I’ve rarely talked to a runner who has not had a knee problem at some point in their running background. The following excerpt from “Healthy Runner’s Handbook” does a terrific job of explaining some of the sources.
“The knee is the largest and most complex joint in the body. Given the enormous stresses to which it is subjected during running, it is natural that knee injuries are common among runners. The potentially debilitating consequences of a knee injury reinforce the need for a focus on prevention.
Knee overuse injuries include patellofemoral pain syndrome (kneecap pain), meniscus wear and tear, tendinitis conditions both above and below the kneecap, bursitis, and loose bodies in the knee.
Overuse knee injuries are usually caused by excessive running, but can be caused by intrinsic risk factors such as poor conditioning or muscle imbalances, and anatomical abnormalities such as a difference in leg length, abnormalities in hip rotation or the position of the kneecap, bow legs, knock knees, or flat feet.
Knee function depends on the highly complex interaction among a number of the surrounding muscles. The most important actions are performed by the quadriceps (straightening) and hamstrings (bending) in the front and back of the thigh, respectively.
Imbalances in strength or flexibility between the quadriceps or hamstrings can predispose the runner to a common overuse knee injury called patellofemoral pain syndrome, which is usually caused by the kneecap tracking improperly in its groove at the front of the bottom of the thighbone. Often, this problem is caused by the excessive tightness of the hamstring muscles in back of the thigh compared to the quadriceps muscles in front of the thigh. In such circumstances, the quadriceps cannot maintain the proper straight-ahead alignment of the lower and upper leg when the person runs; as a result, the lower leg “spins out” during the running cycle, which in turn causes excessive stress to the outer side of the kneecap.
Another common imbalance within the quadriceps muscle group in the front of the thigh, between the outer quadriceps muscle (vastus lateralis) and the inner quadriceps muscle (vastus medialis), can also cause kneecap problems. These two muscles run down either side of the front of the thigh and attach to the kneecap. Part of their role is to stabilize the kneecap. When one side is stronger than the other, the kneecap can be pulled to one side when the person runs. Since runners frequently have comparatively stronger, tighter outer quadriceps muscles than inner quadriceps muscles, the kneecap can be pulled to the outer side. This mechanism is a common cause of patellofemoral pain syndrome in runners.
Tightness in the iliotibial band – a thick, wide band of muscle-tendon tissue running down the outside of the thigh from the hip to just below the knee – is the underlying cause of one of the most prevalent overuse injuries of the knee in runners, a condition known as iliotibial band friction syndrome.
Anatomical abnormalities are the second most common intrinsic risk factor. Several are closely associated with overuse knee injuries in runners:
* Flat feet, or feet that excessively turn inward (pronate) when the person runs – Inward rotation of the lower leg causes the kneecap to track improperly (see page 11).
* Knock knees – Excessive inward angling at the point where the thigh and lower leg meet (Q angle) causes the runner’s weight to be borne on the inside of the knee; an angle of greater than 10 degrees in men and 15 degrees in women is said to predispose that person to knee problems if he or she participates in a rigorous running regimen (see page 13).
* Bow legs – Greater distance over which the iliotibial band must stretch over the outside of the leg may cause tightness at the point where the iliotibial band crosses over the outside of the knee joint (iliotibial band friction syndrome; see page 13).
* Unequal leg length – In the longer leg, the greater distance over which the iliotibial band must stretch may cause inflammation in this tissue over the outside of the knee, perhaps causing iliotibial band friction syndrome (see pages 14-15).
* Turned-in thighbones – Inward-facing kneecaps characteristic of people with this abnormality may cause tracking problems in the kneecap (see page 12).
* Loose kneecaps, high-riding kneecaps (more often seen in very tall people), shallow femoral groove (the groove at the bottom of the thighbone in which the kneecap lies is too shallow) – All three of these anatomical abnormalities can cause the kneecap to track improperly, sometimes so severely that the kneecap completely slips in and out of its proper position (subluxation).
* “Miserable malalignment syndrome” – The combination of thighs that turn inward from the hip, knock knees, and flat feet can cause many problems.
Extrinsic risk factors associated with overuse knee injuries usually involve training errors, inappropriate workout structure, and improper footwear. “