With patient supine, raise afflicted limb by the ankle until the pain is elicited 1) (should occur at < 60°, tension in nerve increases little above this angle). A positive test consists of leg pain or paresthesias in the distribution of pain (back pain alone does not qualify). The patient may also extend the hip (by lifting it off table) to reduce the angle. Although not part of Lasègue’s sign, ankle dorsiflexion with SLR usually augments pain due to nerve root compression. SLR primarily tenses L5 and S1, L4 less so, and more proximal roots very little. Nerve-root compression produces a positive Lasègue’s sign in ≈ 83% of cases 2) (more likely to be positive in patients < 30 yrs of age with HLD 3)). May be positive in lumbosacral plexopathy. Note: flexing both thighs with the knees extended (“long-sitting” or sitting knee extension) may be tolerated further than flexing the single symptomatic side alone
In 1864 Lasègue described the signs of developing low back pain while straightening the knee when the leg has already been lifted. In 1880 Serbian doctor Laza Lazarević described the straight leg raise test as it is used today, so the sign is often named Lazarević's sign in Serbia and some other countries.