Hip Replacements: A Brief History
Hip replacements are one of the most successful and cost-effective interventions in orthopaedic medicine.
By the age of 85, even an average sedentary individual will easily have clocked 160,000 km and an active person maybe over 320,000 km, or almost 8 times around the world. No wonder hips and knees are focal point for osteoarthritis. I have written two previous pieces in relation to these joints. My first was on evolutionary biology of the lower limb. This detailed how the humble ostrich (Struthio camelus) has a far superior evolutionary design compared to us just like the handsome devil below!
They are roughly the same weight as us, yet they can run at top speeds approaching 70 km/h or at an average speed of roughly 60 km/h (it could complete a full marathon in 40 mins). Because their lower extremity is so efficient at generating movement with such great efficiency joint wear is minimal. The method they use has begun to fascinate scientists and engineers as it could help provide answer for prosthesis design, robotics and suspension systems. It is a cause of wonder to me too, as if I had those legs there wouldn’t be any point driving to Buxton as I could gently trot there in 19 minutes without the need for diesel or road tax.
My second article was on the key causes of knee and hip osteoarthritis. Being as the hip joint is, by a small margin, the most replaced joint in the lower limb it makes sense to write about the modern day orthopaedic phenomenon of hip replacements.
The Early History of Hip Implants; Glass and Ivory
Total hip replacement is one of the most successful and cost-effective interventions in orthopaedic medicine. That is a big statement, but it is true. It offers reliable relief of pain and almost immediate improvement in function. Currently about 60, 000 hip replacements are performed in the UK each year, while worldwide the number is over 300, 000. An impressive 90-95% of patients can expect to have their total hip replacement (TKR) functioning at 10 years and 85% will still be functioning at 20 years. The history of hip replacements goes back further than you would think. The story involves early attempts using ivory, glass and even Bakerlite until modern materials such as cobalt and chromium or polyethylene became standards.
First came attempts using ivory! The nineteenth century of course witnessed the introduction of the foundations of modern surgery with techniques such as anaesthesia and asepsis (working in sterile conditions). Remarkably the first total joint replacement was performed in Berlin in 1890 on the knee joint of a 17-year-old woman that had been destroyed by tuberculosis. The joint was replaced using a hinged ivory prosthesis. The surgeon was Themistocles Gluck (fantastic name!). I suspect he used ivory as the Ivory Coast was then a German colony. He was born in Romania in 1853, the son of a famous German doctor who was the attending physician to the royal family. He presented his work to the Tenth International Surgical Congress in Berlin using a complete skeleton fitted with his various joint replacements. At this point these included the wrist, elbow, shoulder, ankle, hip, and knee.
The skeleton became famous and was on display in Berlin until the Second World War, when it was stolen as ‘spoils of war’ by the Russian army along with the entire Berlin medical collection and other arts and antiquities (the Nazis were no less guilty). Meanwhile Gluck’s joint replacements were successful in the short term, but they all ultimately failed because of chronic infection. He later realised, even though he operated using sterile conditions, prior joint infection (such as TB) was a contraindication to joint replacement in the first place. Sadly, because of the opposition of his colleagues, his pioneering work was dismissed during his lifetime and he even remains largely unrecognised to this day.
Next came glass in the 1920’s. This was used to resurface the head of the femur. This was performed by one of the most prominent and innovative orthopaedic surgeons of the first half of the twentieth century. His name was Marius Smith-Petersen. Glass sounds like an unlikely material to use but it does provide a smooth ‘biocompatible’ surface. Unfortunately, as one would expect, the huge forces transmitted through the hip joint meant that these attempts did not last long. Marius Smith-Petersen did go on to experiment with other materials such as Pyrex glass, Bakerlite and various other metal alloys.
The Advent of Metal on Metal Hip Implants
Successful attempts using metallic materials did not happen until 1953. The English surgeon George McKee began performing total hip replacements (replacing both the head of the femur and the socket of the hip joint). These metal-on-metal (MoM) implants using cobalt and chrome were successful for their time. Surprisingly, the prosthesis had a good survival rate, with one study recently demonstrating a 28-year survival rate of 74% which is possibly a bit generous. There were however some problems as wear in a small percentage of patients generated tiny metallic particles which caused toxicity. We will return to this point shortly.
Metal on Polyethylene Hip Implants
Ten years later in the 1960’s another surgeon from Bury in Lancashire, Sir John Charnley, pioneered the modern total hip replacement and spent the next two decades refining all aspects of the procedure. What he did is identical, in principle, to the prostheses used today.
His procedure used three parts; a metal femoral stem, a polyethylene cup and acrylic bone cement – which was borrowed from dentists! Metal-on-polyethylene (M-on-PE) prosthesis are the most widely used method of hip replacements undertaken in the UK today.
Popularised by the early success of the Sir John Charnley polyethylene-based implants almost completely displaced all other bearing surfaces. Currently the M-on-PE bearing provides a safe, predictable and cost-effective bearing for most patients, and for many represent the gold standard in hip replacements. The only concern for M-on-PE prosthesis is that, in a few cases, as the polyethylene implant wears it can generate debris. This debris can cause chronic inflammatory responses in a process called ‘periprosthetic osteolysis’ (apologies for the jargon) which can ultimately lead to implant failure. In fact, polyethylene wear debris is cited as the ultimate cause of most total joint arthroplasty failures today. This has led to some renewed interest in metal-on-metal bearings (MoM).
Controversy Surrounding Metal on Metal Hip Implants
It is worth returning to MoM hip implants as pioneered by our friend George McKee in 1953. MoM implants are attractive because of their durability. They are usually made from a blend of several metals, including chromium, cobalt, nickel, titanium and molybdenum. In fact, The National Registry for Hip Implants in England and Wales recorded 402,051 hip replacements between 2003 and 2011, of which 31,171 were MoM hip implants. Unfortunately, there have been some concerning failure rates associated with MoM hip implants: 5-year revision rates in women aged 55 have been estimated to be 8.3% which is a problem. Added to which, in some instances, there is another potential caveat because of the materials of construction. This is a theoretical risk and depends of the type of MoM prosthesis that is fitted. Please do not be alarmed if you have a MoM prosthesis or know someone who does because the risks are low.
MoM hip replacements have typically used hard metals such as cobalt in order to extend the life of the hip replacement. However, as these metal surfaces erode, metallic ions can filter into the blood stream through local tissue. Cobalt poisoning can potentially be a serious issue. Small amounts of cobalt are needed for animals and humans to stay healthy as it is a component of vitamin B12, which supports the production of red blood cells. But if you are exposed to large amounts, cobalt toxicity can be serious. It can cause patients to suffer from fever, inflammation, and low thyroid levels. Some patients have also reported heart problems, impaired vision and hearing, and organ damage.
DePuy Orthopaedics Lawsuit
The NHS suggests that people with MoM implants should have regular annual health checks as a precautionary measure. It is important to point out that the risk is low, and it does very much depend on the type of MoM prosthesis that is fitted. In 2017, the Medicines and Healthcare products Regulatory Agency (MHRA) published guidelines on monitoring patients with all types of MoM hip implants. Although many MoM implants are safe the worst examples came from a company called Depuy. They made three types of hip prosthesis all of which were especially subject to ‘metallosis’ and high failure rates. This is well documented, and these prostheses are no longer used.
In brief DePuy Orthopaedics are a division of a Johnson and Johnson Company who are the largest worldwide pharmaceutical and medical device company in the U.S. Three of Dupuy’s hip replacement devices caused an unexpected high failure rate in some patients. This resulted in at least 17,000 lawsuits with many more being processed even to this day. In 2013, Johnson & Johnson agreed to settle the more than 8 thousand federal lawsuits with an award of approximately $250 thousand for each claim (ouch!). An additional 2 thousand cases remain in California and many more in other states and local courts. Estimates have since shown that up to 40 percent of the DePuy devices were liable to fail in the first five years after implant, though they were expected to last for 15 years.
As our life expectancies are increasing the next challenge is to ideally provide a replacement that does not fail at all. Research continues using different materials such as ceramics and minimally invasive techniques. Hip replacement surgery now has faster recovery times and lower risk of complications than ever before.