How Does Minimally Invasive Transforaminal Lumbar Interbody Fusion Influence Lumbar Radiologic Parameters?

Highlights

• ADH and PDH of the operated level were significantly increased by MIS-TLIF.

• There was no significant change in the SA of the operated level after surgery.

• Postoperative PDH was significantly decreased at the adjacent levels.

• LL improvement mostly results from an increase of the SA of the cranial level.

Background

Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) has become a popular method of interbody fusion. Clinical outcomes after single-level MIS-TLIF have been reported, but few studies have focused on the radiologic changes in the segmental parameters of the operated and adjacent segments and in lumbar lordosis.

Methods

From March 2009 to September 2016, 117 patients who underwent a single-level MIS-TLIF surgery for lumbar degenerative disease were enrolled in this retrospective study. The anterior disc height (ADH), posterior disc height (PDH), and segmental angle (SA) of the operated and adjacent levels and lumbar lordosis (LL) were evaluated on radiographs obtained pre- and postoperatively at 6- to 12-month follow-up visits. Cage-related parameters including fusion and subsidence rates were analyzed on postoperative computed tomography scans. Clinical assessment used validated outcome scores such as the Oswestry Disability Index questionnaire and the Odom criteria.

Results

ADH and PDH of the operated segment increased significantly after surgery, but no significant changes were seen in the SA of that level. Statistically significant decreases were observed in the PDH of both adjacent segments and increases in the adjacent superior SA. LL showed a slight but statistically significant improvement after surgery that was mostly correlated with a postoperative increase in the adjacent superior SA (r = 0.58; P < 0.001). No significant correlations were found between clinical and radiologic results.

Conclusions

Single-level MIS-TLIF increased disc height but not the SA at the operated level. LL improvement after surgery was mainly associated with the increase of the cranial segmental angle.

Introduction

The surgical approach to spinal disorders that require lumbar arthrodesis has evolved significantly over the years and includes a variety of surgical techniques that range from posterolateral fusion to lumbar interbody fusion techniques.¹

Lumbar interbody fusion has been reported to have higher fusion rates, improved deformity correction, and capability for indirect decompression and increasing of foraminal height.1, 2 It can be performed using 5 main approaches: posterior lumbar interbody fusion, transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion, oblique lumbar interbody fusion/anterior to psoas, and lateral lumbar interbody fusion.¹

Posterior approaches, such as posterior lumbar interbody fusion and TLIF, are frequent options for the treatment of degenerative lumbar disorders, allowing for complete decompression of the spinal canal and nerve roots, restoration of intervertebral height, near-total discectomy, and restoration of segmental lordosis at the fused level. Additionally, the posterior approaches have minimal risk of damaging retroperitoneal structures as opposed to anterior lumbar interbody fusion.3, 4, 5

However, in the posterior lumbar interbody fusion procedure, significant retraction of the thecal sac and nerve roots is required to provide adequate access to the posterior disc space. Hence, the risk of damage to nerve roots or conus medullaris, dural tears, epidural fibrosis, and neuropathic pain usually limit the technique to the lower spine (L3-S1). The TLIF procedure was developed to overcome this limitation by providing a more lateral approach and unilateral exposure of the disc space that involves less neural retraction and decreases the risk of neurologic or dural injury. TLIF enables placement of the graft and the cage within the anterior or middle third of the disc space, aiming to restore lumbar lordosis (LL), and allows preservation of the contralateral lamina, facet, and pars interarticularis.1, 4

As in other open posterior procedures, the iatrogenic injury of soft tissues and paraspinal muscles is an important cause of postoperative low back pain and can adversely affect short- and long-term patient outcomes. Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) was introduced to minimize the morbidity related to muscle trauma without compromising operative and clinical outcomes and is increasingly being used for lumbar arthrodesis. Reported benefits include less intraoperative blood loss, decreased pain and postoperative narcotics use, shortened hospital stay, and faster recovery.1, 6, 7, 8, 9, 10, 11, 12 However, there is a limited number of reports evaluating radiologic changes and their influence on outcomes after MIS-TLIF procedure. The restoration and maintenance of lumbar and segmental sagittal plane alignment are major concerns when performing intersomatic fusion. Factors related to the intersomatic cage influence the anterior and posterior disc space height and therefore the alignment and structural stability of the operated segment.¹³

There is indeed a claim of TLIF to restore segmental lordosis. However, this potentiality of the procedure is not well documented in the literature, in particular with the use of straight cages in minimally invasive (MI) surgery.

In this study, we reviewed our experience with this type of cage in single-level MIS-TLIF and report the differences observed after the surgery in the segmental parameters, either of the operated disc or the adjacent ones, and in LL. In addition, possible correlations of these variables with the clinical outcomes were investigated.