Ulnar Tunnel Syndrome occurs when the ulnar nerve is compressed as it travels through Guyon’s canal, a narrow passageway in the wrist. This condition is a form of peripheral neuropathy, where the nerve restriction leads to changes in sensation and motor control in the hand. The ulnar nerve is one of the three primary nerves supplying the hand. Ulnar Tunnel Syndrome is specifically defined by entrapment at the wrist, differentiating it from the more common Cubital Tunnel Syndrome at the elbow.
The Anatomy and Etiology of Compression
The precise location of this compression is Guyon’s canal, a small, rigid tunnel on the palm side of the wrist near the base of the little finger. This canal is approximately four centimeters long and acts as a conduit for the ulnar nerve and ulnar artery as they enter the hand. Its boundaries are formed by specific bony and ligamentous structures, including the pisiform bone and the hook of the hamate bone, with the roof created by the palmar carpal ligament.
The nerve’s passage through this tightly constrained space makes it vulnerable to external and internal pressures. External causes often relate to chronic, repetitive trauma or sustained pressure applied to the heel of the hand, an issue sometimes called “handlebar palsy” in cyclists. People who use vibrating tools or engage in repetitive gripping motions are also at risk for this type of injury.
Internal causes frequently involve space-occupying lesions that reduce the limited volume of the canal. The most common internal culprit is a ganglion cyst, a benign, fluid-filled sac originating from a nearby joint, which can press directly on the nerve. Other masses, such as lipomas or aneurysms of the ulnar artery, can also lead to compression. Trauma, including fractures of the hamate bone or pisiform bone dislocation, can alter the canal’s structure and impinge the nerve.
Recognizing the Signs of Nerve Damage
A person experiencing Ulnar Tunnel Syndrome notices a combination of sensory and motor changes in the hand, which often develop gradually over time. Sensory symptoms involve paresthesias, commonly described as tingling or a “pins and needles” sensation. This altered feeling is localized to the little finger and the half of the ring finger nearest to it, reflecting the nerve’s distribution.
Depending on the exact point of compression within Guyon’s canal, sensory symptoms may be the only manifestation, or they may be accompanied by motor issues. Motor symptoms result from damage to the deep motor branch of the ulnar nerve, which controls most of the small muscles within the hand. This can lead to noticeable weakness, making tasks like gripping objects or pinching difficult.
In more advanced or prolonged cases, the weakness can cause muscle wasting, known as atrophy, especially in the intrinsic muscles of the hand. Atrophy affects the ability to spread the fingers apart and bring them together. Severe, chronic compression can result in a characteristic hand posture where the ring and little fingers curl inward, sometimes referred to as an ulnar claw hand.
Medical Confirmation and Management Strategies
The process of confirming Ulnar Tunnel Syndrome begins with a physical examination by a physician. The doctor will test for sensory changes in the little and ring fingers and assess the strength of the hand’s intrinsic muscles. A specific test, called Tinel’s sign, involves lightly tapping over Guyon’s canal at the wrist; a positive result reproduces tingling sensations down the nerve’s path.
Diagnostic Testing
To objectively confirm the diagnosis and determine the severity and precise location of the nerve damage, electrodiagnostic tests are frequently employed. Nerve Conduction Studies (NCS) measure how quickly electrical signals travel along the ulnar nerve, helping to identify a focal area of slowing or blockage at the wrist. Electromyography (EMG) assesses the electrical activity of the muscles supplied by the nerve, which helps determine if muscle fibers are being affected.
Imaging techniques are also used. X-rays are used to check for bony abnormalities like fractures, while Magnetic Resonance Imaging (MRI) or ultrasound can visualize soft tissue masses, such as ganglion cysts, that may be causing the compression.
Conservative Care
Management strategies are divided into conservative care for milder cases and surgical intervention for more severe or persistent conditions. Initial conservative care focuses on reducing the pressure and inflammation around the nerve. This involves activity modification, which means avoiding the repetitive motions or prolonged wrist positions that aggravate symptoms. Non-steroidal anti-inflammatory drugs (NSAIDs) can help manage pain and swelling.
A course of physical or occupational therapy is often recommended to help with nerve gliding exercises and to advise on appropriate splinting, particularly if the wrist is held in a position that increases nerve tension.
Surgical Intervention
If symptoms do not improve after a period of conservative treatment, or if the compression is caused by a mass like a cyst, surgical intervention becomes necessary. The goal of surgery is ulnar nerve decompression, which involves opening the confines of Guyon’s canal to permanently relieve pressure on the nerve. If a mass is present, it is removed during the procedure to eliminate the source of the compression.