Knee sprains and related injuries

[Julene]

Knee sprains occur when the ligaments that attach the thighbone (femur) to the shinbone (tibia) are torn. The cartilage pads (menisci), which act as shock absorbers in the knee, may also be injured.

Knee sprains are often caused by bending or twisting the knee when the foot is planted on the ground.
The knee is usually painful and swollen.
The diagnosis is usually based on results of the physical examination.
Resting and keeping the knee immobile are often the only treatment needed, but sometimes severe injuries must be repaired surgically.

(See also Overview of Sprains and Other Soft-Tissue Injuries.)
Several ligaments help hold the knee in place:

Collateral ligaments: These ligaments, located on either side of the knee prevent the knee from moving from side to side too much. The medial collateral ligament is located on the inside of the leg, and the lateral collateral ligament is located on the outside of the leg.
Cruciate ligaments: These ligaments prevent the knee from moving forward or backward too much. The anterior cruciate ligament (ACL) crosses in front of the posterior cruciate ligament (PCL) to form an X.

Cartilage pads (menisci) fill in the space between the thighbone (femur) and shinbone (tibia). They help stabilize and cushion the knee joint.
The most commonly injured structures in the knee are

The medial collateral ligament
The anterior cruciate ligament

Which structures are torn depends on the direction of the force against the knee:

Medial collateral and anterior cruciate ligaments: One or both of these ligaments can be torn the knee is hit from the side while people have their weight on one foot that is firmly planted on the ground, as occurs during a football tackle. Damage is more likely if the knee also twists.
Lateral collateral and anterior cruciate ligaments: These ligaments can be damaged when force against the knee is directed outward. This type of injury can occur when the leg is pushed from the inside.
Anterior and posterior cruciate ligaments: These ligaments can be damaged when the knee is forcefully straightened.
Menisci: The menisci can be damaged when people have their weight on a foot and their knee twists as it is injured.