In today’s article, we are going to delve into the very painful knee injury called Infrapatellar fat pad inflammation or impingement, which is sometimes known as Hoffa’s pad.
First, we need to explain what the Infrapatellar fat pad is before we can go any further:
So Infra means below, the Patella is the knee cap and the fat pad is erm, a pad of fat! So the Infrapatellar fat pad is a pad of adipose tissue, which is technically inside the knee joint but it is not inside the synovium joint capsule. Its exact location is underneath or deep to the patella tendon and the top of the fat pad attaches to the lower part of the patella (knee cap). The bottom of it attaches to the front of the Tibia (shin bone) and it even attaches to the menisci, the intermeniscal ligament and the infrapatellar bursa.
The fat pad is dynamic, it moves, it doesn’t just sit there as a cushion for kneeling. When you flex (bend) your knee, the upper/outer (superolateral) part of the fat pad becomes tensioned, it expands in volume and moves backwards (posteriorly) in the knee. When you extend your knee (fully straighten) the fat pad acts as a cushion and reduces friction between the lateral (outer) patella facets and the Quadriceps tendon. This is why the most aggravating position is in full extension of the knee, but it is possible that full flexion can occasionally be painful due to the squeeze between the patellar tendon and the front of the femur (Mace et al 2016). Due to its role of increasing volume in the joint and reducing friction to enable free and smooth gliding between the tendons and bones of the knee, there have been some correlations found. It has been found that people who naturally have larger fat pads have less cartilage damage, fewer osteophytes and other good stuff! (Cai et al 2015).
The fat pad has an incredible abundance of blood vessels and nerve endings, mainly coming in from the Tibial nerve. This incredible vascularisation and innervation are the main reasons that the fat pad can really swell and can be incredibly painful. What is interesting is that everything is there with a purpose and this is why another role of the fat pad is not just mechanical. More recent thinking has concluded that the fat pad is involved in releasing substances into the knee joint. It has been found that it produces inflammatory mediating substances and fatty acids relating to inflammation. The fat pad secretes IL-6 and its soluble receptor sIL-6R, which does normally occur from adipose tissue in the human body but the fat pad secretes more (Distel et al 2009) and Ioan-Facsinay et al (2013) also found that it releases mesenchymal stem cells.
So it looks like the fat pad plays a major role in the regeneration and repair of the knee joint and could even be part of the reasoning behind osteoarthritis development.
Fun weird fact (We like these at Hawkes Physiotherapy):
Even though the fat pad is just like the fat that you have when you gain weight, gaining weight makes no difference to the amount of fat in the fat pad!
So what is Infrapatellar fat pad impingement?
It was first found by Albert Hoffa in 1904, hence its name and it doesn’t need much explanation as to what it is. Simply, it is either an acute or chronic inflammation or impingement of the infrapatellar fat pad causing pain, swelling and loss of function.
What causes Infrapatellar fat pad impingement?
The cause of symptoms is from the mechanical impingement and loading on the fat pad itself and also from the metabolic effects. The fat pad grows bigger in size and there are effects to the inflammatory response of the fat pad as it increases its substance P fibres, hence the swollen and painful state (Hannon et al 2013).
The most common cause of Infrapatellar fat pad impingement or inflammation is trauma to the front of the knee area, such as falling onto your knee or dislocating your Patella (kneecap) (Genin et al 2017). In some instances, even surgery can cause it depending on the surgical technique but it can be caused cumulatively too from repetitive activities like jumping (Larbi et al 2014).
Brukner et al (2016) also believes that the impingement can be predisposed by a tilted patella, however, Laprade et al (2003) found no differences in patellar positioning in loaded and unloaded activities between painful and pain-free individuals. So although theoretically, this makes biomechanical sense that a tilted and ‘abnormal’ position of the patella should cause problems this is debated as it can be normal in pain-free people.
How common is Infrapatellar fat pad impingement?
An isolated infrapatellar fat pad syndrome has been reported in 1.3% of anterior knee pain cases and increases to 6.8% of all anterior knee pain as a secondary development (Kumar et al 2007).
It is more common in women than men and is also more likely if there are joint laxity issues such as hypermobility syndrome (Larbi et al 2014).
What are the signs and symptoms of Infrapatellar fat pad impingement?
Very irritable and easily stirred up anterior knee pain, which simply means pain at the very front of your knee is the most common symptom of infrapatellar fat pad impingement or inflammation and it is exacerbated from activity. It can be worsened by full extension (locking straight) of the knee and sometimes prolonged flexion (bending) of the knee. Even the basic exercise ‘Straight leg raise‘ can be painful so don’t do that as part of your rehab! Pain can be worse with flat shoes or being barefoot so sometimes people find a slight heel can be alleviating to the pain (Dragoo et al 2012).
The front of the knee over the patellar tendon is very tender to touch and if you apply pressure to the medial (inside) and lateral (outside) of your patella (kneecap) with the knee straight it is also painful. It is very common to find that the last bit of knee extension into the locked position of the knee is painful and sometimes not accessible. (Genin et al 2017). The fat pad becomes chronically inflamed and very puffy at the front and even fatty fibrosis can occur (Borja et al 2013).
How do you diagnose Infrapatellar fat pad impingement?
Clinic assessment and examination is the most accurate way to determine the diagnosis as MRI scans are not 100% conclusive but they can often find localised oedema of the infrapatellar fat pad and a deep fluid-filled infrapatellar bursa. The normal fat pad has clefts in it so when it is inflamed these can’t be seen and the MRI can find fibrosis and calcification in more chronic cases (Genin et al 20017).
Get the patient lying on their back, the examiner passively bends patients’ knee to 30 degrees flexion. One hand supports the back of the upper tibia near the back of the knee and the other hand is used to press onto either side of the patellar tendon. Next, perform the test again but this time with the knee straight. A positive (confirmatory) test is a pain elicited from the pressure (Kumar et al 2007).
These are simply mobilisations performed by as physio to glide the patella in all four directions (up, down, left and right) in different knee positions, especially in full extension. Again, pain from this is a positive (confirmatory) result (Hannon et al 2016).
This is when you extend the knee into the beyond straight position and this has been found to be a very strong indicator of infrapatellar fat pad impingement (Hannon et al 2016).
What else could it be?
As we mentioned previously the fat pad can be a secondary issue to another injury so it is important to check for these. Commonly things such as meniscus injuries and ligament injuries can be the primary diagnosis, for example, swelling of the fat pad is often present after an anterior cruciate ligament (ACL) rupture (Witoński et al 1999).
Other issues could be:
Patellofemoral pain syndrome
Impingement of the infrapatellar plica
Arthrofibrosis “cyclops syndrome” (occurs after ACL surgery)
Osteoarthritis of the knee or the patellofemoral joint
How do you treat Infrapatellar fat pad impingement?
As with most musculoskeletal conditions, conservative treatments should be tried first.
The first thing is to avoid or modify aggravating activities as to not perpetually irritate and inflame the joint. Absolute rest isn’t correct and contrary to popular belief ice may also not be helpful. More information on this can be found here (Click the image):
As we mentioned earlier shoes with a slightly raised heel may be beneficial in the short term.
Taping techniques to offload the fat pad can be useful but the tape may not stay on for long due to the movement of the knee throughout the course of a day.
As with many knee problems weight loss will always have a positive effect if somebody is overweight because the knee takes many times your body weight with daily activities. It is also true to say that higher body fat levels cause higher systemic inflammation but whether this affects the localised inflammation in the fat pad is hard to determine.
Quadriceps weakness is very much a feature of Hoffa’s but it’s not just that easy to train them but you do need to.
At first, if the movement is not tolerated then isometric strengthening can be used to start to load the Quads and even using something like a Compex Neuromuscular electrical stimulator (NMES) can be useful too. If you are training the Quads then don’t work the range into full extension and full flexion as these will stir the injury up. The key with any rehab it to find your injury tolerance and build up from there. More information on injury tolerance can be found here:
Away from the Quads, it has also been found that training of the Gluteus Medius & stretching the hip flexors may help infrapatellar fat pad disorders according to Dragoo et al (2012). Here are some examples below:
Side Plank Off Bottom Leg (Easy Version):
Hip Flexor Stretch (this will need a slight modification: Have pillows under your shin but not under your knee as to keep the weight of your knee):
Aside from assessment, diagnosis, advice and exercise prescription, we can help with symptom relief through manual therapies and we can screen your biomechanics, which is especially important if your injury is non-traumatic. For example, you might have poor movement patterns and motor control so these can be screened for and a plan of action put together to resolve these issues. An example of such a problem is your knee cutting inwards, which is called dynamic valgus and if this is a problem, when ready we can teach you exercises such as below:
Lunges With Valgus Control:
Once the progression of exercise moves from more basic to more advanced then you need to move into more functional exercises. So if you are a sportsperson then you need to build up impact and drill work slowly while always monitoring the signs and symptoms as you advance.
Going back to manual therapies, if there is a restriction in mobility of the patella then mobilisations can carefully be performed and once ready you may need to restore full knee extension with mobilisation techniques. These are not always needed and toleration is key as always (Hannon et al 2016).
Both local anaesthetic and steroid injections are the types of injections used for infrapatellar fat pad syndrome and they lower pain, inflammation and enable the person to get going with their rehab to restore normal function (Mace et al (2016).
Arthroscopic fat pad resection, which is keyhole surgery to essentially cut a bit of the fat pad away. Surgery is quite effective when it is indicated and most people gain good outcomes and even complete resolution. So they have a good or full range of motion with low to no pain and are they able to return to work (Genin et al 2017). Obviously, surgery isn’t a simple solution as swelling and inflammation will result so there is a distinct recovery process and this will massively include Physiotherapy rehab and exercises to get you back to full fitness.
So infrapatellar fat pad injury is not that common and is more often secondary to another issue, either was it is important to get assessed and treated correctly and this is what we do at our physiotherapy clinics in Stoke-on-Trent.
The content in this blog article is provided for general information purposes only and is not meant to replace a physiotherapy or medical consultation.