Spinal Cord Injury

A C4 injury and a T10 injury both damage the spinal cord — but one patient needs a ventilator and the other walks into rehab. The level changes everything.

Spinal cord injury (SCI) level determines what the patient can and cannot do. The key landmark is C4 — the phrenic nerve originates at C3-C5, so complete injuries at C3 or above eliminate diaphragmatic breathing; C4 injuries may have partial or absent diaphragm function and often require ventilatory support. C5 injuries spare the diaphragm but lose hand and trunk function; the patient can flex the elbow (biceps) but cannot extend the wrist. C6 adds wrist extension, C7 adds elbow extension (triceps), and C8-T1 restores hand grip. Thoracic-level injuries preserve upper extremity function entirely; the patient is paraplegic rather than quadriplegic. T1-T6 injuries lose intercostal muscle control and have impaired cough; T6-T12 injuries retain more trunk stability. Lumbar injuries affect the lower extremities with variable motor and sensory loss. Complete versus incomplete injury matters: complete SCI means no motor or sensory function below the level; incomplete injuries (e.g., Brown-Séquard, anterior cord, central cord syndromes) preserve partial function in predictable patterns. Sensory dermatome landmarks help localize the level: C6 = thumb, T4 = nipple line, T10 = umbilicus, L1 = groin.

Key Distinctions

Don't confuse paraplegia (thoracic/lumbar — lower extremities only) with quadriplegia/tetraplegia (cervical — all four extremities). Students mix up neurogenic shock (a sibling atom covering hemodynamic collapse from lost sympathetic tone) with the functional motor-sensory deficits taught here. Central cord syndrome spares lower extremities more than upper — the opposite of what students expect.

Clinical Pearl

C3-4-5 keeps the diaphragm alive. If the injury is at or above C4, plan for a ventilator — breathing depends on that phrenic nerve.