BACKGROUND:Cervical kyphosis post laminectomy is a common iatrogenic,and progressive abnormality of the curvature of cervical spine,and can influence the function of cervical spine of children and adults.OBJECTIVE:To explore the effect of multiple levels of laminectomies on the curvature of cervical spine,and analyze the role of the elastic modulus of cervical intervertebral disc and ligaments on maintaining curvature of postlaminectomy cervical spine.DESIGN,TIME AND SETTING:Three-dimensional finite element analysis was performed in Changzheng Hospital,Second Military Medical University of Chinese PLA between January 2003 and January 2004.MATERIALS:The highly resolution pictures of the cross-section of cervical spine(interval distance of layer 1 mm) were came from male cross-section of cervical spinal of American visible human project,which was freely downloaded from The Visible Human Project.METHODS:The highly resolution pictures of cervical spinal cross-section were used as data to reconstruct the three-dimensional multiple levels postlaminectomy cervical spine models including all structure of spine from cranial base to the first thoracic vertebrae except the vertebral lamina,spinous process,ligamentum flavum,interspinous and supraspinous ligament from the second to the seventh cervical spine.The finite element and elastic modulus of the structures of cervical spine were defined according to previous reports.With this model and Ansys6.1 finite element analysis software,the effect of laminectomy on the curvature of cervical spine and impact of the elastic modulus of intervertebral disc and ligament to the curvature of postlaminectoy cervical spine were analyzed.MAIN OUTCOME MEASURES:The influence of the elastic modulus of cervical intervertebral disc and ligament(anterior and posterior longitudinal ligaments) on the curvature of the postlaminectomy cervical spine.RESULTS:The physical lordosis of multiple levels postlaminectomy cervical spine was reduced after multi-level loading,and the physical lordosis of the superior cervical spine disappeared with only slightly kyphosis.The kyphosis was aggravated after reducing the elastic modulus of intervertebral disc and ligament(anterior and posterior longitudinal ligaments).Following increased elastic modulus of intervertebral disc and ligament,the kyphosis of cervical spine was reduced even disappeared,and gradually regained the normal lordosis of cervical spine.CONCLUSION:Multiple levels cervical laminectomy can significant reduce the physical lordosis of cervical spine,and convert the physical cervical lordosis to cervical kyphosis.The elastic modulus increase of cervical intervertebral disc and ligament can inhibit kyphosis formation post laminectomy.

BACKGROUND: There is not any experimental model that can reflect the pathological change of hormone-induced avascular necrosis of the femoral head in a good way nowadays, which is unfavourable to the further observation of its pathogenesis. OBJECTIVE: The model of the avascular necrosis of the femoral head is induced by giving a large dose of dexamethasone into rabbits, which provides the animal experimental models for the study of clinical pathogenesis. DESIGN, TIME AND SETTING: The randomized controlled animal experiment was performed at the Animal Laboratory, Affiliated Hospital of Anhui Medical University from June 2004 to August 2005. MATERIALS: Sixteen healthy adult New Zealand albino rabbits (50% female and 50% male), weighing 3.0-3.2 kg were selected for this study. Dexamethasone was provided by Jiangsu Lianshui Medical Co., Ltd. etalon: 5 g/L. METHODS: Rabbits were randomly divided into two groups: model and control groups. Dexamethasone of 2.5 mg/kg per day was injected into each rabbit of the model group, and saline of 2 mL was injected into each rabbit of the control group for 6 weeks. MAIN OUTCOME MEASURES: Serum lipid and prothrombin time (pt) were tested before and after the experiment, and the histopathological change was observed with radiography, optical microscrope and transmission electron microscopy at 2, 4 and 6 weeks of dexamethasone administration. RESULTS: Compared with the control group, in the model group cholesterin levels were significantly increased at 2 weeks (P