Muscles That Move the Knee and Ankle

Most of the muscles that move the knee come from the hip and thigh, whereas most of the muscles of the leg actually move the ankle. Some of the muscles that flex and extend the hip also flex and extend the knee. Here’s a brief list of the thigh muscles that affect the knee:

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  • Quadriceps femoris: This four-headed muscle starts in the hip and attaches to the base of the patella via the quadriceps tendon. From there, the quadriceps tendon becomes the patellar. Contracting the quadriceps extends the knee.

  • Hamstring: These muscles originate in the posterior part of the hip, and they flex the knee.

    • The semitendinosus inserts onto the medial superior part of the tibia.

    • The semimembranosus inserts onto the posterior portion of the medial tibial condyle.

    • The biceps femoris inserts onto the lateral side of the fibular head.

  • Tensor fasciae latae: This muscle also originates in the hip. It inserts onto the lateral condyle of the tibia, and its function is to flex the thigh. It also helps stabilize an extended knee.

The anterior compartment is located in front of the interosseus membrane and between the lateral part of the tibial shaft and the medial part of the fibular shaft. The muscles of the anterior compartment of the leg include the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and the fibularis (peroneus) tertius. They all move the ankle and foot.

The lateral compartment is defined as the area between the lateral portion of the fibula, the intermuscular septa (a sheet of connective tissue that divides the compartments), and the deep fascia (connective tissue covering the muscles) of the leg. Following are the main muscles here:

  • The fibularis (peroneus) longus muscle originates on the head and superior part of the fibula.

  • The fibularis (peroneus) brevis originates on the lower part of the fibula.

Both muscles insert onto the bones of the foot and help to evert the foot (move the sole of the foot outwards) and dorsiflex the ankle (bend the ankle to move the foot and toes upward).

The posterior compartment contains the calf muscles, which are divided into superficial and deep groups.

  • Superficial: This group includes the gastrocnemius, soleus, and plantaris muscles:

    • The gastrocnemius originates on the lateral and medial condyles of the femur.

    • The soleus muscle originates on the posterior part of the fibula and tibia.

    • The plantaris originates on the femur just superior to the lateral condyle.

    All three muscles insert onto the calcaneus (which you probably know better as the heel bone). The gastrocnemius is the only muscle of this group that helps flex the knee.

  • Deep: The deep muscle group includes the flexor hallucis longus, flexor digitorum longus, and tibialis posterior. They plantarflex the ankle (bend the ankle so the toes point downward) and flex the toes. Another deep muscle is the popliteus muscle, which originates on the lateral part of the lateral condyle and the lateral meniscus and inserts onto the posterior surface of the tibia. It helps to flex the knee.

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