(A) Clinical symptoms 1. Low back pain Low back pain is the first symptom in most patients, with an incidence of about 91%. Due to the stimulation of the outer layer of the fibrous ring and the posterior longitudinal ligament by the nucleus pulposus, the lower lumbar induction pain is produced by the sinus nerve, and sometimes it can be accompanied by hip pain. 2. Lower limb radiating pain Although high lumbar disc herniation (lumbar 2 to 3, lumbar 3 to 4) can cause femoral neuralgia, it is rare clinically, less than 5%. The vast majority of patients are herniated from lumbar 4 to 5 and lumbar 5 to sacral 1, which manifests as sciatica. Classic sciatica is radiating pain from the lower back to the buttocks, posterior thighs, lateral calves up to the feet, and the pain increases in response to increased abdominal pressure such as sneezing and coughing. The radiating pain is mostly on one side of the limb, and only a very few cases of central or paracentral herniated nucleus pulposus show symptoms in both lower limbs. There are three causes of sciatica: (1) chemical inflammation of the nerve root due to chemical stimulation and autoimmune reaction of the ruptured disc; (2) compression or tension of the herniated nucleus pulposus by the nerve root with inflammation, blocking venous return and further aggravating edema, which increases sensitivity to pain; and (3) ischemia of the compressed nerve root. The above three factors are interrelated and are aggravating factors for each other. 3. Cauda equina symptoms The protruding nucleus pulposus or prolapsed, free disc tissue compresses the cauda equina nerve, and its main manifestations are obstruction of bowel movement and urination, abnormal perineum and perianal sensation. In severe cases, symptoms such as loss of control of urination and defecation and incomplete paralysis of both lower limbs may occur, which are rare in clinical practice. (2) Signs of lumbar disc herniation 1. General signs (1) Lumbar lordosis is a postural compensatory deformity for pain relief. Depending on the relationship between the site of the herniated nucleus pulposus and the nerve root, the spine is bent to the healthy side or to the affected side. If the herniated nucleus pulposus is located on the medial side of the spinal nerve root, the lumbar spine bends to the affected side because the spine bends to the affected side to reduce the tension of the spinal nerve root; conversely, if the herniated nucleus pulposus is located on the lateral side of the spinal nerve root, the lumbar spine bends to the healthy side. (2) Restriction of lumbar movement Most patients have varying degrees of restriction of lumbar movement, which is especially obvious in the acute stage, with the most obvious restriction in forward flexion, because the nucleus pulposus can be further displaced backward in forward flexion and increase the pull on the compressed nerve roots. (3) Pressure pain, percussion pain and sacral spasm The site of pressure pain and percussion pain basically corresponds to the vertebral space of the lesion, and is positive in 80% to 90% of cases. The percussion pain was obvious at the spinous process, which was caused by percussion vibration of the lesion. The pressure point is mainly located at 1 cm of the paravertebral area, and radiating pain along the sciatic nerve may occur. About 1/3 of patients have lumbar sacral spasm. 2. Special signs (1) Straight leg raise test and strengthening test The patient lies supine, extends the knee and passively raises the affected limb. In normal people, the nerve root has 4mm sliding degree, and the lower limb is raised to 60°~70° before feeling discomfort in the N fossa. In patients with lumbar disc herniation, the nerve root compression or adhesion reduces or disappears the sliding degree, and sciatica can occur within 60° of elevation, which is called a positive straight leg elevation test. In positive patients, slowly lowering the height of the affected limb and waiting for the radiating pain to disappear, then passively flexing the affected ankle joint to induce radiating pain again is called a positive strengthening test. Sometimes, because of the large nucleus pulposus, elevation of the healthy lower limb can also pull the dura mater to induce radiating pain in the sciatic nerve on the affected side. (2) Femoral nerve pull test The patient is placed in a prone position with the knee joint of the affected limb fully extended. The examiner elevates the straightened lower extremity so that the hip joint is in hyperextension, and the test is positive when the hyperextension reaches a certain level and pain occurs in the femoral nerve distribution area in front of the thigh. This test is mainly used to examine patients with lumbar 2 to 3 and lumbar 3 to 4 disc herniation. 3, neurological manifestations (1) sensory disorders depending on the location of the affected spinal nerve roots and the abnormal sensation of the innervation area. The positivity rate is more than 80%. In the early stage, the symptoms are mostly skin sensitization, and gradually numbness, tingling and hyperalgesia appear. However, if the cauda equina nerve is involved (central type and paracentral type), the sensory impairment will be more extensive. (2) Decreased muscle strength is seen in 70% to 75% of patients. In the case of lumbar 5 nerve root involvement, the dorsal extension of ankle and toe is decreased, and in the case of sacral 1 nerve root involvement, the toe and plantarflexion of foot is decreased. (3) Reflex changes are also one of the typical signs that are prone to occur in this disease. When the lumbar 4 nerve root is involved, the knee reflex may be impaired, which is active in the early stage and then rapidly becomes hyporeflexic. In sacral 1 nerve root involvement, the Achilles tendon reflex is impaired. Reflex changes are more significant for the localization of the involved nerve.