This research aimed to mechanically analyze vertebral stress concentration in one healthy subject and one subject with osteoporotic first lumbar (L1) vertebral compression fracture by using finite element analysis (FEA). We constructed three-dimensional image-based finite element (FE) models (Th12L2) by using computed tomographic (CT) digital imaging and communications in medicine (DICOM) for each patient and then conducted exercise stress simulations on the spine models. The loadings on the 12th thoracic vertebra (Th12) due to compression, flexion, extension, lateral bending, and axial rotation were examined within the virtual space for both spine models. The healthy and vertebral compression fracture models were then compared based on the application of equivalent vertebral stress. The comparison showed that vertebral stress concentration increased with all stresses in the vertebral compression fracture models. In particular, compression and axial rotation caused remarkable increases in stress concentration in the vertebral compression fracture models. These results suggest that secondary vertebral compression fractures are caused not only by bone fragility but possibly also by the increase in vertebral stress concentration around the site of the initial fracture.
Abstract-The aim of this work is to assess the biomechanical response or load transfer response between osteoporotic (with first lumbar (L1) vertebral compression fracture) and healthy vertebrae in five vertebral physiological motions namely as compression, flexion, extension, lateral bending and axial rotation. For this purpose, an image-basedheterogeneous three-dimensional patient-specific of lumbar and thoracic spinal unit (T12-L2) finite element models for healthy and osteoporotic subjects were created.The finite element analysis have shown that one of the most significant effects of osteoporosis is the tendency to produce higher stress and strain in the cancellous region of the vertebral body. The maximum stress and strain was 4.53 fold (compression) and 5.43 fold (axial rotation) higher for the osteoporotic than the healthy subject, respectively, under the similar loading activity. Uneven stress distribution patterns also have been detected in the osteoporotic vertebrae rather than the healthy vertebrae. All of these characteristicsare reflected bya reduced structural strength and bone mass which might lead to an increased risk of fracture. These results strengthen the paradigm of a strong relationship between osteoporosis and its high susceptibility to fracture.Index Terms-Biomechanics, finite element analysis, osteoporosis, vertebrae. I. INTRODUCTIONOsteoporosis is the most common disease affecting both men and women [1], and it is becoming increasingly prevalent in aging society [2]. Itsclinical significance lies in the high vulnerability and susceptibility to bone fracture [3]. It is characterized by low bone mass and micro-architectural deterioration of bone tissue [4]. Even though osteoporotic fractures can occur anywhere in the human body [5], the most prevalent fracture site is the spine [6], particularly in the elderly population [3]. In Japan, there are more than 10 million osteoporosis patients [7]. It is believed that this number will significantly increase in relation to Japan"s life expectancy continues to rise. In the United States, about 1.5 million fractures due to osteoporosis are reported annually including over 700,000 vertebral fractures with high mortality rates. It was reported that, the survival rate was 72% after one year the symptom was first detected and this figure was then drastically reduced to only 28% after five years. Therefore, early detection of osteoporotic disease play a Manuscript received May 14, 2014; revised July 14, 2014. M. H. Mazlan is with Kyushu University, Japan (e-mail: hazli.010@s.kyushu-u.ac.jp).M. Todo is with the Research Institute for Applied Mechanics, Kyushu University, Japan (e-mail: todo@riam.kyushu-u.ac.jp).Hiromitsu Takano and Ikuho Yonezawa are with the Department of Orthopedic Surgery, Juntendo University School of Medicine, Japan (e-mail: hrtakano@juntendo.ac.jp).significant role in order to improve the health quality of the community and to organize early treatment as preventive and precautionary measures.Human spine is consisted of 24 spinal ...
Abstract:Interbody fusion devices are gaining acceptance as a treatment method of mainly for disc degeneration diseases and other medical conditions. Posterior lumbar interbody fusion (PLIF) cage is used in the procedure to maintain stability and promote fusion between vertebrae. Poly lactic acid (PLA) is assumed to be the alternative material which could provide cheaper material and lower production cost. However, these implants often cause subsidence failure at the endplate, resulting in injury risk and mechanical instability during fusion. In this study, the stress behavior of PLIF cage made by two different materials, Polyether ether ketone (PEEK) and PLA; was studied using finite element method (FEM). By implementing bilateral cages between vertebral bone L4 and L5, and conducting 6 different motion activities onto the model, the stress distribution of L4-L5, and cage bodies was predicted. Simulation results predicted that the cage subsidence occurred at both materials, with an overall of higher cage-endplate stresses for PEEK, in comparison to PLA and controlled configurations. In addition, the stress distribution in PLA cage was better and the maximum von Mises stress was approximately 3 times lower than PEEK cage. Further investigation of PLA cage's mechanical properties should be done experimentally to determine the accuracy and reliability of the simulation.
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