| Screw loosening or pullout has been a challenging problem to pedicle screw fixation in the osteoporotic spine.The objective of this study is to evaluate and compare the biomechanical change and observe the clinical effect of pedicle screw fixation in the osteoporotic spine after vertebral augmentation with polymethylmethacrylate,and to provide warrant for clinical application.Biomechanical studyIn this study,twelve fresh-frozen human cadaveric osteoporotic thoracolumbar spines (T10-L3) were used to make model of L1-2 whole lumbar laminectomy.On the basis of multilevel posterior screw instrumentation from T11-L2,three fixation methods were performed.The specimens were tested in a nondestructive manner load,it produce axial compression and the following six degrees of freedom:flexion,extension,torsion right/left and lateral bending right/left.Data were captured and the stability was analyzed by Digital-Image-Correlation Technique.Twelve fresh-frozen human cadaveric osteoporotic thoracolumbar spines(T10-L3) were inspected by plain radiographs to ensure specimens the absence of structural spinal disorders,previous neoplastic disease,or spinal surgery.In addition,these images confirmed the correct anatomic sagittal and coronal alignment of the specimen.After intact specimen(named A group) analysis,posterior T12-L1 laminectomy was performed and six specimens were chosen and instrumented with pedicle screws from T11-L2(named F1 group).After F1 group analysis,remove all the pedicle screws and inject polymethylmethacrylate into pedicle holes before fix the spine again(named F2 group). Another six specimens were instrumented with pedicle screws after vertebral augmentation with polymethylmethacrylate(named F3 group).The order of testing these nondestructive loads was randomized in each of the reconstruction stages and in each individual specimen.Then twelve vertebrae were chosen for test from L4,5 of the specimens.Four vertebrae were instrumented with pedicle screw without augmentation(named A group). The others were instrumented after pedicle augmentation or vertebral augmentation technique(named B or C group).Screws were tested in a paired testing array between B and C group,randomly assigning the augmentation techniques to opposite sides of each vertebra.Pullout to failure was performed after twelve hours. The result shows all group provided more stability to the specimen than intact spine in all loading modes(P＜0.01).Vertebral augmentation and pedicle augmentation group shows more stability and increase pullout strength to the specimen than no augmentation group(P＜0.05).Vertebral augmentation group shows and increased pullout strength to the specimen than pedicle augmentation group(P＜0.05).No statistical difference of spinal stability was found between vertebral augmentation group and pedicle augmentation (P＞0.05).Clinical studyIn this retrospective study,the clinical effect of pedicle screw fixation after vertebral augmentation with polymethylmethacrylate in 23 osteoporotic patients were retrospectively analysed from January.2004 to Oct.2006.By comparing their X-ray manifestations within one week after operation with that of several months after operation when the patients came to recheck,whether the screws were loosened or pulled-out and if there were any bright lines around screws were observed.All the cases were followed up,and the time was from 6 months to 33 months,with average time of 17 months.The result showed the symptom of back pain and nerval injury of lower extremities in all the patients relieved obviously.Range of spinal motion improved in 21cased,no improved in 2 cases,the rates were 91.3%.Scoliosis and kyphosis deformity were corrected obviously.There were no screw loosening and pullout and no bright lines around screw observed in the X-ray expression of all the cases.ConclusionThe results of biomechanical and clinical study suggest that pedicle screw fixation after vertebral augmentation with polymethylmethacrylate in osteoporotic patients is a reliable and safe technique,it can restore spinal stability and prevent screw loosening and pullout in osteoporotic spine,and can gain a satisfactory clinical outcome. |
