Computational modeling of a prosthetic shoulder: our experience with the anybody modeling system

When wear or tear of the rotator cuff becomes non-treatable, the glenohumeral joint degeneration can lead to upper limb pseudoparalysis, hence requiring a shoulder arthroplasty. Data indicating the performance of today's prostheses remain unsatisfactory and unpredictable when studying the case of massive rotator cuff tear (MRCT). Computational modeling represents a promising tool for exploring new prosthesis design possibilities. Nevertheless, no MRCT-simulation with a musculoskeletal software is available in the literature. The AnyBody Modeling System has been used to reproduce the MRCT-shoulder in vitro and then to propose a novel prosthetic design that would facilitate the patient's abduction movements following a MRCT. Results showed that with a lateral addition of 19mm on the humeral head, a deltoid strength lowering event occurred after 10° of abduction, reaching a level of -19% of the initial strength at 59°. This study has allowed for the generation of a new computational model that simulates a MRCT-shoulder, as well as the proposal of a non-anatomical prosthesis design which purpose is to reduce the required middle deltoid strength during abduction.