Dynamic Radiographs Not Always Essential in Diagnosis of Lumbar Spinal Instability

Objective: Dynamic radiographs are widely used to assess radiological spinal instability. The authors aim to compare the sensitivity of dynamic radiographs versus spontaneous reduction seen on magnetic resonance imaging when compared to a standing lateral radiograph in diagnosing instability. Materials and Methods: This study is a retrospective review of 75 patients from a single center with suspected clinical lumbar spinal instability presenting with back and/or leg pain and had undergone a magnetic resonance imaging of their lumbosacral spine as well as a lumbar radiograph series. The authors compared the criterion sensitivity (in accordance to Posner criteria) of dynamic radiographs versus magnetic resonance imaging. Pearson's chi-square test was used to determine statistical significance. Results: The Posner criteria was satisfied in 45/75 patients (60%) using dynamic radiographs as compared to 32/75 patients (42.6%) when using spontaneous reduction seen on magnetic resonance imaging. This was statistically significant (p<0.01). However, we noted that 29/45 (64.4%) patients with instability diagnosed on dynamic radiographs also had it diagnosed on spontaneous reduction. Conclusion: Posner criteria when applied to spontaneous reduction seen on magnetic resonance imaging has a specificity of 90% and positive predictive value of 90.63%, assuming that satisfaction of Posner criteria on dynamic radiographs indicates true instability. The authors advocate the use of Posner criteria applied to spontaneous reduction to assess for spinal instability. Failure to satisfy the Posner criteria on spontaneous reduction should then prompt the use of a more sensitive modality such as dynamic radiographs.