The first very successful hip prosthesis was designed and implanted in the 1960s by John Charnley of England. Charnley's design used a one piece metal stem with a 22 millimeter diameter head which was cemented into the proximal femur. The acetabular component was made entirely of polyethylene and cemented into the acetabulum. Follow-up studies of the Charnley prosthesis and other similar cemented designs have shown sufficient longevity indicating that the majority of prostheses in surviving patients are still functioning 20 years after implantation. Despite the great success of these hip prostheses, it is recognized that the failure rate increases over time. The mode of failure is typically a loosening of the secure bond between the prosthesis and the bone as well as bone loss associated with this process.

Fig. 13 Pre-operative radiograph of a 59-year-old male with advanced bilateral arthritis.   Figure 14 Post-operative radiograph following bilateral hip replacement performed during a single surgery.

Because of the recognized limits to longevity of these early designs, there has been continued work to improve the design and thereby longevity of hip prostheses. Currently the FDA (the federal agency regulating hip prostheses) has on file about 750 approved designs for hip prostheses. The majority of new designs, however, have proven to be inferior to Charnley's Hip. A few designs however, have probably improved longevity with observed 70% prosthesis survivorship after 20 years.

What is the significance of this history for today's hip replacement patient? Simply because a hip prosthesis is the latest design does not mean it is better and in fact it could be worse. Time gives us the answers. We need to continue to look for prostheses with improved longevity, but a quantum improvement may not be just around the corner and the current expected longevity may be with us for some time to come.

What has changed? The acetabulum is now almost always implanted without cement. The results of the uncemented acetabulum appear equal to cement and there is hope that the longevity will prove better over time. Some designs of uncemented femoral stems have also shown good longevity comparable to the best proven cemented stems. It is widely felt that the bearing surfaces have been improved, which means that this surface wears at a slower rate. Though metal against ultra high density polyethylene is the best proven bearing, there is also evidence to support metal-on-metal as well as ceramic.

Today, development of hip replacement surgery is not limited to efforts to improve the prostheses. Improvements also include surgical approaches that limit the surgical trauma to the soft tissue, thereby accelerating recovery and limiting the possibility of dislocation. Dr. Matta applauds this trend because it is the basis of the anterior approach for hip replacement described herein. Patients need to keep in mind that recovery means both not only recovery from the surgical procedure, but also time to recover from the condition they are in prior to surgery.