A straight leg raise is a test used by medical professionals to help determine whether a sufferer of low back pain is experiencing symptoms consistent with a herniated disc in the spine. A herniated disc occurs when a spinal disc, which is a gel-like capsule situated between vertebrae, begins to bulge and press against various nerves. The straight leg raise is only one test used to help determine whether a patient is suffering from a herniated disc; it cannot, in itself, be used as a positive determination.
In order to execute a straight leg raise test, the patient will lie down flat on his or her back with the legs positioned together and the arms at his or her side. The test can be performed in two different ways: it can be done in a passive manner or an active manner. In the passive test, a medical professional will grab onto the patient's leg and lift it with the knee remaining straight. In the active test, a similar motion will occur, but the patient will actively lift his or her leg rather than relying on the medical professional to lift the leg. The results of the test depend on whether the patient feels any pain when performing the straight leg raise.
Nerve pain is the most common type of pain felt during the straight leg raise. The sciatic nerve runs from the lower back all the way down the back of each leg, and it is very often affected when a disc herniation occurs. Pain in the feet, legs, buttocks, or even lower back can occur as a result of the herniated disc; the straight leg raise is a test used to find out whether the sciatic nerve is being compressed or otherwise damaged as a result of a herniated disc.
A medical professional must be present to interpret the results of the test. If pain is felt when the leg is bent between 30 and 70 degrees, the cause is likely to be a herniated disc, but if pain is felt before the leg reaches the 30 degree mark, the underlying cause of the pain is likely to be something other than a herniated disc. The spinal nerve root is stretched during the exercise, but not usually until the leg reaches the 30 degree mark. If pain is felt before that, the nerve root has not been stretched sufficiently and will therefore not cause pain yet.