Fat pad impingement / Infrapatellar inflammation

Anatomy of the infrapatellar fat pad

The infrapatellar fat pad (commonly known as Hoffa’s fat pad) is located at the anterior (front) of the knee joint. It is a large structure positioned just behind the patellar tendon and the knee cap. It is essentially the soft bit you can push at the front of the knee under your knee cap.

The infrapatellar fat pad has a rich blood and nerve supply making this structure highly sensitive and is considered a key pain generator in many knee conditions. It is enveloped within the knee joint capsule and is intrinsically linked to both the meniscus (the shock-absorbing cushion within the knee joint) and the inner lining of the joint capsule (Bennell et al., 2004). This inner lining is known as the synovial membrane and is also a common site for inflammation and pain. An inflamed synovium is called synovitis. Synovitis can be associated with anterior knee pain (Dragoo et al., 2012).

The exact function of the infrapatellar fat pad is still under investigation, but it is believed to act as a reservoir for cells used to repair the knee after injury. It is also thought to play an important role in the shock absorption and mechanics of the knee during movement (Dragoo et al., 2012).

What causes infrapatellar fat pad impingement/inflammation?

Fat pad impingement occurs when the infrapatellar fat pad can become impinged (pinched) between the patella (kneecap) and the femoral condyle (large bony prominence at the end of the long bone of the thigh). Impingement causes microtrauma within the fat pad, resulting in pain, swelling and inflammation. When the fat pad becomes swollen, the healing process becomes altered, resulting in fibrotic changes within the fat pad. This, in turn, causes further repeated episodes of impingement, driving a vicious circle of pain, swelling and impingement (Bennell et al., 2004).

Infrapatellar fat pad impingement can occur for many reasons, including:

• Overload of the extensor (quadriceps) mechanism such as when running and when kicking a ball during football.
• Hyperextension of the knee (over straightening of the knee), e.g. in gymnastics/dance
• Repeated episodes of kneeling often seen in carpet layers.
• Direct impact to the front of the knee such as after a fall.
• Poor biomechanics – this is often seen in runners due to either week hip muscles or a pronated (flattened) foot arch.

However, the most common cause of infra-patella fat pad inflammation/impingement that we see at Complete is due to other associated knee conditions. Due to its close affiliation with the knee joint the infrapatellar fat pad is also often associated with:

• Osteoarthritis
• Patellofemoral pain
• Ligamentous injuries, e.g. ACL
• Meniscal tears
• Patella tendinopathy
• Post-operative pain following an arthroscopy/keyhole surgery – when you have a knee arthroscopy/keyhole surgery, the surgeon passes though the fat pad with his instrumentation. This can cause prolonged pain and inflammation after the operation. (Draghi et al., 2016).

It is not uncommon that clients attend the clinic with a diagnosis of one of these above conditions, following an MRI scan or X-ray, but their actual pain is arising from the infra-patella fat pad.

How do you know if you have an infrapatellar fat pad inflammation/impingement?

Infrapatellar fat pad inflammation/impingement is a common source of anterior knee pain and is often associated with other knee issues.

How is an infrapatellar fat pad inflammation/impingement diagnosed?

A diagnosis of infrapatellar fat pad inflammation/impingement is made using both a clinical assessment and diagnostic imaging.

The assessment involves:

1. A clinical interview – this is used to understand how your pain started and what factors may be involved in its evolution. A full medical history is also taken. This is to rule out any other issues that may play a part in your pain, such as systemic inflammatory disorders including rheumatoid arthritis.

2. A physical assessment – this includes

• Knee joint range of movement testing.
• Quadricep and hip strength testing.
• Palpation (feeling) of the knee joint structures. This can sometimes be a little painful but is important to locate the structure causing your symptoms.
• Movement tests. Functional tests often include squatting, lunging, single leg balancing, walking and running assessments.

Diagnostic imaging

Although a clinical assessment can provide valuable information about your condition confirmation of an infrapatellar fat pad impingement requires diagnostic imaging. Fat pad impingement/inflammation is best visualised on a magnetic resonance imaging (MRI) scan. MRI is an excellent diagnostic tool routinely used to diagnose soft tissue pathology. Completing an MRI of the lengthy process and often takes between 30 minutes to an hour. This involves you lying still within the machine whilst it takes a sequence of images. The sequence of images forms to a complete view of your knee, from front to back.

Diagnostic ultrasound imaging 

Diagnostic ultrasound has the ability to provide real-time dynamic images of superficial soft tissues and is also used to carry out ultrasound-guided injections.

The infrapatellar fat pad is a superficial structure and therefore can be easily and accurately assessed using this imaging technique. Diagnostic ultrasound imaging is effective at diagnosing chronic fibrotic changes seen within the infrapatellar fat pad as well as inflammation associated with synovitis. Inflammation within the fat pad is visualised using a technique called power Doppler. During this technique, ultrasound imaging is able to observe inflammation within the fat pad.

At Complete your initial assessment will involve a full and accurate diagnosis of your symptoms using a combination of clinical testing and we will also carry out the diagnostic musculoskeletal scan. If you would like more information or would like to book an appointment please contact us on 0207 4823875 or email injections@complete-physio.co.uk.

How do we treat infrapatellar fat pad impingement?

A significant proportion of patients suffering from infrapatellar fat pad impingement/inflammation respond positively to physiotherapy input.

Physiotherapy treatment for infrapatellar fat pad impingement commonly includes:

• Providing information on avoiding aggravating symptoms.
• Produce a specific rehabilitation program to strengthen the muscles surrounding the knee and the hip.
• Prescribe a set of stretches for tight lower limb musculature.
• Re-education of abnormal movement patterns and biomechanics – this may mean changing the way you walk, run, squat or lunge.
• Occasionally your physiotherapist may support your knee by using therapeutic tape, designed to offload the fat pad and help relieve symptoms.
• Soft tissue treatment techniques and acupuncture are sometimes used to help relieve pain and tightness associated with your symptoms.
• Advice on footwear/orthotics if over-pronation of your foot has been implicated.

What if conservative management does not work?

If physiotherapy and a progressive home exercise program have failed to relieve your symptoms then you may be appropriate for an ultrasound-guided injection.

During this technique, a small dose of a powerful anti-inflammatory medication known as a corticosteroid is combined with the short-acting local anaesthetic and injected within the infrapatellar fat pad using real-time ultrasound guidance. Ultrasound-guided injections have been proven to be significantly more accurate at delivering medication to the intended target than landmark guided injections. Research has also shown that this increased rate of accuracy results in fewer post-injection complications, is better tolerated by patients and is capable of providing significant pain relief.

An ultrasound-guided corticosteroid injection is not a standalone treatment. The pain relief experienced from a corticosteroid injection allows you a ‘window of opportunity’ to undertake a specific rehabilitation program. For the best outcome to be achieved Complete strongly recommend a course of physiotherapy commence within 2 weeks after injection, once your pain has settled.

Corticosteroid is an effective medication for reducing pain and inflammation associated with infrapatellar fat pad impingement and particularly useful in the following circumstances:

• If your pain has been persistent for over 3 months or is getting worse.
• If your pain is affecting the ability to sleep and waking you up.
• If your pain is affecting your ability to complete activities of daily living, work or partake in leisure activities
• If your pain is limiting your ability to complete your physio rehabilitation program.

Complete is able to offer a same-day service for ultrasound-guided steroid injections. This is possible due to a highly skilled team of clinicians who are fully qualified physiotherapists, musculoskeletal sonographers, independent prescribers and injection therapists. During your initial assessment not only will you be provided with a formal diagnosis but your clinician will perform an ultrasound-guided injection if appropriate. You are able to self-refer directly into our service. A GP does not need to refer you and you do not need to bring a prescription.

If you would like more information or would like to book an appointment please contact us on 0207 4823875 or email injections@complete-physio.co.uk.