There are five muscles in the deep compartment of the posterior forearm – the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis.
The tendon of the extensor pollicis longus travels medial to the dorsal tubercle at the wrist (the extensor pollicis brevis and abductor pollicis longus travel laterally). This allows the muscle to use the tubercle as a trochlea, increasing its force. Attachments: Originates from the posterior surface of the ulna and interosseous membrane. Attaches to the distal phalanx of the thumb Actions: Extends all joints of the thumb Innervation: Radial Nerve
The tendon of the extensor pollicis longus lies in a groove on the medial aspect of the dorsal tubercle of the radius. Inferior to this, digital twigs of the superficial branch of the radial nerve can be felt crossing the tendon.
When the thumb is extended, a hollow known as the anatomical snuff-box appears between the tendon of the extensor pollicis longus medially and those of the extensor pollicis brevis and abductor pollicis longus laterally. Its floor is formed by the scaphoid and trapezium bones and is crossed by the radial artery. The hollow is limited superiorly by the styloid process of the radius.
in the forearm, it branches into a superficial branch (primarily sensory) and a deep branch (primarily motor).
The superficial branch of the radial nerve descends in the forearm under the brachioradialis. It crosses brachioradialis to enter posterior of forearm near the back of the wrist and supply dorsum of hand. It gives nerve supply to dorsal aspect of thumb ,index finger,and radial side of middle finger except the nail beds,which are supplied by proper digital branches of median nerve.
The deep branch of the radial nerve has a muscular and articular distribution. It winds laterally between the superficial and deep layers of the supinator and often makes direct contact with the radius, being vulnerable in fractures.
At the lower border of the supinator, it meets the posterior interosseous vessels. For the rest of its course, the deep branch of the radial nerve is then termed the posterior interosseous nerve, a name that is sometimes applied to the entire course of the deep branch. The posterior interosseous nerve reaches the interosseous membrane distally and ends in an enlargement from which twigs are distributed to adjacent joints
The superficial branch of the radial nerve provides sensory innervation to much of the back of the hand, including the web of skin between the thumb and index finger.
The radial nerve (and its deep branch) provides motor innervation to the muscles in the posterior compartment of the arm and forearm, which are mostly extensors.
The radial nerve innervates the muscles that extend at the wrist, and these are paralysed. The flexor muscles are innervated by the median nerve, and are unaffected. The wrist undergoes unopposed flexion, and wristdrop results
It passes backward above the upper margin of the interosseous membrane between the radius and the ulna. It then pass down ward between the supinator and abductor pollicis longus and reach the interval betweenn the superficial and deep group of muscles .
Branches: 1-muscular branches 2-recurrent branch takes part in the anastomosis around the elbow. It ends by anastomosis with the ANTERIOR INTEROSSEIOUS arteryand taking part in the anastomosis around the wrist joint.
It descend in the front of interosseous membrane and pierces it in the lower third of the membrane to reach the post.compartment