Pseudoarthrosis of the cervical spine - A comparison of radiographic diagnostic measures

Study Design. A retrospective review was conducted. Objective. To compare the accuracy of two objective radiographic techniques in identifying nonunion after anterior cervical discectomy and fusion. Summary of Background Data. The accuracy of diagnostic methods for detecting pseudarthrosis has been poorly documented. Radiographic criteria mentioned in the literature include perceived motion or change in the Cobb angles between the involved segments on flexion-extension views. Methods. The participants in this study were 27 patients with 29 cervical fusions ranging from one to three levels. Patients were examine and radiographs obtained. The mean follow-up period was 39 months. Two measurements were obtained from lateral flexion-extension radiographs: Cobb angle and the distance between the tips of the spinous processes of the surgically managed levels. The measurements were obtained independently by three physicians in a blinded fashion. Results. The reliability among the observers, as measured by Cronbach's alpha, was 0.95 for the spinous process method and 0.74 for the Cobb angle method. A measurement of more than 2 mm between spinous processes was noted in patients with a known pseudarthrosis. The Pearson correlation between pseudarthrosis and use of the spinous process method was 0.77 (P<0.001). The Pearson correlation between pseudarthrosis and use of the Cobb angle method was 0.28 (P>0.10). The area under the receiver operating characteristic curve for the spinous process method was found to be 0.980, as compared with 0.662 for the Cobb angle method, for the measurement of pseudarthrosis. Conclusions. Measurement of the change in distance between spinous processes is more reproducible and accurate than the Cobb method for making the diagnosis of pseudarthrosis. The authors believe that the measurement of distances between spinous processes on lateral flexion-extension radiographs should be used as a method for evaluating radiographic fusion in patients with pseudarthrosis.