Patellar Tracking Disorder
Patellar tracking disorder occurs when the kneecap (patella) shifts out of place as the leg bends or straightens. In most cases, the kneecap shifts too far toward the outside of the leg, although in a few people it shifts toward the inside.
Your knee joint is a complex hinge that joins the lower leg bones (tibia and fibula) with the thighbone (femur). The kneecap is held in place in the front of the knee joint by tendons on the top and bottom and by ligaments on the sides. A layer of cartilage lines the underside of the kneecap, helping it glide along the groove at the end of your thighbone.
The kneecap can shift or rotate off track if the groove is too shallow or if the cartilage is damaged. Ligaments, tendons, or muscles that are too loose or too tight may also lead to a misaligned kneecap.
A patellar tracking disorder is usually caused by several problems combined. The shape of the patella; too tight or too loose muscles and tendons in the leg, foot, or hip areas; damage to cartilage; and overuse may lead to patellar tracking disorder. See a picture of the muscles and tendons related to patellar tracking disorder.
Also, a severe blow to the inside of a healthy knee can knock a kneecap out of alignment or, in extreme cases, dislocate it. Symptoms of a dislocated kneecap include the knee looking misshapen like a bone is out of place, not being able to bend or straighten the knee, knee swelling, and severe pain.
Sometimes patellar tracking problems run in the family. If you have a family member with knee pain, you may want to take preventive measures, such as strengthening your thigh muscles.
If your kneecap is out of alignment, you may have discomfort or pain, especially when you go down stairs, sit for a long time, stand up from sitting, or squat. This kind of pain, also known as patellofemoral pain, may be caused by patellar tracking disorder.
You also may feel a popping, grinding, slipping, or catching of the kneecap when you bend or straighten your leg. Or you may feel that your knee is buckling or giving way, as though the knee suddenly cannot support your body weight.