Popliteus muscle

The popliteus muscle in the leg is used for unlocking the knees when walking, by laterally rotating the femur on the tibia during the closed chain portion of the gait cycle (one with the foot in contact with the ground). In open chain movements (when the involved limb is not in contact with the ground), the popliteus muscle medially rotates the tibia on the femur. It is also used when sitting down and standing up. It is the only muscle in the posterior (back) compartment of the lower leg that acts just on the knee and not on the ankle. The gastrocnemius muscle acts on both joints.

Popliteus muscle
Popliteus muscle (shown in red)
Dissection video (2 min 22 s)
Details
Origin	lateral femoral epicondyle
Insertion	posterior surface of tibia proximal to soleus line
Artery	Popliteal artery
Nerve	Tibial nerve
Actions	Medially rotates tibia on the femur if the femur is fixed (sitting down) or laterally rotates femur on the tibia if tibia is fixed (standing up), unlocks the knee to allow flexion (bending), helps to prevent the forward dislocation of the femur while crouching
Identifiers
Latin	Musculus popliteus, poplit=ham (pit) of the knee
TA	A04.7.02.050
FMA	22590
Anatomical terms of muscle

Structure

It originates from the lateral surface of the lateral condyle of femur by a rounded tendon, the fibers pass downward and medially and give insertion to the posterior surface of tibia, above the soleal line. The muscle arises within the capsule of knee joint and its tendon separates the lateral meniscus from the lateral ligament of the joint.

Innervation

Nerve supply is via the tibial nerve from spinal roots L5 and S1.

Variation

There is sometimes an additional head from the sesamoid bone in the lateral (outer) head of the gastrocnemius muscle.

Rarely an additional inconstant muscle; the popliteus minor is seen. It originates from the femur on the inner side of the plantaris muscle and inserts into the posterior ligament of the knee-joint.

Peroneotibialis, 14% of population. Origin is inner side of the head of the fibula, insertion into the upper end of the oblique line of the tibia, it lies beneath the popliteus.[1]

Another variant, the cyamella, is a small sesamoid bone embedded in the tendon of the popliteus muscle. It is rarely seen in humans, but has been described more often in other primates and certain other animals. [2]

Function

The popliteus assists in flexing the leg upon the thigh; when the leg is flexed, it will rotate the tibia inward.

It is especially called into action at the beginning of the act of bending the knee, inasmuch as it produces the slight inward rotation of the tibia, which is essential in the early stage of this movement.

When the knee is in full extension, the femur slightly medially rotates on the tibia to lock the knee joint in place. Popliteus is often referred to as the "Key" to unlocking the knee since it begins knee flexion by laterally rotating the femur on the tibia.

Popliteus is also attached to the lateral meniscus in the knee and draws it posteriorly during knee flexion to prevent crushing the meniscus between the tibia and femur as the knee flexes.

Additional images

• 
  Animation
• 
  Deep layer of muscles on the back of the right leg
• 
  Muscles of deep posterior compartment of the right leg

See also

• Posterolateral knee

References

This article incorporates text in the public domain from page 484 of the 20th edition of Gray's Anatomy (1918)

1. Gray, Henry. 1918. Anatomy of the Human Body. Page 485
2. Akansel, Gur; Inan, Nagihan; Sarisoy, H. Tahsin; Anik, Yonca; Akansel, Sertaç (2006). "Popliteus muscle sesamoid bone (Cyamella): Appearance on radiographs, CT and MRI". Surgical and Radiologic Anatomy. 28 (6): 642–645. doi:10.1007/s00276-006-0134-8. PMID 17066262.

External links

• Anatomy photo:15:st-0413 at the SUNY Downstate Medical Center
• PTCentral