Magnetic resonance imaging analysis of soft tissue disruption after flexion-distraction injuries of the subaxial cervical spine

Study Design. A retrospective study was performed with the use of magnetic resonance imaging to evaluate the type and degree of soft tissue disruption . associated with flexion-distraction injuries of the,subaxial spine. Objective. To determine what soft tissue structures are injured in flexion- distraction injuries of the subaxial spine. Summary of Background Data. Prior published reports of unilateral and bilat eral cervical facet dislocations have described the analyzed mechanisms and biomechanics of this injury subtype. No retrospective magnetic resonance i maging analysis of associated soft tissue disruption has been documented. Methods. Magnetic resonance imaging evaluations of the cervical spine were obtained for all, patients with a flexion-distraction injury, Stages 2 (uni lateral facet dislocation) and 3 (bilateral facet dislocation), between Sep tember 1994 and May 1.998. Two neuroradiologists, blinded to both clinical and radiographic findings, graded all the soft tissue structures for eviden ce of attenuation or disruption. The soft tissue structures were graded on a scale of 1 (intact), 2 (indeterminate), or 3 (disrupted). Results. For this study, 48 patients satisfied the inclusion criteria: 25 w ith unilateral facet dislocation and 23 with bilateral facet dislocation. D isruption to the posterior musculature, interspinous ligament, supraspinous ligament, facet capsule, ligamentum flavum, and posterior and anterior lon gitudinal ligaments was found in a statistically significant number of pati ents with bilateral facet dislocation. For most of these structures, disrup tion was found to be statistically significant in patients with a unilatera l facet dislocation, except for the posterior longitudinal ligament, in whi ch significance was not consistently demonstrated using 95% confidence inte rvals in the binomial testing. In a comparison between unilateral and bilat eral facet dislocations using a two-sided Fisher's exact test, it was found that disruption to the anterior and posterior longitudinal ligaments and t he left facet capsule were statistically significant, with all three more p rominent in bilateral facet dislocation. A multivariate analysis between un ilateral and bilateral facet dislocations showed that disruption to the ant erior longitudinal ligament was associated significantly with a bilateral f acet dislocation. Disc disruption was found to be associated significantly with both injury types, but was more common in bilateral facet dislocation, although this difference in intergroup comparisons was not statistically s ignificant. Conclusions. Unilateral and bilateral, facet,dislocations of the subaxial s pine are associated with damage to numerous soft tissue structures that pro vide stability to the, lower cervical spine. Damage to the posterior longit udinal, ligament did not occur consistently in unilateral facet dislocation s. Bilateral facet dislocations were associated significantly with disrupti on to the posterior and anterior, longitudinal ligaments and left facet cap sule, as compared with unilateral facet dislocations. Magnetic resonance im aging allows visualization of these disruptions.