Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Muscular System
Muscles and Fasciae of the Limbs — Muscles of the Lower Limb

The lower limbs are adapted for weight-bearing and locomotion. These large, powerful Muscles account for over 50% of total human body Muscle mass. They are arranged to provide maximum body stability and generate force during movement, including running and jumping. The lower limb muscles are divided into those of the Pelvic Girdle and the free lower limb (Figs. 40 and 41).

The Muscles of the Pelvic Girdle (pelvis) originate from the hip bone, sacrum, and lumbar vertebrae, and insert into the Femur. They are categorized into internal and external pelvic girdle muscles.

The internal muscles of the pelvic girdle are located within the pelvic cavity. These include the iliacus, psoas major, psoas minor, piriformis, and obturator internus muscles.

The iliacus muscle originates in the iliac fossa of the same name, while the psoas major originates from the lumbar vertebrae. Together, these two muscles form a large, common iliopsoas muscle, which exits the pelvis beneath the inguinal ligament and inserts via a common tendon into the lesser trochanter of the femur.

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Fig. 40. Muscles of the right lower limb.

Anterior view:

1 — sartorius muscle; 2 — iliopsoas muscle; 3 — pectineus muscle; 4 — adductor longus muscle; 5 — gracilis muscle; 6 — gastrocnemius muscle (medial HEAD); 7 — soleus muscle; 8 — tendon of extensor hallucis longus; 9 — inferior extensor retinaculum; 10 — superior extensor retinaculum; 11 — extensor digitorum longus; 12 — peroneus brevis (fibularis brevis) muscle; 13 — tibialis anterior muscle; 14 — peroneus longus (fibularis longus) muscle; 15 — quadriceps femoris muscle; 16 — tensor fasciae latae

The iliopsoas muscle flexes the thigh at the hip joint and rotates it laterally. The psoas minor (inconstant) originates from the lumbar vertebrae, with its slender, long tendon inserting into the iliac fascia and iliopubic eminence. The piriformis muscle originates on the anterior surface of the sacrum, exits the pelvic cavity through the greater sciatic foramen, and inserts into the greater trochanter of the femur, rotating the thigh laterally. The obturator internus originates from the margins of the obturator foramen and the obturator membrane, leaves the pelvic cavity via the lesser sciatic foramen, and inserts into the trochanteric fossa, also rotating the thigh laterally.

The external pelvic muscles include the gluteus maximus, medius, and minimus, the tensor fasciae latae, the obturator externus, the superior and inferior gemelli, and the quadratus femoris muscles.

The gluteus maximus is a large, powerful muscle originating from the external surface of the iliac ala, sacrum, and coccyx, and inserting into the gluteal tuberosity of the femur.

This muscle extends the thigh and rotates it laterally, maintains an upright posture, and gives the body a military bearing. The gluteus medius and minimus lie deep to the gluteus maximus. Originating on the external surface of the iliac ala, they insert into the greater trochanter and serve as thigh abductors. The tensor fasciae latae originates from the anterior part of the iliac crest, extends downward, blends into the iliotibial tract ( fascia lata), and tightens it. The obturator externus arises from the pelvic bone around the obturator foramen and the obturator membrane, inserts into the greater trochanter, and laterally rotates the thigh. The quadratus femoris originates from the lateral border of the ischial tuberosity, inserts into the intertrochanteric crest, and rotates the thigh laterally. The superior and inferior gemelli originate from the ischium and insert into the trochanteric fossa of the femur. These muscles also laterally rotate the thigh.

Fig. 41. Muscles of the right lower limb. Posterior view:

1 — gluteus maximus muscle; 2 — iliotibial tract; 3 — biceps femoris muscle; 4 — popliteal fossa; 5 — calcaneal (Achilles) tendon; 6 — gastrocnemius muscle; 7 — semitendinosus muscle; 8 — semimembranosus muscle

Muscles of the Free part of the lower limb. The free lower limb is subdivided into the muscles of the thigh, leg, and FOOT. The Muscles of the Lower Limb differ from those of the upper limb in their arrangement and Structure.

The muscles of the thigh are categorized into anterior, posterior, and medial groups. The anterior group comprises the sartorius and quadriceps femoris muscles. The sartorius is a long, narrow, superficial muscle that runs obliquely across the thigh from top to bottom and medially. It originates from the anterior superior iliac spine and inserts into the tibial tuberosity. This muscle flexes both the hip and the knee, and laterally rotates the thigh. The quadriceps femoris occupies the entire anterolateral surface of the thigh and arises by four heads. Its straight head (rectus femoris) originates from the anterior inferior iliac spine. The other three heads (the lateral, medial, and intermediate vastus muscles) take their origin from the anterolateral surface of the femur. All four heads converge into a single, thick, and broad common tendon that inserts into the tibial tuberosity. Enclosed within this tendon is the Patella, which contributes to The formation of the knee joint. The quadriceps femoris is the sole extensor of the leg at the knee joint. Additionally, the rectus femoris head flexes the thigh at the hip joint.

The posterior group of thigh muscles includes the biceps femoris, semitendinosus, and semimembranosus muscles. The long head of the biceps femoris originates from the ischial tuberosity, whereas its short head arises from the posterior surface of the femur. The muscle inserts into the head of the Fibula. It acts to extend the thigh, flex the leg, and laterally rotate the latter. The semitendinosus and semimembranosus muscles lie medial to the biceps femoris; both originate from the ischial tuberosity and insert into the Tibia. These muscles extend the thigh at the hip joint, flex the leg at the knee joint, and medially rotate the leg.

The Medial Group of thigh muscles consists of five muscles: the pectineus, gracilis, adductor magnus, adductor longus, and adductor brevis. These muscles originate from the pubic and ischial bones and (with the exception of the gracilis) insert onto the femur. All of them adduct the thigh and rotate it laterally. The gracilis inserts into the tibia; it adducts the thigh, flexes the leg at the knee joint, and medially rotates it.

The Muscles of the Leg form three groups: anterior, posterior, and lateral. The anterior group comprises three muscles: the tibialis anterior, extensor digitorum longus, and extensor hallucis longus. All of these arise from the anterior surfaces of the tibia and fibula, as well as the interosseous membrane of the leg. The tibialis anterior inserts into the Base of the first metatarsal and the medial cuneiform bone; it dorsiflexes the foot and elevates its medial border. The long extensors of the digits and the great toe insert into the Phalanges of the respective digits and extend them.

The posterior group of leg muscles comprises six muscles: the triceps surae, popliteus, tibialis posterior, plantaris, flexor digitorum longus, and flexor hallucis longus. The triceps surae is superficial and shapes the posterior contour of the leg. Two of its heads (lateral and medial) originate from the femoral epicondyles and form the gastrocnemius muscle. The third head (deep) arises from the tibia and tendinous arch, forming the soleus muscle. The soleus and gastrocnemius merge into a common (Achilles) tendon that inserts into the calcaneal tuberosity. This muscle acts as a plantarflexor of the foot, while its medial and lateral heads also assist in flexing the leg at the knee joint. The plantaris is a slender muscle originating from the lateral epicondyle of the femur, and its long tendon merges with the calcaneal (Achilles) tendon. The popliteus is a short muscle situated posteriorly on the knee Joint Capsule; it arises from the lateral epicondyle of the femur, inserts into the posterior surface of the tibia, and acts as a flexor of the leg at the knee joint.

The tibialis posterior, flexor digitorum longus, and flexor hallucis longus lie deep to the triceps surae. They originate from the posterior surfaces of the tibia and fibula and the interosseous membrane. The tendons of these muscles pass into the foot posterior to the medial malleolus. The tibialis posterior inserts into the navicular, cuneiform, and 4th Metatarsal Bones, and acts to plantarflex the foot. The digital flexors insert into the respective phalanges.

The Lateral group of leg muscles consists of two muscles — the fibularis (peroneus) longus and brevis — which originate from the fibula. Their tendons pass into the foot posterior to the lateral malleolus. The fibularis brevis inserts into the tuberosity of the 5th metatarsal bone. The tendon of the fibularis longus crosses the sole obliquely to insert into the base of the medial cuneiform and the 1st–2nd metatarsal bones. Consequently, the fibularis longus plantarflexes the foot, everts (pronates) its lateral margin (together with the fibularis brevis), and Supports the transverse arch of the foot.

The foot contains dorsal and plantar muscles. The dorsum of the foot contains two muscles: the extensor digitorum brevis and extensor hallucis brevis. Both originate from the dorsal surface of the calcaneus and insert into the dorsal phalanges of the corresponding digits. The SOLE OF THE foot is divided into three groups: medial (thenar eminence of the great toe), lateral (hypothenar eminence of the little toe), and central. The medial group is formed by three muscles: the abductor hallucis, flexor hallucis brevis, and adductor hallucis. These muscles originate from the Tarsal Bones and insert into the proximal phalanx of the great toe. The lateral group likewise includes three muscles: the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. These muscles originate from the PLANTAR ASPECT OF the calcaneus, the 5th metatarsal bone, and the long plantar ligament, and insert into the phalanges of the little toe. The central group of foot muscles comprises thirteen muscles. The flexor digitorum brevis and quadratus plantae (accessory flexor) originate from the calcaneus; the former inserts into the middle phalanges of the lateral four digits, whereas the quadratus plantae attaches to the tendons of the flexor digitorum longus. Four lumbricals arise from the tendons of the flexor digitorum longus and insert into the proximal phalanges of the 2nd–5th digits. The interossei originate from the metatarsals (within the interosseous spaces) and insert into the phalanges. The plantar interossei adduct the 3rd–5th digits toward the 2nd, whereas the dorsal interossei abduct the 2nd–4th digits laterally (away from the axis, toward the little toe).

The muscles of the lower limb are enclosed by fasciae. The external pelvic muscles and the Muscles of the Free Lower Limb possess a superficial (subcutaneous) fascia, known in the gluteal region as the gluteal fascia, on the thigh as the fascia lata, and on the leg as the crural fascia. The fascia lata is dense, thick, and prominently tendinous in structure. It envelops all the superficial thigh muscles and gives rise to three intermuscular septa that partition the thigh muscles into three distinct groups. This compartmentalization creates osteofascial compartments for the anterior, posterior, and medial thigh muscle groups. In the upper medial thigh (inferior to the inguinal ligament), the fascia lata features a specialized area covering the external (subcutaneous) ring of the femoral canal. The crural fascia, supplemented by two intermuscular septa, separates the lateral leg muscles (fibular muscles) from the anterior and posterior groups. At the level of the ankle joint, the crural fascia forms several transverse thickenings known as retinacula (tendon retainers). These retinacula contribute to the formation of three osteofibrous canals lined with synovial sheaths, through which the tendons of the tibialis anterior, extensor hallucis longus, and extensor digitorum longus pass onto the dorsum of the foot. Posterior to the medial malleolus, deep to the flexor retinaculum, there is another osteofibrous canal containing synovial sheaths for the tendons of the fibularis longus and brevis. On the dorsum of the foot, the fascia is thin and delicate. On the sole, however, the fascia is thick and reinforced by dense bundles of fibrous fibers, which is why the plantar fascia is referred to as the plantar aponeurosis.

The fasciae and muscle tendons of the lower limb participate in the Formation of the femoral and other canals, which are of significant both physiological and practical importance.

The femoral canal, which can be a site for the formation of femoral hernias, is located beneath the medial part of the inguinal ligament. The walls of the femoral canal, which is approximately 2 cm in length, are formed by the inguinal ligament (anteriorly), the femoral vein (laterally), and the Deep Layer of the fascia lata of the thigh (posteriorly). The femoral ring (internal opening of the canal) is situated in the pelvic cavity below the attachment site of the inguinal ligament to the pubic bone. The external opening of the canal is an area in the fascia lata containing openings for Vessels and nerves.