Monday, December 04, 2006

A scary phase in total knee arthroplasty

Total knee arthroplasty(TKA) has revolutionized the care of patients with knee pain. This is one surgery that has given excellent results and has proved to be a boon for the arthritic knee.

Even so, TKA has its problems -

  • By nature a prosthesis has a fixed life. One day it is going to fail. Just as a new car becomes old and starts breaking down, similarly a TKA prosthesis will give way in time. Much of the current research is concentrating on improving the life of the artificial joint.

  • The second problem is that of reproducing the normal knee movements. The normal knee is a complicated joint with sliding, gliding and rotation occurring between the two surfaces as the knee bends. It is difficult for an artificial joint to mimic these movements. Hence an artificial joint is unable to flex (bend) as much. Knee bending is important especially in India for cultural and social reasons. Driven by this patient demand, there is much pressure to make designs which allow more bending (high flexion).

There are many new advances being made in this field. Many of these are truly beneficial, others still to be proved and a few of them are quite useless. Lets review some of these.

  1. Unicondylar knee arthroplasty - Here only one compartment of the joint is replaced (usually the medial). The proposed advantages are that the minimal damage is done to the knee, the other 2 compartments are preserved, no ligaments are cut, surgery can be done in a minimally invasive way, revision to a total knee at a later date is easy. The good news is that the results of the unicondylar knee have come in and many centres are showing over 90% survival for 15 years. The bad news is that only a few patients qualify for this surgery (approx 7% of total patients needing surgery for knee arthritis). This surgery has disastrous results in improperly selected patients (beware of the over enthusiastic surgeon). Another thing the surgeon will not tell you is that a high tibial osteotomy, which is a simpler and cheaper procedure, works just as well. Further revision to a total knee has been cited by many authors to be difficult, disproving an earlier claim.

  2. Minimally invasive surgery (MIS) - There is a lot of interest and media hype about minimally invasive surgery. Unicondylar knees are usually done the MIS way. TKA is also being done with MIS with or without the help of computer navigation. MIS basically means to do the same surgery through a smaller incision with lesser trauma to tissues. Well this concept sounds very appealing, doesn't it ? MIS surgery does allow faster rehabilitation, but the results are the same at the end of 3 - 4 months. Further, because access is not as good as the routine incision, some surgeons have reported errors in making the bone cuts and therefore in the position of the final implants. MIS is not as big an advance as it is being promoted. The advantage gained is not worth it if it is at the cost of implant alignment. I feel a properly aligned routine TKA would work just as well.

  3. Computer assisted surgery (CAS) - Does computer navigation improve TKA results? The only thing that has been proved, is that it improves coronal alignment. Whether this translates into better longevity of the joint is still to be proved. CAS is as good as the operating surgeon. The surgeon needs to feed the computer information about the patients body parameters. He does this by placing probes at fixed points which transmit information to the computer via infra red rays (referencing). Using this information the computer creates a virtual model of the patient's knee. Over here lies the problem. There are a lot of errors in referencing. If wrong information is fed to the computer, wrong information is going to come out. Garbage in is garbage out. And yes, let me make it clear, the computer is not doing the surgery. To summarise, CAS is here to stay and will be indispensable in the future, but today it is of doubtful benefit in routine cases. However it is very useful in complicated cases, like those with deformities.

  4. High Flex Knee - This is one of the new knees that have come into the market. As the name suggests it promises a greater degree of bending of the knee by virtue of its design. But post operative knee flexion depends on many things such as the preop range of motion, the type of arthritis, the weight of the patient etc. Some patients will get flexion and some will not, no matter what implant. So all that this implant does is give those patients who were anyways destined to get good flexion, some more flexion. Even this is doubtful as many reports have come in that the results are the same, high flex or no high flex. Besides there is a real concern that this design may actually accelerate prosthesis damage by increasing stresses.

  5. The rotating platform Knee - This is another attempt to reproduce normal knee movements. By virtue of its design this knee allows some rotation that usually takes place in the normal knee. The proposed advantages are more knee bending and less prosthesis ware and a longer prosthesis life. Unfortunately most reports of long term follow up show no difference in either knee function or prosthesis life.

To conclude there are many attractive & new things happening in knee arthroplasty. A lot of people out there are trying to sell you something new claiming it to be better. But new is not always better. The routine TKA is still the gold standard and it has been proved time and over. This is a very scary phase in TKA surgery and I warn the patient/consumer to do their homework thoroughly before deciding to go ahead with a new and fashionable surgery.

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