11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs - Anatomy and Physiology

Learning Objectives

By the end of this section, you will be able to:

Identify the appendicular muscles of the pelvic girdle and lower limb
Identify the movement and function of the pelvic girdle and lower limb

The appendicular muscles of the lower body position and stabilize the pelvic girdle, which serves as a foundation for the lower limbs. Comparatively, there is much more movement at the pectoral girdle than at the pelvic girdle. There is very little movement of the pelvic girdle because of its connection with the sacrum at the base of the axial skeleton. The pelvic girdle is less range of motion because it was designed to stabilize and support the body.

Muscles of the Thigh

What would happen if the pelvic girdle, which attaches the lower limbs to the torso, were capable of the same range of motion as the pectoral girdle? For one thing, walking would expend more energy if the heads of the femurs were not secured in the acetabula of the pelvis. The body’s center of gravity is in the area of the pelvis. If the center of gravity were not to remain fixed, standing up would be difficult as well. Therefore, what the leg muscles lack in range of motion and versatility, they make up for in size and power, facilitating the body’s stabilization, posture, and movement.

Gluteal Region Muscles That Move the Femur

Most muscles that insert on the femur (the thigh bone) and move it, originate on the pelvic girdle. The psoas major and iliacus make up the iliopsoas group. Some of the largest and most powerful muscles in the body are the gluteal muscles or gluteal group. The gluteus maximus is the largest; deep to the gluteus maximus is the gluteus medius, and deep to the gluteus medius is the gluteus minimus, the smallest of the trio (Figure 11.29 and Figure 11.30).

The left panel shows the superficial pelvic and thigh muscles, the center panel shows the deep pelvic and thigh muscles. The right panel shows the posterior view of the pelvic and thigh muscles.

Figure 11.29 Hip and Thigh Muscles The large and powerful muscles of the hip that move the femur generally originate on the pelvic girdle and insert into the femur. The muscles that move the lower leg typically originate on the femur and insert into the bones of the knee joint. The anterior muscles of the femur extend the lower leg but also aid in flexing the thigh. The posterior muscles of the femur flex the lower leg but also aid in extending the thigh. A combination of gluteal and thigh muscles also adduct, abduct, and rotate the thigh and lower leg.

This table describes gluteal region muscles that move the femur. These muscles make up the iliopsoas group. The psoas major raises the knee at the hip, as if performing a knee attack; it also assists the lateral rotators in twisting the thigh (and lower leg) outward, and assists with bending over and maintaining posture. It originates in the lumbar vertebrae (L1 through L5) and thoracic vertebra (T12). The iliacus raises the knee at the hip, as if performing a knee attack; it also assists the lateral rotators in twisting the thigh (and lower leg) outward, and assists with bending over and maintaining posture. It originates in the iliac fossa, iliac crest, and lateral sacrum. These muscles make up the gluteal group. The gluteous maximus lowers the knee and moves the thigh back, as when getting ready to kick a ball. It originates in the dorsal ilium, sacrum, and coccyx. The gluteus medius opens the thigh, as when doing a split. It originates in the lateral surface of the ilium. The gluteus minimus brings the thighs back together. It originates in the external surface of the ilium. The tensor fascia lata assists with raising the knee at the hip and opening the thighs; it also maintains posture by stabilizing the iliotibial track, which connects to the knee. It originates in the anterior aspect of the iliac crest and the anterior superior iliac spine. These muscles make up the lateral rotators. The piriformis twists the thigh (and lower leg) outward; it also maintains posture by stabilizing the hip joint. It originates in the anterolateral surface of the sacrum. The obturator internus twists the thigh (and lower leg) outward; it also maintains posture by stabilizing the hip joint. It originates in the inner surface of the obturator membrane, the greater sciatic notch, and the margins of the obturator foramen. The superior gemellus twists the thigh (and lower leg) outward; it also maintains posture by stabilizing the hip joint. It originates in the ischial spine. The inferior gemellus twists the thigh (and lower leg) outward; it also maintains posture by stabilizing the hip joint. It originates in the ischial tuberosity. The quatratus femoris twists the thigh (and lower leg) outward; it also maints posture by stabilizing the hip joint. It originates in the ischial tuberosity. These muscles are adductors. The adductor longus brings the thighs back together; it also assists with raising the knee. It originates in the pubis near the pubic symphysis. The adductor brevis brings the thighs back together; it also assists with raising the knee. It originates in teh body of the pubis and in the inferior ramus of the pubis. The adductor magnus brings the thighs back together; it also assists with raising the knee and moving the thigh back. It originates in the ischial rami, the pubic rami, and the ischial tuberosity. The pectineus opens the thigh; it also assists with raising the knee and turning the thigh (and lower leg) inward. It originates in the pectineal line of the pubis.

Figure 11.30 Gluteal Region Muscles That Move the Femur

The tensor fascia latae is a thick, squarish muscle in the superior aspect of the lateral thigh. It acts as a synergist of the gluteus medius and iliopsoas in flexing and abducting the thigh. It also helps stabilize the lateral aspect of the knee by pulling on the iliotibial tract (band), making it taut. Deep to the gluteus maximus, the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris laterally rotate the femur at the hip.

The adductor longus, adductor brevis, and adductor magnus can both medially and laterally rotate the thigh depending on the placement of the foot. The adductor longus flexes the thigh, whereas the adductor magnus extends it. The pectineus adducts and flexes the femur at the hip as well. The pectineus is located in the femoral triangle, which is formed at the junction between the hip and the leg and also includes the femoral nerve, the femoral artery, the femoral vein, and the deep inguinal lymph nodes.

Thigh Muscles That Move the Femur, Tibia, and Fibula

Deep fascia in the thigh separates it into medial, anterior, and posterior compartments (see Figure 11.29 and Figure 11.31). The muscles in the medial compartment of the thigh are responsible for adducting the femur at the hip. Along with the adductor longus, adductor brevis, adductor magnus, and pectineus, the strap-like gracilis adducts the thigh in addition to flexing the leg at the knee.

Figure 11.31 Thigh Muscles That Move the Femur, Tibia, and Fibula

The muscles of the anterior compartment of the thigh flex the thigh and extend the leg. This compartment contains the quadriceps femoris group, which actually comprises four muscles that extend and stabilize the knee. The rectus femoris is on the anterior aspect of the thigh, the vastus lateralis is on the lateral aspect of the thigh, the vastus medialis is on the medial aspect of the thigh, and the vastus intermedius is between the vastus lateralis and vastus medialis and deep to the rectus femoris. The tendon common to all four is the quadriceps tendon (patellar tendon), which inserts into the patella and continues below it as the patellar ligament. The patellar ligament attaches to the tibial tuberosity. In addition to the quadriceps femoris, the sartorius is a band-like muscle that extends from the anterior superior iliac spine to the medial side of the proximal tibia. This versatile muscle flexes the leg at the knee and flexes, abducts, and laterally rotates the leg at the hip. This muscle allows us to sit cross-legged.

The posterior compartment of the thigh includes muscles that flex the leg and extend the thigh. The three long muscles on the back of the knee are the hamstring group, which flexes the knee. These are the biceps femoris, semitendinosus, and semimembranosus. The tendons of these muscles form the popliteal fossa, the diamond-shaped space at the back of the knee.

Muscles That Move the Feet and Toes

Similar to the thigh muscles, the muscles of the leg are divided by deep fascia into compartments, although the leg has three: anterior, lateral, and posterior (Figure 11.32 and Figure 11.33).

The left panel shows the superficial muscles that move the feet and the center panel shows the posterior view of the same muscles. The right panel shows the deep muscles of the right lower leg.

Figure 11.32 Muscles of the Lower Leg The muscles of the anterior compartment of the lower leg are generally responsible for dorsiflexion, and the muscles of the posterior compartment of the lower leg are generally responsible for plantar flexion. The lateral and medial muscles in both compartments invert, evert, and rotate the foot.

This tables describes the muscles that move the feet and toes. These muscles make up the anterior compartment of the leg. The tibialis anterior raises the sole of the foot off the ground, as when preparing to foot-tap; it also bends the inside of the foot upwards, as when catching your balance while falling laterally toward the opposite side as the balancing foot. It originates in the lateral condyle and upper tibial shaft and in the interosseous membrane. The extensor hallucis longus raises the sole of the foot off the ground, as when preparing to foot-tap; it also extends the big toe. It originates in the anteromedial fibula shaft and interosseous membrane. The extensor digitorum longus raises the sole of the foot off the ground, as when preparing to foot-tap; it also extends the toes. It originates in the lateral condyle of the tibia, the proximal portion of the fibula, and the interosseous membrane. These muscles make up the lateral compartment of the leg. The fibularis longus lowers the sole of the foot to the ground, as when foot-tapping or jumping; it also bends the inside of the foot downwards, as when catching your balance while falling laterally toward the same side as the balancing foot. It originates in the upper portion of the lateral fibula. The fibularis (peroneus) brevis lowers the side of the foot to the ground, as when foot-tapping or jumping; it also bends the inside of the foot downward, as when catching your balance while falling laterally toward the same side as the balancing foot. It originates in the distal fibula shaft. These superficial muscles make up the posterior compartment of the leg. The gastrocnemius lowers the sole of the foot to the ground, as when foot-tapping or jumping; it also assists in moving the back of the lower legs up and back toward the buttocks. It originates in the medial and lateral condyles of the femur. The soleus lowers the sole of the foot the ground, as when foot-tapping or jumping; it also maintains posture while walking. It originates in the superior tibia, fibula, and interosseous membrane. The plantaris lowers the sole of the foot to the ground, as when foot-tapping or jumping; it also assists in moving the back of the lower legs up and back toward the buttocks. It originates in the posterior femur above the lateral condyle. The tibialis posterior lowers the sole of the foot to the ground, as when foot-tapping or jumping. It originates in the superior tibia and fibula and in the interosseous membrane. These deep muscles also make up the posterior compartment of the leg. The popliteus moves the back of the lower legs up and back toward the buttocks; it also assists in rotation of the leg at the knee and thigh. It originates in the lateral condyle of the femur and the lateral meniscus. The flexor digitorum longus lowers the sole of the foot to the ground, as when foot-tapping or jumping; it also bends the inside of the foot upward and flexes the toes. It originates in the posterior tibia. The flexor hallicis longus flexes the big toe. It originates in the midshaft of the fibula and in the interosseous membrane.

Figure 11.33 Muscles That Move the Feet and Toes

The muscles in the anterior compartment of the leg: the tibialis anterior, a long and thick muscle on the lateral surface of the tibia, the extensor hallucis longus, deep under it, and the extensor digitorum longus, lateral to it, all contribute to raising the front of the foot when they contract. The fibularis tertius, a small muscle that originates on the anterior surface of the fibula, is associated with the extensor digitorum longus and sometimes fused to it, but is not present in all people. Thick bands of connective tissue called the superior extensor retinaculum (transverse ligament of the ankle) and the inferior extensor retinaculum, hold the tendons of these muscles in place during dorsiflexion.

The lateral compartment of the leg includes two muscles: the fibularis longus (peroneus longus) and the fibularis brevis (peroneus brevis). The superficial muscles in the posterior compartment of the leg all insert onto the calcaneal tendon (Achilles tendon), a strong tendon that inserts into the calcaneal bone of the ankle. The muscles in this compartment are large and strong and keep humans upright. The most superficial and visible muscle of the calf is the gastrocnemius. Deep to the gastrocnemius is the wide, flat soleus. The plantaris runs obliquely between the two; some people may have two of these muscles, whereas no plantaris is observed in about seven percent of other cadaver dissections. The plantaris tendon is a desirable substitute for the fascia lata in hernia repair, tendon transplants, and repair of ligaments. There are four deep muscles in the posterior compartment of the leg as well: the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior.

The foot also has intrinsic muscles, which originate and insert within it (similar to the intrinsic muscles of the hand). These muscles primarily provide support for the foot and its arch, and contribute to movements of the toes (Figure 11.34 and Figure 11.35). The principal support for the longitudinal arch of the foot is a deep fascia called plantar aponeurosis, which runs from the calcaneus bone to the toes (inflammation of this tissue is the cause of “plantar fasciitis,” which can affect runners. The intrinsic muscles of the foot consist of two groups. The dorsal group includes only one muscle, the extensor digitorum brevis. The second group is the plantar group, which consists of four layers, starting with the most superficial.

This figure shows the muscles of the foot. The top panel shows the lateral view of the dorsal muscles. The bottom left panel shows the superficial muscles of the left sole, the center panel shows the intermediate muscles of the left sole, and the right panel shows the deep muscles of the left sole.

Figure 11.34 Intrinsic Muscles of the Foot The muscles along the dorsal side of the foot (a) generally extend the toes while the muscles of the plantar side of the foot (b, c, d) generally flex the toes. The plantar muscles exist in three layers, providing the foot the strength to counterbalance the weight of the body. In this diagram, these three layers are shown from a plantar view beginning with the bottom-most layer just under the plantar skin of the foot (b) and ending with the top-most layer (d) located just inferior to the foot and toe bones.

This table describes intrinsic muscles in the foot. The dorsal group consists of the extensor digitorum brevis, which extends toes 2 through 5. It originates in the calcaneus and the extensor retinaculum. These muscles make up layer 1 of the plantar group. The abductor hallucis abducts and flexes the big toe. It originates in the calcaneal tuberosity and flexor retinaculum. The flexor digitorum brevis flexes toes 2 through 4. It originates in the calcaneal tuberosity. The abductor digiti minimi abducts and flexes the small toe. It originates in the calcaneal tuberosity. These muscles make up layer 2 of the plantar group. The quadratus plantae assists in flexing toes 2 through 5. It originates in the medial and lateral sides of the calcaneus. The lumbricals extend toes 2 through 5 at the interphalangeal joints; they also flex the small toes at the metatarsophalangeal joints. They originate in the tendons of the flexor digitorum longus. These muscles make up layer 3 of the plantar group. The flexor hallucis brevis flexes the big toe. It originates in the lateral cuneiform and in the cuboid bones. The adductor hallucis adducts and flexes the big toe. It originates in the bases of metatarsals 2 through 4, in the fibularis longus tendon sheath, and in the ligament across the metatarsophalangeal joints. The flexor digiti minimi brevis flexes the small toe. It originates in the base of metatarsal 5 and in the tendon sheath of the fibularis longus. These muscles make up layer 4 of the plantar group. The dorsal interossei abducts and flexes the middle toes at the metatarsophalangeal joints; it also extends the middle toes at the interphalangeal joints. It originates in the sides of the metatarsals. The plantar interossei abducts toes 3 through 5; it also flexes the proximal phalanges and extends the distal phalanges. It originates in the side of each metatarsal that faces metatarsal 2 (absent from metatarsal 2).

Figure 11.35 Intrinsic Muscles in the Foot