The Mid-long-term Outcomes Of Expandable Pedicle Screws In Treatment Of Degenerative Lumbar Diseases Combined With Osteoporosis

Background:Osteoporosis frequently involves the spine.It would significantly affect the fixation strength of the screw in spinal surgery.And it is one of the most important risk factors that lead to the fixation failure of lumbar posterior fusion surgery.According to the literature statistics,the failure rate of spinal screw fixation caused by osteoporosis is 4.5%-17.3%.At present,the spine surgeon would choose large diameter or longer screws or use cement-augmented pedicle screws to increase the fixation strength of the screws.But increasing the screw diameter or length would increase the risk of pedicle fractures,nerve injury or anterior cortex rupture,organs and blood vessels damage.Clinical applications of cement-augmented pedicle screws in spine surgery combined with osteoporosis are also very common.Biomechanical studies have shown that cement-augmented pedicle screwscan significantly increase the screw fixation strength.Its pullout strength is increased by181%-352% compared with conventional pedicle screws.But this clinical treatment method also exists some problems.The first problem is the nerve injury and pulmonary embolism caused by bone cement leakage.The leakage rate could reach 26.2% according to literature statistics.The second problem is that the heat generated by bone cement in its solidification process will damage the surrounding tissue,even lead to nervous necrosis.The third problem is that when the cement-augmented pedicle screws was inserted,it would be difficult to remove the screw.If it is forced to take out the screws,it may lead to bone defect of the vertebral body,and brings great difficulties for subsequent surgery.Aiming at these problems,our research team developed a new type of pedicle screw fixation system(expandable pedicle screws,EPS).Biomechanical studies have demonstrated that the fixation strength of the expandable pedicle screws in the vertebral body is significantly stronger than the conventional pedicle screws.Early clinical studies have shown that the application of expandable pedicle screws could significantly reduce the risk of screw loosening.Meanwhile it could also obtain a higher fusion rate and better postoperative efficacy.However,the mid-long-term safety and efficacy in vivo of the expandable pedicle screws has not been reported in our country and abroad.So this study enrolled the patients who received the lumbar spine surgery using the expandable pedicle screws fixation system in our hospital and proceeded long-term follow-up for all the patients.The pre-operative and post-operative functional scores and the imaging data were taken to compare the screw loosening rate,breakage rate,and fusion rate between the groups using expandable pedicle screws group or conventional pedicle screws.Also to summarize the mid-long-term clinical effect of expandable pedicle screws in the lumbar fusion surgery combined with osteoporosis.Objectives: To compare the mid-long-term clinical effect of expandable pedicle screws(EPS)and conventional pedicle screws(CPS)in the lumbar fusion surgery combined with osteoporosis.To evaluate the safety and effectiveness of the application of EPS in themid-long-term follow-up.Methods: From January 2007 to July 2013,406 patients treated with standard posterior lumbar interbody fusion(PLIF)were reviewed.All patients were followed up for a minimum of 3 years.Of the 406 cases,147 of them were males and other 259 were females with an overall mean age of(63.4±4.2)years(range 50~79 years).Among these patients,173 patients received PLIF with expandable pedicle screws(EPS group)and the other 233 patients received PLIF with conventional pedicle screws(CPS group).The pre-operative and post-operative VAS(Visual Analogue scores)and ODI(Oswestry Disability Index)scores were compared to evaluate the function recover conditions.X-ray or CT scans were taken to compare the screw loosening rate,breakage rate,and fusion rate between the two groups.Results:The average follow-up period was(3.7±1.0)years(range 3~8 years).No significant difference was detected between the two groups on pre-operative VAS and ODI scores(P>0.05).After surgeries,VAS and ODI scores at 3 months,6 months and last follow-up visit improved significantly in both groups..In the EPS group,2 screws loosening(0.3%,2/796)occurred in 1 patients(0.6%,1/173),and 7 screws breakage(0.9%,7/796)occurred in 5 patients(2.9%,5/173).In the CPS group,17 screws loosening(1.8%,17/960)occurred in 13 patients(5.6%,13/233),and 4 screws breakage(0.4%,4/960)occurred in 2 patients(0.9%,2/233).The screw loosening rate in EPS group was significantly lower than that in CPS group(P=0.00).The screw breakage rate was higher than that in CPS group,but there was no significant difference(P=0.36).The fusion rate in the EPS group(99.4%,172/173)was significantly higher than that in CPS group(93.6%,218/233)(P=0.00).Conclusions: In the lumbar fusion surgery combined with osteoporosis,expandable pedicle screws can provide lower screw loosening rate and higher fusion rate compared with conventional pedicle screws.It is a safe and reliable implant for osteoporotic spinal surgery.The reliability of the mid-long-term in vivo of EPS is reliable.