the reverse shoulder components and by varying the overall offset of the humerus. LEVEL OF EVIDENCE: Basic Science Study; Computer Modeling.
Authors: Albert Ferrando; Luis Natera; Berta Buch; Paolo Consigliere; Juan Bruguera; Giuseppe Sforza; Ehud Atoun; Ofer Levy Journal: Eur J Orthop Surg Traumatol Date: 2020-10-22
Authors: Helen Razmjou; Varda van Osnabrugge; Mark Anunciacion; Andrea Nunn; Darren Drosdowech; Ania Roszkowski; Analia Szafirowicz; Dragana Boljanovic; Amy Wainwright; Diane Nam Journal: J Shoulder Elb Arthroplast Date: 2021-07-01
Authors: Peter N Chalmers; Spencer R Lindsay; Weston Smith; Jun Kawakami; Ryan Hill; Robert Z Tashjian; Jay D Keener Journal: J Shoulder Elbow Surg Date: 2020-07-23 Impact factor: 3.019