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F r e e S O A P n o t e s w i t h M a s s a g e B o o k f o r A B M P m e m b e r s : a b m p . u s / M a s s a g e b o o k 45 FUNCTIONAL ANATOMY education Popliteus By Christy Cael The triangular-shaped popliteus muscle is located at the back of the knee and forms the floor of the popliteal fossa. The popliteal fossa is a shallow depression outlined medially by the semimembranosis and semitendinosis tendons and medial head of the gastrocnemius, and laterally by the biceps femoris and lateral head of the gastrocnemius. This depression contains several essential structures, including the tibial nerve, common peroneal nerve, popliteal artery and vein, small saphenous vein, and popliteal lymph nodes and vessels. Caution should be exercised when locating the popliteus muscle within the popliteal fossa to avoid compressing these structures. The fibers of the popliteus originate on the lateral condyle of the femur, run deep to the arcuate popliteal and lateral collateral ligaments, and then spread distally and medially to a broad attachment on the posterior tibia. The oblique orientation of the muscle creates rotation at the tibiofemoral joint in addition to flexion of the knee. If the foot is planted or fixed when the popliteus is activated, the femur will rotate laterally on the tibia. If the foot is not fixed, the tibia will rotate medially on the femur. The main function of the popliteus muscle is to unlock the locked, fully extended knee. This "screw- home" mechanism is possible because the medial femoral condyle is larger than the lateral, allowing slight rotation of the knee at end-range extension. As the knee fully extends, the tibia spins externally on the femur until it reaches full external rotation. This is the "locked" position. Locking the knee decreases the work of the quadriceps muscles when standing. A simple way to observe the rotational motion of the screw-home mechanism is to sit in a chair facing forward. Straighten one knee fully, watching the position of your foot as you do so. As you POPLITEUS Attachments • Origin: Lateral condyle of the femur • Insertion: Proximal posterior surface of the tibia Actions • Flexes the knee • Internally rotates the knee Innervation • Tibial nerve • L4–S3

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