Optical 3D surface scanning is used increasingly to assess spinal deformity of patients with scoliosis. However, approaches based on optical 3D scanning often underestimate the spinal deformity. To improve the accuracy of such estimates, deeper understanding is required of scoliosis and its effect on the back shape. We present the PCdare research software which registers 3D surface scans with the corresponding biplanar radiographs semi-automatically and facilitates investigations into the relationship between surface and internal modalities. PCdare revealed very strong correlations between the spinous process line and internal spinal alignment, and a median Cobb angle difference of less than 1° from the clinical gold standard. These results increase confidence in the use of 3D scanning with a “back-shape-to-spine” approach and confirm the applicability of PCdare to investigate the relationship between internal alignment and back shape in research.
