Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Locomotor System
Muscular System
Muscles of the Lower Extremity

Muscles of the Pelvic Girdle. The pelvic girdle is joined almost immovably to the sacral region of the spine, and therefore there are no muscles that cause it to move. The muscles located on the pelvis move the leg at the hip joint and the spine. They are divided into two groups: anterior and posterior-lateral.

The anterior group includes a single large Muscle — the iliopsoas.

The iliopsoas muscle (m. iliopsoas) originates by two heads that function as independent muscles: the psoas major — from the bodies and transverse processes of the last thoracic and the four upper lumbar vertebrae, and the iliacus — from The surface of the iliac fossa (Atlas, Figs. 33, 45). In the region of the inguinal ligament, the heads merge into a common muscle that passes beneath it onto the thigh and attaches to the lesser trochanter. The muscle flexes the hip joint until the thigh touches the anterior abdominal wall, and also laterally rotates the thigh; with a fixed Femur, it flexes the lumbar part of the spine.

The posterior-Lateral group of pelvic girdle muscles comprises: the gluteus maximus, gluteus medius, and gluteus minimus, the tensor fasciae latae, piriformis, obturator internus, gemelli, quadratus femoris, and obturator externus.

The gluteus maximus (m. gluteus maximus) has a large cross-section, and is broad and coarse-fibered (Atlas, Figs. 27, 44, 45). It originates from the external surface of the ilium behind and above the semicircular gluteal lines, from the posterior surface of the sacrum and coccyx, and from the sacrotuberous ligament. The fascicles of muscle fibers run parallel downward and outward; the upper ones terminate in the so-called fascia lata, while the lower ones attach to the gluteal tuberosity of the femur. Here, between the muscle and the greater trochanter, lies a synovial bursa. The muscle extends the leg at the hip joint, and with fixed legs, it extends the trunk.

The gluteus medius (m. gluteus medius) originates from the external surface of the ala of the ilium and lies mainly beneath the gluteus maximus, emerging from under it to the surface only in its upper-anterior part (Atlas, Figs. 27, 44, 46, 47). Here the muscle is covered by a very dense fascia, which together with the bone forms its osteofibrous sheath. The muscle attaches to the greater trochanter of the femur.

The gluteus minimus (m. gluteus minimus) originates from the external surface of the ala of the ilium, but lies even deeper than the gluteus medius, which completely covers it (Atlas, Figs. 46, 47). The muscle attaches to the greater trochanter of the femur.

The gluteus medius and minimus abduct the thigh at the hip joint. By contracting only their anterior fibers, they medially rotate the thigh; by contracting the posterior fibers, they laterally rotate it. When the leg is fixed, these muscles abduct (tilt to the side) the pelvis.

The tensor fasciae latae (m. tensor fasciae latae) is a separated portion of the gluteus medius and originates from the anterior superior iliac spine (Atlas, Fig. 47). The muscle lies between the layers of the fascia lata, which covers all the thigh muscles like a dense sheath. The muscle descends along the lateral surface of the thigh anterior to the greater trochanter, distal to which its fibers weave into the fascia lata. The tendinous fibers of this muscle and the gluteus maximus significantly reinforce the lateral part of the fascia lata, which is referred to here as the iliotibial tract. It attaches to the lateral epicondyle of the Tibia. The function of the muscle is determined by its purpose; in addition, it participates in the flexion and pronation of the thigh.

The piriformis muscle (m. piriformis) originates within the lesser pelvis from the anterior surface of the sacrum (Atlas, Figs. 33, 45-47). Narrowing as it passes laterally and downward, it exits the pelvis through the greater sciatic foramen and attaches to the greater trochanter. The muscle laterally rotates the thigh.

The obturator internus muscle (m. obturatorius internus) originates from the internal surface of the obturator membrane and from the margin of the obturator foramen (Atlas, Figs. 45-47). The converging fascicles of the muscle emerge from the cavity of the lesser pelvis through the lesser sciatic foramen, where they bend at almost a right angle, and the muscle attaches by its tendon into the trochanteric fossa.

The gemelli muscles (mm. gemelli) join the obturator internus as it exits the pelvis (Atlas, Fig. 47). The superior gemellus originates from the ischial spine, and the inferior from the ischial tuberosity. Together with the tendon of the obturator internus, the gemelli attach to the trochanteric fossa of the femur. All three muscles laterally rotate the thigh.

The quadratus femoris muscle (m. quadratus femoris) lies parallel to the inferior gemellus and more distally (Atlas, Fig. 47). Originating from the ischial tuberosity, it attaches to the intertrochanteric crest of the femur. The muscle laterally rotates the thigh.

The obturator externus muscle (m. obturatorius externus) originates from the external surface of截至 the obturator membrane and the margin of the foramen, attaching to the trochanteric fossa (Atlas, Fig. 46). The muscle laterally rotates the thigh.

Muscles of the thigh. Two dense intermuscular septa extend inward from the fascia lata on the sides of the thigh, attaching to the femur along its linea aspera. Together with a third, thin fascial septum, they form an osteofibrous canal enclosing the anterior, medial, and posterior groups of thigh muscles.

The anterior group includes the sartorius and quadriceps femoris muscles.

The sartorius muscle (m. sartorius) is the longest in The Human Body (about 50 cm). It originates from the anterior superior iliac spine, crosses the thigh obliquely downward and medially, and attaches to the tibial tuberosity (Atlas, Figs. 26, 44, 45). The muscle flexes the leg at the Hip and knee joints; it medially rotates the leg and laterally rotates the thigh.

The quadriceps femoris muscle (m. quadriceps femoris) is very massive and occupies the entire anterior and partly the lateral surface of the thigh. It consists of four to some extent distinct heads (Atlas, Figs. 26, 44, 45, 48). One of them — the rectus femoris (m. rectus femoris) — is the most independent, lies in its own fascial sheath, has a bipennate Structure, and originates from the anterior inferior iliac spine; its fascicles continue distally into the common tendon of the muscle. The other three heads of the quadriceps are called the vasti muscles of the thigh. The largest of them is the vastus lateralis, located on the lateral side of the thigh; it originates from the greater trochanter, the linea aspera of the femur, and the lateral intermuscular septum. The vastus medialis, located medial to the rectus femoris, originates from the linea aspera of the femur below the intertrochanteric line and from the medial intermuscular septum. The lateral and medial muscles have a unipennate structure. The vastus intermedius, lying between the vastus lateralis and vastus medialis and deep to the rectus femoris, originates from the anterior and external surfaces of the femur. All four heads unite distally into a single common tendon that flanks the Patella and, under the name of the patellar ligament, attaches to the tibial tuberosity. Above the patella, beneath the muscle tendon, lies a synovial bursa that communicates with the cavity of the knee joint. The quadriceps femoris extends the leg at the knee joint, while the rectus femoris, in addition, acting separately, flexes it at the hip joint to an angle of 90°.

The patella is an intermediate bony support for the distal tendon of the quadriceps (Atlas, Figs. 13, 14, 48). Its significance as a sesamoid bone lies in the fact that it facilitates the transmission of Muscle Action to the leg (creating a more advantageous, wider angle of action) and reduces the sliding area of its tendon over the distal epiphysis of the femur. A subcutaneous synovial bursa is located in the region of the patella.

The Medial Group of thigh muscles consists of the pectineus and gracilis, and the adductor longus, adductor brevis, and adductor magnus (Atlas, Figs. 26, 44, 45). These five muscles are similar to one another in Location and fiber direction, and consequently in their primary function, which is why they are grouped together as the adductor muscles.

The pectineus muscle (m. pectineus) is small; its lateral margin borders the medial part of the iliopsoas; it originates from the pubic crest and attaches to the highest part of the medial lip of the linea aspera of the femur. The muscle flexes the leg at the hip joint while simultaneously adducing and laterally rotating it.

The gracilis muscle (m. gracilis) is ribbon-like, thin, and positioned along the Medial surface of the thigh. Originating from the inferior ramus of the pubis near the Pubic Symphysis, it attaches together with the sartorius to the tibial tuberosity. The muscle adducts the abducted leg and takes part in its flexion at the knee joint.

The adductor longus, adductor brevis, and adductor magnus (mm. abductores) originate from the pubic bone, with the latter also originating from the ischial bone. All three muscles attach to the linea aspera of the femur, with the adductor magnus extending all the way to its medial epicondyle. Like the pectineus and gracilis, they adduct the thigh and laterally rotate it; furthermore, the first two flex the thigh, while the latter extends it.

The posterior group consists of three muscles: the semitendinosus, semimembranosus, and biceps femoris (Atlas, Figs. 27, 44, 45, 47). They share a common origin from the ischial tuberosity, where they are covered by the gluteus maximus, and they attach to the leg, forming the upper BOUNDARIES OF THE popliteal fossa.

The semitendinosus muscle (m. semitendinosus) has a long distal tendon equal to approximately half its length. Deviating medially, it attaches to the tibial tuberosity together with the tendons of the sartorius and gracilis. The tendinous fibers of all three muscles form the so-called pes anserinus here. The latter continues partially into the Fascia of the leg, reinforcing it.

The semimembranosus muscle (m. semimembranosus) originates via a long, flat tendon, features a unipennate structure, and inserts into the medial condyle of the tibia.

The biceps femoris muscle (m. biceps femoris) originates with its long HEAD from the ischial tuberosity, and with its short head from the linea aspera of the femur. The muscle inserts via a common tendon into the head of the Fibula.

All three muscles of the posterior compartment extend the leg at the hip joint and flex it at the knee joint. When the limb is fixed, they act together with the gluteus maximus to extend the trunk at the hip joint. When the knee is flexed, the biceps femoris rotates the leg laterally, whereas the semitendinosus and semimembranosus rotate it medially.

Muscles of the Leg. The leg features three muscle groups: anterior, lateral, and posterior. The muscles of the latter are arranged in two layers—superficial and deep. The medial surface and anterior border of the tibia, as well as both malleoli, are subcutaneous and devoid of muscular coverage. Synovial bursae are located here between the bones and the Skin.

The crural fascia, which is a continuation of the fascia lata of the thigh, is particularly thickened in the region of the anterior muscle group, where the tendinous fibers of the pes anserinus blend into it. Sending two longitudinal intermuscular septa to the fibula, the fascia forms an osteofascial compartment that houses the Lateral Muscle Group. The adjacent muscles originate from the fascia and intermuscular septa. In the region of the Posterior muscle group, the fascia divides into superficial and deep layers. The former covers the triceps surae, while the latter covers the deep muscle layer, forming an osteofascial sheath around them together with the BONES OF THE leg. This sheath also contains the neurovascular bundle of the leg. Anteriorly, above the malleoli, the fascia is reinforced by transverse fibrous fibers attached to the bones, forming the superior extensor retinaculum of the leg (Atlas, Fig. 48). In the region of the malleoli, the fascia forms another thickening known as the inferior extensor retinaculum. Deep fibrous septa extending from it define four canals through which the tendons of the anterior muscle group, enclosed in synovial sheaths, along with Vessels and nerves, pass to the FOOT. Similar osteofascial and synovial sheaths are located inferior to the medial malleolus (transmitting the tendons of the deep posterior group along with vessels and nerves), as well as lateral to the lateral malleolus and on the lateral aspect of the sole, where the tendons of the lateral muscle group run.

The anterior muscle group of the leg comprises the tibialis anterior, extensor digitorum longus, and extensor hallucis longus (Atlas, Figs. 26, 44, 48).

The tibialis anterior muscle (m. tibialis anterior) originates from the lateral condyle and shaft of the tibia; descending along the bone onto the foot, it inserts into the medial cuneiform and first Metatarsal Bones. The muscle dorsiflexes the foot at the ankle joint and inverts it.

The extensor digitorum longus (m. extensor digitorum longus) lies lateral to the tibialis anterior and has a unipennate structure. It originates from the upper third of the tibia, the fibula, and the interosseous membrane; dividing into four tendons, it extends onto the foot and inserts into the dorsal aponeurosis of digits II–V. The muscle not only extends the toes but also everts the foot. The extensor digitorum longus may have a fifth, inconstant tendon, occasionally possessing an independent muscular belly. Positioned most laterally, this belly inserts into the dorsal Base of the fourth and fifth metatarsal bones and everts the foot (a movement crucial for bipedal locomotion).

The extensor hallucis longus (m. extensor hallucis longus) originates from the lower two-thirds of the fibula and the corresponding part of the interosseous membrane. Its long tendon emerges On the surface between the tibialis anterior and the extensor digitorum longus. Emerging at the medial border of the dorsal aspect of the foot, it inserts into the base of the distal phalanx of the great toe. The muscle extends both the great toe and the foot, while slightly inverting the latter.

The lateral group consists of two fibular (peroneal) muscles, of which the brevis lies deeper than the longus (Atlas, Figs. 27, 48, 49).

The fibularis longus muscle (m. peroneus longus) originates from the head and lateral surface of the fibula; it has a bipennate structure. The long tendon of the muscle passes posterior to the lateral malleolus and, having curved around the lateral border of the foot, runs along the sole within the sulcus of the cuboid bone, enclosed in a specialized osteofascial canal lined with a synovial sheath. Crossing the sole obliquely forward and medially, the tendon inserts into the base of the first metatarsal and medial cuneiform bones. The muscle everts and plantarflexes the foot, and also Supports its transverse arch.

The fibularis brevis muscle (m. peroneus brevis) is bipennate in structure; originating from the distal half of the fibular shaft and the intermuscular septa, it descends posterior to the lateral malleolus and inserts into the tuberosity of the fifth metatarsal bone. The muscle everts, plantarflexes, and abducts the foot.

The posterior muscle group of the leg, which is the most powerfully developed, consists of two layers. The superficial layer contains the triceps surae and plantaris muscles, while the deep layer includes the popliteus, flexor digitorum longus, tibialis posterior, and flexor hallucis longus muscles (Atlas, Figs. 27, 44, 48, 49).

The triceps surae muscle (m. triceps surae) has two superficial heads and one deep head. The superficial heads form the gastrocnemius muscle (m. gastrocnemius), which originates from the epicondyles of the femur. Both heads demarcate the inferior boundary of the popliteal fossa, with a synovial bursa situated on each side between the muscle and the bone. The well-developed muscular belly forms the calves in the upper half of the human leg. Distally, the muscle transitions into the calcaneal (Achilles) tendon (tendo calcaneus [Achillis]), which inserts into the calcaneal tuberosity. A synovial bursa is located here. The deep head of the triceps surae forms the soleus muscle (m. soleus), which is broader than the gastrocnemius and not entirely covered by it. The soleus originates from the head and upper third of the fibular shaft, as well as the tibial shaft, and continues into the Achilles tendon. All heads of the triceps surae plantarflex the foot; in addition, the gastrocnemius flexes the leg at the knee joint.

The plantaris muscle (m. plantaris) is vestigial and variable. It has a small belly and a very long tendon. The muscle originates above the lateral epicondyle of the femur, its tendon runs between the gastrocnemius and soleus muscles, and it merges with the Achilles tendon.

The popliteus muscle (m. popliteus) is small and lies on the posterior surface of the knee Joint Capsule. The muscle originates from the lateral epicondyle of the femur and inserts into the posterior surface of the upper part of the tibia. The muscle flexes the leg at the knee joint and subsequently rotates the leg medially.

The flexor digitorum longus (m. flexor digitorum longus) originates from the middle third of the tibia. Its tendon, having curved around the medial malleolus, extends onto the sole and divides into four slips that insert into the bases of the four distal Phalanges. The muscle flexes the toes and plantarflexes the foot.

The tibialis posterior muscle (m. tibialis posterior) lies between and is covered by the flexor digitorum longus and flexor hallucis longus. It originates from the interosseous membrane and the adjacent surfaces of the tibia and fibula. The tendon of the muscle descends posterior to the medial malleolus, crosses anterior to the tendon of the flexor digitorum longus, and upon reaching the sole, inserts into the navicular bone, the three cuneiform bones, and the bases of the second through fourth metatarsal bones. The muscle plantarflexes and inverts the foot, supports its longitudinal arch, and presses the toes against the ground during standing (especially when standing on tiptoe).

The flexor hallucis longus (m. flexor hallucis longus) is the most lateral and largest of the deep muscle layer. The muscle has a bipennate structure. It originates from the fibula, the interosseous membrane, and the Deep Layer of the crural fascia. The long tendon of the muscle curves around the medial malleolus, lies within the groove of the talus on the sole, and then proceeds to the great toe to insert into the base of its distal phalanx (Fig. 1.58). The muscle flexes the great toe, plantarflexes and inverts the foot, and plays a major role in supporting the longitudinal arch of the foot.

Muscles of the foot. In addition to the tendons descending from the leg, intrinsic muscles are also located on the foot.

Two small muscles, often fused at their origin, are located on the dorsum of the foot: the extensor digitorum brevis and the extensor hallucis brevis (Atlas, Fig. 48).

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Fig. 1.58. Muscles of the PLANTAR ASPECT OF the foot:

1 — lumbricals; 2 — flexor hallucis brevis; 3 — tendon of flexor hallucis longus; 4 — abductor hallucis; 5 — plantar aponeurosis (cut); 6 — flexor digitorum brevis; 7 — quadratus plantae; 8 — short muscles of the fifth digit; 9 — tendon of fibularis longus; 10 — adductor hallucis

The extensor digitorum brevis muscle (m. extensor digitorum brevis) lies deep to the tendons of the extensor digitorum longus. Originating from the anterior part of the calcaneus, the muscle divides into four flat bellies that extend anteriorly, blending with the tendons of the extensor digitorum longus of digits I–IV and the extensor hallucis longus to form the dorsal digital expansion on the phalanges of digits I–IV. The muscle extends the toes.

On the sole, the muscles are covered by a very dense fascia—especially in the middle portion—known as the plantar aponeurosis (Fig. 1.58). The latter is anchored to the calcaneal tuberosity, firmly fused with the skin in the metatarsal region, and transitions into the thin dorsal fascia of the foot at the edges of the foot. Lateral and medial intermuscular septa extend deep from the plantar aponeurosis, dividing the plantar muscles into three groups: medial, lateral, and intermediate.

The medial group is formed by the short muscles of the great toe: the flexor, the abductor, and the adductor (Fig. 1.58), with the latter also reinforcing the transverse arch of the foot. The lateral group comprises the short muscles of the little toe (V digit).

The intermediate group of plantar muscles is the most developed, consisting of the flexor digitorum brevis, quadratus plantae, lumbricals, and interosseous muscles of the foot.

The flexor digitorum brevis (m. flexor digitorum brevis), originating from the calcaneal tuberosity and the plantar aponeurosis, divides into four bellies (Fig. 1.58). Their tendons split into two slips and insert onto the lateral surfaces of the middle phalanges of the II–V digits; the tendons of the flexor digitorum longus pass between these slips. The muscle flexes the digits and supports the longitudinal arch of the foot.

The quadratus plantae (m. quadratus plantae) lies beneath the flexor digitorum brevis (Fig. 1.58). It originates from the calcaneus and inserts into the lateral margin of the flexor digitorum longus tendon. The function of this muscle is to straighten the line of pull of the flexor digitorum longus, whose tendinous bundles approach the digits obliquely.

The lumbricals of the foot (mm. lumbricales pedis), appearing as four slender muscle bundles, originate from the four tendons of the flexor digitorum longus; distally, they insert onto the medial margins of the proximal phalanges of the II–V digits, partially blending into their dorsal digital expansions. These muscles flex the proximal phalanges while extending the middle and distal ones.

The interosseous muscles of the foot (mm. interossei pedis)—four dorsal and three plantar—are located in the intermetatarsal spaces. These muscles displace the digits along the sagittal axis, i.e., they adduct and abduct them.

The tendons of the long muscles running along the plantar and dorsal aspects of the foot are enclosed in synovial sheaths that facilitate their gliding. Where they pass beneath fascial retinacula, the tendons are enclosed in osteofibrous canals and held against the bones. On the plantar side of the digits, the flexor tendons, similarly to those in the fingers, travel within osteofibrous and synovial sheaths.