Popliteus Muscle - “The Key of the Knee”
Updated: May 9
In this blog we will focus on the popliteus muscle. The popliteus muscle is often called "The Key of the Knee" because it is responsible for "unlocking" the knee when the leg is in an extended position. Besides this"unlocking" function the popliteus muscle also helps to perform several critical actions during the gait cycle. Before we go over some of those actions let's discuss some basic anatomy and biomechanics related to this important structure. This next section is for us anatomy geeks, feel free to skip to the following section!
ANATOMY & BIO-MECHANICS
The popliteus originates at the lateral condyle of the femur and the posterior horn of the lateral meniscus. The popliteus muscle runs inferiorly and medially in the direction of the tibia. The muscle inserts on the tibia just proximal to the soleal line and just below the tibial condyles. The popliteus muscle is innervated by the tibial nerve.
The popliteus muscle unlocks the knees by laterally rotating the femur on the tibia when the foot is in contact with the ground. When the leg is not in contact with the ground, the popliteus medially rotates the tibia on the femur. It is NOT uncommon for the function of a muscle to change, depending on surface contact and position.
Popliteal Fossa Anatomy Video
Want to learn more about the anatomy behind your knee? Check out our "Popliteal Fossa Anatomy Video".
THE MULTI-FUNCTIONAL POPLITEUS MUSCLE
The popliteus muscle performs multiple functions during the normal gait cycle. To get a better understanding of how important the popliteus muscle is to the gait cycle consider these four important functions. (1)
The popliteus muscle helps produce external rotation of the femur in the propulsion phase of gait.
The popliteus muscle assists the PCL (posterior cruciate ligament) in preventing forward glide of the femur on the tibia.
The popliteus muscle aids the calf muscle (gastrocnemius) with deceleration extension of the knee.
The popliteus muscle assists the subtalar joint in internally rotating the tibia (initial contact during the stance phase of gait).
Running Tip: Over-striding while running is a common way to stress the Popliteus muscle.
Gait Cycle: Want to learn more about the different phases of the gait cycle? Read Dr. Abelson's blog "Designed to Run - The Human Gait Cycle".
Signs and Symptoms
Injury to the knee commonly involves the popliteus muscle. The most common signs and symptoms of a popliteus injury are:
- General pain over the back and lateral side of the knee (especially over the proximal aspect of the popliteus tendon). (4)
- Pain on resisted knee flexion or internal rotation (Supine). There may also be pain with resisted external rotation of the leg with the patient's hip and knee flexed to 90 degrees (This is call a positive Garrick Test). (4)
- Pain directly over the popliteal space (fossa). (4)
Motion Specific Release
There are many ways to use manual therapy to release restrictions in the popliteus muscle. In the video below Dr. Abelson demonstrates one way to do this from a weight bearing position.
The Popliteal Squat Release - Motion Specific Release™: Anytime there is a knee injury you should suspect involvement of the popliteus muscle. Fortunately there are some very effective soft tissue procedures that can be used to help resolve a popliteus injury and improve its overall function. (This video will be public on 02/24/2021)
KINETIC CHAIN CONSIDERATIONS
Besides the popliteus muscle itself, there are some very important kinetic chain consideration that must be considered with any injury to the popliteus muscle (popliteal symptoms).
Muscle imbalances in the hamstrings can affect popliteus strength. If the lateral hamstrings (Biceps Femoris) are stronger than the medial hamstrings (semimembranosus), the popliteus muscle will end up being much weaker and more susceptible to injury. A biceps femoris tendon strain can also mimic a popliteus injury. (3)
Increased foot pronation (hyper-pronation) or a collapsing of the medial arch when running or walking will cause increased stress on the popliteus muscle. (3) Eventually this stress could lead to injury, or compromise in any of the the critical functions performed by the popliteus muscle.
The Lateral Meniscus
As mentioned earlier, the popliteus muscle attaches directly into the posterior horn of the lateral meniscus (by an aponeurosis). Consequently the popliteus muscle pulls the lateral meniscus posterior during knee flexion. This is a great mechanism for preventing meniscus entrapment.
Unfortunately, any tension or restrictions in the popliteus muscle could potentially affect the function of the lateral meniscus. (2)
In fact, a popliteus injury can mimic a meniscus tear (chronic pain, even clicking in the knee). Therefore, any time a practitioner is doing an examination for a possible lateral meniscus tear they must also consider popliteal involvement.
The popliteus muscle is called "The Key of the Knee" for a very good reason. Besides being involved in "unlocking" the knee when the knee is in an extended position, it also helps to perform several critical functions during the gait cycle.
Anytime there is a knee injury you should suspect involvement of the popliteus muscle. Fortunately there are some very effective soft tissue procedures that can be used to help resolve a popliteus injury and improve its overall function. The "Key" to getting the greatest benefit from these procedures, is to consider larger kinetic chain relationships when implementing those procedures.
Mann RA. Biomechanics of running. In Pack RP (ed). Symposium on the Foot and Leg in Running Sports. St. Louis:CV Mosby, 1982:26.
THE POPLITEUS MUSCLE AND THE LATERAL MENISCUS, The Bone and Joint Journal, https://doi.org/10.1302/0301-620X.32B1.93
The Popliteus Muscle, JONATHAN FITZGORDON https://corewalking.com/knee-stuff-popliteus-muscle/
Covey DC. Injuries of the posterolateral corner of the knee. JBJS. 2001 Jan 1;83(1):106-18.
DR. BRIAN ABELSON DC.
Dr. Abelson is the developer of Motion Specific Release (MSR) Treatment Systems. His clinical practice in is located in Calgary, Alberta (Kinetic Health). He has recently authored his 9th and 10th publications which will be available later this year.
Kinetic Health strives to adhere to the best research evidence available, while combining clinical expertise with the specific values of each patient, in a inter-professional and collaborative care environment.
Dr. Abelson is the owner of Kinetic Health, a partner in BKAT Motion Specific Release, and a partner in Rowan Tree Books.