The Lower Limb: Anatomy and Function
The lower limb, or lower extremity, is a crucial part of the human body, responsible for bearing weight, locomotion, and providing stability. Extending from the pelvis to the foot, the lower limb includes several key regions: the hip, thigh, knee, leg, ankle, and foot. Each of these regions is composed of bones, muscles, nerves, and blood vessels that work together to enable movement and support.
Hip
The hip is the proximal region of the lower limb, where it connects to the pelvis. The hip joint, a ball-and-socket joint, is formed by the articulation of the femoral head (the ball) with the acetabulum of the pelvis (the socket). This joint allows for a wide range of movements, including flexion, extension, abduction, adduction, and rotation.
Several muscles support and move the hip joint, including the gluteal muscles (gluteus maximus, medius, and minimus), the iliopsoas (a combination of the iliacus and psoas major muscles), and the adductor group (adductor longus, adductor brevis, adductor magnus, and gracilis). These muscles play a critical role in stabilizing the pelvis and enabling movements such as walking, running, and jumping.
Thigh
The thigh extends from the hip to the knee and contains the femur, the longest and strongest bone in the human body. The femur articulates with the pelvis at the hip joint and with the tibia and patella at the knee joint. The muscles of the thigh are divided into three compartments: anterior, medial, and posterior.
- The anterior compartment contains the quadriceps femoris group (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), which is responsible for extending the knee.
- The medial compartment includes the adductor muscles, which are involved in adducting the thigh.
- The posterior compartment contains the hamstring muscles (biceps femoris, semitendinosus, and semimembranosus), which flex the knee and extend the hip.
The femoral artery supplies blood to the thigh, and the femoral nerve provides innervation to the anterior compartment, while the sciatic nerve innervates the posterior compartment.
Knee
The knee is a hinge joint connecting the thigh to the leg. It is formed by the articulation of the femur, tibia, and patella (kneecap). The knee joint allows for flexion and extension, as well as slight rotation. It is stabilized by several ligaments, including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL).
The knee is also cushioned by menisci, which are two crescent-shaped cartilages (medial and lateral menisci) that distribute weight and reduce friction during movement. The quadriceps muscle group extends the knee, while the hamstrings flex it. The popliteal artery supplies blood to the knee region, and the sciatic nerve branches into the tibial and common peroneal nerves to innervate the surrounding muscles.
Leg
The leg extends from the knee to the ankle and contains two bones: the tibia (shinbone) and the fibula. The tibia is the larger and more medial bone, while the fibula is smaller and located laterally. These bones are connected by an interosseous membrane that provides additional stability.
The muscles of the leg are divided into three compartments: anterior, lateral, and posterior.
- The anterior compartment contains muscles such as the tibialis anterior, which dorsiflex the foot and extend the toes.
- The lateral compartment includes the fibularis (peroneus) longus and brevis muscles, which evert and plantarflex the foot.
- The posterior compartment contains the calf muscles (gastrocnemius and soleus) and other muscles like the tibialis posterior, which plantarflexes the foot and flexes the toes.
The popliteal artery continues as the tibial arteries (anterior and posterior) supply blood to the leg, while the tibial and common peroneal nerves innervate the muscles.
Ankle
The ankle is a hinge joint that connects the leg to the foot. It is formed by the articulation of the tibia, fibula, and talus (a bone in the foot). The ankle joint allows for dorsiflexion and plantarflexion, and it is stabilized by several ligaments, including the deltoid ligament medially and the lateral ligaments (anterior talofibular, calcaneofibular, and posterior talofibular ligaments).
Foot
The foot is the most distal part of the lower limb and is essential for supporting body weight and providing balance and propulsion during movement. It consists of three regions: the hindfoot, midfoot, and forefoot.
- The hindfoot includes the talus and calcaneus (heel bone).
- The midfoot consists of the navicular, cuboid, and cuneiform bones.
- The forefoot contains the metatarsals and phalanges (toe bones).
The arches of the foot (medial, lateral, and transverse) play a crucial role in absorbing shock and providing flexibility. The intrinsic muscles of the foot, along with the extrinsic muscles originating in the leg, control movements such as inversion, eversion, flexion, and extension of the toes.
The dorsal pedis and posterior tibial arteries supply blood to the foot, while the tibial and common peroneal nerves provide sensation and motor control.