Radial Tunnel Syndrome
The radial tunnel is a track through the upper forearm through which a branch of the radial nerve (posterior interosseous nerve) courses en route to innervating the majority of the muscles which help to straighten the fingers, thumb, and the wrist. This nerve is infrequently compressed resulting in vague pain, fatiguability and sometimes weakness unless the pressure is relieved. Radial tunnel syndrome was first described in about 1971 and considerable research has been conducted ever since. Radial tunnel syndrome must be differentiated from the much more common "tennis elbow."
5% or less of people who present with outer elbow and upper forearm pain are actually ultimately believed to have radial tunnel syndrome. In contrast to other nerve impingement syndromes which typically occur much more frequently in women such as carpal tunnel syndrome and cubital tunnel syndrome, this syndrome occurs almost equally in men and women. One-sided involvement is the exception rather than the rule, also in contrast to other entrapment neuropathies. It usually occurs in the dominant side. This has only been reported in adults, not in children, also contrasting with carpal tunnel syndrome.
The radial nerve courses from the upper outer arm to the outer elbow between the brachialis (elbow flexor) and the brachioradialis muscles. Almost directly in front of the elbow the radial nerve divides into the superficial radial (pure sensory) and the posterior interosseous (pure motor) nerves. The posterior interosseous nerve (PIN) dives beneath the leading edge of the supinator muscle otherwise known as the arcade of Frohse. It is here that compression of the PIN may occur. The variation in the amount of tendon at the opening of the radial tunnel, i.e., the arcade, has a lot to do with whether or not the person develops the syndrome. The arcade acts like a gate and the vigor of the supinator muscle contracting closes this gate on the underlying PIN resulting in radial tunnel syndrome. In severe cases, weakness of the muscle innervated by the PIN at the arcade has been carefully recorded by Werner Olaf at the time of surgery by stimulating the supinator muscle to contract.
Radial tunnel syndrome must be differentiated from lateral epicondylalgia (tennis elbow) which is much more common as a cause of outer elbow and upper forearm pain. The main differences are depicted in Table I. The diagnosis of radial tunnel syndrome is perhaps the most difficult and debated of nerve entrapment syndromes in the upper extremities. This is because of the variable symptoms, relatively normal physical exam usually encountered aside from local tenderness, and the lack of a reliable objective diagnostic test. We are currently still studying and debating the utility of nerve conduction study for the posterior interosseous nerve. Nerve conduction studies have proven extremely useful in evaluating people for other nerve entrapment syndromes wherein the nerve is more superficial. The critical distinction to be made is between tennis elbow and radial tunnel syndrome. Rarely, arthritis must be excluded though usually x-rays are not even necessary in evaluating a person with this complaint because they usually have full motion, no swelling, and no grating of the joints through the arc of motion.
In a minority of cases changing one's activities, i.e., modifying the way they use their forearm, will diminish or eliminate the symptoms. The activity most likelyto precipitate symptoms of radial tunnel syndrome is forceful forearm rotation particularly palm upwards (supination). This puts pressure upon the nerve at the arcade of Frohse. Prolonged splinting, nonsteroidal anti-inflammatory medication, elbow bands and sleeves, etc. have not proven beneficial for this or for lateral epicondylitis. In contrast, though cortisone injection does not have any place in the treatment of radial tunnel syndrome it's the main treatment available for lateral epicondylalgia (tennis elbow). Neither is an inflammatory condition and often, surgery is necessary to relieve the symptoms.
The actual distribution of patients going on to require surgery is not known. In my experience, it appears that about half of the people who present with radial tunnel syndrome will require surgical intervention to eliminate the symptoms. The rest of the people who have symptoms that are mild enough don't elect to proceed with definitive surgical treatment or they resolve by activity modification.
Surgery involves the use of one of three exposures either a longitudinal incision (about 4" long) or a more aesthetically acceptable 2" transverse incision over the upper forearm. The objective is to release the arcade of Frohse, ie., open the constrictive gate and thereby decrease the pressure on the posterior interosseous nerve.
Some soreness often persisting from 3-6 months should be anticipated after surgery. The amount of pain experienced after this surgery is usually relatively minor requiring strong analgesics for only a couple of days after surgery. The majority of symptoms are controlled with Tylenol or nonsteroidal anti-inflammatories such as Ibuprofen for a few weeks. Return to work is usually prompt within 1-3 days of surgery sometimes requiring temporary modification, i.e., light duty, while depending on the amount of activity and whether the problem arises in the dominant or nondominant extremity. No absolute restrictions are necessary, however. Exercise with Thera-Putty and lightweight is utilized while occupational and physical therapy are rarely indicated.
Of five hundred cases reported in the literature, the majority of the studies reported indicate 70-80% of patients undergoing surgery for radial tunnel syndrome can anticipate improvement to elimination of symptoms after surgery. This means that perhaps 2 or 3 out of 10 persons operated upon will continue to have discomfort at the same or lesser degree as preoperatively. On the other hand, it also means that about 7 or 8 out of 10 can anticipate improvement of their preoperative symptoms.
Risk of infection is less than 1%. The other major concern is the potential for bruising one of three nerves in the area: the lateral antebrachiocutaneous which gives sensation to the upper outer forearm, the superficial radial nerve which gives sensibility to the top of part of the fingers and the wrist, or the posterior interosseous nerve. Posterior interosseous nerve weakness can result temporarily making lifting of the wrist or fingers difficult for a couple of months. However, this has been a rare occurrence in my experience. A dark complexioned person may experience a prominent scar.