Risk Factors for Adjacent Segment Problems after Posterior Instrumentation of the Cervical Spine

Adjacent segment problems after cervical spine instrumentation are widely reported. They can range from asymptomatic adjacent segment degeneration (ASD) noted on radiographs to symptomatic adjacent segment disease and even instability. While ASD following anterior instrumentation is well studied, there is a paucity of literature on ASD following posterior instrumentation. We intended to identify the risk factors associated with ASD following posterior instrumentation, focusing on pre-operative and surgical parameters. Eighty-seven patients who underwent posterior instrumentation of the cervical spine were recruited. Clinical and radiological examination was performed preoperatively and up to 24 months postoperatively. The collected data included patient demographics, indication for surgery, sagittal parameters (cervical lordosis, C2–7 sagittal-vertical axis), technique of surgery, number of levels instrumented and fused, number of levels decompressed, and the level at which the instrumentation ended. Based on postoperative evaluation, ASD was found in 29.9% of the patients, of which, one patient was symptomatic and required reoperation. Even though, according to our univariate analysis, reduced pre-operative cervical lordosis and the indication of degenerative spondylosis seemed to significantly influence the occurrence of ASD, multivariate regression analysis did not identify any independent risk factors. We also noted that, even though patients may develop ASD after the instrumented fusion of the cervical spine, this may not necessarily develop into symptomatic adjacent segment disease requiring revision surgery.