Background: The purpose of this study was to establish a novel rat model for ligamentum flavum (LF) hypertrophy using lumbar instability and to elucidate the etiology of LF hypertrophy.
Methods: A total number of 30 male rats were used. Lumbar instability was induced by surgical resection of L5/6 posterior elements (n=15). The other rats underwent a sham operation (n=15). After 8 weeks, all rats were taken lateral plain X-rays. The LF from L5/6 in both groups were harvested to investigate histological, immunohistological, and real-time PCR analysis.
Results: According to radiological results, the disc height ratio and extension ratio were larger in the rats in the experimental group than that of in the control group. The HE staining showed that the LF thickness in the experimental group significantly increased in comparison to the control group. The Masson trichrome staining showed that the ratio of elastic fibers to collagen fibers in experimental group was lower than that in the control group. The protein and gene expression of TGF-β1, TNF-α, IL-1β, and Col 1 were significantly higher in the experimental group than that in the control group.
Conclusion: It is the first time that lumbar instability directly induced LF hypertrophy in a reproducible rat model. Lumbar instability could lead to high expression of inflammatory and fibrotic factors in LF, causing the accumulation of collagen fibers and decreasing of elastic fibers.