transforaminal lumbar interbody fusion ( tlif ) was described by harms and jeszenszky in 1998 as an alternative to posterior lumbar interbody fusion ( plif ) and combined anterior / posterior fusion techniques.1 at the time , tlif offered an approach to the disk space that required less traction on the dura and traversing nerve root than plif and avoided the morbidity seen with the anterior approach . since its introduction an early case for interbody fusion was made by yashiro et al , who showed that plif improved the radiographic fusion rate and segmental alignment compared with posterolateral fusion.2 similarly , the tlif technique has been utilized with the theory that the interbody device , with additional bone graft , would improve the overall fusion rate compared with posterolateral fusion . the restoration of disk height ( dh ) and lumbar lordosis are additional goals of the tlif procedure . attention to sagittal balance has been stressed in recent literature3 ; appropriate lordosis has been shown to affect outcomes , including a possible role in adjacent - level degeneration.4 studies have focused on radiographic outcomes of the tlif procedure,5 
 6 showing improvement in dh and segmental lordosis ( sl ) with tlif . the original harms technique suggested placing the bone graft behind the anterior longitudinal ligament ( all ) and then using two round titanium mesh cages as the interbody device . these cages were to be placed in the middle or posterior third of the body . additional biomechanical studies have since shown that anterior placement of the interbody device improves load sharing , reduces subsidence , and allows for improved sagittal contour.7 
 8 this concept has also been suggested in retrospective radiographic reviews.5 
 6 variation in the graft position has been coupled with multiple choices for interbody material , shape , and adjunctive grafting material . these tlif iterations have been discussed throughout the literature,9 
 10 
 11 
 12 but reports consist mostly of patient series without control or comparison groups ; the authors are unaware of any direct , head - to - head comparison of tlif technique with respect to radiographic outcomes and lordosis . the present study was designed to directly compare radiographic outcomes of two different tlif techniques . 1 ) as anteriorly as possible ( preferably on the apophyseal ring ) in the disk space . tlif , or c - tlif.12 the second technique involves the use of a straight spacer ( fig . 1 ) placed obliquely through the disk space . our goal was to determine if the c - tlif technique improved radiographic dh and segmental alignment when compared with the straight cage method of tlif . after institutional review board approval , a retrospective review was conducted of all tlif procedures performed at our institution from january 2006 to november 2011 . no diagnoses were excluded from the study , as we were concerned primarily with radiographic outcomes . inclusion criteria consisted of a standing lumbar radiograph prior to surgery , intraoperative radiographs or immediate postoperative imaging , and at least 1-year follow - up with standing lumbar films . one hundred one patients ( 127 tlif levels ) had adequate follow - up for inclusion in the study . forty patients ( 55 spinal levels ; 17 males and 23 females ) received the kidney - shaped spacer using the c - tlif technique . the remaining 61 patients ( 72 spinal levels ; 16 males and 45 females ) received a straight interbody cage . in the multilevel cases , all c - tlifs were performed by one attending surgeon , and the straight tlifs were performed by two other attending surgeons at our institution . the operative diagnoses included a variety of processes including degenerative and isthmic spondylolisthesis , degenerative and idiopathic scoliosis , and iatrogenic spinal instability after previous surgeries . across diagnoses , the indications for tlif included desire for 360-degree stabilization due to poor bone quality , unstable segment such as mobile degenerative spondylolisthesis , need for additional lordosis , or to preserve foraminal decompression in cases of severe dh loss or asymmetric disk collapse ( such as in degenerative scoliosis ) . the indications for laminectomy in addition to tlif included central stenosis , often from degenerative spondylolisthesis . all patients were positioned prone on a jackson frame and had a posterior midline approach to the spine at the appropriate lumbar level . each patient received a laminectomy when indicated ( see above ) with the unilateral facetectomy required to perform the tlif . an annulotomy was performed under distraction ( if needed ) , and the tlif was performed with the aid of fluoroscopy . the disk space was prepared using a combination of curettes and shavers to remove the remaining disk and cartilaginous end plates . once the disk space was prepared , the interbody spacer was placed according to the attending surgeon 's preference . interbody spacers of both groups were made of either polyetheretherketone ( peek ; with additional autograft bone placed in the center of the graft ) or allograft bone . neither type of graft had any intrinsic lordosis . the procedure for the c - tlif group began by placing autogenous local bone in the disk space behind the all . the spacer was worked around the periphery of the disk space , moving toward its anterior aspect . final impaction was performed until the spacer abutted the cancellous bone graft and all , with its long axis oriented in a medial - lateral direction ( fig . the graft used was a straight , rectangular cage with a bullet nose that aids in entering the disk space . the graft was placed in an oblique fashion toward the midline , as anteriorly as possible within the disk space . both groups received pedicle screw fixation for stabilization of the fusion construct and posterolateral bone grafting ( fig . compression along the pedicle screw / rod construct was performed in all cases to improve the sagittal alignment for both groups . ( a ) anteroposterior and lateral radiograph demonstrating anterior placement of the kidney - shaped interbody cage . the postoperative radiographs were evaluated at first follow - up ( t1 ) , 1-year follow - up ( t2 ) , and final follow - up ( t3 ) . each patient also had imaging on the day of surgery ( t0 ) , which was done either with intraoperative fluoroscopy or via a portable radiograph in the recovery room . the radiographic parameters of interest were dh , sl , and segmental coronal alignment ( sc ) . dh was measured as the distance ( in millimeters ) between the supra - adjacent and subjacent end plates at the midpoint of the involved vertebral bodies . once the measurements were obtained for all radiographs , the preoperative values were subtracted from their subsequent counterparts . this calculation yielded delta values ( dh , sc , sl ) for each time point . the mean delta values were calculated for each point and compared between the groups using a two - tailed t test . after institutional review board approval , a retrospective review was conducted of all tlif procedures performed at our institution from january 2006 to november 2011 . no diagnoses were excluded from the study , as we were concerned primarily with radiographic outcomes . inclusion criteria consisted of a standing lumbar radiograph prior to surgery , intraoperative radiographs or immediate postoperative imaging , and at least 1-year follow - up with standing lumbar films . one hundred one patients ( 127 tlif levels ) had adequate follow - up for inclusion in the study . forty patients ( 55 spinal levels ; 17 males and 23 females ) received the kidney - shaped spacer using the c - tlif technique . the remaining 61 patients ( 72 spinal levels ; 16 males and 45 females ) received a straight interbody cage . in the multilevel cases , all c - tlifs were performed by one attending surgeon , and the straight tlifs were performed by two other attending surgeons at our institution . the operative diagnoses included a variety of processes including degenerative and isthmic spondylolisthesis , degenerative and idiopathic scoliosis , and iatrogenic spinal instability after previous surgeries . across diagnoses , the indications for tlif included desire for 360-degree stabilization due to poor bone quality , unstable segment such as mobile degenerative spondylolisthesis , need for additional lordosis , or to preserve foraminal decompression in cases of severe dh loss or asymmetric disk collapse ( such as in degenerative scoliosis ) . the indications for laminectomy in addition to tlif included central stenosis , often from degenerative spondylolisthesis . all patients were positioned prone on a jackson frame and had a posterior midline approach to the spine at the appropriate lumbar level . each patient received a laminectomy when indicated ( see above ) with the unilateral facetectomy required to perform the tlif . an annulotomy was performed under distraction ( if needed ) , and the tlif was performed with the aid of fluoroscopy . the disk space was prepared using a combination of curettes and shavers to remove the remaining disk and cartilaginous end plates . once the disk space was prepared , the interbody spacer was placed according to the attending surgeon 's preference . interbody spacers of both groups were made of either polyetheretherketone ( peek ; with additional autograft bone placed in the center of the graft ) or allograft bone . neither type of graft had any intrinsic lordosis . the procedure for the c - tlif group began by placing autogenous local bone in the disk space behind the all . the spacer was worked around the periphery of the disk space , moving toward its anterior aspect . final impaction was performed until the spacer abutted the cancellous bone graft and all , with its long axis oriented in a medial - lateral direction ( fig . the graft used was a straight , rectangular cage with a bullet nose that aids in entering the disk space . the graft was placed in an oblique fashion toward the midline , as anteriorly as possible within the disk space . both groups received pedicle screw fixation for stabilization of the fusion construct and posterolateral bone grafting ( fig . compression along the pedicle screw / rod construct was performed in all cases to improve the sagittal alignment for both groups . ( a ) anteroposterior and lateral radiograph demonstrating anterior placement of the kidney - shaped interbody cage . the postoperative radiographs were evaluated at first follow - up ( t1 ) , 1-year follow - up ( t2 ) , and final follow - up ( t3 ) . each patient also had imaging on the day of surgery ( t0 ) , which was done either with intraoperative fluoroscopy or via a portable radiograph in the recovery room . the radiographic parameters of interest were dh , sl , and segmental coronal alignment ( sc ) . dh was measured as the distance ( in millimeters ) between the supra - adjacent and subjacent end plates at the midpoint of the involved vertebral bodies . the cobb method was used to measure the segmental coronal and sagittal alignment . once the measurements were obtained for all radiographs , the preoperative values were subtracted from their subsequent counterparts . this calculation yielded delta values ( dh , sc , sl ) for each time point . the mean delta values were calculated for each point and compared between the groups using a two - tailed t test . one hundred one patients ( 127 tlif levels ) had adequate follow - up for inclusion in the study . forty patients ( 55 spinal levels ; 17 males and 23 females ) received the kidney - shaped spacer using the c - tlif technique . the remaining 61 patients ( 72 spinal levels ; 16 males and 45 females ) received a straight interbody cage . the mean final follow - up for patients in the c - tlif group was 26 months , compared with 22 months for the tlif group ( p  =  0.2734 ) . the mean preoperative sl value was 3.1 degrees in the c - tlif group and 5.6 degrees in the tlif group ( p  =  0.0034 ) . the c - tlif sl values were 7.8 degrees ( t0 ) , 6.5 degrees ( t1 ) , 5.5 degrees ( t2 ) , and 4.9 degrees ( t3 ) . the mean sl values were 4.0 degrees ( t0 ) , 1.8 degrees ( t1 ) , 0.4 degrees ( t2 ) , and 0.1 degrees ( t3 ; fig . 3 ) . when comparing the two groups , the c - tlif group showed statistically significantly greater improvement of sl at all points ( t1 , t2 , and t3 ; p  <  0.0001 ) . 
 postoperative change in segmental lordosis ( in degrees ) between  cantilever  transforaminal lumbar interbody fusion ( c - tlif ) and transforaminal lumbar interbody fusion ( tlif ) after surgery . the mean preoperative dh was 6.4  mm in the c - tlif group and 8.4  mm in the tlif group ( p  =  0.0003 ) . the c - tlif mean dh values were 5.6  mm ( t1 ) , 4.5  mm ( t2 ) , and 3.6  mm ( t3 ) . the tlif group mean dh values were 2.2  mm ( t1 ) , 0.8  mm ( t2 ) , and 0.2  mm ( t3 ; fig . 4 ) . when comparing the two groups , the c - tlif had greater restoration of dh at all points ( t1 , t2 , and t3 ) , which was statistically significant ( p  <  0.0001 ) . transforaminal lumbar interbody fusion ( c - tlif ) and transforaminal lumbar interbody fusion ( tlif ) after surgery . the mean preoperative sc was 3.1 degrees in the c - tlif group and 2.1 degrees in the tlif group ( p  =  0.0226 ) . the c - tlif group mean sc values were 2.0 degrees ( t0 ) , 1.9 degrees ( t1 ) , 1.8 degrees ( t2 ) , and 1.6 degrees ( t3 ) . the tlif group mean sc values were 1.2 degrees ( t0 ) , 1.1 degrees ( t1 ) , 1.0 degrees ( t2 ) , and 1.2 degrees ( t3 ) . several surgical options are available when deciding to perform a plif , tlif , anterior lumbar interbody fusion , or direct lateral approach for interbody fusion . material choices include titanium , peek , machined allograft bone , and structural autograft , among others . studies have assessed the radiographic and fusion outcomes related to the implant choice but there is still sufficient evidence to support one type of interbody device over the other options . the technique of performing the tlif procedure has been evaluated in the literature as well . multiple studies have shown that anterior placement of the spacer is more ideal to minimize the chance of graft subsidence.5 
 6 
 7 
 8 fukuta et al also showed that anterior placement instead of a central location in the vertebral body decreased the chance of nonunion and adjacent - level degeneration.7 kepler and colleagues noted improved outcomes in back and leg pain with improved lordosis and dh after tlif.13 the c - tlif described by anand and colleagues employs a technique that takes advantage of this concept . a curved graft allows for a more anatomic position on the anterior apophyseal ring and makes passing the graft around the periphery to the anterior disk space easier . anand et al reviewed 100 consecutive patients and assessed both radiographic and clinical outcomes.12 however , the authors did not compare the c - tlif to a more conventional method of tlif . this study was designed to compare the c - tlif to the straight cage method because it was felt anecdotally that there was more lordosis and dh achieved using c - tlif . all diagnoses , including degenerative scoliosis , were included in the study and we therefore evaluated the coronal alignment of the tlifs performed as well . our study showed that the c - tlif method was significantly better at improving sagittal plane deformity and indirect decompression of the foramen due to increasing dh . the c - tlif method showed an improvement of lordosis from 3 to 8 degrees at final follow - up . this change was consistent with findings in the study by anand et al ( 2 to 9 degrees).12 in comparison , the sl was essentially unchanged from preoperative value ( 0.1 degree ) at final follow - up of the tlif group . both groups demonstrated an increase in disk space height , but again , the c - tlif group was superior , as the tlif group was nearly at baseline ( improved 0.2 mm ) at final follow - up . of note , improvements in sagittal alignment and disk space height demonstrated some regression over time . the greatest drop - off in both groups occurred between t0 and t1 , which may be due to how imaging was obtained for patients at these times . images for t0 included either intraoperative lateral fluoroscopic images or portable lateral radiographs obtained in the recovery room . in the former , the patient was ideally positioned prone on the operating table ( which is designed to maximize lordosis ) , and in the latter , the patient was lying supine in a bed . in either case , the t0 images were obtained without any weight bearing through the spine . in contrast , images at t1 and beyond were upright lateral radiographs , which may explain the substantial decrease in sl and dh noted between the initial points . settling of the interbody grafts over time may explain the remainder of the lost improvement . one possible explanation for the greater regression toward baseline seen in the tlif group is that the placement of a c - tlif graft anteriorly on the ring apophysis provides stronger support and resistance to subsidence than a graft placed obliquely across the center of the disk space . both the groups showed similar correction of coronal alignment , with those improvements maintained over time . of note , the tlif group demonstrated a change in sc that trended down , but had an increase from 1.0 degrees to 1.2 degrees at the t2 and t3 points , respectively . the cobb method was performed using digital radiology to provide the measurements for sl and sc . there is some variability in the cobb method , which could have introduced measurement errors . in addition , investigators making the measurements were not blinded to the type of interbody device , which could potentially introduce bias . we strove to minimize these effects by utilizing a standardized technique of measurement , repeating the measurements , and having all images measured by the same individuals , who were not the operating surgeons . the straight cage group had a larger preoperative sl and dh , which could potentially give the c - tlif group an advantage in having more opportunity for improvement . however , it can also be more difficult to prepare a collapsed disk space while performing interbody fusions , which could also lead to less correction . because the two techniques under comparison were done by different surgeons , one concern could be raised that the surgeon for the c - tlif group was simply more committed to placing a larger graft in the interspace . however , the subsidence from points t1 to t3 are similar in both groups ; furthermore , it is postulated that lordosis achieved , rather than simply disk space height , is the main value of the technique . finally , this study was purely radiographic ; clinical outcomes were not considered , nor did we assess fusion or complication rates of either procedure . in conclusion , we found that the technique for tlif does have an effect on postoperative sagittal balance and dh . placement of a kidney - shaped spacer anteriorly appears to improve sl and increase dh when compared with a straight cage placed obliquely . further study is needed to determine if the radiographic outcomes correspond to improved clinical outcomes .
study design  retrospective review . 
 objective  the purpose of this study was to determine the radiographic impact of a transforaminal lumbar interbody fusion ( tlif ) versus a cantilever tlif technique on segmental lordosis , segmental coronal alignment , and disk height . 
 methods  a retrospective review was done of all patients undergoing tlif procedures from 2006 to 2011 by three spine surgeons . 
 traditional tlif versus cantilever tlif results were compared , and radiographic outcomes were assessed . 
 results  one hundred one patients were included in the study . 
 patients undergoing the cantilever tlif procedure had a significantly greater change in segmental lordosis and disk height compared with those who underwent the traditional procedure ( p  >  0.0001 ) . 
 conclusions  the cantilever tlif technique can lead to greater change in segmental lordosis based upon radiographic outcomes .