A knee ligament injury includes any damage sustained, whether acutely or through repetitive use, to the intracapsular or extracapsular ligaments of the knee joint. Ligaments are bands of fibrous connective tissue that at the knee connect the bone of the upper leg, the femur, to the bones of the lower leg, the tibia and fibula. They also are vital to the stabilization of the knee joint and to the transfer of forces from the muscles of the hip and thigh across the knee, resulting in movement of the lower leg. Because they are less flexible than muscle tissue and situated at such a vulnerable location, however, the knee ligaments are rather susceptible to injury.
Those structures that commonly sustain knee ligament injury include both the intracapsular ligaments, those found within the knee joint capsule, and the extracapsular ligaments, those that lie outside of the joint capsule. The main intracapsular knee ligaments include the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), and the transverse ligament. Perhaps the best known and most commonly injured, the ACL runs diagonally across the front of the knee joint beneath the patella. The PCL crosses behind the ACL in the opposite direction so that the two form an X, and it is less commonly injured. Rarely injured is the transverse ligament, which runs horizontally across the front of the medial and lateral menisci.
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The main extracapsular ligaments include the collateral ligaments, which run vertically between the leg bones to either side of the knee joint, and the patellar ligament. Collateral ligaments, which are relaxed when the knee is bent and taut when the leg is straight, include the medial collateral ligament (MCL) on the inside of the knee, and the lateral collateral ligament (LCL) on the outside of the knee. An oft-injured knee ligament, the patellar ligament runs vertically from the kneecap to the tibia bone in the lower leg and helps transfer forces from the knee extensor muscles in the thigh across the joint.
A knee ligament injury can either be sustained by a sudden trauma to the joint, often from playing sports, or by a gradual wearing down of the tissue from overuse, such as in frequent squatting. These injuries typically present as strains, in which the ligament is stretched beyond its normal limits, as partial tears, or as complete tears, also known as ruptures. Symptoms of all of these injuries will include pain and swelling, and immediate medical attention is required in addition to application of the RICE formula: rest, ice, compression, and elevation.
Among those who play sports, the ligaments most commonly injured are the ACL, MCL, and PCL, often due to contact injuries. The ACL links the femur to the tibia and is an important stabilizer of the knee, and it is often the first to suffer a tear, either from direct force applied to the knee, or from a non-contact force — a sudden twisting or explosive movement. Of the collateral ligaments, the MCL is located along the inside of the knee, and as such is easily ruptured from lateral contact forces — those applied to the outside of the knee. Lastly, the PCL, which stabilizes the knee joint from behind, can be injured by any blow or explosive movement that results in knee hyperextension, as the back of the knee would be overstretched.
Overuse of the knee joint most typically causes damage to the patellar ligament, which is so heavily involved in extending the knee. Every time the knee extends from a flexed or bent position, the patellar ligament, alternately known as the patellar tendon, absorbs a great deal of force. Injuries to the patellar ligament include strains and, very commonly, tendinitis, which can only be treated by avoiding the repetitive knee-bending movements, as in cycling, running, or squatting, that led to the injury in the first place. As with any knee ligament injury, this damage can take weeks or even months to fully heal and requires medical attention.