Facet Joint Tropism and Degenerative Spondylolisthesis—A Study from the AOSAP Research Collaboration. (May 2014) - Samartzis, D.
Introduction: Degenerative spondylolisthesis (dSpl) is translation of the vertebral body in relation to adjacent levels, mainly attributed to degenerative changes of the intervertebral disc and facet joint complexes, and primarily occurs at L4-L5. Studies have suggested that more sagittal oriented facet joints at L4-L5 are associated with dSpl. However, the role of facet joint tropism (i.e., asymmetry between facet joint orientations) in L4-L5 dSpl remains inconclusive, in particular, in an Asian population and possibly attributed to nonstandardized definitions of tropism. As such, the following study addressed the role of facet joint tropism in relation to L4-L5 dSpl in the Asia Pacific region. Materials and Methods: A multinational, multiethnic cross-sectional image-based study was performed in 34 institutions in the Asia Pacific region. Lateral standing radiographs and axial MRIs and/or CT scans were obtained for patients diagnosed with lumbar dSpl. Imaging assessment consisted of the following: magnitude of slip displacement, level of spondylolisthesis, and left/right L4-L5 facet joint angulations were noted on image assessment. Patients with single level dSpl were included. Patients were further stratified into those presenting with (Group A) or without (Group B) L4-L5 dSpl. Facet joint tropism was defined as 7 degrees difference (Grogan et al 1997) between left and right facet joints and also assessed on receiver operating characteristics (ROC) curve analysis to identify critical values for multivariate analysis. Gender, age, weight/height (body mass index [BMI]), and ethnicity were also noted. Results: The study included 351 patients (36.9% males and 63.1% females) with a mean age of 61.8 years (range: 24-90 years). The mean BMI was 25.6 kg/m 2 (range: 15.4-43.9 kg/m 2 ). There were 267 patients (76.1%) in Group A and 84 individuals (23.9%) in Group B (control). Sex type ( p = 0.295) and BMI ( p = 0.227) did not significantly differ between groups, but elevated age was more pronounced with L4-L5 dSpl ( p = 0.001). There was a statistically significant difference between right and left L4-L5 facet joint angulations between Group A (right mean: 57.5 degrees; left mean: 55.4 degrees) and Group B (right mean: 48.4 degrees; left mean: 46.5 degrees) ( p < 0.001). Based on facet joint tropism of 7 degrees difference between facet angulations, there was no statistically significant difference between groups. ROC analysis identified high sensitivity and specificity of facet joint angulation difference of 15 degrees or greater associated with dSpl. Based on age-adjusted multivariate analysis, facet joint tropism with a critical value of 15 degrees or greater angulation difference noted an odds ratio of 2.34 (95% CI: 1.17-4.67; p = 0.016) associated with dSpl. Slippage was noted with increased facet joint tropism, but the effects could not be discerned. Conclusion: Greater sagittal FJ orientation was associated with dSpl, as was joint tropism. A critical value of 15 degrees FJ angle difference produced a twofold increased likelihood of dSpl. Our study broadens the understanding of FJ morphology and its role in degenerative sagittal plane instability. Acknowledgments This study was funded by AOSpine Asia Pacific. Disclosure of Interest None declared