Forearm

From ArticleWorld

The forearm is the aspect of the arms of all primates that begins at the elbow and ends at the wrist. The forearm is a unique aspect of the arm in that it has motions in several directions.

Anatomy

The forearm consists of two bones, the radius, which lies on the same side as the thumb, and the ulna, which is on the same side as the small finger. The proximal aspects of the bones (the parts closest to the rest of the body) form part of the elbow joint. The distal ends of the bones (the parts furthest away from the body) connect with connective tissue to the wrist bones to form the wrist joints.

The two bones are connected by a thin fibrous band known as the interosseous membrane. The radius and ulna do not stay in the same relationship to one another as there are muscles that allow the forearm to “twist” or to perform what is called pronation and supination. The muscles that allow for this are the supinator muscle, the pronator teres and the pronator quadratus.

The forearm also has two compartments, the anterior compartment and the posterior, or extensor compartment. The anterior compartment flexes the wrist and is supplied by the median nerve. The posterior compartment contains the muscles that extend (or tip back) the wrist and is supplied by the radial nerve.

Two main arteries, the radial and ulnar arteries, run down the inner aspect of the forearm and along the radius. They ultimately have multiple branches, some of which supply the blood to the hand. The cephalic vein, the antebrachial vein and the basilic vein are the primary veins that drain blood from the distal arm.

Function

As mentioned, the forearm has several movements associated with it. The forearm can both flex (bend) and extend (straighten) at the elbow. There are muscles that allow one to put the palm up (supinate) or palm down (pronate). Finally, the forearm contains the muscles that flex and extend the wrist joint.

Diseases

The primary injury affecting the forearm is the fracture. One or both bones can be fractured. A common injury in children is called a “greenstick” fracture of the distal radius. It is caused by a fall while the arm is outstretched in an attempt to catch oneself. The fracture often just buckles the bone and does not actually cause a through and through fracture. The other injury to children is called “nursemaid’s elbow” which occurs when a child’s arm is jerked with the palm upward. This is a mild dislocation of the head of the radius where it inserts in the elbow. This, like the greenstick fracture, heals quickly without residual effect.