Musculoskeletal & Dermatology Command Center
High-yield upper and lower extremity peripheral nerve localization, brachial plexus injuries, inflammatory vs. degenerative arthritis and synovial fluid analysis, blistering dermatoses, cutaneous oncology, and metabolic bone diseases.
Upper Extremity Peripheral Nerve Palsies
| Nerve & Roots | Etiology / Mechanism of Injury | Motor Deficit / Classic Hand Sign | Sensory Territory | Board Pivot Point |
|---|---|---|---|---|
| Radial Nerve (C5–T1) | Midshaft humerus fracture, compression at spiral groove ("Saturday night palsy" / crutches). | WRIST DROP (loss of wrist, finger, and thumb extension; impaired brachioradialis reflex). | Posterior arm, forearm, and dorsal 1st web space of hand. | Accompanies the Deep Brachial Artery (profunda brachii) in the radial groove! |
| Median Nerve (C5–T1) | Supracondylar humerus fracture (proximal) or Carpal tunnel syndrome / lunate dislocation (distal). | Proximal: "Hand of Benediction" when making a fist; Distal: "Ape hand" (thenar atrophy, loss of thumb opposition). | Palmar surface of thumb, index, middle, and radial half of ring finger. | Supracondylar fracture with anterior displacement injures median nerve and brachial artery! |
| Ulnar Nerve (C8–T1) | Medial epicondyle fracture (proximal) or Hook of hamate fracture / Guyon canal compression (distal). | "ULNAR CLAW HAND" on attempting finger extension; loss of intrinsic interossei (cannot abduct/adduct fingers). | Medial 1.5 fingers (little finger and ulnar half of ring finger) and hypothenar eminence. | Ulnar Paradox: Distal lesion causes MORE pronounced clawing than proximal lesion due to intact flexor digitorum profundus! |
| Axillary Nerve (C5–C6) | Anterior shoulder dislocation or Fracture of surgical neck of humerus. | Weakness in shoulder abduction > 15° (deltoid) and external rotation (teres minor). | Skin over lateral deltoid ("regimental badge area"). | Accompanies the Posterior Circumflex Humeral Artery through the quadrangular space! |
| Musculocutaneous (C5–C7) | Upper trunk compression, shoulder trauma. | Loss of forearm flexion (biceps, brachialis) and supination; absent biceps reflex. | Lateral forearm (via lateral antebrachial cutaneous nerve). | Pierces the coracobrachialis muscle. |
Vulnerable Site: Winds superficial around the fibular neck; injured by fibular head fractures, blunt lateral knee trauma, or tight lower leg casts.
Motor Deficit: FOOT DROP (Steppage Gait)
Loss of dorsiflexion (deep peroneal → tibialis anterior) and eversion (superficial peroneal → fibularis longus/brevis). Foot is inverted and plantarflexed at rest. Loss of sensation over the dorsum of foot and 1st web space.
Vulnerable Site: Baker cyst in popliteal fossa, posterior knee dislocation, or entrapment in tarsal tunnel behind medial malleolus.
Motor Deficit: Inability to Curl Toes / Stand on Tiptoes
Loss of plantarflexion (gastrocnemius, soleus) and inversion (tibialis posterior). Foot is dorsiflexed and everted at rest. Loss of sensation over the sole of foot.
