Biologic Fixation of Total Hip Implants

Abstract

Biologic fixation of total hip replacement implants with porous surfaces by means of bone ingrowth became a clinical reality largely through the many experimental studies that were carried out in the 1960s, 1970s, and 1980s. Polymethylmethacrylate bone cement had been the material of choice for implant fixation until then, when it was realized that bone can grow into the porous surfaces of implants if appropriate pore geometries are provided. Porous metals, polymers, and ceramics had been investigated as candidate implants, and porous-coated metal implants were chosen on the basis of the advances in sintering technologies, biocompatibility, and strength considerations (Fig. 1). Consistently obtaining bone growth into functioning total joint replacement components under the conditions of physiologic loading, however, remained a problem. Canine studies were critically important in defining the conditions necessary for consistent bone growth into these devices and thus in the development of porous-surface prostheses for biologic fixation. Our experience with such studies is presented here. Fig. 1 Different types of porous surfaces available for biologic ingrowth. From top to bottom: plasma sprayed surfaces, sintered beaded surfaces with large spheres, sintered beaded surfaces with small spheres, and diffusion-bonded fiber-metal surfaces. The three figures from left to right in each column show representative cross-sections through the porous surfaces. Between 1980 and 1985, more than sixty total hip arthroplasties were performed with use of porous-coated metal components in dogs in order to assess a variety of factors that might influence bone ingrowth. The dog model was chosen because of the large amount of data available on the skeletal renewal dynamics of the dog. In addition, dogs are known to have early development of arthritis of the hip and were thought to provide a good animal model for total hip replacement surgery. The canine acetabulum is also shallower and more dysplastic than the human …