Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: complications of cervical spine surgery: 163. Sagittal alignment parameters associated with adjacent segment pathology after anterior cervical discectomy and fusion

Abstract

BACKGROUND CONTEXT Changes in the cervical alignment from preoperative to postoperative may alter cervical spine mechanics, and increase the rate of early adjacent segment pathology. Correction and restoration of cervical sagittal alignment is crucial in achieving a successful result after an ACDF and potentially decreasing the risk of developing ASD. PURPOSE We sought to evaluate the relationship between cervical spine sagittal alignment and adjacent segment disease (ASD) following anterior cervical discectomy and fusion (ACDF) as determined by radiographic and clinical outcomes. STUDY DESIGN/SETTING Retrospective Cohort Series. PATIENT SAMPLE Patients undergoing ACDF from 2008 to 2015 who developed radiographic signs of ASD(+) were identified and compared to a matched group of ACDF patients who did not develop radiographic evidence of ASD(−) for a period of at least 1 year. Patients were excluded from analysis if they were under 18 years of age at the time of surgery, had postoperative follow up less than 12 months or had an ACDF for cervical spine fracture or infection. OUTCOME MEASURES The number or location of levels fused was recorded and radiographs were reviewed preoperatively, immediately postoperative, and at final follow up. The sagittal parameters measured included change in C2-C7 lordosis, T1 angle, levels fused, sagittal vertical axis (SVA), fusion mass lordosis, proximal and distal adjacent segment lordosis. Patient reported outcomes were obtained in the form of Neck Disability Index (NDI) scores and Visual Analog Scales (VAS) scores for the neck and arm. Radiographic diagnosis of ASD was determined by the presence of new or enlarged osteophytes, endplate sclerosis, disc space narrowing g50%, and/or increased calcification of the anterior longitudinal ligament (ALL) as presented by previous published studies. METHODS Radiographic diagnosis of ASD was determined by the presence of new or enlarged osteophytes, endplate sclerosis, disc space narrowing g50%, and/or increased calcification of the anterior longitudinal ligament (ALL) as presented by previous published studies. Baseline patient characteristics were compared using chi-squared analysis and independent sample t-tests for categorical and continuous data, respectively. Bivariate and multivariate regressions were subsequently used to compare clinical outcomes between procedure groups. Multivariate analyses controlled for differences in baseline patient characteristics. RESULTS A total of 101 ASD(+) patients were identified having underwent ACDF from 2008 to 2015 and compared to 131 ASD(−). The ASD(−) were free of ASD for a period of at least 1 year. The groups were similar with regard to demographic and surgical variables, but with a predominance of males in the ASD group 61.2% (p=.001). Rigid plates were used in 42% of all constructs and were more represented in the ASD(−) than ASD(+) group (48% vs. 33%, respectively, p=.017). The most common levels included in the fusion were C5-7 (28%). For all patients, preoperative lordosis was increased from 4.8p11.4° to 7.9p10.2° postoperatively and improved to 9.4p9.9° at final followup. Patients with greater kyphosis throughout the cervical spine at final followup had increased odds of developing ASD (OR 0.97 per degree, p=.040). Patients with greater preoperative kyphosis through the planned fusion segment had increased odds of ASD (OR 0.93 per degree, p=.003). Patients who lost lordosis through the fusion from initial postop to final followup had greater odds of developing ASD (OR 0.85 per degree, pl0.001). Patients who had greater change in preoperative to postoperative fusion segment lordosis were found to exhibit a greater risk of ASD (OR 1.06 per degree, p=0.019). The SVA and T1 slope angles did not change substantially from preoperative to postoperative and there were no differences between ASD groups. The mean postoperative and final proximal and distal segment lordosis was also not different between groups except for significantly less proximal adjacent segment lordosis in ASD patients at final follow-up (0.2p5.0 vs. 1.4p4.4; p=.026). There were no significant differences between preoperative, postoperative, or change in patient reported outcome surveys in patients with or without signs of radiographic ASD. CONCLUSIONS Patients with a greater preoperative cervical kyphosis and kyphosis through the proposed fusion segment may have greater odds of develeoping radiographic adjacent segment degeneration. Similarly, those that had a greater greater correction of cervical lordosis postoperatively, and those who loss lordosis at the fusion segment also presented with increased odds of developing adjacent segment degeneration. Our results suggest that preoperative and postoperative measures of cervical spine alignment, specifically related to C2-C7 and fusion segment lordosis, may predict the development of radiographic signs of adjacent level pathology following an ACDF.