Purpose: Disc height has been found to be related to disc degeneration and LBP. However, choosing an accurate and efficient measurement for disc height remains controversial. The aim of this study was to evaluate intra- and inter-rater agreement and reliability of seven reported DHI measurement methods on X-ray.
Methods: The adult patients who had standing lateral X-ray of lumbar spine were consecutively recruited (30 for intra- and 288 for inter-rater assessment) in this retrospective study. Seven methods were used to measure the DHI of each lumbar intervertebral disc level. Bland and Altman´s Limits of Agreement (LOA), standard difference, and intra-class correlations (ICC) with 95% confidence intervals were estimated.
Results: The intra-rater reliability in DHI measurements using different methods were ICCs from 0.807 (0.794, 0.812) to 0.922 (0.913, 0.946) by rater 1 (SS) and from 0.827 (0.802, 0.841) to 0.918 (0.806, 0.823) by rater 2 (XC). Method 2, 3, and 5 on all segmental levels had bias (95% CI does not include zero) or/and out of the acceptable cut-off proportion (>50%). A total of 609 outliers in 9174 segmental levels’ LOA range. The inter-rater reliability was good-to-excellent in all but method 2 (0.736 (0.712, 0.759)) and method 5 (0.634 (0.598, 0.667)). ICCs of related lines to good-to-excellent reliability methods was excellent in all but only indirect line in method 1 and 4 (ICCs lie in the range from 0.8 to 0.9). Agreement and inter-rater reliability were compromised by difficulties in accurately identifying the indirect lines and reducing the vertebral rotation.
Conclusions: Following a structured protocol, intra- and inter-rater reliability was good-to-excellent for most DHI measurement methods on X-ray. However, caution should be taken when measuring used complicated method and defining anatomical landmarks during vertebral rotation. A standardized protocol to assess DHI was required in future study.