***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: Study Design . Prospect i ve clinical study . Objective . To test whether elastic stabilization with the Dynesys system ( Zimmer Spine , Minneapolis , MN ) provides enough stability to prevent further progression of spondylolisthesis as well as instability after decompression for spinal stenosis with degenerative spondylolisthesis . Summary of Background Data . In spinal stenosis with degenerative spondylolisthesis , decompression and fusion is widely recommended . However , patients have donor site pain . In 1994 , a dynamic transpedicular system ( Dynesys ) was introduced to the market , stating that stabilization is possible without bone grafting . Methods . A total of 26 patients ( mean age 71 years ) with lumbar spinal stenosis and degenerative spondylolisthesis underwent interlaminar decompression and dynamic stabilization with the Dynesys system . Minimum follow-up was 2 years . Operative data , clinical outcome , and plain and flexion/extension radiographs were obtained and compared to preoperative and postoperative data . Results . Mean leg pain decreased significantly ( P < 0.01 ) , and mean walking distance improved significantly to more than 1000 m ( P < 0.01 ) . There were 5 patients ( 21 % ) who still had some claudication .  A total of 21 patients ( 87.5 % ) would undergo the same procedure again . Radiographically , no significant progression of spondylolisthesis could be detected . The implant failure rate was 17 % , and none of them were clinical ly symptomatic . Conclusions . In elderly patients with spinal stenosis with degenerative spondylolisthesis , dynamic stabilization with the Dynesys system in addition to decompression leads to similar clinical results as seen in established protocol s using decompression and fusion with pedicle screws . It maintains enough stability to prevent further progression of spondylolisthesis or instability . With the Dynesys system , no bone grafting is necessary , therefore , donor site morbidity can be avoided Abstract . Various forms of lumbar instability require a surgical stabilization . As an alternative to fusion , a mobile , dynamic stabilization restricting segmental motion would be advantageous in various indications , allowing greater physiological function and reducing the inherent disadvantages of rigid instrumentation and fusion . The dynamic neutralization system for the spine ( Dynesys ) is a pedicle screw system for mobile stabilization , consisting of titanium alloy screws connected by an elastic synthetic compound , controlling motion in any plane ( non-fusion system ) . This prospect i ve , multi-center study evaluated the safety and efficacy of Dynesys  in the treatment of lumbar instability conditions , evaluating pre- and post-operative pain , function , and radiological data on a consecutive series of 83 patients . Indications consisted of unstable segmental conditions , mainly combined with spinal stenosis ( 60.2 % ) and with degenerative discopathy ( 24.1 % ) , in some cases with disc herniation ( 8.4 % ) , and with revision surgery ( 6.0 % ) . Thirty-nine patients additionally had degenerative spondylolisthesis , and 30 patients had undergone previous lumbar surgery .  In 56 patients instrumentation was combined with direct decompression . The mean age at operation was 58.2 ( range 26.8–85.3 ) years ; the mean follow-up time was 38.1 months ( range 11.2–79.1 months ) . There were nine complications unrelated to the implant , and one due to a screw malplacement . Four of them required an early surgical reintervention . Additional lumbar surgery in the follow-up period included : implant removal and conversion into spinal fusion with rigid instrumentation for persisting pain in three cases , laminectomy of an index segment in one case and screw removal due to loosening in one case . In seven cases , radiological signs of screw loosening were observed . In seven cases , adjacent segment degeneration necessitated further surgery . Mean pain and function scores improved significantly from baseline to follow-up , as follows : back pain scale from 7.4 to 3.1 , leg pain scale from 6.9 to 2.4 , and Oswestry Disability Index from 55.4 % to 22.9 % . These study results compare well with those obtained by conventional procedures ; in addition to which , mobile stabilization is less invasive than fusion . Long-term screw fixation is dependent on correct screw dimension and proper screw positioning . The natural course of polysegmental disease in some cases necessitates further surgery as the disease progresses . Dynamic neutralization proved to be a safe and effective alternative in the treatment of unstable lumbar conditions Controlled clinical trials of the treatment of acute myocardial infa rct ion offer a unique opportunity for the study of the potential influence on outcome of bias in treatment assignment . A group of 145 papers was divided into those in which the r and omization process was blinded ( 57 papers ) , those in which it may have been unblinded ( 45 papers ) , and those in which the controls were selected by a nonr and om process ( 43 papers ) . At least one prognostic variable was maldistributed ( P less than 0.05 ) in 14.0 per cent of the blinded-r and omization studies , in 26.7 per cent of the unblinded-r and omization studies , and in 58.1 per cent of the nonr and omized studies . Differences in case-fatality rates between treatment and control groups ( P less than 0.05 ) were found in 8.8 per cent of the blinded-r and omization studies , 24.4 per cent of the unblinded-r and omization studies , and 58.1 per cent of the nonr and omized studies . These data emphasize the importance of keeping those who recruit patients for clinical trials from suspecting which treatment will be assigned to the patient under consideration OBJECTIVES The aim of this study was to evaluate the outcome of wide surgical decompression and concomitant posterior instrumentation in patients with degenerative lumbar spinal stenosis . METHODS Thirty-seven consecutive patients ( 14 men , 23 women ; mean age 64 years ; range 36 to 82 years ) with degenerative lumbar spinal stenosis were prospect ively evaluated following surgical treatment with spinal decompression and concomitant instrumented posterior fusion . The mean duration of symptoms before surgery was 24 months ( range 12 to 60 months ) . Preoperatively , six patients had degenerative spondylolisthesis ( grade 1 ) and two patients had degenerative lumbar scoliosis .  Decompression was performed at one level in four patients , at two levels in 16 patients , at three levels in 11 patients , and at four levels in six patients . Discectomy was also performed in seven patients . Preoperatively and postoperatively , the patients were assessed by the Oswestry Disability Index and a visual analog scale for overall pain ( leg and low back pain ) . The satisfaction level of the patients for surgical outcome was also question ed . The mean follow-up period was 4.6 years ( range 1 to 7 years ) . RESULTS Preoperatively , the mean Oswestry Disability Index score was 60.5 % and the mean overall pain score was 7.5 . Postoperatively , the Oswestry Disability Index score significantly decreased to 36.8 % and the overall pain score significantly decreased to 3.5 ( p<0.001 ) . Preoperative and postoperative walking distances of the patients were as follows , respectively : more than 1,000 meters ( 6 and 14 patients ) , 500 to 1,000 meters ( 5 and 7 patients ) , less than 500 meters ( 26 and 16 patients ) . Twenty patients did not use any analgesics and eight patients used analgesics on a weekly basis . Twenty-six patients were satisfied with the surgical outcome , nine patients were somewhat satisfied , and two patients were dissatisfied . Overall , the outcomes were excellent to good in 22 patients ( 59.5 % ) . None of the patients required revision surgery . CONCLUSION Most patients with degenerative lumbar spinal stenosis benefit from decompressive surgery . Patients with long-st and ing preoperative symptoms and concomitant diseases often have poor results and are less satisfied with the postoperative outcome Study Design . Prospect i ve comparative r and omized clinical and radiologic study . Objective . This study was conducted to compare the short-term effects of rigid versus semirigid and dynamic instrumentation on the global and segmental lumbar spine profile , subjective evaluation of the result , and the associated complications . Background Data . Lumbar spine fusion with rigid instrumentation for degenerative spinal disorders seems to increase the fusion rate . However , rigid instrumentation may be associated with some undesirable effects , such as increased low back pain following decrease of lumbar lordosis , fracture of the vertebral body and pedicle , pedicle screw loosening , and adjacent segment degeneration . The use of semirigid and dynamic devices has been advocated to reduce such adverse effects of the rigid instrumentation and thus to achieve a more physiologic bony fusion . Material s and Methods . This study compared 3 equal groups of 45 adult patients , who underwent primary decompression and stabilization for symptomatic degenerative lumbar spinal stenosis . The patients of each group were r and omly selected and received either the rigid ( Group A ) , or semirigid ( Group B ) , or dynamic ( Group C ) spinal instrumentation with formal decompression and fusion . The mean ages of the patients who received rigid , semirigid , and dynamic instrumentation  were 65 ± 9 , 59 ± 16 , and 62 ± 10 years , respectively . All patients had detailed roentgenographic study including computed tomography scan and magnetic resonance imaging before surgery to the latest follow-up observation . The following roentgenographic parameters were measured and compared in all spines : lumbar lordosis ( L1–S1 ) , total lumbar lordosis ( T12–S1 ) , sacral tilt , distal lordosis ( L4–S1 ) , segmental lordosis , vertebral inclination , and disc index . The SF-36 health survey and Visual Analogue Scale was used before surgery to the latest evaluation . Results . All patients were evaluated after a mean follow-up of 47 ± 14 months . Both lumbar and total lordosis correction did not correlate with the number of the levels instrumented in any group . Total lordosis was slightly decreased after surgery ( 3 % , P < 0.05 ) in Group C. The segmental lordosis L2–L3 was increased after surgeryby8.5 % ( P < 0.05 ) in Group C , whereas the segmentallordosis L4–L5 was significantly decreased in Group A and C by 9.8 % ( P = 0.01 ) and 16.2 % ( P < 0.01 ) , respectively . The disc index L2–L3 was decreased after surgery in Group A and C by 17 % ( P < 0.05 ) and 23.5 % ( P < 0.05 ) , respectively . The disc index L3–L4 was increased in Group C by 18.74 % ( P < 0.01 ) . The disc index L4–L5 was after surgery decreased in all 3 groups : Group A by 21 % ( P = 0.01 ) , Group B by 13 % ( P < 0.05 ) , and Group C by 13.23 % ( P < 0.05 ) . The disc index L5–S1 was significantly decreased in Group B by 13 % ( P < 0.05 ) . The mean preoperative scores of the SF-36 before surgery were 11 , 14 , and 13 for Groups C , B , and A , respectively . In the first year after surgery , there was a significant increase of the preoperative SF-36 scores to 65 , 61 , and 61 for Groups C , B , and A , respectively , that represents an improvement of 83 % , 77 % , and 79 % , respectively . In the second year after surgery and thereafter , there was a further increase of SF-36 scores of 19 % , 23 % , and 21 % for Groups C , B , and A , respectively . The mean preoperative scores of Visual Analogue Scale for low back pain for Groups C , B , and A were 5 , 4.5 , and 4.3 , respectively , and decreased after surgery to 1.9 , 1.5 , and 1.6 , respectively . The mean preoperative scores of the Visual Analogue Scale for leg pain for Groups C , B , and A were 7.6 , 7.1 , and 6.9 , respectively , and decreased after surgery to 2.5 , 2.5 , and 2.7 , respectively . All fusions healed radiologically within the expected time in all three groups without pseudarthrosis or malunion . Delayed hardware failure ( 1 screw and 2 rod breakages ) 1 year and 18 months after surgery without radiologic pseudarthrosis was observed in 2 patients in Group C. Asymptomatic radiolucent areas were shown around pedicle screws in the pedicles L5 and S1 in 2 , 3 , and 4 cases in Group C , A , and B , respectively . There was no adjacent segment degeneration in any spine until the last evaluation . Discussion and Conclusion . This comparative study showed that all three instrumentations applied over a short area for symptomatic degenerative spinal stenosis almost equally after surgery maintained the preoperative global and segmental sagittal profile of the lumbosacral spine and was followed by similarly significant improvement of both self- assessment and pain scores . Hardware failure occurred at a low rate following dynamic instrumentation solely without radiologically visible pseudarthrosis or loss of correction . Because of the similar clinical and radiologic data in all three groups and the relative small number of patients that were included in each group , it is difficult for the authors to make any recommendation in favor of any instrumentation 
    Output:
    
CONCLUSION It was not possible to reveal any evidence for benefits using DPF compared to rigid fixation in surgery for lumbar spine