Establishment of rabbit lumbar intervertebral disc degeneration model induced by penetration under CT guidance

English Keywords:Intervertebral disc degeneration  Anular fibrosus stabbing  Spiral CT  Magnetic resonance imaging  Rabbit

English Abstract:

  【Abstract】 Objectives: To establish a rabbit model of disc degeneration by induced annulus fibrosus penetration under CT guidance, and to verify its degenerative procedure radiology and pathology. Methods： Eighteen New Zealand white rabbits aged about 3 months and weighing 2.7-3.3kg were used in our experiment, all of them were taken radiographic and MRI examinations preoperatively. The L5/6 discs(stabbed group) were punctured by 18-gauge needle into a depth of about 5mm inthe lateral annulus fibrosus guided by spiral CT. The L3/4 discs(sham group) were punctured at the margin of the disc with no injury to the annulus fibrosus, while the L4/5 discs were taken as control group. Each six rabbits were executed randomly at 4, 8 and 12 weeks postoperatively after radiographic and MRI examinations at 24 hours. The intervertebral space, the changes of vertebrae on radiography and signal intensity of discs on MR images in all groups were analyzed. The disc height relative value(DHRV) was calculated based on intervertebral space of pre- and post- operation(DHRV=postoperative intervertebral space/preoperative intervertebral space ×100), and modified Thompson scoring based on MRI were performed in all groups. Histological and immunohistochemical analysis was assessed in each group. Results: At 4, 8, 12 weeks postoperatively, the discs in control and sham groups showed no decrease of the intervertebral space, no endplate sclerosis and formation of osteophyte of vertebrae on radiography. On MR T2 weighted images, the discs in both control and sham groups showed high signal intensity. Histologically, nucleus pulposus contained a great number of cells with even distribution, and annulus fibrosus presented as concentric lamellae shape. Immunohistochemistry demonstrated strong positive type Ⅰ and negative type Ⅱ collagen in nucleus pulposus of control and sham groups at each time point. At 4 weeks postoperatively, disc height decreased slightly(DHRV=70.78±4.55), and MRI showed lower signal intensity in stabbed discs. Histologically, cell count of nucleus pulposus decreased slightly, while annulus fibrosus became disorganized. At 8 weeks postoperatively, significant decrease of intervertebral space was evidenced(DHRV=50.63±4.04), and endplate osteosclerosis was seen either. MRI revealed a moderate decrease of T2 weight signal intensity images. Histologically, nucleus pulposus was separated by proteoglycan matrix into multiple elliptical shape of cell islands, and the concentric fibrous lamellae distorted, or even fractured. Fibrochondrocyte was found in nucleus pulposus. At 12 weeks postoperatively, successional decrease of intervertebral space(DHRV=44.78±4.55) was found, with obvious endplate sclerosis and formation of vertebrae osteophyte. The T2 weighted signal intensity of the stabbed discs decreased continuously. Histologically, nucleus pulposus was replaced by fibrocartilage tissue, while the fibrous lamellae was induced into fragmentation, and its architecture disintegrated. Immunohistochemical analysis exhibited a progressive increase of type Ⅰ collagen and a progressive decrease of type Ⅱ collagen at 4, 8, 12 weeks postoperatively. The statistic analysis revealed that there was no significant difference of DHRV and modified Thompson scoring between control and sham groups at each time point. But the stabbed group demonstrated decrease of DHRV and increase of modified Thompson scoring, showing significant difference compared with those of control and sham groups at each time point(P<0.05). There was a progressive decrease of DHRV and a progressive increase of modified Thompson scoring in stabbed group, respectively. Both DHRV and modified Thompson scoring in stabbed group showed statistic differences between 4, 8, 12 weeks postoperatively(P<0.05). Conclusions： The percutaneous puncture of annulus fibrosus under CT guidance can induce disc degeneration in rabbit. The procedure is feasible and minimal invasive, which can be confirmed by radiology and pathology.