87 - Radiographic Evaluation of Anterior-to-Psoas Lumbar Interbody Fusion (ATP- LIF) Approach using an Expandable Spacer in Degenerative and Deformity Patients: A Single-Surgeon Retrospective Study

Introduction
ATP-LIF is a relatively new approach which traverses through the extraperitoneal space, between the abdominal aorta and the psoas major muscle. It is theorized to offer improved radiographical and clinical outcomes as compared to the traditional methods that require extensive disruption of patient’s anatomy, which can lead to injury related complications. Moreover, expandable technology is hypothesized to facilitate surgery with a small corridor and provide good segmental restoration when coupled with Partial Anterior Longitudinal Ligament Resection (PALLR). This study aims to evaluate the radiographic results of ATP-LIF with PALLR using expandable spacers in the treatment of degenerative and deformity patients.
Methods
This was a single center, retrospective study consisting of 55 patients undergoing 2-stage ATP-LIF surgery with expandable spacers between November 2019 and June 2021. Exclusion criteria included: < 18 years of age, pregnancy, tumor and trauma patients. One to 3 level patients were considered the degenerative group (DG) and ≥ 4-levels were categorized as the deformity group (DF). The time points for data collection were pre-operative, 6 and 12 months postoperative. Follow-up included the use of AP and Lateral X-rays to obtain the following radiographic measurements: disc height (DH), neuroforamen height (NH), lumbar lordosis (LL), segmental lordosis (SL), coronal cobb angle (CC), pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS).
Results
There were 55 patients included in the study: (n= 35: DG; n= 20 DF); 20 patients in the DG group and 18 patients in the DF group had radiographic follow-up data available at 12 months postoperative. Both groups had significant (p < 0.05) postoperative reduction in PI-LL mismatch (71% showed PI-LL < 10° in DG compared to 65% in DF). DF group also showed increased mean postoperative lumbar lordosis (Δ= 3.4° in DG, Δ= 13.9° in DF), segmental lordosis (Δ= 2° in DG, Δ= 12.5° in DF), and disc height (Δ= 4.8 mm in DG, Δ= 5.5 mm in DF, p< 0.05 in both groups) as well as a greater reduction in coronal cobb angle (Δ= 4.1° in DG, Δ=6.9° in DF) as compared to DG group. Sagittal alignment parameters demonstrated more improvement in the DF group than the DG group, which is evidenced by the following: pelvic tilt (Δ= 2.2° in DG, Δ= 4.2° in DF), and sacral slope (Δ= 3.9° in DG, Δ= -1.2° in DF). DG showed better neuroforamen height increase than DF (Δ= 2.7 mm in DG, Δ= 1.8 mm in DF).
Conclusion
Two stage ATP-LIF with PALLR using expandable spacers is a feasible option for treating patients with spinal pathologies due to degeneration or deformity. This is supported by postoperative improvements in sagittal alignment parameters, lordosis, cobb angle, PI-LL, DH and FH in both groups. Overall, the magnitude of most radiographic improvements was greater in DF than DG. Also, the majority of patients in both groups achieved PI-LL < 10°.