SLR Test – Types, Technique, Clinical Outcome

SLR Test/The straight leg raise test also called the Lasegue test is a fundamental neurological maneuver during the physical examination of the patient with lower back pain aimed to assess the sciatic compromise due to lumbosacral nerve root irritation. This test which was first described by Dr. Lazarevic and wrongly attributed to Dr. Lasegue can be positive in a variety of conditions, being lumbar disc herniation the most common. Nonetheless, there are multiple causes of a positive test such as facet joint cyst or hypertrophy.[rx][rx][rx]. Overall, this test is one of the most commonly performed maneuvers across clinical practice and provides important information when making the clinical decision to refer a patient to a specialist as well as among spinal surgeons to guide therapeutic decision-making.[rx]

Lasegue sign or Straight Leg Raising Test (SLRT) is a neurodynamic exam to assess nerve root irritation in the lumbosacral area.[rx] 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.

Anatomy and Physiology of Straight Leg Raising Test (SLRT)

The Lasegue test is basically a provocation test that evidences radicular irritation in the lumbosacral region by lower limb flexion and can be due to multiple causes. Radicular symptoms are primarily produced by nerve root inflammation by surrounded structures.[rx] The foramina are formed by the pedicle superiorly and inferiorly, ligamentum flavum posteriorly, disc and vertebral body anteriorly, and this small space normally allows the nerve root excursion of 4 mm, however during the straight leg raise test this root excursion can be compromised by several factors. Mechanical compression solely does not always generate radicular symptoms as many patients have asymptomatic foraminal stenosis in MRI,[rx][rx] therefore, positive leg raise test may undergo influence by nerve root irritation secondary to inflammation as well as mechanical compression.

The straight leg raise test is attributed to Charles Lasegue, a French clinician who described two cases of sciatica aggravated by weight-bearing, hip, and knee flexion in “Thoughts of Sciatica” in 1864. Nonetheless, Dr. Lasegue did not describe the test as a provoked pain; instead, his student JJ Forst described the test in his doctoral thesis in 1881, and it was Forst who considered the pain to be produced by hamstring muscle compression to the sciatic nerve.

Nevertheless, it is believed that a Serbian neurologist, Dr. Lazar Lazarevic,[rx] was the first who documented the straight leg raise test as it is known today in the article named “Ischiac postica council”, initially published in the Serbian Archives of Medicine (1880), and republished in Vienna (1884). Dr. Lazarevic described the straight-leg-raising test by explaining sciatic pain by stretching the sciatic nerve based on his experience with six patients. Based on this misinterpretation of the original description, it is recommended to describe the maneuver as the straight leg raise test.

Indications of Straight Leg Raising Test (SLRT)

• PLID
• Low back pain
• Buttock pain
• Leg pain
• Lumbago
• Low back pain

The Technique of Straight Leg Raising Test (SLRT)

The straight leg raise test is performed with the patient in a supine position. The examiner gently raises the patient’s leg by flexing the hip with the knee in extension, and the test is considered positive when the patient experiences pain along the lower limb in the same distribution of the lower radicular nerve roots (usually L5 or S1).

Furthermore, a positive straight leg raise test is determined when pain is elicited by lower limb flexion in an angle lower than 45 degrees. During the test, if the pain is reproduced during the leg straightening, patients usually request that the examiner aborts the maneuver and by flexing the patient’s knee, the buttock pain is usually relieved(Figure 1).

Additional maneuvers have been described to enhance the sensitivity of the test such as the Bragaad’s sign, which consists of concomitant foot dorsiflexion to increase the pain while the examiner completes the leg raise.

An additional maneuver is the crossed straight leg test (crossed over Lasegue), in which the examiner passively flexes the patient’s uninvolved limb while maintaining the knee in extension. A positive test is when the patient reports pain in the involved limb at 40 degrees of hip flexion with the uninvolved limb. A crossed straight test is positive in central disc herniation in cases of severe nerve root irritation.[rx]

Currently, the following technique is popular in practice

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.[rx][rx]

It is noteworthy that ankle dorsiflexion during SLRT may exaggerate the pain, notwithstanding, it is not part of the Lasegue sign.[rx]

Causes of Pain While Performing SLRT

• Stretching of the sciatic nerve
• Displacement of the medulla and conus medullaris
• Nerve compression leads to sensitization at the dorsal root ganglion and posterior horn, which in turn leads to the lowering of the pain threshold.[rx]

Causes of Positive SLRT

• Nerve root irritation – Intervertebral disc prolapse being the most common cause
• Intraspinal tumor
• Inflammatory radiculopathy

Criteria for a true positive SLRT

• Radicular leg pain should occur (radiating below the knee).
• Pain occurs when the leg is between 30 and 60 or 70 degrees from horizontal.[rx][rx]

What findings should not qualify as a positive SLRT?

• Pain occurring in the low back alone.
• Pain occurring in the posterior thigh alone.
• Pain occurring at an angle less than 30 degrees – May indicate non-organicity or hip joint pathology.
• Pain occurring at an angle more than 70 degrees from the horizontal – More likely cause is tight hamstring or gluteal muscles.
• Pain occurs in a normal person at an angle of 80 to 90 degrees.

Issues of Concern of Straight Leg Raising Test (SLRT)

SLRT modifications and its variants: the accuracy of SLRT can be better if it is interpreted with other nerve root tension tests:

• Crossed SLRT – AKA well-leg raising test or Fajersztajn sign. When the contralateral leg is lifted, the patient experiences pain on the affected side. This test is more specific than ipsilateral SLRT.[rx][rx] It becomes positive usually in severe compression and centrally located prolapse. Fajersztajn believed that this sign is due to disc prolapse in the axilla of the root.[rx]
• Reverse SLRT – AKA femoral stretch or Ely test. While the patient is in a prone position, the leg is lifted off the table with both hip and knee joints extended. Some authors may allow knee flexion. This maneuver may reproduce radicular pain in case of upper lumbar radiculopathy, far lateral lumbar disc, or femoral neuropathy. The pain will present in the femoral nerve distribution on the side of the lesion.[rx]
• Braggard test – AKA Sciatic stretch test or Flip test. While raising the leg, the foot is held in a dorsiflexed position, so that the sciatic nerve is stretched more, thereby increasing the intensity of pain or making it possible to elicit the sign early.[rx][rx]
• Reverse flip test – While raising the leg, the foot is held in a plantar-flexed position; this will lessen the pain. But if the patient is complaining of an increase in pain, it can suggest malingering.
• Bowstring sign – Also known as the popliteal compression test or posterior tibial nerve stretch sign. The patient can be examined in sitting or in a supine position. The examiner flexes the knee and applies pressure on the popliteal fossa, evoking sciatica. Some examiners do it after SLRT by flexing the knee to relieve the buttock pain. The pain would be reproduced by a quick snap on the posterior tibial nerve in the popliteal fossa.[rx]

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:

• Sitting SLRT (Bechterew test) – the patient is made to sit at the edge of a table with both hip and knee flexed, then made to extend the knee joint or elevate the extended knee, which reproduces the radicular pain. He/she may be able to extend each leg alone, but extending both together causes radicular pain.[rx]
• Distracted SLRT – the sitting SLRT is performed without the patient’s awareness. The patient is distracted as if the surgeon is examining the foot or pulsation, and slowly, the examiner extends the knee. If the patient is experiencing true radiculopathy, the same pain will be reproduced. Otherwise, we can assume that the patient may be malingering.
• Neri’s sign – while bending forward, the patient flexes the knee to avoid stretching the nerve.[rx]
• The buckling sign – the patient may flex the knee during SLRT to avoid sciatic nerve tension.
• Sicard sign – passive dorsiflexion of ipsilateral great toe just at the angle of SLRT will produce more pain.[rx]
• Kraus-Weber test – the patient may be able to do a sit-up with the knees flexed but not extended.
• Minor sign – the patient may rise from a seated position by supporting himself/herself on the unaffected side, bending forward, and placing one hand on the affected side of the back.
• Bonnet phenomenon – the pain may be more severe or elicited sooner if the test is carried out with the thigh and leg in a position of adduction and internal rotation.

Clinical Significance of Straight Leg Raising Test (SLRT)

Interpretation of SLRT

• Pain radiating down the buttock to the lateral thigh and medial calf – L4 nerve root irritation
• Pain radiating down the buttock to the posterior thigh and lateral calf – L5 nerve root irritation
• Pain radiating down the buttock to the posterior thigh and calf, and lateral foot – S1 nerve root irritation

Interpretation of Positive Reverse SLRT

• L2, L3 or L4 root irritation
• Femoral nerve irritation

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%).[rx]

Tests to Confirm Non-organicity While Performing SLRT

• Pain occurring at an angle less than 30 degrees
• A significant discrepancy between the supine and sitting SLRT
• Touch-me-not or Waddell sign – Widespread and excessive tenderness
• Back pain on pressing down on the top of the head
• Overreaction during testing
• Non-dermatomal and non-myotomal neurologic signs
• Pain during simulated spinal rotation: The patient’s hands remain to the sides with hips rotated. There will not be any spine rotation with this maneuver. But the patient will complain of pain.

References