Radiograph-based intervertebral sagittal translation-to-canal diameter ratio as a quantitative imaging marker for suspected lower cervical instability.

Abstract

To compare radiographic differences between clinically suspected symptomatic lower cervical instability segments and asymptomatic normal segments and to evaluate the value of the radiograph-based intervertebral sagittal translation-to-canal diameter ratio (TCDR) as a quantitative imaging marker for lower cervical instability. This single-center retrospective study screened 197 clinically suspected cases of lower cervical instability. Seventeen cases with multilevel abnormalities but without a clearly identifiable clinically dominant responsible segment were excluded, leaving 180 patients with one clinically prespecified responsible segment. The control group included 60 asymptomatic examinees, with four segments from C3/4 to C6/7 measured in each participant. Group differences in intervertebral sagittal translation, radiographic sagittal canal diameter, intervertebral angulation, TCDR, and related indices were compared. ROC analysis, patient-cluster bootstrap, segment-stratified analysis, patient-level sensitivity analysis, cluster-robust logistic regression, and interobserver reliability analysis were performed. Age and sex did not differ between groups, but segment distribution differed significantly (P < 0.001). TCDR was higher in the study group than in controls (0.170 ± 0.066 vs. 0.067 ± 0.060, P < 0.001). The segment-level AUC of TCDR for lower cervical instability was 0.889 with an optimal cutoff of 0.087, 91.11% sensitivity, and 72.08% specificity. TCDR outperformed absolute intervertebral sagittal translation and intervertebral angulation, was positively correlated with instability (r = 0.631, P < 0.001), showed segment-specific AUCs of 0.811-0.929, and remained independently associated with lower cervical instability after adjustment (OR = 1.26, 95% CI 1.19-1.34, P < 0.001). Radiograph-based TCDR showed good segment-level discriminative ability for clinically suspected lower cervical instability and may serve as an adjunctive quantitative radiographic marker for assessing a responsible segment.