130 - Lateral Lumbar Interbody Fusion Cage Position and Changes in Segmental Lordosis, Lumbar Lordosis, and Foraminal Height on Single-Level Single-Position L4-L5 Patients

Introduction:
Lateral lumbar interbody fusion (LLIF) is a minimally invasive technique that allows access to the disc spaces of the lumbar spine from L1-L2 to L4-L5 for placement of wide, height-restoring interbody devices and affords a wide operative zone to allow for large cage implantation for segmental reconstruction. The determination of proper anterior-posterior (AP) cage placement includes several important considerations including biomechanical factors related to loading and support, the desired lordosis correction, and restoration of foraminal height. While previous studies have demonstrated the effectiveness of cage height and lordosis angles achieve desired lumbar corrections and height restorations, none have demonstrated the effect of AP cage location segmental lordosis (SL) correction, lumbar lordosis (LL), and foraminal height (FH) restoration while controlling for cage dimensions and treatment approach.

Aims/

Objectives:
Investigate the relationship between postoperative changes in SL, LL, and FH with AP cage position while controlling for cage height and lordosis angle.

Study Design/Setting:
Retrospective cohort study at a single institution.

Patient Sample:
All L4-L5 Grade 1 lumbar spondylolisthesis patients treated with single-position LLIF procedures using a 10mm anterior height, 10º lordotic cage with additional posterior instrumentation were included.

Outcome Measures:
Gender; age; body mass index (BMI); estimated blood loss (EBL); total surgical time (TST); length of stay (LOS); pre- and post-operative SL, LL, FH; cage dimensions, cage distance to the spinal canal.

Methods:
Study patients were treated by one of two fellowship-trained spine surgeons between January 2019 to June 2022. Pre- and post-operative radiographic evaluations were done on standing plain film radiographs of the full spine in sagittal and coronal planes by an experienced reviewer. AP cage distance to the spinal cord was normalized to vertebral endplate length of the superior endplate of the inferior treated level. For statistical analysis, Pearson correlations were used to test for significant relationships between normalized cage distance to changes in SL, LL, and FH. Linear regressions tested whether normalized cage distance were predictive of changes in SL, LL, and FH. Statistical significance was set at α=0.05.

Results:
Demographics: Gender: 11M:10F; Age: 62±10yr; BMI: 29.1±3.8kg/m2; TST: 140±28min; EBL: 66±36ml; LOS: 1.1±0.4days. Radiographic Measures: SL, LL, and FH preoperative were 17.7±6.2º, 46.7±10.3º, and 13.5±2.7mm, respectively. SL, LL, and FH postoperative were 20.0±6.0º, 49.5±10.1º, and 16.2±2.0mm, respectively. Cage Measures: distance to spinal canal: 25.9±3.8mm, vertebral endplate length: 45.3±4.9mm, distance normalized to vertebral endplate length: 57±7%. No significant correlations were found between normalized cage distance and change in SL (r=0.167, p=0.469), LL (r=-0.044, p=0.851), or FH (r=-0.056, p=0.809). Linear regressions indicated that normalized cage distance was not a significant predictor of SL (R2=0.028, F=0.545, p=0.469), LL (R2=0.002, F=0.036, p=0.851), or FH (R2=0.003, F=0.060, p=0.809).

Conclusions:
For a standardized 10mm anterior height, 10º angle in the setting of single-position LLIF for DSD, AP cage location was not found to correlate with nor predict changes in SL, LL, and FH. Determination of AP cage location in LLIF procedures for DSD may be more important for biomechanical considerations than for desired lordosis corrections or foraminal height.