we identified relevant articles with the following inclusion criteria : ( 1 ) the target population consisted of adult patients undergoing surgical treatment of lumbar spine degenerative conditions ( excluding tumor trauma and infection ) with a minimum follow - up of 2 years ; ( 2 ) the intervention was posterolateral with or without instrumentation compared with pif ( either plif or transforaminal lumbar interbody fusion with or without instrumentation ) ; and ( 3 ) the outcome measure was patient - centered disease - specific functional outcome . a computerized search of the electronic databases embase ( 19802006 ) and ovid medline and pubmed medline ( 1966february 2006 ) was performed . a hand search of the european spine journal , spine , and the journal of spinal disorders & techniques , as well as bibliographies of identified studies and relevant narrative reviews , was performed to identify further studies . we assessed each published study for the quality of the study design using the newcastle - ottawa 8-point scale for assessment of nonrandomized studies . this scale grades the reporting of the studies based on the representativeness of samples , baseline factors , assessment of outcome , statistical analysis or study design , and length of follow - up . for each eligible study , data were extracted and checked for accuracy . specifically , the sizes and demographic data of the intervention and control groups , type of fusion , underlying diagnoses , length of follow - up , loss to follow - up , fusion rate , radiologic parameters , and clinical outcomes at final follow - up were recorded . because of the variety of clinical outcome tools used in the studies , surgical results were predefined as satisfactory if the patient had a score of less than 40 on the oswestry disability index , a score of greater than 7 on the prolo scale , or a greater than 40% gain in the beaujon score or if the final outcome was rated as excellent or good . an outcome rating of excellent , good , significantly better , satisfied , or success was considered a satisfactory outcome , whereas ratings of fair , poor , same , worse , slightly satisfied , slightly dissatisfied , or unsuccessful were classified as unsatisfactory clinical outcomes . for each study , the abstracted data were entered into review manager software , version 4.2 , for statistical analysis . pooled relative risks ( rrs ) of dichotomous variables ( complication , nonunion , or poor outcome ) and weighted mean differences of continuous variables ( final disc space height and percent of spondylolisthesis slippage ) were calculated with a random - effects model and used to compare pf and pif . statistical heterogeneity of pooled studies was tested and evaluated with the higgins i2 test of heterogeneity at a significance level of p < .1 . we identified relevant articles with the following inclusion criteria : ( 1 ) the target population consisted of adult patients undergoing surgical treatment of lumbar spine degenerative conditions ( excluding tumor trauma and infection ) with a minimum follow - up of 2 years ; ( 2 ) the intervention was posterolateral with or without instrumentation compared with pif ( either plif or transforaminal lumbar interbody fusion with or without instrumentation ) ; and ( 3 ) the outcome measure was patient - centered disease - specific functional outcome . a computerized search of the electronic databases embase ( 19802006 ) and ovid medline and pubmed medline ( 1966february 2006 ) was performed . a hand search of the european spine journal , spine , and the journal of spinal disorders & techniques , as well as bibliographies of identified studies and relevant narrative reviews , we assessed each published study for the quality of the study design using the newcastle - ottawa 8-point scale for assessment of nonrandomized studies . this scale grades the reporting of the studies based on the representativeness of samples , baseline factors , assessment of outcome , statistical analysis or study design , and length of follow - up . specifically , the sizes and demographic data of the intervention and control groups , type of fusion , underlying diagnoses , length of follow - up , loss to follow - up , fusion rate , radiologic parameters , and clinical outcomes at final follow - up were recorded . because of the variety of clinical outcome tools used in the studies , surgical results were predefined as satisfactory if the patient had a score of less than 40 on the oswestry disability index , a score of greater than 7 on the prolo scale , or a greater than 40% gain in the beaujon score or if the final outcome was rated as excellent or good . an outcome rating of excellent , good , significantly better , satisfied , or success was considered a satisfactory outcome , whereas ratings of fair , poor , same , worse , slightly satisfied , slightly dissatisfied , or unsuccessful were classified as unsatisfactory clinical outcomes . for each study , the abstracted data were entered into review manager software , version 4.2 , for statistical analysis . pooled relative risks ( rrs ) of dichotomous variables ( complication , nonunion , or poor outcome ) and weighted mean differences of continuous variables ( final disc space height and percent of spondylolisthesis slippage ) were calculated with a random - effects model and used to compare pf and pif . statistical heterogeneity of pooled studies was tested and evaluated with the higgins i2 test of heterogeneity at a significance level of p < .1 . the literature search identified 2798 potentially relevant citations , 1982 from medline and 816 from embase . degenerative disc disease , recurrent disc herniation , spondylolisthesis , and spinal stenosis were the indications for surgery in the fifth . these studies evaluated 307 patients ( 148 patients in the intervention group [ pif ] and 159 patients in the control group [ pf ] ) . characteristics of included studies abbreviations : ddd , degenerative disc disease ; f , female ; fu , follow - up ; m , male ; mspq , modified somatic perception questionnaire ; vas , visual analog scale . only 1 study stated clearly that the cases represented all the patients who underwent the intervention during the study period after the application of strict inclusion and exclusion criteria . the only prospective study in this review failed to give details on the representativeness of the sample or baseline factors , did not use a validated outcome assessment scale , and did not adequately describe the surgical details or the study design and statistical analysis . validated outcome assessment scales were used in only 1 study , and the mean follow - up period was 2 to 3 years in all but 1 study , which had a 6-year follow - up . by use of the newcastle - ottawa quality assessment scale , the patient - specific functional outcome evaluation tools included the following : oswestry disability index , prolo economic and functional scale , beaujon score , modified somatic perception questionnaire , zung depression scale , and kirkaldy - willis criteria . two studies defined solid fusion when there was formation of crossing bony trabeculae and motion was less than 4 on flexion - extension on radiographs . madan and boeree used the previously mentioned criteria to define union in addition to the criteria of lenke et al . defining bony union , and la rosa et al . added the absence of halo around the implant on radiographs to define solid union . bony fusion was graded according to the classification of brantigan and steffee in the study by lidar et al . the radiologic criteria and classification of fusion data were not reported in 1 study . pooled results showed that nonunion was observed in 3 patients ( 2% ) in the intervention group ( pif ) and 21 patients ( 13% ) in the control group ( pf ) . this was statistically significant ( p = .002 ; rr , 0.21 ; 95% confidence interval [ ci ] , 0.080.56 ) and is shown in fig . 1 . comparison of fusion rate between interbody fusion ( intervention ) and pf ( control ) groups . the intervention group had significantly higher disc height ( weighted mean difference , 3.2 mm ; 95% ci , 1.94.4 mm ) and residual percent slippage ( weighted mean difference , 6.3% ; 95% ci , 3.9%8.7% ) at final follow - up . the various functional outcome assessment instruments used in the included studies are summarized in table 1 . only 1 study used multiple , validated outcome assessment scales.9 this study was the only study in our review that showed a significantly better functional outcome in the control group ( pf ) when compared with the intervention group ( pif ) . the other 4 studies favored the intervention group , although none had sufficient numbers to show a statistically significant difference . by use of the prespecified definitions of satisfactory and unsatisfactory results , 120 patients ( 81% ) had a satisfactory outcome ( good or excellent result ) in the intervention group ( pif ) compared with 122 patients ( 77% ) in the control group ( pf ) , with no difference between the 2 groups ( p = .32 ; rr , 1.6 ; 95% ci , 0.951.18 ) . reported 8 cases in the control group ( pf ) with persistent postoperative low - back pain that required hardware removal . there was no mention of the method used to diagnose the cause of this pain and whether it was improved after the hardware removal . there were also 2 complications in the intervention group ( pif ) : in 1 case there was mechanical failure because of a very short fusion , and in the other the cage could not be inserted because of a very narrow canal . because the last 2 complications could have been avoided by careful preoperative planning and incomplete information is available on the 8 cases of persisting back pain , these 10 complications were eliminated from the final pooled analysis . 3 , showed no statistical difference ( p= .94 ; rr , 0.96 ; 95% ci , 0.412.28 ) between the 2 groups , with a total of 9 complications ( 6% ) in the intervention group ( pif ) and 10 ( 6.2% ) in the control group ( pf ) . the literature search identified 2798 potentially relevant citations , 1982 from medline and 816 from embase . degenerative disc disease , recurrent disc herniation , spondylolisthesis , and spinal stenosis were the indications for surgery in the fifth . these studies evaluated 307 patients ( 148 patients in the intervention group [ pif ] and 159 patients in the control group [ pf ] ) . characteristics of included studies abbreviations : ddd , degenerative disc disease ; f , female ; fu , follow - up ; m , male ; mspq , modified somatic perception questionnaire ; vas , visual analog scale . only 1 study stated clearly that the cases represented all the patients who underwent the intervention during the study period after the application of strict inclusion and exclusion criteria . the only prospective study in this review failed to give details on the representativeness of the sample or baseline factors , did not use a validated outcome assessment scale , and did not adequately describe the surgical details or the study design and statistical analysis . validated outcome assessment scales were used in only 1 study , and the mean follow - up period was 2 to 3 years in all but 1 study , which had a 6-year follow - up . by use of the newcastle - ottawa quality assessment scale , the patient - specific functional outcome evaluation tools included the following : oswestry disability index , prolo economic and functional scale , beaujon score , modified somatic perception questionnaire , zung depression scale , and kirkaldy - willis criteria . two studies defined solid fusion when there was formation of crossing bony trabeculae and motion was less than 4 on flexion - extension on radiographs . madan and boeree used the previously mentioned criteria to define union in addition to the criteria of lenke et al . defining bony union , and la rosa et al . added the absence of halo around the implant on radiographs to define solid union . bony fusion was graded according to the classification of brantigan and steffee in the study by lidar et al . the radiologic criteria and classification of fusion data were not reported in 1 study . pooled results showed that nonunion was observed in 3 patients ( 2% ) in the intervention group ( pif ) and 21 patients ( 13% ) in the control group ( pf ) . this was statistically significant ( p = .002 ; rr , 0.21 ; 95% confidence interval [ ci ] , 0.080.56 ) and is shown in fig . 1 . comparison of fusion rate between interbody fusion ( intervention ) and pf ( control ) groups . the intervention group had significantly higher disc height ( weighted mean difference , 3.2 mm ; 95% ci , 1.94.4 mm ) and residual percent slippage ( weighted mean difference , 6.3% ; 95% ci , 3.9%8.7% ) at final follow - up . the various functional outcome assessment instruments used in the included studies are summarized in table 1 . only 1 study used multiple , validated outcome assessment scales.9 this study was the only study in our review that showed a significantly better functional outcome in the control group ( pf ) when compared with the intervention group ( pif ) . the other 4 studies favored the intervention group , although none had sufficient numbers to show a statistically significant difference . by use of the prespecified definitions of satisfactory and unsatisfactory results , 120 patients ( 81% ) had a satisfactory outcome ( good or excellent result ) in the intervention group ( pif ) compared with 122 patients ( 77% ) in the control group ( pf ) , with no difference between the 2 groups ( p = .32 ; rr , 1.6 ; 95% ci , 0.951.18 ) . all the reported complications excluding nonunion were evaluated and are shown in table 1 . one study reported no complications . reported 8 cases in the control group ( pf ) with persistent postoperative low - back pain that required hardware removal . there was no mention of the method used to diagnose the cause of this pain and whether it was improved after the hardware removal . there were also 2 complications in the intervention group ( pif ) : in 1 case there was mechanical failure because of a very short fusion , and in the other the cage could not be inserted because of a very narrow canal . because the last 2 complications could have been avoided by careful preoperative planning and incomplete information is available on the 8 cases of persisting back pain , these 10 complications were eliminated from the final pooled analysis . 3 , showed no statistical difference ( p= .94 ; rr , 0.96 ; 95% ci , 0.412.28 ) between the 2 groups , with a total of 9 complications ( 6% ) in the intervention group ( pif ) and 10 ( 6.2% ) in the control group ( pf ) . specifically , it included explicit inclusion and exclusion criteria , assessed the methodologic quality of the studies , showed the reproducibility of selection and assessment criteria , and performed a quantitative analysis . a potential selection bias was eliminated by rigorously searching many databases and bibliographies and by conducting all aspects of the selection process in duplicate . the major limitation of this review is related to the poor quality of the included studies , which obviously affected the quality of the cumulative data . none of the included studies met the criteria for a high - quality study on the newcastle - ottawa scale . bhandari et al . stated that the most definitive conclusions can be made only when high - quality randomized trials are pooled . by design , the current analysis focused on comparing pf with pif in the surgical treatment of degenerative lumbar spine disorders with regard to fusion , radiologic correction of deformity , functional outcome , and complications . the radiologic deformity correction ( eg , disc height and listhesis reduction ) was reported differently in the study of lidar et al . and was not pooled . in 1 this review showed an improvement in disc height and slip percent in the pif group , with a tendency toward loss of correction over time . it has been shown that poor sagittal balance postoperatively leads to adjacent segment degeneration and poor results . the retrospective review of madan and boeree , in which multiple functional outcome assessment scales were used and detailed postoperative evaluation was performed , showed better functional outcome in the group treated with pf over interbody fusion . they attributed this to selection bias ( age , sex , extent of listhesis , and disc degeneration ) and the retraction and scarring of the nerve roots and thecal sac . the quality of the studies included in this review made it difficult to reach any conclusion regarding the previously mentioned factors . lowe et al . reported a 90% fusion rate and 85% rate of satisfactory clinical outcomes using the tlif technique . although fusion is often considered a satisfactory surgical outcome , we could not show that the functional outcome was superior in the interbody fusion group compared with the pf group despite the fact that the former group had a higher fusion rate . this in part could be because of the quality and design of the included studies , and a larger sample is needed to detect such a small difference . another potential reason for this is the short follow - up period in most of the included studies . it is possible that with longer follow - up , these results might be different . although the assessment of fusion is important , it is still crucial to recognize other factors , such as confounding comorbidities , preoperative diagnosis , and patient selection , when one is evaluating the functional outcome after degenerative lumbar spine surgery all the interbody fusions in the intervention group were performed by the plif technique , and this was not associated with an increased complication rate compared with the control group . in conclusion , this review suggests that pif improves the fusion rate , correction of disc height , and reduction of spondylolisthesis slip percent . however , there were no significant differences in functional outcome , final segmental or lordotic angles , and complication rates over pf . these conclusions are limited by the poor quality of the included studies ; this indicates the need for sufficiently sized and methodologically sound studies to assess clinically relevant endpoints . until these studies are performed , the current evidence regarding the value of adding posterior lumbar body fusion in the surgical management of degenerative lumbar spine diseases should be interpreted with caution .
backgroundposterolateral fusion ( pf ) is a common method by which to achieve fusion in lumbar spine surgery . 
 it has been reported that posterior interbody fusion ( pif ) yields a higher fusion rate and a better functional and clinical outcome . 
 our objective was to determine whether pif improves the clinical and radiologic outcomes in adults surgically treated for degenerative lumbar spine conditions compared with pf.methodswe performed a systematic search of electronic databases , bibliographies , and relevant journals and meta-analyses.resultsof 2798 citations identified , 5 studies met our inclusion criteria ( none of which was a randomized controlled trial ) , with a total of 148 patients in the pif group ( intervention ) and 159 in the pf group ( control ) . 
 pooled meta - analyses showed that nonunion rates were lower in the intervention group ( relative risk , 0.22 ; 95% confidence interval [ ci ] , 0.080.62 ) . 
 the intervention group had a significantly higher disc height ( weighted mean difference , 3.2 mm ; 95% ci , 1.94.4 mm ) and lower residual percent slippage ( weighted mean difference , 6.3% ; 95% ci , 3.9%8.7% ) at final follow - up . 
 there were no significant differences in segmental or total lumbar lordosis . 
 because of heterogeneity of results , no conclusions could be made with regard to functional benefits.conclusionsthis review suggests that pif achieves a higher fusion rate and better correction of certain radiographic aspects of deformity over pf . 
 it also showed a slight but not significant trend toward a better functional outcome in the pif group . 
 the lack of randomized controlled trials and the methodologic limitations of the available studies call for the planning and conduct of a sufficiently sized , methodologically sound study with clinically relevant outcome measures . 
 until this has been done , the current evidence regarding the beneficial effects of pif should be interpreted with caution .