Blinded reading of radiographs increases the frequency of errors in vertebral fracture detection

We examined the effect of blinding X‐rays to film sequence and patient identity on vertebral fracture detection. A sample of 50 postmenopausal women with low bone density and two sets of spine X‐rays 3.6 years apart was selected; based on prior morphometric studies, about half of the women had experienced new fractures after the initial film. New morphometric and semiquantitative radiologist readings were each performed twice: blinded and unblinded. For morphometry, incident fractures were defined as vertebral height decreases of more than 15% compared with the initial film. The incidence was slightly higher when blinded versus unblinded (5.6 vs. 5.3% of all vertebrae for morphometry, and 9.7 vs. 8.7% for the radiologist), but these differences were not significant. The error rate was investigated by examining the frequency of “fracture reversals”—vertebrae identified as fractured on the initial film but not on the later film. Agreement between blinded and unblinded readings was generally greater than 80% for fractures but less than 10% for “fracture reversals,” suggesting that reversals are not true events but random errors. The number of reversals was higher when the radiologist was blinded (2.1% of all vertebrae vs. 0.8% when unblinded; p = 0.07). The number of vertebrae with increases greater than 15% in size over time was also greater when morphometry readings were blinded versus unblinded: 0.8 versus 0% ( p < 0.05). Although these errors are small, they are similar in magnitude to the annual fracture incidence in many populations. These data show that blinding X‐rays to sequence offers no advantages, increases the frequency of errors, and may inflate incidence rates. We conclude that the assessment of X‐rays for vertebral fractures in clinical trials should not be performed with the evaluator blinded to the sequence of the X‐rays. (J Bone Miner Res 1996;11:1793–1800)