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Thoracohumeral muscle activity alters glenohumeral joint biomechanics during active abduction
Author(s) -
Konrad Gerhard G.,
Jolly John T.,
Labriola Joanne E.,
McMahon Patrick J.,
Debski Richard E.
Publication year - 2006
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.20062
Subject(s) - biomechanics , shoulder joint , joint stability , kinematics , medicine , joint (building) , anatomy , deltoid curve , latissimus dorsi muscle , pectoralis muscle , orthodontics , physical medicine and rehabilitation , structural engineering , physics , alternative medicine , pathology , classical mechanics , engineering
Normal function of the glenohumeral joint depends on coordinated muscle forces that stabilize the joint while moving the shoulder. These forces can either provide compressive forces to press the humeral head into the glenoid or translational forces that may destabilize the glenohumeral joint. The objective of this study was to quantify the effect of pectoralis major and latissimus dorsi muscle activity on glenohumeral kinematics and joint reaction forces during simulated active abduction. Nine fresh‐frozen whole upper extremities were tested using a dynamic shoulder testing apparatus. Seven muscle force combinations were examined: a standard combination and 10%, 20%, or 30% of the deltoid force applied to the latissimus dorsi or pectoralis major tendon, respectively. Pectoralis major and latissimus dorsi muscle activity decreased the maximum angle of glenohumeral abduction and external rotation, and increased the maximum horizontal adduction angle compared to the standard muscle combination. Thoracohumeral muscle activity also created a more anteriorly directed joint reaction force that resulted in anterior translation compared to the standard muscle combination. Therefore, the ratio between anteriorly directed translational forces and compressive forces increased during abduction due to this muscle activity, suggesting that thoracohumeral muscle activity may decrease glenohumeral stability based on the joint position and applied loads. A better understanding of the contribution of muscle forces to stability may improve rehabilitation protocols for the shoulder aimed at maximizing compression and minimizing translation at the glenohumeral joint. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res