Introduction. Lateral anterior lumbar interbody fusion at L5-S1 (LatALIF) is an attractive surgical technique to achieve interbody support at the lumbosacral junction.  LatALIF cages can be secured within the interbody space using an anterior buttress plate or integrated screws.  The purpose of this study was to perform a radiographic comparison of cage subsidence and displacement between L5-S1 LatALIF cages secured with an anterior buttress plate to cages secured with integrated screws.

Methods. Consecutive patients who underwent a L5-S1 lateral ALIF with supplemental posterior fixation by a single surgeon (6/2016-1/2021) were reviewed.  Radiographs were analyzed and compared between two groups based on type of fixation used to secure the L5-S1 LatALIF cage: (1) anterior buttress plate (+PLATE) and (2) integrated screws (+SCREWS). The following measurements at L5-S1 were analyzed on radiographs obtained pre-operatively, before discharge, and at latest follow-up: (1) anterior disc height, (2) posterior disc height, and (3) segmental lordosis.  Cage subsidence was determined by measuring the distance between the cages’ cranial surfaces to the L5 inferior endplate and between the cages’ caudal surfaces to the S1 superior endplate on first post-operative radiographs and latest follow-up radiographs.  Anterior cage displacement was determined by measuring the distance between the cage’s anterior surface to L5’s anterior-inferior endplate on first post-operative and latest follow-up radiographs.

Results. Presented in Table 1. One hundred thirty-nine patients (average age 60.0 ± 14.3 years) were included for analysis.  Sixty-eight patients were treated with +PLATE (follow-up: 12 ± 5 months) and 71 were treated with +SCREW (follow-up: 9 ± 3 months).  Average age, gender distribution, pre-op L5-S1 lordosis, pre-op L5-S1 anterior disc height, and pre-op L5-S1 posterior disc height were statistically similar between the two groups.  After surgery, segmental L5-S1 lordosis and L5-S1 anterior disc heights significantly improved for both groups and each respective measurement was similar between the groups at final follow-up.  Posterior disc heights significantly increased after surgery for +SCREW, but not for +PLATE. As such, posterior disc heights were significantly greater at final follow-up for +SCREW.  Significantly more +PLATE patients had cage subsidence cranially (through L5 endplate: 20.6% v. 2.8%; p<0.01), cage subsidence caudally (through S1 endplate: 27.8% v. 0%; p<0.01), and anterior cage displacement (22.1% v. 0%; p<0.01) compared to +SCREW patients.

Discussion. In this radiographic analysis of 134 patients who underwent lateral L5-S1 ALIFs supplemented by posterior fixation, L5-S1 cages secured with an anterior buttress plate demonstrated significantly higher rates of cage subsidence and anterior cage displacement compared to cages secured with integrated screws. The more durable stability afforded by cages secured with integrated screws makes them a more viable fixation strategy for L5-S1 LatALIFs.