Thigh

The thigh extends from the inguinal crease (or the inguinal ligament) to the knee.

Bony framework:

• The major bone inside the thigh is the femur.

• The proximal end has two bony trochanters, a neck, and a head. The head articulates with the acetabulum of the hip bone to form a ball and socket synovial joint.

• The distal end contains two prominent condyles that articulate with the tibial condyles to form a hinged, synovial knee joint. The patella (or the knee cap) articulates with distal end of the femur to form a patellofemoral joint and is considered part of the knee joint.

Fascia and skin:

• A dense layer of deep fascia, called the fascia lata, wraps around the muscles and neurovasculature of the thigh. It is particularly thickened on the lateral aspect of the thigh to form an iliotibial tract.

• Like any other region of the body, the deep fascia is surrounded by superficial fascia and skin.

Musculature:

The deep fascia sends in intermuscular septa, which attach to the femur and divide the thigh into three compartments: anterior, medial, and posterior compartments. Clinically, increased pressure within these compartments due to acute trauma or chronic repeated injury by exertion could reduce blood supply to the tissues, causing ischemic pain and muscle damage. Fasciotomy might be required in acute and/or intractable cases.

• Muscles of anterior compartment of the thigh include the four quadriceps muscles, iliopsoas, and sartorius. The quadriceps originate from the femur and insert into the tibial tuberosity, producing extension at the knee joint. The rectus femoris part of the quadriceps muscles originates from the hip bone. Together with the iliacus (origin: ilium) and psoas major (origin: lumbar vertebrae) a.k.a. illiopsoas, they produce flexion at the hip joint. Sartorius originates from the anterior superior iliac spine. It crosses both the hip and knee joints to insert into the upper medial side of the tibia, thus producing flexion at both the hip and knee joints.

• Muscles of the medial compartment include the adductors, namely the adductor magnus, brevis, and longus muscles. These originate from the back of the shaft of the femur (near the linea aspera) and cause adduction and medial rotation of the thigh at the hip joint. Gracilis can also be found in the adductor compartment.

• Muscles of posterior compartment of the thigh include three hamstring muscles, namely the biceps femoris, semitendinosus, semimembranosus, and the hamstring part of the adductor magnus. The hamstring muscles originate from the ischial tuberosity. Please note that the biceps femoris, as the name indicates, has two heads. While the long head originates from ischial tuberosity, the short head originates below from behind the shaft of femur. Moreover, the adductor magnus has a wide range of origin involving the ischial tuberosity and associated ischiopubic ramus.

  All hamstring muscles cause flexion of the knee joint, along with extension of the trunk when straightening up from a bent-over position. The biceps femoris (insertion: head of fibula) lies laterally in the posterior region of the thigh and produces lateral rotation at the knee, while semimembranosus and semitendinosus (insertion: proximal tibia) lie medially and produce medial rotation at the knee.

Neurovasculature:

• The anterior compartment’s neurovasculature includes femoral vessels and nerve. The femoral vessels are continuations of the external iliac vessels, while the femoral nerve is a branch of the lumbar plexus (L2, L3, L4). The femoral vessels descend into the popliteal fossa behind the knee as popliteal vessels.

• The medial compartment’s neurovasculature consists of obturator vessels and nerves. They exit the pelvis, pass through the obturator canal, and enter the adductor or medial compartment of the thigh. The obturator vessels are branches of internal iliac vessels, while the obturator nerve is a branch of the lumbar plexus (L2, L3, L4).

• Lastly, the neuronal innervation of the posterior compartment comes from the sciatic nerve, the largest nerve in the body, arising from the sacral plexus. It enters the gluteal region through the greater sciatic foramen, runs downwards on the posterior surface of the short muscles of the hip joint, deep to gluteus maximus, and enters the posterior compartment of the thigh. There it lies deep to the hamstrings, on the posterior surface of the adductor magnus, and divides into tibial and common peroneal/common fibular branches before entering the leg region.

• The arteries of the posterior compartment of the thigh arise from two major sources: the inferior gluteal (upper posterior compartment) and perforating branches of the profunda femoris artery.