The infrapatellar fat pad, commonly known as Hoffa’s fat pad, is a distinct structure within the knee frequently involved in anterior knee discomfort. This specialized cushion is a common, yet often unrecognized, source of pain. Understanding its function and location is the first step toward addressing the knee pain that arises when this tissue becomes irritated.
Anatomical Structure and Location
Hoffa’s fat pad is a mass of specialized adipose tissue situated at the front of the knee joint. It is located directly beneath the patella and behind the patellar tendon. The structure is nestled between the thighbone (femur) and the shinbone (tibia), sitting within the joint capsule but outside the synovial lining.
The fat pad is highly dynamic, changing shape as the knee moves through its range of motion, displacing superiorly and posteriorly during knee flexion. This tissue is richly supplied with blood vessels and, most significantly, a dense network of nerves. This extensive innervation is the primary reason why damage or inflammation causes such intense pain.
Essential Functions of the Fat Pad
The primary function of the infrapatellar fat pad is to act as a protective mechanical cushion for the knee joint. It helps absorb shock and distribute pressure across the knee, preventing the patella from directly impacting the femur during sudden movements or direct trauma. The pad also functions as a space filler, occupying the potential dead space within the joint capsule as the knee moves.
Beyond its physical roles, the fat pad contributes to the knee’s biomechanics. Its high nerve density allows it to provide proprioception—the body’s sense of its own position and movement. This sensory feedback helps the brain monitor and control the precise movements of the knee joint. The fat pad is also recognized as an active endocrine organ involved in the overall inflammatory health of the joint.
Understanding Hoffa’s Impingement Syndrome
The most common condition affecting this structure is Hoffa’s Impingement Syndrome, also known as infrapatellar fat pad syndrome. This occurs when the fat pad becomes inflamed and swollen, causing it to get pinched between the patella and the femur. Once the fat pad swells, it is more susceptible to further pinching, creating a painful cycle of irritation and inflammation.
The impingement is often triggered by repetitive microtrauma, direct injury, or chronic hyperextension of the knee joint. Biomechanical issues, such as tight quadriceps muscles or abnormal kneecap tracking, can also increase the pressure on the fat pad. Individuals who participate in running, jumping, or activities that involve a high degree of knee extension are particularly susceptible.
Symptoms typically involve a sharp or aching pain localized to the front of the knee, specifically below the kneecap. The pain often worsens with activities that force the fat pad into the joint space, such as standing for long periods, squatting, or fully straightening the leg. A medical professional may perform Hoffa’s test, which involves pressing on the area just below the kneecap while the patient contracts their thigh muscles; tenderness indicates fat pad inflammation.
Diagnosis and Treatment Options
Diagnosing Hoffa’s syndrome begins with a thorough physical examination and patient history, focusing on the specific location and nature of the pain. Imaging tests, such as an MRI, are frequently used to confirm inflammation or swelling in the fat pad and to rule out other causes of anterior knee pain. A correct diagnosis is important because the condition is sometimes confused with patellofemoral pain syndrome or meniscal tears.
Treatment focuses on two primary goals: calming the inflammation and addressing the underlying cause of the pinching. Initial care typically involves conservative measures, such as rest, applying ice, and using non-steroidal anti-inflammatory drugs (NSAIDs) to manage pain and swelling. Physical therapy is essential for recovery, aiming to improve flexibility and strengthen the muscles that stabilize the knee.
A physical therapist may also use specialized taping techniques to temporarily alter the kneecap’s position, creating more space for the inflamed fat pad. If conservative treatments fail to provide relief, a corticosteroid injection may be administered directly into the fat pad to rapidly reduce inflammation. Surgical intervention, which involves arthroscopic removal of the inflamed or scarred portion of the fat pad, is generally considered a last resort for chronic, severe cases.