How can directional and fluctuating asymmetry help in the prognosis of scoliosis along the course of the condition?

Fluctuating asymmetry (FA) is an indicator of developmental instability referred to random deviations from mean asymmetry. That average asymmetry is the directional asymmetry (DA), which, in the particular case of adolescent idiopathic scoliosis (AIS), corresponds to a right thoracic and left lumbar curves. Investigating the presence of FA and DA in AIS has never been done, and it is a key element of the pathophysiology of the scoliotic condition. Thirty-six X-rays of patients with AIS were digitized and analysed using Geometric Morphometric analyses to test for both statistical effects. The individual FA score for each patient was calculated using Procrustes ANOVA and a methodology based on the components of shape was used to estimate the individual DA score. DA is a stronger effect than FA (2.12 to 1), as it has been found in other clinical conditions. The individual DA score, with an effect size of 0.58, is a better predictor of the Cobb angle than FA score. The methodology presented in this paper to estimate DA score is a valid approach in the study of asymmetries in AIS. FA should be correlated in future studies with environmental covariates to serve as a variable in the medical prognosis, while DA will serve as a good predictor of the Cobb angle during the course of the condition, avoiding the abuse of X-rays. This potential use of DA should be tested on 3D shape due to the three-dimensional clinical presentation of AIS.

Geometric morphometrics of adolescent idiopathic scoliosis: a prospective observational study.

OBJECTIVE: Adolescent idiopathic scoliosis is the most prevalent type of scoliosis, and its consequences on the human torso have not been deeply studied. In spite of being a 3D condition, clinical management is circumscribed to 2D images among health-care professionals. GMM is a well-recognized tool in the study of 3D shape and symmetry. METHODS: Twenty-four subjects with AIS and 24 controls were subjected to surface scan. Digitization and shape data were extracted and submitted to GMM analysis. 3D shape and asymmetry were correlated with Cobb angle in subjects with X-ray availability. Comparisons of mean shapes were done between each group and its symmetric average shape and between each group at two states: initial and 6 months after. RESULTS: AIS and controls show similar areas of asymmetry, being significantly higher in quantity in AIS (PD = 0.045; PD 0.037; p < 0.001). Significant correlation was observed between Cobb angle and Procrustes asymmetry (r = 0.38; p = 0.01) as happened with 3D shape (r = 0.11; p < 0.001). No significant changes were observed in the 3D shape of both groups 6 months after (AIS, p = 0.51; control, p = 0.304). CONCLUSION: The greater asymmetry observed in AIS was expectable, but the similarity of areas of asymmetry in both groups made us suspect of directional asymmetry in the human torso that could explain the high prevalence of right scoliosis observed in nature. The shape of the torso and the asymmetry should be considered as variables to study in AIS due to its correlation with Cobb angle. Progression of the deformities was not observed in our study, maybe due to short-term follow-up.