The thigh: muscles Lecture 5

Compartments of the thigh The deep fascia of the thigh - fascia lata – covers all muscles around and arranges them into three compartments: anterior compartment of thigh; medial compartment of thigh; posterior compartment of thigh.

Anterior compartment of thigh The anterior compartment of thigh contains the iliopsoas, sartorius and the four large quadriceps femoris muscles: rectus femoris, vastus lateralis, vastus medialis, vastus intermedius. All are innervated by the femoral nerve and perform flexion of hip or extension of knee joins.

Rectus femoris Origin: originates from the anterior inferior iliac spine, the ilium just superior to the acetabulum; Insertion: Quadriceps femoris tendon; Innervation: Femoral nerve; Action: Flexes the thigh at the hip joint and extends the leg at the knee joint.

Vastus medialis: Origin: medial part of intertrochanteric line, medial lip of the linea aspera, medial supracondylar line. Vastus lateralis: Origin: lateral part of intertrochanteric line, margin of greater trochanter, lateral margin of gluteal tuberosity, lateral lip of the linea aspera. Insertion: Quadriceps femoris tendon. Innervation: Femoral nerve. Action: Extends the leg at the knee joint.

Vastus intermedius: Origin: Femur-upper two-thirds of anterior and lateral surfaces. Insertion: Quadriceps femoris tendon. Innervation: Femoral nerve. Action: Extends the leg at the knee joint.

Quadriceps tendon The quadriceps tendon attaches to the base of patella, envelops the patella and continues downward as a patellar ligament. The last one inserts to the tibial tuberosity on the anterior surface of the tibia. As the quadriceps muscle contracts, it pulls on the quadriceps tendon, the patella, the patellar tendon, and the tibia to move the knee from a flexed (bent) position to an extended (straight) position.

Sartorius Origin: Anterior superior iliac spine; Insertion: Anterior surface of tibia just inferomedial to tibial tuberosity; Innervation: Femoral nerve; Action: Flexes the thigh at the hip joint and flexes the leg at the knee joint.

Iliopsoas muscle Psoas major and iliacus muscles are usually referred to as the iliopsoas muscle. Origin: transvers processes of T12-L5 and the lateral aspects of the discks between them; internal lip of iliac crest, and internal surface of iliac wing. Insertion: lesser trochanter of the femur. Action: powerful flexor of the thigh at the hip joint and can also contribute to lateral rotation of the thigh; Innervation: Anterior rami L1,L2,L3 and femoral nerve.

Medial compartment of thigh The medial compartment of thigh contains six muscles: Adductor longus, Adductor brevis, Adductor magnus, Obturator externus, Gracilis, Pectineus. Main action: adduction of hip. All except pectineus, which is innervated by the femoral nerve, and part of the adductor magnus, which is innervated by the sciatic nerve, are innervated by the obturator nerve.

Adductor magnus Origin: the ischiopubic ramus. Insertion: Posterior surface of proximal femur, linea aspera, medial supracondylar line. There are 4 perforations for branches of deep femoral artery and adductor hiatus in the wide tendon of this muscle. Innervation: Obturator nerve. Action: Adducts and medially rotates thigh at hip joint.

Adductor brevis Origin: External surface of body of pubis and inferior pubic ramus. Insertion: Posterior surface of proximal femur and upper third of linea aspera. Innervation: Obturator nerve. Action: Adducts thigh at hip joint.

Adductor longus Origin: External surface of body of pubis. Insertion: Linea aspera on middle third of shaft of femur. Innervation: Obturator nerve (anterior division). Action: Adducts and medially rotates thigh at hip joint.

Pectineus Origin: Superior ramus of the pubis . Insertion: Oblique line extending from base of lesser trochanter to linea aspera on posterior surface of proximal femur. Innervation: Femoral nerve. Action: Adducts and flexes thigh at hip joint.

Obturator externus Origin: External surface of obturator membrane and adjacent bone. Insertion: medial surface of the greater trochanter. Innervation: Obturator nerve (posterior division). Action: lateral rotation of the thigh at the hip joint.

Gracilis Origin: A line on the external surfaces of the body of the pubis, the inferior pubic ramus. Insertion: Medial surface of proximal shaft of the tibia. Innervation: Obturator nerve. Action: Adducts thigh at hip joint and flexes leg at knee joint.

Posterior compartment of thigh The posterior compartment of thigh contains three large muscles termed the 'hamstrings‘: biceps femoris, semitendinosus, semimembranosus. All are innervated by the sciatic nerve. All except the short head of biceps femoris cross both the hip and knee joints. As a group, the hamstrings flex the leg at the knee joint and extend the thigh at the hip joint.

Biceps femoris The biceps femoris muscle is lateral in the posterior compartment of the thigh and has two heads: the long head originates from the inferomedial part of the ischial tuberosity; the short head arises from the lateral lip of the linea aspera on the shaft of the femur. Insertion: Head of fibula. Innervation: Sciatic nerve . Action: Flexes leg at knee joint; extends and laterally rotates thigh at hip joint and laterally rotates leg at knee joint.

Semitendinosus The semitendinosus muscle is medial to the biceps femoris muscle in the posterior compartment of thigh. Origin: Inferomedial part of the ischial tuberosity. Insertion: Medial surface of proximal tibia. Innervation: Sciatic nerve. Action: Flexes leg at knee joint and extends thigh at hip joint; medially rotates the thigh at the hip joint and leg at the knee joint.

Semimembranosus The semimembranosus muscle lies deep to the semitendinosus muscle in the posterior compartment of thigh. Origin: Superolateral impression on the ischial tuberosity. Insertion: medial and posterior surface of medial tibial condyle. Innervation: Sciatic nerve. Action: Flexes leg at knee joint and extends thigh at hip joint; medially rotates thigh at the hip joint and leg at the knee joint.