The Straight Leg Test (SLT), sometimes called the Lasegue sign, is a common physical examination technique used to assess patients with low back pain and symptoms radiating into the leg. This maneuver evaluates potential irritation or compression of the nerves that form the sciatic nerve pathway. The test is a fundamental part of the neurological examination for patients suspected of having radiculopathy, which is pain caused by a compressed nerve root in the spine.
The Purpose of the Straight Leg Test
The Straight Leg Test is categorized as a neurodynamic test, meaning it mechanically stresses the nervous system to see if symptoms are reproduced. It aims to place tension on the spinal cord and the lumbosacral nerve roots (L4, L5, S1, and S2), which contribute to the sciatic nerve. The test works by leveraging the anatomical connection between the lower spinal nerves and the leg. As the leg is raised, the sciatic nerve and its roots are stretched, pulling on the spinal structures.
This mechanical tension is designed to reproduce the patient’s existing pain, numbness, or tingling if a nerve root is compressed or inflamed. Normally, nerve roots have a small amount of space to move, but conditions like a herniated disc can reduce this excursion. The added stretch from the test causes a sudden increase in symptoms if the nerve is irritated. The goal is to determine if the movement causes pain that radiates down the leg, typical of a compromised nerve root, rather than just hamstring tightness.
How the Test is Performed
The Straight Leg Test is performed with the patient lying flat on their back, a position known as supine. The examiner gently raises the affected leg toward the ceiling, ensuring the patient’s knee remains completely straight and extended. The hip is passively flexed until the patient reports the onset of pain or discomfort. The examiner notes the exact angle of hip flexion at which the radiating symptoms begin.
During the procedure, the clinician ensures the patient’s pelvis and lower back do not rise from the table, as this compensatory movement could invalidate the result. Documenting the precise angle is important, as this detail helps distinguish between nerve root compression and simple hamstring tightness. The test may be modified by flexing the patient’s foot upward (dorsiflexion) or having the patient flex their neck, which adds further stretch to the nerve roots and can increase the test’s sensitivity. Both legs are typically tested, starting with the unaffected side, to establish a baseline range of motion.
Understanding the Results
The clinical interpretation of the Straight Leg Test hinges on the type of pain produced and the angle at which it occurs. A positive SLT is specifically defined by the reproduction of the patient’s radiating leg pain or neurological symptoms, not just pain felt in the lower back or hamstring tightness. When this radiating pain occurs between 30 and 70 degrees of leg elevation, it is strongly suggestive of lumbosacral nerve root irritation, most commonly due to a lumbar disc herniation. This range is significant because it is when the tension on the nerve roots is maximized.
Conversely, a negative SLT means the patient may feel normal tightness in the hamstring muscle or pain only in the back, but the characteristic radiating pain down the leg is not reproduced. If symptoms occur at an angle greater than 70 degrees, the pain is more likely related to joint issues or muscular tightness in the hamstring or gluteal region, rather than a significant nerve root compression. A highly specific finding is a positive “crossed” SLT, where raising the unaffected leg reproduces the pain in the symptomatic leg, which is a strong indicator of a large central disc herniation. While the test is highly sensitive for detecting nerve root problems, its results must be considered alongside the patient’s history and other physical examination findings for an accurate diagnosis.