COLLATERAL LIGAMENT INJURY
COLLATERAL LIGAMENT INJURY
Ligaments are tough bands of tissue that connect the ends of bones together.
There are two collateral ligaments, one on either side of the knee, that limit side to side motion of the knee.
The medial collateral ligament (MCL) is found on the side of the knee closest to the other knee.
The lateral collateral ligament (LCL) is found on the opposite side of the knee.
Together, the collateral ligaments also work with the posterior cruciate ligament (PCL) to prevent excessive motion of the tibia posteriorly (back) on the femur.
When the lateral (outside edge) of the capsule is injured, the MCL reduces anterolateral rotatory instability (ALRI).
In other words, the MCL acts as a restraint to rotation. ALRI means there’s too much rotation of the tibia (shinbone) relative to the femur (thighbone).
If an injury causes these ligaments to stretch too far, they may tear. The tear may occur in the middle of the ligament, or it may occur where the collateral ligament attaches to the bone, on either end.
If the force from the injury is great enough, other ligaments may also be torn.
The most common combination is a tear of the MCL and a tear of the anterior cruciate ligament (ACL). The ACL runs through the center of the knee and controls how far forward the tibia moves in relation to the femur.
MCL tears are more common than LCL tears, but a torn LCL has a higher chance of causing knee instability.
One reason for this is that the top of the shinbone (called the tibial plateau) forms a deeper socket on the side nearest the MCL. On the other side, near the LCL, the surface of the tibia is flatter, and the end of the shinbone can potentially slide around more. This difference means that a torn LCL is more likely to cause knee instability.