IMPROVED TECHNIQUES FOR MEASURING INVITRO THE GEOMETRY AND PRESSURE DISTRIBUTION IN THE HUMAN ACETABULUM .1. ULTRASONIC MEASUREMENT OF ACETABULAR SURFACES, SPHERICITY AND CARTILAGE THICKNESS

A unique, highly accurate, non-contacting method for measuring the loaded and unloaded shape and thickness of acetabular articular cartilage employing ultrasound is described. The unloaded cartilage surface is shown to be spherical with localized deviations less than 150 mu m. The calcified cartilage interface is quite irregular with deviations from sphericity of 500 mu m. The centers of the best-fitting spheres to the cartilage surface and the calcified interface are displaced resulting in decreased cartilage thickness in the anterior medial aspect.