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

English Keywords:Disc degeneration  Cartilage endplate  Lesion  Dynamic and static forces  Rats

English Abstract:

  【Abstract】 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, and 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 degeneraion 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.