Minimally Invasive Total Knee Replacement

There is a move across all branches of surgery to perform operations through small incisions, so-called "minimally invasive surgery". The aim is less pain, less time in hospital and quicker rehabilitation. In knee replacement the drive for this has come from the USA, where in a market driven healthcare economy, patients gravitate towards surgeons with progressive and therefore "better" techniques.

Manufacturers of knee replacement components have realised that they can market directly to patients by using the internet. A visit to the websites of Zimmer or Biomet illustrates the point. Both have prominent "patient information" areas which extol the virtues of minimally invasive knee replacement. They are very effectively exploiting one of the basic principles of marketing. Create a demand and then fulfill it. There is considerable confusion as to exactly what is meant by "minimally invasive". This may be partly intentional for reasons I will explain later.

As you are probably aware arthritis of the knee can be treated by replacing either individual bearings of the knee (medial, lateral or patellofemoral) or by total knee replacement. Which is done depends to an extent on the degree of damage to the joint, but there is more to it than that. In the USA it has been traditional to replace the whole knee, on the principle that nothing less will do.

This means that very many patients are given total replacements when partial ones would do.

In my practice in the UK for example 50% of replacements have been partial. In America almost all patients still receive total replacement. The reason for making the distinction between total and partial replacement is that it is straightforward to implant small components through small incisions, but implanting the larger components of a total knee through a small hole is very tricky and time-consuming.

Now there is a small group of American surgeons who have made it their mission to push the boundaries of the big component/tiny incision concept. And very well rewarded financially for doing so, I should add. Their clinical experience has been small and the follow-up short, although you wouldn't think this if you type "minimally invasive knee replacement" into "Google". It is as yet unproven that patients go home earlier, get better movements or have accurate surgery. Many other surgeons have tried this approach and find it too difficult. Hence the blurring of the definition.

Implant manufacturers have introduced "mini" or "reduced" incision surgery, and these too have been loosely termed minimally invasive (which has been used by surgeons to charge a price premium), so anyone can claim to do it if they make their incision a bit smaller. These mini incisions are little different from that used by the majority of knee surgeons, especially if the patient is thin!

The market for partial knee replacement is dominated by just one company Biomet, the remaining manufacturers therefore have to make the case for using a total replacement in as many patients as possible, hence the concept of " minimally invasive replacement". If the incision is small, then logic decrees that it is a small operation.

The principle here should be to do the correct operation for every patient. The size of the incision should be large enough to perform surgery safely and accurately. This does not mean making an incision a yard long for every patient. As many patients as possible should undergo partial knee replacement through truly minimally invasive incisions. The remainder of severely damaged knees may need a wider exposure.

Cramming large pieces of metal through tiny holes seems to me to be a triumph of technique over reason. Indeed in many of the illustrations I have seen of the minimally invasive technique published in the American literature, the damage to the knee hardly justifies partial, let alone total replacement. There are major issues about accuracy of implantation of the components, as vision is so limited. It has been estimated that up to 25% of components are badly aligned. Components that are poorly aligned may give rise to early failure of the knee replacement.

So in a nutshell if you are considering a knee replacement and the topic of minimally invasive surgery comes up, find out what exactly your surgeon means by this. Ask what proportion of your surgeon's patients have partial replacement, as this can be done safely and accurately through small incisions and the clinical results are usually superior to total knee replacement with just as good long-term results.

As ever in orthopaedics, seldom are things what they seem. Manufacture of joint replacements is a worldwide multi-billion dollar industry, subject to the same competitive drive as any other.