Computational investigation on the aetiology of adolescent idiopathic scoliosis

Autor: Schlager, Franz Benedikt Johannes
Přispěvatelé: Wilke, Hans-Joachim, Akbar, Michael
Jazyk: angličtina
Rok vydání: 2019
Předmět:
Popis: The aetiology of scoliosis during adolescence is in most cases (85%) unknown (idiopathic). To investigate potential causes and treatments of scoliosis, a fully parametric finite element model of the spine and chest was developed. This work investigated the principle hypothesis that adolescent idiopathic scoliosis (AIS) is triggered by an asymmetrical load distribution resulting in a malformation of the bone. Furthermore, the impact of a potential asymmetry in the intrapleural pressure (IPP) distribution on the spinal shape was explored. The biomechanical aspect of the hypothesis was analysed using a subject-specific numerical model of the human spine (levels: T1-S1) and rib cage of a healthy 13-year-old male. The finite element model was generated using a self-developed program which allows a rapid semi-automatic generation of numerical models that consider the patient-specific morphology and a predefined flexibility of the main joints. The material properties of the soft-tissue were primarily extracted from literature. The material properties of the spinal segments and costovertebral joints were further optimized to fit the specific range of motion obtained from in vitro tests. In view of the close relationship between the form and function of the skeleton, the bone morphology of the spine and chest was quantified using CT data of individuals. The comparison of the bone morphology of patients, with (n = 21, 15 ± 2 years) and without (n = 48, 23 ± 12 years) AIS, revealed a characteristic morphological pattern in patients with AIS. This pattern included wedging and rotation of the vertebral bodies, differences between the right and left pedicle and facet size, as well as, asymmetrical rib cage deformities. This indicates the presence of an inherent asymmetrical stress distribution along the scoliotic spine. It should be noted, however, that in the non-scoliotic patient group a predisposition towards a characteristic scoliotic curvature was on average also observed. Simulations of various assumed intrapleural pressure distributions suggest that an asymmetrical intrapleural pressure can lead to spinal deformation patterns comparable to those seen in scoliotic spines. In particular, the pressure within the dorsal section of the rib cage had a strong influence on vertebral rotation, whereas the pressure in medial and ventral regions demonstrated a lateral displacement. An asymmetrical pressure between the left and right hemithorax resulted in lateral deviation of the spine towards the side of the reduced magnitude of negative pressure. The application of the IPP, assumed within the numerical model, resulted in a compressive force of 22.3 N in craniocaudal direction of the spine, which corresponds to 2.3 kg of organ weight. This reaction force supports the assumption that the IPP contributes in counterbalancing the weight of the intrathoracic organs. Due to the current lack of a non-invasive method to measure the IPP in vivo, clinical verification of the influence of the IPP on spinal stability remains unclear and challenging. It is known, however, that scoliosis can develop secondarily to surgical interventions of the pleura. In conclusion, the results of this study suggest that the intrapleural pressure distribution has the potential to play a key role in the development of spinal deformities. The interaction between the pleural physiology and the thorax may be an important piece in the puzzle to further understand the biomechanical in vivo condition and explain various spinal pathologies. Furthermore, the developed numerical model is suitable to simulate the biomechanics of the spine and chest. It can be a useful tool to investigate various spinal pathologies and treatment strategies.
Databáze: OpenAIRE
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