ABSTRACT
BACKGROUND CONTEXT: Currently, there is no universally accepted method for assessing radiological fusion shortly after anterior cervical discectomy. Five-year follow-up radiological X-rays demonstrating solid fusion or absence of fusion provided a gold standard for comparison with various assessment methods. PURPOSE: Establishing the most accurate diagnostic test for earlier bony fusion assessment by comparing different cut-off values for the difference in interspinous distance and the change in Cobb angle on dynamic radiological images against the established gold standard. DESIGN: Post-hoc analysis from the NEtherlands Cervical Kinematics (NECK) trial (NTR1289). PATIENT SAMPLE: A total of 40 patients with 1 level herniated disc that underwent anterior discectomy between 2010 and 2014 returned for a 5-year follow-up X-ray. OUTCOME MEASURES: Radiological outcome was assessed quantitatively and qualitatively by fusion on radiographic images 5 years after surgery. METHODS: Radiological dynamic X-rays were reviewed for fusion at 5-year follow-up by a senior spine surgeon. At this timepoint, bony continuity was indisputable and served as gold standard. Cobb angles and interspinous distances on flexion-extension images were measured independently by 2 investigators. Optimum agreement between the gold standard and the 2 methods was assessed, evaluating varying cut-off values, considering sensitivity, specificity, and area under the curve (AUC). RESULTS: Dynamic radiographic assessments revealed fusion in 29 out of 40 patients (mean age: 49 years ± 8; 23 women). For Cobb angle (optimal cut-off: ≤3.0°), the AUC was 0.86 with 100% sensitivity and 72.7% specificity. For interspinous distance (optimal cut-off: ≤1.5 mm), the AUC was 0.89 with 96.6% sensitivity and 81.8% specificity. The highest AUC (0.91) was observed for combined cut-off values (Cobb angle ≤3.0° and interspinous distance ≤2.0 mm), yielding 100% sensitivity and 81.8% specificity. CONCLUSION: The combination of cut-off values ≤3.0° difference for Cobb angle and ≤2.0 mm difference for interspinous distance on lateral flexion-extension X-rays was assessed to be an accurate diagnostic criterion for fusion evaluation. This tool provides a practical and easy applicable method for assessing fusion during follow-up after anterior discectomy.
