The patient lies supine with both lower extremities straight, the examiner holds the patient’s knee with one hand to straighten the knee, the other hand holds the ankle and raises it slowly until the patient has radiating pain in the lower extremities, and records the angle between the lower extremities and the bed at this time, which is the straight leg raising angle. The angle between the lower limb and the bed at this time is recorded as the straight leg elevation angle. Normal people can generally reach about 80˚ without radiating pain. On this basis, the straight leg elevation test can be performed, i.e. the examiner elevates the patient’s lower limb to the maximum, then puts it down about 10˚, and when the patient is not paying attention, suddenly dorsiflexes the foot, which is positive if it can cause lower limb radiating pain. Principle of the test When the lower limb is elevated, the sciatic nerve is stretched, which increases the irritation of the nerve root by the herniated lumbar disc. In the straight leg raise test, lower extremity elevation at 0-20˚ does not cause movement of the nerve root in the spinal canal, so limitations in this range are mostly due to hamstring spasm. After the lower limb elevation exceeds 30˚, it can cause the nerve roots to pull or move downward, with the largest pull being on the lumbar 5 nerve root, followed by the lumbar 4 nerve root. When the elevation angle exceeds 60˚, the lumbar 5 nerve root is subjected to maximum tension and is sufficient to move downward in the spinal canal. Because of the greater pulling force on the lumbar 5 and lumbar 4 nerve roots, the straight leg raise test is mostly positive in patients with lumbar 5 to sacral 1 and lumbar 4 to 5 disc herniation. In patients with more severe lumbar disc herniation, not only the straight leg elevation test on the affected side is positive, but also the straight leg elevation test on the healthy side can be positive because the nerve roots can pull the dural sac when the lower limb on the healthy side is elevated, thus changing the relative position of the contralateral nerve roots and the herniation accordingly and inducing pain. The straight leg raise strengthening test can be used to differentiate between neurogenic or muscle-induced restrictions in straight leg raise. A restriction of straight leg raise due to tension in the iliotibial bundle, hamstrings, or posterior knee capsule is usually negative on the stiffness test.