PURPOSE: To evaluate the association between facet joint tropism (FJT) and spondylolysis, with or without isthmic spondylolisthesis (IS), in a large cohort of patients across a wide age range.
METHODS: We retrospectively analyzed lumbar computed tomography scans from 358 patients (mean age 48.2 ± 20 years), including 191 patients with spondylolysis (137 with IS) and 167 age- and sex-matched controls without spondylolysis. Bilateral facet joint angles (FJA) were measured at L3-L4, L4-L5, and L5-S1. FJT was defined as a right-to-left FJA difference >6°. Absolute FJA differences and the prevalence of dichotomous FJT were compared between groups. Inter- and intra-observer agreement were assessed using intraclass correlation coefficients (ICC).
RESULTS: Inter- and intra-observer agreement for FJA measurements were excellent (ICC = 0.88 for both). Patients with spondylolysis demonstrated more FJA asymmetry than controls at L3-L4 (5.8° versus 3.7%; p = 0.02), L4-L5 (6.6° versus 3.9°; p < 0.01), and L5-S1 (6.7° versus 4.5°; p < 0.01), with a higher prevalence of FJT at all levels (56% versus 38%, 66% versus 36%, and 68% versus 47%, respectively; all p < 0.01). Patients with IS also showed greater FJA asymmetry and more frequent FJT at L3-L4 and L4-L5, but not at L5-S1.
CONCLUSION: Patients with spondylolysis, with or without IS, demonstrated significantly greater facet joint asymmetry and a higher prevalence of FJT than controls. The presence of FJT at adjacent levels suggests that it may represent a generalized anatomical characteristic rather than a purely local phenomenon.
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