The lumbosacral junction acts as a transition point between the mobile lumbar spine and the rigid pelvis. It is thereby susceptible to degenerative changes necessitating fusion at L5-S1. In this study, we compared radiographic outcomes observed from single-level anterior lumbar interbody fusion (ALIF) and transforaminal lumbar interbody fusion (TLIF) at this level.
Retrospective review of single-level ALIF and TLIF with up to one level PSF at L5-S1 between May 2007 and October 2018 was undertaken. X-ray measurements were gathered for lumbar lordosis, segmental lordosis, pelvic tilt, sacral slope, pelvic incidence, pelvic incidence-lumbar lordosis mismatch, anterior/posterior disc height, and sagittal vertical axis. Computed tomography /magnetic resonance imaging was used to determine central canal area, sagittal diameter, foraminal height, and foraminal area.
A total of 47 ALIF patients and 50 TLIF patients were included. Patients averaged 53.7 ± 10.1 yr of age for ALIF and 49.4 ± 14.7 yr old for TLIF (P = .094) with significant differences (P = .0017) seen with gender as ALIF had 60.4% males and TLIF 70.0% females. Single-level ALIF led to significantly (P = .0010) more segmental lordosis (+5.75° ± 7.31°) than TLIF (+0.25° ± 6.55°), though differences in lumbar lordosis were not statistically significant (P = .52). ALIF significantly increased both anterior (+10.4 ± 4.32 mm vs +4.30 ± 3.55 mm; P < .0001) and posterior disc height (+4.33 ± 3.32 mm vs + 2.98 ± 2.07 mm; P = .043) than TLIF. Changes in sagittal vertical axis also significantly differed (P = .030) with ALIF decreasing sagittal vertical axis by 17.8 ± 26.4 mm from +60.3 mm to + 42.5 mm, and TLIF increasing by 0.95 ± 25.8 mm from 39.9 mm to 40.9 mm. Pelvic tilt, sacral slope, pelvic incidence, pelvic incidence-lumbar lordosis mismatch had no significant differences. No statistically significant differences were observed with central canal area, sagittal diameter, foraminal height or foraminal area between ALIF and TLIF.
At L5-S1, the ALIF approach leads to increased segmental lordosis, disc height, while also decreasing sagittal vertical axis to a significant degree than TLIF. However, these two approaches were no different with regards to pelvic parameters and measures of central canal and foraminal decompression.