Hoffa's fat pad

What it means

Behind the kneecap and in front of the lower part of the knee joint sits a triangular pad of fatty tissue known as Hoffa's fat pad, or the infrapatellar fat pad. It fills the gap between the kneecap's tendon, the shin bone, and the thigh bone, cushioning these structures as the knee bends and straightens. Because it sits right in the middle of the knee on MRI images, radiologists comment on it almost every time a knee is scanned, in the same way a report might mention the shape of a bone even when nothing is abnormal.

Why it appears on a CT or MRI report

MRI is the best way to see this soft, fatty tissue, since it shows up as a bright, well-defined triangle wedged behind the kneecap. Radiologists check it for size, swelling, and signal changes that suggest inflammation, scarring, or bruising. Because it lies next to the kneecap tendon, the joint lining, and the front horns of the menisci, it is often described together with those structures, and problems nearby can make the fat pad look abnormal even when it is not the primary issue.

What it usually means

In most reports, the fat pad is simply noted as normal — a landmark, not a finding. When it is abnormal, the most common cause is Hoffa's disease, where the fat pad becomes pinched between the kneecap and thigh bone (often after a blow to the front of the knee, repetitive kneeling, or overuse in running and jumping sports) and becomes swollen and inflamed. This can cause pain at the front of the knee, especially with straightening the leg or kneeling. Less often, the fat pad shows bruising after a direct injury, scarring after previous surgery or trauma, or reactive swelling from arthritis or a nearby tendon problem. Isolated fat pad swelling is usually a benign, self-limiting problem rather than a sign of something serious.

When to follow up

If your report mentions fat pad swelling, oedema, or impingement and you have pain at the front of your knee — particularly with kneeling, squatting, or straightening the leg fully — it's worth discussing with your doctor or a physiotherapist. Most cases improve with rest, activity modification, and physical therapy aimed at strengthening the muscles around the knee. Persistent pain, swelling, or a knee that catches or gives way deserves a clinical exam to rule out other causes, such as a meniscal tear or kneecap tracking problem, that can sometimes cause similar symptoms.

A plain-language way to picture it

Think of the space in front of your knee joint as a small gap between two moving parts, packed with a soft cushion of foam to stop them from grinding against each other. That foam pad is Hoffa's fat pad. Most of the time it just sits there quietly, doing its job. But if it gets repeatedly pinched or bruised, it can swell up like a sponge that's absorbed too much water, and that swelling itself becomes a source of pain at the front of the knee.