Hoffa’s fat pad is a wedge-shaped mass of fatty tissue located inside your knee joint, tucked behind and below the kneecap. It fills the space bounded by the bottom edge of the kneecap, the patellar tendon (the thick band connecting your kneecap to your shinbone), the top of the shinbone, and the rounded ends of the thighbone. Despite being overlooked for decades, it is now recognized as one of the most nerve-rich structures in the knee and a significant source of anterior knee pain when irritated or injured.
Anatomy and Blood Supply
The fat pad is composed primarily of adipose (fatty) tissue divided into lobules by thin fibrous walls called septa. It has its own dedicated blood supply from arteries that run vertically along both sides of it, branching off the same vessels that feed the kneecap. These arteries descend through the fat pad just behind the patellar tendon and connect to each other through two to three smaller horizontal arteries, creating a rich vascular network. That generous blood supply is one reason the fat pad swells so readily when irritated.
What It Does in Your Knee
The fat pad serves as a biomechanical cushion. During movement, it deforms and redistributes to fill the changing spaces between the kneecap, thighbone, and shinbone, reducing friction and absorbing shock. It also helps distribute the lubricating fluid inside your joint more evenly across the cartilage surfaces.
Beyond cushioning, the fat pad has a metabolic role. It secretes hormones like leptin and adiponectin, the same signaling molecules produced by fat tissue elsewhere in your body. In a healthy knee, this is a background process. But in osteoarthritis, immune cells can infiltrate the fat pad, and it begins pumping out inflammatory chemicals. The internal fibrous walls thicken, and new blood vessels grow into the tissue. This transforms the fat pad from a passive cushion into an active participant in joint inflammation.
Why It Causes Pain
Hoffa’s fat pad is densely packed with nerve endings, making it one of the most pain-sensitive structures in the knee. When the fat pad becomes swollen or enlarged, it can get pinched (impinged) between the kneecap and the thighbone during normal movement. This impingement typically affects the upper outer portion of the fat pad.
The resulting condition, called Hoffa’s syndrome or fat pad impingement syndrome, produces a burning or aching pain at the front of the knee, felt deep to and on either side of the patellar tendon near the bottom of the kneecap. The pain is worst when the knee is fully straightened, during active leg extension, or after prolonged sitting with the knee bent. Even tightening your quadriceps with the leg straight can reproduce the discomfort. People with fat pad impingement typically lose some range of motion, and in some cases the restriction can be severe, limiting flexion to as little as 20 degrees. The kneecap itself may feel stiff and harder to move.
On physical exam, the affected fat pad often feels enlarged, firm, and tender when pressed. A clinical maneuver called the Hoffa test can help identify the problem: firm pressure is applied just below the kneecap alongside the patellar tendon while the knee is bent to about 30 degrees, then the knee is straightened. If this reproduces or increases the pain, the test is considered positive.
Common Causes of Fat Pad Irritation
A direct blow to the front of the knee is one of the most straightforward triggers. Falls, dashboard injuries in car accidents, or any impact that compresses the fat pad against the bones behind it can cause bleeding and swelling within the tissue. Repetitive hyperextension (locking or snapping the knee straight forcefully) is another common cause, particularly in dancers, gymnasts, and runners. Chronic overuse gradually irritates the fat pad, leading to swelling that makes impingement more likely with each subsequent movement.
Knee surgery, including arthroscopy, can also irritate the fat pad. Prolonged kneeling, wearing high heels (which shifts weight forward and changes knee mechanics), and altered walking patterns from other injuries can all contribute. In osteoarthritis, the inflammatory changes within the fat pad itself can cause it to enlarge and become symptomatic even without a specific injury.
How It Differs From Patellar Tendonitis
Fat pad impingement and patellar tendonitis can feel similar because pain in both conditions centers around the front of the knee near the patellar tendon. The key difference is the pain pattern. Patellar tendonitis typically hurts most during loading activities like jumping, squatting, or going downstairs, and the tenderness is located directly on the tendon itself. Fat pad pain, by contrast, is worst at full knee extension and is located on either side of the tendon rather than on it. The burning quality of fat pad pain, the restriction in straightening the knee, and a positive Hoffa test all help distinguish the two. MRI is the most reliable way to confirm the diagnosis. On imaging, an irritated fat pad shows swelling (visible as bright areas on certain scan sequences), most commonly in its upper outer portion. In chronic cases, the cartilage on the underside of the kneecap may show thinning or small erosions.
Conservative Treatment Options
Most cases of fat pad impingement respond to non-surgical treatment. The initial focus is on reducing swelling. Applying ice to the area below the kneecap for 15 to 20 minutes, two to three times a day, is a standard starting point. Therapeutic ultrasound with anti-inflammatory gel can also help bring down inflammation.
Taping is one of the more effective hands-on strategies. The goal is to lift the bottom edge of the kneecap away from the fat pad to reduce pinching. A common technique uses strips of rigid or elastic tape applied diagonally along the inner and outer edges of the kneecap, pulling it slightly upward, with a horizontal strip across the top to tilt the lower edge of the kneecap forward. Separate taping to prevent the knee from snapping into hyperextension can also reduce symptoms.
Stretching the quadriceps, particularly the rectus femoris (the muscle that crosses both the hip and knee), helps offload the lower pole of the kneecap. Progressive strengthening of the quadriceps at end-range extension is equally important because it improves control of the knee joint and reduces the tendency to hyperextend during walking, running, or stair climbing. Correcting lower limb biomechanics, including avoiding high heels, rounds out the rehabilitation approach.
When Surgery Is Considered
If months of conservative treatment fail to resolve symptoms, partial removal of the fat pad through arthroscopic surgery is an option. The surgeon trims the damaged or fibrotic portion of the fat pad to eliminate the tissue that is being pinched. This is generally reserved for cases where the fat pad has undergone significant structural changes, such as thickening of the internal fibrous walls or the formation of scar tissue.
The question of whether to preserve or remove the fat pad also comes up during total knee replacement surgery, where the fat pad is sometimes resected simply to give the surgeon better visibility. The evidence here is mixed. One randomized trial of 90 patients found that those whose fat pad was removed had more anterior knee pain one year after surgery. Another study found that preserving the fat pad added operating time but reduced wound complications. Two recent systematic reviews reached opposite conclusions: one favored preservation for better pain outcomes, while the other found no meaningful difference. The emerging consensus leans toward preserving a healthy fat pad when possible and removing it only when it shows clear signs of disease on preoperative MRI.