Statically equivalent load and support conditions produce different hip joint contact pressures and periacetabular strains

The hip is a common site of orthopaedic trauma and disease, and considerable research has been directed toward understanding the development of contact pressures within the joint. Virtually all experimental studies to date have employed proximal femurs compressed along the joint reaction force vector into acetabulae explanted from cadaver pelves. This approach presumes that deformations of the acetabulum are highly localized, and that the pelvis is functionally a rigid body. We have developed a methodology that uses intact pelves loaded through simulation of the abductor mechanism. A direct comparison of the two techniques revealed significantly different joint contact characteristics and periacetabular strains. Fuji film measurements of contact area and pressure were more widely distributed across the acetabulum for the intact pelvis, with significant pressure development in anterior and posterior regions. Contact patterns in the explanted acetabulae were concentrated in the superior portion of the joint. Principal strains from three rosette gages placed near the acetabular rim were also significantly different for the two testing techniques, but were not substantially altered by the presence of Fuji film within the joint. The results indicate that deformation of the entire pelvis and the manner in which loads are applied significantly affect development of contact pressures within the hip joint, and that Fuji film is a suitable technique for recording those patterns.