What Keeps the Knee From Moving Medially to Laterally?

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.