Knee: Muscles

Muscles

There are two groups of muscles at the knee. The four quadriceps muscles on the front of the thigh work to straighten the knee from a bent position. The hamstring muscles, which run along the back of the thigh from the hip to just below the knee, help to bend the knee.

Tendons and ligaments

The quadriceps tendon connects the quadriceps muscle to the patella and provides the power to straighten the knee. The following four ligaments connect the femur and tibia and give the joint strength and stability:

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  The medial collateral ligament (MCL), which runs along the inside of the knee joint, provides stability to the inner (medial) part of the knee.
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  The lateral collateral ligament (LCL), which runs along the outside of the knee joint, provides stability to the outer (lateral) part of the knee.
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  The anterior cruciate ligament (ACL), in the center of the knee, limits rotation and the forward movement of the tibia.
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  The posterior cruciate ligament (PCL), also in the center of the knee, limits backward movement of the tibia.

The knee capsule is a protective, fiber-like structure that wraps around the knee joint. Inside the capsule, the joint is lined with a thin, soft tissue called synovium.