| ObjectiveTo summarize the main radiographical feature of Verbral fracture Nonunion(VFNU) in extended CT reconstruction images, establish novel therapy-oriented classification of VFNU based on the manifestation of extended CT reconstruction images, and investigate the validity of this novel classification with clinical and finite element study.Method1. Clinical studyAll of the senior patients suffered from thoracolumbar spine fracture(Dec2009to March2013) were retrospectively reviewed,36cases of VFNU were included in this study according to inclusion criteria. The reducibility and stability of index vertebrae were evaluated with extended CT reconstruction images, and all of VFNU patients were divided into3subgroups, type A owns the reducibility and stability, which is recommended to treat by percutaneous vertebroplasty in extension posture, type B owns the reducibility, but lacks stability, which should be treated by in situ fixation and fusion in extension posture, type C loses the reducibility, which is eligible for the spine deformity correction by osteotomy or canal decompression. Whether the patients were treated according to this classification and the perioperative complication were recorded. The clinical outcome was investigated by the comparison of VAS and ODI in preoperation,3months after surgery and last follow-up, the transformation of profile of index vertebrae was evaluated radiographically with the local kyphotic Cobb angle and anterior height of VFNU vertebrae in the above time-points. The main radiographical features of39level of VFNU vertebrae were analyzed, including the specific segment, the type of substance in the intravertebral cleft, the starting-points and terminals of intervertebral cleft, to explore the different radiographic feature of type A, B, C.2.Finite element researchAn elderly senior, who suffers from osteoporosis, but owns the normal alignment and profile of thoracolumbar spine was included into this finite element study and accepted CT examination. The finite element3-dimension model of physiological thoracolumbar spine (T11-L3) was established and investigated with Mimics, Rapidfrom and abaqus software, then wedge-shape osteotomy was perfomed in L1vertebral body to stimulate intravertebral bone defect, which is the main feature of VFNU, in order to make the pathological finite element model of type A VFNU, which is named pathological model A. Furtherly, the posterior-inferior region of vertebral body was cut to build a piece of seperated fracture, with the purpose of simulation of the pathological feature of type B VFNU and establishment of corresponding Finite element model which is called as Pathological model B. After that, imitated bone cement augment was performed in pathological model A and B, distributing cement in the whole intervertebral cleft or5mm ahead posterior edge of vertebral body, in order to establish four therapy finite element model,which were called as therapy model A1,B1,A2and B2. All of the models were calculated under the same axial loads of400N, to investigate the validity of physiological model and compare the mechanical status of different models.Result1. Clinical research39level of VFNU vertebrae in36patients were located in the region of T9to L4, in which the thoracolumbar segments were compromised frequently, and16level of VFNU existed in L1. According to extended CT reconstruction images,25level of type A,7level of type B,7level of type C VFNU were identified.24cases of type A VFNU accepted percutaneous vertebroplasty in extension posture,4cases of type B VFNU were treated by in situ fixation and fusion in extension posture, but2 of them also accepted percutaneous vertebroplasty in extension posture like type A patients,6cases of type C VFNU were treated by spinal deformity correction by osteotomy or decompression, no severe complication occured in both of type A and B patients, except that2patients of type B VFNU, who accepted PVP, had notable but asymptomatic bone cement leakage, however1case of type C VFNU had a deep wound infection, and1case got heart function failure during perioperative period. With the radiographic analysis, the starting-points of intervertebral cleft located in the anterior edge of vertebral body (18levels) or disc plate(21level), the termials of cleft located in the intersecting point of pedicle and posterior-inferior edge of vertebral body(18level) or superior disc plate(14level), the fracture line could be displayed clearly in the all coronal CT reconstruction images, however, terminals of intravertebral cleft in type C VFNU located in the trabecular bone region in the middle1/3part of vertebral body(4level), and the middle1/3part of superior disc plate, even thought there were significant collapse or intracanal retropulsion of posterior1/3part of vertebral body, fracture line could rarely be shown except for1patient, the fracture lines lateral cortex united in3patients, or just be shown in anterior-middle part of vertebral body in3patients according to the coronal CT reconstruction images. The different treatment oriented by this novel classification could be effective in the corresponding types of VFNU, by which the VAS, ODI could be improved, local kyphotic angle, and anterior height of VFNU could be corrected significantly.2Finite element researchThe physiological finite element model owns good mechanic conformity with the reported models. Compared with physiological model, there was notable stress, strain concentration in LI vertebral body of pathological model A, mainly distributing beside the posterior cortex and in the posterior-inferior part of vertebral body, which indicated that there was risk of further fracture in this model. Although there was also stress and strain concentration in pathological model B, the extent and level of stress and strain were lower than the corresponding value in pathological model A, furthermore, concentration mainly located in the posterior-inferior fracture piece, which implied that the separated posterior-inferior fracture piece of vertebral body intended to dislocate, and the stress, strain concentration were dispersed after pathological Model A became Model B. According to calculation of therapy model A1,A2, the stress and strain concentration could be dispersed with bone cement augmentation, and the mechanic conduction function of L1vertebral body could be restored after imitated PVP, which indicated that Vertebroplasty could be used effectively in VFNU patients with reliable mechanic stability. However, based on the calculation of therapy model B1,B2, the tendency of stress, strain concentration and displacement of posterior-inferior fracture piece could be found, even though the whole concentration could be dispersed by cement augmentation, which implied that there was risk of dislocation of posterior-inferior fracture piece after bone cement augmentation in pathological model B.ConclusionThoracolumbar segments are the most common region compromised by VFNU.There is difference between the terminals of intravertebral cleft of type A,B and C VFNU, and existence of fracture lines from anterior edge to posterior cortex might explain the mechanism of reducibility of type A and B. The validity of this novel therapy-oriented classification has been investigated by clinical and finite element study, which is beneficial to make more accurate evaluation and select the eligible surgery procedure before operation, and decrease the rate of usage of aggressive operations,like spinal osteotomy and decompresson, in the old patients. |
