A fat pad is a dense cushion of fatty tissue that sits between bones, muscles, or other structures to absorb shock, reduce friction, and protect deeper tissues. Unlike the fat stored under your skin for energy, fat pads are structural. They stay in place even when you lose weight, held together by a network of tough fibrous walls that keep the fatty tissue organized into compartments. Fat pads exist throughout the body, from your knees and heels to your face and eye sockets, and each one serves a specific mechanical purpose.
How Fat Pads Differ From Body Fat
The fat you might think of when you hear the word “fat” is storage fat, the layer beneath your skin that expands and shrinks with your weight. Fat pads work differently. They’re built for structure and protection rather than energy storage. Their internal architecture includes walls of collagen and elastin fibers that create small sealed compartments, almost like a honeycomb filled with fat cells. This design lets them absorb and distribute pressure without collapsing.
Because fat pads serve a mechanical role, your body maintains them even during significant weight loss. They also tend to be more richly supplied with nerve endings than ordinary fat, which helps them relay information about pressure and position to your brain. That same nerve density, however, is also why fat pad injuries can be so painful.
Where Fat Pads Are Found
Knee (Infrapatellar Fat Pad)
The most commonly discussed fat pad sits just below and behind your kneecap, known as Hoffa’s fat pad. It fills the space inside the knee joint, lubricates the joint surfaces, and absorbs pressure during movement. It also provides internal support for the kneecap, working alongside the ligaments that hold the kneecap in place from the outside. This fat pad has an unusually high concentration of nerve fibers, including pain-sensing nerve endings, which likely gives it a secondary role as a sensor for pressure and joint position.
Heel (Calcaneal Fat Pad)
Your heel fat pad is about 18 millimeters thick in a healthy adult and is specifically engineered to handle the repeated impact of walking and running. It has two distinct layers: a superficial layer of tiny micro-chambers attached to the skin on the bottom of your foot, and a deeper layer of larger macro-chambers attached directly to the heel bone. This two-layer system works like a built-in shock absorber, distributing the force of each step across the entire heel.
Face (Buccal Fat Pad)
The buccal fat pad is a rounded pocket of fat on each side of your face, sitting between the chewing muscles and the cheek. First described by the French anatomist Xavier Bichat in 1801, it has a central body with four extensions that spread into different areas of the face. In infants, the buccal fat pad helps with suckling by stabilizing the cheeks. In adults, it cushions the muscles used during chewing, protects nearby nerves and blood vessels, and contributes to the overall shape of your face. It’s the structure targeted in buccal fat removal surgery, a cosmetic procedure aimed at slimming the cheeks.
Eye Socket (Orbital Fat Pads)
Behind your eyelids, several fat pads cushion and protect the eyeball within the bony socket. The lower eyelid alone contains at least three distinct fat compartments arranged along the inner, central, and outer portions. These pads act as a buffer during impacts to the face and help the eye move smoothly in its socket. When these pads weaken or shift forward with age, they become visible as under-eye bags.
Fat Pad Impingement in the Knee
The most common fat pad problem is Hoffa pad impingement syndrome, where the infrapatellar fat pad gets pinched between the kneecap and the thigh bone. This condition is well documented in runners, cyclists, and soldiers. It usually results from either a single traumatic event, like a blow to the knee or a twisting injury, or from repetitive stress over time. Patellar dislocations and ACL tears can also damage the fat pad through shearing forces.
People with this condition typically describe a burning or aching sensation deep in the front of the knee, localized 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 extension, or after sitting with the knee bent for a long time. Most people also notice restricted range of motion, and in some cases the limitation can be significant, with one study reporting severe restriction at just 20 degrees of flexion.
On physical exam, the fat pad may feel enlarged, firm, or tender when pressed. A specific test called the Hoffa test involves pressing firmly just below the kneecap while the knee moves from a bent to a straight position. If this reproduces the pain, it supports the diagnosis. However, Hoffa pad impingement is considered a diagnosis of exclusion because many other conditions cause similar anterior knee pain.
What Impingement Looks Like on Imaging
MRI is the primary tool for evaluating fat pad problems. A healthy infrapatellar fat pad appears bright on most MRI sequences, matching the signal of normal fat elsewhere in the body, with thin dark lines representing the internal fibrous walls. When the fat pad is inflamed or impinged, dark areas appear on certain sequences, representing swelling and fluid accumulation. These changes can range from subtle pockets of edema to extensive hemorrhage after trauma.
In chronic cases, the inflammation can progress to fibrosis, where scar tissue replaces the normal fatty tissue. Fibrosis appears dark on all MRI sequences and can eventually lead to the formation of cartilage or bone-like tissue within the fat pad itself. ACL injuries and nearby fractures commonly cause reactive swelling in the fat pad as well, so radiologists look at the surrounding structures to determine the underlying cause.
Treatment for Fat Pad Problems
Most fat pad impingement in the knee responds to conservative treatment initially. Rest, activity modification, taping techniques that lift the fat pad away from the joint space, and physical therapy focused on improving patellar tracking are typical first steps. Injection of a local anesthetic into the knee can both confirm the diagnosis (if pain disappears completely) and provide temporary relief. Corticosteroid injections are sometimes combined with the anesthetic for longer-lasting effect.
When conservative approaches fail to provide lasting improvement, surgical excision of part of the fat pad is an option. This is typically done arthroscopically and involves removing the damaged or scarred portion of the fat pad to prevent further impingement. Surgery is generally reserved for chronic cases that haven’t responded to months of nonsurgical treatment.
Heel Fat Pad Thinning With Age
A study of over 1,100 people between ages 1 and 96 found that heel fat pad thickness increases from childhood through the mid-30s to mid-40s, then gradually decreases from that point through old age. Men consistently had thicker heel fat pads than women of the same age, and thickness in men correlated well with height and body mass.
As the heel fat pad thins, its ability to absorb impact diminishes. This is one reason heel pain becomes more common in older adults. The loss of cushioning means more force transfers directly to the heel bone with each step. People with significant heel fat pad atrophy often notice a deep, bruise-like ache on the bottom of the heel that worsens with standing or walking on hard surfaces, distinct from the sharp morning pain typical of plantar fasciitis.