The popliteus is a flexor of the knee joint.

The central compartment of the foot contains the flexor digitorum brevis, flexor digitorum longus, quadratus plantae, lumbricals, proximal part of the tendon flexor hallucis longus, and the lateral plantar nerve and vessel.

The ligament of the head of the femur is weak and of little importance in strengthening the hip joint. Its wide end attaches to the margins of the acetabular notch and the transverse acetabular ligament. Its narrow end attaches to the pit in the head of the femur. Usually the ligament contains a small artery to the head of the femur.

The saphenous nerve is the largest cutaneous branch of the femoral nerve. In addition to supplying the skin and fascia on the anterior and medial sides of the leg, the saphenous nerve passes anterior to the medial malleolus to the dorsum of the foot, where it supplies skin along the medial side of the foot as far as the head of the 1st metatarsal.

The oblique popliteal ligament is an expansion of the tendon of the semimembranosus, which strengthens the fibrous capsule posteriorly.

Together, the two-headed gastrocnemius and soleus form the three-headed triceps surae.

The superior extensor retinaculum is a strong, broad band of deep fascia passing from the fibula to the tibia, proximal to the malleoli. The inferior extensor retinaculum is a Y-shaped band of deep fascia that attaches laterally to the anterosuperior surface of the calcaneus. It forms a strong loop around the tendons of the fibularis tertius and the extensor digitorum longus muscle.

The medial sural nerve is derived from the tibial nerve and the lateral sural nerve is derived from the common fibular. The medial and lateral sural nerves unite to form the sural nerve.

The fibular collateral ligament (lateral collateral ligament), rounded and cordlike, is strong. It extends inferiorly from the lateral epicondyle
of the femur to the lateral surface of the head of fibula. The tendon of the popliteus passes deep to the fibular collateral ligament, separating it from the lateral meniscus. The tendon of the biceps femoris is also split into two parts by this ligament.

The fibrous capsule of the knee is deficient on the lateral condyle to allow the tendon of the popliteus to pass out of the joint to attach to the tibia.

The tibialis anterior is the strongest dorsiflexor and inverter of the foot.

The anterior cruciate ligament (ACL), the weaker of the two cruciate ligaments, arises from the anterior intercondylar area of the tibia, just posterior to the attachment of the medial meniscus. It extends superiorly, posteriorly, and laterally to attach to the posterior part of the medial side of the lateral condyle of the femur. The ACL has a relatively poor blood supply. It is slack when the knee is flexed and taut when it is fully extended, preventing posterior displacement.

Dorsiflexors of the ankle include the tibialis anterior, extensors digitorum longus, hallucis longus, and fibularis tertius.

The tibial collateral ligament (medial collateral ligament) is a strong, flat band that extends from the medial epicondyle of the femur to the medial surface of the tibia. At its midpoint, the deep fibers of the tibial collateral ligament are firmly attached to the medial meniscus. The tibial collateral ligament, weaker than the fibular collateral ligament, is more often damaged. As a result, the tibial collateral ligament and medial meniscus are commonly torn during contact sports such as football.

The flexor hallucis longus is the powerful “push-off” muscle during walking, running, and jumping.

A synovial protrusion beyond the free margin of the fibrous capsule onto the posterior aspect of the femoral neck forms a bursa for the obturator externus tendon.

The patellar ligament is extracapsular. The cruciate ligaments and menisci are classified as intra-articular and are found within the knee joint. The popliteal tendon is also intra-articular during part of its course.

The fibrous capsule is reinforced anteriorly by the strong, Y-shaped iliofemoral ligament (of Bigelow) which attaches to the anterior inferior iliac spine and the acetabular rim proximally and the intertrochanteric line distally. The iliofemoral ligament prevents hyperextension of the hip during standing by screwing the femoral head into the acetabulum.

The medial plantar nerve, the larger of the two terminal branches of the tibial nerve, passes deep to the abductor hallucis and runs anteriorly between the muscles and the flexor digitorum brevis on the lateral side of the medial plantar artery.

The most important muscle in stabilizing the knee joint is the large quadriceps femoris, particularly inferior fibers of the vastus medialis and lateralis. The knee joint will function surprisingly well following a ligament strain if the quadriceps is well conditioned.

Both the fibularis longus and brevis evert the foot. The fibularis tertius also aids in eversion of the foot.

The lateral compartment of the foot contains the abductor and flexor digiti minimi brevis.

The plantaris is located in the superficial group of muscles in the posterior compartment.

The main blood supply of the hip joint is from branches of the circumflex femoral arteries (especially the medial circumflex femoral artery) that travel in the retinacula (reflections of the capsule along the neck of the femur toward the head). These retinacular vessels may be damaged in femoral neck fractures and result in avascular necrosis of the femoral head.

When a person is standing with the knee partly flexed, the popliteus contracts to assist the posterior cruciate ligament in preventing anterior displacement of the femur on the tibia.