## Distinguishing Upper vs Lower Trunk Injuries ### Upper Trunk (Erb's Palsy) — C5–C6 **Key Point:** Upper trunk injury affects muscles innervated by suprascapular and axillary nerves, resulting in loss of shoulder and proximal arm function. - **Motor loss:** Shoulder abduction (supraspinatus), external rotation (infraspinatus), elbow flexion (musculocutaneous), and forearm supination - **Clinical presentation:** Arm hangs at side in adduction and internal rotation ("waiter's tip" position when attempting to lift) - **Hand function:** Preserved — intrinsic muscles and grip remain intact ### Lower Trunk (Klumpke's Palsy) — C8–T1 **Key Point:** Lower trunk injury affects ulnar and medial nerve branches, resulting in loss of hand and intrinsic muscle function. - **Motor loss:** Wrist flexion, finger flexion, and intrinsic hand muscles (lumbricals, interossei) - **Clinical presentation:** Claw hand deformity (hyperextension at MCP, flexion at IP joints) - **Sensory loss:** Medial forearm and hand (ulnar distribution) ### Comparison Table | Feature | Upper Trunk (Erb's) | Lower Trunk (Klumpke's) | |---------|---------------------|------------------------| | **Nerve roots** | C5–C6 | C8–T1 | | **Shoulder abduction** | Lost | Preserved | | **Elbow flexion** | Lost | Preserved | | **Hand grip** | Preserved | Lost | | **Intrinsic muscles** | Intact | Paralyzed | | **Claw hand** | Absent | Present | | **Sensory loss** | Lateral arm/forearm | Medial forearm/hand | **High-Yield:** Option B correctly identifies the **preserved hand grip with loss of shoulder abduction and external rotation** — the hallmark discriminator of upper trunk injury. This is the most commonly tested distinction in NEET PG. **Clinical Pearl:** In obstetric brachial plexus injuries (birth trauma), Erb's palsy (upper trunk) accounts for ~85% of cases and is less severe; Klumpke's palsy is rare (~1%) and carries worse prognosis. 
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