L5 Nerve Root Impingement: Work-up and Treatment
For suspected L5 nerve root impingement, obtain MRI lumbar spine without IV contrast if the patient has failed 6 weeks of conservative therapy and is a potential candidate for surgery or epidural steroid injection. 1
Initial Clinical Evaluation
Perform a focused neurologic examination specifically assessing:
- Great toe and foot dorsiflexion strength (L5 nerve root motor function) 1
- Straight-leg-raise test between 30-70 degrees of leg elevation (91% sensitivity but only 26% specificity for disc herniation) 1
- Crossed straight-leg-raise test (more specific at 88% but less sensitive at 29%) 1
- Distribution of sensory symptoms in the L5 dermatome 1
The straight-leg-raise test has high sensitivity but modest specificity, meaning a positive test supports the diagnosis but a negative test does not rule it out. 1
Red Flag Assessment
Immediately evaluate for cauda equina syndrome if any of the following are present:
- Urinary retention (90% sensitivity for cauda equina syndrome) 1
- Fecal incontinence 1
- Saddle anesthesia 1
- Progressive motor deficits at multiple levels 1
If cauda equina syndrome is suspected, obtain urgent MRI lumbar spine without IV contrast immediately—do not wait for conservative therapy. 1
Imaging Strategy
When to Image
Do NOT obtain imaging initially unless red flags are present. 1
Obtain MRI lumbar spine without IV contrast only after:
- 6 weeks of conservative management has failed, AND
- Patient has persistent radiculopathy with physical examination signs of nerve root irritation, AND
- Patient is a potential candidate for surgery or epidural steroid injection 1
Why MRI is Preferred
MRI without contrast is the imaging modality of choice because:
- It correctly predicts the lesion causing radiculopathy in 88% of surgically confirmed cases 2, 3
- CT alone identifies the correct lesion in only 50% of cases 2, 3
- CT myelography achieves 81% accuracy 2, 3
- MRI provides superior soft-tissue visualization of discs, nerve roots, spinal cord, and ligaments 1, 2, 3
When to Use Alternative Imaging
CT lumbar spine without contrast should be reserved for:
- Detailed bony anatomy assessment (osteophytes, ossification) 2
- Surgical planning requiring osseous detail 2
CT myelography is appropriate when:
- MRI is contraindicated (pacemakers, cochlear implants) 2, 3
- MRI is nondiagnostic or severely limited by artifact 2, 3
- Patient has severe claustrophobia 2, 3
Critical Imaging Pitfall
Do not rely on imaging findings alone. Disc abnormalities are common in asymptomatic patients—57% of symptomatic patients with low back pain and 65% with radiculopathy have disc herniation, but 20-28% of asymptomatic individuals also show herniation on imaging. 1 The clinical examination must correlate with imaging findings before proceeding with invasive interventions. 1, 2, 3
Conservative Management (First 6 Weeks)
Advise patients to remain active rather than bed rest, as activity is more effective for acute and subacute low back pain. 1
Provide evidence-based information that:
- Most patients with lumbar disc herniation and radiculopathy improve within the first 4 weeks with noninvasive management 1
- The natural history is favorable with high likelihood of substantial improvement in the first month 1
When to Consider Invasive Intervention
Surgery or epidural steroid injection should be considered only if:
- Conservative therapy for 6 weeks has failed 1
- MRI confirms nerve root compression that correlates with clinical symptoms 1
- Patient preferences, surgical risks, and comorbid conditions have been assessed 1
More than 90% of symptomatic lumbar disc herniations occur at L4/L5 and L5/S1 levels, making L5 nerve root impingement one of the most common radiculopathies. 1
Psychosocial Factors
Assess psychosocial factors and emotional distress, as these are stronger predictors of low back pain outcomes than physical examination findings or pain severity. 1 Identifying patients with risk factors for delayed recovery may help target more intensive interventions. 1