As the name suggests, runner's knee is a common ailment among runners. But it can also strike any athlete who does activities that require a lot of knee bending -- like walking, biking, and jumping. It usually causes aching pain around the kneecap.
Runner's knee isn't really a specific injury. It's a loose term for several specific disorders with different causes. Runner's knee can result from:
Overuse. Repeated bending or high stress exercises such as lunges and plyometrics can irritate the kneecap joint (patellofemoral joint). Overstretched tendons (tendons are the tissues that connect muscles to bones) may also cause the pain of runner's knee.
Direct trauma to the knee, like a fall or blow.
Malalignment. If any of the bones are slightly out of their correct position -- or misaligned -- physical stress won't be evenly distributed through your body. Certain parts of your body may then be subjected to higher stresses. This can cause pain and injury to the joints. Sometimes, the kneecap itself is slightly out of position.
Problems with the feet. Runner's knee can result from hypermobile feet (a condition in which the joints associated with the feet can be move more than what's normal), fallen arches, or overpronation (flat feet). These conditions in which the impact of a step causes the arches of your foot to collapse, may excessively stress joints and tissues of the knee, .
Weak thigh muscles or muscle imbalance. Weakness in thigh muscles causes a disproportional load on isolated sections of the knee cap leading to abnormal wear patterns and pain.
Runner's knee is also called patellofemoral pain syndrome.