What is a Straight Leg Raise Test?
The Straight Leg Raise which is also known by the name of Lasègue’s Sign is a test done on a patient with low back pain in order assess the cause of the low back meaning that whether the low back pain is caused due to a herniated disc or some other pathological condition. This is quite an effective and accurate test to determine the cause of a low back pain. This in addition with radiological studies pinpoint to the underlying cause of back pain so that the treating physician can formulate an effective treatment plan for the patient.
How is Straight Leg Raise Test Done?
The Straight Leg Raise test is done with the patient lying down on the examining table and asking the patient to lift the leg. If the patient is experiencing back pain on the left side then the left leg will be asked to raise and vice versa. The patient is asked to raise the leg till pain is felt in the back. The angle which the leg creates with respect to the floor determines whether the test is positive or negative. To increase the accuracy of the test the patient may also be asked to dorsiflex the ankle and flex the neck along with lifting the leg as this stretches the nerve root and dura.
Why is a Straight Leg Raise Test Done?
As stated, the Straight Leg Raise Test is done to pinpoint the cause of low back pain for a patient as to whether or not it is caused by a disc herniation. This test stretches the sciatic nerve which courses down the back of the leg. If the patient experiences pain behind the leg below the knee when the leg is raised then the test is deemed as positive meaning that one or more nerve roots leading to the sciatic nerve may be compressed or irritated. If Straight Leg Raise Test done on an unaffected leg causes pain in the affected leg then it also points to compression of the nerve root leading to the sciatic nerve. Compression of a nerve root may be caused due to many reasons with disc herniation being the most common cause specifically at the lowest level of the spine which is the L5 level.
Straight Leg Raise Test Interpretation: What is the Diagnostic Significance of Straight Leg Raise Test on Back Pain?
Based on the results of the test, the physician can order further studies and formulate a specific treatment plan for the patient’s symptoms. Some of the interpretations of a Straight Leg Raise Test are:
Negative Straight Leg Raise Test which means that no pain is felt with the test signifies that there is no major disc herniation present but a minor protrusion still needs to be ruled out.
Interpretation of Straight Leg Raise Test which is painful but is not limited signifies a minor disc protrusion and can be treated conservatively
Interpretation of Straight Leg Raise Test with a painful arc of motion signifies a small protrusion with possible compression of the nerve roots. By a painful arc of motion we mean that when the patient is lifting the leg for the test at a certain angle when the patient experiences pain the patient is asked to maintain the leg at that angle and look for specific areas of the symptoms and then try and lift the leg further if possible.
A painful and limited Straight Leg Raise Test but without any other associated neurological symptoms signifies a larger protrusion which may interfere with mobility of the spine.
Interpretation of painful and limited Straight Leg Raise Test with associated neurological deficits signifies severe compression of the nerve roots due to significant disc herniation which impairs both the conduction and mobility of the spine and further investigations in such cases is essential to identify the magnitude of protrusion and nerve root compression.
A negative Straight Leg Raise Test but with associated neurological deficit may signify sciatica which may wax and wane and during periods of remission the patient may have a negative Straight Leg Raise Test. This is also called as ischemic root atrophy meaning that there is significant protrusion and the nerve root is so compressed that it becomes ischemic. In such conditions, the patient will have significant motor and sensory impairment. The patient may not feel any symptoms but anatomically the condition may be much worse that normal.