Abstract: Objective To study the etiology of the degenerative and hypertrophied lumbar ligamentum flavum and its relationship to lumbar spinal stenosis Methods Ligamentum flavum specimens were obtained at operation from a total of 25 cases of LSS and 25 cases of lumbar disc herniation.These slices were selected for HE staining and immunohistochemistry staining. With immunohistology stain ,the expression of the three cytokines –TGF-β1 ,TNF-αand IL-6 were observed and compared between LSS and LDH, which was used to research the etiology of HLF. Results HE stain： LSS group: (1) Large fibrotic areas where collagenous tissue increased were almost consistently observed. (2) Fibrocytes were fewer and fibroblasts were more numerous than normal. The fibrocartilaginous zone near the bone insertion underwent enlargement. (3) Areas of calcification were often observed in the ligamentous tissue of stenotic patients, particularly the most elderly ones. (4) Blood vessels had increased in numbers and inflammatory cells were observed occasionally; immunohistochemistry staining：Comparing the degree of positive expression of TGF-β1 ,TNF-αand IL-6 in ligamentum flavum of LSS and LDH group ,the difference was statistically significant（p<0.01）;Conclusion: In the course of degeneration of LF, we observed that anti-inflammatory cytokines and inflammatory cytokines had gradually increased. Sterile inflammatory cytokines also lead to the degeneration, proliferation and hypertrophy of lumbar LF.

Key words: Lumbar vertebrae, cytokine, Ligamentum flavum, HE staining, Immunohistochemistry