Facet orientation and tropism: Associations with asymmetric lumbar paraspinal and psoas muscle parameters in patients with chronic low back pain

BACKGROUND: Many studies have explored the relationship between facet tropism and facet joint osteoarthritis, disc degeneration and degenerative spondylolisthesis. However, the associations between facet orientation and tropism, and paraspinal muscles have not been studied. OBJECTIVE: To analyze the associations between facet orientation and tropism, and parameters of paraspinal muscles in patients with chronic low back pain. METHODS:Ninety-five patients withchronic low back pain were consecutively enrolled. Their facet joint angles weremeasured on computed tomography (CT) while gross cross-sectional area (GCSA), functional cross-sectional area (FCSA) and T2 signal intensity of lumbar paraspinal and psoas muscle were evaluated on magnetic resonance imaging (MRI). RESULTS: The GCSA and FCSA were significantly smaller for multifidus muscle ( P< 0.001), but significantly larger for erector spinae and psoas muscles ( P< 0.001), in coronally-orientated group than those in sagittally-orientated group. The differences of bilateral GCSA and FCSA of multifidus muscle were significantly larger in facet tropism group than those in no facet tropism group (P = 0.009 and P = 0.019). CONCLUSIONS: Muscular asymmetries may develop in the lumbar region of the spine, which are associated with facet asymmetry in patients with chronic low back pain. Longitudinal studies are needed to understand the causal relationship between facet orientation and tropism and muscular asymmetry in future.