Hip replacements, resurfacing, technology and the future
Hip replacements are one of the greatest achievements of modern surgery. Before this operation was widely available, patients with hip arthritis were condemned to suffer increasing pain, disability and ill-health.
Early attempts at hip replacement were made in the 1920s, when pioneering surgeons used Bakelite and even ivory to make an artificial joint. The modern era of hip replacement surgery began after WW2. Antibiotics, safe anaesthesia and new materials like polyethylene laid the foundations for innovators like Sir John Charnley to develop the total hip replacement (THR). Charnley’s device was made from stainless steel, polyethylene and acrylic bone cement. Charnley was acutely aware of the risks of infection, and he worked with an air-conditioning engineer to develop a clean air operating environment. Charnley’s surgical skills and determination to succeed were matched by his understanding of engineering, and how important it was to develop safe reproducible and consistent methods of assessing patients, doing the surgery and closely monitoring the outcome.
The first Charnley THR was done in 1962 in Wrightington. Charnley’s method quickly spread around the world. Other surgeons such as Muller in Switzerland developed their own hip replacements, and by the late 1960, the techniques were well established and thriving. But so much has changed since then. Let’s explore what came next.
Cemented or uncemented?
Charnley pioneered the use of bone cement to fix the components of the hip replacement into place. He used polymethylmethacrylate which is a polymer that is mixed just before it is used. It forms a putty which is pushed into the bone and sets hard in about 10 minutes. It has been very successful and is still widely used today.
Some orthopaedic surgeons in Europe and the USA were reluctant to use bone cement and preferred to use hip replacement components that fitted into the bone and were held in place by virtue of their shape and a rough outer coating, into which bone grows. These types of hip replacements have been very successful, but they need careful technique because of the risks of breaking the bone.
Most hip surgeons use both types of implants, selecting the appropriate one for an individual patient. As any surgeon will tell you, no two hips are the same: careful patient and implant selection, and meticulous technique are crucial in the long-term success of hip surgery.
The modern era
Charnley and his contemporaries realised that an artificial joint would be at risk of wear and failure. Wear of the plastic cup generated millions of tiny particles of plastic to be released into the joint, causing the bone to react and the implants to loosen. Failure of a hip replacement was often associated with substantial bone loss, making another operation difficult if not impossible to do. The operation was recommended only to be done in older people, who were unlikely to live long enough for their hip replacement to wear out and fail.
As the operation became more widely used, and seemed to be incredibly successful, the indications for using it expanded rapidly, and of course the numbers of failures increased. This stimulated surgeons, engineers and manufacturers to look for new materials and techniques to use, particularly in younger more active patients.
Surgeons such as Freeman, Wagner, Ring and Amstutz used materials such as chromium cobalt alloy and ceramics to try and overcome the problems associated with plastic wear. Some of these materials were very successful, and inspired Derek McMinn and engineer Mike Tuke to develop the Birmingham Hip Resurfacing in the 1990s. This metal on metal (MOM)device revolutionized the treatment of hip arthritis, particularly in younger people who were working and playing sports.
Many of the major orthopaedic manufacturers developed their own MOM hips. Not all of them were successful. Some of them caused terrible problems due to the generation of metal wear particles to which some people are very sensitive. We saw catastrophic failure with substantial damage to bones and muscles. Many of the MOM devices were withdrawn from use, and it was one of the worst problems seen in modern orthopaedic surgery. Here in the UK we developed the National Joint Registry which tracks every joint replacement used since 2003. It acts as an early warning system, reassuring patients, surgeons and the regulators that joint replacement surgery is closely monitored and scrutinized.
Where we are now?
As a result of these problems, we have as a profession become much more careful about using new technology and materials without them being tested thoroughly before adopting them for general use. Most hip surgeons use implants which have a good long-term track record.
The focus these days is on greater understanding of how an individual patient’s biomechanical factors affect the outcome of surgery and using the appropriate implants and surgical technique to reduce the risk of complications. Hip surgery is now mostly done by specialist highly trained orthopaedic surgeons who only do hips. We use techniques such as CT based pre-operative planning, navigation surgical robots to increase accuracy and precision. We have access to 3D printed components which help us to deal with complex hip problems, for which even a few years ago, there was no satisfactory solution
The Future
The Holy Grail of hip surgery is to find a cure for hip arthritis, so that replacement surgery is no longer necessary. Stem Cells show some promise, but there is no convincing evidence that they work consistently, and we are only beginning to understand how to use them. Until then, surgeons will continue to strive to do their best for their patients, and use the techniques and technology available to them, supported by improved regulation and governance.
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