Knee osteoarthritis, a painful condition caused by wear and tear and progressive loss of articular cartilage, is on the increase both in the United Kingdom and globally. It is the most common form of osteoarthritis, and, in England, about one-in-five adults over the age of 45 has the debilitating condition. Scientists are not sure why the prevalence is increasing, though likely explanations include the rise in life expectancy (knee osteoarthritis is more common among older people) and rising rates of obesity, which puts more pressure on the joint. Essentially, longer lives and heavier body weights are putting more wear and tear on our joints.

The condition normally starts on the inside part of the knee and is progressive, with damage to the cartilage then leading to bone-on-bone contact. “There are different grades of osteoarthritis, which are graded by X-ray appearance, but there is unfortunately no correlation between the grade of the disease and the pain,” explains Richie Gill, professor of mechanical engineering at the University of Bath. “Some people with very worn cartilage may experience less pain than those in the early stages of the disease,” he says.

Typically, knee osteoarthritis can be treated successfully with a knee replacement surgical procedure, which involves removing the natural joint structures and replacing them with metal and plastic. Obviously, however, such a procedure is going to be irreversible. Furthermore, the operation is only performed at the end stage of the disease because over time (usually about 10–15 years), the replacement can fail, and revision surgery – more complicated than the original replacement surgery – will need to be carried out. For that reason, Gill says, surgeons rarely offer knee replacement operations to people under the age of about 60 or 65.

“There are different grades of osteoarthritis, which are graded by X-ray appearance, but there is unfortunately no correlation between the grade of the disease and the pain.”

Approximately 15% of knee replacement patients are dissatisfied with their surgery, and younger patients report greater levels of dissatisfaction, as well as a greater incidence of revision. Yet, as the population continues to age, data suggests that demand for the operation will double by 2030, Gill says.

Backlog of patients awaiting surgery

Because patients must wait till a very late stage of the disease for a knee replacement, some experience intense pain for decades before they are able to have a replacement – and thanks to the pandemic, there is currently a backlog of patients waiting for the operation. Some doctors continue to prescribe opioids to manage the pain, despite the evidence that they don’t work and can even create further problems. The only way to treat osteoarthritis in the knee effectively, Gill points out, is to correct the mechanics.

One of the problems with waiting so long to perform knee surgery – apart from the pain caused to the individual patient – is that the condition renders people inactive. And, as Gill points out: “If you are inactive, you have multiple risk factors for other things [like] diabetes [and] cardiac disease, for example.”

So, there are good reasons to treat knee osteoarthritis at an earlier stage, if possible. The main alternative treatment to knee replacement is a surgical technique known as high tibial osteotomy. This involves cutting a wedge of bone out of the top of the tibia to realign the knee, which is then stabilised by screwing a metal plate into the bone on the outside of the joint. The load on the inside of the knee is reduced, and the healthier part of the knee bears more of the weight. If successful, the bone can regrow and the reduced load on the knee can allow the damaged cartilage to regenerate. The plate can then be removed after about a year.

The advantage of osteotomy, says Gill, is that it “preserves your natural joint, and you can do it at earlier stages of the disease”. The benefits tend to last about eight to 10 years, so it is not a permanent solution, and because the plate can cause soft tissue irritation, in some cases patients experience pain and discomfort. Osteotomy is also, unfortunately, a trickier operation to perform than knee replacement, and can take up to two hours to carry out. “The success of osteotomy depends on how well you achieve the correction that you’ve planned,” says Gill. Some surgeons do not offer the operation, precisely because they are concerned about their ability to achieve the planned correction.

Using digital technology to create a perfectly fitting plate

What if you could devise an osteotomy procedure that had higher success rates, enabling more patients to benefit from it, so that they enjoy more years free of pain and are able to engage in physical activity? Gill and his colleagues have developed a solution designed to do just that.

Their solution, known as Tailored Osteotomy for Knee Alignment (TOKA), involves scanning the patient’s knee and then designing the metal plate digitally so that it can be tailored to each individual patient. A 3D printer is then used to manufacture a perfectly fitting medical-grade titanium-alloy plate. The team at Bath has licensed the technology to an SME called Orthoscape, which obtained regulatory approval for the initial clinical trials.

Once the software was developed, the high tibial osteotomy procedure using the personalised plates was performed on eight cadaver leg specimens to test how successful they were in achieving the planned correction. The study found a much greater accuracy in achieving the planned correction angle compared to that achieved using conventional plates.

The next stage was to test the plates virtually using CT scan data from 28 patients. Gill believes this was the first in silico trial in the world to demonstrate the safety of an orthopaedic device. It modelled the stresses that would be exerted on the personalised plates and demonstrated that they would be comparable in safety to the most commonly used generic plates.

It was now time to test the safety of the procedure on live patients. The trial, carried out by the Rizzoli Institute in Bologna, Italy, assessed the mechanical effects of osteotomy in 25 patients. The results have not yet been published, but the pain results, says Gill, were “remarkable”. “Patients are getting significant pain relief at three months and then are really almost back to normal at six months,” he adds.

Quick and simple to perform

The surgery itself is relatively simple, requiring a very small set of instruments. This means that it can be performed quickly, which Gill believes is one of the reasons the trial has been so successful. “There’s always a bit of a learning curve, but the surgeon in Italy who has done 25 can now do it in 25 minutes,” Gill says. Some patients who have received the procedure in the UK are treated as day cases.

Gill is now in the process of launching a much bigger randomised controlled trial to compare the TOKA method with traditional osteotomy using generic plates. Known as the PASHiOn (Personalised Versus Standardised High Tibial Osteotomy) trial, it is funded by Versus Arthritis and will be carried out in collaboration with the NHS. When recruitment is complete, it will involve 88 patients in 10 centres.

“It’s much better to be able to give people joint-preserving treatment…and give them the ability to have active lives which then reduces all their other risk factors.”

If the trial is successful, then Gill would like to see the technology adopted throughout the NHS. Given the long waiting lists for knee replacements, and the benefits both to patients and the NHS of adopting a simpler surgery that can be performed at an earlier stage of the disease, the case for TOKA is difficult to argue with, Gill believes.

The traditional osteotomy technique, he notes, involves “quite a steep learning curve for surgeons.” The TOKA system is different, however: “What we’ve been able to show through the trial we’ve done in Bologna is that surgeons can get to grips with this very quickly, and after a few cases they feel really comfortable with it. If we can get it more widely used, more people would have access to it. For people who were suitable, it would get them a treatment that works at a much earlier stage in their disease process compared to waiting for a knee replacement.”

Those patients, Gill believes, would have a higher quality of life than those that must live with the pain of knee arthritis. “It’s much better to be able to give people joint-preserving treatment earlier on in the disease process and give them the ability to have active lives which then reduces all their other risk factors,” he concludes.