Total hip replacement (THR)

Hip replacements were initially performed in the 1800s with only the femoral head, as in the 'ball' of the ball and socket joint being replaced. The materials used were ivory and even gold! Hip replacement surgery took off after the Second World War, following the introduction of the Austin Moore and Thompson hemiarthroplasties which are now only used in selective cases of hip fracture.

Early pioneers devised Hip Replacements made of various materials including acrylic cement, ceramics, metal and polyethylene. Professor Judet in Paris devised a partial replacement using acrylic, primarily for fractures. Also in Norwich, Mr McKee and Mr Watson-Farrer made a metal on metal hip replacement, some of which lasted 35 years and more. The first reliable & successful THR was devised and promoted around 1960 by Sir John Charnley, who is considered the father of modern hip replacement. Sir John Charnley's 'low friction arthroplasty' was a cemented device using a metal stem and head, with a polyethylene socket (acetabular component). The Charnley Hip and similar devices dominated the field of THR for two to three decades and different concepts were gradually abandoned.

All these early THRs unfortunately suffered from one common flaw, which at the time was impossible to overcome. After being in place for several years, the plastic would wear and the tiny particles of debris produced, would result in a reaction that attacked the interface between the cement and the bone. This reaction caused the bone to resorb, and the then new phenomenon of 'osteolysis and aseptic loosening' which is now commonly known.

Corail Cementless Stem

The cementless system used is the Corail design that has been in clinical use for twenty years with excellent results from the United Kingdom, Scandinavia and France where it was originally designed.

Aseptic loosening was poorly understood at first. Some labelled it 'cement disease' and blamed acrylic bone cement for what was being seen on patients' X-rays. This led to the development of cementless THRs especially in North America. When even these devices suffered from a similar problem it was labelled 'osteolysis'. This is the same process of bone being eaten away, but the pattern is slightly different. It has taken a long time for scientists to understand what was happening and why.

Further attempts to avoid aseptic loosening and osteolysis have led Orthopaedic surgeons to use materials such as titanium, hydroxyapatite, highly cross-linked polyethylene, hard metal alloys and oxinium. Presently in the United Kingdom there is a renewed interest in the use of hard metal-on-metal bearings, with the advancement of metallurgy and the engineering process of product development. Also the emerging clinical evidence for highly cross-linked polyethylene has led to its increasing usage.

Overall the differing types of materials used in hip replacements remains a complex topic, with many potential pitfalls. Be very careful what you read from any commercial source. Implants cost hundreds, if not thousands, of pounds and you will never find a less-than-favourable article often written about a certain type of hip on a commercial website. Concerns and issues regarding a potential hip replacement must be discussed with your surgeon.

X-ray Showing A �Hybrid� Hip

An X-ray showing a 'hybrid' hip replacement, with a larger bearing which results in a larger range of motion and a reduced rate of dislocation as compared to a standard total hip replacement.

Generally for younger and active patients the use of uncemented hip replacements with hard metal-on-metal bearings are recommended in our unit, if a total hip replacement is indicated. These will hopefully have limited wear and last longer than the traditional 'metal on plastic' type of hip replacements. The use of uncemented implants will hopefully prevent the number of loosening of the implants seen, particularly on the socket side of the hip. This remains a problem with traditional cemented total hip replacements. The use of the less wearing metal-on-metal articulation allows the usage of larger 'balls' in the ball and socket hip joint. These larger 'balls' allow patients to have a greater range of motion and a reduced rate of dislocation as compared to other 'standard' hip replacements.

The Corail cementless stem is shown here below with a large metal-on-metal articulation.

For older patients who do not require a high demand of their replacements, there is a 'hybrid' combination of cemented and uncemented hip replacements. The potential use of larger 'balls' again results in a larger range of motion with a reduced rate of dislocation as compared to a standard total hip replacement. Also the use of highly cross-linked polyethylene with an uncemented socket will hopefully result in excellent long term function, as compared to traditional cemented sockets which are the 'weak link' of hip replacements.

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