What does the straight leg raise (SLR) test diagnose?

Straight Leg Raise Test: Diagnostic Purpose and Interpretation

The straight leg raise (SLR) test primarily diagnoses lumbar disc herniation with nerve root compression, with high sensitivity (91%) but modest specificity (26%) for this condition. 1

How the Test Works

• The SLR test is performed by passively raising the patient's leg with the knee extended, which stretches the sciatic nerve and associated nerve roots 1
• A positive test is defined as reproduction of the patient's sciatica (radiating leg pain) when the leg is raised between 30-70 degrees 1
• The test works by creating tension on the lumbosacral nerve roots, particularly at L4/L5 and L5/S1 levels where 90% of symptomatic disc herniations occur 1

Diagnostic Value

• Sensitivity and Specificity:

  • Traditional SLR has high sensitivity (91%) but limited specificity (26%) for diagnosing herniated disc 1
  • The crossed straight-leg-raise test (pain produced when raising the unaffected leg) is more specific (88%) but less sensitive (29%) 1
  • The SLR test becomes less accurate in older patients, with discriminative power decreasing with age 2

• Clinical Applications:

  • Most useful for identifying nerve root compression from disc herniation that may require surgical intervention 3
  • Should be combined with a focused neurological examination that includes evaluation of:
    • Knee strength and reflexes (L4 nerve root)
    • Great toe and foot dorsiflexion strength (L5 nerve root)
    • Foot plantarflexion and ankle reflexes (S1 nerve root)
    • Distribution of sensory symptoms 1, 4

Enhanced Testing Techniques

• Structural Differentiation:
  • Adding hip internal rotation or ankle dorsiflexion to the standard SLR (Extended SLR) improves diagnostic ability by further tensioning the sciatic nerve 5
  • The Slump test (a seated variant of SLR) shows higher sensitivity (84% vs 52%) but slightly lower specificity (83% vs 89%) compared to traditional SLR 3
  • There is substantial agreement between SLR and Slump test results (kappa = 0.69) with good correlation in range of motion (r = 0.64) 6

Clinical Decision Making

• When to Order Imaging:

  • Immediate imaging (preferably MRI) is indicated when a positive SLR is accompanied by:
    • Severe or progressive neurological deficits
    • Suspected cauda equina syndrome (urinary retention has 90% sensitivity)
    • Red flags for cancer, infection, or vertebral compression fracture 4
  • Delayed imaging (after 4-6 weeks) is appropriate for persistent sciatica without improvement 4

• Management Implications:

  • A positive crossed SLR sign predicts poor response to conservative management but good surgical outcomes, with 91% of patients returning to work after laminectomy 7
  • Most patients with positive SLR without red flags should initially receive conservative management 4

Common Pitfalls

• Psychosocial factors are stronger predictors of low back pain outcomes than physical examination findings or pain severity/duration 1
• The SLR test should not be used in isolation but as part of a comprehensive assessment 4
• In obstetric settings, straight-leg raising is used as a screening method to assess motor block recovery after neuraxial anesthesia 1