It is a sharp, sometimes burning pain right at the front of the knee, just below the kneecap. It bites when you stand with your knees locked, when you walk downhill or down stairs, when you sit with your leg stretched out, or at the very end of straightening your leg. Someone may have told you it is your patellar tendon, or "runner's knee", and the exercises you were given have made it worse rather than better. If that sounds familiar, the small cushion of fat that sits behind your kneecap tendon may be the real culprit.
It is called the infrapatellar fat pad, or Hoffa's fat pad, and pinching it is one of the most overlooked causes of front-of-knee pain we see at ACE Sports Medicine. This article explains what it is, how to tell it apart from tendon pain, and what actually helps.
In this article
What is the fat pad and why does it hurt?
Just below your kneecap, tucked behind the patellar tendon and in front of the joint itself, sits a wedge of fatty tissue. Its job is to cushion and fill space as the knee bends and straightens. What makes it interesting is that it is one of the most richly nerve-supplied structures in the whole knee. So when it gets squeezed between the bottom of the kneecap and the thigh bone, it complains loudly, with a sharp or burning pain that feels like it is right on the front of the knee.
The condition was first described by the German surgeon Albert Hoffa in 1904, which is why you will see it called Hoffa's syndrome or Hoffa's fat pad impingement. More than a century later it is still regularly missed, partly because it sits in the same neighbourhood as the patellar tendon and the kneecap joint, and partly because a scan does not always show much.
If your front-of-knee pain has stalled, our physio Mount Gravatt team can usually tell in one assessment whether the fat pad is involved.
How common is fat pad impingement?
Described in 1904, still missed today
Albert Hoffa first described the condition in 1904. Clinical reviews describe it as an underdiagnosed source of front-of-knee pain that is often mistaken for patellar tendinopathy or patellofemoral pain and then loaded the wrong way.
Those numbers say two things. Fat pad impingement on its own is uncommon, but the fat pad joining in on another front-of-knee problem is not, and it changes the plan. A knee that is treated as a tendon problem when the fat pad is the irritated structure tends to get worse with heavy straight-leg loading, because that is exactly the position that pinches it.
Been doing the exercises and getting nowhere? A knee assessment at ACE Sports Medicine in Upper Mount Gravatt can work out which structure is actually driving the pain.
Fat pad or tendon: how do you tell the difference?
There are four clues we look for. First, location: fat pad pain sits just below the kneecap and often either side of the tendon, rather than deep behind the kneecap or on the tendon itself. Second, position: it is worst at the very end of straightening, when the knee is fully extended or pushed slightly past straight, whereas tendon pain is usually worst under load with the knee bent, like a deep squat or jumping. Third, the pinch: gently pinching the soft tissue either side of the patellar tendon, just below the kneecap, reproduces the pain. Fourth, relief: many people notice that standing with a slightly soft knee, rather than locked out, eases it.
Try it now if you like. Sit on a chair, straighten your leg fully and hold it there. If that brings on your familiar pain, and it settles when you let the knee soften, that is a useful clue. It is not a diagnosis, but it points the assessment in the right direction.
What sets it off?
Usually a position, repeated. People who stand for long hours with their knees locked back, dancers and gymnasts who push their knees into hyperextension, netballers and volleyballers who land straight-legged, and anyone whose knees naturally sit slightly past straight are the classic group. A direct knock to the front of the knee, or the swelling after knee surgery, can also irritate the fat pad. And, as mentioned, a rehab programme that pushes the knee hard into full extension, like quad sets with the heel driven into the floor, can keep the pinch going.
Left irritated for long enough, the fat pad can thicken and scar, which is why an early, accurate diagnosis matters more here than with many knee complaints.
What actually helps?
The first step is taking the pinch out of your day. That means learning to stand and walk with a soft knee, adjusting the exercises that drive the knee into hyperextension, and often a short period of taping that tilts the bottom of the kneecap forward to unload the fat pad. Many people notice a change in pain within days of that alone, which is itself a useful confirmation of the diagnosis.
From there, a physiotherapist builds a graded programme that addresses how the knee is loaded: quadriceps strength in the mid range rather than at end range, hip and trunk control so the knee is not collapsing inwards on landing, and, for the athlete, a return-to-sport plan that reintroduces jumping and landing without locking out. For the small number of people whose symptoms persist despite a proper conservative programme, injection and arthroscopic surgery are options that your physio and doctor can discuss with you. Most people never get that far. Fat pad impingement often responds well once it is correctly named and the loading is changed.
When should you seek help?
Front-of-knee pain that has lasted more than a few weeks, or that has not responded to a tendon-style programme, deserves a second look.
Consider getting assessed if
Your pain sits just below the kneecap and is worst with the knee fully straight; standing for long periods, walking downhill or sitting with your leg out sets it off; the exercises you were given for a "tendon" problem have made it worse; the front of the knee is puffy or tender either side of the tendon; or a knock to the front of the knee started it. Sudden swelling, the knee locking or giving way, or an inability to straighten the knee at all need prompt assessment.
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Helping You Perform at Your Best
Our physiotherapy team at ACE Sports Medicine in Upper Mount Gravatt sees front-of-knee pain from across Brisbane's southside every week, and working out whether the fat pad, the tendon or the kneecap joint is driving it is the whole game. Once the right structure is named, the plan is usually straightforward and the change is often quick.