|Origin||Lateral femoral condyle|
Fibrous capsule of the knee joint
Posterior horn of the knee’s lateral meniscus
Head of the fibula via popliteofibular ligament
|Insertion||Posterior surface of the tibia, proximal to the soleal line|
|Action||Lateral rotation of the femur on the tibia|
Medial rotation of the tibia on the femur
Protection of the lateral meniscus
Insignificant amount of knee flexion
|Nerve||Tibial nerve (L5-S1)|
|Artery||Popliteal artery (medial inferior genicular branch)|
Posterior tibial artery (muscular branch)
Location & Overview
The popliteus muscle is a small, somewhat triangular shaped muscle located at the posterior aspect of the knee joint. It plays an important role in the stability and functioning of the knee joint, as it aids in unlocking the knee during the initiation of knee flexion from a fully extended position . The popliteus muscle is situated deep within the popliteal fossa, which is a diamond-shaped region found posterior to the knee . The popliteus is unique because of its inverted origin and insertion, with the tendinous attachment originating from the proximal bone and the fleshy attachment representing the muscle’s insertion . For most muscles, the origin is usually the more stable and fixed attachment point on a bone. While the insertion is the movable attachment point that pulls on a bone to create movement. However, in the case of the popliteus muscle, this relationship is inverted.
In relation to other muscles, the popliteus muscle is positioned deep to the gastrocnemius, plantaris, and the heads of the biceps femoris muscle in the popliteal fossa. It is also located medial to the lateral head of the gastrocnemius muscle and the tendon of the biceps femoris muscle .
The muscle is enveloped by the popliteal vessels and nerves, which include the popliteal artery, medial inferior genicular branch of the popliteal artery, muscular branch of the posterior tibial artery, tibial nerve, and the common peroneal nerve . Furthermore, the popliteus muscle is in close association with the arcuate popliteal ligament, which originates from the posterior aspect of the fibular head and attaches to the lateral condyle of the femur . This ligament lies superficial to the popliteus muscle and helps to stabilise the posterolateral corner of the knee joint .
Origin & Insertion
The popliteus muscle has a unique morphology, with its origin and insertion points inverted compared to most muscles. The tendinous attachment serves as the origin, while the fleshy attachment acts as the insertion .
The origin of the popliteus muscle has several components. The primary origin is a small pit on the lateral surface of the lateral femoral condyle, just below the attachment of the fibular collateral ligament of the knee . Additional origins include a fibrous attachment from the popliteus to the posterior aspect of the fibrous capsule of the knee joint, which is a tough, fibrous structure that encloses and protects the joint. Another component of the popliteus’ origin is a fibrous band that extends from the superior margin of the terminal portion of the tendon and attaches to the superior margin of the posterior horn of the lateral meniscus. The lateral meniscus is a crescent-shaped piece of cartilage in the knee joint that helps with shock absorption and stabilisation. The posterior horn of the meniscus refers to the rear part of the lateral meniscus . Furthermore, there is also another origin which is fibrous band called the popliteofibular ligament, which extends between the head of the fibula and the popliteus tendon .
The insertion of the popliteus muscle is on the popliteal surface of the tibia, which is located on the posterior surface of the tibia, above the soleal line . The muscle fibers of the popliteus run obliquely and inferiorly from this insertion to attach to the tibia, where they help produce the muscle’s actions and stabilise the knee joint during various movements.
The popliteus muscle plays an important role in maintaining knee stability and has several notable actions, which include:
Lateral rotation of the femur: At the beginning of knee flexion, the popliteus muscle laterally rotates the femur on the tibia, helping to “unlock” the knee joint. This action releases the “screw-home mechanism” that occurs during full knee extension, facilitating smoother knee flexion. This generally occurs when the foot is placed on the floor (e.g when the knee is locked out while standing) the popliteus then helps unlock the knee by rotating the femur laterally on the tibia  .
Medial rotation of the tibia: When the knee is flexed, the popliteus muscle contributes to the medial rotation of the tibia on the femur. This medial rotation generally occurs when the foot is not in contact with the ground and the knee is flexed. The popliteus can then help with rotating the tibia medially beneath the femoral condyles  .
Protection of the lateral meniscus: The popliteus muscle helps to protect the lateral meniscus of the knee by pulling the lateral meniscus posteriorly during knee flexion  . The lateral meniscus is a crescent-shaped piece of fibrocartilage which is located within the knee joint, specifically on the outer edge of the top surface of the tibia. The meniscus of the knee acts as a shock absorber between the femur and tibia, and it also helps distribute the body’s weight across the knee. This distribution of weight leads to increased stability and helps prevent damage to the joint. The lateral meniscus is more mobile and less prone to injury than its medial counterpart, this is likely due to the role the popliteus muscle plays in protecting the lateral meniscus. The medial meniscus does not have an equivalent muscle to pierce the joint capsule and connect to it like the lateral meniscus does. Therefore, the lateral meniscus benefits greatly from the role of the popliteus muscle. Conversely, the medial meniscus must depend solely on adjustments in tension, compression, and torsional forces to alter its shape and position, lacking the benefit of a dedicated supporting muscle.
Insignificant knee flexion: The popliteus muscle provides an insignificant amount of knee flexion, working alongside other more primary knee flexors such as the hamstrings and gastrocnemius . Knee flexion is in no way a primary action of this muscle, but it is worth mentioning as some sources overstate the contribution of the popliteus muscle in flexion of the knee joint. Its knee flexion contribution is very minimal, to the point of being considered insignificant.
The popliteus muscle is primarily innervated by the tibial nerve, which is composed of one of the two terminal branches of the sciatic nerve. The sciatic nerve is the largest and longest nerve in the human body. The sciatic nerve, itself, is comprised of nerve fibers from the L4 to S3 segments of the spinal cord, and it separates into the tibial and common fibular (peroneal) nerves at the level of the knee. The tibial nerve is specifically responsible for the innervation of the muscles in the posterior compartment of the leg, including the popliteus   .
The nerve roots that contribute to the innervation of the popliteus muscle are L5, S1. These segments form part of the lower region of the spinal cord, also known as the lumbosacral region. The neurons originating from these roots ultimately form the tibial nerve, which branches off the sciatic nerve in the lower part of the thigh, close to the knee. This nerve, after branching off, travels inferiorly along the posterior aspect of the leg, providing motor innervation to the muscles located there, such as the popliteus   .
Upon reaching the popliteus muscle, the tibial nerve penetrates at the lateral distal margin of the muscle, located inferior to the head of the fibula. Following its entry into the muscle, the nerve divides into anterior, medial, and lateral branches, ensuring widespread distribution throughout the muscle. This comprehensive distribution of nerve fibers allows for the efficient control required for the popliteus muscle’s actions   .
The blood supply to the popliteus muscle is principally provided by two arteries: the medial inferior genicular branch of the popliteal artery and the muscular branch of the posterior tibial artery .
The popliteal artery, which is a direct continuation of the femoral artery, travels through the popliteal fossa at the back of the knee. This artery gives rise to several branches, including the medial inferior genicular artery, which contributes to the vascular supply of the popliteus muscle .
Meanwhile, the posterior tibial artery, one of the terminal branches of the popliteal artery, also plays a role in supplying blood to this muscle. Specifically, the muscular branches of the posterior tibial artery, which diverge to supply various muscles in the posterior compartment of the leg, also extend their reach to the popliteus muscle .
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