Objecive:To discuss the effect of degenerative cervical instability in cervical spondylotic myelopathy pathogenesis and the clinical significance of surgical treatment.Methods:From 2002 to 2006,18 patients with cervical spondylotic myelopathy and cervical instability were treated by anterior subcorpectomy and implanted bone fusion.The cervical extension, flexion lateral X-ray film before and after surgery were analyzed.Results:In 18 cases with cervical instability before surgery, there were 6 cases with one undstable segment,9 cases with 2 u...