What is Hoffa Pad Impingement Syndrome?
The front area of the knee has three main fat pads. These are found in the quadriceps (the large muscle group at the front of the thigh), at the top front of the thigh bone (also known as pre-femoral suprapatellar), and below the kneecap, behind the patellar tendon (widely known as Hoffa’s fat pad). These areas can experience discomfort or pain if they become trapped or ‘impinged’.
The Hoffa pad, which is also called the infrapatellar fat pad (IFP), is particularly significant. It’s located inside the knee joint capsule but not within the joint itself, and takes up most of the space at the front of the knee.
It’s important to note that if the IFP becomes inflamed, it can cause pain in the front of the knee. This inflammation can squeeze on the joint formed by the shin and thigh bone (known as the tibiofemoral joint) or the joint between the kneecap and thigh bone (known as the patellofemoral joint). This condition is called Hoffa pad impingement syndrome. This pad has a rich blood supply and a lot of nerve endings. The nerves that provide sensation to it come from the posterior articular nerve, a branch of a nerve located at the back of the shin.
The IFP is normally attached to the upper part of the patellar tendon, the bottom of the kneecap, the front parts of the knee joint cartilage (medial and lateral menisci), a ligament that connects the menisci, and the front bone layer of the shin. The back of the IFP is covered with a smooth lining (synovium) and it extends to the back, connecting to the space between the two parts of the knee joints. Sometimes, it also connects with the ligament at the front of the knee joint.
What Causes Hoffa Pad Impingement Syndrome?
Injury to the infrapatellar fat pad (IFP), a sensitive area located below the kneecap, typically happens due to a sudden, harsh accident or continuous tiny injuries caused by blunt impacts, a tear in the anterior cruciate ligament (ACL – a major knee ligament), dislocation of the kneecap, or a twisting knee injury. This kind of knee injury, known as Hoffa pad impingement syndrome, can be a source of pain in the front of the knee and is commonly found in people who run, cycle or serve in the military.
The IFP can cause a lot of pain due to its abundant supply of sensitive nerve endings that can respond strongly to substance P, a substance that our bodies produce. Substance P leads to widening of the blood vessels, which encourages more immune cells to go to the injured site. This can potentially lead to swelling within the tissue. This inflammatory process can cause the IFP to thicken and develop fibrous tissue, resulting in the loss of its ability to stretch and flex easily.
Over time, scar tissue builds up and gets in the way of the inner edge of the knee joint and the trochlea (the groove at the end of the thigh bone), which can result in a physical and/or painful block to fully straightening the knee. The IFP also produces various substances like fibroblast growth factor, vascular endothelial growth factor, tumor necrosis factor, and interleukin-6. Together, these substances can contribute to inflammation, the development of fibrous tissue, and pain within the IFP.
Risk Factors and Frequency for Hoffa Pad Impingement Syndrome
We’re not sure how commonly Hoffa pad impingement syndrome, a knee condition, occurs. This is because it’s tough to diagnose and usually responds well to standard treatments. It’s thought that many cases might be missed when using imaging to examine the knee because only about 1% of patients going through a knee procedure called an arthroscopy are found to have it.
Signs and Symptoms of Hoffa Pad Impingement Syndrome
People with Hoffa pad impingement syndrome may describe a burning or aching feeling in the front of the knee. This discomfort is often felt deep around or to the sides of the large tendon beneath the kneecap (patellar tendon) and tends to occur when the knee is fully extended, shifting between bent and straight positions, or kept bent for extended periods. The onset of pain is usually gradual and could be linked back to a previous knee injury or occur spontaneously without a known cause.
Upon examination by a doctor, there is often noticeable discomfort and sensitivity around the patellar tendon, mainly near the bottom of the kneecap. Patients usually have some movement limitation in the knee, with one study finding severe restriction at a 20-degree bend. Pain at the end of knee extension is also common in these individuals. This condition can be identified using the Hoffa test, where the doctor presses below the kneecap while the knee is mildly bent and then fully extends the knee; increased pain indicates a positive result.
- Burning or aching feeling deep around or to the sides of the patellar tendon
- Pain often occurs when the knee is fully extended
- Discomfort and sensitivity found near the bottom of the kneecap
- Movement limitation in the knee
- Pain at the end of knee extension
It’s important not to mistake this knee pain for that caused by damage to the meniscus, which is a piece of cartilage in the knee. Some may also feel pain with tension in the large thigh muscle (quadriceps) with the knee fully extended. An enlarged, firm, or tender IFP and reduced kneecap mobility can also be associated with this condition.
Possible treatment includes an arthroscopic procedure (a minimal invasive surgery using a tiny camera) to release tissue causing the impingement followed by rehabilitation. This rehabilitation involves preventing re-scarring through exercises that fully extend the knee and move the kneecap. A condition known as “infrapatellar plica,” where a ligament in the knee becomes thickened and fibrotic, can cause non-specific symptoms like constant severe knee discomfort made worse by movement, occasional popping or snapping of the knee, and fluid buildup in the knee.
Testing for Hoffa Pad Impingement Syndrome
Sagittal MRI, a specific type of imaging technique, is considered the best option for assessing problems in a body part called the infrapatellar fat pad (IFP), otherwise known as Hoffa’s fat pad. This MRI provides valuable information on the structure and condition of the IFP. In a normal MRI image, the IFP looks similar to fat under the skin, except for some lower signal intensity areas which are fibrous partitions within the fat pad. Also, there might be some vertical and horizontal lines that are even darker on the MRI image.
The MRI also helps to visualize the ligamentum mucosum, a continuation of the IFP, which can sometimes be seen as a bright band in front of the ACL (anterior cruciate ligament), a crucial ligament in the knee, and inserted within a joint area called the intercondylar notch. Blood vessels within the IFP are also visible in the MRI.
In the case of Hoffa pad impingement syndrome, a condition where the fat pad becomes trapped and compressed, the MRI may show an increased signal reflecting harder, fibrous tissue or a decreased signal suggesting inflammation and its related edema (swelling) and bleeding within the fat pad. If there is a suspicion of hardened areas within the fat pad, an X-ray may be suggested to differentiate this from fibrosis, which is the development of extra fibrous connective tissue.
Symptoms of impingement syndrome can often be knee pain, loss of range of motion in the knee, and a positive result on Hoffa’s test — a specific physical exam maneuver for diagnosing this condition. In one study, it was noted that individuals with Hoffa fat pad impingement showed signs of swelling in the MRI in certain areas of the fat pad. However, these changes can also appear in people without fat pad impingement, so physical examination remains a vital part of the diagnosis process and cannot be replaced by MRI findings alone.
Treatment Options for Hoffa Pad Impingement Syndrome
If someone has Hoffa pad impingement syndrome, physical therapy is usually the best course of treatment. The aim of the therapy is to correct how the kneecap moves by strengthening certain muscles in the knee and hip, using a taping technique to relieve stress on the kneecap tendon and fat pad, doing specific stretches, and enhancing body movement involving the gluteal (butt) muscles.
Using tape can help reduce pressure and inflammation in the fat pad located under the kneecap. The tape is applied in a “V” shape on the kneecap when the knee is fully straight. The tape stays on all day, every day until the pain stops. This taping technique, combined with avoiding certain knee movements, can decrease irritation of the fat pad.
Strength training exercises that target the quadriceps muscle, particularly a muscle called the vastus medialis obliquus, will be recommended to help the kneecap move properly. Exercises are also prescribed to strengthen the posterior fibers of the gluteus medius muscle in the hip, which can prevent the knee from moving inward. Sometimes stretches to increase hip rotation are also recommended.
Some medical procedures involve injecting alcohol and local anesthetics such as lidocaine, either singularly or combined with anti-inflammatory medications such as methylprednisolone acetate or hydrocortisone, into the painful area, to provide relief. These treatments have shown promising results in managing Hoffa pad impingement syndrome.
If conservative treatments like physical therapy and injections are not successful, surgery may be considered. The surgery, performed arthroscopically (using a camera and small surgical instruments), involves removing the inflamed area of the fat pad. This procedure is often beneficial and the majority of patients experience few or no post-surgery issues. Arthroscopic removal of the impinged fat pad can lead to a significant reduction or even complete resolution of symptoms in patients with no other related health issues. Partial removal of the fat pad may be just as effective as removing a larger portion and may be a good treatment option.
What else can Hoffa Pad Impingement Syndrome be?
When diagnosing Hoffa pad impingement syndrome, this usually involves evaluating and ruling out a number of other conditions that could potentially trigger pain in the front of the knee and block its extension. Several other conditions need to be thought and reviewed before diagnosing Hoffa pad impingement syndrome, these include:
- Soft tissue issues like bursitis, which often comes from repetitive small injuries or activities that require repeated knee use such as biking. This condition affects any of the four bursae in the front of the knee: the prepatellar, superficial, infrapatellar, deep infrapatellar, and pes anserine bursae.
- Patellar tendinosis, which is typically associated with high-impact jumping sports. This results in pain that is linked to activity and is mainly located at the bottom of the kneecap. It becomes more intense during contraction of the quadriceps muscles.
- Conditions affecting the area within the joint such as plica syndrome, meniscal tears, injuries to the articular cartilage, and osteochondral lesions. Plica syndrome is an inflammation caused by several factors, including injury, overuse, long-term incorrect tracking of the kneecap, diabetes, and inflammatory joint disease.
- Meniscus tears, which usually result from traumatic knee injury, leading to pain and a clicking or catching sensation within the joint.
- Fibrosis or the formation of excess fibrous connective tissue (scar tissue), especially after reconstructive surgery for the anterior cruciate ligament (ACL). Commonly termed as a “cyclops lesion,” this condition tends to restrict knee extension and is usually the second most common cause after graft impingement.
- Anterior interval scarring: this can also block full knee extension, causing pain, decreased ease of movement in the kneecap, and atrophy or wasting away of the quadriceps muscles. The anterior interval, which is the gap between the IFP and the front of the shinbone (tibia), is often identified as a leading cause of extension block following arthroscopic ACL reconstruction.
What to expect with Hoffa Pad Impingement Syndrome
Hoffa pad impingement syndrome, a specific type of knee problem, can often be managed and improved with conservative treatments like physical therapy and steroid injections. In instances where surgery is necessary, the majority of patients are able to return to their pre-injury level of sports activities after undergoing a procedure called arthroscopic debridement. Arthroscopic debridement is a minimally invasive surgery used to remove or repair damaged tissue.
Possible Complications When Diagnosed with Hoffa Pad Impingement Syndrome
Not diagnosing Hoffa pad impingement syndrome in time or missing it altogether could lower a person’s quality of life. It could also mean they have to miss time participating in sports and other fun activities. This condition can lead to increased inflammation and the development of fibrosis, which is the thickening and scarring of connective tissue. If the inflammation pad becomes larger and more fibrous, it might cause stiffness in the knee, leading to changes in walking patterns.
Common consequences of missed or delayed diagnosis of Hoffa pad impingement syndrome:
- Lowered quality of life
- Missed time from sports or activities
- Inflammation and development of fibrosis
- Enlargement and fibrosis of inflammation pad
- Knee stiffness
- Changes in walking patterns
Preventing Hoffa Pad Impingement Syndrome
People, athletes in particular, can help prevent Hoffa pad impingement syndrome – inflammation and swelling of the fat pad in the knee – by doing exercises that strengthen the quadriceps muscles in the front of the thigh. These exercises help promote proper knee cap movement. They are particularly important for people who have flexible knee joints, a history of knee cap dislocation, or previous knee injuries, as these factors increase the risk of developing this condition. Staying informed about this condition is the best way to prevent it.
