A human shoulder simulator for cyclic evaluation of rotator cuff injury and repair

Background/Objectives: Surgical repair of the rotator cuff tendons can lead to unsatisfactory results and the requirement for further surgical treatment. Development of repair techniques is limited by a lack of appropriate functional pre-clinical testing, especially over extended motion cycles. The purpose of this study was to demonstrate the efficacy of a novel shoulder simulator by assessing changes in internal muscle forces following a rotator cuff tear and double-row surgical repair. Methods: The developed shoulder simulator used motors to apply controlled movements/displacements to tendons (supraspinatus, infraspinatus, subscapularis, teres minor, anterior deltoid and middle deltoid) of a cadaveric human shoulder to produce cyclic abduction motion representative of normal shoulder function. The required displacement for each muscle was determined using a musculoskeletal model. The resultant force applied to each tendon during the cycles was measured using a compression load cell. Results: The developed simulator in this proof-of-concept study enabled the contribution of the different muscles involved in the shoulder during abduction to be assessed for the intact shoulder. The shoulder was also tested with a 50% supraspinatus tear and a double row surgical repair of the supraspinatus to assess the change in internal muscle forces. Conclusions: The study indicated that successful cyclic testing of cadaveric samples could be achieved using the simulator and changes in the internal muscle forces of the shoulder were identified following a supraspinatus tear and double-row surgical repair.