Interspinous Motion Measurement Could Serve as a Quantitative Method for Assessing Bony Fusion after Anterior Cervical Corpectomy and Fusion (ACCF)

Study Design. A retrospective diagnostic test study. Objective. To establish quantitative fusion criteria for ACCF. Summary of Background Data. Currently, the criteria of fusion after ACCF remains controversial. Evaluation techniques such as observation of continuous bony trabeculae across the fusion site, were qualitative and conducted by naked eyes, limiting its accuracy. Dynamic fusion indicators such as interspinous motion (ISM), have been successfully utilized in anterior cervical discectomy and fusion (ACDF) for evaluating fusion and detecting pseudarthrosis. However, the accuracy of ISM in ACCF is unclear. Methods. Patients underwent ACCF in our hospital were reviewed. Imaging data including dynamic radiographs and computed tomography (CT) scans were collected. The distance and angle form of ISM (ISM-dis and ISM-ang) were measured on dynamic radiograph, with CT as the gold standard for fusion. The correlation between ISM methods was analyzed using Spearmann correlation. Receiver Operating Characteristic (ROC) curves were used to evaluate the accuracy and generate optimal cut-off values. Three observers independently measured the data twice to determine interobserver and intraobserver reliability. Results. Our study included 178 imaging datasets. ISM-dis showed positive correlation with ISM-ang (r=0.914). The area under ROC (AUC) for ISM-dis and ISM-ang was 0.926 and 0.893. Applying a cutoff value of 1.50 mm to ISM-dis yielded a sensitivity of 87.8% and specificity of 92.3% for detecting pseudarthrosis. For ISM-ang, a cutoff value of 1.75° resulted in a sensitivity of 79.1% and specificity of 92.3%. Intraobserver reliabilities for ISM-dis (0.986, 0.984 and 0.972) were higher than for ISM-ang (0.935, 0.963 and 0.935), as was interobserver reliability (0.985 for ISM-dis and 0.956 for ISM-ang). Fusion rates calculated using ISM-dis and ISM-ang were 52.4% and 61.9%. Conclusion. ISM can serve as an alternative to CT for assessing fusion, with ISM-dis at a 1.50 mm cutoff and ISM-ang at 1.75° demonstrating high diagnostic accuracy.