The thigh is the portion of the lower limb that lies between the hip area and the knee joint. It serves as the main structural and mechanical link that transmits body weight from the trunk to the lower leg during standing, walking, running and jumping. In everyday and clinical descriptions the thigh is frequently discussed with reference to the surrounding hip girdle and the knee complex: see the pelvis and the knee.
Anatomical structure
By definition and anatomical convention, the thigh contains a single long bone: the femur, sometimes described simply as the thigh bone. The femur is robust and adapted to resist large bending and compressive forces. Proximally it articulates with the pelvis at a rounded head in a ball-and-socket arrangement that permits multi‑directional hip motion; distally it participates in the modified hinge joint of the knee.
Muscles, nerves and vessels
The muscular compartments of the thigh are usually grouped as anterior, posterior and medial. Major muscle groups include:
- Anterior compartment: quadriceps femoris (chief knee extensor) and sartorius.
- Posterior compartment: hamstrings (hip extensors and knee flexors).
- Medial compartment: adductors that draw the leg toward the midline.
Innervation and blood supply are critical for function: the femoral nerve and artery primarily serve the anterior compartment, the sciatic nerve gives branches to the posterior compartment, and additional smaller vessels and nerves supply other regions. Lymphatic channels and veins within the thigh are also clinically important for circulation and disease spread.
Functionally, the thigh generates the large forces required for propulsion and postural control. Clinically, it is the site of common injuries such as muscle strains, contusions and femoral fractures; its anatomy is essential knowledge for orthopedic surgery, vascular procedures and regional anesthesia.
Developmentally and evolutionarily the form of the thigh reflects adaptations to bipedal posture: bone geometry, muscle attachments and joint orientation differ between humans and quadrupeds in ways that facilitate upright walking. Anatomical variations between individuals—related to age, sex, activity and genetics—affect strength, range of motion and susceptibility to injury. For broader anatomical context see links to the pelvis, knee and general anatomical references; for the femur specifically consult sources linked to the femur and the concept of a single thigh bone articulating via a ball-and-socket hip joint.