Measurement of rib vertebral angle difference. Intraobserver error and interobserver variation.

STUDY DESIGN: The rib vertebral angle difference was measured on 50 juvenile scoliosis radiographs. Three observers measured each radiograph independently and on three separate occasions to determine interobserver and intraobserver error.

OBJECTIVE: To determine the interobserver and intraobserver error in measuring the rib vertebral angle difference.

SUMMARY OF BACKGROUND DATA: The rib vertebral angle difference is a commonly used measurement, the reliability of which has not been tested rigorously.

METHODS: Fifty standing radiographs of juvenile scoliosis were measured. All patients were Risser 0 at the time of measurement. All angles were measured by the method of Mehta using the same protractor and apical vertebra to avoid confounding variables. Three surgeons individually measured the 50 radiographs randomly and on three separate occasions. All markings were erased before remeasurement.

RESULTS: The intraobserver error was determined to be 4.4 degrees. The interobserver error was 3.6 degrees. The interobserver accuracy was 6.2 degrees.

CONCLUSIONS: The rib vertebral angle measurement is highly reproducible and is a valid measurement.