Une nouvelle méthode pour estimer la torsion géométrique en scoliose idiopathique de l’adolescent

Adolescent idiopathic scoliosis (AIS) is a three dimensional (3D) deformity of the spine. For  most patients, no surgical intervention is required. However, for patients with severe deformities,  surgery is often recommended.  Postero-anterior (PA) and antero-posterior (AP) x-rays are the most common modality for  viewing and evaluating this deformity. From this imaging modality, clinical indices such as the  Cobb angle can quantify and evaluate the severity of AIS. Clinical decision making is often  based on this descriptor. However, the descriptors based on spinal radiographies are two- dimensional (2D) by nature. Therefore, they do not fully describe the deformity in AIS due to its  three-dimensional (3D) nature.  Poncet et al. have studied and presented geometric torsion as a 3D descriptor of AIS. This index  measures a curve’s tendency to twist out of a plane. However, the method presented in their  study is susceptible to errors from an imperfect 3D spinal reconstruction due to the local  approach taken and is presented in a qualitative fashion.  Hence, the objective of this study is to evaluate a new method of estimating geometric torsion in  AIS employing parametric curve fitting techniques based on local arc-length approximations.   The first study attempts to evaluate the sensitivity of the presented method of estimating  geometric torsion against noisy data or 3D reconstruction errors. Two clinical studies will then  present this descriptor as a quantitative measurement of AIS and will attempt to identify potential  new sub-groups and demonstrate the clinical relevance of these new sub-groups.  vi   The first study evaluated the robustness of the new method in estimating geometric torsion in the  presence of reconstruction errors. This study demonstrated that the new method is robust to 3D  spinal reconstruction errors and achieves quantitative measures in a global fashion.    The second study evaluated this new method of estimating geometric torsion in patients with  Lenke type 1 deformities. This study identified two sub-groups based on torsion values, a high  torsion and a low torsion group. These two sub-groups showed differences in the orientation of  the planes of maximum deformity (PMC) in the thoraco-lumbar segment of the spine with the  high torsion group having greater values.  The last study evaluated the surgical results of patients with Lenke type 1 deformities having  been sub-classified in high and low torsion groups. This study showed differences in TLL PMC  with the high torsion group of patients having higher values pre and post-operatively,  These studies present a novel method of estimating geometric torsion in AIS and present this 3D  descriptor quantitatively. They have demonstrated the existence of new sub-groups within  current classification systems that were previously undetected and have shown the clinical  relevance of this new method of estimating geometric torsion in AIS. This project contributes  towards the development of new 3D indices for AIS and opens the door to potential new 3D  classifications.

Keyphrases: Adolescent idiopathic scoliosis, Classification, Geometric torsion, Parametric curve fitting