Biomechanical analysis of osteoporotic spines with diseases using CT-based finite element method

Mazlan, Muhammad Hazli (2016) Biomechanical analysis of osteoporotic spines with diseases using CT-based finite element method. PhD thesis, Kyushu University, Japan.

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Abstract

The eventuality of recurrent fractures on the adjacent level of fractured vertebra is becoming prevalent in this era. To date, the underlying cause of this phenomena is either due to low bone quality or adverse geometrical changes of the vertebral body, as a result of osteoporosis and vertebral compression fractures (VCFs). To further investigate the determinant factor of this phenomenon, an image based finite element analysis (FEA) was used to scrutinize the biomechanical response of spines that have been afflicted by different types of spinal deformities, namely; wedge-shaped, fish-shaped and plana-shaped vertebrae. The evaluation was made based on its structural integrity in accordance to stress and strain distributions, and fracture risks prediction. These findings were then further corroborated by evaluating other associating factors such as kyphotic deformity angle and bone density distribution in order to find the underlying cause of this symptom. The results showed that the low bone density due to osteoporosis has become the dominant factor in inciting the risks of subsequent fractures on the adjacent vertebrae. This is based on the contradictory relation between the number of the failure elements distributions and the degree of the kyphotic deformity angle, as described by the wedge-shaped vertebral fracture model. Obviously, the most highly structural deformed vertebra still could withstand any kinds of high input loads, provided that its structural formation is still intact and has not severely affected by osteoporosis. The high incidence of subsequent fractures following Balloon Kyphoplasty (BKP) in both the augmented and adjacent vertebrae is quickly becoming a clinically unresolvable complication. The underlying cause of this phenomenon is still unknown and to date medical practitioners are still unable to explain the fundamental cause of this phenomenon. To verify this claim, an image-based finite element analysis was used to investigate the effectiveness of BKP treatment of pre-operative and post-operative osteoporotic spine models. The three-dimensional (3D) non-linear finite element (FE) models of the thoracolumbar spine (T11-L3) were developed from CT-scan images. The biomechanical responses were evaluated based on the models’ load sharing mechanisms, load transfer mechanisms, stiffness recovery, stability, and kyphotic deformity restoration. The margin of safety for each of the models was evaluated under incrementally increased loads (1-10kN). This margin would be determined based on the fracture risk evaluation in accordance to the associated onset fracture load. The results showed that the BKP procedures play a significant role in enhancing the structural integrity of the treated spine by lowering the effect of the bone fracturing and optimizing the biomechanical alterations up to its pre-fracture level. However, the phenomenon of high incidence of vertebral bone failures on the augmented and its neighboring vertebrae indicates that the osteoporosis severity is the most influential factor in determining the sufficiency of the BKP treatment. Cage subsidence, pedicle screw loosening and instability are the most prevalent posterior lumbar interbody fusion (PLIF)-related complications. These may be attributed to interrelated mechanical, biomechanical and environmental factors. Current advancement in medical treatment has paved the way for the implementation of unilateral cages in an oblique position to overcome unintended mechanical and clinical shortcomings. To verify this claim, an imagebased finite element analysis (FEA) was used to evaluate several factors; cage subsidence, screw loosening and PLIF construct stability via stress profiles, fracture risk prediction and range of motion (ROM) evaluations in the different type of cage materials and cage orientations. Obviously, obliquely-placed unilateral fusion cage constructs with PI exhibited the most reliable biomechanical constructs by showing the smallest ROM and producing the minimal distortion stress at the cage-endplate and pedicle screw-bone interfaces. Moreover, these results also showed good agreement with the results obtained using fracture risks assessments by showing the lower numbers of deformation elements at the both contact interfaces in normal and traumatic events. In conclusion, biocompatible cage materials and structural symmetry are the most important criteria in achieving biomechanical advantage in PLIF surgery.

Item Type:Thesis (PhD)
Subjects:R Medicine > RC Internal medicine
Divisions:Faculty of Electrical and Electronic Engineering > Department of Electronic Engineering
ID Code:9120
Deposited By:Mr. Mohammad Shaifulrip Ithnin
Deposited On:09 May 2017 15:32
Last Modified:09 May 2017 15:32

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