Facet tropism: comparison of plain film and computed tomography examinations

This study compares the findings of plain film X-ray and computed CT examination in the diagnosis of facet orientation and the presence of tropism. Twenty consecutive patients having lumbar disc disease with sciatica were studied utilizing plain X-ray as well as CT scanning. A chiropractic radiologist read the films to determine if facet facings were sagittally, semi-sagittally or coronally oriented on both CT and plain X-ray study. CT was accepted as the most accurate method to determine the true facet orientation, and plain X-ray interpretation of facet orientation was compared to the CT reading. There was a statistically significant relationship in diagnosing tropism between plain film X-ray and CT readings, with a predictive accuracy that ranged from 58-84% across the three segmental levels. However, the exact concordance of plain film X-ray and CT readings for right and left facet facings was very low. This raises the question of how the profession defines diagnostic accuracy.