Affiliations: Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA, 01748, USA. Tel.: +1 508 497 0218; Fax: +1 508 435 0482; E-mail: [email protected] | Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA, 01748, USA. Tel.: +1 508 497 0218; Fax: +1 508 435 0482; E-mail: [email protected]
Abstract: The strength of the upper extremity in the frontal plane is two times less than in a sagittal plane. Shoulder strength is a limiting factor in upper extremity exertion capability. The purpose of this study was to analytically explain and present the influence of glenoid curvature and the middle deltoid muscle attachment on vertical translations of a humeral head in the superior-inferior direction during elevated arm positions. The paper reports the magnetic resonance results of the glenoid shape of 12 subjects and confirms variability in tangent inclinations and distances of the tangents from the lateral deltoid attachment. It was found that the largest translations of the humerus are during abduction ranging from 0° to 40° and from 140° to 170°. This suggests that both initiation of a movement and raising an arm above shoulder height are critical. The study confirms that the bone surface contacts as well as the muscles are important factors in stability and joint strength. It may provide new information on the sensitivity of the glenoid shape on glenohumeral joint stability and on individual arm strength.
