Root Origin
- Spinal nerve roots: C6, C7, C8, T1
- Plexus: Brachial plexus
- Cord contributions: The lateral cord (C6, C7) sends a branch and the medial cord (C8, T1) sends a branch. These two branches join anterior to the axillary artery to form the median nerve. This dual-cord origin makes the median nerve a truly "median" structure — it carries fibers from nearly every level of the brachial plexus.
- Type: Mixed (motor and sensory)
Course
The median nerve follows the brachial artery like a traveling companion for most of its journey. Here is the path from proximal to distal, described at each landmark an MT would recognize:- Axilla. The nerve forms where the lateral and medial cord branches join, anterior to the axillary artery. At this point it lies deep to the pectoralis major — you cannot palpate it directly, but deep sustained pressure in the axilla can compress it.
- Medial arm. The nerve descends along the medial side of the arm, traveling alongside the brachial artery in the medial bicipital groove — the soft channel between the biceps and triceps. It starts lateral to the artery, then crosses over to the medial side about halfway down the arm. This crossover happens anterior to the artery (the nerve passes in front of it, not behind).
- Distal arm (ligament of Struthers). In about 1% of people, a bony spur called the supracondylar process projects from the medial side of the humerus approximately 5 cm above the medial epicondyle. A fibrous band — the ligament of Struthers — connects this spur to the medial epicondyle, and the median nerve passes beneath it. When present, this is the most proximal entrapment site.
- Anterior elbow. The nerve passes through the cubital fossa (the triangular soft area on the front of the elbow) medial to the biceps tendon and brachial artery. Here it passes beneath the lacertus fibrosus — the broad, flat expansion of the biceps tendon that fans out medially across the forearm flexors. This is the second potential compression site.
- Proximal forearm (between the pronator teres heads). The nerve dives between the two heads of the pronator teres muscle. The humeral head (superficial) and ulnar head (deep) form a muscular arch. The nerve passes between them and can be compressed when the pronator teres is hypertonic or fibrotic. This is the hallmark site of conditions/pronator-teres-syndrome.
- Mid-forearm (under the FDS arch). After exiting the pronator teres, the nerve passes under a fibrous arch at the proximal edge of the flexor digitorum superficialis (FDS). The anterior interosseous nerve — a purely motor branch — separates from the main trunk here and dives deep to supply three muscles (FPL, lateral FDP, pronator quadratus). Compression at this arch causes anterior interosseous syndrome.
- Distal forearm. The nerve descends the forearm between the FDS and flexor digitorum profundus (FDP), staying relatively superficial on the deep surface of FDS. About 5 cm proximal to the wrist crease, the palmar cutaneous branch leaves the main trunk and travels superficially over the flexor retinaculum — it does not enter the carpal tunnel.
- Wrist (carpal tunnel). The main trunk enters the carpal tunnel, passing beneath the flexor retinaculum along with the nine flexor tendons (4 FDS, 4 FDP, FPL). This is the tightest space the nerve passes through, and it is the site of conditions/carpal-tunnel-syndrome — the most common peripheral nerve entrapment worldwide.
- Hand (terminal branches). After exiting the tunnel, the nerve divides into a recurrent motor branch (supplying the thenar muscles) and digital sensory branches (supplying the thumb, index, middle, and radial half of the ring finger). The recurrent branch curves back toward the thumb — "recurrent" because it turns around to go backward.
Motor Distribution
Every muscle the median nerve innervates, listed proximal to distal. Each muscle is cross-linked to its page (most pages do not exist yet — these links establish the wiki architecture for future development).Forearm — Main Trunk
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/pronator-teres | Pronates forearm, weak elbow flexion | Entrapment site — the nerve passes between its two heads |
| anatomy/muscles/flexor-carpi-radialis | Wrist flexion, radial deviation | Tendon is the landmark for finding the median nerve at the wrist (nerve lies just ulnar to it) |
| anatomy/muscles/palmaris-longus | Weak wrist flexion, tenses palmar fascia | Absent in ~14% of people — does not affect hand function |
| anatomy/muscles/flexor-digitorum-superficialis | Flexes PIP joints of digits 2-5 | All four tendons innervated by median nerve; arch over the nerve is an entrapment site |
Forearm — Anterior Interosseous Branch
The anterior interosseous nerve (AIN) is a purely motor branch. It has no cutaneous sensory function, which means compression here causes weakness without numbness — a presentation that confuses students.| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/flexor-pollicis-longus | Flexes IP joint of thumb | Test: pinch tip of thumb to tip of index finger — should form an O, not a triangle |
| anatomy/muscles/flexor-digitorum-profundus (index + middle) | Flexes DIP joints of digits 2-3 | Lateral half only — the medial half (ring + little) is ulnar nerve |
| anatomy/muscles/pronator-quadratus | Pronates forearm (primary deep pronator) | Deep muscle at distal forearm; also stabilizes the distal radioulnar joint |
Hand — Recurrent Motor Branch and Digital Nerves
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/abductor-pollicis-brevis | Abducts thumb (palmar abduction) | First muscle to weaken in CTS — test by resisting thumb abduction perpendicular to the palm |
| anatomy/muscles/opponens-pollicis | Opposes thumb to fingers | The functional hallmark of the human hand — loss makes fine grip impossible |
| anatomy/muscles/flexor-pollicis-brevis (superficial head) | Flexes MCP joint of thumb | Only the superficial head is median; the deep head is ulnar nerve |
| anatomy/muscles/lumbrical-1 | Flexes MCP, extends IP of index finger | The "intrinsic plus" position — MCP flexed, IP extended |
| anatomy/muscles/lumbrical-2 | Flexes MCP, extends IP of middle finger | Lumbricals 3 and 4 (ring, little) are ulnar nerve |
Sensory Distribution
The median nerve provides sensation to the hand through two distinct branches. Understanding which branch covers which area is essential for localizing the compression site.- Palmar cutaneous branch. Exits the main trunk approximately 5 cm proximal to the wrist crease and travels superficially over the flexor retinaculum. It does NOT pass through the carpal tunnel. Supplies sensation to the thenar eminence and central palm.
- Clinical significance: Thenar eminence numbness localizes compression proximal to the carpal tunnel (see Clinical Notes).
- Digital branches. Exit the carpal tunnel and supply sensation to:
- Palmar surface of the thumb (both sides)
- Palmar surface of the index finger
- Palmar surface of the middle finger
- Radial half of the palmar surface of the ring finger
- Dorsal fingertips of the same digits (distal to the DIP joint)
- Clinical significance: Classic "median nerve hand" — numb thumb, index, and middle fingers. Little finger numbness points to ulnar nerve or a more proximal lesion.
Entrapment Sites
The median nerve can be compressed at five distinct sites along its course. Each site produces a different clinical picture. Compression at multiple sites simultaneously is called "double crush" — this is far more common than textbooks suggest.1. Ligament of Struthers
- Location: 5 cm above the medial epicondyle of the humerus
- Structure: Fibrous band from supracondylar process to medial epicondyle
- Prevalence: The supracondylar process is present in approximately 1% of people
- Presentation: Pain and numbness in full median distribution; symptoms worse with elbow extension
- Condition: Supracondylar process syndrome (rare)
- MT relevance: You will almost certainly never see this. Know it exists so you can explain the anatomy to colleagues.
2. Lacertus Fibrosus (Bicipital Aponeurosis)
- Location: Cubital fossa, anterior elbow
- Structure: The flat tendinous expansion from the biceps tendon that spreads medially across the forearm flexors
- Presentation: Forearm aching and weakness; symptoms increase with resisted elbow flexion and supination (these tighten the lacertus)
- MT relevance: Repetitive forceful elbow flexion (think: massage therapists themselves, using the forearm as a tool). Deep work across the anterior elbow should respect this structure.
3. Pronator Teres
- Location: Proximal forearm, between the humeral and ulnar heads of the pronator teres
- Structure: Muscular compression — the two heads squeeze the nerve when the pronator is hypertonic or fibrotic
- Condition: conditions/pronator-teres-syndrome
- Presentation: Aching forearm pain, numbness in full median distribution including the palm (palmar cutaneous branch is affected because compression is proximal to where it branches off). Symptoms worsen with resisted pronation and resisted elbow flexion.
- Key differentiator from CTS: Palmar numbness is present (absent in CTS). Night symptoms are less prominent than in CTS.
- MT relevance: Hypertonic pronator teres responds to specific compression, cross-fiber techniques, and muscle energy technique. Always check this site when CTS symptoms do not respond to standard treatment.
4. FDS Arch (Anterior Interosseous Syndrome)
- Location: Proximal edge of FDS, mid-forearm
- Structure: Fibrous arch where FDS originates
- Condition: Anterior interosseous syndrome (AIN syndrome)
- Presentation: Pure motor — no numbness at all. Weakness of FPL, lateral FDP, and pronator quadratus. The patient cannot make an "OK" sign (pinch of thumb tip to index tip makes a triangle instead of a circle because the IP joints cannot flex fully).
- MT relevance: The absence of numbness is the critical finding. If a patient has forearm weakness without sensory changes, think AIN. Refer for further investigation — this can also result from viral neuritis (Parsonage-Turner syndrome), not just structural compression.
5. Carpal Tunnel
- Location: Wrist, beneath the flexor retinaculum
- Structure: The carpal tunnel is a rigid space — carpal bones form the floor and sides, the flexor retinaculum forms the roof. The median nerve shares this space with nine flexor tendons.
- Condition: conditions/carpal-tunnel-syndrome
- Presentation: Numbness and tingling in thumb, index, middle, and radial half of ring finger. Worse at night (wrist flexion during sleep compresses the nerve). Thenar weakness and atrophy in advanced cases.
- Key feature: The palmar cutaneous branch is NOT affected because it travels over the retinaculum. The thenar eminence skin is spared.
- MT relevance: The most common peripheral nerve compression. Flexor retinaculum release techniques, tendon gliding exercises, and wrist positioning education are within scope. Visible thenar atrophy requires surgical referral (see Clinical Notes).
Clinical Tests
| Test | Procedure | Positive Finding | What It Tells You |
|---|---|---|---|
| ULTT1 (median bias) | Shoulder abduction, elbow extension, wrist and finger extension, forearm supination. Applied as a sequential tensioning of the median nerve from proximal to distal. | Reproduction of the patient's symptoms (numbness, tingling, pain in median distribution). Symptoms increase with cervical lateral flexion away and decrease with lateral flexion toward. | The median nerve is mechanosensitive somewhere along its path. Does not localize the compression site — it tells you the nerve is irritable, not where it is irritable. |
| Phalen's test | Patient holds wrists in full flexion (backs of hands pressed together) for 60 seconds. | Numbness or tingling in median distribution within 60 seconds. | Increased pressure in the carpal tunnel from the flexed position compresses the nerve. Specific to CTS. Sensitivity ~68%, specificity ~73%. |
| Reverse Phalen's (prayer test) | Patient holds wrists in full extension (palms pressed together) for 60 seconds. | Same as Phalen's. | Same mechanism — extension also reduces tunnel volume. Some patients positive on one but not the other. |
| Tinel's sign at wrist | Tap over the median nerve at the wrist crease (just ulnar to the palmaris longus tendon, or ulnar to the FCR tendon if palmaris is absent). | Tingling or electric sensation radiating into the thumb, index, and middle fingers. | Nerve irritability at the carpal tunnel. Low sensitivity (~50%) but reasonable specificity (~77%) — a negative Tinel's does not rule out CTS. |
| Durkan's compression test | Apply direct sustained pressure over the carpal tunnel with both thumbs for 30 seconds. | Reproduction of median nerve symptoms. | More sensitive than Tinel's (~87%) because sustained compression reproduces the pathological mechanism more accurately than tapping. This is the preferred provocation test for CTS. |
| Pronator provocation test | Resisted pronation with elbow extended. Patient pronates against resistance while you palpate the pronator teres. | Reproduction of median nerve symptoms in the forearm or hand. | Compression at the pronator teres level. Differentiates pronator teres syndrome from CTS. If this test is positive AND Phalen's is negative, think proximal compression. |
| AIN pinch test | Ask the patient to make an "O" by touching the tip of the thumb to the tip of the index finger. | The pinch forms a triangle (pulp-to-pulp) instead of a circle (tip-to-tip) because the FPL and lateral FDP cannot flex the distal phalanges. | Anterior interosseous nerve motor deficit. Pure motor finding — no sensory loss accompanies it. |
Clinical Notes
These are the practical observations that matter when you encounter median nerve problems in clinical practice.- Double crush is the rule, not the exception. When the median nerve is compressed at one site, it becomes more vulnerable to compression at a second site. A patient with mild cervical radiculopathy at C6-C7 is significantly more likely to develop CTS. Always assess both the neck and the wrist — treating only the distal site will produce incomplete results. The research suggests that up to 70% of CTS patients have a concurrent proximal compression.
- The palmar cutaneous branch is your best localizer. This small branch exits the main trunk before the carpal tunnel and travels over the retinaculum. If the patient has numbness on the thenar eminence — the fleshy pad at the base of the thumb — the compression is in the forearm, not the wrist. This is the single most useful clinical detail for differentiating CTS from pronator teres syndrome. Ask specifically: "Is the fleshy part at the base of your thumb numb, or just the fingers?"
- Night symptoms point to the wrist. CTS classically wakes patients at night because most people sleep with their wrists flexed, which reduces the tunnel space. Patients who shake their hands to relieve symptoms ("flick sign") almost always have CTS. Pronator teres syndrome, by contrast, is worse with activity and better with rest.
- Pregnancy-related CTS is common and usually temporary. Fluid retention in the third trimester reduces carpal tunnel space. Symptoms typically resolve within weeks after delivery. Aggressive intervention is rarely needed — supportive splinting and gentle nerve gliding are usually sufficient. Do not assume that CTS in a pregnant patient requires the same treatment approach as chronic occupational CTS.
- Thenar atrophy is a red flag. Visible wasting of the thenar eminence indicates advanced, long-standing median nerve compression. The abductor pollicis brevis is the first thenar muscle to atrophy. If you can see flattening at the base of the thumb, refer for surgical evaluation — conservative management alone is unlikely to reverse established atrophy.
- Massage therapists are at risk. Repetitive forceful pronation and sustained wrist positions during treatment put the median nerve at risk in the therapist's own hands. Monitor your own hand symptoms. Ergonomic tool use, forearm techniques (instead of thumb pressure), and regular nerve gliding exercises are protective.
- The median-ulnar boundary is at the ring finger. The median nerve supplies the radial half (thumb side) of the ring finger. The ulnar nerve supplies the ulnar half (little finger side). Patients who report numbness in only part of the ring finger are giving you a precise localization — ask them to show you exactly which side is affected.
Related Nerves
- anatomy/nerves/ulnar-nerve — Medial cord, C8-T1. Supplies the ulnar side of the hand. The most commonly confused nerve in hand distribution — ulnar and median territories share the ring finger. When a patient says "my whole hand is numb," determining whether the little finger is involved differentiates ulnar from median patterns.
- anatomy/nerves/radial-nerve — Posterior cord, C5-T1. Supplies the posterior arm and forearm extensors. Does not overlap with median motor territory, but radial sensory territory on the dorsal hand can be confused with median digital nerve territory at the fingertips.
- anatomy/nerves/musculocutaneous-nerve — Lateral cord, C5-C7. The median nerve's "sibling" — both receive fibers from the lateral cord. The musculocutaneous nerve supplies the anterior arm (biceps, brachialis, coracobrachialis) and lateral forearm sensation. A lateral cord lesion at the brachial plexus would affect both nerves.
- anatomy/nerves/anterior-interosseous-nerve — A purely motor branch of the median nerve. Not a separate nerve from a different cord — it branches off the median trunk in the proximal forearm. Listed here because its clinical presentation (weakness without numbness) is distinct enough that it is assessed and managed differently.
Key Takeaways
- Five entrapment sites exist from the distal arm to the wrist — pronator teres and carpal tunnel are by far the most clinically relevant for MTs.
- The palmar cutaneous branch exits before the carpal tunnel — thenar eminence numbness localizes compression to the forearm, not the wrist.
- Double crush is the rule: always assess both the neck/proximal forearm and the wrist.
- Night symptoms and flick sign point to CTS; activity-related symptoms point to pronator teres syndrome.
- "LOAF" muscles (Lumbricals 1-2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis superficial head) — everything else in the hand is ulnar.