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

Musculoskeletal system
Skeleton of the limbs
Bones of the upper extremities and their joints

The Functions of the upper and lower human limbs differ significantly. The upper limbs serve as Organs of labor; they are highly mobile and capable of performing A wide variety of extremely precise movements. The lower limbs function primarily for support and locomotion. Their Bones and joints are more robust, and their mobility is limited compared to that of the upper limbs.

The Skeleton of both the upper and lower limbs constitutes a system of levers sharing a similar structural plan. The limbs consist of a girdle and a free part. The BONES OF THE girdle articulate with the Axial Skeleton. The Free part of each limb (upper and lower) comprises three segments: the proximal (upper) segment consists of a single bone, the middle segment contains two bones, and the distal (lower) segment is composed of multiple bones.

The Skeleton of the upper limbs consists of the Pectoral Girdle (shoulder girdle) and the free upper limbs (Fig. 26). The pectoral girdle on each side comprises two bones: the clavicle and the scapula.

Only the clavicle articulates directly with the axial skeleton. The scapula is effectively interposed between the clavicle and the free part of the upper limb.

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Fig. 26. Bones of the upper limb.

Anterior view:

1 — clavicle; 2 — sternal end; 3 — scapula; 4 — coracoid process of the scapula; 5 — glenoid cavity of the scapula; 6 — humerus; 7 — coronoid fossa of the humerus; 8 — medial epicondyle of the humerus; 9 — trochlea of the humerus; 10 — coronoid process; 11 — ulnar tuberosity; 12 — ulna; 13 — HEAD of the ulna; 14 — Carpal Bones; 15 — 1st–5th Metacarpal bones; 16 — Phalanges of the fingers; 17 — styloid process of the radius; 18 — radius; 19 — head of the radius; 20 — crest of the greater tubercle; 21 — intertubercular sulcus; 22 — greater tubercle; 23 — lesser tubercle; 24 — head of the humerus; 25 — acromion

Bones of the pectoral girdle. The pectoral girdle comprises the paired scapulae and clavicles, which are connected by joints.

The clavicle is a paired, curved long bone possessing a shaft and two ends: the sternal and acromial ends.

The clavicle is easily palpable in the living human body. Its functional role is vital, as it holds the shoulder joint away from The thoracic cage, thereby ensuring a wide range of arm movements.

The scapula is a flat, triangular bone applied to the posterior thoracic wall at the level of the II to V Ribs. Its dorsal surface is divided by a transversely oriented ridge—the spine of the scapula—into two fossae: the supraspinous and infraspinous fossae. Laterally, the scapular spine extends into the acromion, which features an articular surface for articulation with the clavicle. Three angles are distinguished on the scapula: the inferior, lateral, and superior angles. The superior border of the scapula transitions laterally and anteriorly into the coracoid process. The thickened lateral angle of the scapula bears the glenoid cavity, which articulates with the head of the humerus.

The skeleton of the free upper limb consists of the humerus, the bones of the forearm (the ulna and radius), and the hand (carpal bones, metacarpal bones, and phalanges).

The humerus is a long bone possessing a shaft and two extremities: the proximal and distal epiphyses. The proximal epiphysis is enlarged and forms a spherical head that articulates with the glenoid cavity of the scapula. Just below the head lie two tubercles (the greater and lesser tubercles), which serve as sites for Muscle attachment. A longitudinal groove separates these tubercles and lodges the long tendon of the biceps brachii muscle. The bone is relatively slender at the junction between the proximal epiphysis and the shaft. Due to its frequent involvement in traumatic injuries, this region is designated as the surgical neck of the humerus. The distal epiphysis is expanded and terminates in a condyle for articulation with the ulna and radius within the elbow joint. Flanking the condyle are the lateral and medial epicondyles, which are readily palpable in the region of the elbow joint.

The bones of the forearm are classified as long bones. There are two of them: the ulna lies medially (closer to the midline of the body), while the radius is situated alongside the ulna on the lateral side of the forearm. The proximal ends of the ulna and radius participate in The formation of the elbow joint, whereas their distal ends contribute to the radiocarpal joint together with the proximal row of carpal bones. The proximal epiphysis of the ulna is enlarged and features two processes—the olecranon (posteriorly) and the coronoid process (anteriorly)—separated by the trochlear notch. The lateral aspects of the upper and lower epiphyses bear articular facets for articulation with the adjacent radius.

On the medial side of its proximal and distal epiphyses, the radius features corresponding articular facets for articulation with the ulna. The expanded distal end of the radius bears an articular surface that forms a joint with the proximal row of carpal bones.

The bones of the hand comprise the carpal bones, metacarpal bones, and the bones (phalanges) of the digits.

The carpus consists of 8 spongy (short) bones arranged in two rows of four bones each, featuring articular surfaces for articulation with neighboring bones. The metacarpus contains five short tubular metacarpal bones, each exhibiting a base, a shaft, and a head. The bases of the metacarpal bones bear articular surfaces for articulation with the distal row of carpal bones, while their heads articulate with the bases of the proximal phalanges. The digital bones are short tubular bones (phalanges) arranged sequentially. Four of the digits possess three phalanges each: proximal, middle, and distal (terminal). The sole exception is the thumb, which features only two phalanges (proximal and distal).

The JOINTS OF THE upper limb are structured to permit diverse movements with a wide range of motion. The hand is particularly mobile, capable of powerful and dexterous grasping. The sternoclavicular joint is the sole articulation connecting the pectoral girdle (clavicle and scapula) and the entire upper limb to the axial skeleton. This joint allows elevation and depression of the clavicle around the sagittal axis, and consequently of the scapula and the entire upper limb. Anterior and posterior Movements of the clavicle occur around a vertical axis, while circumduction takes place around an axis passing longitudinally through the clavicle. The sternoclavicular joint is formed by the Articulation of the clavicle with the Sternum. It is saddle-shaped in Morphology and multiaxial in function. An intra-articular cartilaginous disc situated within the joint cavity smooths out irregularities between the articular surfaces. The joint is reinforced by strong ligaments connecting the clavicle to the sternum and the first rib. Laterally, the clavicle articulates with the scapula to form the acromioclavicular joint. This joint is plane in shape and has limited mobility, with its movements restricted by taut, robust ligaments.

The shoulder joint connects the free upper limb (arm) to the pectoral girdle. It is formed by the head of the humerus and the glenoid cavity of the scapula. The articular surface of the humeral head is spherical in shape, permitting a wide range of movements. The articular capsule is thin and lax, reinforced by only a single ligament, which is one of the factors predisposing this joint to dislocations. The tendon of the long head of the biceps brachii, enclosed in a synovial membrane, passes directly through the cavity of the shoulder joint.

The elbow joint is a composite articulation consisting of three distinct joints: the humeroulnar, humeroradial, and proximal radioulnar joints. The humeroulnar joint is formed by the articulation of the humerus with the trochlear notch of the ulna. It is a hinge (ginglymus) joint with a single axis of rotation, permitting flexion and extension of the forearm. The humeroradial joint is formed by the spherical head of the distal epiphysis of the humerus and the articular fovea of the radial head. It is spheroidal in Structure.

The proximal radioulnar joint is formed by the radial notch of the ulna and the articular circumference of the radius. It is a pivot (trochoid) joint with a longitudinal axis of rotation (along the axis of the forearm). All three component joints of the elbow are enclosed within a common articular capsule, which is reinforced by ligaments that hold the articulating bones in close apposition and stabilize the joint. This complex permits movements around both the frontal axis (flexion and extension of the forearm) and the longitudinal axis (pronation and supination of the forearm and hand).

Rotation in the proximal radioulnar joint occurs synchronously with the corresponding movement in the distal radioulnar joint, which is formed by the ulnar notch of the radius and the articular surface of the ulnar head. This joint is likewise cylindrical in shape. Together with the proximal radioulnar joint, it constitutes a combined articulation sharing a common longitudinal axis of rotation along the forearm.

A strong interosseous membrane spans the space between the radius and ulna, binding these bones together and serving as an origin site for numerous forearm and hand Muscles.

The radiocarpal joint, which connects the forearm to the hand, is formed by the articular surface of the radius, the articular disc near the ulnar head, and the proximal row of carpal bones. Structurally, it is a complex, compound joint; functionally, it is ellipsoid in shape and biaxial. It is reinforced by collateral and other ligaments. This joint permits flexion and extension around the frontal axis, as well as abduction and adduction of the hand around the sagittal axis.

Between the first (proximal) and second (distal) rows of the carpal bones lies the hinge-like, slightly movable midcarpal joint. It has a complex structure. The joint is reinforced by several short dorsal and palmar ligaments, and its joint cavity communicates with the cavities of the intercarpal joints formed by the articular surfaces of adjacent carpal bones.

The carpometacarpal joints are formed by the articular surfaces of the bases of the metacarpal bones and the bones of the second distal row of the carpus. The carpometacarpal joint of the first digit (thumb) differs from the other four joints in that it is isolated from them, and its articular surfaces are saddle-shaped. The shape of the articular surfaces and the loose Joint Capsule allow for movement around two axes. As a result, the thumb can be opposed to the little finger, which is essential for grasping objects.

The metacarpophalangeal joints are formed by the heads of the metacarpal bones and the bases of the first (proximal) phalanges. They are ellipsoidal in shape, allowing the fingers to move around two axes: frontal (flexion-extension) and sagittal (abduction-adduction).

The interphalangeal joints are typical hinge joints that allow for only one type of movement — flexion or extension.

Review and Self-Assessment Questions:

1. Name the bones of the upper extremity and describe their structural features.

2. Which bone is located between the sternum and the scapula, and what is its function?

3. What Classification of bone shape do the carpal bones belong to? How are they arranged relative to one another?

4. How is the sternoclavicular joint classified in terms of its shape and structure?

5. Describe the Structure and function of the shoulder joint.

6. Describe the Structural Features of the elbow joint. What movements are possible in this joint?

7. Which anatomical structures form the radiocarpal joint? What is the shape of this joint, and what movements does it perform?

8. State the Anatomical Features of the carpometacarpal joint of the first digit (thumb).