Fusion rate for stand-alone lateral lumbar interbody fusion: a systematic review

Abstract

BACKGROUND

Lateral lumbar interbody fusion (LLIF) is used to treat multiple conditions, including spondylolisthesis, degenerative disc disorders, adjacent segment disease, and degenerative scoliosis. Although many advocate for posterior fixation with LLIF, stand-alone LLIF is increasingly being performed. Yet the fusion rate for stand-alone LLIF is unknown.

PURPOSE

Determine the fusion rate for stand-alone LLIF.

STUDY DESIGN

Systematic review.

METHODS

We queried Cochrane, EMBASE, and MEDLINE for literature on stand-alone LLIF fusion rate with a publication cutoff of April 2020. LLIF surgery was considered stand-alone when not paired with supplemental posterior fixation. Cohort fusion rate differences were calculated and tested for significance (p<0.05). All reported means were pooled.

RESULTS

A total of 2,735 publications were assessed. Twenty-two studies met inclusion criteria, including 736 patients and 1,103 vertebral levels. Mean age was 61.7 years with BMI 26.5 kg/m². Mean fusion rate was 85.6% (range, 53.0%–100.0%), which did not differ significantly by number of levels fused (1-level, 2-level, and ≥3-level). Use of rhBMP-2 was reported in 39.3% of subjects, with no difference in fusion rates between studies using rhBMP-2 (87.7%) and those in which rhBMP-2 was not used (83.9%, odds ratio=1.37, p=0.448). Fusion rate did not differ with the addition of a lateral plate, or by underlying diagnosis. All-complication rate was 42.2% and mean reoperation rate was 11.1%, with 2.3% reoperation due to pseudarthrosis. Of the studies comparing stand-alone to circumferential fusion, pooled fusion rate was found to be 80.4% versus 91.0% (p=0.637).

CONCLUSIONS

Stand-alone LLIF yields high fusion rates overall. The wide range of reported fusion rates and lower fusion rates in studies involving subsequent surgical reoperation highlights the importance of proper training in this technique and employing a rigorous algorithm when indicating patients for stand-alone LLIF. Future research should focus on examining risk factors and patient-reported outcomes in stand-alone LLIF.

Introduction

The general approach for lateral lumbar interbody fusion (LLIF) surgery was first described in 1997 by Mayer et al. [1]. Since that time, patented variations of LLIF procedures have been iteratively defined and include extreme lateral interbody fusion (XLIF, NuVasive, Inc., San Diego, CA, USA) and direct lateral interbody fusion (DLIF, Medtronic Sofamor Danek, Minneapolis, MN, USA) [2], [3], [4]. LLIF utilizes a lateral surgical approach to the lumbar spine and involves manipulation of the psoas muscle to visualize the spine directly. As a minimally invasive technique, LLIF allows for direct visualization of the lumbar spine while minimizing the required surgical exposure and obviating the need for mobilizing the great vessels when compared with anterior interbody lumbar fusion (ALIF). For these reasons, LLIF has gained in popularity as an approach to achieve interbody fusion for a variety of conditions, including spondylolisthesis, degenerative disc disease, adjacent segment disorder (ASD), and degenerative scoliosis [4], [5], [6], [7].

Posterior stabilization is often combined with LLIF, most commonly consisting of pedicle screw fixation during or subsequent to LLIF to increase construct stability, reduce subsidence risk, and increase the likelihood of fusion success [8,9]. Compared with the addition of posterior stabilization, stand-alone LLIF constructs demonstrate greater persistent range of motion as well as endplate stresses [10,11]. The arguments in favor of a stand-alone approach are primarily clinical advantages, including indirect decompression, high surface area for fusion, and avoidance of complications and morbidity related to anterior or posterior approaches [9, 12]. These benefits of stand-alone LLIF may enable this technique to become a realistic option for revision surgery as well.

Many argue that supplemental posterior fixation (PSF) is necessary to achieve adequate fusion in the setting of a lateral approach, yet stand-alone LLIF is increasingly being performed. Whether stand-alone LLIF results in reliable fusion is currently unknown. Furthermore, whether certain factors (eg, smoking exposure, augmentation with recombinant bone morphogenetic protein-2 [rhBMP-2], or prior laminectomy) impact LLIF fusion rate remains unclear. The purpose of this study was to systematically review the literature to determine fusion rate in the setting of stand-alone LLIF and to examine the impact of these additional factors on fusion rate in the setting of stand-alone LLIF. These data will be valuable to patients and surgeons alike in understanding the likelihood of fusion success after stand-alone LLIF.