Humeral head translation decreases with muscle loading

• Published in: Journal of shoulder and elbow surgery 2008, Vol.17 (1), p.132-138
• Main Authors: Kedgley, Angela E., MESc, Mackenzie, Geoffrey A., BESc, Ferreira, Louis M., BSc, BESc, Drosdowech, Darren S., MD, FRCSC, King, Graham J.W., MD, MSc, FRCSC, Faber, Kenneth J., MD, MHPE, FRCSC, Johnson, James A., PEng, PhD
• Format: Article
• Language: English
• Subjects: Aged; Biological and medical sciences; Biomechanical Phenomena; Cadaver; Female; Fundamental and applied biological sciences. Psychology; Humans; Humerus - physiology; Male; Middle Aged; Muscle, Skeletal - physiology; Orthopedics; Shoulder Joint - physiology; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2007.03.021

This study was conducted to determine the effect of in vitro passive and active loading on humeral head translation during glenohumeral abduction. A shoulder simulator produced unconstrained active abduction of the humerus in 8 specimens. Loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and anterior, middle, and posterior deltoid muscles was simulated by use of 4 different sets of loading ratios. Significantly greater translations of the humeral head occurred both in 3 dimensions (P < .001) and in the sagittal plane (P < .005) during passive motion when compared with active motion from 30° to 70° of abduction. In the sagittal plane, passive abduction experienced a resultant translation of 3.8 ± 1.0 mm whereas the active loading ratios averaged 2.3 ± 1.0 mm. There were no significant differences in the translations that were produced by the 4 sets of muscle-loading ratios used to achieve active motions. This study emphasizes the importance of the musculature in maintaining normal ball-and-socket kinematics of the shoulder.