MRI-based measurements of spondylolisthesis and kyphosis in degenerative cervical myelopathy

BACKGROUND: To provide normative data and to determine accuracy and reliability of preoperative measurements of spondylolisthesis and kyphosis on supine static magnetic resonance imaging (MRI) of patients with degenerative cervical myelopathy. METHODS: T2-weighted midsagittal images of the cervical spine were in 100 cases reviewed twice by one junior observer, with an interval of 3 months, and once by a senior observer. The spondylolisthesis slip (SSlip, mm) and the modified K-line interval (mK-line INT, mm) were assessed for accuracy with the standard error of measurement (SEm) and the minimum detectable change (MDC). Intraobserver and interobserver reliability levels were determined using the intraclass correlation coefficient (ICC). RESULTS: The SEm was 0.5 mm (95% CI 0.4–0.6) for spondylolisthesis and 0.6 mm (95% CI 0.5–0.7) for kyphosis. The MDC, i.e., the smallest difference between two examinations that can be detected with statistical certainty, was 1.5 mm (95% CI 1.2–1.8) for spondylolisthesis and 1.6 mm (95% CI 1.3–1.8) for kyphosis. The highest reliability levels were seen between the second observation of the junior examiner and the senior observer (ICC = 0.80 [95% CI 0.70–0.87] and ICC = 0.96 [95% CI 0.94–0.98] for SSlip and mK-line INT, respectively). CONCLUSIONS: This study provides normative values of alignment measurements of spondylolisthesis and kyphosis in DCM patients. It further shows the importance of taking measurement errors into account when defining cut-off values for cervical deformity parameters and their potential clinical application in surgical decision-making.