title: Glenohumeral joint reaction forces increase with critical shoulder angles representative of osteoarthritis-A biomechanical analysis.
abstract: Osteoarthritis (OA) of the glenohumeral joint constitutes the most frequent indication for nontraumatic shoulder joint replacement. Recently, a small critical shoulder angle (CSA) was found to be associated with a high prevalence of OA. This study aims to verify the hypothesis that a small CSA leads to higher glenohumeral joint reaction forces during activities of daily living than a normal CSA. A shoulder simulator with simulated deltoid (DLT), supraspinatus (SSP), infraspinatus/teres minor (ISP/TM), and subscapularis (SSC) musculotendinous units was constructed. The DLT wrapping on the humerus was simulated using a pulley that could be horizontally adjusted to simulate the 28° CSA found in OA or the 33° CSA found in disease-free shoulders. Over a range of motion between 6° and 82° of thoracohumeral abduction joint forces were measured using a six-axis load cell. An OA-associated CSA yielded higher net joint reaction forces than a normal CSA over the entire range of motion. The maximum difference of 26.4 N (8.5%) was found at 55° of thoracohumeral abduction. Our model thus suggests that a CSA typical for OA predisposes the glenohumeral joint to higher joint reaction forces and could plausibly play a role in joint overloading and development of OA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1047-1052, 2016.
authors.affiliation: Department of Orthopedics, Balgrist University Hospital, Zürich, Switzerland.
authors.forename: Arnd F
authors.initials: AF
authors.lastname: Viehöfer
authors.affiliation: Department of Orthopedics, Balgrist University Hospital, Zürich, Switzerland.|Institute for Biomechanics, ETH Zurich, Switzerland.
authors.forename: Jess G
authors.initials: JG
authors.lastname: Snedeker
authors.affiliation: Institute of Mechanical Systems Organization, Zurich University of Applied Sciences ZHAW, Winterthur, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Baumgartner
authors.affiliation: Department of Orthopedics, Balgrist University Hospital, Zürich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Gerber
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D010003:Osteoarthritis / Q000503:physiopathology*; D012785:Shoulder Joint / Q000502:physiology*
keywords: biomechanics; critical shoulder angle; etiology; osteoarthritis; shoulder