Facet orientation and tropism: associations with spondylolysis.

STUDY DESIGN: Cross-sectional study.

OBJECTIVE: To evaluate the association between lumbar spine facet joint orientation, facet joint tropism, and spondylolysis identified by multidetector computed tomography (CT) in the community-based Framingham Heart Study.

SUMMARY OF BACKGROUND DATA: The association between lumbar spondylolysis and facet orientation and tropism remains unclear.

METHODS: This study was an ancillary project to the Framingham Heart Study. Three thousand five hundred twenty-nine participants of the Framingham Heart Study aged 40 to 80 years underwent multidetector CT imaging to assess aortic calcification. One hundred ninety-one subjects were included in this ancillary study. Facet joint features and spondylolysis were evaluated on CT scans. The final analyzed sample included 104 men with mean age 51.90+/-11.25 years and 84 women with mean age 53.61+/-10.20 years. The association between spondylolysis and facet orientation and tropism was examined using univariate and multivariate analyses.

RESULTS: Spondylolysis was prevalent in 11.5% of the total population. chi2 test demonstrated a significant sex difference in prevalence of spondylolysis (P=0.0154), with almost 3 times higher prevalence among men. There was no statistically significant difference in facet orientation and continuous facet tropism between individuals with and without spondylolysis at the L5 level (P=0.49 to 0.91). After adjustment for age, sex, and body mass index, no significant association between the occurrence of spondylolysis and facet orientation and tropism was found. In the studied sample the prevalence of facet joint osteoarthritis was significantly higher in individuals with spondylolysis than in those without spondylolysis at both sides of L4-L5 spinal level (P=0.044 at the right side and P=0.003 at the left side) and at left side of L5-S1 level (P=0.038).

CONCLUSIONS: We did not find an association between facet orientation, facet tropism, and spondylolysis. One of the possible explanations for this is that the high prevalence of facet joint osteoarthritis in individuals with spondylolysis in the studied sample might have led to diminished differences in facet orientation.