Testing the median nerve involves a combination of sensory checks, motor strength tests, and provocative maneuvers that compress or stretch the nerve to reproduce symptoms. Whether you’re checking for carpal tunnel syndrome, a more proximal entrapment near the elbow, or a traumatic injury, each test targets a different aspect of nerve function. Here’s how each one works and what the results mean.
Where the Median Nerve Supplies Sensation
Before testing, you need to know the median nerve’s territory. On the palm side of the hand, it supplies sensation to the thumb, index finger, middle finger, and the thumb-side half of the ring finger. It also covers a strip of skin over the center of the palm and the lateral (thumb-side) portion of the palm. On the back of the hand, it supplies the fingertips of the thumb and index finger. Any sensory test should focus on these areas and compare them to the pinky side of the hand, which is supplied by the ulnar nerve and serves as a built-in control.
Light Touch and Sensory Threshold Tests
The simplest bedside test is light touch. Lightly brush a fingertip or cotton wisp across the pad of the index finger, then compare the sensation to the same spot on the pinky. Ask whether the two sides feel the same. Decreased sensation on the index or middle finger, with normal feeling on the pinky, points to a median nerve problem.
For more precise measurement, clinicians use Semmes-Weinstein monofilaments: thin nylon fibers of graded thickness pressed against the skin until they bend. Each filament corresponds to a specific force, and the thinnest one the patient can reliably feel is recorded. In healthy adults, the median nerve territory typically registers a monofilament score around 2.87, meaning very fine touch is detectable. A higher score (thicker filament needed) suggests sensory loss. Two-point discrimination is another option: the examiner touches the fingertip with one or two points simultaneously, gradually narrowing the gap until the patient can no longer tell the difference. Normal fingertip discrimination is roughly 3 to 5 millimeters.
Phalen’s Test (Wrist Flexion)
Phalen’s test is the single most widely studied provocative test for carpal tunnel syndrome. To perform it, hold both wrists in full flexion, letting the backs of the hands press together, with the fingers relaxed and pointing downward. Hold this position for 60 seconds. The flexed wrist increases pressure inside the carpal tunnel, compressing the median nerve.
A positive result is tingling or numbness in the thumb, index, or middle finger during that 60 seconds. The symptoms should match the median nerve territory. A meta-analysis covering 48 studies found Phalen’s test has a sensitivity of about 70% and a specificity of 80%, meaning it correctly identifies roughly 7 out of 10 people who have carpal tunnel syndrome and correctly rules it out in 8 out of 10 who don’t. One study that strictly enforced the 60-second hold with fingers extended reported even higher numbers: 85% sensitivity and 90% specificity. Cutting the hold time to 30 seconds drops sensitivity but raises specificity, so the full minute matters.
Tinel’s Sign (Nerve Percussion)
Tinel’s sign tests whether a nerve is irritable at a specific point. To check the median nerve at the wrist, tap firmly with a fingertip or reflex hammer over the carpal tunnel, right between the fleshy mounds at the base of the thumb and the pinky. A positive result is a tingling or electric shock sensation that shoots into the thumb, index, or middle finger.
Tinel’s sign is less sensitive than Phalen’s test, picking up fewer true cases, but a strong positive response is fairly specific to nerve irritation at that location. It’s most useful when combined with other tests rather than relied on alone.
Durkan’s Compression Test
Durkan’s test (also called the carpal compression test) applies direct, sustained thumb pressure over the carpal tunnel for 30 seconds. The examiner presses both thumbs firmly into the space just distal to the wrist crease, directly over the nerve. A positive test reproduces the patient’s tingling or numbness in the median nerve territory.
In meta-analysis data, Durkan’s test has a median sensitivity of about 67%, slightly below Phalen’s. Its advantage is simplicity: it doesn’t require the patient to hold any position, and it can be done even in people with limited wrist flexibility.
Motor Testing: Thumb Strength and the OK Sign
The median nerve powers three small muscles at the base of the thumb (the thenar muscles) that control thumb movement away from the palm and the ability to touch the thumb pad to the other fingertips. Testing motor function tells you whether nerve damage has progressed beyond numbness to actual muscle weakness.
For the most reliable bedside motor test, have the person sit with palms facing up. Ask them to press the pad of their thumb firmly against the pad of their pinky finger. Then try to pull the thumb away by pushing its base toward the thumb side of the hand. You’re isolating the abductor pollicis brevis muscle, which is exclusively supplied by the median nerve. Weakness or an inability to resist your force indicates motor involvement.
The “OK sign” is another quick screen. Ask the person to make a circle by touching the tip of the thumb to the tip of the index finger, forming an O shape. With a significant median nerve injury, the thumb and index finger can’t curve properly, and the circle collapses into a pinch or triangle. This happens because the muscles that flex the thumb tip and the index fingertip lose their nerve supply.
Testing for Entrapment at the Elbow
Not all median nerve problems originate at the wrist. Pronator syndrome involves compression higher up, where the nerve passes through the forearm muscles near the elbow. The key distinguishing feature is that pronator syndrome causes numbness over the palm itself (from the palmar cutaneous branch), while carpal tunnel syndrome spares the palm because that branch branches off before the carpal tunnel.
To test specifically for pronator syndrome, press your thumb firmly over the pronator teres muscle in the upper forearm and hold for 30 seconds. Reproduction of tingling or paresthesias is a positive result. This compression test is one of the most common positive findings in surgically confirmed pronator syndrome cases, and it does not typically trigger symptoms in isolated carpal tunnel syndrome, making it useful for telling the two apart.
You can also have the person pronate their forearm (rotate palm down) against resistance while the elbow is slightly bent, between 0 and 45 degrees of flexion. Increased pain or tingling during this maneuver suggests the nerve is being compressed by the pronator teres. Notably, standard nerve conduction studies are often negative in pronator syndrome, so clinical tests carry extra weight in this diagnosis.
Nerve Conduction Studies
Nerve conduction studies (NCS) are the gold standard for confirming median nerve problems and grading their severity. The test measures how fast electrical signals travel through the nerve and how strong the signal is when it arrives. Two key numbers matter: sensory latency and motor latency. Sensory latency above 3.5 milliseconds or motor latency above 4.4 milliseconds at the wrist indicates slowing consistent with carpal tunnel syndrome.
The American Academy of Orthopaedic Surgeons uses electrodiagnostic results as one of the primary criteria for classifying carpal tunnel syndrome into mild, moderate, or severe. In mild cases, only sensory fibers are slowed. In moderate cases, motor fibers are also affected. In severe cases, the electrical signal may be absent altogether, indicating significant nerve damage. These results help guide treatment decisions, particularly whether surgery is warranted.
Ultrasound Imaging
Ultrasound can visualize the median nerve directly, measuring its cross-sectional area at the wrist. In healthy individuals, the nerve measures about 8.6 square millimeters inside the carpal tunnel. The commonly used diagnostic threshold for carpal tunnel syndrome is 10 square millimeters: a nerve swollen beyond that size suggests compression.
There’s an important caveat with sex differences. Healthy men average about 9.4 square millimeters, with the upper limit of normal approaching the 10 square millimeter cutoff. Women average about 7.7 square millimeters. This means the standard threshold may miss some cases in women and over-diagnose in men. Clinicians increasingly use sex-specific reference values for more accurate interpretation. Another approach compares the nerve’s size at the wrist to its size in the forearm: a significant difference suggests localized swelling at the carpal tunnel rather than a naturally larger nerve.
Combining Tests for Accuracy
No single test is definitive on its own. The AAOS recommends starting with a structured clinical evaluation, often using a scoring tool called the CTS-6 questionnaire combined with a hand diagram where the patient marks their symptoms. A CTS-6 score below 5 corresponds to less than 25% probability of carpal tunnel syndrome, a score between 5 and 11.5 puts it at 25 to 79%, and a score of 12 or higher corresponds to 80% or greater probability.
In practice, a typical evaluation combines the symptom history with Phalen’s test, Tinel’s sign, motor testing of the thumb, and sensory comparison between the index and pinky fingers. When results are ambiguous or surgery is being considered, nerve conduction studies and ultrasound provide objective confirmation and severity grading. For patients whose numbness extends into the palm or whose nerve conduction results are normal despite clear symptoms, testing for pronator syndrome at the elbow is a logical next step.