Lasegue test (also called Straight Leg Raise Test (SLR) ) is used to assess the sciatic compromise due to lumbosacral nerve root irritation.
It is recognized as the first neural tissue tension test to appear in the literature. It was first described by Charles Lasègue 1.
The evaluation of the findings from the Lasegue Test (SLR) requires that the range of motion measured and the symptoms produced are compared with the contralateral side and with expected norms.
It is generally agreed that the first 30 degrees of the Straight Leg Raise Test serves to take up the slack or crimp in the sciatic nerve and its continuations. Using symptom reproduction below 40 degrees as a criterion for a positive Lasegue Test (SLR) test result has been found to increase the sensitivity to 72%.
Pain in the 0- to 30-degree range may indicate the presence of:
Lasegue Test is positive if:
The Lasegue Test has a high sensitivity for a low lumbar disc protrusion but has a low specificity 2:
This test is used to indicate the nerve root irritation.
The patient sits on the edge of the examining table and is asked to flex his or her hip with the leg extended at the knee.
This test corresponds to the Lasègue sign. When nerve root irritation is present, the patient will avoid the pain by leaning backward and using his or her arms for support. This test can also be used to identify simulated pain. If the patient can readily flex the hip without leaning backward, then a previous positive Lasègue sign must be questioned. The examiner can also perform this test in the same manner as the test for the Lasègue sign by passively flexing the hip with the knee extended.
For patients who have difficulty lying supine, a modified straight leg raise test in the lateral position is possible:
Between 30 and 70 degrees, the spinal nerves, their dural sleeves, and the roots of the L4, L5, S1, and S2 segments are stretched with an excursion of 2–6 mm. After 70 degrees, although these structures undergo further tension, other structures also become involved. These additional structures include the hamstrings, gluteus maximus, hip, lumbar, and sacroiliac joints.
Confounding the results from the Straight Leg Raise Test test are the nonneural structures such as the sacroiliac joint, lumbar zygapophyseal joints, hip joint, muscles (hamstrings), and connective tissue. These structures may limit leg elevation and provoke patient discomfort during testing.
The Straight Leg Raise Test test places a tensile stress on the sciatic nerve and exerts a caudal traction on the lumbosacral nerve roots from L4 to S2. During the Straight Leg Raise Test, the L4–L5 and S1–S2 nerve roots are tracked inferiorly and anteriorly, pulling the dura mater caudally, laterally, and anteriorly.
Tension in the sciatic nerve, and its continuations, occurs in a sequential manner developing:
The inferior and anterior pull on the nerve root, and the relative fixation of the dural investment at the anterior wall, produces a displacement that pulls the root against the posterior-lateral aspect of the disk and vertebra. In addition, any space-occupying lesions situated at the anterior wall of the vertebral canal at the fourth and fifth lumbar and first and second sacral segments may interfere with the dura mater or nerve root structures.
The following caveats are important for accurate assessment of the Straight Leg Raise Test:
The patient often attempts to avoid the pain by lifting the pelvis on the side being examined. The angle achieved when lifting the leg is estimated in degrees. This angle gives an indication of severity of the nerve root irritation present (genuine Lasegue test is at 60° or less).
Sciatica can also be provoked by adducting and internally rotating the leg with the knee flexed. This test is also described as a Bonnet or piriformis sign (adduction and internal rotation of the leg stretches the nerve as it passes through the piriformis).
Increases in sciatic pain on raising the head (Kernig sign) and/or passive dorsi-flexion of the great toes (Turyn sign) are further signs of significant sciatic nerve irritation (differential diagnosis should consider meningitis, subarachnoid hemorrhage, and carcinomatous meningitis).
Sacral or lumbar pain that increases only slowly as the leg is raised or pain radiating into the posterior thigh is usually attributable to degenerative joint disease (facet syndrome), irritation of the pelvic ligaments (tendinitis), or increased tension or shortening in the hamstrings (indicated by a soft end point, usually also found on the contralateral side). It is important to distinguish this “pseudo-radicular” pain (pseudo-Lasègue sign) from genuine sciatica (true Lasegue test).
If one leg is lifted and pain occurs on the opposite side, it suggests a herniated disk or a tumor. This may be called the Crossed Over Lasegue sign and usually indicates a rather large medial intervertebral disk protrusion.
Disk extrusions usually lead to nerve compression syndromes with radicular pain. The pain in the sacrum and leg is often exacerbated by coughing, sneezing, pushing, or even simply walking. Mobility in the spine is severely limited by pain, and there is signifficant tension in the lumbar musculature. Sensory and motor deficits and impaired reflexes are additional symptoms that occur with nerve root com pression.
Often the affected nerve root can be identified by the description of the paresthesia and radiating pain in the dermatome. Extrusions of the fourth and fifth lumbar disks are especially common, while extrusions of the third lumbar
disk are less so. Disk extrusions involving the first and second lumbar disks are rare.
The Lasegue sign is usually positive (often even at 20–30°) in compression of the L5–S1 nerve root (typical sciatica). In these cases, even passively raising the normal leg will often elicit or exacerbate pain in the lower back and the affected leg (crossed Lasegue sign). In nerve root compression syndromes from L1 through L4 with involvement of the femoral nerve, the Lasègue sign is usually only slightly positive.
When the femoral nerve is irritated, the reverse Lasègue sign and/or pain from stretching of the femoral nerve can usually be triggered.
Pseudo-radicular pain must be distinguished from genuine radicular pain (sciatica). Pseudo-radicular pain is usually less circumscribed than radicular pain. Facet syndrome (arthritis in the facet joints), sacroiliac joint syndrome, painful spondylolisthesis, stenosis of the spinal canal, and postdiskectomy syndrome are clinical pictures that frequently cause pseudo-radicular pain.
Neurodynamic testing is used to evaluate the mechanical extensibility and/or compression of neural structures of the lumbar spine. These tests include the slump test, the Lasègue test (straight leg raising), the reverse Lasègue test, and the femoral nerve traction test.