Objective:To evaluate the medium and long-term clinical efficacy of the treatment of lumbar degenerative diseases in Dynesys dynamic internal fixation combined with decompression.Methods:From March 2008 to March 2015, 145 patients (84 males and 61 females, mean age 55.9±7.1 years old) with symptoms of lumbar degenerative diseases (69 lumbar disc herniation, 53 lumbar spinal stenosis and 23 I grade lumbar degenerative spondylolisthesis) were treated by the lumbar discectomy using Dynesys dynamic internal fixation combined with decompression. The clinical symptoms before and after surgery were assessed by visual analogue scale (VAS), Japanese Orthopaedic Association (JOA) and Oswestry disability index (ODI). Lumbar lateral radiographs were used to measure the height of intervertebral space between the surgical segment and the adjacent segment. The range of motion (ROM) between the surgical segment and the adjacent segment was measured by lumbar dynamic position X-ray. Surgical and adjacent segments degenerative were classified according to the Pfirrmann grade classification.Results:The VAS score, ODI and JOA score of lower back and lower limbs in patients with lumbar disc herniation were improved from 6.6±1.7, 7.1±1.4, 63.1%±10.2%, 12.5±2.4 preoperatively to 2.6±1.0, 2.8±0.9, 30.9%±9.8%, 22.4±2.1 at the latest follow-up. The differences were statistically significant. The VAS score, ODI score and JOA score of lower back and lower limbs in patients with lumbar spinal stenosis were improved from 6.3±2.2, 6.9±1.3, 63.4%±8.5%, 12.8±2.7 preoperatively to 2.4±1.2, 2.8±1.0, 35.1%±12.0%, 22.2±2.2 at the latest follow-up. The differences were statistically significant. The VAS score, ODI score and JOA score of lower back and lower limbs in patients with I degree lumbar degenerative spondylolisthesis were improved from 5.7±2.3, 6.7±0.9, 65.7%±10.0%, 12.5±2.7 preoperatively to 2.2±1.2, 2.7±1.1, 37.0%±11.8%, 22.4±2.6 at the latest follow-up. The differences were statistically significant. Comparing to preoperational value, the height of the operative segment and caudal intervertebral space were decreased at the 1 year postoperatively and last follow-up. But the difference was not significant. As for cranial adjacent segment, the height of intervertebral space preoperatively was decreased from 12.1±1.9 mm preoperatively to 11.7±1.6 mm at 1 year postoperatively, and to 11.3±1.8 mm at the latest follow-up. The difference between them was statistically significant ( F=6.46, P=0.001). The ROM of surgical segments was decreased from 7.6°±2.2° preoperatively to 5.5°±1.6° at 1 year postoperatively, and to 2.9°±1.4° at the latest follow-up. The difference between them was statistically significant ( F=267.9, P<0.001). Conversely, the ROM of cranial and caudal segments was increased from 8.2°±2.4°, 6.5°±1.6° preoperatively to 9.1°±2.1°, 7.1°±1.9° at 1 year postoperatively, and to 10.6°±2.5°, 7.2°±1.8° at the latest follow-up. The difference between them was statistically significant ( F=38.66, 3.81, P<0.001, 0.023). At the latest follow-up, 120 (51.9%) adjacent segments were to be defined adjacent segment degeneration which includes 103 radiological adjacent segment degeneration and 17 symptomatic adjacent segment degenerations. Conclusion:Dynesys dynamic internal fixation combined with decompression could achieve satisfying mid- and long-term therapeutic effect in the treatment of lumbar degenerative diseases. The ROM of surgical segments decreased with time, although part of the ROM was still retained at the latest follow-up. However, it does not seem to avoid the degeneration of adjacent segment.