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 ...

Few biomechanical data exist regarding whether the polyetheretherketone (PEEK) spacer or titanium spacer is better for posterior lumbar interbody fusion (PLIF). This study evaluated the biomechanical influence that these types of spacers with different levels of hardness exert on the vertebra by using finite element analysis including bone strength distribution. To evaluate the risk of spacer subsidence for PLIF, we built a finite element model of the lumbar spine using computed tomography data of osteoporosis patients. Then, we simulated PLIF in L3/4 and built models with the hardness of the interbody spacer set as PEEK and titanium. Bones around the spacer were subjected to different load conditions. Then, fracture elements and some stress states of the two modalities were compared. In both models of PLIF simulation, fracture elements and stress were concentrated in the bones around the spacer. Fracture elements and stress values of the model simulating the PEEK spacer were significantly smaller compared to those of the titanium simulation model. For PLIF of osteoporotic vertebrae, this suggested that the PEEK spacer is in a mechanical environment less susceptible to subsidence caused by microfractures of bone tissue and bone remodeling-related fusion aspects. Therefore, PEEK spacers are biomechanically more useful.

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