How do you assess for sciatica?

Assessment of Sciatica

Sciatica is diagnosed primarily through a focused history and physical examination that identifies radiating leg pain below the knee in a sciatic nerve distribution, combined with specific nerve root tension tests, particularly the straight leg raise (SLR) test. 1

Clinical History

Key Symptom Identification

• Pain distribution: The defining feature is lower limb pain radiating below the knee and into the foot and toes in the distribution of the sciatic nerve, suggesting nerve root compromise due to mechanical pressure or inflammation 1, 2
• Pain characteristics: Document the location, frequency, duration, and any history of previous symptoms and treatment responses 1

Red Flag Assessment

Immediately evaluate for conditions requiring urgent intervention:

• Cauda equina syndrome: Urinary retention (90% sensitivity), fecal incontinence, bilateral motor weakness, saddle anesthesia 1, 3
• Cancer risk factors: History of cancer (increases probability from 0.7% to 9%), unexplained weight loss, failure to improve after 1 month, age >50 years 1
• Infection indicators: Fever, IV drug use, recent spine procedures, immunosuppression 1
• Progressive neurologic deficits: Motor deficits at multiple levels, rapidly worsening symptoms 1

Physical Examination

Neurological Assessment by Nerve Root Level

Perform a systematic examination testing specific nerve root distributions 4, 5:

• L4 nerve root: Knee strength and knee reflexes
• L5 nerve root: Great toe and foot dorsiflexion strength
• S1 nerve root: Foot plantarflexion and ankle reflexes, sensory distribution

Nerve Root Tension Tests

Standard Straight Leg Raise (SLR) Test 4, 5:

• Flex the hip with knee extended to passively stretch the sciatic nerve
• Positive test: Reproduction of the patient's sciatica when leg is raised between 30-70 degrees
• Sensitivity: 91% (high—rules out sciatica if negative)
• Specificity: 26% (modest—many false positives)

Crossed SLR Test 4, 5:

• Pain reproduced when raising the unaffected leg
• Sensitivity: 29% (low—misses many cases)
• Specificity: 88% (high—strongly indicates disc herniation if positive)

Enhanced Testing for Improved Accuracy 6, 7:

• Bragard test: Add passive ankle dorsiflexion at end of SLR (more sensitive than standard SLR)
• Slump test: Performed sitting, slowly extend painful leg then passively bend neck
• Bowstring test: At end of SLR, flex knee slightly and press on peroneal/tibial nerves in popliteal fossa to reproduce exact pain
• These additional tests take <2 minutes and improve both sensitivity and specificity 6

Diagnostic Triage Classification

Place patients into one of three categories to guide management 1:

1. Nonspecific low back pain (>85% of cases)
2. Back pain with radiculopathy or spinal stenosis (sciatica with nerve root involvement)
3. Back pain with specific spinal cause (tumor, infection, cauda equina syndrome, fracture, ankylosing spondylitis)

Imaging Indications

Immediate Imaging (MRI Preferred) 4, 3, 5:

• Severe or progressive neurological deficits
• Suspected cauda equina syndrome
• Red flags for cancer, infection, or fracture
• Significant trauma

Delayed Imaging (After 4-6 Weeks) 4, 3, 2:

• Persistent sciatica without improvement despite conservative management
• Consideration of surgical intervention
• Persistent positive SLR test with functional limitations

Important caveat: Imaging may not correlate with symptoms in approximately 28% of cases—images showing pathology don't always explain the pain, and vice versa 8

Common Pitfalls to Avoid

• Don't rely solely on SLR: The test has only 52-91% sensitivity and decreases significantly with age, dropping below 50% in patients >60 years 4
• Don't confuse referred pain with radicular pain: Many patients and clinicians use "sciatica" to describe any leg pain, but true sciatica is nerve root pain radiating below the knee 9
• Don't ignore psychosocial factors: These are stronger predictors of outcomes than physical examination findings alone 3, 5
• Don't assume negative SLR rules out sciatica in older patients: Use additional tests (Slump, Bowstring, Bragard) to improve diagnostic accuracy 6, 7
• Don't order immediate imaging without red flags: The clinical course is generally favorable with most symptoms improving within 2-4 weeks 2, 9

Clinical Course Expectations

Most acute sciatica has a favorable natural history, with pain and disability improving within 2-4 weeks with or without treatment 2, 9. Conservative management is first-line for the initial 6-8 weeks unless red flags are present 9.