You can test for median nerve function through several clinical tests, primarily focusing on sensation and motor function, and provocation maneuvers designed to elicit symptoms of nerve compression. The most common test is the Carpal Compression Test (Durkan's Test).
Carpal Compression Test (Durkan's Test)
This test specifically assesses for Carpal Tunnel Syndrome (CTS), a condition where the median nerve is compressed at the wrist.
- Procedure:
- The patient sits or stands comfortably.
- The examiner places their thumb over the carpal tunnel region on the volar (palm) aspect of the patient's wrist. This area is typically located at the proximal wrist crease, between the tendons of palmaris longus and flexor carpi radialis.
- Firm, direct pressure is applied over the median nerve for up to 30 seconds.
- Positive Result: The test is considered positive if the patient experiences pain, paresthesia (tingling or prickling), or numbness in the median nerve distribution within that 30-second window. This distribution typically includes the thumb, index finger, middle finger, and the radial half of the ring finger.
Other Tests for Median Nerve Function
In addition to Durkan's Test, other assessments include:
- Phalen's Test: The patient flexes their wrists and holds them together for 60 seconds. A positive test reproduces symptoms in the median nerve distribution.
- Tinel's Sign: Tapping over the carpal tunnel elicits tingling or electric shock sensations in the median nerve distribution, indicating nerve irritation.
- Sensory Testing: Assessing sensation in the median nerve distribution using light touch, pinprick, or vibration. Decreased or altered sensation can indicate nerve damage.
- Motor Testing: Evaluating the strength of muscles innervated by the median nerve. Key muscles to test include:
- Abductor Pollicis Brevis: The muscle that abducts the thumb perpendicular to the palm. Weakness suggests median nerve involvement.
- Opponens Pollicis: The muscle that allows the thumb to touch the tip of the little finger. Weakness suggests median nerve involvement.
Electrodiagnostic Studies
- Nerve Conduction Studies (NCS) and Electromyography (EMG): These tests can objectively assess the function of the median nerve by measuring the speed of nerve impulses and the electrical activity of the muscles it supplies. NCS can help localize the site of nerve compression, while EMG can identify muscle denervation.
By combining these clinical and electrodiagnostic tests, clinicians can accurately assess median nerve function and diagnose conditions such as Carpal Tunnel Syndrome.
