What Keeps the Knee From Moving Medially to Laterally?

The knee is an incredibly complicated joint consisting of three bones whose ends are covered in cartilage: the tibia, the patella and the femur. Beside the tibia in the lower leg, on the exterior portion or lateral side, is the fibula, a smaller, thinner bone. Although the fibula articulates with neither the patella nor femur, it is an important structure of the knee. Four ligaments connect these bones and cartilage to each other: the two collateral ligaments, the anterior cruciate ligament and the posterior cruciate ligament. Additionally, 12 muscles extend from the upper leg to the lower leg, thereby crossing the knee joint. Several of these muscles are attached to the bones of the knee via tendons.

All of these structures support the knee joint. This joint is designed like a hinge, with the primary movements being flexion (bending) and extension (straightening). Several structures prohibit lateral and medial, or side-to-side, movements of the knee joint.

Collateral Ligaments

• Two collateral ligaments connect the femur and shin bones and provide side-to-side support. The lateral collateral ligament (LCL) connects the femur to the fibula, along the outside of the leg. The LCL provides lateral support for the knee, keeping it from bending outwards. The medial collateral ligament (MCL) connects the femur to the tibia, along the inside of the leg. The MCL provides medial support for the knee, keeping it from bending towards the inside.

Medial Muscular Support

• Although the MCL is primarily responsible for the medial stability of the knee, three muscles contribute slight medial support. The semitendinosus, sartorius and gracilis muscles all originate in the pelvic area and insert on the medial (or interior) side of the tibia.

Iliotibial Band

• The LCL contributes to the lateral stability of the knee, but it is greatly aided by a variety of other muscles and structures. One such structure is the iliotibial band. This thick band of fascia begins at the iliac crest, or top of the hip bone, runs down the outside of the leg and attaches to all three bony structures of the knee.

Lateral Muscular Support

• Like the iliotibial band, the biceps femoris, popliteus and lateral head of the gastrocnemius muscles provide lateral support for the knee. The biceps femoris is one of the hamstring muscles located on the back of the thigh. This muscle originates in the pelvic area and attaches to the lateral side of the tibia as well as the fibula. Both the popliteus muscle and the lateral head of the gastrocnemius muscle originate from the lateral side of the femur to provide lateral support to the knee joint.