RESUMEN
Objective To establish a novel chronic compressive cervical spinal cord injury rat model,to validate the chronic pathological characteristic.Methods Fifty-four SD rats were randomly divided into 3 groups,including control group(n =6),acute compressive group(4 h,24 h,respectively.n =6),and chronic compressive group(4 h,12 h,24 h,48 h,72 h and 1week,respectively.n =6).Two sizes of water-absorbing polyurethane polymer sheets were implanted into C5～6 epidural space on postero-lateral side in acute and chronic compressive group respectively,to induce a consistent compression in the cord after expanded.While a laminectomy on C5～6 was performed only in control group.The neurological integrity,MRI signal change in the cords,large motoneuron number in the ventral horn,and myelin staining intensity on posterior funiculus were studied.Results In the acute group at 4-24 h,the compression was confirmed significantly on T2WI image,as well as hypointense signal change intramedullary.These changes were consisted with intramedullary bleeding,tissue necrosis.Large motoneuron number(P ＜ 0.05),rather than myelin staining intensity (P ＞ 0.05),was significantly decreased compared with the control group and chronic compressive group.BBB score was 6.0 at 24 h.In the chronic group:cord distortion with progressive compression was observed on T2WI image,but without intramedullary bleeding signal change.At 4-12 h,intramedullary edema,central canal distortion were seen in the cords.Large motoneuron number and myelin staining intensity decrement were not significant(P ＞0.05).BBB score was 20.6.At 24-72 h,central canal enlargement,venous congestion,and edema were observed.Large motoneuron number was less than that in the control group.In the compressive epicenter,nerve fiber disorganization or rupture was observed.Myelin staining intensity decreased significantly after 48 h and 72 h compression (P ＜0.05).BBB score was 19.3.At lweek,vacuolation changes were noted and large motoneuron decreased (P ＜ O.05),as well as myelin density and staining intensity (P ＜ 0.05),suggesting nerve fiber demyelination.BBB score was 17.5.In the control group,there was no neurological deficit and pathological change in the cords.Conclusion The pathology and MRI characteristic consistent with chronic compressive injury change,which proved this method is able to induce a chronic course on the rat model,and established a reliable model foundation for cervical myelopathy.