Muscles Acting on the Knee and Leg

Quadriceps femoris

• Large muscle group at the front of the thigh

  • made up from rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

Rectus femoris

Origin: straight head originates from the anterior inferior iliac spine; reflected head originates from the ilium just superior to the acetabulum

Insertion: Quadriceps femoris tendon

Main Action: Flexes the thigh at the hip joint and extends the leg at the knee joint

Innervation: Femoral Nerve L2, L3, L4

Vastus lateralis

Origin: Femur— lateral part of the intertrochanteric line, margin of greater trochanter, lateral margin of gluteal tuberosity, lateral lip of the linea aspera

Insertion: Quadriceps femoris tendon and lateral margin of patella

Main Action: Extends the leg at the knee joint

Innervation: Femoral Nerve L2, L3, L4

Vastus medialis

Origin: Femur—medial part of intertrochanteric line, pectineal line, medial lip of the linea aspera, medial supracondylar line

Insertion: quadriceps femoris tendon and medial border of patella

Main Action: Extend the leg at the knee joint

Innervation: Femoral Nerve L2, L3, L4

Vastus intermedius

Origin: Femur—upper 2/3 of anterior and lateral surfaces

Insertion: Quadriceps femoris tendon and lateral margin of patella

Main Action: Extends the leg at the knee joint

Innervation: Femoral Nerve L2, L3, L4

Sartorius

Origin: anterior superior iliac spine

Insertion: medial surface of tibia just inferomedial to tibial tuberosity

Main Action: flexes the thigh at the hip joint and flexes the leg at the knee joint

Innervation: Femoral Nerve L2, L3

Biceps femoris

Origin: Long head—inferomedial part of the upper area of the ischial tuberosity, Short head—lateral lip of linea aspera

Insertion: head of fibula

Main Action: flexes leg at knee joint; extends and laterally rotates thigh at hip joint and laterally rotates leg at knee joint

Innervation: Sciatic Nerve L5, S1, S2

Semitendinosus

Origin: Inferomedial part of the upper area of the ischial tuberosity

Insertion: Medial surface of proximal tibia

Main Action: Flexes leg at knee joint and extends thigh at hip joint; medially rotates thigh at hip joint and leg at knee joint

Innervation: Sciatic Nerve L5, S1, S2

Semimebranosus

Origin: Superolateral impression on the ischial tuberosity

Insertion: groove and adjacent bone on medial and posterior surface of medial tibial condyle

Main Action: Flexes leg at knee joint and extends thigh at hip joint; medially rotates thigh at hip joint and leg at knee joint

Innervation: Sciatic Nerve L5, S1, S2

Popliteus

Origin: lateral femoral condyle

Insertion: posterior surface of proximal tibia

Main Action: stabilizes knee joint (resists lateral rotation of tibia on femur); unlocks knee joint (laterally rotates femur on fixed tibia)

Innervation: Tibial Nerve L4 to S1