Exerperimental Study On The Minimum Cement Volume In Vertebroplasty

Objective: Percutaneous vertebroplasty has commonly used in treating osteoporotic vertebral compression fracture,which is an effective and minimally invasive,and has a well clinical effect since the clinical application.With percutaneous vertebroplasty gradually applying in clinic application,some clinical complications are being valued by patients and physicians,and bone cement getting into the spinal canal would lead to double lower limbs neurological symptoms.However,it was observed that several adverse reactions,including decreased blood pressure,dyspnea,hypoxemia,cardiac arrest,and even death,occured in patients follownig bone cement implantation.Complications of percutaneous vertebrolplasty are mainly bone cement leakage and adjacent vertebral fractures or affected vertebrae fracture again.Clinical trials have reported that bone cement leakage rate was from 22% to 82%.The most important factor affecting the leakage was the correlation of injected volume: with higher percentages of injected cement leading to increased rates of cement leaks.Another common complication was adjacent vertebral fractures after vertebroplasty.With the increasing stiffness of the fractured vertebra wouldl bring greater pressure to the adjoining vertebrae.Biomechanical and clinical studies showed that too high a volume of bone cement was the reason of failured vertebroplasty.In order to avoid aforementioned complications,the minimum amounts of bone cement should be recommended.The purpose of this study was to investigate the minimum percentage of bone cement fill volume restoring vertebral stiffness in vertebroplasty.Methods: Four sets of embalmed samples and age(65±3years)were enrolled in our study,T11-L3 centrums were dislodged.The fractures,tumors and congenital malformation were ruled out by X-ray.Each specimen resected the paravertebral muscles,the upper and lower endplate and the intervertebral disc,the anterior and posterior longitudinal ligament and soft tissue.Single free specimen was made.Bone mineral density was measured with dual-energy X-ray absorptiometry,taking similar bone density 15 specimens to do the experiment,and the remaining five did preliminary experiment,random number.Each vertebrae was then compressed at a speed of 5mm/min until the vertebral body fractured.The fracture was confirmed by the nonlinear deformation in a real-time load-deformation graph.After fracture,vertebroplasty was done using low-viscosity bone cement(doughing time)from the same manufacturer by pedicle.Position of needle and bone cement were monitored via C-arm X-ray machine.After fracture vertebroplasty was performed,3 times in the same fracture vertebral body.The first bone cement of 5 % of fractured vertebral body volume was injected through the left pedicle and the second 5 %(combined 10 %)via the same pedicle.The manoeuvre was performed for the third(combined 15 %)through the right pedicle.The biomechanical testing was carried out before the fracture,after the fracture and after each cement injection.Every time was performed in the testing machine and vertebral body specimens were compressed at a speed of 5mm/min up to 500 N.Biomechanical testing was synchronously recorded by computer and compressive stiffness(before the fracture,after the fracture and after each cement injection)was calculated.The repeated measures analysis of variance and the paired test were carried out in five consecutive time points.Results: The vertebral body volume before vertebral fracture,measured by the CT method,was(32.28±7.29)cm3 and was reduced after fracture to(29.70±6.58)cm3.The volume loss was(2.59±1.32)cm3.The vertebral body height before vertebral fracture was(24.32±1.96)mm and was reduced after fracture to(23.23±1.94)mm.The height loss was(1.09±0.25)mm.Cement leakage was detected in 5 injections of three vertebral bodys.NO.5 vertebral body was detected 0.2ml in the third;Cement leakage was detected in NO.6(two times during the second injection-0.1ml,once in the third-0.1ml).NO.13 was detected cement leakage(two times during the second injection-0.1ml,once in the third-0.1ml).Compressive stiffness before vertebral fracture was(712.03±197.03)N/mm and was reduced after fracture to(401.87±132.72)N/mm.After vertebral fracture stiffness was reduced to 56% compared to the pre-fracture level,and was partially restored to 70%(496.64±157.39)N/mm after 5% bone cement fill;10% was partially restored to 89%(630.33±170.67)N/mm.;and 15% was partially restored to 91%(646.82±179.78)N/mm.There was statistically significant between 5% bone cement fill and 10%(P<0.05),But there was no significant difference between 10% bone cement fill and 15%(P>0.05).Conclusions: In previous studies,the same volume of cement was used irrespective of vertebral body size,however,the fractured vertebra was conventionally injected bone cement 2-3ml up to a maximum of 5 ml according to clinical experience.Our study showed that the size of the vertebral body was taken into account,percentage of fill was relatively fixed,but the volume of vertebral body was changing.According to the experimental study,we should do preoperative CT of vertebral fracture,and exactly calculate the volume of fractured vertebral body and the amount of bone cement injection to reduce complications of bone cement leakage for successful vertebroplasty.Stiffness of the fracture vertebral body increased with the increasing of bone cement filling rate for vertebroplasty.10% of bone cement fill was the limit beyond which no substantial increase in compressive stiffness and is the minimum volume of cement for vertebroplasty.In the average thoracolumbar vertebra this means 2–4 ml of bone cement.