The infrapatellar fat pad, also known as Hoffa’s fat pad, is a specialized cushion of fatty tissue located within the anterior compartment of the knee joint. This structure is situated directly behind the patellar tendon and beneath the kneecap, or patella. It is considered an intracapsular but extrasynovial tissue, meaning it sits within the joint capsule but outside the synovial lining that produces joint fluid.
Location and Mechanical Function
The infrapatellar fat pad occupies the space between the front of the femur (thigh bone) and the top of the tibia (shin bone), filling what would otherwise be an empty area within the knee joint. It is bounded superiorly by the lower edge of the patella and anteriorly by the patellar tendon itself. The fat pad’s flexible structure, composed of fat lobules separated by fibrous cords, enables it to adapt its shape during knee movement.
A primary mechanical function of the fat pad is shock absorption, serving as a buffer to cushion the patella from direct impact and pressure. It also acts as a space filler, ensuring the joint cavity remains congruent throughout the full range of motion. Changes in knee position cause the fat pad’s pressure and volume to shift, helping to stabilize the patella and the patellar ligament during articulation and contributing to the distribution of synovial fluid.
Biological and Sensory Roles
Beyond its physical duties, the infrapatellar fat pad has significant biological characteristics that influence the knee’s overall health. The structure is highly vascularized and possesses a rich supply of nerve endings, including branches from the femoral, tibial, and common fibular nerves. This extensive innervation makes the fat pad one of the most sensitive structures within the knee, explaining why injuries to it can cause intense pain.
The fat pad is also recognized for its role in proprioception, the body’s ability to sense the position and movement of the knee joint. Sensory nerve fibers within the fat pad contribute mechanoreceptor signals that help the brain understand the knee’s spatial orientation. As an adipose tissue, the fat pad releases specific signaling molecules, known as adipokines and cytokines, which influence inflammatory processes within the joint environment and link it to conditions like osteoarthritis.
Common Sources of Infrapatellar Fat Pad Pain
The most frequently recognized source of pain originating from this area is Hoffa’s syndrome, or infrapatellar fat pad impingement. This condition occurs when the fat pad becomes inflamed, enlarged, and physically pinched between the lower end of the femur and the back of the patella. Activities involving repeated or forced hyperextension of the knee, such as certain sports or excessive standing, can cause the tissue to be squeezed.
Trauma to the front of the knee can also lead to swelling and inflammation, making the fat pad more susceptible to impingement. Once irritated, the tissue swells, and the resulting hypertrophy occupies more space, increasing the likelihood of chronic pinching and a cycle of pain. Since the fat pad is densely innervated, this localized compression produces a sharp, burning, or aching pain typically felt just below the kneecap. Generalized inflammation, often called infrapatellar fat pad syndrome, can also be associated with underlying issues like chronic knee osteoarthritis or abnormal patellar tracking.
Treatment Options for Fat Pad Impingement
Initial management for infrapatellar fat pad impingement focuses on conservative strategies aimed at reducing inflammation and mechanical irritation. Resting the knee and applying ice helps decrease acute swelling and pain. Nonsteroidal anti-inflammatory drugs (NSAIDs) are often recommended to manage pain and reduce the inflammatory response.
Targeted physical therapy is a primary long-term approach, focusing on improving lower limb biomechanics to prevent future pinching. This involves strengthening the quadriceps and hamstring muscles to ensure proper patellar tracking and control of the knee joint. Patients are also taught to avoid activities that involve knee hyperextension, sometimes using taping techniques to unload the fat pad. For cases that do not respond to conservative care, a physician may recommend a corticosteroid injection into the fat pad to provide potent, localized anti-inflammatory relief. Surgical intervention, such as arthroscopic partial resection or debridement of the inflamed or fibrotic tissue, is reserved for chronic cases that remain severely painful.