Published on 01 April 2008
Jane Tadman reports on the increasing popularity of unicompartmental knee replacements.
Happy with his new knees – Andrew Fulljames at work in his garden.
Although joint replacement surgery has been one of the big successes of the past 20 or 30 years in treating severe arthritis, it remains something of a blunderbuss approach, often resulting in large amounts of healthy bone and cartilage being unnecessarily removed.
Now, one in four people with painful knee osteoarthritis (OA) are able to undergo a far less invasive surgical procedure than a total knee replacement (TKR); a unicompartmental knee replacement (UKR), which involves replacing only the part of the knee which is affected by arthritis.
Partial knee replacement surgery (UKR) is becoming more and more popular and now accounts for almost eight per cent of all 65,000 knee replacement operations performed in England and Wales.
Patients who have had UKR find they spend less time in hospital and have a quicker recovery period. They may also have a better function, because the ligaments and other parts of the knee remain undisturbed. This is speeded up even further if they have the operation carried out using a technique called minimally invasive surgery, in which the surgeon makes smaller than usual incisions in the body – between 4–5 inches instead of 8–12 inches.
It tends to be carried out on slightly younger patients. While the average age of a typical TKR patient is 70, for a UKR patient it is 65, sometimes a little younger.
“UKR is a focussed surgical treatment of a specific pattern of osteoarthritis affecting just one part of the knee, involving the preservation of the non-damaged parts of the knee,” explained Andrew Price, orthopaedic surgeon and reader in musculoskeletal science at Oxford University’s Nuffield department of orthopaedic surgery.
“The UKR provides people with a better mobility than a TKR, and although patients cannot return to contact sports such as rugby or football they can walk as much as they like, cycle, play tennis, golf and even sometimes skiing. There are significant benefits to this type of surgery.”
There is, however, a downside in that there is an ongoing debate about whether the UKR lasts as long as a TKR. One of the most common reasons for implant failure is loosening. In fact according to the Swedish Arthroplasty Register, they become loose four times as often as TKR.
Orthopaedic surgeon at the Robert Jones and Agnes Hunt Orthopaedic Hospital in Oswestry, Steven White, says: “UKRs should last as long as TKRs but it is recognised that younger patients who are more active are more likely to wear out or loosen a UKR. Therefore, for patients under, say, 55 years of age, they have to recognise that they would eventually have to have the UKR revised in future to a TKR.”
Andrew Amis, professor of orthopaedic biomechanics at Imperial College’s departments of Mechanical Engineering and of Musculoskeletal Surgery, says that although the UKR is becoming more popular, it is still not nearly as often performed as TKRs. “There is clear evidence that surgeons are performing TKRs in cases that might be suitable for the UKR,” he added. “We believe that surgeons would be less apprehensive about doing the UKR if they had more secure data about long-term survival.”
Now Arthritis Research UK is funding both Professor Amis and Mr Price to carry out two separate pieces of research which they hope will provide new evidence about the longevity of the UKR, and lead to it being more frequently performed.
Professor Amis is looking at ways in which fixation can be improved. Working with orthopaedic surgeon colleagues at Charing Cross Hospital, he will run a small clinical trial of people who had UKR surgery to test how their bone reacts to surgery, by performing pre and post-operative x-rays and bone density scans.
Using these scans to make computer models, he and his team will then create an accurate simulation of what will happen to the joint a year after surgery. “It’s likely to show that parts of the bone get weaker but maybe other parts get stronger,” he said. “We can run different implant designs on the computer to try and preserve bone structure. If data can be produced to show how best to design and fix these implants it should lead to increased use and better long-term results.”
Cemented or uncemented
Mr Price, meanwhile, is comparing two different types of UKR, cemented and uncemented. The former is more common, but he and colleagues who regularly perform the surgery have found that so-called radiolucent lines (lines that represent a layer of fibrous tissue at the interface of bone and joint) are detectable by fluoroscopic x-ray after surgery, which may indicate that the joint is likely to come loose.
He aims to compare cemented with uncemented types of implant to examine whether uncemented leads to less radiolucency, and therefore improved stability and longevity.
“This is an important question to answer as the uncemented joint may reduce the incidence of loosening and revision surgery,” he said. Fifty patients, who have undergone either cemented or uncemented UKRs, will take part in the study. All have tiny marker balls positioned around the implant at the time of surgery which are detectable by an imaging technique known as Roentgen Stereophotogrammetric Analysis (RSA).The balls are then used to measure the migration of the implant in relation to the bone, an early sign of loosening, and will be detected by RSA x-rays performed after 3, 6 and 12 months. Movement of the implant indicates that thefixation will fail early.
“The point of our study is to provide evidence that the uncemented UKR may offer advantages to patients, and we hope our scientific and clinical trial will lead to its greater use,” added Mr Price.