Power tools at the ready! The life-changing science behind hip and knee replacements

Dusty Springfield plays softly in the background … surgeon Mohammad Faisal at work. Photograph: Graeme Robertson/The Guardian

Ian Doncaster is remarkably chipper for a man about to undergo major surgery. “I have a busy life. So it’s nice to have a break,” he jokes. It is 8.30am on a chilly December morning and here at Warwick hospital he is about to receive a new knee – or part of one.

At 62, Doncaster has always been active: he played rugby when young, until a knee injury and subsequent operation meant he had to trade that in for a host of other sports. But now the knee is causing problems again. As a self-employed chartered engineer, he needs to be able to get up and down tower blocks. Even going hiking with his wife seems a wistful dream. “Going forward, it’s only going to get worse,” he says.

Which is why Doncaster is having a patellofemoral replacement, a type of partial knee replacement: a procedure in which the worn-out cartilage that covers the end of the femur and underside of the kneecap will be removed and implants inserted.

Pre-op, he has the air of someone who has watched a YouTube video or two. “It’s brutal stuff. They cut the knee in half. They rip it apart. I mean, orthopaedic surgery is carpentry, isn’t it?” Doncaster says. He’s not wrong: when it comes to joint replacements, the tools of the trade wouldn’t look out of place in a workshop.

After donning a gown and receiving anaesthetic into his spine, Doncaster is wheeled into the theatre and his leg swiftly wrapped in a yellow antimicrobial film. A blue drape is hung in front of his chest; behind it he is chatting away.

Half a dozen or so nurses clad in blue scrubs and masks are ready for action. What is undoubtedly a big day for Doncaster is just a normal morning for the team: typically, such operations are finished in just over an hour. The nurses check they have the right patient, and the right procedure, ensure all the instruments – from hefty power tools to delicate scalpels – are primed for use, and stand relaxed yet ready to pass instruments, accept bloodied swabs, or dispose of excess bone cement.

Somewhere in the room, a radio is playing Dusty Springfield as the consultant orthopaedic surgeon, Mohammad Faisal, picks up a scalpel and cuts into Doncaster’s knee. The tissue peels to the sides and is hooked back. Next, Faisal dissects the muscle and something white becomes visible: the bone. He taps the knee. From the sound, he says, it is clear the cartilage between the kneecap and femur has eroded away. He flips Doncaster’s kneecap over and picks up a large power drill to secure a jig and cutting guide to the femur. Then Faisal reaches for the power saw. Off comes the top of the femur, with flecks of bone flying around the blade.

Faisal fits another guide before picking up a trial implant, a hammer and a rod-like instrument. He applies the latter to the former, and hits it. Hard.

According to the National Joint Registry (NJR), which covers England, Wales, Northern Ireland, the Isle of Man and Guernsey, there were 99,043 primary hip replacement procedures in 2022 and 98,469 primary knee replacement procedures, a figure that includes partial replacements. (“Primary” meaning it is the first time that particular joint has been replaced in the patient.)

Prevalence is highest in people in their mid to late-70s. Data from NHS England for 2021/22 reveals that, among women aged 75 to 79, the rate of hip replacements was 621.8 per 100,000; while for knee replacements, including partial ones, it was 649.2 per 100,000. For men of a similar age, the figures were 420.6 and 587.7 per 100,000 respectively. But these are no longer operations of old age.

“Hip and knee replacements are getting more and more common because we are doing them earlier,” says Faisal.

Not only have implants become longer-lasting, surgical techniques have advanced and risks have decreased, not least as such operations are often done using spinal, rather than general, anaesthesia. These factors also make subsequent, or revision, replacements more common.

People are also becoming heavier: the NJR statistics reveal the average BMI of a hip-replacement patient is 28.7 – overweight – while for knee replacement patients it is 30.7, which is obese.

“If you’re heavy you’ll wear your joints down quicker,” says Faisal. “People don’t realise that until they get into trouble.”

Hip and knee replacements have been around since the late 19th century. Some of the first were carried out by Prof Themistocles Gluck in Germany, who put ivory implants in patients with tuberculous. Later, in the early 20th century, synthetic materials such as glass, acrylic or various metal alloys were used. But the outcomes were mixed, with problems including infections, shattered glass and wear and loosening of implants.

Hip and knee replacements are getting more and more common because we are doing them earlier

Mohammad Faisal, surgeon

In the 1960s, a British orthopaedic surgeon called John Charnley revolutionised such operations. Charnley not only developed a new type of “low-friction” hip replacement but devised the technique for the operation itself. The approach was hugely successful. And the rest, as they say, is history.

Under the theatre lamp, Faisal’s second patient – 78-year-old Lesley Gisbourne – is about to have her hip replaced. Her tissues glisten as a huge incision is held open by retractors, the light illuminating a ball and socket that has never before seen the light of day.

In what seems like a blink of an eye, Faisal has taken the electric saw and the top of Gisbourne’s femur is in his hand. About the size of a plum, it rolls around his palm like a huge, gleaming marble. Again, the power tools are wielded: a huge drill with a fearsome attachment is used to remove tissue from the socket of the joint, and a hammer swung to knock new components into place.

The juxtaposition of the crude, hefty procedure with the refined skill, knowledge and dexterity required to carry it out is startling. Yet as Faisal picks up the new ball for the joint – a smooth, polished, silvery sphere – there is a sense of hope. Because when Gisbourne wakes up, she will finally have the chance to walk without pain.

The ubiquity of joint replacements belies their huge impact on patients: while routine for the health service, they can be transformative for those who receive them. Data from NHS England reveals 93% of hip replacement patients thought the results of their operation were excellent, very good or good. “They are called ‘forgotten hips’,” says Faisal. “Because after a year patients are able to get back to all their normal activities.” Satisfaction with knees is lower, Faisal notes, because the joint is more complex and its movements not so easily replicated by implants. Yet 87% of patients rate their outcomes similarly positively.

But there is room for improvement. Researchers have been developing materials that wear down slower yet remain biocompatible. The latter, Faisal notes, is crucial. “In the lab, metal-on-metal hips were thought to be the best thing because they would last for a very long time,” he says. “But in the body, because of the metal shedding, they caused a reaction.” The upshot was a medical scandal.

Prof Richard M Hall of the University of Birmingham, an expert in medical engineering, says that new materials such as highly cross-linked polyethylene have boosted the life of implants – a crucial development given that patients are living longer and having replacements earlier. “The latest results have suggested that wear in implants containing these materials is extremely low – up to 15 years post-implantation,” he says.

Other researchers, including Dr Edgars Kelmers of the University of Leeds, have been working on “smart joints” that contain a host of sensors. These, says Kelmers, could allow researchers to gather data on the stresses and strains in the joints. “We need data to know how an implant is performing and how to improve it in the future,” he says.

These hi-tech implants might bring other benefits, too: temperature sensors could give early warning of an infection, while movement sensors could give patients confidence to exercise and feel safe in the knowledge that any problems would be quickly detected. The Persona IQ smart knee from Zimmer Biomet can collect data on step count, walking speed and rate, distance travelled, stride length and knee movement.

There are also potential advances in how knee and hip replacements are carried out. “We have robotics, and navigation, to put components in more precisely, to try and help us balance the knee better,” said Chethan Jayadev, a consultant orthopaedic knee surgeon at the Royal National Orthopaedic Hospital in Stanmore.

If you’re heavy you’ll wear your joints down quicker. People don’t realise that until they get into trouble

Mohammad Faisal, surgeon

While knee and hip replacements are likely to remain a staple of the NHS workload, experts are also finding ways to avoid them, and to preserve or even regenerate dodgy joints – be it through cartilage transplants or stem-cell therapies. The former can involve implanting cartilage cells or even solid pieces of cartilage, while the latter typically involves harvesting stem cells from the patient, then transferring them into the damaged joint.

Prof Mark Campbell of the University of Ottawa, however, points out that stem-cell approaches have faced criticism over a lack of evidence that they work. “We’re a long way away from having stem-cell therapy for joint cartilage regeneration supported by a strong evidence base, and widely endorsed by medical societies,” says Campbell.

These concerns have led several national regulatory bodies to discontinue the use of stem-cell therapy for joints until the evidence base improves.

Jayadev agrees that most cell-based techniques for cartilage repair have limited supporting evidence, although he notes some forms of cartilage cell transplantation are reliable, as are approaches using plugs of healthy cartilage. But even then there is a problem: these therapies are not suitable for worn-out joints.

“My best analogy for that really would be a road,” says Jayadev. For some people, he says, their cartilage is generally in good shape, with only a small patch eroded – similar to the way some roads have potholes. “That’s a situation where regenerative surgery such as cartilage repair or stem-cell transplantation is most effective,” he says. If that fails, there is the possibility of localised repairs with small metal, or cross-linked polyethylene, implants.

Unfortunately, by the time most people see a surgeon about their joint pain, the whole surface of the road is worn out. In other words, large areas of cartilage have broken down and osteoarthritis has set in. This means the joint may have a number of problems besides worn cartilage, says Jayadev, which regenerative surgeries cannot fix.

“Joints can be considered as organs for movement,” says Jayadev. “Like other organs of the body, [such as] the kidney or liver, joints can undergo failure. That’s what osteoarthritis is.”

The upshot is that joints with osteoarthritis have an abnormal signalling environment. “Stem cells and cartilage cells need the right signals to change into normal, healthy material,” says Jayadev.

For most patients, this leaves two options. “You either have to avoid the road, or you have to re-lay the road,” says Jayadev. The former involves modifying activities, braces, or surgeries that correct the alignment of the joint to reduce the pressure it experiences, while the latter corresponds to a joint replacement.

The problem is that for those in the early stages of osteoarthritis, where surgery may not be needed, there is little on offer besides weight loss, physiotherapy and injections for temporary pain relief – leading to what Jayadev calls the “treatment gap”. “That’s a big area of concerted effort – what can you do for that group of patients?” he says.

It is not the only chasm patients face. Once eligible for a replacement, many have to endure lengthy waiting lists.

Having decided last August to go ahead with an operation, Doncaster was offered a date in November – although he had to reschedule it because of a holiday. Warwick hospital currently has a Vanguard mobile operating theatre in situ, together with a dedicated team of physiotherapists and nurses who check on patients at home after the operation, boosting its capacity to carry out such procedures and rapidly discharge patients.

However, across the NHS, knee and hip-replacement patients are among those waiting the longest for their procedures, with the drop in such surgeries during the pandemic, as well as cancellations during recent doctors’ strikes, contributing to a backlog.

The website of West Suffolk NHS Foundation trust – one of the few to clearly publish its waiting times – reveals the average wait for a hip or knee replacement is currently 57 or 59 weeks respectively. This, despite the NHS constitution including a right for patients to receive such surgery within 18 weeks.

But it can be worth the wait. For patients such as Gisbourne the outlook is bright, with a new hip offering her the chance to be pain-free at last.

“Pain-free and jiving,” Faisal smiles.