What does a straight leg raise (SLR) indicate?

The Straight Leg Raise Test: Diagnostic Significance and Clinical Utility

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

Mechanism and Proper Technique

The SLR test is performed by:

• Flexing the hip with the knee extended
• Passively stretching the sciatic nerve
• Observing for reproduction of the patient's sciatica

A positive test is defined as reproduction of the patient's sciatica when the leg is raised between 30 and 70 degrees of elevation. 1

Diagnostic Value

For Lumbar Disc Herniation

• Sensitivity: 91% (95% CI, 82% to 94%)
• Specificity: 26% (95% CI, 16% to 38%) 1
• Age significantly affects test results - younger patients show higher rates of positive SLR:
  • 100% positive in 10-19 years age group
  • 87% positive in 20-29 years age group
  • Positivity decreases with advancing age 2

Crossed Straight Leg Raise Test

• When the unaffected leg is raised and reproduces sciatica in the affected leg
• Specificity: 88% (95% CI, 86% to 90%)
• Sensitivity: 29% (95% CI, 24% to 34%) 1
• Associated with herniated lumbar disc in 97% of patients 3

Clinical Applications

1. Diagnostic Tool:

   • Primary screening test for lumbar disc herniation
   • Most commonly used for patients with sciatica 4
   • Most effective for L4/L5 and L5/S1 herniations (which comprise 90% of symptomatic disc herniations) 1

2. Monitoring Tool:

   • Used to monitor neurological status after neuraxial anesthesia
   • Recommended as a screening method to assess motor block recovery 1
   • Ability to straight-leg raise (lifting heel off bed against gravity) indicates adequate neurological recovery 1

Limitations and Pitfalls

• Diagnostic accuracy decreases with age (AUC decreases from 0.730 in 16-25 year olds to 0.515 in 76-85 year olds) 5
• May be negative despite radicular pain due to LDH, particularly in older patients 2
• Lower accuracy compared to MRI for diagnosing lumbar disc herniation 5
• Gender differences exist: positive SLR is 1.3 times more likely in men than women 2

Enhanced Testing Methods

To improve diagnostic accuracy, consider:

• Adding hip internal rotation or ankle dorsiflexion to the standard SLR (Extended SLR)
• Using the Slump test (seated variant of SLR) which has higher sensitivity (84% vs 52%) but slightly lower specificity (83% vs 89%) than standard SLR 4

Clinical Decision-Making Algorithm

1. Perform standard SLR test
2. If positive: High suspicion for disc herniation (especially in younger patients)
3. If negative but clinical suspicion remains high:
   • Perform crossed SLR (higher specificity)
   • Consider Slump test (higher sensitivity)
   • Evaluate for other neurological signs
4. Consider patient age when interpreting results (lower reliability in older patients)
5. Correlate with other clinical findings and imaging when necessary

The SLR test remains a valuable clinical tool for diagnosing nerve root compression, particularly from disc herniation, but must be interpreted in the context of the patient's age and overall clinical presentation.