Capsular elasticity and joint volume in recurrent anterior shoulder instability.

It is commonly claimed that unstable shoulders have an altered capsular elasticity and increased joint volume. To find out if there is a correlation between anterior instability and increased joint volume, 20 patients were examined while undergoing arthroscopic surgery of the shoulder. There were four anterior subluxators, 11 anterior dislocators, and five bilateral dislocators, and in all patients the contralateral shoulder was also examined. During continuous saline infusion, a pressure/volume curve was recorded within the range of 0-180 mm Hg. Joint volume was correlated with body surface area. Among the 15 patients with unilateral instability, there was no correlation between joint volume and body surface area. There were no differences in joint volume or capsular elasticity between the healthy and the unstable shoulder in any patient. It is concluded that capsular elasticity and joint volume contribute little to anterior shoulder instability and that instability probably depends more on damage to other stabilising structures in the joint.