Tennis elbow, also known as extensor tendonitis of the elbow, is a common overuse injury in active sportspeople. However, not all pain outside the elbow and forearm is tennis elbow. One rare cause of lateral elbow and forearm pain is radial tunnel syndrome, also known as posterior interosseous nerve syndrome. What is radial tunnel syndrome, and what can you do about it?
What is radial tunnel syndrome?
Radial tunnel syndrome describes a compression or pinching of the radial nerve branches passing through the outside of the elbow.
The radial nerve starts high up in the brachial plexus. It passes down the upper arm to the elbow. At the outside of the elbow, the radial nerve splits into two nerves. One branch supplies the skin of the thumb and the top of the hand. The second branch, the posterior interosseous nerve, dives deep into the radial tunnel to supply the muscles at the top of the forearm. The pressure of the nerve within this tunnel leads to radial tunnel syndrome.
Radial tunnel syndrome causes
Causes of compression or irritation of the posterior interosseous nerve in the radial tunnel include the following:
- Lump, cyst or ganglion in the radial tunnel.
- Scar tissue formation in the muscles that make up the radial tunnel.
- Osteoarthritis or swelling in the outer elbow joint.
- Repeated nerve traction from excessive forearm rotation.
Presentation of Posterior Interosseous Nerve Syndrome
Overall, symptoms are often vague and mimic other conditions. The average time to diagnosis is about 2-3 years.
This condition is more common in women aged 30 to 50. At-risk sportspeople include tennis players, swimmers, powerlifters, and violinists.
Generally, people experience aching pain on the outside of the elbow and top of the forearm. Then, they find they lose grip strength. Weakness can progress to involve the fingers and thumb. In severe cases, a wrist drop develops. Sensation in the forearm and wrist is often normal.
When assessing someone, it is essential to exclude other causes of weakness and pain in the forearm, such as tennis elbow, nerve trapping from the neck, or inflammatory neuropathy.
Test for radial tunnel syndrome
Specific to radial tunnel syndrome, sportspeople have weakness in thumb strength, pain with resisted forearm rotation, and tenderness to palpation of the nerve in the radial tunnel (positive Tinel’s sign).
Radial tunnel syndrome vs tennis elbow
Radial tunnel syndrome is often confused with tennis elbow. However, there are definite differences between the two conditions.
First, people with tennis elbow have tenderness at the lateral tip of the elbow (lateral epicondyle), unlike those with radial tunnel syndrome, where tenderness is in the forearm. Also, tennis elbow does not cause significant forearm weakness or wrist drop.
Sometimes, these conditions can occur together, making diagnosis challenging.
Investigations
Often, a diagnosis is difficult due to the vague presentation. However, tests that can confirm a diagnosis include:
- Nerve conduction studies are performed to assess the nerve supply to the forearm muscles. However, nerve studies are often normal.
- An MRI scan of the elbow shows compression by a lump, ganglion, or scar tissue. In addition, muscles such as the supinator may show swelling or shrinkage. Sometimes, an MRI shows other conditions, such as tennis elbow or biceps tendonitis.
Treatment
Once posterior interosseous nerve syndrome has been diagnosed, we recommend conservative treatment for 6 months.
These treatments include:
- Splinting of the wrist at night and during the day
- NSAIDS and a cortisone injection to help with the pain. Also, a cortisone injection targeting the posterior interosseous nerve in the radial tunnel helps to confirm the diagnosis.
- Activity modification in the short term to stop the ongoing irritation of the nerve
- Exercises to regain strength in the forearm, wrist, and thumb include wrist extension, finger extension, thumb extension, and abduction.
- Neural flossing of the radial nerve to improve nerve mobility and function.
Surgery
In cases that fail simple treatments, we consider decompression surgery of the posterior interosseous nerve. Surgeons perform this surgery either with a small open incision or a keyhole. However, surgical results are not always successful, with only 65% of patients having excellent or good results.
Other frequently asked questions about radial tunnel syndrome:
How effective is a cortisone injection at relieving pressure on the posterior interosseous nerve?
An injeciton serves two purposes. Firstly, if an injection relieves symptoms, it confirms a diagnosis of radial tunnel syndrome. Secondly, a cortisone injection can reduce the pressure on the nerve and improve symptoms.
How helpful are investigations in diagnosing radial tunnel syndrome?
Generally, investigations are not great at diagnosing this condition. Sometimes, we see changes in nerve studies that suggest pressure on the radial nerve. Other times, an MRI scan of the elbow shows swelling and wasting of the forearm muscles supplied by the radial nerve. However, most of the time, the investigations show nothing. Nonetheless, they exclude other causes of forearm pain and weakness, such as tennis elbow or impingement of nerves at the neck.
Final word from Sportdoctorlondon
Radial tunnel syndrome is an uncommon cause of forearm pain and weakness in sportspeople. Because diagnosis can be difficult, you should see an experienced sports medicine consultant who can make an accurate diagnosis and recommend appropriate treatment.
Leave A Comment