Hoffa's Fat Pad Edema

The fat pad. Hoffa’s fat pad fills the space at the front of the knee behind the patellar tendon, below the kneecap. It sits inside the joint capsule but outside the joint lining, and it has a rich supply of blood vessels and nerves, which is one reason it can be a source of pain at the front of the knee (Dragoo et al., 2012).

Edema and signal change. On the MRI images that make fluid bright and suppress the signal from fat, healthy fat looks dark. An area that looks bright is reported as edema, high signal, increased signal or hyperintensity. These words describe the picture. They do not say what caused it or whether it hurts, which is why the report usually adds where in the fat pad it is and what sits around it.

The words around it. These are the terms you are most likely to see on a knee MRI report that mentions the fat pad.

It is common in knees that do not hurt. In a study of 64 people aged 14 to 40 with kneecap pain and 70 without, bright signal in the fat pad was found in 58 percent of the patients and 51 percent of the people without pain, and it was not linked with having the pain once age, sex, weight and sport were accounted for (van der Heijden et al., 2016).

The superolateral kind goes with how the kneecap sits. In 1,134 knees of older adults with or at risk of knee arthritis, 13.4 percent showed superolateral edema. It was much more common in knees with the highest-riding kneecaps than in knees with the lowest, and a kneecap sitting further to the outside and the angle of its groove were also linked, more weakly (Widjajahakim et al., 2017). A review of 21 studies agreed on a high-riding kneecap, a tendon attachment set further out on the shin and the angle of the groove, and found no link with age or body mass index (Abelleyra Lastoria et al., 2023).

How firm that link is. These studies compared knees with and without the edema at one point in time, so they show a link, not a cause. The link with a high-riding kneecap is the most consistent, and the exact cause of the edema is still debated. In 8 of 16 female university volleyball players it was found in both knees, and every one of the 16 had normal knee function and a normal examination (Mehta et al., 2015).

After surgery, it may be scar. Injury and surgery, including keyhole surgery and ACL reconstruction, can leave scarring in the fat pad (Dragoo et al., 2012). In 97 people scanned three months after an ACL reconstruction, 21 had severe scarring. A year after surgery they scored lower on how the knee felt and worked, and had less range to straighten and bend, than the people with mild scarring (Yoshida et al., 2025). The ACL injuries page covers the rehabilitation.

In an arthritic knee, it is read as a sign of the joint lining. Radiologists score signal change in the fat pad as Hoffa-synovitis, a sign of an irritated joint lining. On a scan without contrast dye it picks up most synovitis but also flags knees without it, so it is a pointer rather than proof (Roemer et al., 2009). The knee osteoarthritis page covers how arthritis is assessed and treated.

It is not a diagnosis. The same bright signal turns up in painless knees, beside kneecap and tendon problems, in arthritic joints and after surgery. Whether the fat pad is the source of your pain is decided by where it hurts, what brings it on and the examination.

The fat pad, the patellar tendon and the kneecap joint sit within a few centimetres of each other, and a scan can show changes in more than one. How the pain behaves is usually the better guide.

• Fat pad. Pain below the kneecap on either side of the tendon, sometimes with mild puffiness there, worse when the knee straightens fully, with long standing and when you stand with the knee pushed back past straight. It is often described as an ache or a burning (Dragoo et al., 2012), and pressing on the fat pad while you straighten the knee brings it on (Hoffa’s test). In ten donor knees, the pressure inside the fat pad was highest with the knee fully straight, lowest around 60 degrees of bend, and rose again past 100 degrees (Bohnsack et al., 2005).
• Patellar tendon. Pain in one spot at the lower tip of the kneecap that rises with jumping, landing and loaded knee bends. A single-leg squat on a slope (decline squat), or straightening the knee against resistance, brings it on. The patellar tendinopathy page covers it.
• Kneecap joint. Pain spread behind or around the kneecap rather than in one spot below it, brought on by stairs, squats, running and long sitting with the knees bent. The patellofemoral pain page covers it.
• More than one at once. Superolateral edema was more common in people with tendinosis at the top of the patellar tendon than in matched people without it (16 of 65 against 4 of 65), and a high-riding kneecap was more common too; tendinosis at the lower end of the tendon showed no such link (Delorme and Jibri, 2021). The patellar tendinosis guide explains that report wording, and the pain below the kneecap guide the other causes of pain in this spot.

No single test settles it. I put the location, the movements that hurt and the report together, and the plan follows the pattern rather than the scan.

The research on treating fat pad pain is thin. A 2023 systematic review found no studies of treatment for Hoffa’s fat pad syndrome that met its criteria (Abelleyra Lastoria et al., 2023), and the surgical studies that exist are of low quality (Rooney et al., 2015), so what follows rests on a narrative review, those studies and one trial in arthritic knees, and is kept modest.

• Ease the position that pinches it. Avoiding pushing the knee back past straight (hyperextension) and changing how you stand and walk are part of the long-term plan described in a review of fat pad problems (Dragoo et al., 2012). In practice that means not standing with the knee locked back and breaking up long periods of standing.
• Taping. Tape applied to take pressure off an irritated fat pad is part of the same review’s plan (Dragoo et al., 2012). I have not found a trial of it for fat pad pain, so I treat it as an add-on to try, kept only if it makes the exercises easier.
• Strengthening. Quadriceps exercises done with the foot on the ground, and strengthening for the side of the hip (gluteus medius), are the exercise pieces the review describes (Dragoo et al., 2012). When kneecap pain sits alongside, the patellofemoral pain page sets out the evidence for hip and knee strengthening.
• Injections. Injections of a local anaesthetic and a steroid into the fat pad have been tried (Dragoo et al., 2012). In a randomised trial of 60 people aged 45 and over with inflamed, arthritic knees, an ultrasound-guided steroid injection into the fat pad did not ease pain or reduce joint swelling more than saline over 12 weeks (Zhang et al., 2026). An injection is a decision for your doctor, not a response to the scan.
• Surgery. A systematic review of 24 studies found that removing part of the fat pad in Hoffa’s disease can improve symptoms, but the studies were of low quality and the authors called for randomised trials (Rooney et al., 2015). Removing scar from the fat pad has been used for a knee that cannot fully straighten after ACL reconstruction (Dragoo et al., 2012). Surgery is for a fat pad that still limits you after a fair course of non-surgical care, and that is a surgeon’s decision.
• What that means for your report. Edema in the fat pad is not on its own a reason for an injection or an operation. The plan follows the pattern of your pain.

I start with where it hurts and what brings it on. Pain either side of the tendon that is worse standing with the knee straight points to the fat pad; pain in one spot at the tip of the kneecap that rises with jumping and loaded bends points to the tendon; pain spread around or behind the kneecap with stairs and sitting points to the kneecap joint. I ask about earlier injuries and surgery, and I check the hip, because a hip problem can be felt at the front of the knee.

On examination I look at how you stand and whether the knee pushes back past straight, press around the tendon and the fat pad as the knee bends and straightens, watch a squat and a step-down, and test the strength of the thigh and hip. I read the report alongside that, giving more weight to how the knee behaves than to the signal in the fat pad. If something on the report points elsewhere, such as a mass, I refer you to your family doctor; a knee that locks or a hot, swollen joint needs medical assessment the same day. I cannot order imaging; when further imaging would change the plan, I flag it and refer you.

The plan starts by easing what pinches the fat pad: how you stand, not pushing the knee back past straight, and trimming the activities that flare it. Taping is an option early on. Strength work for the thigh and hip builds from there, back to the running, jumping or standing work you need, guided by how the knee responds the next day. After surgery I work within your surgeon’s plan, and if the knee is losing range rather than gaining it, I let your surgical team know.