Anatomy of the Elbow:
The elbow joint allows the arm to bend and straighten (flexion and extension) but also, in conjunction with the wrist joint allows the forearm to rotate to place the hand down (to use a keyboard (pronate)) or up (to carry a plate (supinate)).
Bones and Joints:
The elbow joint is made up of three bones. These are the humerus, radius and ulna.
The humerus runs from the shoulder joint to the elbow. At the elbow the humerus widens and has two bony prominences, one on the inside of the elbow (the medial epicondyle) and one on the outside of the elbow (the lateral epicondyle). The lateral epicondyle acts as the attachment for the extensor muscles (which bend the fingers and wrist back) and lateral ligaments. The medial epicondyle acts as the attachment for the flexor muscles (which bend the fingers and wrist down).
The end of the humerus forms 2 articulations. The capitellum is a hemi-spherical surface, which articulates with the round bowl shaped head of the radius. This joint allows rotation of the forearm (supination and pronantion0. The Trochlea is a grooved surface, which articulates with the olecranon of the ulna, allowing flexion and extension. The radius has a small bowel shaped head at the elbow at the wrist it broadens to form ¾ of the wrist. The ulna forms most of the hinge of the elbow joint and only a relatively small portion of the wrist joint.
The radius and ulna run from the elbow to the wrist. A very strong interosseous ligament connects the 2 bones. At the wrist and elbow there are small joints, which allow the 2 bones the radius to rotate around the ulna.
Muscles:
The elbow is flexed principally by Brachialis rather than Biceps, which although a flexor of the elbow is the principal supinator of the forearm (rotator of the hand to carry a plate).
The elbow is extended principally by the Triceps. The Anconeus is a small muscle which also contributes a small amount to extension.
The muscles which attach to the lateral epicondyle includes; Extensor Carpi Radialis Brevis, Extensor Carpi Radialis Longus, Extensor Indicis, Extensor Digiti Minimi, Extensor Digitorum Comunis, Extensor Carpi Ulnaris. These principally extend the wrist and fingers and supinate the forearm.
The muscles which attach to the medial epicondyle include; Pronator Teres, Flexor Carpi Ulnaris, Flexor Digitorum Comunis, Flexor Carpi Radialis, Palmaris Longus. These principally flex the fingers and wrist and pronate the forearm.
Bursa:
The olecranon bursa is a small fluid filled sack or Bursa overlying the olecranon process of the ulna. This acts to reduce friction between the skin and the underlying bony prominence.