Total Hip Replacement
Joint Replacement is not a very recent concept. Arthroplasty or Joint Replacement had its inception in the mid-nineteenth century when surgeons when surgeons attempted to produce extra-articular pseudarthrosis by simple resection of ankylosed joints but failed as these joints were not stable. Several investigators tried Interpositional Arthroplasty with muscle, fat, fascia, Bakelite, Glass, etc.which led to early failures. In 1940, Smith-Petersen developed the Vitallium mould Interpositional Arthroplasty which produced comparatively good results.
The modern era of Total Hip Replacement began in the 1960s when Sir John Charnley developed the principles of low-friction Arthroplasty for Total Hip Replacement. Now this is a fairly routine operation and the chances that you’ll be completely happy with the outcome of Total Hip Replacement are about 98%.
The conventional Total Hip Prosthesis consists of a stemmed stainless steel component for the femoral head articulating with a high density polyethylene acetabular component and both being securely fixed to the supporting bone with polymethylmethacrylate cement.
Recent Developments in Total Hip ReplacementThe plastic socket made of Ultra High Molecular Weight Polyethylene is the implant’s weakest point as the plastic wears away at a rate of about one mm per year against a metal ball giving the artificial joint a life expectancy of about 15 years.
Recently developed Cross-Linked Polyethylene wear at a slower rate in the lab and are expected to increase the life expectancy of the implants. Microscopic plastic debris produced by daily wear may migrate between the implant and the bone. The body reacts to these foreign particles by producing osteolytic enzymes that erodes the bone leading to loosening of the implants.
The metal parts of the implants are made up of Cobalt-chrome or Titanium which are extremely well tolerated by the body.Recently developed Metal-on-Metal Hips where both ball and socket are made up of Cobalt-chromehave very low wear rates and allow greater range of movements in the hips compared to plastic sockets. However, there is a growing concern about the long-term frictional release of cobalt or chrome ions from the joint which may lead to Metallosis.
Most recent development is Ceramic-on-Ceramic hips where the ball and socket are made of ceramic, usually Aluminium Oxide. Rate of wear is even less than with metal-on-metal surfaces, and there are no metallic ions to worry about. There is a small risk of ceramic component fracturing (1 in 25,000) which may require re-operation. The ceramic-on-ceramic total hip is the best modern implant for all patients, especially for the young and the active. The drawback is that they are comparatively much more expensive than the conventional implants.