The popliteus muscle is a small muscle that forms the floor of the popliteal fossa. It belongs to the deep posterior leg muscles, along with tibialis posterior, flexor digitorum longus and flexor hallucis longus.
The popliteus muscle plays an important role in the gait cycle by initiating the flexion of the fully extended (“locked”) knee. Thus, the popliteus is referred to as the “key to unlock the knee”. In addition, the popliteus muscle is the main stabilizer of the dorsal knee region.
|Origin||Lateral condyle of femur, posterior horn of lateral meniscus of knee joint|
|Insertion||Posterior surface of proximal tibia|
|Innervation||Tibial nerve (L4-S1)|
|Blood supply||Inferior medial and lateral genicular arteries (popliteal artery), posterior tibial recurrent artery, posterior tibial artery, nutrient artery of tibia|
|Function||Unlocks knee joint; Knee joint stabilization|
In this article, we will discuss the anatomy and function of the popliteus muscle.
Origin and insertion
The popliteus muscle originates from the lateral condyle of femur by a strong tendon called popliteus tendon. The popliteus tendon courses in the groove for popliteus muscle on the lateral aspect of the lateral femoral condyle. This tendon is joined medially by tendinous fibers arising from the posterior horn of the lateral meniscus. In addition, the popliteofibular ligament connects the popliteus tendon to the medial aspect of the head of the fibula.
The popliteus tendon then expands into a triangular muscle belly that passes inferomedially over the posterior joint capsule of the knee joint. The popliteus muscle inserts on the posterior surface of the proximal tibia (medial two-thirds) above the soleal line, which is the origin point of the soleus muscle.
The popliteus muscle is situated deep in the popliteal fossa, forming its floor. The popliteus tendon arises within the capsule of the knee joint, hence it is intracapsular. On its posterior aspect, the popliteus tendon is crossed by the arcuate popliteal ligament, the fibular collateral ligament and the tendon of biceps femoris.
Upon passing underneath the arcuate ligament, the popliteus tendon is replaced by the fleshy portion of the popliteus muscle. Posteriorly, the popliteus muscle is covered by an investing fascia that is reinforced by a dense aponeurotic expansion, largely derived from the tendon of semimembranosus muscle. Posterior to the investing fascia of popliteus are the gastrocnemius, plantaris, tibial nerve and popliteal artery and vein.
The popliteus muscle receives nervous supply from the tibial nerve (L4-S1), a branch of the sciatic nerve.
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The popliteus receives arterial blood supply mainly from branches of the popliteal artery, namely the inferior medial and lateral genicular arteries. In addition, it receives smaller contributions from the posterior tibial recurrent artery, the proximal part of the posterior tibial artery and the nutrient artery of the tibia.
Despite its anatomical classification, the role of the popliteus muscle as a flexor of the knee is quite insignificant. However, the popliteus muscle plays an important role in initiating flexion of the fully extended (“locked”) knee. Thus, the popliteus is referred to as “the key to unlock the knee”, making it essential for the processes of walking, standing up, and sitting down.
The popliteus muscle can produce two types of actions; lateral rotation of the femur or medial rotation of the tibia. These actions are dictated by the phase of the gait cycle:
- During the closed chain phase of the gait cycle, the foot is in contact with the ground. The tibia is laterally rotated (about 5º) on the femur, which “locks” the knee joint. With the tibia fixed in position, the popliteus muscle acts on its origin and laterally rotates the femur on the tibia. This movement “unlocks” the knee and allows flexion to occur.
- During the open chain (swing) phase of the gait cycle, the foot is above the ground and the tibia is free to move. Therefore, the popliteus muscle can act on its insertion to medially rotate the tibia on the femur. This action provides stability to the tibia during knee flexion.
The popliteus muscle is also the main stabilizer of the dorsal knee region via its connections to the posterior joint capsule and popliteofibular ligament. In addition, the popliteus muscle pulls the lateral meniscus dorsally during knee flexion and femoral lateral rotation, thus preventing its entrapment.
The popliteus muscle may be injured in conjunction with a rupture of the anterior cruciate ligament or injuries involving the lateral meniscus. These types of injuries most often occur in sports due to a direct blow to the anteromedial aspect of the knee in the flexed position. In contrast, an isolated injury of the popliteus muscle is rather rare.
Clinically, the affected patients present with an unnatural lateral rotation of the tibia when flexing the knee. Other associated symptoms include muscle swelling, edema or bleeding.