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.
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.
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.
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
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.
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.
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.
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.
* 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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