| [Background]Degenerative lumar spondylolisthesis (DLS) is the slippage of one vertebra relative to the adjacent vertebrae due to spinal degenerative changes, DLS is not identifiable defect in the posterior neural arch. The main manifestations are mechanical low back pain, the radicular pain with numbness, paraesthesia, and sensory or motor deficit, and neurogenic claudication. This condition typically presents in individuals older than age 50 years, it occurs predominantly at the L4/5 level, and is approximately four times more common in females than in males. Previous studies showed that an overall incidence of DLS was 8.7% With the aging of the population, it will have the increasing incidence, lead to a diminished quality of life among the elderly, add the economic burden on families and society.DLS was first described by Junghanns in 1930, many studies have been undertaken in an attempt to explore its etiology and pathogenesis, but so far this are still controversial. Previous studies showed that DLS was the result of multiple factors, such as systematic and local. Pregnancy, joint laxity, and oophorectomy are thought to be predisposing factors of this condition in females. Local factors include lumbar disc degeneration, facet joint degeneration, soft tissue degeneration and relaxation. Degenerative changes, sagittal orientation of facet joints and facet tropsim have been described as predisposing factors. However, these results are considerable controversy.Many studies had showed that facet joints orientation were more sagittal in DLS, sagittal orientation of facet joints have been described as risk factors. The facet joints coronal orientation in infant stage becomes gradually more sagittal. This is subjected to shearing forces, allow the lumbar vertebra to slip forward. But some authors do not confirm the relationship between sagittal orientation of facet joints and DLS. It is unclear on the cause of sagittal orientation of facet joints, the results remain controversy. There exist two different points of view. On the one hand, the sagittal orientation of facet joints is a primary cause, or risk factor of DLS. The sagittal orientation of facet joints is congenital morphology in DLS patients. Love et al have suggested that sagittal orientation of facet joints was the pathological change of facet joints in DLS, and caused by the secondary remodeling after facet joint degeneration. The changes of sagittal orientation of facet joints are extremely complex and are the result of the interaction of various factors, for example, lumbar degeneration, large lumbosacral angle, relaxation of ligaments, pregnancy, hormone levels. All these factors lead to the increasing force in facet joints, the development of facet joint osteoarthritis(OA). The secondary remodeling of facet joints results in more sagittal orientation of facet joints. Fujiwara et al have found a significant association between sagittal orientation and OA of the lumbar facet joint, even in patients without degenerative spondylolisthesis. Pfirrmann et al have suggested that the sagittal orientation of facet joints is in response to pathological and biomechanics changes of facet joints. The sagittal facet joints may existed mechanical flaws on the posterior column, reduced the contact area of facet joint, increased the local force of facet joint, accelerated the degeneration of facet joints. Dai suggested that facet tropism was a predisposing factor to the development of disc degeneration and subsequent spondylolisthesis. Cyron and Hutton confirmed that facet joints with tropism tended to rotate toward the side with more coronal facet joints, and resulted in greater contact force on more sagittal facet joints. This may predispose these segments to develop degenerative changes.The degeneration of lumbar facet joint is closely related with the abnormal stress loads. The degeneration of facet joint may be induced by increasingly local stress. Many studies have confirmed abnormal stress could resulted in cartilage degeneration, There are high stress theory and low stress theory. Under low stress, the initial pathological changes of cartilage were chondrocytes degeneration. Under high stress, the disrupted matrix was found at the early stage. Although mechanical loads is the important reason to cause cartilage injury, but the exact mechanism is still unknown that how OA developes from cartilage injury. Although lumbar facet joint degeneration is similar to other synovial joints, OA is the main feature. But the pathogenesis of lumbar facet joint OA is not clear. There is few studies on the relationship between the degeneration and orientation changes of lumbar facet joint and stress. The aim of the experimental study is to build an animal model of facet joint loaded stress, to investigate pathological changes of degenerative facet joint and the expression of cytokines in facet joint cartilage, to explore mechanism of facet joints degeneration induced by abnormal stress and relationship between facet joint degeneration and orientation changes of facet joints. In retrospective case-control study,60 patients with DLS and 60 people free from spinal diseases were randomly selected. The facet angles were measured, then facet tropism was calculated. The severity of degeneration of facet joints was evaluated. The clinical study is to investigate the relationship between the facet tropism and the severity of degeneration of facet joints in DLS, and to explore its clinical significance. [Objective]1. To build an animal model of lumbar disc degeneration, to explore the feasibility of rabbit lumbar disc degeneration induced by needle aspirating the nucleus, to establish a reliable, effective, reproducible rabbit lumbar disc degeneration model for the study on the effect of the lumbar disc degeneration on facet joint degeneration.2. To build an rabbit model of facet joint loaded extension spring, to investigate pathological changes of degenerative facet joint under high stress and the effect of high stress on the lumbar facet joint degeneration.3. To observe orientation changes of facet joint under high stress, to explore the effect of high stress on the orientation of facet joint.4. To observe orientation changes of facet joint after degeneration, explore the relationship between orientation changes of facet joint and facet joint degeneration.5. To observe the expression of inflammatory cytokines in degenerative cartilage of facet joint, explore the role of cytokines in degenerative cartilage of facet joint.6. To investigate the relationship between the facet tropism and the severity of degeneration of facet joints in DLS, and to explore its clinical significance.[Methods]1. The L3/4 and L5/6 disc of 24 six-month-old healthy New Zealand white rabbits were included in the experimental group, the L2/3 and L4/5 disc were included in the control group. After intravenous pentobarbital, they were lied down as left lateral position, separated bluntly along the right posterolateral intermusecular by the right posterolateral approach, exposed transverse process and disc. The posterolateral annulus fibrosus were punctured by a 21 G needle with 10ml sterile disposable syringe parallel to the endplate. The needle was trapped with sterile plastic sleeve as to hold 5mm length and control 5mm depth. Lumbar discs in both groups were scaned with magnetic resonance imaging(MRI) at postoperative 6 weeks under anesthesia, and the severity of disc degeneration was observed and analyzed.2. Forty-two six-month-old New Zealand white rabbits were randomly divided into 4 groups:contral group(A Group, n=6), disc degeneration group(B Group, n=12), facet joint loading group(C Group, n=12), disc degeneration and facet joint loading group(D Group, n=12). The facet joints at L3/4 and L5/6 level in C Group and D Group were loaded extension spring to establish an animal model of facet joints degeneration induced by abnormal stress.3. The rabbit lumbar spines were harvested at 4 months and 8 months respectively, received MicroCT scaning, then facet joint angles were measured on transverse plane, the orientation changes of facet joint under high stress were observed.4. The facet joints were harvested for safranin O-fast green staining, the cartilage structure, matrix color were observed. Mankin histological-histochemical grading has been used to assess the severity of cartilage degeneration.5. Immunohistochemical staining was performed to investigate the expression of IL-1β,IL-6,TNF-αin facet joint cartilage.6. Sixty from 102 patients with DLS, treated in our hospital during May 2004 to August 2009, were randomly selected.60 age- and sex- matched people free from spinal diseases were selected as control group from a group of 300 coming for routine physical examination. The facet angles at L3/4, L4/5 and L5/S1 level on axial MRI were measured, then facet tropism was calculated. The severity of degeneration of facet joints was evaluated by using a 4-grade scale. The relativity analysis of obtained parameters was performed.7. Statistical analysis:Statistical analysis was performed using SPSS 13.0 statistical software. Measurement data were expressed by using X±S. Comparison between two groups, if they were measurement data, independent-sample t test would be used, if they were enumeration data or ranked data, we would apply Mann-Whitney U. Comparison among multiple groups were conducted using One-way ANOVA or Welch, and multiple comparisons were conducted using LSD or Dunnett T3, if they were measurement data. Comparison among multiple groups were conducted using Kruskal-Wallis H if they were enumeration data or ranked data, and multiple comparisons were conducted using Mann-Whitney U, significant level was corrected. The correlation analysis between Mankin score and facet joint angle was performed with bivariate correlation (Pearson test). Bivariate correlation (Spearman test) was used to analyzed the correlation between facet tropism and the severity of facet degeneration. Significant level was a=0.05.[Results]1. The MRI T2-weighted imaging at postoperative 6 weeks showed that the signal of nucleus pulposus was reducing and darken at L3/4 and L5/6 level, but the signal of nucleus pulposus was high at L2/3 and L4/5 level. The Thompson classification of MRI was significantly different (U=114.000, P=0.000) between the experimental group (mean rank 70.13) and the control group (mean rank 26.88) by using Mann-Whitney U test. 2. One-way ANOVA showed that there was significant difference in the facet angles among 4 groups (4 months F=3.862, P=0.016; 8 months F=4.775, P=0.006). Multiple comparisons were conducted using LSD, there was no significant difference in the facet angles between A Groups and B Group (P> 0.05), between C Group and D Group (P>0.05). Facet angles were smaller in C Group and D Group than those in A Groups and B Group (P<0.05). Facet angles at 8 months were smaller than those at 4 months in each group (P< 0.05).3. Gross specimen of facet joints in rabbit lumbar:cartilage surface of facet joint was gray white, semitransparent, smooth, with elastic capsule. Mildly degenerative cartilage was yellow, thinning. There was cartilage defects, exposed subchondral bone in severely degenerative articular, with fusion and osteophyte on sides. But there was cartilage in the central area.4. Mankin score:One-way ANOVA showed that there was significant difference in the severity of facet joint degeneration among 4 groups (4 months F=38.538, P=0.000; 8 months F=55.125, P=0.000). Multiple comparisons were conducted using LSD, there was no significant difference in the facet angles between A Groups and B Group (P>0.05), between C Group and D Group (P >0.05). Facet joint degeneration was more severe in C Group and D Group than that in A Groups and B Group (P<0.05). Facet joint degeneration at 8 months was more severe than that at 4 months in each group (P<0.05). There was negative correlation between facet joint degeneration and facet joint angle (4 months r=-0.527, P=0.000; 8 months r=-0.424, P=0.003).5. Immunohistochemical staining:There was positive expression of IL-1βin individual chondrocytes of the upper cartilage in A Group and B Group at 4 months, no expression of IL-6 and TNF-α. There was positive expression of IL-1β, IL-6 and TNF-αin chondrocytes of the middle and upper cartilage in A Group and B Group at 8 months, in chondrocytes of the full cartilage in C Group and D Group at 4 months. But the expression intensity of cytokines was significantly decreased in severe degeneration. The expression of IL-1βwas more intensive than that of IL-6 and TNF-a.6. The left facet joints were sagittally oriented than the right facet joints, but the difference was statistically significant only at L3/4 (t=3.047,P=0.003) and L4/5 (t=3.710, P=0.000) in the DLS group. The present results showed that facet joints at L3/4 (t=4.178, P=0.000) and L4/5 (t=6.703, P=0.000) level were more sagittally oriented in the DLS group than those in the control group. The facet tropism was significant difference among three levels in the DLS group (t=10.440, P=0.000), the facet tropism at L4/5 was greater than that at L3/4 (P=0.000) and L5/S1 (P=0.02) in the DLS group, but there was no significant difference among three levels in the control group (F=2.577, P=0.079). The severity of facet tropism was no significant difference among three levels in the DLS group (χ2=23.647, P=0.000) and the control group (χ2=7.633, P=0.022). The facet tropism at L4/5 was more severe than that at L3/4 and L5/S1 in the DLS group (P<0.017). The facet tropism in the DLS group was more severe than that in the control group (P<0.05). The facet tropism increased with the severity of degeneration of facet joints in both groups, there was positive correlation between the facet tropism and the severity of degeneration of facet joints in both groups (P<0.05).[Conclusions]1. Needle aspirating the nucleus is available for reproducting the disc degeneration without destroying the immune barrie and overall structure of disc, providing effective animal model to study the effect of disc degeneration on lumbar facet joints.2. The results show that facet joints in rabbits undergo osteoarthrotic changes in response to local abnormal stress-loading and confirm the rabbits as a suitable model for the study of degenerative spinal disorders. The longer the stress, the more severe facet joint degeneration. More severe facet joint degeneration, more sagittal orientation of facet joint. There was negative correlation between facet joint degeneration and facet joint angle.3. The chondrocytes in the degenerative cartilage could synthese and secrete cytokines abnormally. Cytokines involved in cartilage matrix degradation and changes in cell function. Cytokines play an important role in different periods of facet joint degeneration. Positive intensity of expression of cytokines and the severity of OA is not parallel.4. Facet tropism was quite common in lower lumbar level. There was a positive correlation between the facet tropism and the severity of degeneration of facet joints. Facet tropism was not simply due to secondary osteoarthritic remodeling but also part of the pre-existing morphologic abnormality. The facet tropism increased the risk in the development of DLS. The facet tropism and the severity of degeneration of facet joints had an important etiologic meaning in the occurrence of DLS. |
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