[Passive stabilizers of the glenohumeral joint. A biomechanical study]

Passive glenohumeral joint stability was tested in ten cadaveric shoulder specimens, before and after venting of the intra-articular space. Force-displacement diagrams were measured with anterior, posterior and inferior excursion, in the neutral position, in 90 degrees of abduction and in a combination of 90 degrees of abduction and 90 degrees of external rotation. Displacement at 50 N prior to venting averaged 11.17 +/- 6.48 mm posteriorly, 7.15 +/- 5.51 mm anteriorly and 3.41 +/- 3.73 mm inferiorly. Venting of the joint increased displacement by 47% anteriorly, 49% posteriorly and 61% inferiorly. In addition, mathematical model calculation was used to estimate the destabilizing force present at the glenohumeral joint capsule during physiological arm motion. This force approximated 970 N, clearly more than passive stabilizers alone can provide. It is therefore assumed that in addition to passive glenohumeral joint stabilization, significant active forces are effective during arm motion.