Goal for boards: Be able to go from weak muscle → nerve → root → lesion site in both upper and lower limbs.
For extremity localization, always think in triads: weak movement + reflex change + sensory map. If all line up in one root → radiculopathy. If they don’t → think nerve or plexus.
| Root | Key Movement | Example Muscle | Reflex |
|---|---|---|---|
| C5 | Shoulder abduction | Deltoid | Biceps (C5–6) |
| C6 | Elbow flexion, wrist extension | Biceps, ECRL/B | Brachioradialis (C5–6) |
| C7 | Elbow extension, wrist flexion | Triceps, FCR | Triceps (C6–7) |
| C8 | Finger flexion | FDP, FDS | None specific (helpful clinically) |
| T1 | Finger abduction/adduction | Interossei | None specific |
Quick memory: C5 = shoulder, C6 = wrist extension (“6-shooter”), C7 = triceps, C8 = finger flexion, T1 = finger abduction.
| Nerve | Roots | Key Muscle (Test) | Sensory Area | Classic Lesion |
|---|---|---|---|---|
| Axillary | C5–6 | Deltoid – shoulder abduction (15–90°) | “Regimental badge” lateral shoulder | Surgical neck humerus fracture; shoulder dislocation |
| Musculocutaneous | C5–7 | Biceps – elbow flexion, supination | Lateral forearm | Upper arm trauma, rarely isolated |
| Radial | C5–T1 | ECRL/B, EDC – wrist & finger extension | Dorsal hand (radial side) | “Saturday night palsy”, crutches, mid-shaft humerus fracture → wrist drop |
| Median | C5–T1 |
Forearm: pronator teres (pronation) Hand: APB, opponens pollicis (thumb opposition) |
Palmar 1–3½ digits | Carpal tunnel; proximal lesion → “hand of benediction” |
| Ulnar | C8–T1 | Interossei – finger abduction/adduction, Froment sign | Medial 1½ digits (palmar & dorsal) | Cubital tunnel, Guyon canal – “claw hand”, weak grip |
Simple memory: “RAD wrist” (radial – wrist extension), “MEDian = thumb opposition & sensation to 3½ fingers”, “ULNAR = interossei – PAD/DAB (adduct/abduct).”
If interossei are out → think ULNAR or T1, not median or C7. Test by asking patient to hold a card between fingers (palmar interossei) or spread fingers against resistance (dorsal interossei).
| Root | Landmark | Mnemonic / Tip |
|---|---|---|
| C5 | Lateral upper arm (deltoid area) | Same as axillary nerve sensory area |
| C6 | Thumb & radial forearm | “6-shooter thumb” |
| C7 | Middle finger | “7 = middle” (central digit) |
| C8 | Little finger & ulnar border of hand | Think “8 = pinky & ring” |
| T1 | Medial forearm/arm | Close to arm–chest junction |
Board pattern: C6 thumb, C7 middle, C8 little finger. If numbness fits this AND reflex matches → radiculopathy; if only hand area, think peripheral nerve.
| Root | Key Movement | Example Muscle | Reflex |
|---|---|---|---|
| L2 | Hip flexion | Iliopsoas | None reliable |
| L3 | Hip flexion, knee extension | Quadriceps | Patellar (L3–4) |
| L4 | Ankle dorsiflexion | Tibialis anterior | Patellar (L3–4) |
| L5 | Great toe extension, hip abduction | EHL, gluteus medius | None specific |
| S1 | Plantarflexion, eversion | Gastrocnemius, peroneus longus | Achilles (S1) |
Memory: “L4 to the floor” (dorsiflexion); “S1 = S-run” – push off, plantarflexion & Achilles reflex.
| Nerve | Roots | Key Muscle (Test) | Sensory Area | Classic Lesion |
|---|---|---|---|---|
| Femoral | L2–4 | Quadriceps – knee extension | Anterior thigh, medial leg (saphenous) | Retroperitoneal bleed, pelvic surgery; ↓ knee jerk |
| Obturator | L2–4 | Adductors – hip adduction | Medial thigh | Pelvic surgery, obturator canal lesions – gait instability |
| Sciatic | L4–S3 | Hamstrings – knee flexion | Back of thigh, splits into tibial & peroneal | Hip dislocation, injections too medial → sciatic neuropathy |
| Tibial | L4–S3 | Gastrocnemius, soleus – plantarflexion; toe flexors | Sole of foot (plantar) | Tarsal tunnel, popliteal lesions – difficulty toe-walking |
| Common fibular (peroneal) | L4–S2 |
Deep branch: tibialis anterior – dorsiflexion Superficial branch: peronei – eversion |
Dorsum of foot, lateral leg | Fibular head compression (“foot drop nerve”) |
| Superior gluteal | L4–S1 | Gluteus medius/minimus – hip abduction | No major cutaneous branch | Trendelenburg gait (pelvis drops opposite side) |
| Inferior gluteal | L5–S2 | Gluteus maximus – hip extension | No major cutaneous branch | Difficulty climbing stairs, rising from chair |
Memory: “DEEP fibular = DEEP space” (1st web space sensory); “SUPERficial fibular = SUPERficial dorsum” of foot.
Common fibular nerve is the most commonly injured lower limb nerve. Foot drop with preserved plantarflexion and inversion = fibular; if inversion also weak, think L5 radiculopathy.
| Root | Landmark | Tip |
|---|---|---|
| L1 | Inguinal region | “L1 = 1nguinal” |
| L2 | Upper anterior thigh | Proximal thigh |
| L3 | Medial knee | “3 on the knee” |
| L4 | Medial leg & medial malleolus | “L4 to the floor” – medial ankle |
| L5 | Dorsum of foot, great toe | Classic L5 radiculopathy spot |
| S1 | Lateral foot, little toe | “S1 = Small toe & Sole (lateral)” |
| S2 | Posterior thigh & calf | “S2 = back of leg too” |
| S3–5 | Perianal (“saddle” area) | Cauda equina / conus lesions |
Board pattern: L4 → medial ankle, L5 → dorsum & big toe, S1 → lateral foot/little toe, S3–5 → saddle anesthesia.
Saddle anesthesia + urinary retention = RED FLAG Cauda Equina/Conus. Needs urgent MRI and neurosurgical evaluation.
| Pattern | Key Findings | Localization |
|---|---|---|
| Wrist drop | Weak wrist/finger extension; triceps may be spared; sensory loss dorsum of hand | Radial neuropathy (spiral groove or PIN) |
| C7 radiculopathy | Weak triceps + wrist/finger extensors, ↓ triceps reflex, pain/numbness to middle finger | C7 root (disc at C6–7) |
| Carpal tunnel | Numbness in thumb–middle fingers, worse at night, thenar weakness (late) | Median neuropathy at wrist |
| Ulnar claw | Weak finger ab-/adduction, clawing of 4th/5th digits, sensory loss ulnar 1½ fingers | Ulnar neuropathy (elbow or wrist) |
| C8/T1 radiculopathy | Weak interossei, finger flexors, sensory loss medial forearm/hand; often neck pain | C8 or T1 roots (e.g., Pancoast tumor) |
Key distinction: Root lesions usually involve multiple nerves + reflex change + neck pain. Single nerve lesions follow a named nerve territory and may spare reflexes.
| Pattern | Key Findings | Localization |
|---|---|---|
| Foot drop – peroneal neuropathy |
Weak dorsiflexion & eversion Normal plantarflexion & inversion Sensory loss dorsum of foot/lateral leg Often from leg crossing, fibular head compression |
Common fibular nerve at fibular neck |
| Foot drop – L5 radiculopathy |
Weak dorsiflexion and inversion (tibialis anterior + posterior) Sensory loss lateral leg + dorsum foot, great toe May have back pain, positive straight-leg raise |
L5 root (e.g., L4–5 disc) |
| Femoral neuropathy |
Weak knee extension, ↓ patellar reflex Sensory loss anterior thigh/medial leg |
Femoral nerve (e.g., retroperitoneal bleed, pelvic surgery) |
| S1 radiculopathy |
Weak plantarflexion, ↓ Achilles reflex Sensory loss lateral foot/little toe |
S1 root (L5–S1 disc) |
Memory: If plantarflexion & Achilles are normal and only dorsiflexion is weak → more likely fibular nerve than L5 root.
Foot drop localization:
• Fibular nerve: foot drop, normal inversion & reflexes, local compression risk.
• L5 root: foot drop + weak inversion, +/- back pain, dermatomal sensory loss, reflexes often normal.
| Clinical Sign | Likely Localization |
|---|---|
| Shoulder abduction weakness + lateral shoulder numbness | Axillary nerve (C5–6) |
| Wrist/finger extension weakness (“wrist drop”) | Radial nerve (vs C7 radiculopathy if triceps/reflex involved) |
| Night numbness in thumb–middle finger, thenar atrophy | Median neuropathy at wrist (carpal tunnel) |
| Weak finger ab-/adduction, ulnar 1½ finger numbness | Ulnar nerve (elbow/wrist) |
| Knee extension weakness + ↓ patellar reflex | Femoral neuropathy or L3–4 root lesion |
| Positive Trendelenburg sign (pelvis drops opposite side) | Superior gluteal nerve (L4–S1) |
| Foot drop with preserved plantarflexion & inversion | Common fibular neuropathy |
| Saddle anesthesia + bladder dysfunction | Cauda equina / conus medullaris |
On RITE/boards, “pure motor + single nerve territory” = neuropathy; “motor + sensory + reflex + back/neck pain in dermatomal pattern” = radiculopathy. Use the myotome–dermatome–nerve triads above to localize fast.
