Lesion localization

Mechanism: Cervical disc herniation (C4–C5) or foraminal stenosis; cervical spondylosis.

Nerve(s): C5 fibres of the axillary, suprascapular, musculocutaneous, and dorsal scapular nerves

Motor: Weak shoulder abduction (deltoid); Weak elbow flexion (biceps)

Sensory: Numbness over the lateral upper arm / deltoid

Reflex: Diminished biceps reflex

Classic sign: Shoulder and lateral arm pain with weak abduction; ↓ biceps jerk.

C5 supplies the deltoid and contributes to biceps; its dermatome is the lateral arm. Note the axillary nerve gives the same motor/sensory picture but spares the biceps.

Mechanism: C5–C6 disc herniation — the most common cervical radiculopathy after C7.

Nerve(s): C6 fibres of the musculocutaneous and radial nerves (biceps, brachioradialis, wrist extensors)

Motor: Weak elbow flexion (biceps, brachioradialis); Weak wrist extension

Sensory: Numbness of the thumb and lateral forearm

Reflex: Diminished brachioradialis (and biceps) reflex

Classic sign: Thumb/index numbness with weak wrist extension; ↓ brachioradialis jerk.

C6 → wrist extensors and biceps; dermatome = thumb and radial forearm. Distinguish from carpal tunnel (spares the forearm; no reflex change).

Mechanism: C6–C7 disc herniation — the single most common cervical radiculopathy.

Nerve(s): C7 fibres of the radial (triceps, extensors) and median (wrist flexors) nerves

Motor: Weak elbow extension (triceps); Weak wrist flexion; Weak finger extension

Sensory: Numbness of the middle finger

Reflex: Diminished triceps reflex

Classic sign: Middle-finger numbness with a weak triceps and ↓ triceps jerk.

C7 is the triceps level and the middle finger dermatome. Radial nerve palsy also drops the triceps reflex but spares wrist flexion and gives dorsal-hand rather than middle-finger sensory loss.

Mechanism: C7–T1 disc herniation; less common.

Nerve(s): C8 fibres of the median (AIN) and ulnar nerves (long finger flexors), and radial (EPL)

Motor: Weak finger flexion (grip); Weak thumb extension

Sensory: Numbness of the little finger and medial hand

Classic sign: Weak grip with little-finger numbness; reflexes usually preserved.

C8 drives the long finger flexors and extensor pollicis; dermatome = medial hand. Ulnar neuropathy looks similar but spares thumb extension and FDP to the index finger.

Mechanism: L3–L4 disc herniation or lateral recess stenosis.

Nerve(s): L4 fibres of the femoral (quadriceps, saphenous) and deep fibular (tibialis anterior) nerves

Motor: Weak knee extension (quadriceps); Weak ankle dorsiflexion / inversion (tibialis anterior)

Sensory: Numbness of the medial leg and medial malleolus

Reflex: Diminished patellar reflex

Classic sign: Medial leg numbness, weak quads, ↓ knee jerk.

L4 is the knee-jerk level and the medial leg dermatome. Femoral neuropathy also drops the knee jerk but spares tibialis anterior.

Mechanism: L4–L5 disc herniation — the most common lumbar radiculopathy.

Nerve(s): L5 fibres of the deep fibular (EHL, tibialis anterior), superficial fibular, and superior gluteal nerves

Motor: Weak great toe extension (EHL); Weak ankle dorsiflexion (partial foot drop); Weak hip abduction (gluteus medius)

Sensory: Numbness of the lateral leg and dorsum of the foot

Classic sign: Dorsum-of-foot numbness, weak EHL, Trendelenburg gait; no reliable reflex change.

L5 has no good reflex. Weak hip abduction separates L5 root from a common fibular nerve lesion, which spares the gluteals (superior gluteal nerve is L4–S1 but leaves before the sciatic).

Mechanism: L5–S1 disc herniation.

Nerve(s): S1 fibres of the tibial (plantarflexors, Achilles), superficial fibular (evertors), inferior gluteal, and sural nerves

Motor: Weak ankle plantarflexion (gastrocnemius/soleus); Weak ankle eversion; Weak hip extension (gluteus maximus)

Sensory: Numbness of the lateral foot, little toe, and posterior calf

Reflex: Diminished Achilles reflex

Classic sign: Posterior leg pain to the lateral foot, can't toe-walk, ↓ ankle jerk.

S1 = ankle jerk + lateral foot. Tibial nerve lesion also weakens plantarflexion but adds sole numbness and spares eversion.

Mechanism: Traction on the neck during delivery (shoulder dystocia) or a fall on the shoulder that widens the head–shoulder angle.

Nerve(s): Suprascapular, axillary, musculocutaneous nerves; C5–C6 part of the radial nerve

Motor: Weak shoulder abduction (deltoid, supraspinatus); Weak shoulder external rotation (infraspinatus, teres minor); Weak elbow flexion (biceps, brachialis); Weak forearm supination

Sensory: Numbness over the lateral arm, lateral forearm, and thumb

Reflex: Diminished biceps and brachioradialis reflexes

Classic sign: Waiter's tip: arm adducted, internally rotated, elbow extended, forearm pronated.

Everything C5–C6 goes: axillary, suprascapular, musculocutaneous territories, plus the C5–C6 parts of radial (brachioradialis, supinator). Hand intrinsics are spared.

Mechanism: Upward traction on an abducted arm — grabbing a branch while falling, or a breech delivery. Also thoracic outlet syndrome (cervical rib / Pancoast tumour).

Nerve(s): Ulnar nerve; medial root of the median nerve (all hand intrinsics); T1 sympathetics

Motor: Weak intrinsic hand muscles (interossei, lumbricals, thenar, hypothenar); Weak finger flexion

Sensory: Numbness of the medial forearm and medial hand

Classic sign: Total claw hand (all lumbricals out) ± Horner's syndrome if T1 sympathetic fibres are involved.

C8–T1 carries all the intrinsic hand muscles via median and ulnar nerves. Horner's (ptosis, miosis, anhidrosis) is the clue that the lesion is at the root/trunk rather than a peripheral nerve.

Mechanism: Shoulder dislocation, crutch palsy, or proximal humeral fracture.

Nerve(s): Axillary, radial, thoracodorsal, upper & lower subscapular nerves

Motor: Weak shoulder abduction (deltoid); Weak elbow extension (triceps); Weak wrist and finger extension; Weak arm adduction/extension (latissimus dorsi)

Sensory: Numbness over the lateral shoulder (regimental badge); Numbness of the posterior arm, posterior forearm, and dorsal hand

Reflex: Diminished triceps reflex

Classic sign: Axillary + radial nerve palsy together: deltoid wasting with wrist drop.

The posterior cord feeds STAR-U (subscapulars, thoracodorsal, axillary, radial). All extensor compartments plus the deltoid are lost.

Mechanism: Rare in isolation; direct trauma or infraclavicular injury.

Nerve(s): Musculocutaneous nerve; lateral root of the median nerve; lateral pectoral nerve

Motor: Weak elbow flexion (biceps, coracobrachialis); Weak forearm pronation (pronator teres); Weak wrist flexion on the radial side (FCR)

Sensory: Numbness of the lateral forearm

Reflex: Diminished biceps reflex

Classic sign: Musculocutaneous palsy plus the lateral-root (C5–C7) part of the median nerve.

Lateral cord → musculocutaneous nerve + lateral root of median + lateral pectoral. Hand intrinsics are spared because the median's C8–T1 fibres come from the medial cord.

Mechanism: Infraclavicular trauma, thoracic outlet.

Nerve(s): Ulnar nerve; medial root of the median nerve; medial pectoral, medial brachial & antebrachial cutaneous nerves

Motor: Weak intrinsic hand muscles (interossei, lumbricals, thenar, hypothenar); Weak finger flexion

Sensory: Numbness of the medial forearm and medial hand

Classic sign: Ulnar palsy plus the medial-root part of the median: claw hand with thenar weakness.

Medial cord → ulnar nerve + medial root of median + medial cutaneous nerves. Clinically overlaps with a lower trunk lesion but without Horner's.

Mechanism: Fracture of the surgical neck of the humerus; anterior shoulder dislocation; intramuscular injection too high.

Nerve(s): Axillary nerve

Motor: Weak shoulder abduction (deltoid) beyond 15°; Weak shoulder external rotation (teres minor)

Sensory: Numbness over the lateral shoulder (regimental badge)

Classic sign: Flattened shoulder contour (deltoid wasting) with a numb regimental-badge patch.

C5–C6 via the posterior cord. Abduction is initiated by supraspinatus (suprascapular n.), so the first 15° are preserved.

Mechanism: Mid-shaft humeral fracture; 'Saturday night palsy' (arm draped over a chair); crutch pressure.

Nerve(s): Radial nerve at the spiral groove

Motor: Weak wrist extension (wrist drop); Weak finger extension; Weak thumb extension; Weak brachioradialis (elbow flexion in mid-pronation)

Sensory: Numbness of the dorsal first web space / dorsal hand; Numbness of the posterior forearm

Classic sign: Wrist drop with a numb dorsal thumb web; triceps intact.

Below the spiral groove the triceps branches have already left, so elbow extension and the triceps reflex are spared. Grip looks weak only because the wrist can't be stabilised in extension.

Mechanism: Crutch palsy; shoulder dislocation.

Nerve(s): Radial nerve in the axilla

Motor: Weak elbow extension (triceps); Weak wrist extension (wrist drop); Weak finger extension; Weak thumb extension

Sensory: Numbness of the posterior arm and forearm; Numbness of the dorsal first web space / dorsal hand

Reflex: Diminished triceps reflex

Classic sign: Wrist drop plus a weak triceps and absent triceps jerk.

Proximal to the triceps branches, so everything in the posterior compartment goes. Compare with the spiral-groove lesion, which spares the triceps.

Mechanism: Compression under the flexor retinaculum — repetitive use, pregnancy, hypothyroidism, RA, acromegaly, dialysis.

Nerve(s): Median nerve at the wrist (carpal tunnel)

Motor: Weak thumb abduction and opposition (thenar muscles — LOAF)

Sensory: Numbness of the palmar lateral 3½ digits (thumb, index, middle, half of ring)

Classic sign: Thenar wasting ('ape hand'), positive Tinel's/Phalen's; palm over the thenar eminence is spared.

The palmar cutaneous branch leaves proximal to the tunnel, so sensation over the thenar eminence is preserved — a key discriminator from a more proximal median lesion. Forearm flexors are intact.

Mechanism: Supracondylar fracture of the humerus (children); pronator syndrome.

Nerve(s): Median nerve at the elbow

Motor: Weak thumb abduction and opposition (thenar muscles — LOAF); Weak flexion of the index and middle fingers (FDS, lateral FDP); Weak forearm pronation; Weak wrist flexion with ulnar deviation on attempted flexion

Sensory: Numbness of the palmar lateral 3½ digits (thumb, index, middle, half of ring); Numbness over the thenar eminence (palmar cutaneous branch)

Classic sign: Hand of benediction when trying to make a fist (index and middle stay extended); ape hand at rest.

Everything median goes: pronators, radial wrist flexor, lateral half of FDP, FDS, FPL, LOAF and the palmar cutaneous branch. Compare carpal tunnel, which spares all forearm muscles and the thenar-eminence skin.

Mechanism: Medial epicondyle fracture; leaning on the elbow; cubital tunnel compression; 'funny bone' trauma.

Nerve(s): Ulnar nerve at the elbow (cubital tunnel)

Motor: Weak finger abduction/adduction (interossei); Weak flexion of the ring and little fingers at the DIP (medial FDP); Weak wrist flexion with radial deviation on attempted flexion (FCU); Weak thumb adduction (adductor pollicis — Froment's sign)

Sensory: Numbness of the medial 1½ digits (little finger, half of ring) — palmar and dorsal; Numbness over the hypothenar eminence

Classic sign: Mild claw of digits 4–5, interosseous wasting (guttering), Froment's sign; ulnar paradox: clawing is milder than with a wrist lesion.

The proximal lesion knocks out medial FDP, so the DIP joints of digits 4–5 can't flex — which paradoxically makes the claw less obvious. Dorsal-hand sensory loss confirms the lesion is above the wrist (the dorsal cutaneous branch leaves ~5 cm proximal).

Mechanism: Hook of hamate fracture; handlebar palsy (cyclists); laceration.

Nerve(s): Ulnar nerve at the wrist (Guyon's canal)

Motor: Weak finger abduction/adduction (interossei); Weak thumb adduction (adductor pollicis — Froment's sign); Weak lumbricals to digits 4–5 (clawing)

Sensory: Numbness of the palmar medial 1½ digits (little finger, half of ring)

Classic sign: Pronounced claw hand of digits 4–5 (MCP hyperextension, IP flexion); dorsal hand sensation spared.

FDP is intact so the DIP joints flex hard against unopposed extensors → a worse claw than the elbow lesion (the ulnar paradox). The dorsal cutaneous branch has already left, so the dorsum of the hand feels normal.

Mechanism: Rare — heavy lifting, shoulder surgery, coracobrachialis entrapment.

Nerve(s): Musculocutaneous nerve

Motor: Weak elbow flexion (biceps, brachialis); Weak forearm supination

Sensory: Numbness of the lateral forearm

Reflex: Diminished biceps reflex

Classic sign: Weak supinated elbow flexion with a numb lateral forearm; brachioradialis still flexes the elbow in mid-pronation.

C5–C7 via the lateral cord. Coracobrachialis, biceps, brachialis; continues as the lateral antebrachial cutaneous nerve.

Mechanism: Axillary lymph node dissection / mastectomy; stab wound; carrying heavy backpacks.

Nerve(s): Long thoracic nerve

Motor: Weak scapular protraction (serratus anterior); Can't abduct the arm above 90° (loss of scapular upward rotation)

Sensory: —

Classic sign: Winged scapula — the medial border lifts off when the patient pushes against a wall.

C5–C7 straight off the roots, so it can be injured while the rest of the plexus is fine. Serratus anterior holds the scapula to the chest wall and rotates it upward for full abduction.

Mechanism: Suprascapular notch entrapment; overhead athletes; scapular fracture.

Nerve(s): Suprascapular nerve

Motor: Weak initiation of shoulder abduction (supraspinatus, 0–15°); Weak shoulder external rotation (infraspinatus)

Sensory: —

Classic sign: Posterior shoulder pain with infraspinatus wasting; abduction weak in the first 15°.

C5–C6 from the upper trunk. No cutaneous branch. Deltoid is intact, so abduction above 15° recovers.

Mechanism: Pelvic fracture, retroperitoneal haematoma (anticoagulants), lithotomy position, hip surgery, diabetic amyotrophy.

Nerve(s): Femoral nerve

Motor: Weak knee extension (quadriceps); Weak hip flexion (iliopsoas, partially)

Sensory: Numbness of the anterior thigh; Numbness of the medial leg (saphenous nerve)

Reflex: Diminished patellar reflex

Classic sign: Knee buckles on stairs; absent knee jerk; numb anterior thigh and medial leg.

L2–L4. Saphenous nerve is the terminal sensory branch — medial leg to the medial malleolus. Compare L4 root: also drops the knee jerk but adds tibialis anterior weakness.

Mechanism: Pelvic fracture, obturator hernia, pelvic surgery, prolonged labour.

Nerve(s): Obturator nerve

Motor: Weak hip adduction (adductor group)

Sensory: Numbness of the medial thigh

Classic sign: Leg swings laterally when walking; numb medial thigh.

L2–L4 through the obturator foramen. Adductors and gracilis.

Mechanism: Posterior hip dislocation / surgery; misplaced gluteal injection (upper-medial quadrant).

Nerve(s): Superior gluteal nerve

Motor: Weak hip abduction (gluteus medius, minimus, TFL)

Sensory: —

Classic sign: Trendelenburg sign: the pelvis drops on the opposite side when standing on the affected leg; waddling gait.

L4–S1. Remember: standing on the lesioned leg, the *contralateral* hip drops (the affected abductors can't hold the pelvis level).

Mechanism: Posterior hip dislocation; gluteal injection.

Nerve(s): Inferior gluteal nerve

Motor: Weak hip extension (gluteus maximus)

Sensory: —

Classic sign: Difficulty rising from a chair or climbing stairs; gluteus maximus lurch (trunk thrown backward).

L5–S2. Gluteus maximus only.

Mechanism: Posterior hip dislocation, hip surgery, misplaced gluteal injection, piriformis syndrome.

Nerve(s): Sciatic nerve

Motor: Weak knee flexion (hamstrings); Weak ankle dorsiflexion (foot drop); Weak ankle plantarflexion; Weak ankle eversion and inversion; Weak toe movement

Sensory: Numbness of the entire leg and foot below the knee, except the medial leg (saphenous)

Reflex: Diminished Achilles reflex

Classic sign: Flail foot: everything below the knee except the saphenous strip.

L4–S3. The knee jerk is preserved (femoral). Common fibular and tibial deficits combined plus the hamstrings.

Mechanism: Fracture of the fibular neck; tight cast; prolonged leg crossing or squatting; bedrest.

Nerve(s): Common fibular (peroneal) nerve

Motor: Weak ankle dorsiflexion (foot drop); Weak ankle eversion; Weak toe extension

Sensory: Numbness of the lateral leg and dorsum of the foot

Classic sign: Foot drop with steppage gait; can't stand on heels; numb dorsum of the foot.

L4–S2. Deep fibular = dorsiflexors + first web space; superficial fibular = evertors + dorsum. Hip abduction is normal, which separates it from an L5 root lesion. Inversion is preserved (tibialis posterior — tibial n.).

Mechanism: Knee dislocation, popliteal laceration, tarsal tunnel syndrome (distal).

Nerve(s): Tibial nerve

Motor: Weak ankle plantarflexion; Weak ankle inversion; Weak toe flexion

Sensory: Numbness of the sole of the foot

Reflex: Diminished Achilles reflex

Classic sign: Can't stand on tiptoe; numb sole; foot everted at rest (unopposed fibularis).

L4–S3. Compare S1 root: also weak plantarflexion but spares the sole and adds eversion weakness.