The Mechanism Of Recollapse Of The Augmented Vertebrae After Percutaneous Vertebral Augmentation For Osteoporotic Vertebral Fractures With Intravertebral Vacuum Cleft On Basis Of The Microcosmic Differentiation

Part 1 Effect of intravertebral vacuum cleft within osteoporotic vertebral compression fractures on therapeutic efficacyBackgroundPrevious studies have reported high incidence of the recollapse of the augmented vertebrae after percutaneous vertebral augmentation(PVA)for osteoporotic vertebral compression fractures(OVCFs)with intravertebral vacuum cleft(IVC)during long-term follow-up and previous IVC might be considered an important predisposing factor for recollapse,but the prior studies could not find a significant correlation.ObjectiveThe purpose of our present study is to determine the pathogenesis and characteristic of IVCs and furthermore assess the long-term therapeutic efficacy of PVA for OVCFs with IVC.MethodsA retrospective review was performed on 148 patients who underwent PVA to treat single OVCFs from January 2010 to December 2014.52 patients with the IVC sign(IVC group)and 96 patients without the IVC sign(non-IVC group)were identified in our study,respectively.The follow-up period was a minimum of 2 years.The difference of preoperative baseline including age,sex,BMD,fracture level,preoperative vertical compression ratio(VCR)and local reduction angle(LKA),preoperative VAS scores between IVC and non-IVC patients was compared.Comparisons of the radiological and clinical finding between the two groups were made post-operatively(immediate,at 1 year and at 2 years).Additionally,the rate of cement leakage and adjacent vertebral frature would be also compared.ResultsIVC incidence correlated with older patient age and severe demineralization.Other baseline parameters showed no significant differences.In the immediate postoperative period,all patients benefited from significant improvement in vertebral body height and kyphotic angle correction(P<0.05).However,significant recollapse was observed at the 2 year post-operative follow-up for the IVC group with compared to the non-IVC patients.It was significantly higher in the IVC group than that in the non-IVC group including VCR,LKA,progressive height loss,Progressive kyphotic angle and VAS scores at the 2 year post-operative(P<0.05).There was no significant difference in the rate of cement leakage or adjacent vertebral fractures.ConclusionPVA treatment was initially effective in all patients with OVCFs.However,significant recollapse of the augmented vertebrae with IVCs was found with long-term follow-up.Careful observation and extended follow-up of patients with these conditions is recommended.Part 2 Risk factors for recollapse of the augmented vertebrae after percutaneous vertebral augmentation for osteoporotic vertebral fractures with intravertebral vacuum cleftBackgroundSeveral studies have reported a high incidence of recollapse of the augmented vertebrae after percutaneous vertebral augmentation(PVA)for osteoporotic vertebral fractures(OVCFs)with intravertebral vacuum cleft(IVC)at long-term follow-up.Up to date,no critical factors related to recollapse of the augmented vertebrae after PVA have been clearly described.ObjectiveTo determine risk factors related to recollapse of the augmented vertebrae after PVA for OVCFs with the IVC.MethodsFifty-two patients treated with PVP for single OVCFs with the IVC were retrospectively reviewed.The follow-up period was at least 2 years.Vertebral height loss≥15%or kyphotic angle ≥10° at the final follow-up in relation to the immediately postoperative values were adopted as a definition of recollapse of the augmented vertebrae.Correlation analysis and multiple logistic regression analyses were performed to elucidate the related clinical or radiological factors for recollapse of the augmented vertebrae including age,gender,bone mineral density,preoperative fracture severity,locations of IVC sign,distribution patterns of Polymethylmethacrylate(PMMA),reduction rate,reduction angle.ResultsAssuming the increase of height loss more than 15%as a criterion of recollapse,only cleft filling pattern of PMMA in the IVC area was a significant risk factor for recollapse of the augmented vertebrae(P<0.01).Assuming ≥ 10° progression of kyphotic angle as a criterion,cleft filling pattern of PMMA and higher values of reduction angle was as two significant risk factors for recollapse of the augmented vertebrae(P<0.01).No significant difference was found in other clinical and radiological factors(P>0.05).ConclusionCleft filling pattern of PMMA and higher values of reduction angle may play an important role in inducing recollapse of the augmented vertebrae after PVP for OVCFs with the IVC.Careful observation of patients with these conditions is necessary to prevent deterioration of their clinical course.Part 3 Biomechanical effects of different cement distribution pattern in the varied location of intravertebral vacuum cleft within osteoporotic vertebral compression fracturesBackgroundIn conjunction with previous reports,the location of intravertebral vacuum cleft(IVC)and different distribution pattern of cement in the area could be possibly two important risk factors of the recollapse of the augmented vertebrae after percutaneous vertebral augmentation(PVA)for osteoporotic vertebral fractures(OVCFs)with intravertebral vacuum cleft(IVC).To date,however,no biomechanical studies have been performed to research biomechanical effects of the two risk factors on the biomechanical stability of the augmented vertebrae.ObjectiveBased on the microcosmic differentiation of Traditional Chinese Medicine and modern advanced treatment technique,a three-dimensional finite element analysis would be used to investigate the difference of biomechanical stability in the different cement distribution pattern of the varied locations of IVC within OVCFs and provide a biomechanical basis for the recollapse of the augmented vertebrae from the microcosmic differentiation perspective of TCM.MethodsIn a validated osteoporotic T11-L1 FE model,T12 was designated as the affected vertebrae and a OVCFs FE model with the varied locations of an IVC was simulated in T12.Then,a different distribution pattern of cement in the IVC would be also simulated including four FE models:the cleft filling pattern in the superior IVC,the cleft filling pattern in the inferior IVC,the interdigitated filling pattern in the superior IVC and the interdigitated filling pattern in the inferior IVC.The magnitudes and distributions of the von Mises stress in cortical bone,cancellous bone and adjacent vertebral endplate were calculated and compared for the four models under different physiologic conditions of loading.ResultsFor the four FE models,distribution of maximum von Mises stress in the frature area of cortical bone was concentrated at the rear of the fracture area and the unfracture area of cortical was at the cortical area adjacent to the corresponding endplate.Compared with the cleft filling pattern,the interdigitated filling pattern of cement could decrease the maximum stress of both cortical and cancellous bone in T12.Meanwhile,the interdigitated filling pattern in the superior IVC could also decrease maximum cortical stress of the unfrature area;however,the interdigitated filling pattern in the inferior IVC could not further decrease the cortical stress of the unfrature area,and on the contrary,increase maximum cortical stress of the unfrature area.there was no significant difference in the adjacent vertebral endplate among the four models.ConclusionCompared with the cleft filling pattern,cement interdigitated filling pattern could improve the stability of the augmented vertebrae.However,when the IVC is adjacent to the inferior endplate,the interdigitated filling pattern could increase maximum cortical stress of the unfrature area although it could decrease the stress of the fracture area in the cortical bone and cancellous bone.Hence,we should carefully choose the corresponding filling pattern of cement for the inferior IVC.