Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis

Background: We studied the incidence, prevalence, and radiographic progress ion of symptomatic adjacent-segment disease, which we defined as the develo pment of new radiculopathy or myelopathy referable to a motion segment adja cent to the site of a previous anterior arthrodesis of the cervical spine, Methods: A consecutive series of 374 patients who had a total of 409 anteri or cervical arthrodeses for the treatment of cervical spondylosis,vith radi culopathy or myelopathy, or both, were followed for a maximum of twenty-one years after the operation. The annual incidence of symptomatic adjacent-se gment disease was defined as the percentage of patients who had been diseas e-free at the start of a given year of follow-up in whom new disease develo ped during that year. The prevalence was defined as the percentage of all p atients in whom symptomatic adjacent-segment disease developed within a giv en period of follow-up, The natural history of the disease was predicted wi th use of a Kaplan-Meier survivorship analysis. The hypothesis that new dis ease at an adjacent level is more likely to develop following a multilevel arthrodesis than it is following a single-level arthrodesis was tested,vith logistic regression. Results: Symptomatic adjacent-segment disease occurred at a relatively cons tant incidence of 2.9 percent per year (range, 0.0 to 4.8 percent per year) during the ten years after the operation, Survivorship analysis predicted that 25.6 percent of the patients (95 percent confidence interval, 20 to 32 percent) who had an anterior cervical arthrodesis would have new disease a t an adjacent level within ten years after the operation. There were highly significant differences among the motion segments,vith regard to the likel ihood of symptomatic adjacent-segment disease (p < 0.0001); the greatest ri sk was at the interspaces between the fifth and sixth and between the sixth and seventh cervical vertebrae, Contrary to our hypothesis, we found that the risk of new disease at an adjacent level was significantly lower follow ing a multilevel arthrodesis than it was following a single-level arthrodes is (p < 0.001), More than two-thirds of all patients in whom the new diseas e developed had failure of nonoperative management and needed additional op erative procedures. Conclusions Symptomatic adjacent-segment disease may affect more than one-f ourth of all patients within ten years after an anterior cervical arthrodes is. A single-level arthrodesis involving the fifth or sixth cervical verteb ra and preexisting radiographic evidence of degeneration at adjacent levels appear to be the greatest risk factors for new disease. Therefore, we beli eve that all degenerated segments causing radiculopathy or myelopathy shoul d be included in an anterior cervical arthrodesis, Although our findings su ggest that symptomatic adjacent-segment disease is the result of progressiv e spondylosis, patients should be informed of the substantial possibility t hat new disease will develop at an adjacent level over the long term.