A 35-year-old man is brought to the emergency department after diving into the shallow end… — USMLE Step 3

A 35-year-old man is brought to the emergency department after diving into the shallow end of a swimming pool and striking his head. He complains of severe posterior neck pain and bilateral upper extremity paresthesias. He is immobilized on a rigid backboard with a cervical collar. Vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $128/82 \text{ mmHg}$ , pulse $88/\text{min}$ , and respiratory rate $16/\text{min}$ . Neurological examination reveals $4/5$ motor strength in both upper extremities and $5/5$ strength in the lower extremities. There is decreased sensation to pinprick in the C5 and C6 dermatomes bilaterally. Deep tendon reflexes are $1+$ in the upper extremities and $2+$ in the lower extremities.

Arrange the following imaging modalities in the correct chronological sequence for the step-wise diagnostic evaluation of this patient's suspected cervical spine injury, from the initial emergency assessment to delayed stability testing.

1Non-contrast computed tomography (CT) of the cervical spine
2Magnetic resonance imaging (MRI) of the cervical spine without contrast
3Dynamic flexion-extension cervical spine radiographs

Answer

The correct sequence is: Non-contrast CT of the cervical spine, followed by MRI of the cervical spine, and finally Dynamic flexion-extension cervical spine radiographs.

The standard of care for evaluating suspected cervical spine injury with neurologic deficits begins with a non-contrast CT to rapidly exclude bony fractures. Because this patient has upper extremity paresthesias and weakness (highly suggestive of central cord syndrome, often from hyperextension during diving), an MRI is the immediate next step to evaluate the spinal cord parenchyma, discs, and ligaments. Finally, dynamic flexion-extension radiographs are reserved for delayed follow-up (usually 1-2 weeks later) to uncover hidden ligamentous instability once acute pain and muscle spasms have resolved.

Step-by-Step Solution

Perform non-contrast CT of the cervical spine.

Identifies or excludes acute bony fractures, subluxations, and gross malalignments.

CT is highly sensitive for bony injuries and is the primary screening modality in high-risk trauma patients to prevent catastrophic cord injury during subsequent patient manipulation.

Perform MRI of the cervical spine without contrast.

Evaluates soft tissue structures, including the spinal cord, nerve roots, intervertebral discs, and posterior ligamentous complex.

The patient has objective neurologic deficits (upper extremity weakness and paresthesias) suggesting a spinal cord injury (e.g., central cord syndrome) or acute disc herniation that cannot be visualized on a CT scan.

Perform dynamic flexion-extension cervical spine radiographs.

Assesses for latent or dynamic ligamentous instability.

This functional test requires the patient to actively flex and extend their neck. It must be delayed until acute muscle spasm subsides and unstable fractures are completely ruled out to avoid iatrogenic cord injury.

Key Concept

In high-risk cervical spine trauma, the imaging sequence progresses from rapid evaluation of bony stability (CT), to detailed assessment of soft tissue and cord integrity (MRI for neurologic deficits), and finally to functional stability testing (delayed dynamic radiographs).

Estimated Time:1m 30s

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