15.18: Muscles that Move the Thigh
The thigh's motion is primarily governed by muscles originating in the pelvic girdle and inserted into the femur. One crucial muscle, the iliopsoas, is a combination of the psoas major and the iliacus muscles, sharing a common insertion point on the lesser trochanter of the femur.
Three other significant muscles are the gluteus maximus, gluteus medius, and gluteus minimus. The gluteus maximus originates from the posterior surface of the ilium, sacrum, and coccyx, and the thoracolumbar fascia and inserts on the iliotibial tract and the gluteal tuberosity of the femur. It primarily acts as the chief extensor of the femur. Conversely, in its reverse muscle action, it powerfully extends the torso at the hip joint.
The gluteus medius and minimus originate anterior to the origin of the gluteus maximus and insert on the greater trochanter of the femur. The gluteus medius muscle functions as a potent abductor of the femur at the hip joint and is a common site for intramuscular injection because of its accessible location. Deep to the gluteus maximus muscle are six muscles — the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris, which function as lateral rotators of the femur at the hip joint.
Additionally, the tensor fasciae latae muscle is located on the thigh's lateral surface, inserted into the lateral condyle of the tibia. This muscle, along with its tendons and gluteus maximus muscles, helps form the iliotibial tract. As the name suggests, this muscle is enveloped by the fascia lata, a dense connective tissue encircling the entire thigh.
Lastly, on the medial aspect of the thigh are three unique muscles — the adductor longus, adductor brevis, and adductor magnus. These muscles originate from the pubic bone and insert into the femur, adducting the thigh and demonstrating the unique ability to rotate the thigh both medially and laterally. The adductor longus also flexes the thigh while the adductor magnus extends it. The pectineus muscle also plays a part in adducting and flexing the femur at the hip joint.
