动静力失衡对大鼠颈椎不同节段椎间盘退变影响的显微CT形态学和组织学研究

Effects of imbalance of dynamic and static forces on the disc degeneration of cervical spine at different levels in rats: a micro-CT morphology and histology study

目的：评价大鼠动静力失衡颈椎退变模型对C4～C7各节段终板磨损面积、椎间高度和椎间盛邀变的影响．并分析终板磨损面积和椎间高度与椎间盘退变的相天性。方法：24只3月龄雌性SD大鼠随机分为模型组（14只）和对照组（10只）。对照组仅做皮肤切口；模型组大鼠横向切断颈背部肌肉以及韧带，制作大鼠动静力失衡颈椎退变模型。术后12周、18周、24周分三次取大鼠颈椎标本。标本取材后进行显微CT扫描以及番红O快绿染色。测量C4／5、C5／6、C6／7各个节段椎间高度，计算上述三个节段的终板磨损比例，并对椎间盘赶退变程度进行评分。应SPSS13．0比较不同组相同节段椎间盘的终板磨损率，椎间高度和退变评分，并分析终板磨损率与椎间盘退变之间的相关性。结果：显微CT扫描发现模型组术后12周各个节段软骨终板均出现明显的磨损．磨损主要位于终板的腹侧。颈椎节段越高，磨损程度越轻。术后18周、24周，模型组C5／6、C6／7软骨终板磨损比例明显大干对照组，有统计学意义（P〈0．05）。术后各个时间点，模型组不同节段终板磨损率情况不同，其中C6／7节段明显大于C4／5节段（P〈0．05）。组织学切片显示，软骨终板的形念学改变早期以磨损为主，晚期则出现了大量钙化。术后12周，模型组C5／6、C6／7椎问高度明显低于对照组，术后18周、24周时高度进一步下降。术后12周．模型组的各节段椎间盘退变评分明显高于对照组（P〈0．05）。术后24周时，模型组C4／5退变评分为11．5±1．0分，C5／6为11．8±1．0分．C6／7为12．8±0．8分。不同节段椎间盘退变评分差异有显著性（P〈0．05），其中C6／7椎间盘邀变评分最高．明显大于C4／5、C5／6节段（P〈0．05）。相关分析显示：终板磨损比例与椎间髓高度、椎间盘退变评分具有明显的相关性。结论：在大鼠动静力失衡颈椎退变模型中C6／7终板磨损比例较大，椎间盘高度降低出现较早，组织学上椎间盘邀变程度也较严重，是该模型椎间盘退变的主要节段。软骨终饭的形态学改变与椎间高度的降低和椎间盘退变程度有明硅的相关性。

Objectives： To evaluate the effects of imbalance of dynamic and static forces on the cartilage endplate lesion, intervertebral disc height（IDH） and histological score from C4-C7 in a rat model of cervical spine degeneration, and the correlation between the cartilage endplate lesion and IDH. Methods： 24 Sprague Dawley female rats with the age of 3 months were assigned randomly into model group and control group（n= 14 and 10）. The control group was treated with skin incision only; the back of the neck muscles and ligaments of model group were transverse cutting. The C4-C7 segments were harvested at 12, 18 and 24 weeks after surgery. Specimens were scanned using micro CT, anti stained with Safranine O/fast green. Lesions of the cartilage endplate were identified on axial CT images, and the ratio of lesion area to the whole endplate area was calculated. IDH was measured and disc degeneration （DD） was graded for each sample. Results： The cartilage endplate lesion was presented on the ventral side of cartilage endplates with the greater lesion for lower levels at 12 weeks after surgery in the model group. The more severe lesion in C5/6 and C6/7 was seen in the model group compared with the control group at 18 and 24 weeks （P〈0.05） respectively. The lesion varied with levels and the C6/7 lesion was more severe than C4/5 （P〈0.05）. The histological results showed the lesion shrunk and calcified in situ at 18 and 24 weeks. Compared with the control group, the IDH was lower of the C5/6 and C6/7 in the model group at 12 weeks. The DD score of the model group was 11.5±1.0, 11.8±1.0 and 12.8±0.8 at the C4/5, C5/6 and C6/7 level respectively, which changed significantly among levels. The C6/7 DD score was larger than which of the other levels（P〈0.05）. The lesion was correlated with DD score at 12, 18 and 24 weeks（P〈0.05） and IDH at 18 and 24 weeks（P〈0.05）, respectively. Conclusions： Our results suggest that the current rat model generate significant disc degeneration at C6/7 level with larger cartilage endplate lesion, lower IDH and higher DD score compared with C4/5 and C5/6 level. The cartilage endplate lesion is associated with IDH and DD scores.