THE RELATIONSHIP BETWEEN THE DESIGN, POSITION, AND ARTICULAR WEAR OF ACETABULAR COMPONENTS INSERTED WITHOUT CEMENT AND THE DEVELOPMENT OF PELVIC OSTEOLYSIS

Between 1983 and 1987, an acetabular component with a unique chamfered -cylinder design was inserted without cement in 134 hips. With use of this design, initial stability is achieved through a cylindrical inter ference fit with the peripheral rim of the acetabulum, without the nee d for pegs, spikes, or screws. At an average of sixty-four months (ran ge, forty to ninety-six months) after implantation, follow-up data wer e available for 113 hips (ninety-three patients). No component had bee n revised for loosening or was radiographically loose. However, the pr evalence of balloon-like osteolysis of the pelvis was 17 per cent (nin eteen hips). This bone loss was generally not associated with pain or other symptoms. Ten of the nineteen hips that were associated with pel vic osteolysis (including six of the nine that were associated with os teolysis of the ilium) had been reconstructed with use of an acetabula r component that had no holes in the shell (that is, the shell was com pletely solid). This finding indicates that, while elimination of hole s through the acetabular shell may have advantages, it will not preven t pelvic osteolysis. The osteolysis of the ilium was associated with a lateral opening of the acetabular component of more than 50 degrees ( p < 0.0001). All of the hips in this series had insertion of a porous- ingrowth femoral resurfacing component made of titanium alloy. These c omponents are no longer used. Revision of the femoral side due to oste olysis provided a unique opportunity to inspect directly forty-two cli nically well functioning acetabular components. All of the polyethylen e liners and acetabular shells were found to be rigidly fixed. Inflamm atory tissue at the periphery of the implant-bone interface resulted i n circumferential resorption of periacetabular bone despite rigid fixa tion of the component. This is direct evidence that a process of bone resorption similar to that reported at the cement-bone interface of ce mented acetabular components can occur at the implant-bone interface o f components inserted without cement. At the reoperation, a communicat ion that had led to the pelvic osteolysis was found through areas of b one resorption at the periphery of the implant-bone interface. These a reas were essentially cystic and were filled with a mixture of fluid a nd friable, yellow-tan tissue. It appeared that the osteolytic process had expanded into the soft cancellous bone and marrow while being con tained by the denser cortical shell of the pelvic bones. Thus, even wi th an implant designed to achieve a tight peripheral fit, osteolysis o f the pelvis occurred. Although fixation of the acetabular component h as been improved by porous-ingrowth technology, bone resorption remain s a problem. Compared with the cement-bone acetabular interface, porou s ingrowth may offer increased resistance to the ingress of joint flui d and wear debris into the implant-bone interface, but fluid and debri s may seek other pathways away from the interface, including the soft cancellous bone of the pelvis.