Transsacral interbody fixation versus transforaminal

CLINICAL ARTICLEJ Neurosurg Spine 32:824–831, 2020

Surgical correction of adult spinal deformity (ASD) often requires a long fusion from the thoracic spine across the lumbosacral junction in order to maintain

stability and maximize patient outcomes. Pseudarthrosis is one of the most common complications encountered after long fusion to the sacrum, and typically occurs at lumbosacral junctions. Rates of pseudarthrosis at the lum-

bosacral junction have been reported to range from 10% to 16%.10,12, 18,19 Patients undergoing long fusions to the sacrum for deformity who develop pseudarthrosis may experience increased levels of pain, loss of deformity correction, pro-gressive deformity, or neurological deficit. Additionally, patient-perceived surgical outcomes measures such as the Oswestry Disability Index (ODI), Short Form-36 (SF-36),

ABBREVIATIONS ALIF = anterior lumbar interbody fusion; AP = anteroposterior; ASD = adult spinal deformity; BMI = body mass index; ODI = Oswestry Disability Index; PLIF = posterior lumbar interbody fusion; SRS-22 = Scoliosis Research Society Outcome Instrument 22; SVA = sagittal vertical alignment; TLIF = transforaminal lumbar interbody fusion; TSF = transsacral fixation. SUBMITTED April 2, 2019. ACCEPTED December 3, 2019.INCLUDE WHEN CITING Published online February 14, 2020; DOI: 10.3171/2019.12.SPINE19397.

Transsacral interbody fixation versus transforaminal lumbar interbody fusion at the lumbosacral junction for long fusions in primary adult scoliosisHong-Lei Yi, MD,1 Michael Faloon, MD,2 Stuart Changoor, MD,2 Thomas Ross, RN,3 and Oheneba Boachie-Adjei, MD3

1Department of Orthopaedic Surgery, General Hospital of Southern Theatre Command of People’s Liberation Army, Guangzhou, China; 2Department of Orthopaedic Surgery, St. Joseph’s University Medical Center, Paterson, New Jersey; and 3Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, New York

OBJECTIVE Achieving fusion at the lumbosacral junction poses many technical challenges. No data exist in the litera-ture comparing radiographic or clinical outcomes between the different surgical techniques of transsacral fixation (TSF) with rods and transforaminal lumbar interbody fusion (TLIF) in conjunction with iliac fixation. The purpose of this study was to compare the clinical outcomes and radiographic fusions of TSF to TLIF in patients with adult spinal deformity undergoing long fusions across the lumbosacral junction.METHODS Patients with primary adult spinal deformity who underwent long fusions from the thoracic spine across the lumbosacral junction with different approaches of interbody fusion at the L5–S1 level were reviewed. Patients were subdivided by approach (TSF vs TLIF). Fusion status at L5–S1 was evaluated by multiple radiographs and/or CT scans. Scoliotic curve changes were also evaluated preoperatively and at final follow-up. Clinical outcomes were assessed by Scoliosis Research Society Outcome Instrument 22 and Oswestry Disability Index scores.RESULTS A total of 36 patients were included in the analysis. There were 18 patients in the TSF group and 18 patients in the TLIF group. A mean of 14.00 levels were fused in the TSF group and 10.94 in the TLIF group (p = 0.01). Both groups demonstrated significant postoperative radiographic improvement in coronal parameters. The fusion rates for TSF and TLIF groups were 100% and 88.9%, respectively (p < 0.05). Eight patients in the TSF group had pelvic fixation with unilateral iliac screws, compared to 15 patients in the TLIF group (p = 0.015). No statistical differences in patients’ reported outcomes were seen between groups.CONCLUSIONS Despite similar clinical and radiographic outcomes between both groups, TSF required fewer iliac screws to augment stability of the lumbosacral junction while achieving a higher rate of fusion. This study suggests that TSF may decrease potential instrument-related complications requiring revision while decreasing operating room time and implant-related costs.https://thejns.org/doi/abs/10.3171/2019.12.SPINE19397KEYWORDS transsacral fixation; minimally invasive surgery; pelvic instrumentation; adult spinal deformity; lumbar; sacral

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and Scoliosis Research Society Outcome Instrument 22 (SRS-22) scores have been shown to be significantly lower in adult patients with pseudarthrosis than in those achiev-ing solid fusion.18,19

For this reason, circumferential fusion with a structural interbody cage/bone graft has been advocated to promote arthrodesis. Multiple approaches and techniques to achiev-ing lumbosacral interbody fusion have been described in-cluding anterior lumbar interbody fusion (ALIF), poste-rior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF). Each approach has well-described advantages and disadvantages. ALIF allows for the release of the anterior longitudinal ligament and the placement of a lordotic cage with a large footprint, which can help restore sagittal alignment, indirectly decompress neuroforamina, and enhance fusion rates.6 However, the approach increases surgical time and adds approach-re-lated morbidity including risk of injury to major vascular structures and the sympathetic plexus, which can cause retrograde ejaculation in males. The TLIF or PLIF from the posterior approach has also been a reliable technique for treating ASD and avoiding the potential complications inherent with an anterior approach. However, the posterior approach places both exiting and traversing nerve roots as well as the thecal sac itself at greater risk because these structures must necessarily be exposed and retracted dur-ing graft insertion.8,9

Transsacral interbody fusion and instrumentation, also called transsacral fixation (TSF), is a novel minimally invasive technique that has been introduced to take ad-vantage of the naturally occurring tissue plane between the sacrum and the peritoneal contents.7 Through a small paracoccygeal incision, discectomy can be performed and an axially directed cylindrical implant may be inserted percutaneously through this so-called presacral space and across the L5–S1 and L4–5 disc spaces to achieve an in-terbody arthrodesis. The biomechanical profile of TSF has previously been characterized in multiple cadaveric stud-ies, and this device appears to compare favorably to other fusion constructs (TLIF, PLIF, and ALIF).1,11,13,20

However, there is no published clinical study that di-rectly compares radiographic changes, fusion rates, and complications at the L5–S1 level between TSF versus TLIF with posterior long instrumentation for patients with ASD. This study aims to evaluate the clinical, ra-diographic, and patient-perceived outcomes between the 2 techniques when used in patients with ASD undergoing long fusions across the lumbosacral junction.

MethodsPatient Selection

This study was performed under an IRB-approved pro-tocol. Patients with ASD undergoing long fusions across the lumbosacral junction performed by a single surgeon at a major academic institution between June 2008 and October 2011 were included in the analysis. A retrospec-tive comparative cohort study of prospectively collected data in 2 patient populations was performed. Consecutive patients with primary adult deformity undergoing spinal fusion with a long construct from T12 or higher to the sa-

crum and/or ilium were studied. For the purposes of this study, only patients with ASD who did not require 3-col-umn osteotomies or anterior column releases for deformi-ty correction were included in this study. In other words, patients in this study were indicated for posterior-only ap-proaches for ASD in which TLIF is typically used.

Patients were divided into 2 cohorts based on the in-terbody fusion at the L5–S1 segment: 1) TLIF, and 2) TSF. Patients with a primary diagnosis other than adult idiopathic scoliosis, adult kyphoscoliosis, or degenerative scoliosis were excluded. In addition, patients undergoing revision procedures or with any history of previous spine surgery, those without complete preoperative and postop-erative assessment scores, or those with less than 2 years of follow-up were also excluded. Forty patients were ini-tially identified, with 4 patients excluded due to failure to meet the minimum follow-up; 36 patients were included in the analysis. Eighteen cases underwent interbody fu-sions of the L5–S1 segment via a posterior transforaminal approach (i.e., TLIF), and 18 were treated using a TSF ap-proach and implant (Table 1).

Surgical TechniquesFor each of the patients, correction of deformity was

performed prior to discectomy and fixation of the L5–S1 segment. This was done in a similar fashion in both co-horts via patient positioning and release of the posterior elements, including the use of facetectomies. For the TLIF group, interbody approaches were performed on the side of the concavity of the curve by using the standard technique at L5–S1 during the long posterior fusion procedure, just prior to pedicle screw instrumentation. At this level, TLIF was performed specifically with the aim of achieving fu-sion at the lumbosacral junction. The average interbody fusion levels were 3.5 (range 2–6 levels) with PEEK cages (16 patients) or structural allograft (2 patients) and recom-binant human bone morphogenetic protein–2 (rhBMP-2). Fifteen patients had unilateral sacropelvic fixation.

For the TSF group, technical aspects of transsacral discectomy, fusion, and fixation have been described else-where.16 Transsacral instrumentation was performed im-

TABLE 1. Preoperative demographic data in 38 patients with primary adult scoliosis

Variable TSF, n = 18 TLIF, n = 18 p Value

Average age in yrs 57.33 ± 5.01 57.89 ± 6.98 0.81Sex (F/M) 17/1 16/2Diagnosis Idiopathic scoliosis 9 9 De novo scoliosis 9 8 Kyphoscoliosis 0 1Osteoporosis/osteopenia 2/8 0/7 0.49BMI 24.61 ± 3.72 23.44 ± 3.47 0.38No. of fusion vertebrae 14.00 ± 3.16 10.94 ± 3.61 0.01Pelvic fixation 8 15 0.015Follow-up in mos 28.67 ± 4.47 33.44 ± 11.53 0.12

Continuous variables are expressed as the mean ± SD.


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mediately following closure of the posterior fusion and instrumentation wound, under new sterile preparation and draping. In terms of interbody grafting at L5–S1, rhBMP-2 and absorbable collagen sponge were used in the disc space in addition to demineralized bone matrix (Fig. 1). One-level TSF fusions (L5–S1) were done in 12 cases, whereas 2-level TSF fusions (L4–S1) were done in 6 cases. Eight patients had unilateral iliac fixation.

Radiographic and Clinical EvaluationAll patients had pre- and postoperative standing an-

teroposterior (AP) and lateral scoliosis radiographs, which were digitally measured using electronic PACS software. Coronal Cobb angle measurements were used for the main and fractional scoliotic curves on the AP films. Lateral radiographs were used to record T5–12, L5–S1, and L1–sacrum sagittal Cobb measures. Radiographic coronal balance (i.e., coronal vertical alignment) was measured as a C7 plumb line distance in centimeters from the center sacral line. Similarly, radiographic sagittal balance (i.e., sagittal vertical alignment [SVA]) was a C7 plumb line measured in centimeters as the distance from the posterior to superior aspect of the S1 body.21 The standard practice of measurement was used; positive values were to the right of the central line and negative values were to the left.

Clinically significant pseudarthrosis referred to clini-cally relevant persistent pain, or change in pain, at the lumbosacral junction > 1 year postoperatively requiring advanced imaging. Fusion mass was assessed by 2 inde-pendent spine and scoliosis Fellows who did not partici-pate in the surgery. Fusion was assessed both clinically and radiographically, and was defined clinically as the absence of pain at the lumbosacral junction with flexion and extension, and radiographically defined as the pres-

ence of bridging bone across the disc space with no radio-lucency around the TSF/TLIF implant, in addition to the absence of pedicle or iliac screw loosening or fracture. If fusion status was not certain, thin-slice (1–2 mm), high-resolution CT scans were obtained at the 2-year follow-up. Clinical outcomes and visual analog scale pain scores were collected for all patients during regularly scheduled office visits at pretreatment and last follow-up. Clinical outcomes were measured by the SRS-22 as well as ODI scores.

Statistical AnalysisDistribution of variables was calculated as the mean ±

SD of measurements. Statistical analysis of radiographic parameters and clinical scores between pre- and postop-erative records was performed using SPSS software (IBM Corp.). The t-test was used to assess the difference of con-tinuous measures between the 2 groups. Fisher’s exact test was used to test for significance of categorical variables. Significance was set at p < 0.05.

ResultsDemographic Data

Table 1 displays demographic data for the study popu-lation groups. There were no significant differences be-tween groups for age, sex, body mass index (BMI), or di-agnosis. The TSF group consisted of 17 women and 1 man with an average age of 57.33 years, and the TLIF group had 16 women and 2 men with an average age of 57.89 years. The TSF group had 9 patients with adult idiopath-ic scoliosis and 9 with degenerative scoliosis. The TLIF group had 9 patients with adult idiopathic scoliosis, 8 with degenerative scoliosis, and 1 with kyphoscoliosis. There

FIG. 1. AP and lateral preoperative (left) and postoperative (right) radiographs demonstrating a case example of a patient who underwent TSF.



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were 8 patients with osteopenia and 2 with osteoporosis in the TSF group compared to 7 patients with osteopenia and none with osteoporosis in the TLIF group. The mean BMI in TSF patients was 24.61, and it was 23.44 in the TLIF group. The mean follow-up for the TSF group was 28.7 months and for the TLIF group it was 33.4 months without significant difference. An average of 14.00 levels were fused in the TSF group and 10.94 in the TLIF group (p = 0.01). Eight patients in the TSF group and 15 in the TLIF group underwent pelvic fixation with unilateral iliac screws (p = 0.015). No patients were currently smoking at the time of surgery.

Radiographic ParametersTable 2 shows the mean pre- and postoperative radio-

graphic parameters for both groups. There were no sta-tistically significant differences between the 2 groups other than preoperative thoracolumbar/lumbar angle. Both groups demonstrated radiographic improvement in the

coronal Cobb angles that were significant from the preop-erative to postoperative periods (p < 0.001). With regard to sagittal measurements, TSF and TLIF groups experienced similar increases in lordosis regionally at L1–S1 (7.9° for TSF vs 4.7° for TLIF, p > 0.05).

By contrast, with regard to sagittal angulation of the L5–S1 segment, patients who underwent TSF actually in-creased lordosis, whereas patients who underwent TLIF lost lordosis overall. The difference of the change was not statistically significant (change of 1.0° vs −0.3°, p > 0.05). Additionally, SVA improved in the TSF group and dete-riorated in TLIF group (−5 mm vs 10.1 mm, p > 0.05). This also did not achieve statistical significance. Thoracic kyphosis and coronal balance maintained well in both groups.

Nine patients in TSF group and 3 patients in TLIF group underwent CT scanning at 1 more year of follow-up. No apparent pseudarthrosis or nonunion at L5–S1 was identified in the TSF group (Fig. 2). There were 2

TABLE 2. Radiographic data in 38 patients with primary adult scoliosis

Variable TSF, n = 18 TLIF, n = 18 p Value

Thoracic Cobb* Preop 46.89° ± 18.09° 37.57° ± 21.67° 0.15 Postop 30.13° ± 11.82° 21.72° ± 14.56° 0.07 p value (pre-postop) <0.001 <0.001Thoracolumbar/lumbar Cobb* Preop 61.39° ± 17.70° 48.84° ± 15.44° 0.02 Postop 31.16° ± 10.58° 23.42° ± 18.38° 0.09 p value (pre-postop) <0.001 <0.001T5–12 kyphosis Preop 33.75° ± 21.26° 28.1° ± 18.22° 0.33 Postop 30.6° ± 7.88° 30.81° ± 11.51° 0.95 p value (pre-postop) 0.47 0.49L1–S1 lordosis Preop 38.27° ± 13.51° 37.41° ± 12.16° 0.83 Postop 46.16° ± 9.04° 42.12° ± 9.33° 0.12 p value (pre-postop) 0.07 0.18SVA, mm Preop 28.44 ± 41.96 (range −54, 124) 25.28 ± 26.85 (range −16, 86) 0.82 Postop 23.44 ± 37.55 (range −58, 100) 35.39 ± 45.32 (range −23, 150) 0.39 p value (pre-postop) 0.61 0.33CVA, mm Preop −16.61 ± 34.79 (range −98, 41) −12.0 ± 24.14 (range −59, 29) 0.65 Postop −14.5 ± 20.33 (range −53, 26) −12.39 ± 26.54 (range −49, 50) 0.82 p value (pre-postop) 0.81 0.94L5–S1 lordosis Preop 22.04° ± 5.31° 21.40° ± 5.92° 0.73 Postop 23.02° ± 4.66° 21.09° ± 4.70° 0.19 p value (pre-postop) 0.16 0.66

CVA = coronal vertical alignment.Continuous variables are expressed as the mean ± SD. No significant differences were noted between 2 groups in any of the above demo-graphic variables except for preoperative thoracolumbar/lumbar curve (p = 0.02).* Preoperative versus postoperative, p < 0.05.


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patients in TLIF group with radiographically identified pseudarthrosis, with broken rods and with sacral screw loosening at the L5–S1 level (Fig. 3). In the TSF group, 2 adverse events related to the presacral technique were encountered: 1 case of superficial wound infection treated with topical care, and 1 case of implant malposition that required revision surgery. Of note, none of the subjects in this series sustained an intraoperative bowel or other visceral injury as a result of the insertion of instruments or the fixation device through the presacral space. Addi-tionally, another case of superficial infection was seen in the thoracic portion of the incision. Late complications in-cluded sacral fracture (n = 1); instrumentation failure of a broken rod above L5 (n = 1); and last, proximal junctional kyphosis was seen in 2 patients ultimately requiring re-vision surgery. A total of 5 patients required secondary surgery. There was 1 patient who experienced persistent radiculopathy who was managed conservatively.

In the TLIF group, perioperative dural tear was ob-served in 2 patients and superficial wound infection in 1 patient, none of which required secondary surgical treat-ment. There were 5 separate late complications besides the 2 previously mentioned pseudarthroses at the L5–S1 level that required reoperation. There were 2 cases of sacroiliac dysfunction defined as persistent pain at the sacroiliac joint; 1 of these was revised with percutaneous fusion of the sacroiliac joint. Of note, both of these patients had ip-silateral iliac fixation. In addition, 1 of the 2 cases with proximal junctional kyphosis required extension of fu-sion to a more proximal level. One additional patient with

pseudarthrosis at the thoracolumbar level required a revi-sion arthrodesis. There was no difference in reoperation rates between the TSF and TLIF groups (5/18 vs 5/18).

OutcomesPreoperative and most recent follow-up SRS and ODI

outcomes scores were studied (Fig. 4). The SRS-22 total score for the TSF group was 3.11 preoperatively and 3.76 postoperatively, whereas the SRS-22 total score for the TLIF group increased from 2.81 to 3.21 after surgery. The mean ODI score for the TSF group was 34.78 preopera-tively and 20.89 postoperatively, and for the TLIF group it was 29.00 preoperatively and 20.89 postoperatively. The improvement was slightly better in the TSF group for the ODI and SRS score. These results indicate clinical and statistically significant improvements for both groups at longer than 2-year follow-up (p < 0.05). There were no significant differences in regard to changes in SRS or ODI scores between the TSF and TLIF groups from the preop-erative period to last follow-up.

DiscussionPseudarthrosis at the lumbosacral junction is one of

the most common complications following long fusions in adult deformity correction. This complication has been at-tributed to multifactorial contributions including the large lumbosacral loads and cantilever pullout forces across this region and the poor bone quality frequently found within the sacrum. Interbody fusions at the lumbosacral interval are useful in addressing these clinical scenarios because they augment the stability of the anterior column, yield greater bone formation in compression, and bring about better fusion rates. As mentioned, a number of approaches have been developed for lumbosacral interbody fusion including ALIF, PLIF, TLIF, and TSF.6,8,9 However, it is not currently known which approach can achieve the best results because each approach entails its own risk profile. The purpose of this study was to compare the radiograph-ic changes and clinical outcomes for 2 separate cohorts undergoing TSF and TLIF procedures supplemented with posterior instrumentation for ASD.

Our fusion rate was 100% in the TSF group and 88.9% in the TLIF group—without significant difference. These results are consistent with a systematic review regarding 700 patients with axial interbody arthrodesis of the L5–S1 segment.23 Of note, the overall pseudarthrosis rate at L5–

FIG. 3. Coronal (left) and sagittal (right) CT images demonstrating pseudarthrosis at the L5–S1 level in a patient who underwent TLIF.

FIG. 2. Sagittal view of successfully fused TSF at the L5–S1 level (ar-row).



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S1 following axial interbody arthrodesis was 6.9% (95% CI 1.0%–16.2%). Although a possible limitation of our study could be underpowering, our results demonstrate that both techniques can achieve comparable lumbosacral fusion rates in long fusions from the thoracic spine to the sacrum in adult deformity surgery. However, it should be noted that the increased stiffness attributed to the trans-sacral instrumentation can diminish the utilization rate of the pelvic/iliac instrumentation. In each group (TSF and TLIF) the rates of unilateral iliac screw fixation were 8/18 and 15/18, respectively (p = 0.015). This may be explained by the biomechanical study of TSF in a long construct per-formed in human cadaveric spines.

Fleischer and coauthors13 compared the S1 screw strain among 4 different constructs: pedicle screw alone (L2–S1), pedicle screw with an anterior interbody device, ped-icle screw with axial fixation, and pedicle screw with iliac screws. The results showed that S1 screw strain was the greatest in pedicle screw alone, decreased by 38% after anterior interbody augmentation, decreased by 75% af-ter using axial fixation, and decreased by 78% after iliac screw augmentation. This study demonstrated that TSF can provide similar biomechanical properties compared to iliac screw fixation and better stiffness than anterior in-terbody fusion in terms of protecting the S1 screw in long constructs.

When used in lumbar degenerative spondylosis, fusion rates with minimally invasive transsacral fusion have been reported at 85%–96%.5,14, 15, 22, 24–29 None of these studies evaluated transsacral interbody fusion in the setting of a long-segment instrumented construct. Rather, these stud-ies reported outcomes for short-segment fusions in the setting of low-grade spondylolisthesis or degenerative disc disease. It is thus difficult to compare our data to these be-cause the clinical settings in which transsacral fusion was used were quite different.

When applied in long-segment fusion for ASD, a study by Anand et al.4 that included 28 patients reported no complications of pseudarthrosis at an average follow-up of 22 months. With a longer follow-up, another 2 studies by

the same group (and probably a continuation of the same population) observed 2 pseudarthroses in 34 patients with ASD at a mean follow-up of 39 months and 5 pseudar-throses in 46 patients at a mean follow-up of 48 months.2,3 They reported lumbosacral fusion rates of 94% in their 2013 study and 89% in their 2014 study. Although slightly comparable lower rates than the current study, the mean number of levels included in the fusions of their reported cohort was no more than 6 levels; our study includes a mean of 14 levels of segments in the fusions.

Differences between our data and prior studies can also be seen in regard to pelvic fixation. No iliac screws were used in the study by Anand et al. for any of the patients, even those with osteopenia or osteoporosis.3 This finding may account for the lower fusion rate in their study. In oth-er words, TSF can obtain good results with less iliac screw fixation, but this does not mean that iliac screw fixation can or should be eliminated. The decision to use unilateral or bilateral iliac screw fixation supplemented with TSF is a worthy discussion for future study consideration. For the TLIF group, our pseudarthrosis rate compares reasonably well to those reported in the literature for long fusions to the sacrum for adult scoliosis (10%–16%).10,18,19

Radiographic changes of segmental lordosis at the L5–S1 level were also evaluated in this study and demonstrat-ed interesting results. Patients in the TSF group increased lordosis, whereas patients who underwent TLIF lost lor-dosis despite the fact that the difference of change did not achieve statistical significance (change of 1.0° vs −0.3°, p > 0.05). These results are consistent with the outcome of previous studies.9,16 By contrast, Jagannathan et al.17 found that the TLIF technique significantly restored seg-mental lordosis at L5–S1 and that the segmental lordotic angle could be recovered by 20°. One primary difference in technique that was described was the use of bilateral facetectomies by chevron osteotomies and placement of a larger interbody graft as anteriorly as possible to maxi-mize the lordotic potential.

In the current study, correction of the lumbar deformity with instrumentation occurred prior to addressing the L5–

FIG. 4. Comparison of SRS-22 (left) and ODI (right) scores determined preoperatively and at final follow-up for both groups. Both TSF and TLIF groups experienced significant improvements in outcome scores. Figure is available in color online only.


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S1 segment. Also of note, the choice not to use the distract-ing capabilities of the TSF screw or TLIF cage was made to use the device as an instrument of solid fixation rather than distraction at the bottom of a long construct. Given that preoperative SVA and lumbar lordosis were a mean of 28.44 mm and 38.27° for the TSF group compared with 25.28 mm and 37.41° for the TLIF group, large corrections were not required in either group, which is probably re-flected in the postoperative results. Disc space distraction and segmental lordosis through the presacral interbody fusion device may be an extremely valuable tool and cer-tainly warrants further research.

This study has some weaknesses that could affect the applicable generalization of its results—including its retro-spective design, the small sample size of patients, and the limited follow-up. All patients in this series had a mini-mum of 2 years of follow-up with average follow-up of no more than 3 years. Prior literature supports the finding that 70% of nonunions occur within the first 2 years and 94% within 4 years.1–3 Thus, the current study might un-derestimate the true prevalence of nonunion in this patient population. A larger randomized series and longer follow-up are needed to clearly identify the differences in TSF and TLIF treatments for patients with ASD.

A second potential limitation of this study is the fact that the 2 groups showed significant differences in fusion levels (14 in TSF vs 10 in TLIF), which may represent a confounding variable as well as understating the compara-tive rigidity of the TSF. Kim et al. reported several risk factors for pseudarthrosis—including age older than 55 years, thoracolumbar kyphosis, and more than 12 fused segments.18,19 Theoretically speaking, this should have increased the rate of pseudarthrosis in the TSF group. In fact, there was no difference between the 2 groups, which may imply that TSF can provide more anterior column support and better stiffness of the instrumented level.

Last, another potential weakness is that CT scans were not obtained on a regular standardized basis for every pa-tient. CT scanning was seen to be the standard method to identify union. Despite this, most prior literature regarding the high nonunion rate in the adult deformity population at L5–S1 was based on radiographic and clinical parameters because of the unexpectedly high expense and radiation exposure of CT scans.2,3,5,27,28 Our radiographic assessment included coronal, sagittal, flexion, and extension films. CT scans were obtained when fusion status was not certain or in the clinical setting of persistent pain. This limits the precision not only of our study but of the overall described rate in the literature.

ConclusionsOn the basis of this study, both the TSF and TLIF

strategies resulted in a high fusion rate at L5–S1 (100% vs 88.9%) without significant statistical difference. Less iliac screw fixation was required to augment the stability of the lumbosacral segment by using the TSF technique. This may potentially decrease the overall medical cost and complications related to pelvic fixation. This study also suggests that axial lumbar interbody fusion and TSF tech-niques can lead to a competitive improvement compared

with the preoperative period in patient-reported outcomes based on SRS and ODI questionnaires. The SRS and ODI outcomes scores in the 2 groups were statistically identi-cal at the ultimate follow-up time points. Therefore, both approaches seem to be valid for long ASD fusions to the sacrum in patients who have not had prior spine surgery or spine fusions.

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DisclosuresDr. Faloon is a consultant for and receives grants/research support from K2M. Dr. Boachie-Adjei receives grants/research support from, is a consultant for, and is on the Speaker’s Bureau of K2M. He is also a consultant for and is on the Speaker’s Bureau for WEIGAO.

Author ContributionsConception and design: Yi, Boachie-Adjei. Acquisition of data: Faloon, Ross. Analysis and interpretation of data: Yi, Changoor, Ross. Drafting the article: Faloon, Changoor. Critically revising the article: Faloon, Ross, Boachie-Adjei. Reviewed submitted ver-sion of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Faloon. Study supervision: Boachie-Adjei.

Supplemental InformationPrevious PresentationsPortions of this work were presented at the EuroSpine Annual Meeting, October 16–18, 2019, Helsinki, Finland.

CorrespondenceMichael Faloon: St. Joseph’s University Medical Center, Paterson, NJ. [email protected].


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Transsacral interbody fixation versus transforaminal