Noninvasive estimation of internal spinal alignment in patients with adolescent idiopathic scoliosis using PCdare and back shape asymmetry

Optical 3D surface scanning is used increasingly to assess spinal deformity in patients with adolescent idiopathic scoliosis (AIS), largely because it avoids additional radiation burden. However, such approaches generally underestimate the extent of the abnormality. Improving the accuracy of such estimates requires a deeper understanding of AIS and its effect on back shape. We present a unique platform with publicly available code that contains noninvasive and nonionizing approaches to estimating the Cobb angle of the primary curve, called primary Cobb angle (pCA) and internal spinal alignment (ISL) in patients with AIS. Our approaches use asymmetries of the back shape during upright standing, the Adam's forward bending test, bending forward, and lateral bending. The results have revealed strong (0.75 [0.53, 0.87]) to excellent (0.91 [0.81, 0.96]) correlations [95% confidence interval] and a median pairwise absolute error (IQR) of 3.4° (6.8°) between the estimated pCAs and clinical gold-standard assessments in 30 patients. The correlations (IQR) between estimated shape of ISLs and their references were very strong (0.87 (0.24)) to excellent (0.94 (0.03)), and the median root mean square error (IQR) between estimated and reference ISL was 6.9 mm (3.3 mm). These results indicate confidence both in the use of 3D scanning using a "back-shape-to-spine" approach and in the establishment of optical 3D surface scanning approaches for scoliosis screening and monitoring in clinical practice.