Gait abnormality due to spinal instability after lumbar facetectomy in the rat

Development of a novel animal model of lumbar vertebral endplate lesion by intervertebral disk injection of monosodium iodoacetate in rats

PURPOSE

Vertebral endplate lesions (EPLs) caused by severe disk degeneration are associated with low back pain. However, its pathophysiology remains unclear. In this study, we aimed to develop a vertebral EPL rat model mimicking severe intervertebral disk (IVD) degeneration by injecting monosodium iodoacetate (MIA) into the IVDs and evaluating it by assessing pain-related behavior, micro-computed tomography (CT) findings, and histological changes.

METHODS

MIA was injected into the L4-5 and L5-6 IVDs of Sprague-Dawley rats. Their behavior was examined by measuring the total distance traveled and the total number of rearing in an open square arena. Bone alterations and volume around the vertebral endplate were assessed using micro-CT. Safranin-O staining, immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining were performed for histological assessment.

RESULTS

The total distance and number of rearing times in the open field were significantly reduced in a time-dependent manner. Micro-CT revealed intervertebral osteophytes and irregularities in the endplates at 12 weeks. The bone volume/tissue volume (BV/TV) around the endplates significantly increased from 6 weeks onward. Safranin-O staining revealed severe degeneration of IVDs and endplate disorders in a dose- and time-dependent manner. Calcitonin gene-related peptide-positive nerve fibers significantly increased from 6 weeks onward. However, the number of osteoclasts decreased over time.

CONCLUSION

Our rat EPL model showed progressive morphological vertebral endplate changes in a time- and concentration-dependent manner, similar to the degenerative changes in human IVDs. This model can be used as an animal model of severe IVD degeneration to better understand the pathophysiology of EPL.

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.

Development of a Novel Rat Intervertebral Disc Degeneration Model by Surgical Multifidus Resection-Induced Instability

OBJECTIVE

This study aimed to investigate whether surgical resection of multifidus in rats could generate a reliable model of intervertebral disc degeneration (IVDD).

METHODS

Instability of the lumbar spine in Sprague-Dawley rats was induced by multifidus resection. Longissimus changes were examined by hematoxylin and eosin staining and immunohistochemistry. Specific protein and mRNA changes in the nucleus pulposus (NP) were quantified by Western blot and reverse transcription-polymerase chain reaction. Bone alterations were assessed using X-ray imaging, and disc changes were evaluated by hematoxylin and eosin staining, immunofluorescence, and immunohistochemistry.

RESULTS

Fat infiltration and increased tumor necrosis factor-α expression in the longissimus were detected following surgery. Reverse transcription-polymerase chain reaction and Western blot results demonstrated that the inflammation and catabolism in the NP were increased after the surgical intervention. Moreover, X-ray imaging showed that the disc height had decreased and bone spurs had formed at the vertebral rims. Histological analyses further revealed degeneration of the annulus fibrosus, endplate, and NP. Furthermore, in contrast to the sham group, the collagen II expression was reduced, while matrix metalloproteinase-13 was increased in the surgery group.

CONCLUSIONS

Surgical resection of the multifidus in rats resulted in a reproducible IVDD model. Because the present procedure does not impart direct injury to the intervertebral disc, it can better imitate the pathological states in humans. Therefore, our rat multifidus resection model might help us further understand the intrinsic pathophysiology of IVDD.

Effects of Different Static Progressive Stretching Durations on Range of Motion, Myofibroblasts, and Collagen in a Posttraumatic Knee Contracture Rat Model

OBJECTIVE

The purpose of this study was to investigate the effects of different durations of static progressive stretching (SPS) on posttraumatic knee contracture in rats, including range of motion (ROM), gait analysis, myofibroblast proliferation, and collagen regulation.

METHODS

The posttraumatic knee contracture model was established, and male Wistar rats were randomly divided into the 20-minute SPS treatment, 30-minute SPS treatment (S30), 40-minute SPS treatment, untreated, immobilization, and control groups. At Week 1, 2, and 4 of treatment intervention, joint ROM and gait were measured and compared. Knee joint samples stained with hematoxylin and eosin and Masson trichrome were used to observe alterations in pathological structures. Collagen density and cell numbers in the posterior joint capsule were used to assess joint capsule fibrosis and inflammation. Immunohistochemistry was used to detect type I collagen and α-smooth muscle actin expression.

RESULTS

The S30 group improved the most; ROM, stance, mean intensity, print area, and stride length were 115 (SD = 5) degrees, 0.423 (SD = 0.074) seconds, 156.020 (SD = 7.952), 2.116 (SD = 0.078) cm2, and 11.758 (SD = 0.548) cm, respectively. The numbers of myofibroblasts, fibroblasts, and inflammatory cells decreased, and collagen proliferation was significantly suppressed in the S30 group compared with the other groups.

CONCLUSION

S30 significantly improved posttraumatic knee contracture in rats, with reduced type I collagen and α-smooth muscle actin expression, decreased the numbers of myofibroblasts and inflammatory cells, suppressed fibrotic and inflammatory changes in the joint capsule, and increased joint mobility. This study provided basic evidence for an optimal standard-of-care treatment approach for posttraumatic knee joint contracture in rats, which may have significance for humans.

Development of a rat model with lumbar vertebral endplate lesion

PURPOSE

Vertebral endplate lesion (EPL) caused by severe disc degeneration is associated with low back pain. However, there is no suitable animal model to elucidate the pathophysiology of EPL. This study aimed to develop a rat model of EPL and evaluate rat behavior and imaging and histological findings.

METHODS

The L4-5 intervertebral discs of Sprague-Dawley rats were transperitoneally removed, except for the outer annulus fibrosus and cartilage endplate, in the EPL group. The L4-5 discs were not removed and simply exposed in the sham group. Changes around the vertebral endplate on magnetic resonance imaging (MRI) and computed tomography (CT) were evaluated. Additionally, pain-related behavioral and histological assessments were performed.

RESULTS

In the EPL group, a low-signal area around the vertebral endplate was observed on T1-weighted and T2-weighted fat-saturated MRI at 8 weeks or later after surgery. In the same group, CT showed osteosclerosis around the vertebral endplate at 12 weeks after surgery. The sham group did not show abnormal imaging features on the MRI and CT. Behavioral evaluation showed that the EPL group had a significantly longer grooming time than the sham group. Conversely, the 12-week postoperative locomotion time and the 1- and 12-week postoperative standing times were significantly shorter in the EPL group than in the sham group. Histological evaluation showed a high degree of vertebral endplate degeneration and an increased number of osteoclasts and proportion of nerve fibers expressing calcitonin gene-related peptide in the EPL group compared to those in the sham group.

CONCLUSION

Our rat EPL model showed pain-related behavioral patterns and an increased expression of pain-related neuropeptide. This model could contribute to the study of the pathophysiology of EPL and will help in the treatment of low back pain in the future.

Experimental Rat Model of Bony Defects in the Facet Joint Maintained with Bone Wax for the Study of Spinal Pain

Purpose

Studies using experimental rat models for low back pain due to facet-joint defects are scarce. This study used a novel experimental rat model to determine whether bony defects induced by facetectomy could be maintained by bone wax, thus mimicking spondylolysis, and to analyze the effect of the facetectomy on rat behavior.

Patients and Methods

Twelve 10-week-old male Wistar rats weighing 300–350 g were divided into group A (n = 6) that underwent unilateral facetectomy of the right L5-6 facet joint and group B (n = 6) that additionally applied water-soluble bone wax at the facetectomy site. The difference in the left and right stride length, detected by the footprint test, and change in the left and right facet joint area were compared before and 4 weeks after the experiment.

Results

Even though the difference between the left and right stride lengths of groups A and B was not statistically significant, in contrast to group A, group B showed a shorter stride length on the right side (p = 0.22 and 0.46, in group A and group B, respectively). The right facet joint area, where the facetectomy was performed, was significantly smaller in group B 4 weeks after surgery, but not in group A (p = 0.50 and < 0.01, in group A and group B, respectively).

Conclusion

Based on the results, we concluded that the bony defects, induced by facetectomy at the L5-6 facet joint, were maintained with bone wax. This study will provide an experimental model for bony defects in the facet joint.

WISP-1 induced by mechanical stress contributes to fibrosis and hypertrophy of the ligamentum flavum through Hedgehog-Gli1 signaling

Ongoing chronic fibrosis and hypertrophy of the ligamentum flavum (LF) is an important cause of lumbar spinal canal stenosis (LSCS). Our previous work showed that WNT1-inducible signaling pathway protein 1 (WISP-1) is a critical driver of LF fibrosis. However, the potential mechanism has not been explored. Here, we found that Gli1 was upregulated in hypertrophic LF tissues and required for fibrogenesis in fibroblasts. Moreover, mechanical stretching increased the expression of WISP-1 in LF fibroblasts. Furthermore, WISP-1 induced fibrogenesis in vitro through the Hedgehog-Gli1 pathway. This conclusion was supported by the fact that WISP-1 activated the Hedgehog-Gli1 pathway in LF fibroblasts and that cyclopamine attenuated the effect of WISP-1-induced fibrogenesis. WISP-1 also promoted the transition of fibroblasts into myofibroblasts via the Hedgehog pathway. Importantly, a hypertrophic LF rabbit model induced by mechanical stress also showed pathological changes in fibrosis and elevated expression of WISP-1, Gli1, and α-SMA. Therapeutic administration of cyclopamine reduced collagen expression, fibroblast proliferation, and myofibroblast differentiation and ameliorated fibrosis in the mechanical stress-induced rabbit model. Collectively, our findings show mechanical stress/WISP-1/Hedgehog signaling as a new fibrotic axis contributing to LF hypertrophy and identify Hedgehog signaling as a therapeutic target for the prevention and treatment of LF fibrosis.

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.

Painful intervertebral disc degeneration and inflammation: from laboratory evidence to clinical interventions

Low back pain (LBP), as a leading cause of disability, is a common musculoskeletal disorder that results in major social and economic burdens. Recent research has identified inflammation and related signaling pathways as important factors in the onset and progression of disc degeneration, a significant contributor to LBP. Inflammatory mediators also play an indispensable role in discogenic LBP. The suppression of LBP is a primary goal of clinical practice but has not received enough attention in disc research studies. Here, an overview of the advances in inflammation-related pain in disc degeneration is provided, with a discussion on the role of inflammation in IVD degeneration and pain induction. Puncture models, mechanical models, and spontaneous models as the main animal models to study painful disc degeneration are discussed, and the underlying signaling pathways are summarized. Furthermore, potential drug candidates, either under laboratory investigation or undergoing clinical trials, to suppress discogenic LBP by eliminating inflammation are explored. We hope to attract more research interest to address inflammation and pain in IDD and contribute to promoting more translational research.

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.

Increased Substance P Immunoreactivity in Ipsilateral Knee Cartilage of Rats Exposed to Lumbar Spine Injury

OBJECTIVE

The present study aimed to investigate whether experimentally induced lumbar facet-joint OA lead to degenerative changes and enhanced SP expression within the ipsilateral neurosegmentally linked tibiofemoral cartilage.

METHODS

Adult male Sprague-Dawley rats were assigned to left side L5-L6 facet mechanical compression injury (surgery) (n = 6), L5-L6 facet exposure with no compression (sham) (n = 5), or naïve (no surgery) (n = 4) groups. The morphology of the tibiofemoral articular cartilage was assessed using a modified Mankin scoring system. Immunohistochemistry was used to examine the density of chondrocytes stained positive for SP (cells/cm²) in the ipsilateral tibiofemoral cartilage at 28 days postintervention.

RESULTS

Tibiofemoral cartilage in the surgery group showed consistent loss of superficial zone chondrocytes, mild roughening of the articular surface and occasional chondrocyte clusters as well as a greater density of SP mainly in the superficial cartilage zone compared with sham and naïve groups, although they also had a basic SP-expression.

CONCLUSION

Our results support the hypothesis that neurogenic mechanisms may mediate the spread of SP to neurosegmentally linked heterologous joints affecting the distal cartilage homeostasis. These findings contribute additional insight into the potential role of neurogenic inflammation with implications in the pathophysiology of chronic inflammatory joint disease and OA.

Pathomechanism of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the main contributor to low back pain, which is a leading cause of disability worldwide. Although substantial progress has been made in elucidating the molecular mechanisms of IDD, fundamental and long-lasting treatments for IDD are still lacking. With increased understanding of the complex pathomechanism of IDD, alternative strategies for treating IDD can be discovered. A brief overview of the prevalence and epidemiologic risk factors of IDD is provided in this review, followed by the descriptions of anatomic, cellular, and molecular structure of the intervertebral disc as well as the molecular pathophysiology of IDD. Finally, the recent findings of intervertebral disc progenitors are reviewed and the future perspectives are discussed.

Estrogen Deficiency Exacerbates Intervertebral Disc Degeneration Induced by Spinal Instability in Rats

STUDY DESIGN

An experimental animal study of osteoporosis (OP) and intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to clarify the effects of estrogen deficiency and supplement on cervical IDD induced by bilateral facetectomy in rats.

SUMMARY OF BACKGROUND DATA

The relationship between IDD and OP is still controversy with the wide prevalence in aged people.

METHODS

Seventy-two Sprague-Dawley female rats were randomly divided into ovariectomy (OVX) group, facet joints resection of C4-6 (FR), FR-OVX group, estrogen replacement therapy (ERT, based on the FR-OVX group) group, and sham group. Specimens of C4-6 segment were harvested at 12 and 24 weeks. The microstructures of C5 vertebrae, vertebral endplate lesions and calcification, and IDD of C5/6 disc were evaluated by micro-computed tomography (micro-CT) and histology. The protein and gene levels of aggrecan, Col2α1, matrix metalloprotease (MMP)-3, and MMP-13 in the C5/6 and C4/5 discs were measured.

RESULTS

Microstructures of C5 vertebral body were weakened significantly after ovariectomy, while restored effectively with estradiol supplementation. The facetectomy led to significant IDD, and the IDD was aggravated when combined with OVX. The IDD of the ERT group was alleviated effectively and similar to that of the FR group in intervertebral disc height, vertebral endplate lesions and calcification, and disc degeneration scores. In addition, the estrogen supplement maintained the extracellular matrix by decreasing MMP-3 and MMP-13, and increasing aggrecan and Col2α1 expression.

CONCLUSION

The present study demonstrated that estrogen deficiency exacerbated IDD induced by spinal instability, while estrogen supplementation alleviated the progression of disc degeneration related to osteoporosis.

LEVEL OF EVIDENCE

N/A.

A Mouse Intervertebral Disc Degeneration Model by Surgically Induced Instability

STUDY DESIGN

An experimental study to develop a mouse model of lumbar intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to develop a mouse lumbar IDD model using surgically induced instability and to compare the findings of this model to those in human IDD.

SUMMARY OF BACKGROUND DATA

Previously, various kinds of inducers have been used to reproduce IDD in experimental animals; however, there is yet no standard mouse lumbar IDD model without direct injury to intervertebral disc.

METHODS

A total number of 59 C57BL/6J male mice at 8 weeks old were used. Instability of lumbar spine was induced by surgical resection of posterior elements, including facet joints, supra- and interspinous ligaments. We then analyzed time course changes in radiographical (n = 17) and histological analyses (n = 42), and compared these findings with those in human IDD.

RESULTS

Radiographical analyses showed that the disc height began to decrease in the first 2 weeks after the surgery, and the decrease continued throughout 12 weeks. Bone spurs at the vertebral rims were observed in the late stage of 8 and 12 weeks after the surgery. Histological analyses showed that the disorder of the anterior anulus fibrosus (AF) was initially obvious, followed by posterior shift and degeneration of the nucleus pulposus (NP). Proteoglycan detected in inner layer of AF and periphery of NP was decreased after 8 weeks. Immunohistochemistry displayed the increase of type I and X collagen, and matrix metalloproteinase 13 in the anterior AF.

CONCLUSION

Surgical resection of posterior elements of mouse lumbar spine resulted in reproducible IDD. Because the present procedure does not employ direct injury to intervertebral disc and the radiological and histological findings are compatible with those in human IDD, it may contribute to further understanding of the native pathophysiology of IDD in future.

LEVEL OF EVIDENCE

N/A.

Chronic low back pain: a mini-review on pharmacological management and pathophysiological insights from clinical and pre-clinical data

Globally, low back pain (LBP) is one of the most common health problems affecting humans. The lifetime prevalence of non-specific LBP is approximately 84%, with the chronic prevalence at about 23%. Chronic LBP in humans is defined as LBP that persists for more than 12 weeks without a significant pain improvement. Although there are numerous evidence-based guidelines on the management of acute LBP, this is not the case for chronic LBP, which is regarded as particularly difficult to treat. Research aimed at discovering new drug treatments for alleviation of chronic mechanical LBP is lacking due to the paucity of knowledge on the pathobiology of this condition, despite its high morbidity in the affected adult population. For a debilitating condition such as chronic LBP, it is necessary to assess the sustained effects of pharmacotherapy of various agents spanning months to years. Although many rodent models of mechanical LBP have been developed to mimic the human condition, some of the major shortcomings of many of these models are (1) the presence of a concurrent neuropathic component that develops secondary to posterior intervertebral disc puncture, (2) severe model phenotype, and/or (3) use of behavioural endpoints that have yet to be validated for pain. Hence, there is a great, unmet need for research aimed at discovering new biological targets in rodent models of chronic mechanical LBP for use in drug discovery programs as a means to potentially produce new highly effective and well-tolerated analgesic agents to improve relief of chronic LBP. On a cautionary note, it must be borne in mind that because humans and rats display orthograde and pronograde postures, respectively, the different mechanical forces on their spines add to the difficulty in translation of promising rodent data to humans.

Animal models for studying the etiology and treatment of low back pain

Chronic low back pain is a major cause of disability and health care costs. Effective treatments are inadequate for many patients. Animal models are essential to further understanding of the pain mechanism and testing potential therapies. Currently, a number of preclinical models have been developed attempting to mimic aspects of clinical conditions that contribute to low back pain (LBP). This review focused on describing these animal models and the main behavioral tests for assessing pain in each model. Animal models of LBP can be divided into the following five categories: Discogenic LBP, radicular back pain, facet joint osteoarthritis back pain, muscle-induced LBP, and spontaneous occurring LBP models. These models are important not only for enhancing our knowledge of how LBP is generated, but also for the development of novel therapeutic regimens to treat LBP in patients. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1305-1312, 2018.

Mechanical stress induces elastic fibre disruption and cartilage matrix increase in ligamentum flavum

Lumbar spinal stenosis (LSS) is one of the most frequent causes of low back pain and gait disturbance in the elderly. Ligamentum flavum (LF) hypertrophy is the main pathomechanism of LSS, but the reason for its occurrence is not clearly elucidated. In this study, we established a novel animal model of intervertebral mechanical stress concentration and investigated the biological property of the LF. The LF with mechanical stress concentration showed degeneration with elastic fibres disruption and cartilage matrix increase, which are similar to the findings in hypertrophied LF from patients with LSS. By contrast, decreased Col2a1 expression was found in the LF at fixed levels, in which mechanical stress was strongly reduced. These findings indicate that mechanical stress plays a crucial role in LF hypertrophy through cartilage matrix increase. The findings also suggest that fusion surgery, which eliminates intervertebral instability, may change the property of the LF and lead to the relief of patients' symptoms.

Three-dimensional micro-computed tomography analysis for spinal instability after lumbar facetectomy in the rat

PURPOSE

Intervertebral disc degeneration is thought to contribute to low back pain. However, the pathophysiological mechanisms remain controversial. In a previous study, we developed an animal model that showed delayed gait disturbance after lumbar facetectomy in the rat. We believe that this gait disturbance was caused by low back pain, although the mechanisms of this gait abnormality remain unknown. The purpose of this study was to evaluate structural changes of the lumbar spine after facetectomy in the rat utilizing three-dimensional micro-computed tomography (3DμCT) compared to histology.

METHODS

Thirty male SD rats were divided into three groups. In the Sham group (n = 13), only exposure of bilateral facet joints at the L4-5 level was performed. In the Experimental group (n = 13), complete resection of bilateral L4-5 facet joints was achieved. Naïve rats (n = 4) were used for controls. At 7-week postoperative, 3DµCT and histological analyses were performed.

RESULTS

On 3DµCT images, increased disc height and endplate irregularities at the L4-5 segment and decreased disc height at adjacent segments were observed in the Experimental group. Histological scores were also higher in the Experimental group than the Sham Group.

CONCLUSIONS

Degenerative changes were observed at the facetectomy level. These may correspond with the previously reported delayed gait disturbance after facetectomy. This animal model may be useful to create mechanically induced disc degeneration without direct tissue damage to the disc.