Association between multifidus fatty infiltration and lumbar facet degeneration in unilateral disc herniation: a retrospective study.

OBJECTIVE

To examine in patients with unilateral lumbar disc herniation (LDH) whether multifidus fatty infiltration (FI) grades are associated with ipsilateral facet joint degeneration and morphology at the same segment, analyzed separately at L4/5 and L5/S1.

METHODS

This retrospective study comprised 172 patients with unilateral LDH treated between February 2022 and June 2024 (L4/5, n = 88; L5/S1, n = 84). On MRI and CT, multifidus cross-sectional area (CSA) and FI were measured and FI was graded I-IV. Facet outcomes included the following: Pathria grade, facet cross-sectional area (FCA), facet asymmetry ratio (FAR), and facet angles-facet joint orientation (FJO) and facet joint tropism (FJT). Segment-specific associations between FI grade and outcomes were evaluated using GLM-ANCOVA adjusted for age and body mass index (BMI), with Bonferroni-adjusted pairwise comparisons and tests for linear trend. Affected-side Pathria grade (1-4) was used as the outcome applying ordinal logistic regression.

RESULTS

Baseline characteristics were comparable between segments. Higher FI grades were associated with greater affected-side facet degeneration at the same segment. At L4/5 a clear linear increase was observed, and Grades III/IV exceeded Grades I/II in post hoc comparisons. Ordinal logistic results were consistent: FI grade independently associated with a higher Pathria grade (L4/5, OR = 1.42; 95% CI, 1.02-1.92; P = 0.038 and L5/S1, OR = 1.26; 95% CI, 1.03-1.40; P = 0.021). Multifidus CSA was not independently associated at either segment (P > 0.05).Facet angles (FJO/FJT) did not differ across FI grades (all P > 0.05). The main effects of sex and the group × sex interaction were not significant; age and BMI also showed no consistent associations.

CONCLUSION

In unilateral LDH, higher multifidus FI grades were associated with more severe ipsilateral facet degeneration at the same segment, most clearly at L4/5.