Compliance and viscoelasticity of canine shoulders loaded in vitro.

Humeral and scapular components of normal canine shoulders were used to load each other in a special testing jig permitting measurement of subchondral plate deflection on each side of the joint. In eleven shoulders, at three loading rates, the humeral compliance (mu deflection kg load-1) was always greater than that of the glenoid fossa (geometric mean ratio = 6.0). On sustained compression, there was prominent stress relaxation most suggestive of intraosseous hydraulic flow.