Experimental study of periacetabular deformations before and after implantation of hip prostheses

This work is based upon an experimental simulation of one-legged stance, under loads close to the average body weight. Skeletons, harvested from fresh non-embalmed cadavers, included pelvis, two lumbar vertebrae, and both femurs. Periacetabular deformations were studied using tridirectional strain gauges before and after implantation of different types of acetabular prostheses in eight pelves: conventional polyethylene-cemented sockets, polyethylene sockets cemented into a metallic device, metal-backed cemented sockets, and hemispherical cementless press-fit cups with porous or hydroxyapatite coating. Strain measurements showed the persistence of important bone deformations at implant periphery. Mean values of normal periacetabular deformations were significantly reduced in two out of five acetabula implanted with cemented implants. In contrast, mean values of normal and circumferential deformations increased when polyethylene sockets were cemented into acetabular reinforcement devices, but this augmentation was significant in only one out of two cases. After implantation of cementless hemispherical metal-backed cups, periacetabular bone deformations also increased, but modifications were significant in a single case. Results are discussed according to the type of fixation (cemented or cementless), and to the difference in rigidity between implant and bone. There was no clear relation between implant stiffness and the magnitude of bone deformations.