Did you know that fat can hurt? Well, not all fat but the fat around your patellar tendon, called the fat pad.
The fat pad is a small amount of fat located beneath and to the sides of your patellar tendon. When you straighten your knee, you will squeeze the fat pad and you will see two small (or sometimes large) mounds just below your knee cap. The fat pad provides extra cushioning for your tendon and knee cap.
Sometimes, a runner will inadvertently pinch the fat pad. As the foot hits the ground, your leg wants to turn inward form the force of gravity. Your foot rolls to the ground, tibia and femur turn inward and the patella (knee cap) goes along for the ride. The arch of your foot and your hip muscles counter this natural rotation. The result is a controlled deceleration much like stretching a spring giving you just the right amount of inward turn.
Some runners have a little too much rotation either from a collapsing forefoot (known as excessive pronation) or from weak hips. When your leg turns inward too fast, your patella, which normally rides along with the turn of the tibia and femur, gets left behind. With the patella lagging behind the inward turn, one of the mechanical problems that crops up is a pinching of the fat pad (others include focal overloading of the joint cartilage, patella tendon or iliotibial band) between your knee cap and either the femur (thigh bone) or tibia (shin bone).
The fat pad has an abundance of nerve and blood supply thanks to the synovium which surrounds it. When you pinch it, the pain is often sharp, well localized and generally only occurs with either weight bearing or with straightening of the knee. You rarely feel the aching, stiffness or sense of fullness that accompanies degenerative joint disease or the clicking and locking found with mensical tears.
Fat pad impingement is a diagnosis made by exclusion because there are few physical findings. As a result, it is often missed. Diagnosis by exclusion means that you have systematically ruled out other potential causes of knee pain. The history (the location of the pain, onset, characteristics of the symptoms, intensity and duration of the symptoms, factors which aggravate and alleviate the symptoms) along with the physical examination help the practitioner eliminate a number of causes. For fat pad impingement, the history typically includes:
- Running (or some other weight bearing activity)
- The pain is well localized to the front of the knee or to the side of the patella tendon.
- The pain is usually sharp and can last for several hours or days once provoked.
- Going up and down steps or squatting will aggravate the symptoms.
- Rest, analgesics or non-steroidal anti-inflammatory drugs alleviates the discomfort.
The two key findings from the physical examination are both from palpating specific areas of the knee which reproduce the symptoms. Applying pressure over the side of the patella tendon and over the fat pad will typically cause a familiar pain. Occasionally, straightening the knee will also reproduce the symptoms.
If you have fat pad impingement, you may need a special brace or have your knee professionally taped to reduce the stretch on your fat pad. Injured tissue does not like to be stretched and the fat pad is no different. By decreasing the stretch, you reduce or stop the irritation and help the tissue heal. You should also make sure your hip rotator muscles are strong to help control the movement of your femur (read As The Hip Turns for more details). If these steps do not work, you may need an injection of local steroids by your physician or, in rare cases, surgical excision of the tissue.
Pain in the front of the knee can sometimes be due to an inflamed fat pad. Before you make the number one mistake every injured athlete makes, have your knee evaluated by your physician, or physical therapist. Problems seem much smaller and easier to overcome when you have all of the facts.
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Author. Speaker. Therapist.
P.S. If you would like to hear more about the secrets I use with runners who have knee pain, come to a 4 hour seminar I am doing at the Texas Physical Therapy Association's 2005 Annual Conference and Student Conclave in Houston, Texas on October 22nd entitled: "Runner's Knee: The 10 Mistakes Athletes Make".