Objective:To evaluate the effects and mechanism of radiation-sterilized allogeneic bone sheets in inducing vertebral plate regeneration after laminectomy in sheep. Methods:Twelve adult male sheep (aged 1.5 years and weighing 27 kg on average ) provided by China Institute for Radiation Protection underwent L3-4 and L4-5 laminectomy.Then they were randomly divided into two groups:Group A (n =6) and Group B (n =6).The operated sites of L4-5 in Group A and L3-4 in Group B were covered by "H-shaped" freeze-drying and radiationsterilized allogeneic bone sheets ( the experimental segments),while the operated sites of L3-4 in Group A and L4-5 in Group B were uncovered as the self controls ( the control segments ). The regeneration process of the vertebral plate and the adhesion degree of the dura were observed at 4,8,12,16,20 and 24 weeks after operation.Xray and CT scan were performed in both segments of L3-4 and L4-5 at 4 and 24 weeks after operation. Results:In the experimental segments,the bone sheets were located in the anatomical site of vertebral plate,and no lumbar spinal stenosis or compression of the dura was observed.The bone sheets were absorbed gradually and fused well with the regenerated vertebral plate.While in the control segments,the regeneration of vertebral plate was not completed yet,the scar was inserted into the spinal canal,compressing the dura and the spinal cord,and the epidural area almost disappeared. Compared with the control segments, the dura adhesion degree in the experimental regenerated segments was much milder (P ＜0.01 ),the internal volume of the vertebral canal had no obvious change and the shape of the dura sack remained well without obvious compression. Conclusions:Freeze-drying and radiation-sterilized allogeneic bone sheets are ideal materials for extradural laminoplasty due to their good biocompatibility,biomechanical characteristics and osteogenic ability.They can effectively reduce formation of post-laminectomy scars,prevent recurrence of post-laminectomy spinal stenosis,and induce regeneration of vertebral plates.1.Department of Orthopaedics,Affiliated Union Hospital of Tongji Medical College,Huazhong University of Science and Technology,Wuhan 430022,China;2.Medical Tissue Bank, China Institute for Radiation Protection,Taiyuan 030000,China;3.Department of Medical Biology,Tongji Medical College,Huazhong University of Science and Technology, Wuhan 430030,China