Patellofemoral Pain Syndrome (Runners Knee)
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There are several fat pads of the knee; the one below the patella behind the patella tendon is called the Hoffa fat pad, or infrapatellar fat pad. Hoffa’s fat Pad was named after the man who first reported on it in 1904, Albert Hoffa. Fat pads are found around the body. Large clusters of fat cells form a protective cushion in areas that need additional help to absorb impact or protect soft tissue from the movement of underlying harder tissues.
The Hoffa fat pad is located at the front of the knee, and it sits under the patella tendon between the lower border of the patella and the tibial tuberosity. The Hoffa fat pad is a small fat pocket below the knee joint that protects the patella tendon, patella bone, and bone surfaces from the movement of the tibia and femur bones.
There are other fat pads of the knee in positions that need protection. The suprapatellar quadriceps fat pad is above the patella behind the quadriceps tendon. The suprapatellar prefemoral fat pad is also above the patella but adjacent to the femur, behind the synovial membrane. The Posterior fat pad sits at the back of the knee. A further fat pad on the lateral aspect of the knee sits underneath the iliotibial band, just above Gerdy’s tubercle.
Impingement of the knee’s infrapatellar fat Pad is caused by knee movements that compress the fat Pad. These movements can cause the fat pad in the knee to become pinched between the femur and the tibia or the femur and the patella.
There are four main causes of Hoffa’s fat pad impingement: biomechanics, repeated hyperextension in sport, acute hyperextension with an injury, and direct trauma.
With biomechanics, the fat pad is more susceptible to being pinched if there is excessive movement of the knee into extension (straightening of the knee), such as with hypermobility. Therefore, these individuals are more at risk of this condition. Also, patella mal-tracking has been linked with Hoffa fat pad impingement, especially in younger patients (Subhawong et al., 2010).
Other reasons for excessive knee extension may include a previous injury to the knee’s ligaments. Damage to ligaments can cause poor control of movements of the knee, such as knee extension. Repeated compression of the fat pad can cause damage, inflammation, and potentially scar tissue formation. Hoffa fat pad scarring can be seen as a result of injury and subsequent insufficiency of the ACL ligament. (Draghi et al., 2016)
Hyperextension of the knee is common in some sports that cause full extension of the knee with high force. Fast bowlers in cricket are an excellent example of this.
Other sports can have a greater risk of hyperextension injuries. These tend to be sports where the foot is fixed to the ground, but the body can continue moving. Any sports where studded shoes are worn, such as football or skiing, are examples of this, as well as dancing.
Direct trauma to the fat pad, such as an injury of landing on or getting hit in the knee or a dislocation of the patella, can cause a sudden onset of fat pad pain and inflammation.
The typical symptoms of a Hoffa fat pad impingement are; pain felt at the front of the knee, which can be on either side of the kneecap or more focused below the knee cap. Sometimes it can be specific to behind the patella tendon. In some cases, it may feel hot and swollen to the touch, and the skin at the front of the knee may be visibly red. The pinched fat pad becomes irritated and inflamed with repeated pinching. Because of the rich nerve supply to the Hoffa fat pad, knee fat pad inflammation, injury, or damage can be very painful.
Usually, it is most painful with the knee in full extension, and keeping the knee slightly bent will be more comfortable. Fully straightening the knee puts more pressure on the fat pad and will increase their pain. When we stand, our knees are in extension. Therefore, it can be painful to stand for long periods. Ascending and descending stairs are also common causes of pain. In moderate or severe cases event bending the knee fully can be painful.
Diagnosis of any musculoskeletal condition starts with a thorough subjective history of the individual. Hearing what they report on how and when their symptoms began, their symptoms, and what pattern the symptoms follow. From this history, an assessment can be made of the likely conditions. This will determine the physical evaluation required.
Most medical professionals will include some general physical assessments, such as looking at how you move, including some of the actions that trigger your pain. Other parts of the assessment will focus on assessing strength, flexibility, and special tests. These “special tests” are orthopaedic tests developed to put more stress on particular structures. Most of these tests have been used for many years and scrutinized, often clinically tested. In most cases, a combined approach of using “special tests”, a physical examination, and listening to a subjective history will provide the clinician with the best picture to interpret what is causing the issue.
There is a “special test” for the Hoffa fat pad. The test, known as a Hoffa’s test or Hoffa pinch test, involves pressing either side of the patella tendon when the knee is flexed and repeating the pinch with the knee in extension. Some clinicians will hold this pressure from the flexed position through the movement into extension. A positive test is a reproduction of the individual’s symptoms. Additionally, if taking the knee into full or hyperextension aggravates their symptoms, this can be suggestive of Hoffa fat pad impingement syndrome.
For additional clarification of the diagnosis, an MRI image of the knee will show inflammatory changes to the fat pad to confirm the outcome of the physical assessment. MRI may also show other changes, such as scarring or cysts that may have formed (Saddik et al., 2004).
Activity modification is the most effective way to help settle the irritation and pain of a fat pad impingement by avoiding hyperextension and reducing activities that aggravate your pain. Targeted stretches and massage to the muscles around the knee, such as the quadriceps, hamstring, and calf, can be helpful, and over-the-counter anti-inflammatories can also help.
From your assessment, your physical therapist should understand what has caused you to develop an inflamed fat pad. They should also understand what factors might be continuing to irritate it that are specific to you and therefore what modifications you need to make.
For the long-term resolution, it is essential to address the cause of the injury. This may improve the proprioception around the knee for someone with hypermobility and increase strength and control of the leg and knee with exercises. Additionally, looking at walking or running gait can be very important if this contributes to the onset of pain or if it contributes to recovery.
Taping can be effective in helping alleviate the pressure of the kneecap on the fat pad. It can be applied with ridged tape, sometimes called zinc oxide tape, or with elastic sports tapes like KT tape.
Application with elasticated sports tape can be made in many different ways. Trying several different versions can be helpful in finding what works best for you. The technique that offers the most pain relief for you is how you should tape.
One version uses three strips of tape in a triangle around your knee cap. Two strips start overlapped from the top of your shin bone and stretch on either side of your knee cap. These are to be attached to the third strip running horizontally across the top of your knee. The bottom two strips should be applied with some stretch to the tape, and the recoil of the tape will help lift the patella to alleviate the pressure on the fat pad.
Most people will recover in 8 to 12 weeks, but in some cases, it can take up to 6 months to fully recover. Repeated fat pad impingement, personal biomechanics, and the individual’s conditioning will affect recovery time. The other risk factors of Hoffa fat pad impingement mentioned above will impact recovery time, as will adherence to activity modification.
Corticosteroids are strong anti-inflammatories and help reduce inflammation in more severe or persistent cases. In some cases, getting the pain and inflammation to settle may be harder, and additional treatment is required. In a minority of cases, a corticosteroid injection will be offered. This is usually done by a consultant, sports doctor or specialist physical therapist. Using ultrasound, the cortico-steroid can be guided into the fat pad.
Surgery for fat pad irritation should be a last resort when all other treatments have been exhausted. If activity modification, physiotherapy, taping and medication do not prove effective over an appropriate period, such as six months. And if injections have not provided adequate improvement, surgery may be necessary. With surgery, the fat pad may be debrided, resected or excised. As the fat pad has a function, removal of it can have complications in the future.
This is not medical advice, and we recommend a consultation with a medical professional such as James McCormack to achieve a diagnosis. He offers Online Physiotherapy Appointments for £45.
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