Vertebral augmentation has been widely used for treating the osteoporotic vertebral compression fractures. However, the occurrence of new fractures in adjacent vertebrae is also common. In order to understand the mechanism of adjacent vertebral fractures to prevent its happening, many scholars have carried out a lot of experiments and clinical studies by different research methods for years. As a result, many theories about the mechanism of adjacent vertebral fracture have been formed. Including the patients' general conditions (age, gender, bone mineral density, body mass index, et al), material characteristics of bone cement, distribution of bone cement (volume of bone cement and under-endplate distribution, acentric or bilateral distribution, compact and solid cement filling pattern, bone cement leakage), factors of spinal sagittal imbalance, factors of anti-osteoporosis treatment and the behavioral therapy, the location of initial injured vertebral level, the degeneration of adjacent disc, all of above were considered as potential risk factors. However, various researches lead to diverse conclusions because of different methods were used and different research factors were included, some conclusions were even opposite. Therefore, it is still controversial that whether some of the risk factors were effective. In this research, the current researches and the reliability and limitations of various research methods were reviewed to put forward a relatively objective interpretation, in order to provide evidences for understanding the risks of adjacent vertebral fracture after vertebral augmentation, and to provide reference for treatment.

Objective Finite element method was used to clarify the biomechanics effect of cement intervertebral leakage during vertebral augmentation.Present a novel classification of bone cement intervertebral leakage.Analyze the effect of stress changing of bone cement intervertebral leakage on adjacent endplate by finite element method.Methods Based on Churojana's classification method,we redefined diverse kinds of intervertebral leakage:as the Type Ⅰ (intervertebral-extradiscal leakage),Type Ⅱ (intradiscal leakage) and Type Ⅲ (combined leakage).Type Ⅱ was also been divided into Ⅱa (anterior),Ⅱb (central),Ⅱc(posterior),Ⅱd (lateral) and Ⅱe (cross-region) due to the location of the leaked bone cement.All the Type Ⅱ cases were divided into 1 or 2 two subtypes according to whether the cement had reached the adjacent vertebral endplate.We established 3D reconstruction of volunteer thoracolumbar spine using Mimics 17.0 software,and using Geomagic 2015 to generate L1 vertebral compression fracture model.In the Ansys 17.0 software,we simulated the L1 bone cement leakage into the T12/L1 intervertebral space model.After validating the validity of the model,calculate the solution of the intact model,non-leakage model and various leakage models,the stress distribution of the caudal endplate of T12 was analyzed in neutral,flexion,extension,lateral bending and torsion.Results The maximum stress of inferior endplate of T12 vertebra of intact model is 11.476 MPa,19.517 MPa,16.879 MPa,42.346 MPa,43.033 MPa,6.568 MPa,6.568 MPa in neutral,flexion,extension,left bending,right bending,left rotation,right rotation respectively.For the non-leakage model,the maximal stress of adjacent vertebral endplate was 12.967 MPa (112.99％),23.134 MPa (118.53％) and 20.403 MPa (120.88％) in neutral,flexion and extension compared to the intact model.No significant increasing can be found in other conditions.Compared to the non-leakage model,the stress of adjacent vertebral endplate is similar when type Ⅰ leakage occurs.In type Ⅱ leakage,the Ⅱa1 was 28.506 MPa (123.40％) in the flexion;the Ⅱa2 was 84.791 MPa (366.52％) in the flexion;the Ⅱb2 was 14.138 MPa (122.82％) in the neutral and 27.313 MPa (118.06％) in the flexion;the Ⅱc1 was 19.695 MPa (128.50％) in the extension;the Ⅱc2 was 67.740 MPa (441.97％) in the extension,and the Ⅱd2(right) was 123.940 MPa (285.83％) in the right bending.In the left/right rotation motions,the stress values are small,ranging from 5.095-15.585 MPa.Conclusion After vertebral augmentation,the stress of adjacent vertebral endplate increased slightly.Type Ⅰ leakage did not further increase the stress of adjacent vertebral endplates.Type Ⅱ leakage increases the stress of adjacent endplates in the direction of leaked cement.Subtype 2 of Type Ⅱ offer more stress than subtype 1.When the peripheral type of leakage (Ⅱa,Ⅱc and Ⅱd) occurred,if the spine flexes in the direction of leakage,then the stress increase of adjacent endplates will increase further.

Objective:To evaluate the clinical efficacy and changes between Dynesys and Posterior lumbar interbody fusion (PLIF) in the treatment of two-level lumbar degenerative disease.Methods:43 consecutive patients with lumbar degenerative disease were treated using the Dynesys or PLIF between June 2010 and June 2012. In all patients, 23patients were implanted Dynesys and other patients for PLIF. The follow-up period was at least 60 months. Used the Visual analogue scale (VAS) and Oswestry disability index (ODI) to evaluate the clinical outcomes. And during the follow-up period, collected the data for the intervertebral height and the range of motion (ROM), for the operation section and the upper adjacent vertebral. MRI and Grading Scale from the University of California at Los Angeles (UCLA) were used to define the change of intervertebral disc signal.Results:The ODI index and VAS score both improved significantly at the final follow-up evaluation ( P<0.05), as compared to the basal line values. And in terms of imaging, there were no significant difference in the vertebral height of the operation section and the upper adjacent vertebral. The range of motion (ROM) for the operative section in the group of PLIF was significantly lower than that in Dynesys group ( P<0.05). And when it comes to the upper adjacent vertebral space, it was higher at the same time ( P<0.05). According to the UCLA Grading Scale, there were 3 cases in the Dynesys group and 11 in the PLIF group had radiological adjacent degeneration, the difference was significant between two groups ( P<0.05). And when it comes to the second intension, there were 3 patients in PLIF groups (TLIF 1; PLIF 2) but only 1 in Dynesys groups. Conclusion:Dynesys and PLIF are both effective for lumbar degenerative disease and show good medium and long-term clinical and radiographic results. But when it comes the risks in developing ASD and the ROM of adjacent segments, Dynesys stabilization can be the better choice.

In Vivo Dosimetry ; Radiotherapy Dosage ; Radiometry/methods* ; Electronics ; Radiotherapy, Intensity-Modulated/methods* ; Phantoms, Imaging ; Algorithms