Lower limb

The lower limb is the appendicular part of the body, comprising the following regions:

• Gluteal region (including buttocks)

• Hip (situated laterally to the buttocks)

• Thigh (a.k.a. femoral region, with hamstring and adductor compartments)

• Knee

• Leg

• Ankle (a.k.a. talocrural region)

• Foot

The lower limb is connected to the axial skeleton through the sacroiliac joint and plays a vital role in supporting body weight and facilitating movement.

Anatomically, a demarcation line separates the lower limb from the axial body (including the anterior and lateral abdominal wall, back, and perineum). This line connects the following anatomical structures from front to back:

“Starting from the pubic tubercle → along the inguinal ligament (inguinal crease) → anterior superior iliac spine → iliac crest → posterior superior iliac spine → dorsolateral surface of the sacrum → coccyx → sacrotuberous ligament → ischial tuberosity → ischiopubic ramus → pubic symphysis → finishing back at the pubic tubercle”.

Bony framework:

• The primary bone of the thigh is the ‘femur’. Proximally, it’s head fits into the acetabular fossa of the pelvic bone to form the hip joint. The hip joint is a is a ball and socket synovial joint that allows a wide range of movements, including flexion, extension, adduction, abduction, medial and lateral rotation, and circumduction.

• Distally, the femur’s condyles articulate with the tibial condyles to form the knee joint. The fibula does not contribute to the knee joint articulation.

• The tibia and fibula are interconnected via the superior and inferior tibiofibular joints and the interosseus membrane, but little movement occurs between them.

• Distally, both tibia and fibula articulate with the talus to form the ankle joint.

• Both the knee and ankle joints are hinge-type synovial joints, allowing for flexion and extension movements.

• The foot consist of seven tarsal bones, five metatarsals, and phalanges. Several small joints in the feet include the intertarsal, tarsometatarsal, metatarsophalangeal, and interphalangeal joints.

• Inversion and eversion (moving foot inwards and outwards, respectively) occur at the intertarsal joints.

• Muscles and ligaments support the tarsals and metatarsals in the feet, creating longitudinal and transverse arches. The arches play a crucial role in absorbing and transmitting forces during locomotion.

Muscles and innervation:

Various skeletal muscles cover the bones of the lower limb. These muscles are innervated by lumbar and sacral spinal nerves, forming lumbar and sacral plexuses on the posterior abdominal and lateral pelvic walls:

• Two major nerve branches arising from the lumbar plexus (L2, L3, L4 spinal segments) are the femoral and obturator nerves. The femoral nerve innervates the anterior thigh muscles, while the obturator nerve innervates the muscles of the adductor compartment of the thigh.

• Several branches arise from the sacral plexus, traversing through the greater sciatic foramen to enter the gluteal region. Here, they innervate the large gluteal muscles and the deep lateral rotators of the hip joint. The largest branch is the sciatic nerve, descending through the posterior thigh and innervating the hamstring muscles. It then splits into tibial and common peroneal nerves. The latter further splits into deep and superficial peroneal nerves around the neck of the fibula. These three nerves innervate the muscles of the leg region: the tibial nerve for the posterior (flexor) compartment, the deep peroneal nerve for the anterior (extensor) compartment, and the superficial peroneal for the lateral (peroneal) compartment. The tibial nerve further splits into medial and lateral plantar nerves, continuing to innervate the muscles of the sole of the foot.

• In addition to muscle innervation, each major peripheral nerve also provides cutaneous sensory innervation to the lower limb. Their sensory areas and dermatomes can be tested as part of sensory neurological examination to localize peripheral nerve lesions.

Vasculature:

• The major artery supplying the lower limb is the femoral artery, the distal continuation of the external iliac artery once it crosses underneath the inguinal ligament. In the thigh, the femoral artery traverses through the hiatus magnus of the adductor magnus muscle to enter the popliteal fossa, where it is called the popliteal artery. The popliteal artery further splits into the anterior and posterior tibial arteries, supplying the anterior and posterolateral compartments of the leg. The anterior tibial artery continues on the dorsum of the foot as the dorsalis pedis artery, while the posterior tibial artery continues into the sole of the foot as the medial and lateral plantar arteries.

Superficial veins:

• Two prominent superficial veins of the lower limb arise from a dorsal venous arch located on the dorsum of the foot. These are the great and small saphenous veins.

• The superficial veins drain into the deep venous system. For instance, the great saphenous vein ascends on the medial side of the foot, leg, and thigh and drains into the deep femoral vein, while the small saphenous vein ascends on the lateral side of foot and leg to drain into the popliteal vein.

Communications of the lower limb with other region:

The lower limb connects with other body regions. For instance:

• It connects with the abdomen through a weak area between the pelvic bone and the inguinal ligament, where femoral hernia can be found.

• The gluteal region of the lower limb communicates with the pelvis via the greater sciatic foramen and with the perineum via the lesser sciatic foramen. Branches of the lumbosacral plexus and piriformis enter the gluteal region from the pelvis via the greater sciatic foramen. Similarly, the pudendal nerve passes through the lesser sciatic foramen to make its way from the gluteal region into the perineum.