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

Musculoskeletal System
Skeleton of the Limbs
Bones of the Lower Limbs and Their Articulations

The Skeleton of the lower limbs (Fig. 27) consists of the Pelvic Girdle (paired hip bones) and the free lower limb (BONES OF THE thigh, leg, and FOOT). The bones of the Lower limb girdle are more massive and thicker than those of the upper limb, as they are adapted to support the weight of the entire body both at rest and during dynamic loads such as walking, running, and jumping.

The pelvic girdle is formed by a paired, massive, flattened hip bone, with the sacrum located posteriorly between these bones.

Up to the age of 12–14 years, the hip bone consists of three separate bones connected by Cartilage: the ilium, pubis, and ischium. The fused bodies of these bones form the acetabulum, which serves as the articular surface for articulation with the HEAD of the Femur. The ilium is located above the acetabulum, the ischium inferiorly and posteriorly to it, and the pubis anteriorly and inferiorly. The ischium and pubis bound a large, oval-shaped obturator foramen closed by the obturator membrane, which is composed of Connective Tissue. Posteriorly, the hip bones articulate with the sacrum, and anteriorly with each other, forming the bony pelvis.

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Fig. 27. Bones of the lower limb.

Anterior view:

1 — sacrum; 2 — sacroiliac joint; 3 — superior ramus of pubis; 4 — symphysial surface of pubis; 5 — inferior ramus of pubis; 6 — ramus of ischium; 7 — ischial tuberosity; 8 — body of ischium; 9 — medial epicondyle of femur; 10 — medial condyle of Tibia; 11 — tibial tuberosity; 12 — body of tibia; 13 — medial malleolus; 14 — Phalanges; 15 — Metatarsal Bones; 16 — Tarsal Bones; 17 — lateral malleolus; 18 — Fibula; 19 — anterior border of tibia; 20 — head of fibula; 21 — lateral condyle of tibia; 22 — Patella; 23 — lateral epicondyle of femur; 24 — femur; 25 — greater trochanter of femur; 26 — neck of femur; 27 — head of femur; 28 — ala of ilium; 29 — iliac crest

The skeleton of the free lower limb follows a structural plan similar to that of the upper limb and consists of three segments: the femur, the bones of the leg (tibia and fibula), and the Bones of the foot (tarsals, metatarsals, and phalanges).

The femur is the largest tubular bone in The Human Body. Its upper (proximal) end (epiphysis) features a head that articulates with the hip bone. A long, slender neck connects the spherical head to the shaft of the femur. Near the transition from the neck to the shaft, the femur has two massive tubercles for Muscle attachment. The lower epiphysis of the femur is thickened and bears two prominences—the condyles, through which the femur articulates with the tibia and the patella—as well as two laterally projecting epicondyles: the medial and lateral.

The patella is a large, flattened bone embedded within the tendon of the quadriceps femoris muscle. Its posterior surface lies against the lower end of the femur. The patella is an integral component of the knee joint.

The skeleton of the leg consists of two long tubular bones: the tibia and the fibula. The tibia is thicker than the fibula. Its upper end is massive and thick, featuring articular surfaces for connection with the femoral condyles and the head of the fibula. The lower end of the tibia extends on its inner (medial) side into a flattened process known as the medial malleolus. The sharp anterior border of the tibia lies directly beneath the Skin.

The fibula is a slender, long bone with thickened ends, located laterally to the tibia. The upper end of the fibula forms a joint with the lateral surface of the upper epiphysis of the tibia, while the lower end terminates in a flattened lateral malleolus. Together with the medial malleolus and the Inferior surface of the tibia, the lateral malleolus participates in The formation of the ankle joint.

The bones of the foot, much like those of the hand, are divided into three groups: the tarsal bones, the metatarsal bones, and the phalanges.

The tarsal bones comprise seven bones arranged in two rows. The largest of these are the talus, which participates in the Formation of the ankle joint, and the calcaneus lying directly beneath it. The other tarsal bones (the cuboid, navicular, and three cuneiform bones) are located anterior to the calcaneus and talus. Five short tubular metatarsal bones lie anterior to the tarsals. The first metatarsal bone is shorter and thicker than the others. The bones of the toes are short tubular bones called phalanges. The great toe has two phalanges, whereas the remaining four toes each have three.

The JOINTS OF THE lower limbs are adapted to perform Functions of support and locomotion. The lower limb joints are large, reinforced by A large number of ligaments, and possess a smaller range of motion than their upper limb counterparts. Consequently, the joints of the lower limbs are stronger and more stable, enabling them to withstand significant loads.

Each hip bone articulates posteriorly with the sacrum via the sacroiliac joint. Anteriorly, a amphiarthrosis—the Pubic Symphysis—lies between the hip bones.

The sacroiliac joint is formed by the auricular articular surfaces of the sacrum and the hip bone. This joint is plane and practically immobile. Posteriorly and anteriorly, it is reinforced by thick, strong ligaments that connect the hip bone not only to the sacrum but also to the lower lumbar vertebrae.

The pubic symphysis is formed by the opposing symphysial surfaces of the pubic bones. Between these surfaces lies a fibrocartilaginous interpubic disc containing a small cleft-like cavity. The pubic symphysis is reinforced superiorly and inferiorly by strong ligaments.

The Pelvis as a whole. The hip bones and the sacrum, connected via the sacroiliac joints and the pubic symphysis, form the pelvis (Fig. 28). The pelvis is a bony ring enclosing a cavity that houses Internal Organs, Blood Vessels, and nerves. The pelvic brim, passing through the sacral promontory along the arcuate line of the iliac bones and the upper margin of the symphysis, divides the pelvis into two parts: the greater (false) pelvis and the lesser (true) pelvis. The greater pelvis is bounded laterally by the alae of the hip bones and posteriorly by the body of the fifth lumbar vertebra. The lesser pelvis is situated below the pelvic brim and is bounded posteriorly by the sacrum, laterally by the inner surfaces of the hip bones, and anteriorly by the pubic symphysis.

In adult men and women, the pelvis exhibits distinct Sexual Dimorphism. In women, the pelvis is wider and shorter, and all its dimensions are larger than in men. The bones of the female pelvis are thinner than those of the male pelvis. The sacrum in men is narrower, with the promontory protruding noticeably forward. In women, the sacrum is wider, and the promontory is less pronounced than in men. The angle formed by the inferior rami of the pubic bones (the subpubic angle) is acute in men (approximately 70–75°). In women, this angle approaches a right angle or may even be obtuse (90–100°). The ischial tuberosity and the iliac wings of the female pelvis are spaced further apart and flared outward to a greater degree. Thus, the distance

Fig. 28. Pelvis. Lines indicating the dimensions of the greater pelvis and the inlet of the lesser pelvis are shown:

1 — greater pelvis; 2 — ala of ilium; 3 — iliac crest; 4 — anterior superior iliac spine; 5 — anterior inferior iliac spine; 6 — lesser pelvis; 7 — acetabulum; 8 — pubic crest; 9 — pubic tubercle; 10 — ischium; 11 — ischial tuberosity; 12 — inferior ramus of pubis; 13 — subpubic arch; 14 — obturator foramen; 15 — right sacroiliac joint; 16 — sacrum.

I — distance between the two most distant points of the iliac wings; II — distance between the two anterior superior spines; III — transverse diameter of the pelvic inlet; IV — oblique diameter of the pelvic inlet. The distance between the two anterior superior iliac spines in women is 25–27 cm, and in men 22–23 cm. The superior aperture (inlet) of the female lesser pelvis is wider and shaped like a transverse oval. In men, this opening appears as a longitudinal oval. The main dimensions of the lesser pelvis are given in Table 7. The conjugate (direct diameter) of the pelvic inlet is the distance between the promontory and the upper margin of the symphysis. The direct diameter of the pelvic outlet is the distance between the tip of the coccyx and the inferior margin of the pubic symphysis. The transverse diameter of the inlet is the distance between the points on the pelvic brim most distant from each other on the right and left sides. The transverse dimension (intertuberous diameter) is the distance between the inner margins of the ischial tuberosities. The oblique diameter of the inlet is the distance between the sacroiliac joint on one side and the iliopectineal eminence on the other.

Thus, the distinguishing Features of the female pelvis lie in its larger dimensions, including the pelvic outlet. This is related to The primary function of the pelvis—serving as a container for the fetus developing within the Uterus. During childbirth, the fetus exits the uterine cavity through the pelvic outlet.

Table 7. Dimensions of the lesser pelvis in females (f) and males (m)

The pelvis of a newborn infant is funnel-shaped. Its anteroposterior diameter exceeds the transverse diameter, the sacral promontory is poorly defined, the superior aperture is rounded, and the ilium is positioned more vertically. Following birth, the shape and dimensions of the pelvis change gradually. The ischial tuberosities move further apart, and the lesser pelvis assumes a cylindrical shape. Rapid pelvic growth occurs during Puberty.

Joints of the free lower limb. The hip joint is formed by the head of the femur and the deep acetabulum of the hip bone. It is a ball-and-socket (spheroidal), multiaxial joint reinforced by five strong ligaments: four strengthen the Joint Capsule and limit the range of motion, while the fifth lies intracapsularly and attaches to the pit of the femoral head. The hip joint allows for flexion (moving the thigh forward) and extension around the frontal axis, abduction and adduction around the sagittal axis, as well as inward and outward rotation around the longitudinal axis.

The knee joint is the largest joint in the human body. It is formed by the condyles of the inferior (distal) epiphysis of the femur, the superior articular surfaces of the tibia, and the posterior surface of the patella. Inside the joint lie two half-moon-shaped menisci—the medial and lateral menisci—which are fused with the joint capsule and compensate for the incongruity between the articular surfaces of the articulating bones. The capsule and the knee joint itself are reinforced by numerous strong ligaments that not only guide but also restrict movement, providing stability to the joint during walking and standing. The knee joint performs flexion and extension of the leg (around the frontal axis), as well as rotational movements (when the leg is flexed, around the longitudinal axis).

The bones of the leg are connected by an interosseous membrane and two slightly movable tibiofibular joints, formed by the articular surfaces of the upper and lower epiphyses of the tibia and fibula, and reinforced by the anterior and posterior tibiofibular ligaments.

The ankle joint connects the bones of the leg to the foot. It is a classic hinge (ginglymus) articulation with a single axis of rotation—the transverse (frontal) axis. The joint is formed by the inferior articular surface and medial malleolus of the tibia, the articular surface of the lateral malleolus of the fibula, and the superior and lateral articular surfaces of the talus. The medial and lateral malleoli of the two leg bones embrace the trochlea of the talus in a fork-like manner. The joint capsule is reinforced laterally and medially by strong ligaments.

The inferior surface of the talus participates in the formation of joints with the calcaneus (subtalar joint) and the navicular bone (talocalcaneonavicular joint). The tarsal bones also form the calcaneocuboid and cuneonavicular joints. All joints formed by the tarsal bones and reinforced by dorsal, plantar, and interosseous ligaments have very limited mobility. The distal row of tarsal bones (cuboid and cuneiforms) forms slightly movable tarsometatarsal joints with the five metatarsal bones.

The metatarsophalangeal joints are spheroidal in shape. They are reinforced by plantar and collateral ligaments. The mobility of these joints is limited, allowing for flexion and extension, as well as slight abduction and adduction. The interphalangeal joints are hinge-shaped and possess only a single axis of rotation—the transverse axis—around which flexion and extension of the toes are possible.

The bones of the foot, connected by slightly movable joints and reinforced by thick and strong ligaments—including the powerful long plantar ligament—are adapted to perform weight-bearing and locomotor functions. Together with their connecting joints, these bones form upwardly convex arches known as the arches of the foot (Fig. 29). There are five longitudinal arches, corresponding to the five metatarsal bones, and one transverse arch. The longitudinal arches rest posteriorly on the calcaneal tuberosity and anteriorly on the heads of the metatarsal bones. When bearing weight on these points, the arched Structure OF THE foot acts as a spring under METABOLISM/18.html">The Influence of gravity, cushioning shocks during walking and running.

The arches are supported by the so-called ties of the foot. The ligaments act as passive ties, whereas the Muscles acting upon the foot function as its active ties.

Fig. 29. Arches of the foot:

A — diagram of the longitudinal (second) arch of the foot: 1 — calcaneus; 2 — talus; 3 — navicular bone; 4 — intermediate cuneiform bone; 5 — second metatarsal bone; 6 — phalanges of the toes. B — diagram of the transverse arch of the foot: I–V — transverse section of the metatarsal bones