Joints of the Lower Limbs

The ankle is a hinged synovial joint formed between the articular surfaces of the distal tibia, distal fibula, and talus. The ankle primarily allows plantar flexion and dorsiflexion of the foot. The subtalar joint and the other tarsal bones create many synergistic articulations, allowing for a wide range of motion (ROM)–plantar flexion, dorsiflexion, eversion, inversion, abduction, and adduction. The movements are generated by large muscle groups that originate in the leg and insert as well as act upon the bones of the foot and tarsus.

The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons that allow for flexibility as well as dynamic and static support. The foot has 3 primary arches and multiple ligaments that are essential to its structure. The arches are important in absorbing weight during standing, walking, and running and the ability to adapt to uneven terrain during locomotion.

The knee joint is made up of the articulations between the femur, tibia, and patella bones, and is one of the largest and most complex joints of the human body. The knee is classified as a synovial hinge joint, which primarily allows for flexion and extension with a more limited degree of translation and rotation. The supporting structures of the knee joint include a joint capsule, the lateral and medial menisci, and multiple ligaments that help ensure mobility and stability of the knee.

The lower leg, or just “leg” in anatomical terms, is the part of the lower limb between the knee and the ankle joint. The bony structure is composed of the tibia and fibula bones, which articulate with each other at the proximal and distal tibiofibular joints. The muscles of the leg are grouped into the anterior, lateral, and posterior compartments by extensions of fascia and exert their action on the ankle, foot, and toes.

The hip joint is a ball-and-socket joint formed by the head of the femur and the acetabulum of the pelvis. The hip joint is the most stable joint in the body and is supported by a very strong capsule and several ligaments, allowing the joint to sustain forces that can be multiple times the total body weight. Tolerating these forces is possible thanks to the bony alignment and substantial support from the static and dynamic stabilizers of the hip. Several muscle groups attach to the components of the hip joint, allowing for the joint's range of motion. The muscles that attach to the hip joint include those of the gluteal region and thigh.

The popliteal fossa or the “knee pit” is a diamond-shaped, fat-filled, shallow depression on the posterior aspect of the knee joint. The popliteal fossa is located at the dorsal aspect of the knee and contains an increased number of lymph nodes as well as structures of the neurovascular system that travel from the thigh to the lower leg. The boundaries are formed by various muscles of the thigh and leg.