What is the infra-patella fat pad?
The infra-patella fat pad (sometimes known as Hoffa’s fat pad) is inferior to the patella and deep to the patella tendon. It’s intracapsular and attached to the joint line and menisci. The superior lateral fat pad is often impinged at the lateral joint line. The exact role is not fully understood; however, it may add congruency to the joint. Some people have a rather large fat pad, others not so and some textbooks describe it as the most pain sensitive tissue in the body (I dread to think how they tested that!)
Most of the time the pain is caused by inflammation. It gets engorged with cytokines and fluid and becomes larger – thus can become compressed / irritated by the kneecap. The fat pad is the most innervated structure in the knee, and it is an incredibly irritable structure.
How do we diagnose fat pad irritation?
It’s very much a clinical diagnosis and has a fairly consistent set of symptoms.
- It’s usually quite distinct with patient’s able to point to the pain
- It’s tender on palpation (Hoffa’s sign)
- It’s aggravated by prolonged standing and walking
- It’s worse in near terminal extension and hyperextension
- It likes to stand in flexion
- Heels can relieve pain
- Flat shoes can aggravate it
- It’s usually swollen / visual oedema
We can see the fat pad very clearly on ultrasound but we can’t diagnose based on US features and an MRI would be required.
What causes infra-patella fat pad pain?
- Post arthroscopy – the portal scars go through the fat pad
- Numerous or forceful direct blows to the fat pad
- Hyperextension injury or poor control of extension / proprioceptive control
- Patella instability
- Tight lateral structure / poor glute control leading to supero-lateral impingement
How do we treat infra-patella fat pad pain?
Stage 1 – settle the pain and get the inflammation down
- No barefoot walking / flat shoes such as pump or Uggs – indoor shoes with a slight heel.
- Minimise aggravating activities / relative rest
- Ice massage – oil the skin and ice massage 3-5 mins at least once a day in the evenings
- Taping to offload with rigid tape or k-tape
Stage 2 – reconditioning. This varies hugely – don’t push into pain as the fat pad is very irritable
If it’s from trauma or post op – use stage 1, then recondition the limb with a good strength and conditioning plan. If there is an unstable patella causing the fat pad impingement use quads strengthening and work on proprioception to improve the patient’s position of knee and reduce the irritation. If there is a hyperextending knee causing the fat pad impingement strengthen the hamstrings and work on proprioception to improve the patient’s position of knee and reduce the irritation. If there is lateral fat pad impingement, figure out what is pinching down on the lateral fat pad. If it is the lateral retinaculum and ITB / anteverted femoral head and poor control of femoral rotation then glutes strength and release lateral structures. Stretching, STR and foam rolling alters the pennation angle of the vastus lateralis and makes the fibres more vertical and less able to lateralise the patella. If there is also patella-femoral pain and fat pad impingement the safe zone to work in is 20-40 degrees. Start with isometrics in this range to build strength and progress from there.
These strategies need to be guided by a physiotherapist who has worked with many fat pad impingement patients.
Ultrasound guided injections for infra-patella fat pad pain
If the above-mentioned treatment strategies are not helping then we can perform an ultrasound guided steroid injection into the knee joint and the steroid will diffuse in to the fat pad and help to settle the inflammation.