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

Musculoskeletal system
Structure of the skeleton
Skeleton of the limbs

BONES OF THE upper limb. The scapula (shoulder blade) is a flat triangular bone located on the DORSAL SIDE OF the rib cage at the level of Ribs II–VII (Fig. 1.20, A). The scapula has three angles (superior, inferior, and lateral, or glenoid), three borders (superior, lateral, and medial), and two surfaces.

The costal surface of the scapula is slightly concave (subscapular fossa). The dorsal surface is divided by an almost transverse ridge—the spine of the scapula—into the supraspinous and infraspinous fossae. The spine itself extends laterally into a prominent process, the acromion, which articulates with the clavicle via an articular facet at its free end. The spine and the inferior angle of the scapula are easily palpable in a living person.

The lateral angle bears a concave glenoid cavity, separated from the rest of the scapula by a slightly constricted neck. Above and below the cavity, the supraglenoid and infraglenoid tubercles are visible.

In the lower limb, they correspond to the Femur, the bones of the lower leg (Tibia and Fibula), and the FOOT, which consists of the tarsus, metatarsus, and Phalanges. The carpus and tarsus, both containing numerous bones, share a similar structural pattern. Furthermore, the Skeleton of the human hand and foot retains the number of bones characteristic of the primitive pentadactyl limb.

During the evolution of higher vertebrates, the clavicle appears in the Pectoral Girdle skeleton, functionally replacing an ancient bone, the procoracoid. Another ancient bone, the coracoid, loses its independence, becoming the coracoid process of the scapula.

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Fig. 1.20. Bones of the pectoral girdle:

A — right scapula, posterior view; B — right clavicle, inferior view; 1 — superior, 2 — inferior, and 3 — lateral angles; 4 — medial, 5 — lateral, and 6 — superior borders; 7 — spine; 8 — supraspinous fossa; 9 — infraspinous fossa; 10 — acromion; 11 — scapular notch; 12 — coracoid process; 13 — neck; 14 — infraglenoid tubercle; 15 — sternal and 16 — acromial ends of the clavicle

On the superior border of the scapula, a notch is visible, lateral to which rises the coracoid process, curved anteriorly and laterally.

The clavicle (clavicula) is curved like an elongated S and is easily palpable under the Skin (Fig. 1.20, B). Positioned horizontally, this bone connects the manubrium of the Sternum with the acromion. Articular surfaces are located at the ends of the bone. The Functional Significance of the clavicle is immense. It holds the shoulder joint at a proper distance from the rib cage, thereby allowing free movement of the limb. As a result, the upper limb hangs behind the body's line of gravity. In humans, the clavicle is the first bone to ossify.

The humerus is a typical long tubular bone, consisting of a shaft and two ends (Fig. 1.21). The proximal end terminates in a HEAD, separated by a faint anatomical neck from the lesser and greater tubercles. The lesser tubercle lies anteriorly, the greater tubercle lies laterally, and the intertubercular groove runs between them. Inferiorly, the tubercles continue as crests. The constricted part of the bone below the tubercles is called the surgical neck (where fractures most commonly occur). The crest of the greater tubercle continues down toward the deltoid tuberosity.

Fig. 1.19. Skeleton of the free forelimb and its girdle in fossil vertebrates:

A — Devonian lobe-finned fish; B — Permian stegocephalian; C — Triassic reptile: 1 — dermal bones of the pectoral girdle (Г — clavicle); 2 — scapula; 3 — humerus, 4 — radius, and 5 — ulna; 6 — skeleton of the hand; 7 — coracoid; 8 — procoracoid; 9 — glenoid cavity on the bones of the pectoral girdle. Skeleton of the forelimb: Г — reptile, Д — bird, Е — bat, Ж — human. 1 — humerus; 2 — bones of the forearm; 3 — Carpal Bones; 4 — Metacarpal bones; 5 — phalanges. Skeleton of the hindlimb: З — human; И — dog; К — horse: 1 — pelvic bones; 2 — femur; 3 — bones of the lower leg; 4 — Bones of the foot

Fig. 1.21. Right humerus:

A — posterior view; B — anterior view; 1 — head; 2 — anatomical neck; 3 — greater tubercle; 4 — lesser tubercle and 5 — its crest; 6 — intertubercular groove; 7 — crest of the greater tubercle; 8 — surgical neck; 9 — deltoid tuberosity; 10 — nutrient foramen; 11 — coronoid fossa; 12 — medial epicondyle; 13 — trochlea; 14 — capitulum; 15 — lateral epicondyle; 16 — olecranon fossa

The flattened and laterally expanded distal end of the bone forms two articular surfaces: the medial, pulley-shaped trochlea, which articulates with the ulna, and the lateral, rounded capitulum, which articulates with the radius. Above the trochlea anteriorly lies the coronoid fossa, and posteriorly, the large olecranon fossa. During flexion and extension of the arm at the elbow joint, the corresponding processes of the ulna fit into these fossae. On the sides of the distal end, the rough lateral and medial (more prominent) epicondyles project, serving as attachment sites for Muscles.

The radius has a head at its proximal end with an articular facet that articulates with the capitulum of the humerus (Fig. 1.22). Around its circumference, the head is surrounded by a vertical articular rim (articular circumference) that participates in the articulation with the ulna. The constricted portion below the head is called the neck, below which a rough area, the radial tuberosity, is visible. The tendon of the biceps brachii Muscle attaches to this tuberosity. The trihedral shaft of the radius has its sharp interosseous border facing the corresponding border of the ulna. The interosseous membrane is stretched between these borders, providing a large surface area for muscle attachment.

Fig. 1.22. Bones of the right forearm, anterior view:

1 — olecranon; 2 — trochlear notch; 3 — coronoid process; 4 — ulnar tuberosity; 5 — ulna; 6 — its head; 7 and 8 — styloid processes; 9 — radius; 10 — radial tuberosity; 11 — neck; 12 — head

The distal end of the radius is expanded, and its ellipsoidal articular surface faces the carpus. On its medial side, there is an articular facet for articulation with the head of the ulna, and on the lateral side, the styloid process.

The ulna has a large, crescent-shaped trochlear notch at its proximal end, which opens anteriorly and glides along the trochlea of the humerus during movement (Fig. 1.22). This trochlear notch is bounded posteriorly and superiorly by the olecranon (easily palpable under the skin), and anteriorly and inferiorly by the coronoid process. Lateral to the Base of the latter is a concave articular surface—the radial notch—which articulates with the head of the radius, and below it, a crest to which the supinator muscle of the forearm attaches. On the anterior surface of the shaft, below the coronoid process, lies the ulnar tuberosity. The distal end of the bone forms the head. On the side facing the radius, the head has an articular surface, and on the medial side, the styloid process.

The hand (manus) is divided into three parts: the wrist (carpus), the metacarpus, and the phalanges of the digits (Fig. 1.23). The wrist (carpus) consists of eight small bones arranged in two rows. The proximal row of the carpus contains (from the radius to the ulna): the scaphoid, lunate, triquetrum, and pisiform; the distal row contains the trapezium, trapezoid, capitate, and hamate bones.

The first three bones of the proximal row, excluding the pisiform, are part of the radiocarpal joint. The pisiform bone is a sesamoid bone and does not have a cartilaginous stage of development. All carpal bones are firmly bound together by ligaments attached to their dorsal and palmar sides. Therefore, the mobility of the wrist is minimized. The carpal bones form an arch with its concavity facing the palm.

Fig. 1.23. Bones of the right hand, dorsal view:

1 — scaphoid; 2 — lunate; 3 — triquetrum; 4 — pisiform; 5 — trapezium; 6 — trapezoid; 7 — capitate; 8 — hamate; 9 — base of the III metacarpal; 10 — heads of the II—V metacarpals; 11 — proximal; 12 — middle and 13 — distal phalanges; I—V — metacarpal bones

The metacarpus consists of five tubular metacarpal bones which, except for the first, lie in the same plane and decrease in length from the II to the V. The II—V metacarpal bones are arranged in a row, leaving three interosseous spaces between them. Each metacarpal bone consists of a body (shaft), a base resting on the bones of the distal carpal row, and a head articulating with the proximal phalanx of the digit. The I metacarpal bone is set apart. The proximal ends of all metacarpal bones are widened at their bases. The base of the first metacarpal bone has a saddle-shaped surface, and its body is wide and flattened.

The phalanges (phalanges digitorum)—proximal, middle, and distal—are present in the skeleton of the II—V digits; the first digit lacks a middle phalanx (Fig. 1.23). The proximal phalanges are the longest, and the distal ones are the shortest. The phalanges are elongated bones, widened at their ends. Their proximal end has a concave surface corresponding to the head of the metacarpal bone. The distal end of the proximal and middle phalanges has a trochlear articular surface.

JOINTS OF THE upper limb bones. The scapula has no direct contact with the bones of the trunk. It connects to them via the clavicle, which articulates with the sternum. However, the scapula is primarily secured to the trunk bones by muscles.

The sternoclavicular joint (articulatio sternoclavicularis) is formed by the medial end of the clavicle and the clavicular notch of the manubrium of the sternum (Atlas Fig. 6). The joint is saddle-shaped but allows multi-axial movement because it contains an articular disc. The Joint Capsule is reinforced by ligaments extending to the first rib and to the contralateral clavicle.

At its lateral end, the clavicle forms a plane joint with the acromion and is connected by a ligament to the coracoid process. Both joints of the clavicle can be palpated through the skin.

The shoulder joint (articulatio humeri) is the most mobile joint in the body. It is classified as a ball-and-socket (spheroidal) multiaxial joint (Atlas Fig. 8). The joint is formed by the head of the humerus and the glenoid cavity of the scapula. The cavity is significantly smaller than the head and is deepened along its margin by a glenoid labrum. Even so, the area of the cavity is only about 1/4 of the area of the humeral head. With a relatively loose joint capsule, this provides significant mobility but reduces its stability.

Fig. 1.24. Possible movements in the shoulder joint:

A — frontal axis: flexion—extension; B — sagittal axis: abduction—adduction; C — vertical axis: rotation

From above, the joint is protected by the strong coracoacromial ligament, which, together with the acromion, forms the coracoacromial arch over it. The arch protects the joint but limits abduction and flexion of the arm. The capsule loosely surrounds the joint and is reinforced only by the weak coracohumeral ligament.

A unique feature of the joint is that the tendon of the long head of the biceps brachii muscle passes through its cavity, enclosed in the intertubercular sulcus by a synovial sheath that facilitates its sliding. The tendon presses the head of the humerus against the glenoid cavity of the scapula (Atlas Fig. 8).

Movements in the joint are possible around the following axes: frontal (flexion and extension), sagittal (adduction and abduction), and vertical (external and internal rotation), as well as circumduction (Fig. 1.24).

The elbow joint (articulatio cubiti) is a compound joint, as it combines three joints: the humeroulnar, humeroradial, and proximal radioulnar joints (Atlas Fig. 9). They are enclosed in a common capsule, which is loose and relatively thin anteriorly and posteriorly, but reinforced by collateral ligaments. In addition, the neck of the radius is held in the radial notch of the ulna by the annular ligament.

Flexion and extension, i.e., movement around the frontal axis, are possible in the humeroulnar and humeroradial joints.

In the cylindrical (pivot) radioulnar joint, the radius rotates around a vertical axis. At the same time, rotation also occurs in the spheroidal humeroradial joint. The distal ends of the forearm bones form the distal radioulnar joint, which is cylindrical in shape and Functions in combination with the proximal joint of the same name. Due to movements in these three joints, the hand can be turned palm forward (supination) and palm backward (pronation); during supination, the forearm bones lie parallel to each other, whereas during pronation, the radius crosses over the ulna (Fig. 1.25). The space between the forearm bones is spanned by the interosseous membrane (see Atlas).

The radiocarpal joint (articulatio radiocarpea) is formed by the distal end of the radius and three bones of the proximal carpal row (Fig. 1.26). The pisiform bone does not participate in this joint. The joint is ellipsoidal in shape: it allows movements around two axes—frontal (flexion and extension) and sagittal (abduction and adduction). The ulna does not participate in this joint, as it is separated from it by a triangular cartilaginous disc. The joint is reinforced by collateral ligaments originating from the styloid processes, as well as dorsal and palmar accessory ligaments (Atlas Fig. 10).

Fig. 1.25. Position of the hand and forearm bones:

A — in supination; B — in the neutral position; C — in pronation; D — during internal rotation in the shoulder joint. The radius and the corresponding part of the hand are shown in black

The midcarpal joint (articulatio intercarpea) is formed between the proximal and distal rows of carpal bones, resulting in complex contours of its articular surfaces (Fig. 1.26). The articulating bones here are connected by numerous short, strong ligaments that limit movements occurring around two axes.

Fig. 1.26. Joints of the hand:

A — joints of the hand: 1 — hinge; 2 — ellipsoid; 3 — saddle; 4 — ball-and-socket; B — skeletal relief of the flexed hand: 1 — head of the ulna; 2 — proximal carpal bones; 3 — bases of the metacarpal bones; 4 — head of the II metacarpal bone; 5 — interphalangeal joints of the index finger; 6 — head of the I metacarpal bone

Mobility in this joint increases the range of motion of the hand occurring at the wrist joint. The bones in each row are interconnected by tight ligaments.

Carpometacarpal joints (articulationes carpometacarpeae) are formed between the bones of the distal carpal row and the bases of the metacarpal bones (Fig. 1.26). Four of them (II—V) are plane joints with tight joint capsules. Characterized by low mobility compared to other joints of the hand and occupying a central position, they mechanically form the stable base of the hand. The first carpometacarpal joint (between the trapezium and the I metacarpal bone) is a saddle joint (Atl. Fig. 10). It allows for adduction and abduction of the thumb relative to the index finger, opposition of the thumb to the other digits, and circumduction.

Metacarpophalangeal joints (articulationes metacarpophalangeae) are spheroidal (ball-and-socket) in shape (Fig. 1.26 and see Atl.), but movements along the vertical axis are restricted by the ligamentous apparatus. Within the capsule of the I metacarpophalangeal joint, two sesamoid bones are embedded, protecting it on the palmar side.

Interphalangeal joints are hinge joints with collateral strengthening ligaments; movements in them are possible only around the frontal axis (Fig. 1.26 and Atl. p. 19).

Since many of these joints of the hand lie directly beneath the skin and are not covered by muscles, they largely shape the dorsal relief of the hand (Fig. 1.26, B).

Thus, during Human Evolution, the skeleton of the hand underwent the following changes:

✵ the phalanges of the thumb increased in size;

✵ the carpometacarpal joint of the thumb acquired a pronounced saddle shape;

✵ the thumb, as well as the trapezium and scaphoid bones, shifted in the palmar direction;

✵ the phalanges of digits II—V shortened and straightened, which proved highly important for The Development of fine, differentiated hand movements.

Bones of the lower limb. The hip bones (ossa coxae) (Fig. 1.27), which form the pelvis (Fig. 1.28), each consist of three bones in individuals under 16 years of age — the ilium, pubis, and ischium (see below). At the junction where all three bones meet, the articular acetabulum is formed. Medial to it, the pubis and ischium enclose the large obturator foramen.

Fig. 1.27. LATERAL VIEW OF the right hip bone:

1 — iliac crest; 2 — rough lines for attachment of the abdominal oblique muscles; 3 — anterior superior iliac spine; 4 — ala of the ilium; 5 — posterior, 6 — anterior, and 7 — inferior gluteal lines; 8 — anterior inferior iliac spine; 9 — greater sciatic notch; 10 — posterior superior and 11 — posterior inferior iliac spines; 12 — acetabulum, its lunate surface (13) and acetabular fossa (14); 15 — body of the pubis; 17 — pubic tubercle; 16 — superior and 18 — inferior rami of the pubis; 19 — obturator foramen; 20 — body; 21 — inferior and 22 — superior rami of the ischium; 23 — ischial tuberosity; 24 — ischial spine; 25 — lesser sciatic notch

Fig. 1.28. Female pelvis (anterior view):

1 — arcuate line of the ilium; 2 — sacrum; 3 — sacroiliac joint; 4 — ala of the ilium; 5 — pubic crest; 6 — obturator foramen; 7 — Pubic Symphysis; 8 — pubic angle; 9 — ischial tuberosity; 10 — rami of the pubis; 11 — pubic tubercle; 12 — acetabulum; 13 — anterior inferior and 14 — anterior superior iliac spines

The ilium (os ilium) contributes to the acetabulum with its body, from which the ala (Fig. 1.27) — a broad bony plate — extends upward and slightly laterally. Superiorly, the ala is bounded by the thick iliac crest, at the anterior end of which project two anterior (superior and inferior) iliac spines. The posterior border of the ala forms the greater sciatic notch, which is partially bounded by the ischium. Three semicircular gluteal lines run along the outer surface of the ilium, and the arcuate line runs along its inner surface. Posteriorly, the latter terminates at the auricular surface, which articulates with the sacrum, with the iliac tuberosity lying above it.

The pubic bone (os pubis) closes the pelvis anteriorly. With its body, it contributes to The formation of the acetabulum (Fig. 1.27). Its two rami — the superior (horizontal) and inferior, joined to each other at an angle — enclose the obturator foramen on the superior and medial sides. The pubic crest runs along the superior ramus, ending at the pubic tubercle (Atl. Fig. 11). The medial borders of both bones are rough and form the pubic symphysis. The inferior rami, diverging to the sides, form the pubic angle.

The ischium (os ischii) also contributes to the Formation of the acetabulum with its body (Fig. 1.27). Its two rami — superior and inferior — enclose the obturator foramen inferiorly and laterally. At the junction of the two rami lies the ischial tuberosity, which Supports the body when sitting. Above the tuberosity, the ischial spine projects from the posterior border of the bone, separated from it by the lesser sciatic notch.

The femur (femur) is the largest and longest long bone in The Human Body, having a head at its proximal end, separated from the shaft by a neck (Fig. 1.29). At the junction of the neck and shaft, two trochanters project — the greater and lesser trochanters, connected on the posterior surface of the bone by the intertrochanteric crest, and anteriorly by the intertrochanteric line. On the medial side, at the base of the greater trochanter, the trochanteric fossa is visible.

The linea aspera runs along the entire posterior surface of the shaft, its two Lips, diverging inferiorly, enclosing the triangular popliteal surface. Proximally, the lateral lip continues into the gluteal tuberosity. The distal end of the bone consists of two condyles — lateral and medial, separated by the intercondylar fossa. The lateral, slightly projecting rough PARTS OF THE condyles are called epicondyles. Inferiorly and posteriorly, both condyles are covered with articular Cartilage, which merges anteriorly into a single common articular surface. The Patella (patella), the largest sesamoid bone in the body, articulates with this surface.

Fig. 1.29. Right femur:

A — anterior view; B — posterior view; 1 — head; 2 — fovea for head of femur; 3 — neck; 4 — greater trochanter; 5 — lesser trochanter; 6 — intertrochanteric line; 7 — trochanteric fossa; 8 — intertrochanteric crest; 9 — lateral and 10 — medial lips of the linea aspera; 11 — pectineal line; 12 — gluteal tuberosity; 13 — popliteal surface; 14 — lateral condyle; 15 — medial condyle; 16 — intercondylar fossa; 17 — lateral epicondyle; 18 — medial epicondyle; 19 — patellar surface

The tibia occupies a medial position in the lower leg (Fig. 1.30). The trihedral shaft of the bone is expanded at its proximal end, forming two condyles—lateral and medial—separated by the intercondylar eminence (Fig. 1.30). On the lateral and posterior aspect of the lateral condyle, there is an articular facet for articulation with the head of the fibula. The anterior border of the tibial shaft continues superiorly into the tibial tuberosity. The expanded distal end of the bone extends medially into the medial malleolus and bears a concave articular surface that articulates with the talus of the foot. On the lateral side of the distal end, There is a fibular notch connected by a syndesmosis (and sometimes a joint) to the fibula.

Fig. 1.30. Bones of the right lower leg:

A — anterior view; B — posterior view; 1 — lateral epicondyle; 2 — intercondylar eminence; 3 — medial epicondyle; 4 — tibial tuberosity; 5 — tibia; 6 — medial malleolus; 7 — lateral malleolus; 8 — fibula; 9 — its head

Fig. 1.31. Bones of the right foot, lateral view:

1 — talus; 2 — its head and 3 — articular surface; 4 — calcaneus; 5 — calcaneal tuberosity; 6, 7, 8 — I, II, and III cuneiform, 9 — cuboid, 10 — navicular, 11 — Metatarsal Bones; 12 — phalanges

The fibula is relatively thin. At its upper end, it bears a head with an articular facet that articulates with the tibia; its distal end is extended into the lateral malleolus, which connects with the lateral surface of the talus.

The tarsus consists of seven bones (Fig. 1.31). Two of them—the talus and calcaneus—make up the proximal row, while four—the I, II, and III cuneiforms and the cuboid bone—make up the distal row. The navicular bone is located between the two rows on the medial side of the foot.

The talus articulates superiorly with the bones of the lower leg via a trochlear articular surface that is wider anteriorly. The forward-directed part of the bone—the head—connects with the navicular bone.

Ontogeny of the limb skeleton. The limb skeleton, like the Skeleton of the Trunk, passes through Connective Tissue, cartilaginous, and bony stages in its development.

Limbs arise in the embryo as paired outgrowths of the trunk and initially resemble paddles. During the second month of development, their mesenchymal core begins to transform into cartilage, which becomes segmented. When the mesenchymal zones between these segments disappear, joint cavities are formed.

Ossification begins in the embryo at 6—7 weeks of development and is characterized by the appearance of an ossification center in the clavicle, which develops intramembranously (bypassing the cartilaginous stage) (Fig. 1.33). All other bones develop endochondrally starting from the end of the second month of intrauterine life (see Atl.). The sternal end of the clavicle is cartilaginous in the newborn and is replaced by bone at 18—25 years of age. In the scapula, the primary ossification center arises in the region of its neck and body during the prenatal period (2 months). Other ossification centers appear after birth: in the coracoid process at 1 year, in the acromion at 15—18 years, and on the medial border at 15—19 years. Scapular development is completed by age 20—21. Ossification of the cartilaginous precursor of the hip bone begins in the 4th month of prenatal development with the appearance of three primary centers in the bodies of the ischium (4 months), pubis (5 months), and ilium (6 months). Cartilaginous layers between these bones persist until 14—16 years of age (Fig. 1.34). Secondary ossification centers in the spines, crest, and ischial tuberosity fuse with the hip bone by 20—25 years of age. In the epiphyses of long bones, ossification centers appear only after birth. The exceptions are the epiphyses of the femur and tibia facing the knee joint, where most newborns already have a small ossification center.

The appearance of these centers serves as an important indicator of fetal maturity and is taken into account during forensic autopsies.

The hand and foot are convenient subjects for studying the Development of the Skeletal System, as these Regions of the skeleton differ from others in their Abundance of ossification centers.

In the newborn hand (Fig. 1.35), all carpal bones, the heads of the II—V metacarpals, and the bases of the I metacarpal and phalanges remain cartilaginous. At three to five months of age, a single ossification center appears in the capitate and hamate bones; at two to three years, in the triquetrum; at three to four years, in the lunate; at five years, in the scaphoid; and at five to six years, in the trapezium and trapezoid bones of the wrist. The ossification center in the pisiform bone appears at ten to twelve years of age.

During Embryogenesis OF THE hand, the digits grow most rapidly. In children, the wrist is relatively shorter and the phalanges are longer than in adults. Individual and sex-related Variability in the timing of hand bone ossification in children (Belogorsky, 1973) is shown below:

The calcaneus is the largest bone of the tarsus; it articulates superiorly with the talus and anteriorly with the cuboid. Posteriorly, the bone is elongated and thickened, forming the calcaneal tuberosity, which serves as a support during standing and as the attachment site for the tendon of a powerful muscle.

The navicular bone, occupying a central position in the tarsus, articulates with all of its bones except for the calcaneus.

The cuneiform bones (I, II, and III) are arranged in a single transverse row. Proximally, they articulate with the navicular bone, and distally, with the first three metatarsal bones. The first cuneiform bone, which supports the I metatarsal bone, is the largest.

The cuboid bone is located at the lateral margin of the foot; it articulates posteriorly with the calcaneus, anteriorly with the IV and V metatarsals, and medially with the navicular and III cuneiform bones.

The metatarsus is represented by five bones (Fig. 1.31). Just as in the metacarpus, the I bone is the thickest, and the II is the longest. Each metatarsal bone has a base,

resting on the tarsus, a head articulating with the proximal phalanx of the corresponding digit, and a body. The base of the V metatarsal bone is laterally extended into a tuberosity that is easily palpable through the skin.

There are three phalanges in digits II–V, and two in digit I (Fig. 1.31). All phalanges, especially the middle ones, are significantly shortened, and in digit V, the middle phalanx is often fused with the distal one.

Joints of the lower limb. The pelvis is formed by the hip bones, sacrum, and coccyx (Fig. 1.28). Anteriorly along the midline, both hip bones are joined by fibrocartilage at the pubic symphysis (symphysis pubica) (Fig. 1.32). Within this cartilage, there is a small longitudinal fluid-filled cleft. Therefore, the symphysis should be considered a hemiarthrosis rather than a synchondrosis. In pregnant women, especially towards delivery, this cleft becomes slightly larger and the cartilage softer, allowing the bones to separate slightly during the passage of the fetus.

The hip bones articulate via their auricular surfaces with the corresponding surfaces of the sacrum, forming a flat, almost immobile sacroiliac joint (articulatio sacroiliaca) surrounded by powerful ligaments. Posteriorly, the pelvis is reinforced by ligaments running from the lateral parts of the sacrum to the ischial tuberosity (sacrotuberous ligament) and its spine (sacrospinous ligament) (Atl. Fig. 11). These ligaments participate in forming the lower lateral walls of the pelvis and, together with the sciatic notches, define the greater and lesser sciatic foramina. The obturator foramen is closed by the obturator membrane (hence its name).

Fig. 1.32. Frontal section of the pubic symphysis:

1 — superior and 2 — inferior rami of the pubic bone; 3 — spongy bone; 4 — fibrocartilage and 5 — cleft of the pubic symphysis; 6 — superior and 7 — arcuate pubic ligaments

Fig. 1.33. Development of the clavicle:

1 — primary and 2 — secondary ossification centers

Fig. 1.34. Hip bone of a five-year-old child: A — internal and B — external aspect;

1 — ilium; 2 — iliac crest (cartilaginous) and 3 — auricular articular surface; 4 — ischial spine; 5 — superior ramus of the ischium; 6 — cartilaginous ischial tuberosity (begins to ossify at about 15 years of age); 7 — inferior ramus of the ischium; 8 — cartilage layer between the pubic and ischial bones (replaced by Bone tissue between 3 and 12 years of age); 9 — inferior ramus of the pubic bone; 10 — cartilage at the site of the future symphysis; 11 — superior ramus of the pubic bone; 12 — anterior inferior iliac spine (cartilaginous, ossification center appears at 12–14 years of age); 13 — cartilage layer at the junction of the three bones fusing into a single hip bone at 14–16 years of age (in the areas marked by arrows, ossification centers appear at 7–9 years, participating in the formation of the acetabulum); 14 — iliac tuberosity

A distinction is made between the greater and lesser pelvis (Fig. 1.28). The boundary between them (the pelvic inlet) is formed by the base of the sacrum, the arcuate line on the iliac bones, and the pubic crest on the pubic bones. The greater pelvis is open superiorly and serves as a bony support and protection for the abdominal viscera. The lesser pelvis is somewhat narrowed inferiorly. The plane of the pelvic inlet forms an angle of 45–60° with the horizontal. The magnitude of this angle depends on body posture and the degree of lumbar lordosis. In women, this angle is larger than in men; in adults, it is smaller than in newborns.

In no other part of the skeleton are sexual differences as pronounced as in the pelvis. The male pelvis is narrower and taller, and the sagittal diameter of the pelvic inlet is greater than the transverse diameter. In women, the pelvis is wider and shorter, the wings of the iliac bones are flared more laterally, and the pubic angle is significantly larger than in men; the transverse diameter of the pelvic inlet is longer than the sagittal diameter. All Features of the female pelvis are adaptations for childbirth and typically manifest in girls after 10 years of age. However, the difference in the width of the pubic angle is noticeable as early as 5 years of age.

The hip joint (articulatio coxae) is formed by the head of the femur and the acetabulum (Atl. Fig. 12). It is a ball-and-socket (cotyloid) joint with three axes of rotation. Circumduction is also possible within it. The femoral head is largely enclosed by the acetabulum, which is deepened by a ring-like fibrocartilaginous labrum surrounding its margin. The joint capsule is tightly taut and surrounded by strong, short ligaments. The most powerful of these (and the strongest in the human body) is the iliofemoral ligament; it reaches a thickness of up to 1 cm and reinforces the anterior wall of the joint capsule (Atl. Fig. 12). The ligament of the head of the femur runs from the femoral head to the bottom of the acetabulum. It serves as a soft cushion between the articulating bones, and Blood Vessels travel through it to the head.

The knee joint (articulatio genu) is formed by the condyles of the femur and tibia, and the patella (Atl. Figs. 13, 14). The joint has an extensive capsule, and its synovial membrane features numerous folds. Fat is deposited in some of these folds. The joint cavity communicates with many periarticular synovial subtendinous bursae. Anteriorly, the joint is protected by the patella, which lies within the tendon of the quadriceps femoris muscle.

The uniqueness of the knee joint lies in the presence of intra-articular menisci and ligaments. Crescent-shaped, thick-edged cartilaginous menisci (lateral and medial) lie between the condyles of the femur and tibia. The intra-articular cruciate ligaments extend from the intercondylar eminence of the tibia to the walls of the intercondylar fossa of the femur. Together with the strong collateral ligaments and the menisci, the cruciate ligaments prevent hyperextension of the leg at the knee joint and stabilize it during standing.

Movements in the knee joint occur around the frontal axis (flexion and extension). Due to the menisci and the shape of the articular surfaces, when the knee is flexed (and the collateral ligaments are relaxed), slight movements around the vertical axis are possible, i.e., outward and inward Rotation of the lower leg. Thus, the knee joint is a modified hinge (condylar) joint.

Both bones of the lower leg are connected to each other at the proximal end by a slightly movable plane joint, at the distal end by a syndesmosis, and between their shafts by an interosseous membrane (Atl. Fig. 15).

The ankle joint (articulatio talocruralis) is formed between the distal ends of the leg bones and the trochlea of the talus. It is held in position by the malleoli of the leg bones and several collateral ligaments (Atl. Figs. 16, 17). Movements occur around the frontal axis (flexion and extension).

Ligament sprains are common in the ankle joint. This occurs during plantarflexion combined with supination, when the narrower posterior part of the talar trochlea enters the mortise between the malleoli. In this case, sudden weight-bearing causes a lateral movement (adduction) due to the unstable wedging of the narrow trochlea, resulting in a sprain of the lateral collateral ligament (commonly referred to as 'rolling the ankle'). Sometimes, an avulsion fracture of a portion of the malleolus at the site of ligament attachment can even occur.

The subtalar joint consists of two anatomically separate joints between the talus, calcaneus, and navicular bones (Atl. Fig. 17). The joint is spherical in shape, allowing for slight supination and pronation of the foot.

The joints between the remaining Tarsal Bones (intertarsal joints) are slightly movable, as they are reinforced by strong ligaments.

The tarsometatarsal joints are plane joints, and movements in them are limited (Atl. Fig. 17).

The metatarsophalangeal joints, formed by the heads of the metatarsal bones and the proximal phalanges of the toes, are spheroidal.

The interphalangeal joints are hinge joints, have collateral ligaments, and allow flexion and extension.

The bones of the foot form two arches: longitudinal and transverse (Fig. 1.31). The medial side of the longitudinal arch consists of the calcaneus, talus, navicular, cuneiform, and I–III metatarsal bones, while the lateral side consists of the calcaneus, cuboid, and IV–V metatarsal bones. Posteriorly, the arch rests on the calcaneal tuberosity, and anteriorly on the heads of the I and V metatarsal bones. The longitudinal arch is supported by the strong plantar ligament, stretched between the calcaneus and the bases of the metatarsal bones, as well as by muscles. The lateral side of the arch serves as a support during standing and walking and is therefore called the supporting arch, in contrast to the medial side, which acts as a spring during walking and is called the spring arch. The transverse arch is most clearly pronounced in the region of the cuneiforms, cuboid, and bases of the metatarsal bones.

Fig. 1.35. Skeleton of the hand and distal forearm (diagrams from radiographs, after Rokhlin):

1 — a four-month-old boy; 2 — a one-and-a-half-year-old boy; 3 — a three-and-a-half-year-old boy; 4 — a four-year-old girl; 5 — a six-year-old boy; 6 — an eight-year-old boy; 7 — a ten-year-old girl. Emerging ossification centers are shown in black

Fig. 1.36. Skeleton of the foot and distal lower leg (diagrams from radiographs, after Rokhlin):

1 — a five-month-old boy; 2 — an eleven-month-old boy; 3 — a one-year-and-four-month-old boy; 4 — a three-year-old boy; 5 — a five-year-old boy. Emerging ossification centers are shown in black

The ossification center in the distal epiphysis of the radius appears at one and a half years of age, the epiphyseal ossification centers of the metacarpals and phalanges at 2–3 years, and the distal epiphyseal center of the ulna only at 8 years. Fusion of the epiphyses with the diaphyses (synostosis) in the metacarpals and phalanges occurs at 15–19 years of age, with the first metacarpal bone fusing earlier than the others. The distal epiphyses of the forearm bones fuse at 20 years of age.

In the foot (Fig. 1.36), ossification centers appear in the following order: in the talus and calcaneus—at the 6th–7th month of fetal development; in the cuboid—just before birth; in the third cuneiform bone—In the second half of the first year, in the first cuneiform bone—at 1.5–2 years, in the second cuneiform—at 2–3 years of age; in the navicular—at 3–5 years. The distal epiphyses of both bones of the lower leg appear between 1 and 2 years of age. Ossification of the epiphyses of the metatarsals and phalanges begins at 2–3 years of age. Fusion of the epiphyses with the diaphyses in the metatarsals and phalanges occurs at 15–19 years, and the distal epiphyses of the lower leg bones fuse at an average of 18 years.

The described data on the developmental Anatomy of the skeleton, which are easily established radiographically, are of practical importance. Since the skeletal system develops as part of the Organism as a whole, its condition can provide an objective Assessment of the overall physical development of children and adolescents. Furthermore, based on the changes occurring in the skeleton of the hand and foot, a specialist can estimate the approximate biological age of the subject, ranging from 1 year to nearly 20 years, which is particularly important when official records are unavailable.