Partial knee replacement explored

Research published in The Knee1 concluded that a partial knee replacement (PKR) is “functionally superior” and offers cost savings when compared to total knee arthroplasty (TKA). It can also offer benefits to the patient by offering a less invasive surgical technique which can result in a reduced hospital stay and less postoperative pain. Consultant orthopaedic surgeon at Macclesfield General Hospital, Mr Graham Keys, has been performing partial knee replacement surgery for about six years. He first came across the technique during orthopaedic training in Oxford where one of the wellknown partial knee replacements was designed. He said: “I got involved in the research and started to understand some of the PKR concepts and, for me, it offered a sensible fit for some of the problems I see in patients with knee arthritis.” Mr Keys believes that surgeons should go through an instructional surgical course before they undertake a PKR. He said. “In the United States, when the FDA approved one of the more popular half knee replacements, the Oxford Partial Knee, it designated that surgeons should attend a live instructional course before doing the procedure. I think that this is something that should be copied in the UK.” The PKR procedure requires the surgeon to work with the other half of the knee and the patello-femoral joint. It is technically more challenging than a TKA. “Surgeons need to be properly educated in the surgical technique for partial knee replacement surgery. Most of the orthopaedic companies that sell partial knee replacement’s are keen on educating surgeons. There are various courses available for this purpose. My experience has been mostly with the Oxford Partial Knee and the course that I first experienced when I was training in Oxford has now progressed and is run on a regular basis. It is a very good course, covering all aspects of indications, surgical techniques and ongoing care of patients. I would certainly suggest that anyone keen on pursuing partial knee replacement surgery should attend a course of this nature.” The course that Mr Keys has referred to is organised by the Orthopaedic Skills Academy, set up by the manufacturers of the Oxford Partial Knee. “Not only do you see the surgeon doing a live video link operation, but you can interact with that surgeon. Having done this myself, I know how instructive it can be. The surgeon is able to find out more about the difficulties that others may have encountered with the operation. Even those who have done a few PKR operations can come back and learn more. The events organised by the Orthopaedic Skills Academy also include lectures about the principles of PKR and delegates are then able to ‘play around’ in the laboratories with a variety of plastic knees.” “There are many reasons for considering a PKR,” said Mr Keys. “Firstly, it is less destructive, as you are retaining around two-thirds of the knee joint. We know that the kinematics of the half knee works in a similar way to a normal knee, whereas with a TKA the kinematics are very different. With a PKR you do not touch the ligaments so you retain all the cruciates and the collateral ligaments so stability is inherent in the partial knee. The main short term advantage of a PKR is in terms of the physiological insult to the patient. It is a smaller procedure, done through a smaller incision, it violates less of the soft tissues and, as you are taking away less bone it also tends to be less painful. Patients, generally recover more quickly and get back to what they would describe as a normal level of activity faster.

Suitable candidates

“Between 20% and 30% of patients who present with osteoarthritis are suitable candidates for PKR. Where the arthritis is purely in one half of the knee, where there is no inflammation as the cause of the arthritis, and where the X-rays show that it is down to bone, patients have pain and disability that requires a knee replacement. Age is, generally, irrelevant, as is the sex of the patient and whether they are inactive or active. Provided only half of the knee joint is affected, and the patient can bend their knee to more than 90°, provided they can extend within 10° of full extension, then those patients would be suitable candidates for a PKR.” Mr Keys would be happy to perform the operation on patients who have something similar to rheumatoid arthritis. However, he would not perform the procedure on inflammatory arthritis that will, potentially, affect all compartments in the knee. “I would also try and avoid using the technique on morbidly obese patients because there is no data on this sector, and common sense suggests that complications are probably going to be higher. Also, I would not undertake the procedure on anyone who has had a previous high tibial osteotomy (HTO). “Patients who had very good flexion before the operation will usually achieve good flexion afterwards too, whereas with a TKA, patients with very good flexion before the operation will often lose a degree of flexion,” said Mr Keys. In the long term the advantages of a PKR are no greater than for a TKA. “We know that the 10, 15 and even 20 year results now are almost equivocal between the two. We know that they can last for a long period of time, but on the positive side you have two bites of the cherry because a partial knee can be converted to a standard primary TKA, no matter when you do it, in over 90% of patients. So you don’t have to use a revision prosthesis, whereas a total knee of course, in up to 90% of cases you have to convert it to a revision prosthesis.” Mr Keys believes that any joint replacement surgery should be reserved for people who have got full thickness articular cartilage loss in the joint. He said: “I think in that situation HTO does not give as good results but, by the same token, putting a joint replacement in someone that does not have full thickness articular cartilage loss, in my experience, gives variable results. I would certainly reserve HTO for patients that still have some articular cartilage left in their joint and still have some malalignment. For patients with full thickness articular cartilage loss I prefer to go down the route of joint replacement surgery.” Mr Keys explains more about the reduced length of hospital stays for patients having undergone a PKR. He said: “We have shown that the length of the patients stay in hospital is often reduced with this less invasive type of procedure. Often the patient is able to go home within 24 hours or 48 hours. I think the average length of stay of my PKR patients is between two and three days and with TKA patients it is more like four or five days.”