Introduction

Isthmic spondylolistheses are more frequently being treated with interbody fusion via anterior (ALIF) or posterior (TLIF) approaches. Robust comparisons of radiographic and patient-focused clinical outcomes are lacking. We compared segmental and regional radiographic parameters between ALIF with posterior spinal fusion and TLIF for surgical treatment of L5-S1 isthmic spondylolisthesis. Secondarily, we compared patient-reported outcome measures (PROMs) between techniques.

Methods

We reviewed pre- and post-operative radiographs as well as Patient-Reported Outcomes Measurement Information System (PROMIS) elements for patients who received L5-S1 interbody fusions for isthmic spondylolisthesis in the Mass General Brigham (MGB) health system between 2016-2020. Intraclass correlation testing and nonparametric independent and paired t-tests were used for reliability and validity assessments, respectively.

Results

A total of 47 patients were included for analysis; 31 (66%) underwent ALIF and 16 (34%) were treated with TLIF. First and final postoperative X-rays were obtained at 29 days (SE 5) and 385 days (SE 50) following surgery, on average. ALIF demonstrated significantly greater generation of segmental lordosis than TLIF, both at first postoperative visit (11.7º vs 1.5º, p < 0.001) and at final follow up (9.0º vs -0.1º, p < 0.001) (Figure 1). Significantly greater regional L4-S1 lordosis was also observed for the ALIF group at both time points (6.4º vs 0.2º, p = 0.01, first postoperative visit; 7.5º vs 2.5º, p = 0.03, final follow up). ALIF also demonstrated a significantly greater increase in disc height than TLIF, both at first postoperative visit (9.8 vs 5.5mm, p = 0.002) and final follow up (8.4 vs 3.8mm, p < 0.001). Disc height significantly decreased over time in both cohorts (ALIF 9.8 vs 8.4mm, p = 0.03; TLIF 5.5 vs 3.8mm, p = 0.01). No differences in preoperative and postoperative PROMIS components were detected between techniques. Intragroup analysis revealed significant improvements in physical function, pain interference, and the physical subsection of global health between pre- and postoperative time points for ALIF patients; TLIF patients demonstrated improvements in pain interference and pain intensity following surgery. 

Figure 1. Preoperative, first postoperative, and final follow up radiographs of ALIF (A, B, C) and TLIF (D, E, F) constructs with segmental and L4-S1 lordosis calculated.

Discussion

This work furthers understanding regarding the important role of sagittal alignment and the substantial influence of the lumbosacral junction on global parameters of spinal balance. ALIF generated greater segmental lordosis, regional lordosis, and restoration of disc height compared to TLIF following treatment for isthmic spondylolisthesis. These differences persisted at one year follow up. We also found equivalence across PROMs between techniques, with patients in both groups benefitting from surgery across PROMIS parameters. Surgeons should consider these projected differences in radiographic outcomes as well as clinical and approach related factors when selecting the optimal surgical intervention for L5-S1 isthmic spondylolisthesis.