The patient was male, 30 years old. He was admitted to the hospital on 23.11.2000 with weakness of left thumb and finger extension for three months. The patient’s first symptom was an upper respiratory tract infection, followed by significant left lateral elbow pain, which was ineffective with anti-inflammatory and analgesic treatment. The pain was relieved after 2 weeks and disappeared after 4 weeks. At this time, he was unable to extend his thumb and fingers. Local examination at admission: drooping thumb and fingers deformity, no drooping wrist deformity. The muscle strength of the ulnar carpal extensors, common finger extensors, long thumb extensors, short thumb extensors, long thumb extensors, intrinsic index finger extensors, and intrinsic little finger extensors were all 0o. EMG showed that the spontaneous electrical activity of the examined muscles was ++ to ++++; there was no motor unit in the recruitment response and the motor conduction velocity (MCV) was significantly slowed; some muscles had compound muscle action potential (CMAP), but the wave amplitude was extremely low; this suggested that the interosseous posterior nerve was almost There was almost complete damage to the posterior interosseous nerve. The radial extension of the long and short wrist muscles had a strength of 5o. There was no sensory impairment. The admission diagnosis: viral neuritis of the posterior interosseous nerve. The procedure was performed under brachial plexus block anesthesia and epidural anesthesia. The radial nerve was found in the humerus and brachioradialis interval and traced down to the distal 1 cm of the bifurcation of the motor and sensory branches, and the posterior interosseous nerve showed typical salami-like changes up to 8 cm long. the lesion was excised and the ipsilateral peroneal nerve was repaired with a 10 cm micrograft. After complete hemostasis, a small amount of several butylose was placed to close the wound layer by layer, and one drainage tube was left in place. The plaster support was fixed in 135o flexion elbow position. The lesioned nerve segment was sent to pathology section, which showed wavy arrangement of neuronal cells with cellular degeneration. There was focal inflammatory cell infiltration and fibrous tissue hyperplasia in between, and inflammatory cell infiltration was also seen in the fibrous tissue. Postoperative treatment included neurotrophic drugs and local infrared irradiation. The stitches were removed 10 days after surgery, and electrical stimulation therapy and passive movement and “impulse transmission” exercises were started after the removal of the plaster cast in 3 weeks. From 6 to 12 months postoperatively, they gradually started to perform power-assisted and active exercises and resistance exercises. The muscles examined were the extensor digitorum generalis, the ulnar extensor carpi radialis, the long thumb extensor, the long thumb extensor and the intrinsic extensor of the index finger. The electromyography showed that there was no significant recovery of muscle strength, and the electromyography showed ++ spontaneous potentials; there were neoplastic potentials in the common extensor digitorum communis; the MCV latency was prolonged; there was CMAP, but the wave amplitude was extremely low. At 6 months postoperatively, the muscle strength of the common extensor muscle was 2o and that of the long thumb extensor muscle was 1o. The EMG showed that the spontaneous potentials were +~++; there were regenerative complex potentials in the common extensor muscle and the ulnar carpal extensor muscle in simple phase; the MCV latency was prolonged compared to the healthy side; the CMAP wave amplitude was 70% lower than that of the healthy side. At 12 months after surgery, the muscle strength of the extensor digitorum generalis was 4o, and the muscle strength of the long and short extensor muscles and the long thumb extensor muscle was 3o. The EMG showed spontaneous potentials +; the recruitment response was in simple-mixed phase; the MCV was prolonged by about 30% compared with the healthy side; the CMAP wave amplitude was about 50% lower than the healthy side. The EMG showed prolonged spontaneous electrical activity insertion potential; the recruitment response was in mixed phase; MCV was about 20% longer than the healthy side; CMAP wave amplitude was about 30% lower than the healthy side. At 24 months postoperatively, the muscle strength of all extensor muscles was 5o. The EMG showed that the spontaneous generating activity disappeared; the recruitment response was in mixed-interference phase; MCV was slightly slower than the healthy side; CMAP wave amplitude was slightly lower than the healthy side. After 24 months of postoperative follow-up, there was complete functional recovery. Discussion: Posterior interosseous neuritis is a rare disease. Its etiology is unclear, and it is commonly followed by systemic infectious diseases. This case had a typical course, including no history of trauma, sudden onset, history of upper respiratory tract infection before the onset, typical lateral elbow pain, ineffective general analgesics, followed by relief and weakness of the corresponding muscle group, and finally functional impairment. Intraoperatively, the lesioned nerve segment was found to have typical salami-like changes. The pathological section showed a wavy arrangement of neuronal cells with cellular degeneration. There was focal inflammatory cell infiltration and fibrous tissue hyperplasia in between, and inflammatory cell infiltration was also seen in the fibrous tissue. In view of the above, the case was considered to be a neuritis caused by a virus. In this case, the duration of the disease was 3 months. Although a long neuropathic segment was found intraoperatively, and the grafted nerve segment was 10 cm long, the function was completely restored after 24 months of follow-up because of timely surgery, postoperative adjuvant drug treatment and adherence to orderly functional rehabilitation.