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The popliteus muscle, located in the lower leg, is often referred to as the key to the knee. Its primary function is to unlock the knee joint by laterally rotating the femur on the tibia when the foot is in contact with the ground. The popliteus tendon passes beneath the lateral collateral ligament (LCL) and the tendon of the biceps femoris. It is one of the main stabilisers of the knee joint, causing both medial and lateral rotation of the knee.
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What You'll Learn
The popliteus muscle is key to unlocking the knee
The popliteus muscle is a small, thin, flat, triangular-shaped muscle located in the lower leg, behind the knee. It is a deep muscle of the knee joint, forming the floor of the popliteus fossa. It is also the only muscle in the posterior compartment of the lower leg that does not influence the ankle joint.
The popliteus muscle is often referred to as "the key to unlocking the knee". This is because its primary function is to unlock the knee joint by laterally rotating the femur on the tibia when the foot is in contact with the ground. This movement unlocks the knee and allows flexion to occur, enabling activities such as walking, standing up, and sitting down.
During the closed-chain phase of the gait cycle, when the foot is on the ground, the tibia is laterally rotated on the femur, locking the knee joint. With the tibia fixed in position, the popliteus muscle acts to laterally rotate the femur on the tibia, thus unlocking the knee.
In contrast, during the open-chain phase, when the foot is off the ground, the tibia is free to move. Here, the popliteus muscle acts on its insertion point to medially rotate the tibia on the femur. This action provides stability to the tibia during knee flexion and prevents the crushing of the meniscus between the tibia and femur.
The popliteus muscle is, therefore, crucial in the biomechanics of the knee joint, enabling essential activities such as walking and maintaining stability during weight-bearing activities.
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The knee joint relies on muscles and ligaments for stability
The popliteus muscle, located in the lower leg, is often referred to as the "key of the knee" or the "key to unlock the knee". This is because its primary function is to unlock the knee joint by laterally rotating the femur on the tibia when the foot is in contact with the ground. During the closed-chain phase of the gait cycle, the foot is on the ground, and the tibia is laterally rotated on the femur, locking the knee joint. With the tibia fixed in this position, the popliteus muscle acts to rotate the femur on the tibia, thus unlocking the knee. This action of the popliteus muscle is essential for walking, standing up, and sitting down.
The popliteus muscle also helps to stabilise the knee joint during weight-bearing activities. It is one of the main posterolateral stabilisers of the knee joint, causing both medial and lateral rotation of the knee. It also works as a smaller stabiliser in regard to internal rotation anterior translation and varus force. The popliteus muscle pulls the lateral meniscus posteriorly during knee flexion and femoral lateral rotation, thus preventing its entrapment.
The biceps femoris and the synergistic semitendinosus and semimembranosus muscles are responsible for flexing the lower leg at the knee.
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The popliteus muscle is a small but important muscle
During the closed-chain phase of the gait cycle, when the foot is in contact with the ground, the tibia is laterally rotated on the femur, locking the knee joint. With the tibia fixed in this position, the popliteus muscle acts to rotate the femur on the tibia, thus unlocking the knee. This action of the popliteus muscle is referred to as "the key to unlock the knee".
In addition to its role in unlocking the knee, the popliteus muscle also helps to stabilise the knee joint during weight-bearing activities. It provides stability to the tibia during knee flexion and prevents entrapment of the lateral meniscus. The muscle also plays a role in controlling the internal and external rotation of the tibia during the gait cycle, which includes walking and running.
The popliteus muscle is susceptible to injury, especially in anatomical smaller knees, and poor movement patterns and posture can leave it prone to weakness. Iatrogenic injury to this muscle is common, and it can lead to a poor functional prognosis, particularly following knee reconstruction surgery.
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The popliteus muscle is prone to weakness and injury
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is a deep muscle of the knee joint, forming the floor of the popliteus fossa. It is one of the main posterolateral stabilisers of the knee joint, causing both medial and lateral rotation of the knee. This allows for the unlocking of the knee and the initiation of flexion.
The popliteus muscle can also be strained, causing pain at the back of the knee, ranging from mild to severe. This pain can be increased by walking downhill or extensive running, as well as standing on a slightly bent knee or rotating the knee. Chronic popliteus muscle strain can produce pain first thing in the morning, and runners with a chronic popliteus condition will experience pain at the beginning of a run.
Popliteus tendinopathy, also known as popliteus tendon tenosynovitis, is a gap in the tendon of the popliteus. It is an uncommon condition that often occurs in athletes and people with a history of other knee ligament injuries after trauma. It can be caused by overuse of the popliteus muscle-tendon unit.
To treat a popliteus injury, initial swelling can be addressed with a cold compress or ice pack. Non-operative management is usually advocated, involving early weight-bearing and functional rehabilitation. There are also exercises to strengthen the affected popliteus muscle, such as using a resistance band to perform external rotation of the hip and knee flexion.
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The popliteus muscle is involved in the gait cycle
The popliteus muscle is a small, thin, flat, triangular-shaped muscle in the lower leg. It is a deep muscle of the knee joint, forming the floor of the popliteal fossa. It is one of the main posterolateral stabilisers of the knee joint, causing both medial and lateral rotation of the knee.
The popliteus muscle plays a significant role in the gait cycle by initiating the flexion of the fully extended ("locked") knee. It is often referred to as "the key to unlock the knee", making it essential for walking, standing up, and sitting down. The muscle produces 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, when the foot is in contact with the ground, the tibia is laterally rotated on the femur, "locking" 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 action stabilises the tibia during knee flexion.
During the open-chain (swing) phase of the gait cycle, when the foot is above the ground and the tibia is free to move, the popliteus muscle medially rotates the tibia on the femur. This action is observed when the involved limb is not in contact with the ground. The popliteus muscle also pulls the lateral meniscus posteriorly during knee flexion and femoral lateral rotation, preventing its entrapment.
The popliteus muscle is susceptible to injuries, especially during sports activities, due to its small size and anatomical location. It may be injured in conjunction with a rupture of the anterior cruciate ligament or injuries involving the lateral meniscus.
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Frequently asked questions
The popliteus muscle locks the knee by rotating the tibia inward.
The popliteus muscle is located in the lower leg, behind the knee.
The primary function of the popliteus muscle is to unlock the knee joint and initiate flexion when the knee is fully extended. It also helps to stabilise the knee joint during weight-bearing activities and controls the rotation of the tibia during the gait cycle.
Injury to the popliteus muscle can lead to weakness and poor functional prognosis. It is also associated with knee pain and can be prone to iatrogenic injury, especially following knee reconstruction surgery.
The biceps femoris, semitendinosus, semimembranosus, and quadriceps femoris muscles are also involved in flexing the lower leg at the knee joint.
