pedicle screw instrumentation in the lumbar spine has become popular because rigid fixation is achieved quickly , providing for early patient mobilization after surgery . modern fusion techniques , including the use of pedicle screws , structural interbody grafts and biologics , have resulted in significant improvements in radiographic evident segmental fusion ; however , this has not translated into comparable improvements in successful clinical outcomes after lumbar fusion surgery4,21 ) . beside this , rigid fusion causes the chronic back pain associated with back muscle atrophy and limitation of motion . additionally , the accelerated degeneration of spinal motion segments adjacent to rigidly fused segment(s ) has become increasingly recognized as a drawback of spinal fusion procedures5,7,14,18 ) . fixed sagittal imbalance , flat - back syndrome , and pseudoarthrosis are also potential complications associated with rigid fusion of the lumbar spine9 ) . based on studies in which patients with partial fusion showed the same clinical outcomes as patients with solid fusion , it might be hypothesized that a reduction in , rather than an elimination of , segmental motion results in the alleviation of pain2,5,12,17 ) . these findings suggest the need for alterative procedures and techniques that do not require fusion for the treatment of painful degenerative spine disease . therefore , various kinds of dynamic stabilization systems have designed to stabilize the segment while preserving motion and unloading the disc and facet joint3,15 ) . the nflex controlled stabilization system is a novel pedicle based dynamic stabilization that incorporates the insertional techniques of traditional pedicle screw fixation devices , while potentially providing the segmental stabilization with preservation of some motion at stabilized segments . in an earlier clinical study using the nflex device , it was proved as clinically effective with few complications during a short - term follow - up1 ) . in this study we describe the extended two - year clinical experience with the nflex controlled stabilization system focusing on the clinical outcomes and complications . west chester , pa , usa ) consists of polyaxial titanium alloy pedicle screws that are fixed to a semi - rigid polycarbonate urethane - sleeved rod . the integrated polycarbonate urethane ( pcu ) spacer is surrounded by a central titanium ring , to which a pedicle screw is locked . the controlled pistoning of this spacer along the axis of the central titanium core provides a shock absorber effect , reducing the overall rigidity of the construct . the rods are low profile , may be used in single- or multi - level applications , and require a relatively short distance between screws of only 9 mm . the rod may be attached to pedicle screws in the standard fashion , with one pedicle screw attached to the titanium ring of the sleeve and one or more pedicle screws attached to the solid portion of the titanium rod ( fig . flexion is necessarily coupled with elongation and extension is coupled with compression of the posterior segments ; therefore , any device hoping to provide support through physiologic translational motion ( flexion - extension ) would be required to elongate and compress as well ( fig . the pcu spacer ( bumper elements ) is not bonded to the titanium components of the rod . therefore , when the distance between the pedicles ( dbp ) increases and decreases during the translational movement ( flexion and extension ) , the rod is able to elongate and compress to accommodate this change , as well as toggle to accommodate angulation . compressive loads are borne primarily by the spacer , as opposed to the titanium core . the titanium core provides resistance to translation of one vertebra relative to the adjacent vertebra . biomechanical study of this device demonstrated that in all loading modes , the n - flex device provided a decompressed lumbar segment with sufficient stability ( i.e. , greater than the intact case ) but significantly less rigid than a similar segment stabilized with a solid rod , suggesting the applicability of this implant as a dynamic fixation device in clinical practice6,28 ) . five institutes participated in a retrospective assessment of 72 consecutive patients who underwent nflex controlled stabilization between september 2006 and july 2007 , at one level with or without rigid fusion at a contiguous level . of these 72 patients , 65 were available for 2-year follow - up . the study group consisted of 26 men and 39 women with an average age of 54.5 years ( range 19 - 86 ) . the nflex controlled stabilization system was applied for a non - fusion stabilization , or hybrid fusion , which is one or more segment fusion with one segment non - fusion stabilization at an adjacent segment . the non - fusion stabilization was used for patients with degenerative disc disease ( ddd ) , spinal stenosis with instability ( single or multi - level ) , degenerative spondylolisthesis ( grade 1 ) , adjacent segments diseases , and multi - level degenerative stenosis with scoliosis . hybrid fusion was applied for single or multi - level fusion indicated patients with substantial pathologies at an adjacent level , but not enough to warrant fusion . patients with profound osteoporosis ( t - score < -2.5 ) , isthmic spondylolisthesis , bilateral spondylolysis , bilateral facetectomy or insufficiency , fracture , infection , and metastatic spine tumors were not indicated . in this study group , device was applied for ddd in 29 patients ( 44.6% ) , spinal stenosis with degenerative spondylolisthesis in 16 patients ( 24.6% ) , degenerative spinal stenosis in 9 patients ( 13.8% ) , adjacent segment disease ( asd ) after fusion in 6 patients ( 9.2% ) , and spinal stenosis with degenerative lumbar scoliosis in 5 patients ( 7.7% ) ( table 1 ) . nine patients had prior lumbar surgeries , including 2 discectomies , and 6 lumbar fusion procedures . non - fusion application was done in 25 patients and hybrid fusion was done in 40 patients . the nflex controlled stabilization was implanted using standard surgical procedures for standard posterior lumbar spinal surgery . standard midline incisions and subperiosteal retraction of the paraspinal muscles exposing the affected segment was used in most cases . it some cases , however , bilateral paraspinal ( wiltse ) approach were used in order to minimize muscle disruption . the entry point of pedicle screw must be located at the external junction of the facet joint and transverse process . care was taken to place the screws lateral to the facet joints , at 30 - 45 lateromedial angle and parallel to the upper end plate of the corresponding vertebrae . this instrument allows bending within a few mm of the dynamic section of the rod , while protecting this area from being contoured and potentially damaged . preoperative imaging studies included anteroposterior ( ap ) and lateral static plain radiographs , as well as dynamic flexion / extension x - rays . lumbar computed tomography ( ct ) and magnetic resonance imaging ( mri ) was also performed in most cases . patients completed visual analogue scale ( vas ) and oswestry disability index ( odi ) questionnaires at pre- and postoperative evaluations . the patients generally returned for follow - up evaluations at 3 and 6 weeks ( one center assessed patients at 4 weeks ) , 3 months , 6 months , 12 and 24 months . in some cases , follow - up evaluations were conducted through phone interviews . a thorough neurologic examination was performed pre - operatively and at most post - operative points , as were static and dynamic lumbar plain films to evaluate for implant integrity . west chester , pa , usa ) consists of polyaxial titanium alloy pedicle screws that are fixed to a semi - rigid polycarbonate urethane - sleeved rod . the integrated polycarbonate urethane ( pcu ) spacer is surrounded by a central titanium ring , to which a pedicle screw is locked . the controlled pistoning of this spacer along the axis of the central titanium core provides a shock absorber effect , reducing the overall rigidity of the construct . the rods are low profile , may be used in single- or multi - level applications , and require a relatively short distance between screws of only 9 mm . the rod may be attached to pedicle screws in the standard fashion , with one pedicle screw attached to the titanium ring of the sleeve and one or more pedicle screws attached to the solid portion of the titanium rod ( fig . flexion is necessarily coupled with elongation and extension is coupled with compression of the posterior segments ; therefore , any device hoping to provide support through physiologic translational motion ( flexion - extension ) would be required to elongate and compress as well ( fig . the pcu spacer ( bumper elements ) is not bonded to the titanium components of the rod . therefore , when the distance between the pedicles ( dbp ) increases and decreases during the translational movement ( flexion and extension ) , the rod is able to elongate and compress to accommodate this change , as well as toggle to accommodate angulation . compressive loads are borne primarily by the spacer , as opposed to the titanium core . the titanium core provides resistance to translation of one vertebra relative to the adjacent vertebra . biomechanical study of this device demonstrated that in all loading modes , the n - flex device provided a decompressed lumbar segment with sufficient stability ( i.e. , greater than the intact case ) but significantly less rigid than a similar segment stabilized with a solid rod , suggesting the applicability of this implant as a dynamic fixation device in clinical practice6,28 ) . five institutes participated in a retrospective assessment of 72 consecutive patients who underwent nflex controlled stabilization between september 2006 and july 2007 , at one level with or without rigid fusion at a contiguous level . of these 72 patients , the study group consisted of 26 men and 39 women with an average age of 54.5 years ( range 19 - 86 ) . the nflex controlled stabilization system was applied for a non - fusion stabilization , or hybrid fusion , which is one or more segment fusion with one segment non - fusion stabilization at an adjacent segment . the non - fusion stabilization was used for patients with degenerative disc disease ( ddd ) , spinal stenosis with instability ( single or multi - level ) , degenerative spondylolisthesis ( grade 1 ) , adjacent segments diseases , and multi - level degenerative stenosis with scoliosis . hybrid fusion was applied for single or multi - level fusion indicated patients with substantial pathologies at an adjacent level , but not enough to warrant fusion . patients with profound osteoporosis ( t - score < -2.5 ) , isthmic spondylolisthesis , bilateral spondylolysis , bilateral facetectomy or insufficiency , fracture , infection , and metastatic spine tumors were not indicated . in this study group , device was applied for ddd in 29 patients ( 44.6% ) , spinal stenosis with degenerative spondylolisthesis in 16 patients ( 24.6% ) , degenerative spinal stenosis in 9 patients ( 13.8% ) , adjacent segment disease ( asd ) after fusion in 6 patients ( 9.2% ) , and spinal stenosis with degenerative lumbar scoliosis in 5 patients ( 7.7% ) ( table 1 ) . nine patients had prior lumbar surgeries , including 2 discectomies , and 6 lumbar fusion procedures . non - fusion application was done in 25 patients and hybrid fusion was done in 40 patients . the nflex controlled stabilization was implanted using standard surgical procedures for standard posterior lumbar spinal surgery . standard midline incisions and subperiosteal retraction of the paraspinal muscles exposing the affected segment was used in most cases . it some cases , however , bilateral paraspinal ( wiltse ) approach were used in order to minimize muscle disruption . the entry point of pedicle screw must be located at the external junction of the facet joint and transverse process . care was taken to place the screws lateral to the facet joints , at 30 - 45 lateromedial angle and parallel to the upper end plate of the corresponding vertebrae . this instrument allows bending within a few mm of the dynamic section of the rod , while protecting this area from being contoured and potentially damaged . preoperative imaging studies included anteroposterior ( ap ) and lateral static plain radiographs , as well as dynamic flexion / extension x - rays . lumbar computed tomography ( ct ) and magnetic resonance imaging ( mri ) was also performed in most cases . patients completed visual analogue scale ( vas ) and oswestry disability index ( odi ) questionnaires at pre- and postoperative evaluations . the patients generally returned for follow - up evaluations at 3 and 6 weeks ( one center assessed patients at 4 weeks ) , 3 months , 6 months , 12 and 24 months . in some cases , follow - up evaluations were conducted through phone interviews . a thorough neurologic examination was performed pre - operatively and at most post - operative points , as were static and dynamic lumbar plain films to evaluate for implant integrity . all patients were treated with a construct that provided a single dynamic level ( non - fusion ) . two patients underwent two single - level dynamic constructs at non - contiguous levels ( l3 - 4 and l5-s1 ) . instrumented rigid fusion was performed at contiguous levels in 40 patients ( the so called " hybrid fusion " ) , placed either cephalad or caudal to non - fusion stabilized segment . twenty - eight patients received a single - level rigid fusion combined with one level dynamic stabilization . eight patients received a two - level rigid fusion combined with one level dynamic stabilization , and 4 patients received a 3-level rigid fusion , plus one level dynamic stabilization . dynamic stabilization was used at the contiguous superior level in 33 ( 82% ) of patients receiving the " hybrid " fusion , and was placed at the inferior end of the fused segment(s ) in 7 ( 18% ) of patients receiving the hybrid fusion . the mean follow - up period was 25.6 months ( range 23 - 34 months ) . the mean vas score improved from 8.1 preoperatively to 3.8 postoperatively ( p<0.001 ) , representing a 53% improvement . there was a statistically significant improvement in vas across all indications , with the exception of pain scores in patients with prior fusions treated for asd and degenerative lumbar scoliosis . there was a favorable trend in these subgroups , however , as the asd patients had a mean improvement of 20% and the scoliosis patients had a mean improvement of 53% functional status also showed significant improvement , with a mean pre - operative odi score of 44.5 improving to 21.8 ( p<0.001 ) postoperatively , representing a 51% improvement . the level of odi improvement was similar across all indications and statistically significant with the exception of patients with scoliosis . although the 5 patients with scoliosis showed a favorable trend with a mean improvement in odi of 62% , statistical significance was not achieved . these results may have been affected by the small number of patients in the asd and scoliosis subgroups . in addition , patients with severe disability or worse ( odi 41 or greater ) at follow - up comprised only 8% of the total , whereas 69% of the total had severe disability pre - operatively . improvements in pain ( vas ) after surgery are presented in fig . 4 and improvements in functional status ( odi ) male that had a prior 3 level fusion from l3-s1 , that was topped off at l2 - 3 . one patient underwent a re - operation for a loose locking cap on the pedicle screw . this patient was treated with a dynamic level at l1-l2 , but no pedicle screws could be placed in l2 . consequently , the dynamic segment spanned l1-l3 . these circumstances likely created an unusually long lever arm , likely causing the screw to loosen . non - device related complications included : one re - operation due to advanced osteoporosis , cage migration at a non - dynamic ( fusion ) level ; device removal due to infection in a patient with lupus ; one patient requiring adjacent level surgery ; and one patient who succumbed from causes not related to spinal disease or surgery . it should be noted that all symptomatic patients were evaluated for the presence of implant - related complications . all patients were treated with a construct that provided a single dynamic level ( non - fusion ) . two patients underwent two single - level dynamic constructs at non - contiguous levels ( l3 - 4 and l5-s1 ) . instrumented rigid fusion was performed at contiguous levels in 40 patients ( the so called " hybrid fusion " ) , placed either cephalad or caudal to non - fusion stabilized segment . twenty - eight patients received a single - level rigid fusion combined with one level dynamic stabilization . eight patients received a two - level rigid fusion combined with one level dynamic stabilization , and 4 patients received a 3-level rigid fusion , plus one level dynamic stabilization . dynamic stabilization was used at the contiguous superior level in 33 ( 82% ) of patients receiving the " hybrid " fusion , and was placed at the inferior end of the fused segment(s ) in 7 ( 18% ) of patients receiving the hybrid fusion . the mean follow - up period was 25.6 months ( range 23 - 34 months ) . the mean vas score improved from 8.1 preoperatively to 3.8 postoperatively ( p<0.001 ) , representing a 53% improvement . there was a statistically significant improvement in vas across all indications , with the exception of pain scores in patients with prior fusions treated for asd and degenerative lumbar scoliosis . there was a favorable trend in these subgroups , however , as the asd patients had a mean improvement of 20% and the scoliosis patients had a mean improvement of 53% functional status also showed significant improvement , with a mean pre - operative odi score of 44.5 improving to 21.8 ( p<0.001 ) postoperatively , representing a 51% improvement . the level of odi improvement was similar across all indications and statistically significant with the exception of patients with scoliosis . although the 5 patients with scoliosis showed a favorable trend with a mean improvement in odi of 62% , statistical significance was not achieved . these results may have been affected by the small number of patients in the asd and scoliosis subgroups . in addition , patients with severe disability or worse ( odi 41 or greater ) at follow - up comprised only 8% of the total , whereas 69% of the total had severe disability pre - operatively . improvements in pain ( vas ) after surgery are presented in fig . 4 and improvements in functional status ( odi ) male that had a prior 3 level fusion from l3-s1 , that was topped off at l2 - 3 . one patient underwent a re - operation for a loose locking cap on the pedicle screw . this patient was treated with a dynamic level at l1-l2 , but no pedicle screws could be placed in l2 . consequently , the dynamic segment spanned l1-l3 . these circumstances likely created an unusually long lever arm , likely causing the screw to loosen . non - device related complications included : one re - operation due to advanced osteoporosis , cage migration at a non - dynamic ( fusion ) level ; device removal due to infection in a patient with lupus ; one patient requiring adjacent level surgery ; and one patient who succumbed from causes not related to spinal disease or surgery . it should be noted that all symptomatic patients were evaluated for the presence of implant - related complications . still the fusion is the gold standard of surgical management in lumbar degenerative disc diseases8 ) . but many reports have been documented inevitable side effects of the fusion such as chronic back pain , and adjacent segment degeneration9 ) . to overcome these undesirable effects , motion preservation technologies such as total disc replacement and posterior dynamic stabilization system non - fusion posterior dynamic stabilization systems have gained popularity recently . it is hypothesized that abnormal load transmission across a degenerated spinal motion segment leads to abnormal segmental motion , altered biomechanics and , subsequently , pain19,25 ) . when used in a non - fusion application , the goal of dynamic stabilization is to control , rather than eliminate , segmental spinal motion in order to reduce abnormal load transmission across an intervertebral disc and/or facet joint , while avoiding the drawbacks associated with rigid fusion . this is accomplished by limiting segmental motion to a range close to normal and/or by preventing the spine from adopting positions or postures that lead to abnormal load transmission . limiting segmental motion may also be useful to control motion in the iatrogenically destabilized spine ; to increase anterior load sharing to augment interbody fusion ; and to provide less rigid stabilization in the aging spine3,15 ) . additional goals of dynamic stabilization are to cause minimal disruption and to preserve future surgical options . of several dynamic stabilization devices , especially pedicle based dynamic stabilization system ( pbds ) has the property of intrinsic dynamic nature contrary to other static devices such as interspinous spacer . subsequent clinical trials in the treatment of degenerative lumbar diseases using pedicle - based dynamic stabilization system were made . one of the most extensively - used posterior dynamic stabilization systems is the dynesys dynamic stabilization system ( zimmer spine ) , in which pedicle screws are connected across spinal motion segments with non - elastic bands to provide controlled motion . early clinical outcomes have shown dynamic stabilization using this system to be effective in lessening pain and disability at in patients with degenerative spondylolisthesis and central or lateral canal stenosis . other pedicle - based dynamic stabilization systems have developed and reported their clinical outcomes13,22,26 ) . one of reasons for discrepancies between theoretical advantage and clinical outcomes is due to design flaw in pbds . the ideal pbds should simulate the normal functional spinal unit , which has normal kinematics , normal load transfer pattern with load sharing , and active change of center of rotation . beside these , normal spine has a unique pattern of motion on sagittal plane as well as coronal and axial plane . the distance between upper and lower pedicle ( dbp ) is changing during the flexion - extension . most pbdss in current market designed to have fixed dbp during translational movement when it is implanted . this design flaw can contribute to abnormal kinematics , abnormal loading , metallic failure and unwanted clinical outcome . this device consists of polyaxial titanium pedicle screws that are fixed to a semi - rigid polycarbonate urethane - sleeved rod . the integrated pcu spacer is surrounded by a central titanium ring , to which a pedicle screw is locked . therefore , when the dbp changing during translation , the rod is able to elongate and compress to accommodate this change , as well as toggle to accommodate angulations . compressive loads are borne primarily by the spacer , as opposed to the titanium core . the controlled pistoning of this spacer along the axis of the central titanium core provides translational motion , and a shock absorber effect , reducing the overall rigidity of the construct28 ) . earlier clinical and radiographic studies using this device revealed compatible outcomes from the traditional treatment and preserved the limited extent of rom at the stabilized segment1 ) . although dynesys system is currently widely used , it is troublesome and complicated in the procedure of inserting of polycarbonate urethane spacer and polyester cord of dynesys to pedicle screw . this dynamic rod is a semi - rigid polycarbonate urethane - sleeved and it can be fixed usual polyaxial titanium alloy pedicle screws . though this surgical procedure is exactly same to traditional pedicle screw fixation , it is easy to insert the dynamic rod . the nflex dynamic rod was tested for static and fatigue durability according to the american society for testing materials specification number f1717 out to 10 million cycles . and the result was shown a higher level of strength than several commercially available rigid pedicle screw systems . mullholland et al.19 ) stated that a dynamic stabilization is a system that would alter movements favorably and load transmissions of a spinal motion segment , without the intension of fusion of the segment . this leaves the spinal segment mobile , its intention is to alter load - bearing patterns of the motion segment and to control any abnormal motions at the segment . actually , the dynamic stabilization system was named as an instrumentation that permits axial loading to promote the fusion . thus use of this term would not be suitable for the system that alters the load - bearing pattern and control motion . furthermore , current pbds has no dynamic nature , it just limits the rom with a limited amount of load sharing , which means that it does not reflect the dynamic nature of functional spinal segments . galbusera et al.10 ) stated that " dynamic " may be a misleading word from an engineering point of view , since it suggests a time or velocity dependency which does not exist . for this reason , the authors prefer the term " controlled stabilization " in stead of " dynamic stabilization . " actually , the definition by mullholland and sengupta was made on the basis of chronic back pain in ddd . in fact , non - ddd applications ( such as spinal stenosis , spondylolisthesis , and recurrent disc herniation ) were more common in the literature . in this viewpoint , the definition of the dynamic stabilization system in non - ddd applications should be different from that in ddd applications . in such cases , the spine was decompressed and then the dynamic stabilization was added for the enforcement of the weakened spine by decompression . in this situation , the dynamic stabilization is a supportive device that can strengthen the decompressed spine . therefore , the basic concept of the dynamic stabilization in degenerative spinal disease is an " internal brace " that can add the stability to a weakened decompressed spine . by stabilizing the decompressed spine , a dynamic stabilization can help prevent or delay further degeneration of the spine with controlled motion . thus , the dynamic stabilization system would be defined as a system that would stabilize the decompressed ( weakened ) spinal motion segment without fusion and control some range of motion , and lead to a new degenerative process ( fig . 8) . in an earlier clinical study using nflex stabilization system1 ) , authors have found that the nflex dynamic stabilization system , when used as a nonfusion dynamic stabilization system , provides improvements in pain and function scores compared to those found in use of the dynesys system , although the follow - up is much shorter ( average 8.1 months ) . in addition , the preliminary data compared favorably to the odi scores of the posterolateral fusion group in a randomized prospective clinical trial , as the percentage of nflex patients with severe disability was only 13% ( compared to 47% in the posterolateral fusion group ) . finally , from the small number of patients that have been measured , 53% have demonstrated partial preservation of normal rom . furthermore , there have been no rod - related adverse events and the option of later converting a dynamically stabilized segment to a fusion is preserved . in the present study , as like the earlier clinical study1 ) , the nflex system has proven effective in improving pain and function scores after two years . we observed one case of rod failure in this series ; however , this failure was identified in march 2008 , 1 year post - operatively . the rod manufacturer engaged the authors in an analysis of this event , along with a small number of similar events , to more clearly identify relevant patient pathology and intraoperative considerations . this thorough , proactive approach led to more detailed patient selection and surgical technique guidance . importantly , preloading the dynamic end of the rod could compromise the dynamic portion of the titanium ring and polymer sleeve construct , and overload the titanium core . specifically , certain patient pathologies , such as sagittal or coronal deformity , spondylolisthesis , facet insufficiency or hypermobility may contribute to excessive loading , and should be avoided at the dynamic level . the segment intended for stabilization must provide enough stability to load share with the rod . manipulating the dynamic end of the rod by persuasion , or applying compression or distraction , will preload the rod , and should be avoided . this study focused only on the clinical outcomes after the application of the nflex controlled stabilization system . unfortunately , detailed radiographic results including rom after operation , the overall rate of screw loosening , and preventing effects of adjacent segment degeneration were not studied . however , the clinically relevant benefits of a less rigid segment are yet to be seen . over time , sustained clinical improvement , and absence of implant related complications or re - operations will be important and perhaps differentiating factors in support of these devices . long term level i evidence will not be available for many years , so the rationale for utilizing dynamic stabilization will continue to be based on the belief in a theoretical benefit from controlling , rather than completely eliminating motion , supported with biomechanical data and the ongoing compilation of level iii evidence . pedicle - based dynamic stabilization using the nflex controlled stabilization system seems effective in improving pain and function scores , with sustained clinical improvement after two years . the incidence of adverse events and re - operation was not inconsistent with the authors ' experience with rigid fusion . with appropriate patient selection and surgical implantation , dynamic stabilization may be considered an effective alternative to rigid fusion based on medium term follow - up .
objectivepedicle - based dynamic stabilization systems , in which semi - rigid rods or cords are used to restrict or control spinal segmental motion , aim to reduce or eliminate the drawbacks associated with rigid fusion . in this study , we analyzed the two - year clinical outcomes of patients treated with the nflex ( synthes spine , inc . ) , a pedicle - based dynamic stabilization system.methodsfive sites participated in a retrospective study of 72 consecutive patients who underwent nflex stabilization . 
 of these 72 patients , 65 were available for 2-year follow - up . 
 patients were included based on the presence of degenerative disc disease ( 29 patients ) , degenerative spondylolisthesis ( 16 patients ) , lumbar stenosis ( 9 patients ) , adjacent segment degeneration ( 6 patients ) , and degenerative lumbar scoliosis ( 5 patients ) . 
 the clinical outcome measures at each assessment were visual analogue scale ( vas ) to measure back pain , and oswestry disability index ( odi ) to measure functional status . 
 radiographic assessments included evidence of instrumentation failure or screw loosening.resultssixty-five patients ( 26 men and 39 women ) with a mean age of 54.5 years were included . 
 mean follow - up was 25.6 months . 
 the mean vas score improved from 8.1 preoperatively to 3.8 postoperatively , representing a 53% improvement , and the odi score from 44.5 to 21.8 , representing a 51% improvement . 
 improvements in pain and disability scores were statistically significant . 
 three implant - related complications were observed.conclusionposterior pedicle - based dynamic stabilization using the nflex system seems effective in improving pain and functional scores , with sustained clinical improvement after two years . with appropriate patient selection 
 , it may be considered an effective alternative to rigid fusion .