Quantitative determination of articular pressure in the human shoulder joint

The objective of this study was to determine experimentally the effect of i ndividual variations in articular surface geometry on the shoulder joint pr essure distribution in functionally important arm positions. The location a nd size of the load-bearing areas and maximal pressures of 10 cadaver shoul der joints were examined at 30 degrees 90 degrees and 150 degrees of abduct ion (+/-90 degrees external rotation) and 120 degrees flexion with pressure -sensitive film. Only parts of the glenoid cavity were involved in the load transfer, some specimens showing central and other bicentric (superior-inf erior) pressure maxima during abduction and Flexion. The load-bearing areas were more central at external rotation, suggesting that the humeral head i s not a perfect sphere. The maximal pressure was recorded at 90 degrees of abduction with 90 degrees external rotation, with 5.1 MPa for the elevation for single- and >10 MPa for double-arm weight. The study demonstrates that shoulder joint pressure cannot be calculated analytically but depends on s ubtle variations of joint incongruity.