This is a test for lumbosacral nerve root irritation for example, due to disc prolapse.
With the patient laid on their back:
Severe root irritation is indicated when straight raising of the leg on the unaffected side produces pain on the affected side. A central disc prolapse is likely with risk to the cauda equina and consequently, of bladder dysfunction.
Pain upon straight leg raising before the leg is raised 30 degrees cannot be due to disc prolapse as the nerve root is not stretched within this range. Another explanation of nerve root irritation must then be sought.
Lasègue's sign is said to be positive if the angle to which the leg can be raised (upon straight leg raising) before eliciting pain is <45°.
Last edited 11/2018 and last reviewed 11/2018