“Supervisory authority of the knee”

A complex sensory organ that is so much more than just fatty tissue – this is how orthopedic specialist Prof. h.c. PD Dr. med. Matthias Steinwachs sees the infrapatellar fat pad. In an interview the head physician at the department of Orthobiology & Cartilage Regeneration at Schulthess Clinic in Zurich explains why the sensitive knee joint structure is once again up for discussion.

So why is it that the infrapatellar fat pad is involved in almost every action of the knee joint?
PD Dr. Steinwachs: The main reasons for its high irritability are its microstructure and its central position. The infrapatellar fat pad lies in a triangle between the kneecap, the condyles and the tibia articular surface. It is touched and deformed every time the joint is bent or extended. It can register all mechanical changes in the joint. This is thanks to a network of supply lines. Because the infrapatellar fat pad consists not only of fat. It has an intensive blood circulation and, thanks to its high proportion of monocytes, is also involved in immune responses. In addition it is heavily innervated. The rapid C fibres are evidence of a regulatory function of the infrapatellar fat pad.

Like a spider in a web, you might say. But some things require further research, don’t they?
PD Dr. Steinwachs: It’s true that we don’t yet know all there is to know about this highly sensitive structure behind the kneecap. But that’s not surprising. If we consider even a relatively well-researched structure such as the meniscus, we will see that not all aspects have been fully explained. It’s true we have known about the existence of the infrapatellar fat pad for a long time. But only a few years ago was it shown in a self-examination that this is the site of the most intensive perception of pain in the entire knee joint. The pain map that arose from this study is still doing good service for us today in locating the region where pain is triggered in arthroscopies. Incidentally, there are many new findings to be discussed in this area.

Could you give us an example?
PD Dr. Steinwachs: In the past it was normal to remove a part of the infrapatellar fat pad when performing procedures in the knee joint. When in a chronically irritated state, in particular, it thickens and hampers visibility in arthroscopic procedures. Today I would recommend injuring it as little as possible as otherwise heavy scarring can occur. However, if it is chronically inflamed and causes pain at every step, a partial resection is often unavoidable.

But in case of doubt , leave the infrapatellar fat pad because of its presumed regulatory functions?
PD Dr. Steinwachs: This is what I would argue. It represents a sort of supervisory authority in the knee and appears to be responsible for its internal climate. We believe that in addition to acting as a trigger point for pain it also takes on the tasks of muscle control: What is the position of the joint partners in relation to each other? What is the patellar tendon doing? How high is the mechanical load on the joint? To what extent must the musculature counter the extension of the infrapatellar fat pad, to achieve stability? It falls to the infrapatellar fat pad to answer these sen­sorimotor questions. It thus also serves to protect against mechanical irritations.

To target the related sensorimotor functions of the infrapatellar fat pad, pressure points are incorporated into the new GenuTrain …
PD Dr. Steinwachs: … which makes sense. After all , this represents a different way of addressing the infrapatellar fat pad. Like in acupressure. From this we are familiar with the positive effect upon defined pressure points. In this way we can link in a myocutaneous therapy concept. There are often problems with the sensorimotor system after operations. The support triggers certain processes in the musculature by stimulation of the skin and also provides stability – a useful combination.

Images: Bauerfeind, privat