Classification of Neurological Deficits in L5 Fractures
The American Spinal Injury Association (ASIA) Impairment Scale is the most reliable and valid classification system for assessing neurological deficits in patients with L5 fractures, providing consistent information between different care providers and predicting outcomes based on entry grade, sacral sensation, sphincter function, and specific motor functions. 1, 2
Recommended Classification Systems
Primary Classification Tool: ASIA Impairment Scale
- Grade A: Complete injury - No motor or sensory function preserved in sacral segments S4-S5
- Grade B: Incomplete injury - Sensory but not motor function preserved below neurological level including S4-S5
- Grade C: Incomplete injury - Motor function preserved below neurological level, with more than half of key muscles below level having muscle grade less than 3
- Grade D: Incomplete injury - Motor function preserved below neurological level, with at least half of key muscles below level having muscle grade of 3 or more
- Grade E: Normal - Motor and sensory function normal
Alternative Classification Systems
- Frankel Scale: Shows high inter-rater reliability (94-100%) in thoracolumbar fractures 1
- Sunnybrook Cord Injury Scale: Demonstrates good reliability but slightly lower inter-rater agreement than Frankel scale 1
- Functional Independence Measure (FIM): Useful for assessing functional outcomes
Specific Neurological Assessment for L5 Fractures
Motor Assessment
- L5 myotome evaluation: Hip abduction, knee flexion, ankle dorsiflexion, great toe extension, foot inversion
- Abductor hallucis (AbH) motor function: Critical predictor of neurological outcomes in L5 injuries 1
Sensory Assessment
- L5 dermatome: Lateral leg, dorsum of foot, first three toes
- Sacral sensation: Particularly important as a positive prognostic indicator 2
- Perineal pinprick sensation: Absence predicts poor bladder recovery 1
Autonomic Function Assessment
- Urethral and rectal sphincter function: Voluntary control correlates significantly with bladder recovery (p < 0.01) 1
- Ankle spasticity: Highly accurate predictor of neurogenic bladder dysfunction in thoracolumbar injuries 1, 2
Prognostic Factors in L5 Fractures
Positive Prognostic Indicators
- Sacral sparing: Preservation of sensation in sacral segments suggests incomplete injury with better recovery potential 2
- Voluntary sphincter contraction: Strong predictor of bladder function recovery 1
- L5 level injury: Better neurological recovery compared to higher thoracic injuries due to higher concentration of lower motor neurons and potential for "root escape" 1
Negative Prognostic Indicators
- Absence of perineal pinprick sensation: Predicts poor bladder recovery 1
- Complete neurological deficit (ASIA A): Poorest prognosis for recovery 1
Clinical Pearls and Pitfalls
Important Considerations
- Anatomic level of injury based on neurological examination is a better predictor of recovery than radiological fracture location 1, 2
- L5 burst fractures with neurological deficits have promising prognosis after surgical intervention 3
- Neurological deficits in L5 fractures do not necessarily correlate with the degree of canal stenosis 3
Common Pitfalls
- Initial neurological assessment may be unreliable due to factors such as cognitive impairment, intoxication, concomitant head injury, or neurogenic shock 2
- Both Frankel and Sunnybrook scales may be insensitive to significant recovery in motor, sensory, bladder, or walking functions without showing scale changes 1
- Delayed diagnosis of neurological deficits can lead to permanent neurological damage 1
By using the ASIA Impairment Scale as the primary classification system and considering specific prognostic factors like sacral sensation and sphincter function, clinicians can accurately assess neurological deficits in L5 fractures and better predict outcomes for these patients.