Digitization of three-dimensional spine curvature profile in adolescent idiopathic scoliosis using anatomical palpation

The need for spaced radiological follow-up of adolescents with idiopathic scoliosis (AIS) stimulates the development of radiation-free methodologies to document spinal curvature parameters. The aim of the study was to develop a methodology, referred to as A-Palp, using index finger pulp palpation to assess 3D spinal curvature in the standing position in patients and control group. To estimate repeatability for 2D/3D curvature angles, three manual palpations of spinal curvature were performed by one examiner using an index finger pulp calibrated in an optoelectronic system to acquire these curvature angles in the sagittal and frontal planes and in the 3D plane of maximum curvature. The intrarater repeatability was analysed by generalisability theory and the dependability index phi combined with a decision D-study to judge the number of desirable repetitions. The A-Palp/radiograph concurrent validity of 2D/3D apex angles was studied by linear regression and Bland-Altman plot. For the scoliosis angle in AIS patients, the phi index was excellent, above 0.9, with a standard error of measurement and minimal detectable change below 3 degrees and 9 degrees, respectively. For A-Palp/radiograph comparison, 95% of 2D and 3D measurement results were between 8 degrees and 11 degrees below and 12 degrees and 5 degrees above the radiographic apex angle, respectively, with a bias below 3 degrees. The good repeatability and concurrent validity show that this innovative radiation-free 3D methodology seems suitable for the assessment of AIS patients when the same examiner repeats the measurement two or three times according to the D-study.