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 reach full knee extension, your foot should turn out slightly. This happens when the tibia turns on the femur. You can also observe it by standing and gently locking (fully extending) and unlocking (slightly flexing or softening) the knee.
Hyperextension of the knee can damage the popliteus muscle, creating pain and swelling in the back of the knee, as well as dysfunction in the lower extremity. The popliteus is also vulnerable to injury when planting and pivoting around the lower extremity. Weakness or inhibition of the hamstring muscles, particularly with rotational movements, may contribute to excessive stress, pain, trigger point activation, and dysfunction in the popliteus muscle.

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

Palpating the Popliteus
Position: client prone with knee slightly flexed.
1. Standing at the client’s side facing the knee, locate the medial tibial condyle with your fingertips.
2. Curl your fingertips posteriorly onto the distal border of the popliteal fossa, finding the posterior shaft of the tibia.
3. Palpate and follow the oblique fibers of the popliteus toward the lateral femoral condyle.
4. Resist as the client performs internal rotation of the knee with a neutral foot to ensure proper location.

Client Homework—Seated Hurdler Stretch with Twist
1. Sit up straight and face forward, with one leg extended straight out and the other bent and tucked.
2. Keeping your back and knee straight, lean forward.
3. Grasp your ankle (or if you are able, your toes) and gently rotate your knee in and out without rotating your hip.
4. Gently stretch the back of the knee, then repeat on the other leg.

Christy Cael is a licensed massage therapist, certified strength and conditioning specialist, and instructor at the Bodymechanics School of Myotherapy & Massage in Olympia, Washington. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (Lippincott Williams & Wilkins, 2009). Contact her at functionalbook@hotmail.com.

Editor’s note: The Client Homework element in Functional Anatomy is intended as a take-home resource for clients experiencing issues with the profiled muscle. The stretches identified in Functional Anatomy should not be performed within massage sessions or progressed by massage therapists, in order to comply with state laws and maintain scope of practice.