One-Level Lumbar Degenerative Spondylolisthesis and Posterior Approach: Is Transforaminal Lateral Interbody Fusion Mandatory?: A Randomized Controlled Trial With 2-Year Follow-Up

Challier, Vincent MD; Boissiere, Louis MD; Obeid, Ibrahim MD; Vital, Jean-Marc MD, PhD; Castelain, Jean-Etienne MS; Bénard, Antoine MD, PhD; Ong, Nathalie MD; Ghailane, Soufiane MS; Pointillart, Vincent MD, PhD; Mazas, Simon MS; Mariey, Rémi MD; Gille, Olivier MD, PhD

doi: 10.1097/BRS.0000000000001857
Randomized Trial
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Study Design. A monocentric open-label randomized controlled trial (MRCT).

Objective. Comparison of clinical and radiological outcomes between isolated instrumented posterior fusion (PLF) and associated instrumented posterior fusion and interbody fusion by transforaminal approach (PLF + TLIF) for patients suffering from one-level lumbar degenerative spondylolisthesis (DS) undergoing surgery.

Summary of Background Data. DS is a common cause of symptomatic lumbar stenosis. PLF has shown better clinical outcome than decompression with noninstrumented posterolateral fusion. TLIF with interbody cage showed better fusion rate than PLF. There is a need for randomized controlled trials to compare PLF with and without TLIF as to clinical and radiological outcomes.

Methods. This is a MRCT comparing PLF and TLIF techniques in surgical treatment of DS. Sixty patients were included in a secured database from 2009 to 2011 and randomized into two groups: 30 PLF with posterior pedicle screws and intertransverse autologuous graft, and 30 TLIF in which an interbody fusion by transforaminal approach was added. Data included clinical (pain and disability), surgical (blood loss and operating time), and radiological (alignment and fusion) parameters at baseline and 2-year follow-up. Comparison was made by Student t test and Chi-square test.

Results. There was a significant improvement in each group for pain and disability but no difference between the groups. Radiographic assessment showed better posterolateral fusion rate for TLIF without superiority in segmental lordosis improvement. A case of deformity cascade with spino-pelvic mismatch at baseline was noted in PLF.

Conclusion. Posterior decompression and instrumented fusion is an efficient technique that proved its significant clinical benefit in the surgical treatment of DS. TLIF did not show its superiority neither in clinical nor alignment parameters despite a better fusion rate. These results suggest that TLIF is not mandatory in this specific indication. Sagittal alignment analysis by standing full-body images should be considered in DS care.

Level of Evidence: 2

*Spine Unit 1, Bordeaux University Hospital, Gironde, France

Clinical Epidemiology Unit, Bordeaux University Hospital, Gironde, France.

Address correspondence and reprint requests to Vincent Challier, MD, Spine Unit 1 GROUPE Hospitalier Pellegrin-Tripode 7e étage, place Amélie Raba-Léon 33076 Bordeaux cedex, France; E-mail: challier.vincent@gmail.com

Received 18 March, 2016

Revised 31 July, 2016

Accepted 2 August, 2016

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: grants.

Article Outline

In 1782, a Belgian Obstetrician named Herbiniaux observed the impossibility of the passage of the child's head through the superior pelvic strait because of a major slippage of the lumbo-sacral junction.1 The term spondylolisthesis was invented by Kilian in 1853 after cadaveric analysis of lumbosacral specimens from women who died during child-birth.2 Lambl, Neugebauer, and Chiari, cited by Friberg,3 appeared to be the first to specifically study spondylolisthesis. Meyerding4 established the first classification of the severity of the slippage and proposed a fusion procedure for treatment. In 1930, Junghanns,5 who analyzed hundreds of specimens in Schmorl's collection, described 11 cases of spondylolisthesis with an intact posterior arch and called them pseudospondylolisthesis. MacNab, who was unsatisfied with this denomination because the slippage was real, reported 27 cases of what he called degenerative spondylolisthesis6 (DS). MacNab considered DS as type three in the Wiltse, Newman, and Macnab classification modified by Wiltse and Rothmann.7–9

Surgical treatment of DS has evolved with technology leading to various posterior approach solutions, including isolated laminectomy, laminectomy associated with posterolateral bone grafting, instrumented posterolateral bone grafting, and circumferential fusion. Herkowitz and Kurz10 demonstrated better clinical outcomes when posterolateral grafting was associated with neurologic decompression. Fischgrund et al.11 showed that instrumented posterolateral grafting was superior in terms of fusion rate to grafting without instrumentation. According to some authors, fusion rate is correlated to clinical improvement and circumferential fusion leads to better outcomes than instrumented posterolateral fusion (PLF) in lumbar degenerative surgery.12–14

Interbody fusion (IF) through a posterior approach was first described in 1944 by Briggs and Milligan who tried placing bone chips in the interbody space after discectomy in order to enhance the fusion rate.15 In 1946, Jaslow proposed a technique using spinous processes,16 but the procedure was popularized by Cloward in 1953,17 who insisted on the importance of removing cartilaginous and disc tissue with dedicated instrumentation in order to achieve good bony fusion. The development of posterior lumbar IF (PLIF) devices such as carbon fiber Brantigan cages filled with autologous or allogenic bone grafts allowed surgeons to increase the stability of the anterior column through a posterior approach.18 In addition to carbon fiber,18,19 other materials are commonly used to manufacture IF devices, including titanium mesh20 and polyetherketone.21 The PLIF technique entails passing through the canal using a bilateral posterolateral approach and involves neurologic risks such as dural tear or postoperative radiculopathy22 in addition to nonunion by facet joint lesions, requiring instrumented posterior fixation.23 In an effort to decrease the neurologic risks, Harms and Jeszenszky24 was the first to propose transforaminal lumbar IF (TLIF) permitting circumferential fusion, stability, improvement of segmental and regional alignment, and cost-effectiveness.25–29 Furthermore, PLIF and TLIF techniques have been compared, demonstrating the advantage of TLIF in terms of neurologic impairment and laminar protection.30,31

In the setting of DS, numerous studies have been published in the past few years comparing PLIF to PLF. In 2014, Liu et al.32 performed a meta-analysis including four randomized controlled trials (RCTs) and five comparative observational studies with moderate-quality evidence of superiority of the PLIF group for clinical satisfaction and radiographic fusion; furthermore, no significant difference was found in terms of complication rate, blood loss, and operating time. To the best of the current authors’ knowledge, there is a paucity of studies comparing TLIF and PLF for degenerative lumbar conditions,33,34 with no RCT exclusively involving one-level lumbar DS. Recently, superiority of TLIF techniques over PLF for management of DS treatment has been questioned,35–37 despite a significant rise in the use of IF in this indication during the past decade.38 Moreover, according to an analysis of the Nationwide Inpatient Database on 48,911 patients who had surgery for lumbar DS, IF was found to be the most commonly used technique between 2001 and 2010.39

The purpose of this RCT was to compare TLIF and PLF for the treatment of one-level lumbar DS with a 2-year follow-up.

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MATERIALS AND METHODS

Study Design and Population

This study is a mono-centric, randomized, open-label, controlled trial comparing two types of posterior fusion techniques: posterolateral instrumented fusion alone (PLF group) and posterolateral instrumented fusion with IF using a transforaminal approach (PLF + TLIF group).

Patients were included if aged less than 75 years, having been informed about clinical trial objectives and risks, covered by the health insurance system, suffering from DS indicating one-level surgical fusion due to either motor deficit or invalidating low back pain, leg pain, or both despite 6 months optimal medical treatment. Exclusion criteria were previous lumbar fusion, previous spine trauma, presence of at least one major contraindication to surgery and/or general anesthesia, presence of at least one contraindication to either TLIF or PLF, severe radiological osteoporosis, active cancer at time of inclusion into the study, unlikely to comply with the requirements of the study and/or to complete the study for any reason, or under any administrative or legal supervision.

The two randomized groups were balanced with a 1:1 ratio. The description of the randomization process40 was kept confidentially in the clinical epidemiology unit of Bordeaux University Hospital. Randomization was centrally managed via a secured website the day before surgery for each patient. All included patients have given informed consent. This study was approved by the regional ethical committee and registered on clinicaltrials.gov, identifier: NCT00869882.

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Surgical Features

Instrumented Posterolateral Fusion (PLF)

Patients were carefully placed in the prone position and operated through a posterior approach under general anesthesia. Polyaxial pedicle screw instrumentation was inserted, followed by posterior neural decompression depending on the type of stenosis. Subperiosteal dissection was performed between the transverse processes and lateral aspects of the facet joints. Two rods were placed and locked to the pedicle screws in compression to optimize segmental lordosis. Autologous bone graft was laid onto the freshened vertebral aspects.

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Interbody Fusion by Transforaminal Lateral Approach (PLF + TLIF)

After unilateral foraminotomy, nerve roots are retracted, the disc nucleus is removed entirely, and endplate decortication is performed. The most anterior part of the disc space is packed with cancellous bone and then a cage filled with bone is inserted into the anterior portion of the interspace. Cage placement is radiologically verified. The end of the procedure is the same as for PLF.

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Data Collection and Outcome Measures

Clinical and Surgical Parameters

Oswestry Disability Index (ODI),41,42 radicular and lumbar Visual Analog Scale (VAS) pain assessment, and health-related quality-of-life (HRQOL) short-form 36 (SF36)43 scores were collected. Estimated blood loss (EBL) and procedure duration (PD) were also analyzed. Major intraoperative complications were defined as those leading to surgical revision.

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Radiographic Analysis

Fusion was not only assessed by a trained surgical fellow in both groups using the Lenke and Bridwell classification44,45 (Table 1) on conventional antero-posterior radiographs but also measuring the angle between the endplates of the operated interbody space in flexion-extension on lateral radiographs with motion of less than 5° considered as fused as shown by Cleveland et al.46,47

Radiologic alignment was also assessed on lateral views using a validated software48,49 (SPINEVIEW, Paris, France) by measuring L1S1 lumbar lordosis (LL) (the angle between the superior endplate of L1 and the superior sacral endplate), pelvic incidence (PI) (the angle between the perpendicular to the superior sacral endplate and the line from the center of the femoral heads to the middle of the superior sacral endplate), pelvic tilt (PT) (the angle between the line passing through the center of the femoral heads and the center of the sacrum and avertical line), and segmental lordosis of the treated level (SL) measured by the angle between the superior endplate of the upper vertebra and the inferior endplate of the lower vertebra as described by Goldstein et al.50

Data were prospectively collected at baseline and 2-year follow-up and included clinical, surgical, and radiographic parameters, and then classified into primary and secondary outcomes measures represented in Table 2.

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Statistical Considerations

Comparison between the two groups was made between baseline and 2-year follow-up for each group and between the groups by Student t test for continuous variables and Chi-square and Fisher exact test for noncontinuous variables. Statistical significance was considered as reached when P < 0.05.

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RESULTS

Population Studied and Eligibility

Between 2009 and 2011, 60 patients suffering from DS were included as shown in Figure 1.

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Analysis at Baseline

There was no significant difference in terms of demographic, clinical, or radiographic parameters between the two groups (Table 3). The majority of the patients were slightly overweight females over 60 years of age. The distribution of disability level by ODI score at baseline is reported in Table 4. More than 50% of both groups had severe disability or worse (ODI > 40). The level of the procedure was primarily L4-L5 (PLF group: n = 28, TLIF group n = 25).

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Analysis at 2-Year Follow-Up

Primary Outcomes

In terms of fusion assessment, almost all patients (96.7%) in the PLF + TLIF group achieved type A or B fusion according to the Lenke & Bridwell classification, whereas only half (56.7%) of the PLF group achieved A or B fusion (Table 5). Movement of less than 5° in flexion/extension radiographs was found in only 43.3% of the PLF group and 93.3% of the PLF + TLIF group, and this difference was statistically significant (P < 0.05).

In terms of SL, there was no statistically significant change of mean values within or between the two groups. Comparing the number of individuals showing an increase of more than 3°, there was a significant superiority of PLF + TLIF over PLF (36.7% and 13.3%, respectively). The course between baseline and 2 years is shown in Figure 2. SL initially increased between baseline and 2 months followed by a progressive decrease in SL to values not significantly different from baseline.

In PLF group, six patients experienced a major complication: two dural-tears that had to be repaired, two wound infections necessitating surgical revision, and one revision for adjacent segment disease in an obese woman, who had an associated spino-pelvic mismatch at baseline and necessitated corrective surgery and extended fixation (T12-ilium). This revision failed to achieve optimal restoration of sagittal alignment leading to a rod failure at 18 months. In the PLF + TLIF group, three patients had major complications, including one pedicle fracture with screw loosening necessitating revision for fusion extension and two revisions to repair a dural tear, one of which resulted in radicular pain that subsequently resolved.

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Secondary Outcomes

Significant clinical improvement in all scores (VAS, ODI, SF-36) between baseline and 2-year follow-up was demonstrated in both groups with no significant difference between the groups. No major change in mean spino-pelvic alignment parameters was observed whether or not a cage was implemented.

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DISCUSSION

This is the first 2-year follow-up RCT comparing PLF to PLF + TLIF for one-level lumbar DS in terms of clinical and radiographic outcomes.

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Analysis at Baseline

Analysis at baseline showed results in agreement with preexisting data in literature, notably in the reports by Matsunaga et al.51,52 and Jacobsen et al.s53 The majority of the patients were slightly overweight women over 60 years of age presenting with low back pain, leg pain, and neurologic claudication. In the current authors’ opinion, radiographic full-body analysis is essential in patients with lumbar degenerative diseases, particularly in DS, in which modifications of spino-pelvic alignment have been shown in numerous studies.54–58 Barrey et al.59 demonstrated that DS patients had a higher PI, lower LL, compensated by higher PT than asymptomatic subjects without DS. Mean PI was not as high in the present cohort, but lumbar hypolordosis and pelvic retroversion were observed, suggesting an at risk profile that may contribute to the slippage in DS patients, in addition to degenerative changes in facet joint orientation as shown recently by Smorgick et al.60

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Primary Outcomes

The current demonstration that PLF + TLIF provides better fusion rates than isolated PLF is consistent with the findings of the only RCT comparing these two techniques published by Høy et al.33 PLF + TLIF group has demonstrated good to excellent fusion rates in numerous studies25,28,61–64 using standard radiographic assessment. The reader should note, however, that the Lenke classification used in the present study has yet to be validated. Moreover, computed tomography (CT)-scan is known to be the most accurate imaging system to evaluate quality of fusion.47 In any event, in patients operated for DS, fusion rates have not been consistently correlated with clinical outcomes.65

Regarding SL improvement, no difference was shown between the two groups at 2-year follow-up, which is consistent with previously published data.63 The timeline analysis demonstrated a slight augmentation of 3° in the PLF + TLIF group at 3 months followed by a progressive decrease. These results are inconsistent with recent published studies by Jagannathan et al.27 and Ould-Slimane et al.26 who found a mean SL increase of 11.0° and 7.2°, respectively. This could be explained by differences in the surgical techniques. In the former study, bilateral facet joint resection was performed, and monoaxial screws were used in the latter study. This suggests that using polyaxial screws with unilateral facetectomy might be insufficient to achieve significant improvement of SL.

In terms of revision rate, there was a statistically significant difference between the two groups; however, the two revisions for wound infection in the PLF group may have overly biased the revision rate. One revision was performed for corrective surgery in the PLF group in a patient who presented with an associated spino-pelvic mismatch that was overlooked at baseline. This example shows the relevance of sagittal alignment evaluation in the decision-making process. When sagittal deformity, as defined by Schwab et al.,66 is associated with DS, it is important to treat both with extended fusion and corrective osteotomies. Schroeder et al.67 and the ZASS group68 recently demonstrated the need for individualized care and called for future studies identifying variables such as age, low back pain, dynamic instability, and the type of stenosis as criteria for appropriate care. However, the current findings demonstrate that sagittal alignment parameters should be also included among these variables. In this perspective, a novel classification of DS proposed by Gille et al.69 might be helpful to distinguish specific entities.

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Secondary Outcomes

Shorter mean PD and a trend for less EBL in the PLF group were observed and seem logical, as implementation of TLIF cage necessitates additional time. In terms of complications, the current data failed to show significant difference between the two groups and are consistent with previous studies comparing small groups of patients.26,70 However, analysis of larger cohort such as the NIS database allowed Norton et al.39 in 2015 to demonstrate fewer complications with PLF than with TLIF, the overall complication rate of which was 22.6%.

In terms of clinical outcomes, there was a significant improvement in all scores for both groups without superiority of one above the other. These findings contrast with a hypothesis of several authors. s et al.70 showed superiority of PLF + TLIF technique in a retrospective multivariate analysis, suggesting that foraminal decompression associated with the removal of the disc, the nociceptive pain generator, could explain a better clinical improvement as also hypothesized by previous authors.71,72 However, the current results are consistent with comparisons performed that were unable to show superiority of PLF + TLIF over PLF in improvement of HRQOL scores.33,35–37 In a recent retrospective comparative study of the two techniques in the setting of L4L5 DS, Gottschalk et al.36 failed to show any clinical superiority, but they did find an increase of cost in the combined group, and suggested that TLIF should be considered on a case-by-case basis. In addition, the present analysis by ODI groups demonstrates that up to 18% of each group remains severely disabled at 2 years. As the number of lumbar fusion procedures has dramatically increased over the last 20 years,38,39,73–75 a tailor-made approach that takes into account important baseline parameters would probably improve clinical outcomes.

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Limitations and Future Works

This study has several limitations, including a relatively low number of subjects, short follow-up, and no CT scan evaluation of the fusion rate. Future studies should focus on evaluating benefits of IF in specific radio-clinical entities of DS such as cases associated with focal kyphosis or sagittal malalignment.

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CONCLUSION

Posterior decompression and instrumented fusion is an effective technique, which proved its significant clinical benefit for patients with DS. Adding a TLIF failed to show clinical superiority over instrumented PLF alone in this RCT despite a better fusion rate. These results suggest that adding TLIF is not mandatory in this specific indication. Sagittal spino-pelvic alignment assessed by full-body radiographs should be considered in the decision-making process and evaluation of DS patients, specifically those with some degree of associated spinal deformity.

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Key Points

* Adding TLIF did not show its clinical superiority in this RCT despite a better fusion rate.

* Adding TLIF is not mandatory in this specific indication.

* Sagittal alignment should be taken in account for the decision-making process in DS patients.

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Keywords:

degenerative spondylolisthesis; interbody fusion; randomized controlled trial; sagittal alignment

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