Role of Epiligament in Ligamentum Flavum Hypertrophy in Patients with Lumbar Spinal Canal Stenosis:a Pilot Study

Innovative surgical and stress-stimulated rat model of ligamentum flavum hypertrophy

Background and purpose

Animal models of LFH are still in the exploratory stage. This study aimed to establish a reliable, efficient, and economical model of LFH in rats for the study of human ligamentum flavum (LF) pathological mechanisms, drug screening, development, improvement of surgical treatment, disease prevention, and other aspects.

Methods and materials

Forty rats were divided into an experimental group and a sham group of 20 rats. The experimental group (n = 20) was treated with an innovative operation combined with stress stimulation at the L5-L6 segments, the L5 and L6 spinous processes, transverse processes, and supraspinous ligaments were excised, along with removal of the paraspinal muscles at the L5-L6 level. One week after surgery, the rats were subjected to slow treadmill running daily. In the experimental group (n = 20), the spinous process, transverse process, supraspinous ligament and paraspinous muscle of L5 and L6 were excised. And for a week after the surgery, the rats ran on a treadmill at a slow pace every day. While the sham group (n = 20) was treated with sham operation only. Seven weeks later, MRI, immunohistochemistry (IHC), and western blot (WB) will be performed on the LF of the L5-6 segment in the two groups of rats.

Results

MRI results showed that the LF in the experimental group was significantly thicker than that in the sham group. Masson staining results indicated that LF thickness, collagen fiber area, and collagen volume fraction (CVF) were significantly higher in the experimental group than in the sham group. IHC and WB showed that the expression of TGF-β1, COL1, and IL-1β in the LF of the experimental group was significantly higher than that in the LF of sham group.

Conclusion

Through innovative surgical intervention combined with stress stimulation, a relatively reliable, efficient, and convenient rat LFH model was established.

Increased matrix metalloproteinase-2 in ligamentum flavum hypertrophy and the regulation of MMP-2/TIMPs by elastin-derived peptides

The study aimed to examine matrix metalloproteinase-2 (MMP-2) expression in a rat ligamentum flavum (LF) hypertrophy model in vivo, and the effect of elastin-derived peptides (EDPs) on MMP-2 and tissue inhibitors of metalloproteinases (TIMPs) in rat LF cells in vitro. Surgical destabilization was performed at the rat spinal L3/4 level to induce increased mechanical stress. Rats were killed at 6- and 12-weeks postsurgery for histological staining, immunohistochemical staining, RT-qPCR and western blot. 100 µg/mL EDPs were applied to isolated normal rat LF cells, with or without pretreatment of elastin receptor complex (ERC) inhibitors, to assess the expression of MMP-2, TIMP-1, and TIMP-2. Spinal destabilization led to LF hypertrophy, observed through increased LF thickness and area, along with histological changes of chondrometaplasia and elastic fiber degradation. LF was also stained positively for Col I and Col II, where elastic fiber has broken down. MMP-2 expression was notably elevated in the hypertrophied LF, accompanied by increased TIMP-2 and TIMP-3 levels. EDPs were found to suppress MMP-2 expression and reduce TIMP-1 and TIMP-2 levels in rat LF cells. Interestingly, exposure to EDPs led to a significant rise in MMP-2/TIMP-1 and MMP-2/TIMP-2 ratios, dependent on the ERC. Collectively, the study suggests that increased MMP-2 activity contributes to elastic fiber degradation in hypertrophied LF, generating EDPs that further enhance the MMP-2/TIMPs ratio in LF cells in an ERC-dependent manner. Further research is essential to delve into the mechanisms of EDPs in LF hypertrophy.

An in vivo model of ligamentum flavum hypertrophy from early-stage inflammation to fibrosis

Multi-joint disease pathologies in the lumbar spine, including ligamentum flavum (LF) hypertrophy and intervertebral disc (IVD) bulging or herniation contribute to lumbar spinal stenosis (LSS), a highly prevalent condition characterized by symptomatic narrowing of the spinal canal. Clinical hypertrophic LF is characterized by a loss of elastic fibers and increase in collagen fibers, resulting in fibrotic thickening and scar formation. In this study, we created an injury model to test the hypothesis that LF needle scrape injury in the rat will result in hypertrophy of the LF characterized by altered tissue geometry, matrix organization, composition and inflammation. An initial pilot study was conducted to evaluate effect of needle size. Results indicate that LF needle scrape injury using a 22G needle produced upregulation of the pro-inflammatory cytokine Il6 at 1 week post injury, and increased expression of Ctgf and Tgfb1 at 8 weeks post injury, along with persistent presence of infiltrating macrophages at 1, 3, and 8 weeks post injury. LF integrity was also altered, evidenced by increases in LF tissue thickness and loss of elastic tissue by 8 weeks post injury. Persistent LF injury also produced multi-joint effects in the lumbar IVD, including disc height loss at the injury and adjacent to injury level, with degenerative IVD changes observed in the adjacent level. These results demonstrate that LF scrape injury in the rat produces structural and molecular features of LF hypertrophy and IVD height and histological changes, dependent on level. This model may be useful for testing of therapeutic interventions for treatment of LSS and IVD degeneration associated with LF hypertrophy.

Comparison of ligamentum flavum thickness between central and lateral lesions in a patient with central lumbar spinal canal stenosis

Thickened ligamentum flavum has been considered as a major cause of central lumbar spinal canal stenosis (CLSCS). Previous studies have demonstrated that ligamentum flavum thickness (LFT) is correlated with aging, degenerative spinal stenosis, and disc degeneration. Thus, hypertrophy of the ligamentum flavum is a major cause of CLSCS, and measurement of LFT has been considered a morphologic parameter in the diagnosis of CLSCS. To our knowledge, comparison of LFT between central and lateral lesions has not been reported. In addition, no research has analyzed best clinical cutoff values of central ligament flavum thickness (CLFT) and lateral ligament flavum thickness (LLFT). This study aimed to compare CLFT with LLFT in patients with CLSCS and further compare the CLFT and LLFT findings between the 2 groups to analyze LFT variation. Both CLFT and LLFT samples were collected from 101 participants with CLSCS and from 103 participants in the control group who underwent lumbar magnetic resonance imaging without evidence of CLSCS. Axial T2-weighted lumbar magnetic resonance scans were acquired at the L4 to 5 facet joint level from each participant. Average CLFT value was 2.25 ± 0.51 mm in the control group and 4.02 ± 0.74 mm in the CLSCS group. Average LLFT value was 2.50 ± 0.51 mm in the control group and 3.38 ± 0.66 mm in the CLSCS group. CLSCS patients had significantly higher CLFT and LLFT (both P < .001). Regarding the validity of both CLFT and LLFT as predictors of CLSCS, a receiver operating characteristic estimation revealed that the most suitable cutoff value for CLFT was 3.10 mm, with sensitivity of 95.0%, specificity of 94.2%, and an area under the curve of 0.97. The best cut-off value of LLFT was 2.92 mm, with sensitivity of 78.2%, specificity of 77.7%, and area under the curve of 0.87. We have 4 important new findings: The mean CLFT is significantly lower than that of the mean LLFT in the normal control group; CLFT and LLFT are both significantly associated with CLSCS; Increase rate of CLFT is faster than that of LLFT in the CLSCS group; and CLFT is a more sensitive measurement parameter to predict CLSCS than LLFT.

Transcriptome-wide association study reveals candidate causal genes for lumbar spinal stenosis

Aims

Lumbar spinal stenosis (LSS) is a common skeletal system disease that has been partly attributed to genetic variation. However, the correlation between genetic variation and pathological changes in LSS is insufficient, and it is difficult to provide a reference for the early diagnosis and treatment of the disease.

Methods

We conducted a transcriptome-wide association study (TWAS) of spinal canal stenosis by integrating genome-wide association study summary statistics (including 661 cases and 178,065 controls) derived from Biobank Japan, and pre-computed gene expression weights of skeletal muscle and whole blood implemented in FUSION software. To verify the TWAS results, the candidate genes were furthered compared with messenger RNA (mRNA) expression profiles of LSS to screen for common genes. Finally, Metascape software was used to perform enrichment analysis of the candidate genes and common genes.

Results

TWAS identified 295 genes with permutation p-values < 0.05 for skeletal muscle and 79 genes associated for the whole blood, such as RCHY1 (PTWAS = 0.001). Those genes were enriched in 112 gene ontology (GO) terms and five Kyoto Encyclopedia of Genes and Genomes pathways, such as 'chemical carcinogenesis - reactive oxygen species' (LogP value = -2.139). Further comparing the TWAS significant genes with the differentially expressed genes identified by mRNA expression profiles of LSS found 18 overlapped genes, such as interleukin 15 receptor subunit alpha (IL15RA) (PTWAS = 0.040, PmRNA = 0.010). Moreover, 71 common GO terms were detected for the enrichment results of TWAS and mRNA expression profiles, such as negative regulation of cell differentiation (LogP value = -2.811).

Conclusion

This study revealed the genetic mechanism behind the pathological changes in LSS, and may provide novel insights for the early diagnosis and intervention of LSS.

Histological difference in ligament flavum between degenerative lumbar canal stenosis and non-stenotic group: A prospective, comparative study

BACKGROUND

Ligament flavum (LF) hypertropy is the main etiopathogenesis of lumbar canal stenosis (LCS). The purely elastic LF undergoes a morphological adaptation including a reduction in the elastic fibers and a consequent increase in the collagen content, fibrosis, cicatrization, and calcification. However, the morphometric analysis can delineate the LF in patients with LCS from those without LCS, which would help in better understanding LCS pathogenesis.

AIM

To compare the histopathological changes in LF between the degenerative LCS and non-stenotic (non-LCS) group.

METHODS

The present prospective study was conducted in 82 patients who were divided into two groups, namely LCS and non-LCS. Demographic details of the patients such as duration of symptoms, level of involvement, and number of segments were recorded. The LF obtained from both groups was histopathologically examined for the fibrosis score, elastic fiber degeneration, calcification, and chondroid metaplasia. Morphometrical details included a change in elastin and collagen percentages, elastin/collagen ratio, elastic fiber fragmentation, and ligamentocyte numbers. All parameters were compared between the two groups by using the independent t test, Chi-square test, and Pearson’s correlation test.

RESULTS

Out of 82 cases, 74 were analysed, 34 in LCS and 40 in non-LCS group. The mean ± SD age of presentation in LCS and non- LCS group was 49.2 ± 8.9 and 43.1 ± 14.3 respectively. The LCS group (n = 34) exhibited significant differences in fibrosis (P = 0.002), elastic fiber degeneration (P = 0.01), % elastic fragmentation (66.5 ± 16.3 vs 29.5 ± 16.9), % elastic, content (26.9 ± 6.7 vs 34.7 ± 8.4), % collagen content (63.6 ± 10.4 vs 54.9 ± 6.4), reduction of elastic/collagen (0.4 ± 0.1 vs 0.6 ± 0.1), and ligamentocyte number (39.1 ± 19.1 vs 53.5 ± 26.9) as compared to non-LCS group (n = 40). The calcification (P = 0.08) and Pearson’s correlation between duration and loss of elastin was not significant. The difference in LF morphology is consistent in patient’s ≥ 40 years of age among the groups as found in subgroup analysis. Similarly in the patents < 40 and > 40 in the non-LCS group.

CONCLUSION

LF is vital in the pathogenesis of LCS. The purely elastic LF undergoes a morphological adaptation that includes a reduction in the elastic fibers with a consequent increase in the collagen content, fibrosis, cicatrization, and calcification. The present study provides a detailed morphometric analysis to semiquantitatively delineate the LF changes in patients with LCS from those in patients without LCS.

The increased motion of lumbar induces ligamentum flavum hypertrophy in a rat model

BACKGROUND

The purpose of this study was to establish a novel rat model for ligamentum flavum (LF) hypertrophy using increased motion of lumbar and to elucidate the etiology of (LFH).

METHODS

A total number of 30 male rats were used. The increased motion of lumbar 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, flexion ratio, and extension ratio were larger in the rats in the experimental group than that of in the sham group. The HE staining showed that the LF thickness in the experimental group significantly increased in comparison to the sham group. The Masson trichrome staining showed that the ratio of elastic fibers to collagen fibers in experimental group was lower than that in the sham 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 sham group.

CONCLUSION

A relatively safe, simple, and rapid rat model of LFH using increased motion of lumbar was established. The increased motion of lumbar could lead to high expression of inflammatory and fibrotic factors in LF, causing the accumulation of collagen fibers and decreasing of elastic fibers.

Ligamentum flavum fibrosis and hypertrophy: Molecular pathways, cellular mechanisms, and future directions

Hypertrophy of ligamentum flavum (LF), along with disk protrusion and facet joints degeneration, is associated with the development of lumbar spinal canal stenosis (LSCS). Of note, LF hypertrophy is deemed as an important cause of LSCS. Histologically, fibrosis is proved to be the main pathology of LF hypertrophy. Despite the numerous studies explored the mechanisms of LF fibrosis at the molecular and cellular levels, the exact mechanism remains unknown. It is suggested that pathophysiologic stimuli such as mechanical stress, aging, obesity, and some diseases are the causative factors. Then, many cytokines and growth factors secreted by LF cells and its surrounding tissues play different roles in activating the fibrotic response. Here, we summarize the current status of detailed knowledge available regarding the causative factors, pathology, molecular and cellular mechanisms implicated in LF fibrosis and hypertrophy, also focusing on the possible avenues for anti-fibrotic strategies.