Effect of joint compression on inferior stability of the glenohumeral joint

To determine the relative importance of negative intraarticular pressure, c apsular tension, and joint compression on inferior stability of the glenohu meral joint we studied 17 Fresh, normal adult cadaver shoulders using a "3 degrees of freedom" shoulder test apparatus. Translations were measured in intact and vented shoulders while a 50-N superior and inferior directed for ce was applied to the shoulder Three different joint compressive loads (22 N, 1 1 1 N, 222 N) were applied externally. Tests were performed in 3 posit ions of humeral abduction in the scapular plane (0 degrees, 45 degrees, 90 degrees) and in 3 positions of rotation (neutral, maximal internal, and max imal external). After tests of the intact and vented shoulder the glenohume ral ligaments were sectioned and tests were repeated. With minimal joint co mpression of 22 N, negative intraarticular pressure and capsular tension li mited translation of the humeral head on the glenoid. Increasing the joint compressive load to 1 1 1 N resulted in a reduction of mean inferior transl ation from 11.0 mm to 2.0 mm at 0 degrees abduction, From 21.5 mm to 1.4 mm at 45 degrees abduction, and from 4.5 mm to 1.2 mm at 90 degrees abduction . With a compressive load of 1 1 1 N, venting the capsule or sectioning of glenohumeral ligaments had no effect on inferior stability Clinical relevance: Glenohumeral joint compression through muscle contracti on provides stability against inferior translation of the humeral head, and this effect is more important than negative intraarticular pressure or lig ament tension.