Measurement of spinal kyphosis - Implications for the management of Scheuermann's kyphosis

Study Design. Repeat clinical radiograph measurement of kyphosis was performed. Objectives. To evaluate precision in kyphosis measurement, the presence of intra- and interobserver error, and the effect of endplate selection and curve magnitude on error. Summary of Background Data. One study thus far has shown no interobserver difference in readings and an error interval of +/-11degrees. Methods. Four experienced examiners measured 30 radiographs of varying angles of kyphosis without preselected end vertebrae twice using the Cobb method. Results. The mean intraobserver variance was 4.3degrees (95% confidence interval, +/-9.6degrees). One examiner had significantly better precision (P = 0.02) than the other examiners, who had no significant difference among them (P = 0.41). This examiner's mean intraobserver difference was 2.3degrees (95% confidence limit, +/-6.2degrees). The 95% confidence limit for the interobserver difference was +/-8.7degrees. The vertebral error index did not have a rank correlation with precision between readings. Magnitude of curve did not correlate with variance in measurement. Conclusions. The broad range in intra- and interobserver differences in the measurement of kyphosis should be taken into account in making management decisions or evaluating the success or failure of a treatment program. Careful technique in measurement may allow for improvement in individual precision.