Lasegue sign or Straight Leg Raising Test (SLRT) is a neurodynamic exam to assess nerve root irritation in the lumbosacral area. It is an integral element to the neurological exam for patients presenting with low back pain with or without radicular pain. The other less commonly used name is Lazarevic sign.
Traditionally, Ernest-Charles Lasegue (1816-1883) is considered the first physician who verbally described this sign and emphasized its importance in patients with sciatica. Albeit, he did not write it in his publications. Publication of the sign was by one of Lasegue's students, JJ Forst, who described it in his doctoral thesis titled Contribuition a l’etude Clinique de la Sciatique in 1881. Both Lasegue and Forst proposed that the sharp pain elicited by the test was due to compression of the sciatic nerve by muscular contraction. Historically, Lazarevic (1851-1891) was the first physician who published this sign in 1880 with a sound pathophysiological explanation. The latter suggested sciatic nerve stretching as the cause of pain while doing the test. His explanation had backing by Lucien de Beurmann cadaveric experiment in 1884. Then several modifications were introduced to SLRT, and different methods were implemented to provoke pain in irritated nerve roots. These modifications intended to improve SLRT accuracy and some other tests could be complementary. Of note, although there is no general agreement on interpreting the results of SLRT and its variants, performing a combination of tests can enhance their accuracy.
Anatomy Related to SLRT
In the lumbar region, the nerve roots cross the intervertebral disc above neural foramina through which they exit. The neural foramen is bounded by the pedicle superiorly, ligamentum flavum posteriorly, and the vertebral body with disc anteriorly. Within the neural foramen, the nerve root is surrounded by loose areolar tissue and lightly tethered to adjacent solid structures. This arrangement allows the nerve roots some room for movement while the limbs move. In other words, in normal conditions, there is a slack nerve root pathway within the foramen. The normal average excursion of lumbosacral nerve roots is about 4 to 6 mm, which decreases with age. This range of motion grants normal individuals a greater degree of hip flexion (with an extended knee) than patients with nerve root irritation, lumbar disc prolapse for instance. In the case of disc prolapse, the already existed slack nerve root pathway is taken up by the pathology. The loss of nerve root movement is mainly due to adhesion secondary to the local inflammation and could be due to mechanical compromise as well. Both mechanisms work together to reduce the SLR angle. During SLRT, first the tension, and then the movement appears distally followed by proximally, along the course of sciatic nerve and nerve roots as the hip is flexed.
Causes of Pain While Performing SLRT
Causes of Positive SLRT
Patient positioning is supine for this test. The involved lower limb is raised with the knee extended. This should evoke pain. The examiner then repeats the maneuver with the leg flexed at the knee, and the thigh flexed on the pelvis. This should not evoke pain.
The patient should be informed about the steps of the test, what to expect during the exam, and to describe the pain distribution. The patient should be examined in a neutral supine position with the head slightly extended. During the exam, the hips and legs should stay neutral. No hips abduction or adduction is allowed as well as no leg internal or external rotation is permitted. The affected leg is then passively and slowly raised by the ankle with the knee fully extended. Upon eliciting pain, the examiner stops further leg elevation and records the range of motion along with the area of pain distribution.
It is noteworthy that ankle dorsiflexion during SLRT may exaggerate the pain, notwithstanding, it is not part of the Lasegue sign.
What findings should not qualify as a positive SLRT?
SLRT modifications and its variants: the accuracy of SLRT can be better if it is interpreted with other nerve root tension tests:
Less frequently used nerve root irritation tests:
For the sake of completion, other tests and signs of nerve root tension or irritation are discussed succinctly below:
Interpretation of SLRT
Interpretation of Positive Reverse SLRT
Sensitivity and Specificity of the Test
The sensitivity of ipsilateral SLRT is 72 to 97%, and specificity is 11 to 66%; whereas the crossed SLRT sensitivity is 23 to 42% which is less than ipsilateral SLRT but more specific (85 to 100%).
Tests to Confirm Non-organicity While Performing SLRT
A female nurse or chaperone is mandatory to be present with a female patient while performing SLRT by a male doctor. If the patient is wearing a sari or skirt, she may feel inhibition to raise the leg, which can lead to resistance in the movement and further misinterpretation of SLRT; this is reasonably avoidable with the presence of a chaperone.
The patient may be in severe pain for which he or she may need proper counseling during examination and positioning should be done without hurting the patient further.
Proper communication between the doctor and nurse will help in eliciting SLRT properly without creating false positives.
The nurse should provide comfort and explain the test to the patient. During the test, the nurse should observe the patient for pain or discomfort.
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