The knee joint is a type of hinge joint that allows the knee to bend forwards and backwards. For most athletic activities the knee is a critical region as it must act both to support the weight of the body, as well as flex and extend to generate the propulsive forces needed to move the body. To help with these tasks is a complex set of muscles that surround the knee. It is essential that these muscles possess adequate strength, flexibility, and coordination as we rely on them to protect and stabilize the knee during virtually every athletic activity.
For example, with sports such as basketball or soccer, the muscles of the knee must contract during running, jumping, or to initiate rapid changes in direction. Similar demands on the knee can be seen within a wide variety of sports such as hockey, football, baseball, racquet sports, and martial arts. These athletic motions require explosive muscle contractions at the knee, but also require finely tuned muscle balance and coordination to control the knee and prevent excessive strain during these movements.
For the knee to stay healthy and retain optimal function it is absolutely critical that there is adequate strength, flexibility, and coordination of the surrounding muscles. However, maintaining proper function at the knee in itself is not enough. In fact, for the knee to stay injury-free, proper function is needed at other regions of the leg and trunk.
For example, in addition to problems in the knee muscles, knee injury can also be linked to problems at the adjacent joints, such as the foot, hip, and pelvis. This is because the knee is directly connected to these structures through the tibia and femur, as well as the surrounding muscles.
This interconnectedness is referred to as the kinetic chain. We can think of the knee as one link in the kinetic chain, but each link can be affected by any of the other links. This can be a big problem for the knee, because the foot and hip move differently than the knee. For example, both the hip and the foot are designed to move in all three planes: front to back, side to side, and in rotation. The knee, however, is designed to move primarily in only one plane: forward and backward. If even a minor problem, such as excessive tightness, weakness, joint restriction, poor muscle balance, or faulty alignment, exists in the hip or foot, that can cause the knee to move excessively into a side-to-side or twisting direction.
This abnormal knee motion will result not only in excessive strain and overload to the bone and ligaments of the knee joint, but will place even further demand on the muscles that surround the knee in an attempt to protect the knee and correct the abnormal movement. This does not mean that the foot or hip will themselves be painful; in fact, the knee is often the site that first develops pain, even if the knee is not the primary cause of the problem!
This situation( when pain develops in one area as a result of a problem in another region) is referred to as “movement compensation.” Because of the repetitive, high-force motions associated with sports, even a minor movement compensation will be greatly magnified and prevent the athlete from properly controlling the knee and generating the propulsive forces required for the athletic movements. As this occurs, instead of forces being transferred effectively through the muscles and joints of the kinetic chain, the forces become concentrated at the knee, which is the site of the movement compensation.
Due to the impact that movement compensation has on the knee, it is critical that the entire kinetic chain be evaluated to ensure all areas are functioning properly. Failure to identify and correct the compensation will not only prolong the injury process, but will also lead to the injury recurring.