3D PERSONALIZED RADIOGRAPHIC RECONSTRUCTION OF THE HUMAN PELVIS

The pelvis is an essential element in the study of scoliosis since it constitutes the base of the spine and its orientation may affects post ural balance. In order to study the role of the pelvis in the evolutio n and treatment of this disease, a new technique for the 3D personalis ed reconstruction of the pelvis was developed. It consists in identify ing and digitizing 19 pelvic anatomical landmarks on posters-anterior and lateral x-rays and to reconstruct them in 3D with two techniques: the DLT algorithm developed by Marzan (1976) and, for 6 of the 19 land marks, an adaptation of it called DLT with confidence coefficients. Th e latter takes into account the confidence given to the identification of the landmarks on each x-rays. Two methods were used to validate th e reconstruction of the pelvis, The first one, used for 11 scoliotic p atients and ? dry pelvis specimens, consists in applying the reconstru ction algorithm in an inverse way on the 3D coordinates of the reconst ructed landmarks to obtain their 2D retroprojection on the x-ray plane s, and thus comparing the retroprojected coordinates with the 2D digit ized coordinates. The second method consists in measuring a dry pelvis specimen and comparing the 3D measured landmarks with the ones recons tructed with the x-rays of this specimen, For the first validation, re sults have shown that the lowest retroprojection errors (less than 2.5 +/- 2.6 mm) for the scoliotic patient group are located on the superi or base of the sacrum, on the sacral curve and on the acetabula, while the highest (6.4 +/- 7.2 mm) were on the iliac crests. For the dry sp ecimens, the retroprojection errors were below the millimeter. The sec ond validation method showed 3D differences of 2.4 +/- 1.2 mm between measured and reconstructed landmarks of a dry specimen, which is of th e same order of magnitude as what is reported in the literature for ve rtebrae. The reconstruction of the pelvis is thus considered adequate and its graphical wireframe representation allows to visualise and mea sure clinical indices concerning its orientation in space. Moreover, t he reconstructed landmarks will be used to develop a personalised geom etrical and mechanical model of the pelvis which, when integrated with the one for the spine and rib cage, will allow to simulate in a more realistic manner the biomechanical behaviour of the scoliotic trunk, p articularly for the study of orthopaedic treatments with braces leanin g on it.