NUMERICAL ANALYSIS (FINITE ELEMENT METHOD) OF BRACE EFFECTS ON THE ADOLESCENT IDIOPATHIC SCOLIOSIS DURING 24 HOURS

In the adolescent idiopathic scoliosis (AIS) treatment, a brace is prescribed to the patients who have 20 to 45° curves on their spines to prevent the disorder's advancement. For the analysis of Milwaukee brace effects during time, finite element models (FEMs) of the spine (the thoracolumbar region) and the ribcage (contained 10 pairs of the ribs and the sternum) were prepared for two patients. For modeling the spine part, a new element was used in which a disc (as viscoelastic 3D beam) and a vertebra (as rigid link) were modeled as an element and the ribs and the sternum modeled by 3D elastic beams. The gravity, Milwaukee brace constraints and the forces of the brace's different regions were considered as the FEM boundary conditions. By running the patients' FEMs, the spine deformities of each patient were predicted for 24 h. For AIS patients, the brace should not only correct the deformity of the spine by inserting the forces, but also support the spine from the bending moments being caused by the gravity forces in different spine regions. Moreover, in studying scoliosis pathomechanisms, the stresses in different levels of the vertebra are important. Therefore, the bending moments and compressive stresses, caused by the gravity forces, were calculated in each level of the vertebra and the brace forces effects on them were analyzed. According to the patients' FEM responses, for the female patient: lumbar scoliosis was increased, thoracic scoliosis was decreased and kyphosis and lordosis were increased, and for the male patient: lumbar scoliosis was increased, kyphosis was increased and lordosis was decreased. In standing position, the brace forces reduced the bending moment and the compressive stress in vertebral levels of thoracolumbar region for the female patient and increased them for the male patient.