Dance Anatomy & Kinesiology

The Knee and Patellofemoral Joints 245

Individual Muscles of the Knee

Anterior Muscles of the Knee

The anterior muscles of the knee are the quadriceps femoris group. Because the knee flexes in the

opposite direction (with the distal segment moving posteriorly vs. anteriorly) to many of the other synovial

joints, anterior muscles of the knee produce extension of the knee. This is in contrast to the spine, hip,

shoulder, elbow, wrist, and fingers, where concentric contraction of anterior muscles from anatomical

position produces flexion at their respective joints.

Quadriceps Femoris

The quadriceps femoris group is located on the front of the thigh, and as its name indicates (L. quattuor,

four + capus, head), it is composed of four muscles: the rectus femoris (L. rectus, straight + femoris,

femur) vastus lateralis (L. lateral great muscle), vastus intermedius (L. intermediate great muscle),

and vastus medialis (L. medial great muscle). The rectus femoris, seen in figure 5.6A, is the only one

of this muscle group that crosses the hip joint, and its function as a flexor of the hip was discussed in

chapter 4. The remaining quadriceps, the three vasti muscles (L. vastus, great) seen in figure 5.6B,

originate from the femur and so can produce joint movement only at the knee, not the hip. As their

names suggest, the vastus medialis is the most medially located of the vasti, and the lateralis is

the most laterally located. The vastus intermedius lies between these two muscles and underneath

the rectus femoris. The tendons of all four of the quadriceps muscles converge to form the quadriceps

femoris tendon. The quadriceps femoris tendon attaches to the superior patella, and the patella is then

attached to the tuberosity of the tibia via the patellar tendon. Hence, although the quadriceps converge

onto the patella, the continuing attachment of the patella onto the tibia allows the quadriceps femoris

group to act as powerful extensors of the knee.

All of the quadriceps act as prime movers to produce knee extension such as in a frappé or main-

tain knee extension such as in the gesture leg during a rond de jambe. When the knee is in weight-

bearing positions, gravity tends to produce knee flexion, and the quadriceps play a key antigravity func-

tion in movements such as pliés, walking, running, and jumping. Given this antigravity function, it is not

surprising that the quadriceps are one of the strongest muscle groups in the body. They are capable

of generating greater than 1,000 pounds (454 kilograms) of force (Hamill and Knutzen, 1995; Smith,

Weiss, and Lehmkuhl, 1996).

Attachments and Primary Actions of the Quadriceps Femoris

Muscle Proximal attachment(s) Distal attachment(s) Primary action(s)

Quadriceps femoris (KWOD-ri-seps FEM-o-ris)

Rectus femoris

(REK-tus FEM-o-ris)

Anterior inferior iliac spine

Posterior head: just above

acetabulum

Tibial tuberosity via patellar

tendon

Knee extension

(Hip flexion)

Vastus medialis

(VAS-tus me-dee-A-lis)

Medial and posterior surfaces

of femur

Quadriceps femoris tendon

and medial border of patella

Knee extension

Vastus intermedius

(VAS-tus in-ter-ME-dee-us)

Anterior and lateral aspects

of femur

Quadriceps femoris tendon

and superior border of patella

Knee extension

Vastus lateralis

(VAS-tus lat-er-A-lis)

Upper lateral and posterior

surfaces of femur

Quadriceps femoris tendon

and lateral border of patella

Knee extension

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