Radial tunnel syndrome
Compression neuropathy of the radial nerve is considered somewhat more rare than the other compression neuropathies of the upper extremity. The radial tunnel proper is somewhat ill defined, but it is usually considered the area where the radial nerve exits between the brachioradialis and the brachialis muscles to where it drives below the proximal edge of the supinator muscle (Frohse arcade) and distal edge of the supinator.
The deep branch of the radial nerve can be compressed by 5 structures within the radial tunnel. The most common site of compression is at the proximal fibrous edge of the supinator muscle, known as the arcade of Frohse. The most proximal structure that can compress the deep branch of the radial nerve is the fibrous fascia over the radiocapitellar joint. The next structures that can compress the deep branch of the radial nerve are the radial recurrent artery and the venae comitantes, known as the leash of Henry, although this is uncommon. Lastly, the deep branch of the radial nerve can also be compressed by the distal edge of the supinator muscle, which is known to be fibrous in 50-70% of patients.
These may include pain in the upper extensor forearm; dysesthesia in a superficial radial nerve distribution; and weakening of the extension of the fingers, thumb, or wrist.
Posterior interosseous syndrome
Causes may include entrapment of the nerve within supinator muscle, distal edge of the supinator muscle fracture or dislocation of the radial head, tumors (eg, ganglion, lipoma), and iatrogenic causes resulting from open reduction/internal fixation of proximal radius fractures.
Patients may report proximal forearm pain. No sensory deficit is described, but partial-to-complete motor paralysis of the extensors is reported. Often, the brachioradialis and extensor carpi radialis brevis/extensor carpi radialis longus, which are innervated by more proximal branches, are spared. Therefore, any remaining wrist extension also displays radial deviation.
Superficial radial nerve syndrome (Wartenberg syndrome)
The superficial radial nerve exits between the brachioradialis and the extensor carpi radialis longus tendons at the junction of the proximal two thirds to distal one third of the forearm. The superficial radial nerve then courses in a superficial subcutaneous plane to provide sensation to the dorsal aspect of the hand from the thumb to the junction of the ring and long fingers. Sensation to the digits is provided up to the area of approximately the dorsal proximal interphalangeal joint.
Possible sites of compression include: Fascial bands in the subcutaneous plane at its exit site, the tendons of the brachioradialis, and the extensor carpi radialis longus tendons compress the nerve.
Patients report decreased sensation, paresthesia, and tingling in the distribution of the superficial radial nerve. A position Tinel and compression sign is present at the site of exit of the superficial radial nerve. The symptoms are often provoked by extreme pronation of the wrist.