The change in ratio of convex and concave lung volume in adolescent idiopathic scoliosis: a 3D CT scan based cross sectional study of effect of severity of curve on convex and concave lung volumes in 99 cases.

To study the effect of the degree of scoliosis, degree of hypokyphosis/lordosis and rotation of apical vertebra on individual lung volume (measured with CT scan) in asymptomatic adolescent idiopathic scoliosis (AIS) patients. Individual (right and left) lung volume, angle of kyphosis and rotation of apical vertebra, were measured in 77 asymptomatic AIS patients having right thoracic curve, using modern computed tomography (CT) scan. To compare, lung volumes were measured in 22 normal persons (control group). The ratio of "right to left lung volume (convex to concave side)" was obtained and compared among these groups. With increased Cobb's angle, ratio of convex to concave lung volume increased. For Cobb's angle more than 40 degrees, it was increased significantly (P = 0.0042). A significant degree of correlation was found between axial rotation angle of apical vertebra and right to left lung volume ratio (P = 0.0067, r = 0.271). A significant inverse correlation was found between the angle of kyphosis and right to left lung volume ratio, i.e., as the angle of kyphosis decreased the convex to concave lung volume ratio increased (P = 0.0109, r = -0.255). In asymptomatic, AIS patients, with increase in degree of curvature, and rotation of apical vertebra, the ratio of convex to concave side lung volume increases; indicating concave side lung volume is comparatively more affected (decreased) than convex side lung volume. On the other hand with decrease in the angle of kyphosis the convex to concave lung volume ratio increases indicating kyphotic angle has an inverse relation to convex to concave lung volume ratio.