Straight Leg Raise and Nerve Tension Signs
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Direct answer
The straight leg raise test is a provocative examination for lumbosacral nerve root tension, done by flexing the hip with the knee extended. A positive test reproduces sciatic pain below the knee, typically between about 30 and 70 degrees, pointing to L5 or S1 root irritation, most often from disc herniation. It is sensitive but not specific, so the crossed and femoral stretch variants help confirm the level.
What you must remember
- Lasegue sign: the ipsilateral straight leg raise, with sciatic pain reproduced below the knee between about 30 and 70 degrees.
- Crossed SLR: raising the unaffected leg reproduces pain in the affected leg, a finding highly specific for a large medial disc herniation.
- Femoral nerve stretch: performed prone with the knee flexed and the hip extended; anterior thigh pain indicates irritation of the L2 to L4 roots.
- Bragard sign: ankle dorsiflexion added during the straight leg raise intensifies sciatic pain, confirming neural rather than muscular origin.
- Sensitivity: the straight leg raise is sensitive for lumbar root pathology but nonspecific, so a positive result alone does not prove herniation.
- Sciatic root levels: the sciatic nerve carries the L4 to S3 roots, with L5 and S1 most commonly involved in lumbar disc disease.
- Hamstring tightness: gives stretch pain at the back of the thigh that is not reproduced by dorsiflexion as neural tension is.
A right-leg pain assessment, step by step
A 42-year-old man has right buttock and calf pain after lifting, with a normal knee examination. The sequence of tests localises the root and separates neural tension from hamstring tightness before imaging is ordered.
- Perform the straight leg raise: passively flex the hip with the knee extended, noting the angle at which sciatic pain begins and whether it is reproduced below the knee.
- Add ankle dorsiflexion: if dorsiflexion intensifies the pain at a lower angle, the sciatic nerve is the source rather than the hamstrings.
- Test the crossed SLR: if raising the unaffected leg reproduces the pain in the affected leg, a large disc herniation is likely.
- Perform the femoral stretch: prone knee flexion with hip extension; anterior thigh pain suggests upper lumbar root irritation at L2 to L4.
- Check the neurology: reflexes, power and sensation at each myotome and dermatome confirm which root is affected.
- Image the level: MRI of the lumbar spine is ordered when findings persist or a motor deficit is present.
Traps in nerve tension testing
Examiners test whether you can localise the root with the right test and avoid overreading a single sign.
- Trap: taking a positive straight leg raise as proof of disc herniation. Correct: the test is sensitive but nonspecific, so the level and neurology must be confirmed.
- Trap: mistaking hamstring tightness for sciatic tension. Correct: the Bragard sign and the distribution of pain help separate neural from muscular causes.
- Trap: using the straight leg raise to localise upper lumbar roots. Correct: the femoral stretch test is the test for the L2 to L4 roots.
Frequently asked questions
What is the difference between the Lasegue sign and the crossed straight leg raise?
The Lasegue sign is the ipsilateral straight leg raise, in which sciatic pain is reproduced below the knee on elevating the symptomatic leg. The crossed straight leg raise reproduces pain on elevating the unaffected leg and is highly specific for a large disc herniation.
What does a positive femoral nerve stretch test indicate?
A positive femoral nerve stretch test, with anterior thigh pain on prone knee flexion and hip extension, indicates irritation of the upper lumbar roots from L2 to L4. It is distinct from the sciatic straight leg raise and localises the lesion to a higher level.
How does the Bragard sign help in straight leg raise testing?
The Bragard sign is ankle dorsiflexion performed during the straight leg raise, and it intensifies sciatic pain when neural tension is the cause. Hamstring tightness does not produce this change, which helps separate a neural from a muscular source of symptoms.
Which nerve roots does the straight leg raise test assess?
The straight leg raise test assesses the sciatic nerve, which carries the L4 to S3 roots, with L5 and S1 most commonly involved in lumbar disc disease. It is therefore a test of lumbosacral root tension rather than of the upper lumbar levels.
Is a positive straight leg raise enough to diagnose a lumbar disc herniation?
No, a positive straight leg raise is sensitive but nonspecific, so it does not by itself prove a lumbar disc herniation. Confirmation requires a neurological examination of the involved root and MRI of the lumbar spine where findings persist.