Anatomy of the lower limb

The lower limb is the weight-bearing appendage comprising the pelvic girdle and the free limb: thigh, leg and foot. Its bones and joints support standing and movement, while organised muscle compartments, nerves and blood vessels connect these regions. In anatomical usage, the leg means only the region between the knee and ankle.

What forms the pelvic girdle and hip joint?

The pelvic girdle consists of the hip bones, which connect the free lower limbs to the trunk. Each hip bone develops from the ilium, ischium and pubis: respectively its broad upper part, posteroinferior part and anteroinferior part. These parts unite around the acetabulum, the socket for the head of the thigh bone.

Posteriorly, the hip bones meet the sacrum, the fused vertebral bone at the base of the spine, at the sacroiliac joints. Anteriorly, they meet at the pubic symphysis, a joint containing a fibrocartilaginous disc. Together, the hip bones, sacrum and coccyx form the bony pelvis.

The hip joint is a ball-and-socket synovial joint, meaning that its joint cavity contains lubricating synovial fluid. It joins the acetabulum to the head of the femur, the thigh bone. The acetabular labrum, a fibrocartilage rim, deepens the socket; the capsule and surrounding ligaments help stabilise the joint.

Which bones and joints form the thigh and leg?

The femur extends from the hip to the knee. Its rounded head connects to the shaft through the neck, while the greater and lesser trochanters are projections for muscle attachment. Distally, towards the foot, its condyles are rounded joint surfaces that articulate with the shin bone.

The patella is a sesamoid bone, a bone embedded in a tendon. It lies within the tendon of quadriceps femoris, the anterior thigh muscle group that straightens the knee. The knee joint includes articulations between the femur and shin bone and between the femur and patella. Its menisci are fibrocartilage pads that help accommodate the opposing joint surfaces.

The tibia is the medial, or inner, weight-bearing bone of the leg. The fibula lies laterally, towards the outer side, and does not articulate with the femur. The bones meet at proximal and distal tibiofibular joints and are connected along their shafts by an interosseous membrane, a sheet of fibrous tissue.

The ankle joint joins the lower ends of the tibia and fibula to the talus, the foot bone beneath them. The medial and lateral malleoli are the ankle projections of the tibia and fibula. They form the sides of a socket around the talus, allowing mainly upward and downward movement of the foot.

Which bones, joints and arches form the foot?

A tarsal bone belongs to the group of bones forming the hindfoot and midfoot. These include the talus, calcaneus, navicular, cuboid and cuneiforms. The calcaneus forms the heel; the metatarsals extend forwards towards the toes, whose bones are the phalanges.

The subtalar joint lies between the talus and calcaneus. Together with neighbouring tarsal joints, it contributes to inversion and eversion: turning the sole inwards and outwards. Metatarsophalangeal joints connect the metatarsals to the toes, and interphalangeal joints connect adjacent toe bones.

The foot has medial and lateral longitudinal arches, running from heel to forefoot, and a transverse arch across its width. The medial longitudinal arch includes the calcaneus, talus, navicular, cuneiforms and medial metatarsals. The lateral longitudinal arch includes the calcaneus, cuboid and lateral metatarsals.

Ligaments, which connect bones, and tendons, which connect muscles to their attachments, help support the arches. The plantar calcaneonavicular ligament supports the head of the talus. The plantar aponeurosis, a strong fibrous sheet in the sole, also helps maintain the longitudinal arches.

What are the muscle compartments of the thigh and leg?

A muscle compartment is a group enclosed by deep fascia, the connective tissue surrounding muscles, and partitions called intermuscular septa. Compartments generally share actions and nerve supply. The thigh has anterior, medial and posterior compartments; the leg has anterior, lateral and posterior compartments, with the posterior compartment divided into superficial and deep groups.

Flexion bends a joint, whereas extension straightens it. Hip adduction moves the thigh towards the midline, and abduction moves it away. At the ankle, dorsiflexion brings the top of the foot towards the shin, while plantarflexion points the foot downwards.

These patterns have important exceptions. The hamstring part of adductor magnus receives the tibial division of the sciatic nerve, while its adductor part receives the obturator nerve. Pectineus usually receives the femoral nerve, and the short head of biceps femoris receives the common fibular division of the sciatic nerve.

In the adjacent 3D model, rotate and zoom, switch layers, or hide and isolate selected structures to compare their spatial relationships.

How do the lumbar and sacral plexuses supply the lower limb?

A nerve plexus is a network formed by interconnecting anterior rami, the front branches of spinal nerves. The lumbar plexus forms within psoas major, a muscle beside the lumbar spine, principally from L1–L4. Its femoral nerve arises from L2–L4 and passes beneath the inguinal ligament, the fibrous band extending from the anterior superior iliac spine to the pubic tubercle.

The femoral nerve supplies the anterior thigh muscles and carries sensation from the anterior thigh. Its saphenous branch carries sensation from the medial leg and foot. The obturator nerve, also from L2–L4, passes through the obturator canal in the hip bone to supply most medial thigh muscles.

The sacral plexus lies on the anterior surface of piriformis, a muscle crossing the posterior pelvic wall, and receives contributions from L4–S4. Its sciatic nerve arises from L4–S3, leaves the pelvis usually below piriformis and enters the posterior thigh. Its tibial and common fibular components separate at a variable level.

The tibial nerve supplies the posterior leg and continues into the sole. The common fibular nerve winds around the fibular neck before dividing into superficial and deep fibular nerves. These supply the lateral and anterior leg compartments respectively; the deep fibular nerve also supplies muscles on the top of the foot.

How does arterial blood reach the foot?

The external iliac artery becomes the femoral artery as it passes beneath the inguinal ligament. In the upper thigh, the deep artery of the thigh branches from it and supplies much of the thigh musculature.

The femoral artery continues through the adductor canal, a passage between thigh muscles. After passing through the adductor hiatus, an opening in adductor magnus, it becomes the popliteal artery behind the knee. The popliteal artery divides into anterior and posterior tibial arteries.

The anterior tibial artery enters the anterior leg and continues onto the top of the foot as dorsalis pedis. The posterior tibial artery gives off the fibular artery, descends through the posterior leg and passes behind the medial malleolus. It divides into medial and lateral plantar arteries supplying the sole.

Where does the great saphenous vein run?

The great saphenous vein is a superficial vein, meaning that it lies in tissue superficial to the deep fascia. It begins from the medial side of the dorsal venous network on the top of the foot and passes anterior to the medial malleolus.

It ascends along the medial leg and thigh, then passes through an opening in the thigh's deep fascia to join the femoral vein. Perforating veins connect superficial veins with deep veins. Venous valves help direct blood towards the heart.