262. Do large increases in disc space height have consequences after ACDF?

Abstract

BACKGROUND CONTEXT During anterior cervical discectomy and fusion (ACDF), distraction of the disc space is used to assist with decompression and graft insertion. In patients with significant preoperative disc space collapse, there may be a large increase in disc space height postoperatively after graft insertion. There are concerns that this acute increase may increase the stresses across the graft-endplate interface and may lead to subsidence or affect other radiographic or clinical outcomes. PURPOSE The aim of the present study was therefore to characterize the difference in preoperative and postoperative disc space height, and to determine the association of an increased change in disc space height with clinical and radiographic outcomes following ACDF. STUDY DESIGN/SETTING Retrospective cohort analysis. PATIENT SAMPLE Analysis was performed on patients who underwent a single-level ACDF by one of two senior spine surgeons between 2008 and 2015 for cervical radiculopathy and/or myelopathy, with a minimum of 6 months of clinical and radiographic follow-up. OUTCOME MEASURES Radiographs were reviewed preoperatively and immediately postoperatively, and at final follow up. Disc height was measured as the anterior vertebral distance (AVD), mid-vertebral distance (MVD), and posterior vertebral distance (PVD) on preoperative and immediate postoperative radiographs. Sagittal parameters were also measured, and included C2-C7 lordosis, T1 angle, fusion segment lordosis, sagittal vertical axis (SVA), proximal and distal adjacent segment lordosis. Visual Analogue Scale (VAS) neck, VAS arm, and Neck Disability Index (NDI) scores were collected at each postoperative clinical visit. The rates of adjacent segment disease, reoperation, successful fusion and subsidence (postoperative disc space collapse >2mm) were determined. METHODS Radiographs were reviewed preoperatively and immediately postoperatively, and at final follow-up, along with patient reported outcomes. Multivariate regressions were used to control for baseline patient characteristics. RESULTS A total of 120 patients met inclusion criteria. Mean follow-up length was 29 months, and mean age was 46.9 years, mean BMI was 28.4, and 45.4% of patients were female. Increased preoperative to postoperative disc height change in all regions was associated with development of distal adjacent segment disease (AVD OR 1.89, p=0.013; MVD OR 1.75, p=0.043; PVD OR 2.07, p=0.014), but not proximal adjacent segment disease. increased change in AVD was associated with a greater change in preoperative to postoperative C2-C7 lordosis, fusion segment lordosis and proximal segment lordosis. Increased change in AVD was also associated with increased preoperative to final change in lordosis. No other associations were found between preoperative to postoperative difference in AVD, MVD or PVD and preoperative, immediate postoperative or final sagittal parameters. Additionally, no associations were found between preoperative to postoperative disc height change and any clinical outcomes. Rates of reoperation, fusion, and subsidence did not vary based on preoperative to postoperative disc height change. CONCLUSIONS This study found that a greater difference in preoperative to postoperative disc space height following ACDF was associated with the development of distal adjacent segment degeneration; however, it was not associated with most radiographic outcomes, or any patient-reported outcomes. Large changes in disc space height may not be benign, and further study is needed to characterize the etiology of ASD associated with these changes. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.