What is Radial Tunnel Syndrome?
Radial tunnel syndrome is a condition where pressure on the posterior interosseous nerve (PIN) causes pain as the nerve moves through the radial tunnel. The PIN branch runs through the elbow to the back of the forearm and provides signals to move muscles in the forearm and to sense information from the back of the wrist. This is a rare condition and it only causes pain while not affecting the ability to feel or move. This is different from PIN compression syndrome, where the PIN nerve gets squeezed, damaging the larger protective fibers of the nerve. This could lead to a weakness in the wrist extensor muscles and pain.
The PIN moves between the two-headed origin of a muscle called the supinator, and around the radial neck, which is an area located near the elbow. It then crosses above a muscle that helps in thumb movement, called abductor pollicis longus (APL), and runs just behind the interosseous membrane down the forearm. The nerve’s sensory supply to the back of the wrist is located in the fourth compartment on the back of the wrist. It’s important to note that the PIN doesn’t supply the skin with nerves.
There are different opinions among experts about radial tunnel syndrome. Some even question whether it really exists or not.
What Causes Radial Tunnel Syndrome?
The radial nerve starts from the back part of a network of nerves in your shoulder (the brachial plexus) and is located just behind a large artery called the axillary artery. This nerve moves along the back of the armpit and extends three branches that give sensation to the back of your arm and control the two parts of a muscle the triceps. The nerve then continues its journey through a passage near your shoulder joint, keeping company with an artery named the profunda brachii artery.
The radial nerve then travels between a bone in your upper arm, the humerus, and the triceps in the back compartment of your arm. Here, it moves across the back edge of your humerus in a groove known as the spiral groove, shifting from a position inside to outside your arm. During this crossing, it sends branches to provide sensation to the arm and forearm and control parts of the triceps and a muscle called the anconeus. The nerve then penetrates a membrane separating muscles in your arm and proceeds towards the front, before a bone protrusion at your elbow, nestled between two muscles: the brachioradialis and the brachialis. Here, the nerve gives the ability to move and feel the muscles named extensor carpi radialis longus, extensor carpi radialis brevis, brachioradialis, and brachialis. When it reaches the elbow, the radial nerve splits into its ending branches: the superficial sensory branch, PIN, and a branch to ECRB.
The radial tunnel is defined as a five-centimeter potential space in the back part of the forearm extending from the level of the radiocapitellar joint (near the elbow) to the near edge of a muscle called the supinator. The brachioradialis, ECRL, and ECRB muscles border it on one side, with the biceps tendon and brachialis muscle on the other. The bottom of the radial tunnel is the capsule of the radiocapitellar joint.
While the actual radial artery isn’t found in the radial tunnel, its first branch (the radial recurrent artery) is. This artery moves towards the top on the supinator muscle and forms a connection with the front branch of the profunda brachii (deep brachial) artery. PIN compression, known as the ‘leash of Henry’, often occurs at the site of the radial recurrent artery. The radial artery continues towards the bottom in the forearm between the brachioradialis and flexor carpi radialis. It passes between the flexor carpi radialis and the first dorsal extensor compartment near the wrist bones and gives off the superficial palmar branch. Lastly, it travels between the two sections of the first dorsal interosseous muscle and forms the deep palmar arch when it joins the deep branch of the ulnar artery.
Risk Factors and Frequency for Radial Tunnel Syndrome
Radial tunnel syndrome is a rare condition that is often misdiagnosed due to its uncommon nature and clinical characteristics. It is thought to affect about 0.003% of people each year. It’s more commonly found in males, with almost three cases in every 100,000, compared to about one case in every 100,000 in women.
- Radial tunnel syndrome is commonly mistaken for PIN compression syndrome, a condition defined by true muscle weakness which happens due to the compression of PIN (an important nerve) in your arms.
- Some even view radial tunnel syndrome as an early stage of PIN compression syndrome. This happens before the structure of the PIN nerve is affected, causing weakness.
Signs and Symptoms of Radial Tunnel Syndrome
Radial tunnel syndrome is a condition that causes aching pain in the upper forearm, on the thumb side. This pain gets worse when turning or twisting the forearm or lifting heavy weights. Some people, even though they don’t have feeling in the thumb and index finger web space, may experience tingling sensations there. People with this condition often feel pain when gently pressing the forearm’s outer side, a few centimeters below the bony bump on the arm’s outer side, called the lateral epicondyle. This is the primary symptom found during a physical examination.
Radial tunnel syndrome can be confused with another condition called lateral epicondylitis or tennis elbow. Distinguishing between them is hard, and around 5% of people experience both conditions at once. People with tennis elbow typically feel pain on the outer side of the elbow, not on the upper forearm. Tests to provoke the pain include resisted supination (twisting the palm face-up) and extending the middle finger. These maneuvers should trigger pain without weakness, but if there’s any weakness, it could be triggered by the pain. More tests like bending the wrist or rotating the forearm can produce the pain by increasing pressure in the radial tunnel. Unlike another condition—posterior interosseous nerve (PIN) syndrome—radial tunnel syndrome shouldn’t cause weakness in wrist extensor muscles, as PIN syndrome does.
There’s a test known as the “rule of nine,” described by Loh et al., that helps evaluate patients with a vague, unspecified elbow or forearm pain. For this test, the underside of the patient’s elbow is marked into nine grid-like circles. The grid starts on the outer arm side, with number one and moves down in a pattern so that number four is the upper circle in the middle row, number seven is in the upper circle of the inner row, and number nine is the lower circle in the inner row. Each zone is gently pressed, and patients can respond with “painful,” “uncomfortable,” or “nothing.” In cases of radial tunnel syndrome, zones one and two will cause pain. Zones five and six are related to the median nerve (another arm nerve), and the inner row zones serve as controls. If the patient feels pain in zones seven to nine, it suggests that the diagnosis may be different.
Testing for Radial Tunnel Syndrome
Magnetic resonance imaging (MRI) is not typically used for diagnosing a condition called radial tunnel syndrome, as the results often show nothing unusual. However, it can be beneficial to figure out if the posterior interosseous nerve (PIN), a major nerve in the arm, is trapped in common places or to identify other potential causes of nerve pressure, like tumors, fluid-filled sacs called ganglion cysts, or abnormally grown bone tissue known as heterotopic ossification.
Another technique to diagnose issues is electrodiagnostic studies, tests that evaluate the electrical activity of muscles and nerves. These are also usually normal in radial tunnel syndrome cases because the PIN’s large fibers do not get affected. However, these tests can help doctors rule out other nerve disorders such as foraminal stenosis, a condition where the openings in the spinal bones narrow, putting pressure on the nerves.
One useful diagnostic tool for radial tunnel syndrome is injecting a local anesthetic into the radial tunnel, an area located on the outside of the elbow. This can help reduce pain, confirming the syndrome. However, doctors should be careful to avoid injecting the anesthetic into the lateral epicondyle, a bony bump on the outside of your elbow. If this happens, it may relieve pain caused by a different elbow condition known as lateral epicondylitis, mistakenly suggesting it’s radial tunnel syndrome instead.
Treatment Options for Radial Tunnel Syndrome
Radial tunnel syndrome, a condition that causes pain in the forearm, is usually treated without surgery. This would typically involve changing any activities that might be causing the problem, using anti-inflammatory medication, and wearing removable splints. These practices include avoiding movements that involve keeping your elbow extended and your wrist flexed and your forearm twisted inward.
In some cases, radial tunnel steroid injections can also be tried to alleviate discomfort. Serious cases that don’t respond to these treatments may require surgery. This surgery involves releasing the radial tunnel and is usually performed from the back of the forearm.
If surgery is needed, the surgeon will carefully inspect the area and remove any sources of pressure that could be causing the problem. Unfortunately, we don’t have many studies comparing non-surgical and surgical treatments for radial tunnel syndrome, so it’s unclear how long non-surgical treatments should be tried before considering surgery.
Surgeons can approach the affected nerve in your forearm from three different angles, which they choose based on their comfort level and the specific needs of the case. It’s also possible to perform the surgery from the front of the forearm if needed.
During surgery, a cut is made along a specific groove in your forearm. The surgeon will carefully protect certain nerves and blood vessels during the procedure. They will then relieve the pressure on your deep radial nerve by making a few strategic cuts.
A couple of alternative surgical techniques involve making a cut slightly more towards the front of the forearm, or going in between specific muscles. These approaches allow the surgeon access to the affected nerve.
Finally, a front-of-the-forearm surgical approach can be used to relieve pressure on the radial nerve higher up in the arm if necessary. This would be useful if there is suspected nerve compression not just in the forearm but also above the elbow. An MRI scan can help determine if this procedure might be needed. In this surgery, the surgeon would follow the radial nerve down where it splits and releases any points of compression.
What else can Radial Tunnel Syndrome be?
When trying to diagnose radial tunnel syndrome, doctors also have to consider other conditions that may cause similar symptoms such as:
- Lateral epicondylitis (tennis elbow)
- PIN compression syndrome
- Brachial plexopathy
- Cervical stenosis
- Cervical foraminal stenosis.
Here’s a brief overview of these conditions:
Brachial Plexopathy: This is an injury to the brachial plexus, a complex network of nerves that send signals from your spine to your shoulder, arm, and hand. Its symptoms can vary depending on where the injury is. It can be diagnosed by a detailed physical exam, EMG (a test that checks the health of the muscles and the nerves that control them), and sometimes an MRI scan of the neck/shoulder.
Cervical Foraminal Stenosis: This condition involves the pinching or compression of the nerves in the neck (cervical spine) as they pass through the holes or “foramina” from where they exit the spinal cord. Symptoms may include pain, numbness, tingling, and weakness in different parts of the body, depending on which nerve is affected. Doctors often use an MRI to confirm this diagnosis and sometimes, targeted injections to identify the problematic levels.
Cervical Stenosis: Here, the spinal canal in the neck is narrowed, which may compress the spinal cord. The key sign of this condition is myelopathy – a disorder that results from severe compression of the spinal cord leading to hand clumsiness and possibly issues with walking. A reflex test known as a Hoffman test can often indicate this condition.
Lateral Epicondylitis (“Tennis Elbow”): This is where the tendons in your elbow are overloaded, usually due to repetitive motion of the wrist and arm. Symptoms can include pain and tenderness in the bony knob on the outside of your elbow. This pain can also be felt during activities where these muscles are in use.
In the diagnosis of these conditions, electrodiagnostic studies can be helpful for PIN compression syndrome and spinal pathology. However, in radial tunnel syndrome, these tests are usually normal.
What to expect with Radial Tunnel Syndrome
In a study of 25 patients with radial tunnel syndrome, a condition that causes arm and hand pain, 72% of the patients experienced complete relief from their forearm pain after being injected with 2 ml 1% lidocaine and 40 mg of triamcinolone. This result was noticed six weeks into the treatment, and 60% of the patients remained pain-free even two years later.
On the other hand, surgical treatment called ‘radial tunnel release’, which intends to alleviate pressure and reduce pain, doesn’t provide immediate relief. Recovery is a gradual process that can take up to 9 to 18 months, and the procedure is moderately successful, with a success rate ranging from 60% to 70%.
Possible Complications When Diagnosed with Radial Tunnel Syndrome
There can be problems after a radial tunnel release surgery. These can include symptoms returning because the nerve gets trapped again, bleeding, infection, and accidental damage to a nerve during the surgery.
Potential Complications:
- Returning symptoms due to nerve entrapment
- Bleeding
- Infection
- Accidental injury to a nerve during surgery
Preventing Radial Tunnel Syndrome
Radial tunnel syndrome is a condition that can often be distinguished from another condition known as PIN compression syndrome. The main symptom of radial tunnel syndrome is a specific type of pain in the back and side of the upper part of the forearm (we call this dorsoradial proximal forearm pain), without any noticeable weakness. However, the diagnosis can be tricky because some patients might appear weak during the physical examination due to the presence of pain.
A study conducted by Sotereanos and his team looked back at 28 surgical procedures to relieve the radial tunnel syndrome (these procedures are known as radial tunnel releases). Their findings showed that approximately 39% of these procedures resulted in good outcomes, meaning the patients’ symptoms improved. However, patients who had other nerve-related conditions like carpal tunnel or cubital tunnel syndromes, or those involved in worker’s compensation claims, tended to report less satisfaction after the surgical release procedure.
