INTRAARTICULAR PRESSURE OF THE SHOULDER

Nine fresh frozen cadaveric shoulders were used to examine the changes in intraarticular pressure (IAP) of the shoulder joint and the positi on of the humeral head under various loads to determine the relationsh ip between these parameters. All the soft tissues superficial to the r otator cuff were removed. The position of the humerus relative to the scapula was monitored using an electromagnetic tracking system before and after venting the capsule with 0, 0.5, and 1.0 kg of load applied to the humerus inferiorly in addition to the weight of the arm. Simult aneously, the IAP was monitored using a pressure transducer before ven ting the capsule. Venting had a significant effect on the position of the humeral head: the positions of the head after venting were signifi cantly lowered in all loading conditions. The average IAP was -76 cm H 2O without load, and the value decreased in a linear fashion with incr eased load; the correlations were significant in four of six shoulders without dislocation. The correlations were less significant between t he pressure and the position, and there were no significant correlatio ns between the load and the position. IAP, which is determined primari ly by the load applied, is important to stabilize the shoulder inferio rly. Because IAP is intimately related to the external load and the re sponse is specific to individuals, examination of IAP response to exte rnal load may be helpful in characterizing various instabilities of th e shoulder.