Human Anatomy and Physiology (with Age-Related Features of the Child's Body) - Sapin, M. R., & Sivoglazov, V. I. 2002

Musculoskeletal System
The Study of Bones and Their Joints (Osteoarthrology)
Skeleton of the Limbs

The Functions of the upper and lower limbs in humans differ. The upper limbs serve as Organs of labor; they are highly mobile and capable of performing A wide variety of very precise movements. The lower limbs serve for support and locomotion. Their Bones and joints are more massive, and their mobility is limited compared to the upper limbs.

The Skeleton of the limbs—both upper and lower—is a system of levers with a similar structural plan. The limbs consist of a girdle and a free part. The BONES OF THE girdle connect to the Axial Skeleton. The Free part of the limbs (upper and lower) consists of three segments: the proximal (upper) is represented by a single bone, the middle by two bones, and the distal (lower) consists of multiple bones.

Bones of the upper limbs and their connections

The skeleton of the upper limbs consists of the Pectoral Girdle (shoulder girdle) and the free upper limbs (Fig. 22). The pectoral girdle has two bones on each side—the clavicle and the scapula. Only the clavicle connects to the axial skeleton via a joint. The scapula is, as it were, inserted between the clavicle and the free upper limb.

Bones of the pectoral girdle. The pectoral girdle is composed of the paired scapula and clavicle joined together by joints. The clavicle is a paired, curved tubular bone featuring a body and two ends: the sternal and acromial ends.

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Fig. 22. 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 — Metacarpal bones 1–5, 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

The clavicle is easily palpable in a living person. Its functional role is very important: it holds the shoulder joint away from The thoracic cage, ensuring freedom of arm movement.

The scapula is a flat, triangular bone that lies against the posterior surface of the thoracic cage with its costal surface. The dorsal surface is divided by the spine of the scapula into two fossae: the supraspinous and infraspinous fossae. The spine laterally continues into the acromion, which bears an articular surface for articulation with the clavicle. The scapula has three borders—medial, lateral, and superior—and three angles—inferior, lateral, and superior. The superior border transitions into the coracoid process, and the thickened lateral angle terminates in the glenoid cavity, which forms a joint with the head of the humerus.

JOINTS OF THE pectoral girdle. The sternoclavicular joint is formed by the sternal end of the clavicle and the clavicular notch of the manubrium of the Sternum. An intra-articular disc lies between the saddle-shaped articular surfaces, fusing peripherally with the Joint Capsule, which is reinforced by several ligaments. Due to the intra-articular disc, the sternoclavicular joint is triaxial, with its range of motion limited by ligaments. Movements forward and backward, elevation and depression, as well as slight rotation can occur in this joint. In addition, circumduction is possible in this joint. During circumduction, the acromial end of the clavicle, and with it the scapula, describes an ellipse.

The acromioclavicular joint is flat and slightly movable, connecting the clavicle to the scapula. This joint is reinforced by the coracoclavicular and costoclavicular ligaments. The strong extra-articular coracoacromial ligament acts as the arch of the shoulder joint, limiting the abduction of the upper limb (arm) to the side.

Bones of the free upper limb. The bones of the free upper limb include the humerus, two forearm bones, and the hand bones, which comprise the carpal bones, metacarpal bones, and phalanges of the fingers.

The humerus is a long tubular bone consisting of a body and two extremities (epiphyses). The upper epiphysis features a spherical head that articulates with the scapula. The anatomical neck separates the head from the body of the bone. Below the anatomical neck lie the greater tubercle (laterally) and the lesser tubercle (medially), separated by a sulcus, where Muscles attach. Below the tubercles is the surgical neck, where bone fractures occur more frequently than in other areas. The lower, thickened end of the humerus bears a condyle with articular surfaces for articulation with the forearm bones. On the sides of the condyle are the medial and lateral epicondyles. Above the condyle are two fossae: the coronoid fossa anteriorly and the olecranon fossa posteriorly.

The forearm bones are represented by two bones. The ulna is located medially, and the radius is located laterally. Between the bones is the interosseous space of the forearm, closed by a Connective Tissue interosseous membrane.

The ulna is a long tubular bone. Its upper epiphysis is massive and features two processes—the olecranon process (posteriorly) and the coronoid process (anteriorly)—separated by the trochlear notch, which articulates with the trochlea of the humerus. On the lateral surface of the coronoid process is the radial notch, forming a joint with the articular circumference of the head of the radius. On the lower epiphysis of the ulna (its head) are the articular circumference for articulation with the ulnar notch of the radius and the medially located styloid process.

The radius is also a long tubular bone. Its upper epiphysis (head) features an articular fovea for articulation with the capitulum of the humerus and an articular circumference for articulation with the radial notch of the ulna. The distal epiphysis bears an articular surface for articulation with the upper (proximal) row of carpal bones and a laterally located styloid process. On the medial margin of the distal epiphysis is the ulnar notch for articulation with the ulna.

The hand is divided into three sections: the carpus, metacarpus, and digits. The carpal bones (8 bones) are arranged in two rows of four bones each. The proximal row contains (starting from the thumb) the scaphoid, lunate, triquetrum, and pisiform. The distal row is formed by the trapezium (greater multangular), trapezoid, capitate, and hamate bones. The carpal bones form a bony arch, convex dorsally and concave toward the palm. The transverse ligament stretched over the concavity turns the sulcus into the carpal tunnel, through which Muscle tendons, Blood Vessels, and nerves pass to the hand.

The metacarpal bones are five short tubular bones featuring a base, body, and head.

The skeleton of the fingers is formed by phalanges, of which digits II–V have three each (proximal, middle, and distal/terminal), and the thumb has two (proximal and distal). Phalanges are short tubular bones that comprise a base, body, and head.

Joints of the free upper limb. The bones of the free upper limb form the Shoulder and Elbow joints, as well as numerous joints of the hand.

The shoulder joint is formed by the spherical head of the humerus and the thickened glenoid cavity of the scapula, which is supplemented peripherally by a fibrocartilaginous glenoid labrum. The joint capsule is thin and loose, reinforced only by the coracohumeral ligament. The tendon of the long head of the biceps brachii, enclosed in a synovial sheath, passes through the joint cavity.

According to the shape of its articular surfaces, the shoulder joint is a typical ball-and-socket joint. Movements in the joint occur around three axes: frontal (flexion—extension), sagittal (adduction—abduction), and vertical (internal and external rotation). Circumduction is also possible in the shoulder joint.

The elbow joint is formed by three bones: the humerus, ulna, and radius. This results in a complex joint comprising the humeroulnar, humeroradial, and proximal radioulnar joints. These three joints share a single joint capsule, reinforced by collateral ligaments, and a single joint cavity. The elbow joint is classified as a hinge joint, allowing flexion and extension. However, its proximal radioulnar joint (together with the distal radioulnar joint) performs rotational movements around the longitudinal axis of the forearm.

Joints of the forearm bones. The forearm bones are connected to each other by two radioulnar joints and the interosseous membrane stretched between the radius and the ulna. The proximal radioulnar joint is incorporated into the elbow joint, whereas the distal radioulnar joint is independent. Both radioulnar joints are cylindrical in shape and form a single combined joint with a longitudinal (vertical) axis of rotation passing through the heads of the radius and ulna. During movements in these joints (pronation and supination), the ulna remains stationary, while the radius rotates around it.

The wrist joint and joints of the hand bones. The wrist joint is a compound joint formed by the carpal articular surface of the radius and the bones of the first (proximal) row of carpal bones: the scaphoid, lunate, and triquetrum. The joint capsule is reinforced by collateral, dorsal, and palmar ligaments. Based on the shape of its articular surfaces, the wrist joint is ellipsoidal with two axes of movement. Flexion and extension occur around the transverse (frontal) axis, while abduction and adduction of the hand take place around the sagittal axis. Minor rotational movements are also possible.

The midcarpal joint is located between the bones of the First and Second rows, and intercarpal joints are found between individual carpal bones. The distal row of carpal bones forms flat carpometacarpal joints, which, together with the midcarpal and intercarpal joints, form a rigid foundation for the hand.

The carpometacarpal joint of the first digit (thumb) has a unique Structure. The articular surfaces that form it (the trapezium and the first metacarpal bone) are saddle-shaped; this joint allows for adduction, abduction, and opposition of the thumb to the little finger and other digits of the hand. The metacarpophalangeal joints are spheroidal in shape, whereas the interphalangeal joints are hinge-like. All these joints are reinforced by robust collateral and palmar ligaments, enabling the hand and its fingers to perform precise, highly differentiated movements.

Review and Self-Assessment Questions:

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

2. Which bones articulate with the clavicle and scapula, and what joints do they form?

3. What distinctive Structural and functional features characterize the shoulder and elbow joints?

4. What TYPES OF JOINTS (in terms of Structure and function) connect the forearm bones to each other and to the other bones of the upper limb?

5. List and name the carpal bones. With which other bones do they form joints?

6. How does the carpometacarpal joint of the first digit (thumb) differ in structure and function?