61. ALIF vs TLIF for isthmic spondylolisthesis: differences in radiographic outcomes

BACKGROUND CONTEXT Patients with a diagnosis of isthmic spondylolisthesis have higher sacral slope, pelvic tilt, pelvic incidence and lumbar lordosis compared to patients without isthmic spondylolisthesis. Several fusion techniques have been used to treat isthmic spondylolisthesis in adults, including anterior lumbar interbody fusion (ALIF) and transforaminal interbody fusion (TLIF). Compared to other fusion techniques, ALIF has shown better sagittal alignment outcomes, particularly restoration of segmental lordosis. PURPOSE The purpose of this study was to evaluate which fusion technique provides the better radiological outcome for adult lumbar isthmic spondylolisthesis. STUDY DESIGN/SETTING This study was a retrospective analysis of prospectively collected data from a single, high-volume academic medical center. PATIENT SAMPLE Patients who underwent lumbar fusion for isthmic spondylolisthesis from 2014 to 2019 were included in the analysis. Surgery was indicated after failure of conservative treatment to address radiculopathy and/or neurogenic claudication. Patients were excluded if they were under 18 years of age at the time of surgery, presented with a tumor or infection, or underwent revision surgery. OUTCOME MEASURES Preoperative and postoperative radiographic parameters were collected including sacral slope, pelvic tilt, pelvic incidence, lumbar lordosis, segmental lumbar lordosis, and the vertebral slip percentage. METHODS Patient and surgical characteristics including age, gender, smoking status, body mass index (BMI), Charlson Comorbidity Index (CCI), number of levels decompressed and number of levels fused were collected. Preoperative and final radiographic outcomes were obtained from an institutional electronic medical record. For analysis, patients were divided into two groups based on surgical technique: combined anterior fusion with posterior stabilization (ALIF-PLDF) or anterior and posterior fusion through a posterior approach (TLIF). RESULTS A total of 101 patients were included in final analysis, with 52 patients in the ALIF-PLDF group and 49 patients in the TLIF group. Mean age was greater in the TLIF group (p=0.017). Patients in the TLIF group were more likely to have a history of smoking (p=0.008), to have a greater CCI score (p=0.003), and to have higher number of levels decompressed. On analysis of radiographic parameters, preoperative sacral slope was higher in in the ALIF-PLDF group than the TLIF group (p=0.071). Postoperative overall lumbar lordosis was lower in the TLIF group (p=0.036). Postoperative segmental lumbar lordosis and the delta value for segmental lumbar lordosis were both lower in the TLIF group (p=0.030 and p=0.001). The TLIF group had a significant increase in PI-LL mismatch (p=0.032). Both groups had significant decrease in vertebral slip percent (p CONCLUSIONS Our data highlights that patients undergoing ALIF have a significant increase in segmental lordosis from their preoperative baseline. Interestingly, patients undergoing TLIF have significantly less postoperative change in segmental lumbar lordosis when compared to ALIF. When treating patients with isthmic spondylolisthesis, the ALIF approach has benefits not only in its capacity to restore segmental lordosis, but also by providing significant reduction in vertebral body slip. Our results suggest that, when compared to the TLIF approach, ALIF may be associated with better outcomes in terms of critical radiographic parameters. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.