The forearm is the lower portion of the arm, found between the elbow and wrist joints. Beneath the skin, and the fat stored just beneath the skin, are 20 muscles: eight in the palm side, and 12 in the back side. Supplying these muscles are several major arteries and nerves, namely the ulnar artery and median and ulnar nerves in the front compartment and the radial artery and radial nerve in the back compartment. The deepest structures in the forearm are the two long bones, the radius and ulna.
At the upper and lower ends of the forearm are the elbow and wrist joints, respectively. The elbow, which connects the tops of the radius and ulna and the bottom of the humerus in the upper arm, is a type of synovial joint known as a ginglymoid or hinge joint. Movements possible at the joint are flexion and extension, or the bending and straightening of the elbow.
The wrist is the connection between the radius and the carpal bones of the hand. It can produce the movements of flexion and extension, as well as adduction and abduction, or the waving of the hand from side to side. Two other joints are found between the wrist and elbow, the proximal and distal radioulnar joints, which are where the radius and ulna meet at their top and bottom ends and that permit rotation of the forearm.
In the front compartment of the forearm are eight muscles, all found on the palm side of the arm. These muscles are mostly responsible for flexion or curling inward of the hand and fingers as well as for pronation, the palm-down rotation of the arm. They include five superficial muscles, the flexor carpi radialis, palmaris longus, flexor carpi ulnaris, pronator teres, and flexor digitorum superficialis, and three deep muscles, the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.
The back compartment of the forearm includes 12 muscles that are largely involved in the movements of extension or straightening of the wrist and fingers and the palm-up rotation of the arm. They include four superficial, two intermediate, and six deep muscles. The brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris are in the superficial compartment. The extensor digitorum and extensor digiti minimi are in the intermediate compartment. The abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, supinator, and anconeus are in the deep compartment.
Supplying these muscles with essential nutrients and innervating them to produce movement and respond to external stimuli are several blood vessels and nerves, respectively. The front and back compartments of the forearm are distinguished from one another not by the location of the muscles and tendons contained within but by the blood vessels and nerves permeating each. In the anterior compartment, the major artery is ulnar artery, so named because it runs down the medial or ulnar side of the arm, the side of the pinky finger.
The major nerves of this compartment are the median nerve, which runs down the middle of the arm and enters the hand via the carpal tunnel in the wrist, and the ulnar nerve, which innervates the ulnar side of the arm. In the back compartment, blood is received from the radial artery, which is found along the lateral or radial side of the arm. The major nerve is the radial nerve, which is situated along the same side of the arm, that of the thumb.