The infrapatellar (Hoffa’s) fat pad explained
There are various fat pads, but the one at the knee that causes a lot of problems is the infrapatellar fat pad, also known as Hoffa’s fat pad after the man who first described it.
The fat pad has been shown to be very pain sensitive. It is rich with nerve endings that can fire off messages of pain to the brain, and it is therefore of no surprise that people with fat pad problems are often in a lot of pain.
The fat pad is often overlooked, with clinicians concentrating on joint surfaces, cartilage, ligaments and tendons, and dismissing the patient if these structures appear normal on imaging.
So what can go wrong in this funny pad of fat? There are two very different scenarios. The first is mechanical. The fat pad gets a trauma to it. Now this may be an obvious one off blow to the knee, or where the patient straightens their knee at speed and feels an immediate very sharp pain in the fat pad. Or, as is seen more commonly the fat pad may get nipped between the patella and the tibia, and microtrauma leads to a macro problem. In either of these situations it is common to see an inflammatory response. This is a problem as inflammation leads to swelling, and leads to the scenario where the fat pad gets pinched and caught even more. This feeds into a vicious cycle that many patients get completely stuck in. Furthermore, once the fat pad becomes big it alters the way the kneecap moves, and this in turn can lead to high pressure under the patella, which is also often painful.
Can anything be done? Yes! The first is to try and break the vicious cycle of inflammation and swelling. I often recommend ice massage to oiled skin, right on to the fat pad, (the ice-it-away is really effective for this), and will often tape the kneecap off the fat pad. Wearing a slight heel can help stop the patella knocking onto the fat pad, and most definitely avoiding standing with the knee locked back.
A treating clinician should also be assessing if there are other factors contributing to squashing the fat pad. These may, for example be quadriceps tightness, or poor movement patterns, particularly in people who are hypermobile.
There are also non-mechanical sources of problem in the fat pad, and these should be referred to as metabolic. This is seen with obesity and osteoarthritis of the knee.
Let’s take obesity. When someone is carrying excess fat they will have systemic inflammation. This is one of the reasons for raised cardiovascular risk, but the fat pad becomes inflamed and can hurt. The good news is that weight loss not only reduces load to the knee but also with immediate effect has been shown to reduce the inflammatory state of the knee.
In osteoarthritis it appears that the fat pad changes its state to produce unhelpful pro-inflammatory cells. As the fat pad is housed within the capsule of the knee the fat pad drives further joint breakdown that clearly is undesirable. The good news here is that any efforts to reduce the inflammatory state of the fat pad will have a positive effect on the inflammatory state of the whole knee.
To conclude, as weird as it is, this little pad of fat under the kneecap can be a very painful and persistent source of problem. Make sure you seek the right help to treat the problem, and help you get back to the things you love doing.
If you want to understand this in more depth why not look at my webinar on the fat pad https://t.co/juxILqftIm