What causes arm weakness greater than leg weakness after blunt trauma?

Central Cord Syndrome from Spinal Cord Injury

Arms weaker than legs after blunt trauma is most commonly caused by central cord syndrome, a specific pattern of spinal cord injury that results from hyperextension mechanisms or direct cervical spine trauma, typically affecting the central gray matter and medial corticospinal tracts that control upper extremity function more than lower extremity function.

Mechanism of Injury

Central cord syndrome occurs through two primary mechanisms in blunt trauma:

• Hyperextension injury: The spinal cord is compressed between the vertebral body anteriorly and the ligamentum flavum posteriorly, with the central portion of the cord being most vulnerable to ischemic injury 1
• Direct compression: Cervical spine fractures, dislocations, or traumatic disc herniations can directly compress the central cord 1

The pattern of greater arm weakness than leg weakness results from the anatomic organization of the corticospinal tracts within the spinal cord, where fibers controlling the upper extremities are located more medially (centrally) than those controlling the lower extremities 1.

Clinical Presentation Pattern

The hallmark clinical features include:

• Disproportionate upper extremity weakness: Motor function is more severely impaired in the arms than the legs, often with the hands being most affected 1
• Variable sensory loss: Typically presents with a "cape-like" distribution of sensory impairment over the shoulders and upper arms, though this may be incomplete 1
• Bladder dysfunction: Often present due to involvement of central autonomic pathways 1

Associated Injury Patterns

Central cord syndrome in blunt trauma is strongly associated with:

• Cervical spine fractures or spinal cord injury: Found in 74% of patients with vertebral artery injuries, indicating the high frequency of cervical spine involvement in these mechanisms 2
• Skull base fractures: Present in a significant proportion of patients with blunt cerebrovascular injuries, suggesting severe cervical hyperextension forces 2
• Pre-existing cervical stenosis: Elderly patients with degenerative cervical spine disease are at higher risk even with relatively minor trauma 1

Critical Diagnostic Approach

Immediate cervical spine imaging with CT is mandatory when this pattern is identified, as the injury represents a neurological emergency requiring spine stabilization and potential surgical decompression 1.

• Maintain cervical spine immobilization until imaging excludes unstable fractures or dislocations 1
• MRI of the cervical spine should follow CT to evaluate for cord edema, hemorrhage, or ligamentous injury that may require surgical intervention 1
• Do not assume the weakness is from peripheral nerve injury or "stingers" without imaging, as this delay can worsen neurological outcomes 2

Common Pitfalls to Avoid

• Attributing symptoms to peripheral nerve injury: The bilateral nature and disproportionate arm-to-leg weakness pattern distinguishes central cord syndrome from brachial plexus injuries, which are typically unilateral 1
• Delaying imaging in "minor" trauma: Elderly patients with pre-existing stenosis can develop central cord syndrome from seemingly minor mechanisms 1
• Removing cervical immobilization prematurely: Even with normal CT, MRI may reveal ligamentous injury requiring continued immobilization 1

Prognosis and Recovery Pattern

Recovery typically follows a predictable sequence:

• Lower extremity function returns first, followed by bladder function, then proximal upper extremity function, with hand function recovering last 1
• Younger patients without pre-existing stenosis have better outcomes than elderly patients with degenerative changes 1
• Early surgical decompression may improve outcomes in patients with persistent cord compression, though optimal timing remains debated 1