Minimally invasive total knee replacement surgery is a specific approach surgically at the time of the operation in order to undertake a total knee replacement. It is something that is commonly discussed on the internet and in the lay press, and it is certainly a hot topic of debate among orthopaedic surgeons.
The principle of minimally invasive surgery is that it reduces the amount of soft tissue trauma to the knee and therefore allows quicker recovery with less pain and less bleeding. However, the term minimally invasive is probably an inappropriate one as a definition of minimal is "the least possible", which in this context would refer to the least possible incision size. A more appropriate term would be "less invasive" because the incision and the soft tissue approach have to be large enough to allow adequate access to the knee joint in order to place the components of the knee replacement into an anatomical position.
The reason that minimally invasive knee surgery and hip surgery is popular with the public, is because of the way it is marketed in that it allows the surgery to be done through a small incision. The length of the incision is of secondary benefit and is certainly not the prime reason to be doing this surgery. In fact, the original two incision hip replacement surgery, which was very popular in the USA has now essentially become a defunct operation, due to the fact that the numbers of complications rose dramatically with this minimally invasive approach.
Because less invasive knee arthroplasty by definition will allow less visualisation of the knee joint at one time, it becomes a much more technically demanding operation with a significant learning curve. (Show incision size of minimally invasive TKR versus normal TKR).
Less invasive knee replacement surgery is not a technique for every patient, and more importantly it is not a technique that every surgeon should be employing. There are certain patients where it is very difficult to use a less invasive soft tissue approach such as very muscular patients, grossly obese patients, patients with a short patella tendon and patients with other unique anatomical variants. However, the principles of less invasive surgery can be applied.
The principles of less invasive surgery are to reduce soft tissue trauma, by reducing the size and position of the incision in the soft tissues to minimise disruption of the quadriceps mechanism (link). This is aided by not everting (flipping the kneecap over) the patella during surgery (show picture), which in itself damages the soft tissues, and can cause dysfunction to the quadriceps mechanism.
Because the soft tissue window of exposure is reduced, it also means that the whole of the knee joint cannot be seen at the same time. This can pose problems and in order to undertake the operation, the principle of using a 'mobile window' is used. By appropriate adjustments of retractors, different parts of the knee joint are brought into view at the appropriate time during the surgical procedure, in order to undertake the operation.
On the courses where I teach other surgeons about minimally invasive knee surgery, I emphasise strongly to them, that the most important part of knee replacement surgery, is the technical aspect of putting the knee replacement in the right place. If they do attempt minimally invasive surgery or less invasive surgery if there are any concerns about the alignment or position of the prosthesis, I would advise them to immediately convert to a standard approach. The cosmetic element of less invasive knee arthroplasty, is from a surgical point of view, the least important. However, with less invasive techniques, the scar length for a knee replacement can be reduced significantly to almost half the length of a routine scar incision. (See picture).
Less invasive surgery is a demanding technique and requires a significant learning curve. This is reflected by the high risk of complications with minimally invasive surgery, which includes malalignment of the prosthesis which will make the knee replacement fail at an earlier stage.
The advantages of minimally invasive surgery are:
* to allow quicker rehabilitation of the knee due to the decreased soft tissue trauma.
* There is also less bleeding and less pain, which contributes to the quicker rehabilitation.
* It is said that a greater range of motion is achieved compared to a conventional approach.
* There is a quicker return to function.
* There is a shorter length of stay in the hospital which can be reduced down to about two to three days, compared to an average of seven to ten days with a standard knee replacement approach.
* By reducing the length of stay in hospital, this has a secondary effect which I believe it to reduce the risk of hospital acquired infections including MRSA as well as reducing the risks of DVT and pulmonary embolus due to early mobilisation.
* My patients undergo minimally invasive or less invasive knee replacement surgery follow an accelerated rehabilitation programme which commences on the day of surgery. This includes immediate range of motion exercises, quadriceps strengthening, hyper-extension stretching and early walking (preferably on the day of surgery).
Computer aided navigation (CAS)
The issues regarding alignment can be improved with computer aided navigation surgery. (Link).
It is apparent to us as orthopaedic surgeons, that the most important criteria of success of a knee replacement is the alignment with which the prosthesis is placed. There is good evidence in the orthopaedic literature that malalignment of the prosthesis beyond as little as 3° can reduce the survivorship and long term success of a knee replacement.
It was on this background that computer aided navigation tools and techniques have been developed. (Show picture). Currently these techniques are still under assessment and investigation. I personally am involved with working on these navigation aids and techniques to assess their value and help improve the techniques.
The technique involves the use of markers within the bones (show picture), which are read by a computer using infra-red beams to determine the alignment and position of the limb and the knee joint, to allow the components to be placed more accurately and more reliably.
The added advantage of computer aided navigation is that it is ideally suited for less invasive knee replacement surgery, as using the computer navigation system, means that you do not have to see all of the knee at the same time, as you are able to see a computer screen which is representing graphically the important land marks of the knee (show picture). Therefore the soft tissue trauma can be minimised further without compromising the alignment and end result of a knee replacement.
Copyright © 2001 to 2013 TheKneeDoc - All Rights Reserved.