Facteurs biomécaniques de risques de la cyphose jonctionnelle proximale

Spinal deformities such as scoliosis are a group of musculoskeletal disorders requiring surgical instrumentation in cases of severe pathological curvatures (e.g. Cobb angle > 40° for scoliosis) (Weinstein 2001; Morcuende and Weinstein 2003). Spinal instrumentation is a surgical procedure that stabilizes the spine and fuses vertebrae with implanted devices, such as metallic rods, screws and hooks. Although this treatment allows effective correction of pathological spinal curvatures (Weinstein 2001), the occurrence of postoperative complications can sometimes lead to a revision of the instrumentation. The first cause of revision surgery is the proximal junctional kyphosis (PJK) (Schairer, Carrer et al. 2013), having a prevalence between 20% and 43% (Yang and Chen 2003; Yagi, King et al. 2012). PJK appears as a hyperkyphosis of non instrumented proximal vertebrae. Several retrospective studies have been conducted to identify its causes. Risk factors related to PJK occurrence and progression include the proximal dissection of the posterior soft tissues, the joint capsule degeneration, the pre- and postoperative sagittal balance, the thoracoplasty, the bone quality, the obesity and the stiffness of the instrumentation (Glattes, Bridwell et al. 2005; Kim, Bridwell et al. 2005; DeWald and Stanley 2006; Kim, Lenke et al. 2007; Yagi, King et al. 2012). It is also reported that PJK could be associated to the number of instrumented vertebrae, the type of proximal implant or the construct configuration at upper instrumented vertebra. However, pathomechanisms of PJK are still controversial because findings reported in the literature are sometimes contradictory and not able to isolate the effect of a specific variable on PJK. In addition, no computational study has reported the impact of several surgical variables on biomechanical indices related to PJK. The objective of this Master project was therefore to develop a biomechanical model of spinal instrumentation in order to analyze and better understand the postoperative pathomechanisms of proximal junctional spinal segment. Six surgical variables potentially increasing the risk for PJK occurrence have been analyzed. In order to achieve this objective, a multibody model was developed and validated to computationally simulate surgical instrumentations of six adult patients affected by PJK. For each case, the spinal tridimensional geometry was reconstructed using two calibrated preoperative radiographs (postero-anterior and lateral). In these models, each vertebra was