EXPERIMENTAL-STUDY OF PERIACETABULAR DEFORMATIONS BEFORE AND AFTER IMPLANTATION OF HIP PROSTHESES

This work is based upon an experimental simulation of one-legged stanc e, under loads close to the average body weight. Skeletons, harvested from fresh non-embalmed cadavers, included pelvis, two lumbar vertebra e, and both femurs. Periacetabular deformations were studied using tri directional strain gauges before and after implantation of different t ypes of acetabular prostheses in eight pelves: conventional polyethyle ne-cemented sockets, polyethylene sockets cemented into a metallic dev ice, metal-backed cemented sockets, and hemispherical cementless press -fit cups with porous or hydroxyapatite coating. Strain measurements s howed the persistence of important bone deformations at implant periph ery. Mean values of normal periacetabular deformations were significan tly reduced in two out of five acetabula implanted with cemented impla nts. In contrast, mean values of normal and circumferential deformatio ns increased when polyethylene sockets were cemented into acetabular r einforcement devices, but this augmentation was significant in only on e out of two cases. After implantation of cementless hemispherical met al-backed cups, periacetabular bone deformations also increased, but m odifications 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 r elation between implant stiffness and the magnitude of bone deformatio ns.