The elbow joint, a hinge type of synovial joint, is located 3 cm inferior to the epicondyles of the humerus

The spool-shaped trochlea and spheroidal capitulum of the humerus articulate with the trochlear notch of the ulna and the slightly concave superior aspect of the head of the radius

humeroulnar and humeroradial articulations

The fibrous layer of the joint capsule surrounds the elbow joint

It is attached to the humerus at the margins of the lateral and medial ends of the articular surfaces of the capitulum and trochlea.

Anteriorly and posteriorly it is carried superiorly, proximal to the coronoid and olecranon fossae. 

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The collateral ligaments of the elbow joint are strong triangular bands that are medial and lateral thickenings of the fibrous layer of the joint capsule

The lateral, fan-like radial collateral ligament extends from the lateral epicondyle of the humerus

which encircles and holds the head of the radius in the radial notch of the ulna. Forming the proximal radioulnar joint and permitting pronation and supination of the forearm.

The medial, triangular ulnar collateral ligament extends from the medial epicondyle of the humerus to the coronoid process and olecranon of the ulna and consists of three bands:

(1) the anterior cord-like is strongest  bandposterior fan-like band is the weakest, and (3) the slender oblique band deepens the socket for the trochlea of the humerus.

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 However, the chief flexors of the elbow joint are the brachialis and biceps brachii 

the brachioradialis and pronator teres assist the chief flexors in producing slower flexion.

he chief extensor of the elbow joint is the triceps brachii, especially the medial head, weakly assisted by the anconeus.

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The three olecranon bursae are

The subcutaneous olecranon bursa is exposed to injury during falls on the elbow and to infection from abrasions of the skin covering the olecranon.

Repeated excessive pressure and friction, as occurs in wrestling, for example, may cause this bursa to become inflamed, producing a friction subcutaneous olecranon bursitis

 Subtendinous olecranon bursitis is much less common. It results from excessive friction between the triceps tendon and olecranon, for example, resulting from repeated flexion/extension of the forearm as occurs during certain assembly-line jobs.

Avulsion of the medial epicondyle in children can result from a fall that causes severe abduction of the extended elbow, an abnormal movement of this articulation.

The resulting traction on the ulnar collateral ligament pulls the medial epicondyle distally

Traction injury of the ulnar nerve is a frequent complication of the abduction type of avulsion of the medial epicondyle.

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Posterior dislocation of the elbow joint may occur when children fall on their hands with their elbows flexed.

Dislocations of the elbow may result from hyperextension or a blow that drives the ulna posterior or posterolateral due to posterior ulnar band being weak

The ulnar collateral ligament is often torn, and an associated fracture of the head of the radius, coronoid process, or olecranon process of the ulna may occur

Injury to the ulnar nerve may occur, resulting in numbness of the little finger and weakness of flexion and adduction of the wrist.

The head of the radius articulates with the radial notch of the ulna. The radial head is held in position by the anular ligament of the radius

The fibrous layer of the joint capsule encloses the joint and is continuous with that of the elbow joint.

The synovial membrane lines the deep surface of the fibrous layer and non-articulating aspects of the bones.

The strong anular ligament, attached to the ulna anterior and posterior to its radial notch, surrounds the articulating bony surfaces and forms a collar that, with the radial notch, creates a ring that completely encircles the head of the radius 

This arrangement allows the radius to rotate within the anular ligament without binding, stretching, or tearing the synovial membrane

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Supination is produced by the supinator (when resistance is absent) and biceps brachii (when power is required because of resistance)

Pronation is produced by the pronator quadratus (primarily) and pronator teres (secondarily)

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The proximal radioulnar joint is supplied mainly by the musculocutaneous, median, and radial nerves.

Pronation is essentially a function of the median nerve, whereas supination is a function of the musculocutaneous and radial nerves.

The sudden pulling of the upper limb tears the distal attachment of the anular ligament, where it is loosely attached to the neck of the radius.

The radial head then moves distally, partially out of the anular ligament. 

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The distal (inferior) radioulnar joint is a pivot type of synovial joint (Fig. 6.69). The radius moves around the relatively fixed distal end of the ulna.

The rounded head of the ulna articulates with the ulnar notch on the medial side of the distal end of the radius

A fibrocartilaginous articular disc of the distal radioulnar joint

binds the ends of the ulna and radius together and is the main uniting structure of the joint 

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The fibrous layer of the joint capsule encloses the distal radioulnar joint but is deficient superiorly.

Anterior and posterior ligaments strengthen the fibrous layer of the joint capsule of the distal radioulnar joint

These relatively weak transverse bands extend from the radius to the ulna across the anterior and posterior surfaces of the joint.

During pronation of the forearm and hand, the distal end of the radius moves (rotates) anteriorly and medially, crossing over the ulna anteriorly

The anterior and posterior interosseous arteries supply the distal radioulnar joint