The radial tunnel is an anatomical space in the forearm, near the elbow. This confined region, formed by muscles and connective tissues, serves as a passageway for structures, including a significant nerve. Its arrangement can sometimes lead to compression. Understanding its structure is key to comprehending conditions that cause pain or discomfort in the forearm and hand.
Anatomy of the Radial Tunnel
The radial tunnel is in the proximal forearm, extending from the radial head near the elbow to the supinator muscle’s inferior border. This region is approximately 5 centimeters long. Its boundaries are formed by muscles like the supinator, extensor carpi radialis longus, extensor carpi radialis brevis, and brachioradialis.
The tunnel is not an open space but a potential area where structures can be constricted. Fibrous fascial bands, strong connective tissues, course superficial to the radial head, contributing to its boundaries. The radial recurrent artery and its accompanying veins, sometimes called the leash of Henry, also pass through this area. The fibrous edge of the extensor carpi radialis brevis (ECRB) and the supinator muscle’s proximal and distal edges further define this space.
The Radial Nerve’s Journey Through the Tunnel
The radial nerve, originating from the brachial plexus, travels down the arm and splits near the elbow into a superficial and a deep branch. The deep branch, also known as the posterior interosseous nerve (PIN), enters the radial tunnel, passing under the fibrous arcade of Frohse. This arcade is often the most common point of compression.
The deep branch courses through the supinator muscle, a muscle that helps rotate the forearm. As it exits the supinator, it becomes the posterior interosseous nerve (PIN). The superficial branch, in contrast, primarily provides sensory information, traveling from below the elbow to the wrist, hand, and fingers. The deep branch provides motor function to most extensor muscles in the posterior arm and forearm, enabling movements like straightening the wrist, fingers, and thumb.
Understanding Radial Tunnel Syndrome
Radial Tunnel Syndrome (RTS) occurs when the radial nerve or its deep branch (PIN) is compressed or irritated within the radial tunnel. This compression causes pain and weakness in the arm. Friction from surrounding forearm muscles can irritate or inflame the nerve.
Common symptoms include deep pain in the back or top of the forearm, often a dull or burning ache. This pain can extend from the elbow to the wrist and may worsen with forearm rotation or wrist straightening. Activities like extensive forearm/wrist use, heavy lifting, or excessive elbow extension can aggravate symptoms. Patients may also experience tenderness on the outside of the elbow and wrist weakness, making gripping or lifting difficult. The pain might be more noticeable at night or the day after strenuous use.
Contributing factors often involve repetitive arm and wrist motions, such as those in typing or using a screwdriver. Activities with constant push-and-pull motions, like throwing, or excessive gripping, pinching, or wrist bending can also cause the syndrome. A direct blow to the elbow or forearm may also contribute. RTS is more prevalent in individuals 30-50 years old, with women being more susceptible.