Measurement reliability of dynamic x-rays of the cervical spine: an experimental model

A blind test of measurement reliability was performed in vitro using lateral x-rays of cervical vertebrae. Dry specimens of C3 and C4 were mounted in a movable frame and flexion/extension was simulated. Lateral x-rays were taken for each degree from 15 degrees flexion to 15 degrees extension. Then the x-rays were measured by four raters. The results show a high level of absolute measurement error. This suggests caution in accepting existing literature data on cervical x-ray measurements unless some indicator of the personal measuring accuracy of the rater is specified. The procedure described in this paper can be used to ascertain such accuracy.