Elbow joint

The elbow joint (art. cubiti) is formed by three bones: humerus, radius and ulna. The bones form three joints enclosed in a common joint capsule.

1. The humeroulnaris joint (art. humeroulnaris) is block-shaped, formed by the connection of the block of the humerus and the block-shaped notch of the ulna.
2. The humeroradialis joint is a spherical joint that is the articulation of the head of the humerus and the glenoid cavity of the radius.
3. The proximal radioulnar joint (art. radioulnaris proximalis) is cylindrical in shape, formed by the articular circumference of the radius and the radial notch of the ulna. The general joint capsule is free. On the humerus, the joint capsule is attached relatively high above the articular cartilage of the trochlea of the humerus, therefore the coronoid and radial fossae and the fossa of the olecranon are located in the joint cavity. The lateral and medial epicondyles of the humerus are located outside the joint cavity. On the ulna, the joint capsule is attached below the edge of the articular cartilage of the coronoid process and at the edge of the trochlear notch of the olecranon. On the radius, the capsule is attached to its neck.

The joint capsule is strengthened by ligaments.

The ulnar collateral ligament (lig. collaterale ulnare) originates below the edge of the medial epicondyle of the humerus, fan-shaped, and is attached along the entire medial edge of the block-shaped notch of the ulna.

The radial collateral ligament (lig. collaterale radiale), starting at the lower edge of the lateral epicondyle of the humerus, is divided into two bundles. The anterior bundle embraces the neck of the radius from the front and is attached to the anterolateral edge of the trochlear notch of the ulna. The posterior bundle of this ligament embraces the neck of the radius from behind and is woven into the annular ligament of the radius.

The annular ligament of the radius (lig. annulare radii) begins at the anterior edge of the radial notch of the ulna, loops around the neck of the radius, and attaches at the posterior edge of the radial notch. The square ligament (lig. quadratum) is located between the distal edge of the radial notch of the ulna and the neck of the radius.

The elbow joint can move around the frontal axis - flexion and extension of the forearm with a total volume of up to 170°. When flexed, the forearm deviates slightly medially and the hand rests not on the shoulder, but on the chest. This is due to the presence of a notch on the block of the humerus, which facilitates a screw-like displacement of the forearm and hand. Around the longitudinal axis of the radius in the proximal radioulnar joint, the radius rotates together with the hand. This movement occurs simultaneously in both the proximal and distal radioulnar joints.

In the lateral projection of the elbow joint (the forearm is flexed at 90°), the line of the X-ray joint space is limited by the block-shaped notch of the ulna and the head of the radius on one side and the condyle of the humerus on the other. In the direct projection, the X-ray joint space is zigzag-shaped and has a thickness of 2-3 mm. The joint space of the proximal radioulnar joint is also visible.

The bones of the forearm are connected by means of discontinuous and continuous connections. The continuous connection is the interosseous membrane of the forearm (membrana interossea antebrachii). It is a strong connective tissue membrane stretched between the interosseous edges of the radius and ulna. Below the proximal radioulnar joint, a fibrous cord is visible between both bones of the forearm - the oblique chord (chorda obliqua).

Discontinuous joints include the proximal radioulnar joint and the distal radioulnar joint, as well as the joints of the hand.

The distal radioulnar joint (art. radioulnaris distalis) is formed by the junction of the articular circumference of the ulna and the ulnar notch of the radius. This joint is separated from the radiocarpal joint by the articular disc (discus articularis), located between the ulnar notch of the radius and the styloid process of the ulna. The joint capsule of the distal radioulnar joint is free, attached along the edge of the articular surfaces and the articular disc. The capsule usually protrudes proximally between the bones of the forearm, forming a saccular depression (recessus sacciformis).

The proximal and distal radioulnar joints together functionally form a combined cylindrical joint with a longitudinal axis of rotation (along the forearm). In these joints, the radius, together with the hand, rotates around the ulna. In this case, the proximal epiphysis of the radius rotates in place, since the head of the radius is held in place by the annular ligament of the radius. The distal epiphysis of the radius describes an arc around the head of the radius, which remains motionless. The average range of rotation in the radioulnar joints (supination and pronation) is approximately 140°.

Movement of the forearm at the elbow joint. The range of motion (flexion - extension) around the frontal axis is 150°. Rotation of the radius together with the hand around the longitudinal axis of the forearm (pronation and supination) is 90-150°. The following muscles perform movements at the elbow joint.

Flex the forearm: brachialis, biceps brachii, pronator teres.

Extend the forearm: triceps brachii, antecubital muscle.

Turn the forearm inward (pronation): muscle - pronator teres, pronator quadratus.

Rotate the forearm outward (supination): supinator muscle, biceps brachii.

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