Development of a vertebral endplate 3-D reconstruction technique.

The increase of low back problems has stimulated the development of different analysis and evaluation techniques. Among these methods, the direct linear transformation (DLT) technique is commonly used to reconstruct the spine in three dimensions by means of its known image coordinates on radiographs. Despite its efficiency and precision, general reconstruction of some standard anatomical landmarks (7-11) does not give all the necessary data for a detailed analysis of the intrinsic geometrical characteristics of lumbar vertebrae. Thus, in order to obtain such geometrical information a three-dimensional (3-D) reconstruction vertebral endplate contour technique has been developed. This technique involves 1) iterative optimization and reconstruction processes of the vertebral endplate centroid and 2) 3-D reconstruction of vertebral endplate contour. Validation based on mathematical simulations demonstrated that two or three iterations are necessary to correct (within 2 mm) the endplate centroid position for simulated error higher than 10 mm. Other validations based on 3-D reconstructions of a chamfered tube and a dry vertebra contours of known dimensions have given mean errors of 2 mm. Application on a healthy subject demonstrated the potential of this 3-D reconstruction technique. Finally, 3-D data obtained on vertebral endplates would allow the development of new clinical measurements that could be used to evaluate the lumbar spine geometrical behavior and orthoses biomechanical effects.