Anatomy of the Elbow and Forearm

Functional Anatomy of the Elbow and Forearm

• The elbow consists of 3 bones (humerus, radius, and ulna) and 2 joints (humeroulnar and humeroradial) that enable elbow flexion and extension.
• The forearm consists of 2 bones (radius and ulna) and 2 joints (proximal radioulnar joint and distal radioulnar joint) that enable forearm pronation and supination.

Joints of the Elbow and Forearm

• Humeroulnar joint provides most of the structural stability to the elbow through the trochlear notch of the ulna interlocking with the trochlea of the humerus.
• Humeroradial joint is formed by the capitulum of the humerus and the fovea of the radius, permitting continuous contact during pronation and supination.
• Proximal radioulnar joint is an articulation of the head of the radius and the radial notch of the ulna.
• Distal radioulnar joint is a rotation of the distal end of the radius around the distal end of the ulna.
• Supination and pronation occur at both joints and in the forearm.

Bony Landmarks of the Elbow and Forearm

• Distal humerus (anterior) features: trochlea, capitulum, medial epicondyle, lateral epicondyle, ulna nerve sulcus, and radial fossa.
• Distal humerus (posterior) features: trochlea, medial epicondyle, lateral epicondyle, lateral supracondylar ridge, and olecranon fossa.
• Proximal ulna (lateral) features: olecranon process, trochlear notch, coronoid process, and ulnar tuberosity.
• Proximal ulna (anterior) features: olecranon process, trochlear notch, coronoid process, and radial notch.
• Radius features: head, radial tuberosity, and neck.
• Ulna features: head and styloid process.

Supporting Structures of the Elbow

• Articular capsule: a thin connective tissue encasing 3 articulations.
• Medial (ulna) collateral ligament: crosses the elbow medially from the medial epicondyle to the coronoid and olecranon processes, providing stability in resisting cubital valgus forces.
• Lateral (radial) collateral ligament: crosses the elbow laterally from the lateral epicondyle to the annular ligament, providing stability in resisting cubital varus forces.
• Annular ligament: a band of fibers that circles the radius, maintaining contact between the radius and humerus.

Muscles of the Elbow and Forearm

• Biceps brachii: originates from two proximal insertions, inserts into the radial tuberosity, and acts to flex the elbow joint and supinate the forearm.
• Brachialis: originates from the lower half of the humerus, inserts into the coronoid process of the ulna, and acts to flex the elbow joint.
• Brachioradialis: originates from the lateral epicondyle of the humerus, inserts into the styloid process of the radius, and acts to flex the elbow joint.
• Triceps brachii: originates from three attachment points, inserts into the olecranon process of the ulna, and acts to extend the elbow joint.
• Anconeus: originates from the lateral epicondyle of the humerus, inserts into the lateral portion of the olecranon and upper ulna, and acts to extend the elbow joint.
• Supinator: originates from the lateral epicondyle of the humerus, ulna, and annular and radial collateral ligaments, inserts into the upper third of the radius, and acts to supinate the forearm.
• Pronator teres: originates from the humeral head and coronoid process of the ulna, inserts into the midpoint of the lateral surface of the radius, and acts to pronate the radioulnar joint and flex the elbow joint.
• Pronator quadratus: originates from the palmar surface of the ulna, inserts into the palmar surface of the radius, and acts to pronate the radioulnar joint.