Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Bone Articulations
Articulations of the Bones of the Upper Extremity

Connections of the BONES OF THE Pectoral Girdle. They can be divided into three groups.

1. Interarticular connections of the girdle bones. The acromioclavicular joint, articulatio acromioclavicularis, is formed between the acromion and the clavicle. The Joint Capsule is tight and reinforced by the acromioclavicular ligament. Additionally, the joint is stabilized by the coracoclavicular ligament. This joint is virtually immobile.

2. Proper ligaments of the scapula are represented by the coracoacromial and superior transverse scapular ligaments. The coracoacromial ligament extends from the apex of the acromion to the coracoid process. It forms the "coracoacromial arch," which protects the shoulder joint from above and limits the Movements of the humerus in this direction. The superior transverse scapular ligament spans across the scapular notch.

3. Connections between the girdle bones and the Axial Skeleton. The sternoclavicular joint, articulatio sternoclavicularis, is located between the clavicle and the manubrium of the Sternum. It is formed by the sternal end of the clavicle and the clavicular notch of the manubrium (Fig. 5.5). The articular surfaces are covered with fibrocartilage and are saddle-shaped. An articular disc is located within the joint cavity. Movements of the clavicle upward and downward occur around the sagittal axis, while forward and backward movements occur around the vertical axis. Circumduction is possible around both of these axes. The joint capsule is reinforced by bundles of the anterior and posterior sternoclavicular ligaments, as well as the interclavicular and costoclavicular ligaments.

The scapula is connected to the thoracic wall via Muscles. This type of connection is called a synsarcosis.

Connections of the free upper limb. This group includes the connections between the bones of the free upper limb and the pectoral girdle (the shoulder joint), as well as the intrinsic connections within the free upper limb itself.

The shoulder joint, articulatio humeri, is formed by the HEAD of the humerus and the glenoid cavity of the scapula. The glenoid cavity is deepened by the glenoid labrum (Fig. 5.6).

The joint capsule attaches to the scapula along the margin of the glenoid labrum and to the humerus along the anatomical neck, leaving both tubercles outside the joint cavity. The capsule of the shoulder joint is reinforced by the coracohumeral and glenohumeral ligaments. The coracohumeral ligament originates from the coracoid process and blends into the superior and posterior aspects of the capsule. The glenohumeral ligaments are located within the thickness of the joint capsule.

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Fig. 5.5. Sternoclavicular joint:

1 — articular disc; 2 — interclavicular ligament; 3 — anterior sternoclavicular ligament; 4 — clavicle; 5 — 1st rib; 6 — costoclavicular ligament; 7 — sternum

In shape, the shoulder joint is a typical ball-and-socket (spheroidal), multiaxial joint. It is the most mobile of all synovial joints. Movements in the shoulder joint occur in all directions: flexion and extension around the frontal axis; abduction and adduction around the sagittal axis; medial and lateral Rotation of the arm around the vertical axis; and circumduction when transitioning from one axis to another. The tendon of the long head of the biceps brachii Muscle passes through the joint cavity.

The elbow joint, articulatio cubiti, is formed by three bones: the humerus, ulna, and radius. Three simple joints are formed between them: the humeroulnar, humeroradial, and proximal radioulnar joints (Fig. 5.7). All three articulations share a common capsule and a single joint cavity, which is why they are combined into a single (compound) joint. The articular surfaces are covered with hyaline Cartilage.

Fig. 5.6. Shoulder joint:

1 — tendon of the biceps brachii muscle; 2 — head of the humerus; 3 — glenoid cavity of the scapula; 4 — glenoid labrum; 5 — axillary bursa

The humeroulnar joint, articulatio humeroulnaris, is formed by the trochlea of the humerus and the trochlear notch of the ulna. In shape, the joint is spiral, or cochlear, and uniaxial.

The humeroradial joint, articulatio humeroradialis, is formed by the capitulum of the humerus and the articular fossa of the radial head. In shape, the joint is ball-and-socket.

The proximal radioulnar joint, articulatio radioulnaris proximalis, is formed by the Articulation of the head of the radius with the radial notch of the ulna. In shape, the joint is cylindrical.

All three joints are enclosed within a single common joint capsule that covers the olecranon, radial, and coronoid fossae of the humerus while leaving the epicondyles free. On the sides, the joint capsule is reinforced by strong radial and ulnar collateral ligaments. The head of the radius is encircled by the annular ligament.

Flexion and extension of the forearm occur around the frontal axis in the humeroulnar and humeroradial joints. The former Functions as a spiral joint (a variation of a hinge joint). Because the axis of the humeral trochlea runs obliquely relative to the long axis of the arm, during flexion the distal forearm deviates slightly in a medial direction—meaning the hand moves toward the chest rather than the shoulder joint. This is a functionally advantageous position for the upper limb, which must be maintained when providing first aid for fractures of the upper extremity bones.

Fig. 5.7. Elbow joint:

1 — humerus; 2 — proximal radioulnar joint; 3 — ulnar collateral ligament; 4 — humeroulnar joint; 5 — ulna; 6 — interosseous membrane of the forearm; 7 — radius; 8 — tendon of the biceps brachii muscle; 9 — annular ligament of the radius; 10 — radial collateral ligament; 11 — humeroradial joint.

The humeroradial joint is spheroidal in shape, but the actual movements occurring within it take place around the frontal axis (flexion and extension) and the vertical axis (medial and lateral rotation, i.e., pronation and supination). Rotation occurs simultaneously in the proximal radioulnar (cylindrical) joint as well. Lateral movements in the humeroradial joint are absent due to the presence of the interosseous membrane.

Connections of the forearm bones. The epiphyses of the ulna and radius are connected to each other by the proximal and distal radioulnar joints (Fig. 5.8). The interosseous membrane of the forearm (syndesmosis) spans almost the entire length between these bones. It connects both bones of the forearm without hindering movements in the aforementioned joints.

As already noted, the proximal radioulnar joint is part of the elbow joint. The distal radioulnar joint is an independent pivot joint: its articular fossa is located on the radius, while the head is on the ulna.

The proximal and distal radioulnar joints function together, forming a combined pivot joint. Movement around the vertical axis is performed by the radius together with the hand. Meanwhile, the ulna remains stationary.

Fig. 5.8. Connections of the forearm bones:

1 — proximal radioulnar joint; 2 — trochlear notch of the ulna; 3 — oblique cord; 4 — ulna; 5 — distal radioulnar joint; 6 — articular disc (triangular fibrocartilage); 7 — carpal articular surface; 8 — radius; 9 — interosseous membrane of the forearm; 10 — tendon of the biceps brachii muscle; 11 — annular ligament of the radius

Fig. 5.9. Connections of the bones of the hand:

1 — radius; 2 — interosseous membrane of the forearm; 3 — ulna; 4 — distal radioulnar joint; 5 — articular disc; 6 — midcarpal joint; 7 — carpometacarpal joints; 8 — metacarpophalangeal joint; 9 — interphalangeal joints; 10 — metacarpophalangeal joint of the thumb; 11 — radiocarpal joint

The radiocarpal joint, articulatio radiocarpalis, is formed by: the carpal articular surface of the radius, supplemented medially by the articular (triangular) disc, and the articular surfaces of the proximal row of Carpal Bones, excluding the pisiform bone (Fig. 5.9). These carpal bones are firmly connected to each other by interosseous ligaments, thus forming a single articular surface. The triangular articular disc fuses with the radius and separates the head of the ulna from the carpal bones; therefore, the ulna does not participate in The formation of the radiocarpal joint.

The joint is ellipsoidal in shape. Flexion and extension occur around the frontal axis, abduction and adduction occur around the sagittal axis, and circumduction (conical movement) occurs during the transition from one axis to another.

The joint capsule is reinforced on both sides by the radial and ulnar collateral ligaments of the carpus, respectively. On the PALMAR AND DORSAL surfaces of the joint are the palmar and dorsal radiocarpal ligaments.

Connections of the bones of the hand. According to the Classification of the bones of the hand, the following main joints are distinguished: between the bones of the proximal and distal rows of the carpus — the midcarpal joint; between individual bones of the proximal and distal rows of the carpus — the intercarpal joints; between the bones of the distal carpal row and the Metacarpal bones — the carpometacarpal joints; between the metacarpal bones and the proximal Phalanges — the metacarpophalangeal joints; between the proximal and middle, and the middle and distal phalanges — the interphalangeal joints.

The midcarpal joint, articulatio mediocarpalis, is located between the proximal (except for the pisiform) and distal rows of the carpal bones. The articulating surfaces of this joint form an S-shaped articular cleft and are reinforced by strong ligaments, making it a slightly movable joint.

The intercarpal joints, articulationes intercarpales, are situated between individual bones of the proximal or distal rows of the carpus. They are formed by the flat, mutually opposed surfaces of the articulating bones. Interosseous ligaments firmly bind the bones of the distal carpal row to each other, so that no movement occurs between them. The pisiform bone forms its own connection (joint) with the triquetral bone.

It should be noted that the radiocarpal and midcarpal joints functionally constitute a single combined joint — the wrist joint, articulatio manus. The proximal row of carpal bones acts as a bony disc in this joint.

The carpometacarpal joints, articulationes carpometacarpales, are connections between the bones of the distal carpal row and the bases of the metacarpal bones. Here, the thumb joint is isolated, while the others share a common joint cavity and capsule, which is reinforced by the dorsal and palmar carpometacarpal ligaments. They are flat and have limited mobility. All four bones of the distal carpal row and metacarpals II–V are very firmly interconnected, forming a solid mechanical foundation for the hand.

The Formation of the carpometacarpal joint of the first digit involves the trapezium and the first metacarpal bone, which have a saddle shape. Movements in it occur around two axes. Flexion and extension of the thumb together with its metacarpal bone take place around the frontal axis; during flexion, the thumb moves toward the palm, opposing the other digits (opposition), and returns to its initial position. Abduction and adduction of the thumb toward the index finger occur around the sagittal axis. As a result of the combination of movements around these two axes, circumduction is possible in the joint.

Numerous ligaments are present on the palmar and dorsal surfaces of the hand, connecting the carpal bones to one another, as well as the carpal bones to the bases of the metacarpal bones. They are particularly well developed on the palmar surface, forming a strong radiate ligament of the carpus.

Connections of the bones of the digits. The metacarpophalangeal joints, articulationes metacarpophalangeae, are formed by the heads of the metacarpal bones and the fossae at the bases of the proximal phalanges. Collateral ligaments are located on the sides of these joints. Stronger palmar ligaments are situated on the palmar surface. The deep transverse metacarpal ligament connects the heads of metacarpals II–V, preventing them from spreading apart and thereby reinforcing the rigid foundation of the hand.

In shape, metacarpophalangeal joints II–IV are condyloid (spherical). Flexion and extension occur around the frontal axis, abduction of the fingers occurs around the sagittal axis, and circumduction is also possible. Movements around the vertical axis do not occur in these joints due to the absence of rotatory muscles.

The metacarpophalangeal joint of the thumb is hinge-like (ginglymus) in shape. Two sesamoid bones (lateral and medial) are embedded in the palmar part of the joint capsule. Flexion and extension around the frontal axis take place within it.

The interphalangeal joints, articulationes interphalangeae, are located between the proximal and middle, and the middle and distal phalanges of digits II–V, as well as between the proximal and distal phalanges of digit I. The capsule is reinforced by palmar and lateral (collateral) ligaments, which preclude lateral movements. The joints are hinge-like in shape. Movements in them are performed exclusively around the frontal axis: flexion and extension of the phalanges.