Impact of postures on Cobb angle measurements in mouse models

Abstract

Scoliosis is defined by a Cobb angle measurement that exceeds 10° from the anterior-posterior standing radiograph. Its diagnosis and management decisions rely on the stringent assessment of the curve magnitude. There are quadrupedal animal models like pigs, rabbits and rats, bipedal animal models like chickens and non-human primates. There are also guppy and zebrafish which are widely used in genetic model establishment. The mouse is suitable for either the mechanical model or the genetic model, and the genetic background is clear with a relatively high gene homology, which makes it a promising animal model for future scoliosis study. In humans, the effect of positioning error on Cobb angle measurements and the measurement error expected from variations in imaging have been investigated intensively. As there is no study that describes these two kinds of error in animal models, the study objective is to test the effect of postures on the angle measurement as well as to establish a standard for mouse imaging. In the present study, we first collected 77 mice for radiography. During the experiment, we described the criteria for a standard right posture in terms of body symmetry. We found that the incidence of scoliosis in the mouse population was around 28.6%. There was a big variation in curve magnitude as well. We took weekly X-rays for 24 mice and found a large variation in the multiple-time measurements. In the second part of the study, we collected 82 mice and designed 14 postures that may vary during imaging. The results showed that tilting of the head (>30°) and the imbalance of the pelvis greatly affected the curve magnitude with huge effect size (Glass’s delta) over 1.50. Our work exemplified the importance of standard protocol during imaging when using animal model in the scoliosis study. This is important for all imaging studies in these animals. We recommend utilizing this standard in studying various disorders of the spine.