Interpreting a Positive Straight Leg Test
To understand the source of a patient’s low back pain, one important tool in a doctor’s arsenal is the Straight Leg Raise test (also known as the Lasègue test or Lazarević’s sign). This classic test has been used since the late 19th century to look for sciatic nerve sensitivity and related spinal cord and disc troubles.
How is a Straight Leg Raise test performed?
The easiest and most effective way to perform a Straight Leg Raise test is to start with the patient lying on their back on the examination table or on the floor without a pillow under their head. The test is passive, meaning the patient relaxes while letting the examiner perform the work—the patient does not raise their own legs. Speicalized physical therapy products are not needed for this test.
Each leg is examined individually, starting with the unaffected leg, the leg that is not experiencing symptoms. The examiner lifts the leg with one hand under the heel, keeping the other hand on the thigh so that the leg remains straight. The leg is moved through its arc, hingeing at the hip, until the patient notes tightness or pain in the back of the leg or the back.
Starting with the leg that is unaffected by pain will provide a helpful baseline so the examiner will know what is normal for the patient before testing the second leg.
Possible results break down like this:
- No pain, tightness, or limitation is considered a negative result (although disc protrusion or internal derangement remains a possibility)
- Pain but no limitation in the range of movement
- A reproducible, painful arc at specific degrees of movement
- Painful and limited range of movement
- No pain, no limitation, but neurological deficits occur outside the test
Interpreting Positive Straight Leg Test Results
A positive result of the test is noted when the patient experiences pain in the back or the back of the leg during testing.
Patients who report back pain during the Straight Leg Raise test are likely being affected by a disc herniation, which is applying undue pressure on the spinal cord. Disc herniation could cause pain to radiate into the leg as well.
Patients who report pain primarily in the leg, but not the back, are more likely to be experiencing pressure on the nerve outside of the spinal column, laterally in the leg itself.
Pain that occurs in the leg and back when the leg is raised to between 30 and 70 degrees of flexion suggests lumbar disc herniation at the nerve roots between the fourth lumbar and first sacral discs.
Possible causes of pain when the leg is raised at less than 30 degrees of flexion include acute spondyloithesis, disc protrusion or extrusion, or even a tumor of the buttock.
When pain occurs only at greater than 70 degrees of flexion, possibilities include pathology of the hip capsule, hip, or sacroiliac joints, or simple tightness of the hamstrings or gluteus.
Additional Testing Can Reveal More
After the initial exam reveals symptoms of either back or leg pain, the test can be performed again in a similar manner, but this time with the patient tucking their chin toward their chest, and/or with the examiner dorsiflexing the foot. There are three possible reactions to these modified tests:
- Less pain
- More pain
- No change in pain
Pain that increases with this neck flexion or foot dorsiflexion indicates a possible problem within the spinal cord, such as herniation, tumor, or meningitis.
Pain that does not increase with the chin tucked hints that the trouble is in the hamstring area or in the lumbosacral or sacro-iliac joint.