PAPER 030: A CREATIVE APPROACH TO BLINDING OF OUTCOMES: THE BLINDING OF FEMORAL FIXATION (BOFF) STUDY

Abstract

Purpose: Although blinding of outcome assessors is crucial to minimize bias in clinical trials, the majority of surgical trials do not blind these individuals in part due to practical difficulties inherent in surgical interventions. We devised and tested techniques to blind outcome assessors in trials of femoral neck fracture fixation.

Method: We developed three techniques to mask radiographs of femoral neck fractures fixated with cancellous screws or dynamic hip screws: Blackout, Subtraction, and Overlay. 50 orthopaedic trauma surgeons assessed 32 radiographs blinded with each of these techniques. We considered:

1. The ability to mask the surgeons (the proportion of radiographs in which the surgeons were able to correctly identify the implant and the Bang Blinding Index);

2. Surgeons’ ability to accurately rate the quality of reduction in blinded images;

3. Surgeons’ perceptions of difficulties rating the blinded images.

Results: All three techniques achieved low proportions of correct identification of cancellous or dynamic screws (14.9% for Blackout, 26.9% for Subtraction, 22.1% for Overlay) and high proportions of “don’t know” responses (72.3%, 48.4%, 52.8% respectively). The Bang Blinding Indices were close to 0 (perfect blinding) for all three techniques (−0.024 to 0.008). The interrater reliability of quality of reduction in the blinded images (ICC = 0.55 – 0.57) was similar to the reliability of the unblinded radiographs (ICC = 0.60). Surgeons perceived the Overlay images as much more difficult to rate in 6.9% of radiographs, compared with 9.7% of Subtraction images (p=0.25) and 28.0% of Blackout images (p< 0.001).

Conclusion: Three techniques of blinding radiographs of femoral neck fractures successfully mask surgeons to the type of implant fixated, do not compromise reliability of reduction ratings, and do not make the rating process substantially more difficult. Trialists should explore creative approaches such as these to blind as many individuals as possible when designing trials, and should incorporate rigorous approaches to testing the success of blinding.