The blood supply to the posterior compartment of the forearm occurs predominantly through branches of the radial, posterior interosseous, and anterior interosseous arteries (Fig. 7.92).
The posterior interosseous artery originates in the anterior compartment from the common interosseous branch of the ulnar artery and passes posteriorly over the proximal margin of the interosseous membrane and into the posterior compartment of the forearm. It contributes a branch, the recurrent interosseous artery (see Fig. 7.66B), to the vascular network around the elbow joint and then passes between the supinator and abductor pollicis longus muscles to supply the superficial extensors. After receiving the terminal end of the anterior interosseous artery, the posterior interosseous artery terminates by joining the dorsal carpal arch of the wrist.
The anterior interosseous artery, also a branch of the common interosseous branch of the ulnar artery, is situated in the anterior compartment of the forearm on the interosseous membrane. It has numerous perforating branches, which pass directly through the interosseous membrane to supply deep muscles of the posterior compartment. The terminal end of the anterior interosseous artery passes posteriorly through an aperture in the interosseous membrane in distal regions of the forearm to join the posterior interosseous artery.
The radial artery has muscular branches, which contribute to the supply of the extensor muscles on the radial side of the forearm.
Deep veins of the posterior compartment generally accompany the arteries. They ultimately drain into brachial veins associated with the brachial artery in the cubital fossa.
The nerve of the posterior compartment of the forearm is the radial nerve (Fig. 7.92). Most of the muscles are innervated by the deep branch, which originates from the radial nerve in the lateral wall of the cubital fossa deep to the brachioradialis muscle and becomes the posterior interosseous nerve after emerging from between the superficial and deep layers of the supinator muscle in the posterior compartment of the forearm.
In the lateral wall of the cubital fossa, and before dividing into superficial and deep branches, the radial nerve innervates the brachioradialis and extensor carpi radialis longus muscles.
The deep branch innervates the extensor carpi radialis brevis, then passes between the two layers of the supinator muscle and follows the plane of separation between the two layers dorsally and laterally around the proximal shaft of the radius to the posterior aspect of the forearm. It supplies the supinator muscle and then emerges, as the posterior interosseous nerve, from the muscle to lie between the superficial and deep layers of muscles.
The posterior interosseous nerve supplies the remaining muscles in the posterior compartment and terminates as articular branches, which pass deep to the extensor pollicis longus muscle to reach the wrist.
The hand (Fig. 7.93) is the region of the upper limb distal to the wrist joint. It is subdivided into three parts: the wrist (carpus), the metacarpus, and the digits (five fingers including the thumb).
The five digits consist of the laterally positioned thumb and, medial to the thumb, the four fingers—the index, middle, ring, and little fingers.
In the normal resting position, the fingers form a flexed arcade, with the little finger flexed most and the index finger flexed least. In the anatomical position, the fingers are extended.
The hand has an anterior surface (palm) and a dorsal surface (dorsum of hand).
Abduction and adduction of the fingers are defined with respect to the long axis of the middle finger (Fig. 7.93). In the anatomical position, the long axis of the thumb is rotated 90° to the rest of the digits so that the pad of the thumb points medially; consequently, movements of the thumb are defined at right angles to the movements of the other digits of the hand.
The hand is a mechanical and sensory tool. Many of the features of the upper limb are designed to facilitate positioning the hand in space.