Jiro Sakamoto

Kanazawa University, Kanazawa, Ishikawa, Japan

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Publications (45)27.89 Total impact

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    ABSTRACT: Background context: Kyphotic deformity associated with vertebral fracture is believed to be a significant risk factor for additional vertebral fractures. However, previously published research is limited. Purpose: The purpose of this study was to estimate the biomechanical stresses that kyphotic deformity, with an initial vertebral fracture, place on adjacent vertebrae using three-dimensional finite element (FE) of the spine, head, and ribs. Study design: This study is based on the basic science. Methods: Total Human Model for Safety, a three-dimensional FE model of the human body, was used and adjusted to represent an elderly osteoporotic woman. The 12th thoracic vertebra (T12), which is a frequent site of osteoporotic vertebral fractures, was transformed to a wedge shape at 0°, 10°, and 20° to create a normal model, a 10° kyphosis model, and a 20° kyphosis model. Additionally, compensated postures were created for the 10° and 20° kyphosis models. Thus, five models were created: (A) a normal model, (B) a 10° kyphosis model, (C) a 20° kyphosis model, (D) a 10° kyphosis model with compensated posture, and (E) a 20° kyphosis model with compensated posture. Compressive principal stresses (CPSs) on T1-L5 in each model were calculated. Results: The highest CPS value was 7.78 MPa placed on the anterior part of the T10 vertebra in the 20° kyphosis model. In the 20° kyphosis model, the higher CPS values showed bimodal peaks at T6 and T7 in the midthoracic spine and at T10 and T11 in the two superior adjacent vertebrae. The maximum CPS values in the A, B, C, D, and E models at T10 were 3.12, 6.74, 7.78, 6.61, and 5.78 MPa. At T11, they were 1.70, 4.41, 6.45, 4.07, and 4.79 MPa. Conclusions: The existence of an initial vertebral fracture at T12 caused an increase in stress on adjacent vertebrae. Higher CPS values showed bimodal peaks in midthoracic vertebrae and in two superior adjacent vertebrae when T12 was transformed to a wedge shape in the 20° kyphosis model.
    The spine journal: official journal of the North American Spine Society 11/2014; 15(4). DOI:10.1016/j.spinee.2014.11.019 · 2.43 Impact Factor
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    ABSTRACT: Analyses of the bone mass alone of osteoporotic vertebrae are not sufficient to predict fracture risks and assess the recovery of bone strength during drug treatment. Instead, finite element analyses (FEAs) is superior, because changes in the vertebral strength are strongly dependent on the inner vertebral stress distribution, which is related to the individual bone shape and bone density distribution in cancellous and cortical region. To investigate how FEAs can detect drug effects, we performed patient-specific FEAs of the first lumbar vertebra of osteoporotic patients at five time points (before therapy, and after 6 and 12 months and 2 and 3 years of therapy) during a 3-year drug treatment with alendronate and vitamin D, in four osteoporotic female patients in this study. The FEAs revealed notable decreases in the compressive principal strains in cancellous bone, but these decreases did not necessarily correspond to increases in the bone densities. In addition, statistical analyses by Friedman's test (nonparametric analysis) showed that evaluation based only on the average compressive principal strains over the 3-year treatment identified drug effects significantly, suggesting that compressive principal strain is an useful indicators for monitoring drug effects. Our data implied that compressive fracture of the vertebrae may be prevented as a result of the drug treatment, in a manner that was optimally detectable by patient-specific FEAs.
    Journal of Biomechanical Science and Engineering 01/2011; 6(4):248-261. DOI:10.1299/jbse.6.248
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    ABSTRACT: Patient-specific nonlinear finite element analysis (FEA) is promising for evaluating the recovery of vertebral strength. Vertebral strength is closely related to inner vertebral stress distribution and is used to assess the fracture risk for individual osteoporotic patients during drug treatment. Moreover, stress distribution is affected by individual bone shape, bone density distribution and nonlinear behavior of the mechanical properties of bone. To investigate the effectiveness of FEA considering these factors for the evaluation of drug treatment effects, patient-specific nonlinear FEAs of the first lumbar vertebrae in patients undergoing a 3-year drug treatment were performed. Changes in fracture load and distribution of failure elements in the FE models at four time points (before therapy, and after 6 and 12 months and 3 years of therapy) were compared with those of average bone density. The FEAs demonstrated that failure elements decreased notably, and fracture load increased gradually by the 3-year time point, suggesting that the vertebrae were strengthened as a result of drug treatments. Furthermore, statistical tests indicated that mechanical evaluation using the nonlinear FEAs is more sensitive for evaluating drug effects on osteoporotic bone than assessments based on average bone density.
    Journal of Biomechanical Science and Engineering 01/2010; 5(5). DOI:10.1299/jbse.5.499
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    ABSTRACT: Osteoporosis can lead to bone compressive fractures in the lower lumbar vertebrae. In order to assess the recovery of vertebral strength during drug treatment for osteoporosis, it is necessary not only to measure the bone mass but also to perform patient-specific mechanical analyses, since the strength of osteoporotic vertebrae is strongly dependent on patient-specific factors, such as bone shape and bone density distribution in cancellous bone, which are related to stress distribution in the vertebrae. In the present study, patient-specific general (not voxel) finite element analyses of osteoporotic vertebrae during drug treatment were performed over time. We compared changes in bone density and compressive principal strain distribution in a relative manner using models for the first lumbar vertebra based on computer tomography images of four patients at three time points (before therapy, and after 6 and 12 months of therapy). The patient-specific mechanical analyses indicated that increases in bone density and decreases in compressive principal strain were significant in some osteoporotic vertebrae. The data suggested that the vertebrae were strengthened structurally and the drug treatment was effective in preventing compression fractures. The effectiveness of patient-specific mechanical analyses for providing useful and important information for the prognosis of osteoporosis is demonstrated.
    01/2010; 3(1):31-40. DOI:10.1016/j.jmbbm.2009.03.001
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    ABSTRACT: Hip resurfacing is becoming a popular procedure for treating osteonecrosis of the femoral head. However, the biomechanical changes that occur after femoral resurfacing have not been fully investigated with respect to the individual extent of the necrosis. In this study, we evaluated biomechanical changes at various extents of necrosis and implant alignments using the finite element analysis method. We established 3 patterns of necrosis by depth from the surface of femoral head and 5 stem angles. For these models, we evaluated biomechanical changes associated with the extent of necrosis and the stem alignment. Our results indicate that stress distribution near the bone-cement interface increased with expansion of the necrosis. The maximum stress on the prosthesis was decreased with stem angles ranging from 130° to 140°. The peak stress of cement increased as the stem angle became varus. This study indicates that resurfacing arthroplasty will have adverse biomechanical effects when there is a large extent of osteonecrosis and excessive varus or valgus implantation of the prosthesis.
    The Journal of arthroplasty 10/2009; 25(8):1282-9. DOI:10.1016/j.arth.2009.09.002 · 2.67 Impact Factor
  • J. Sakamoto · Y. Nakada · H. Murakami · N. Kawahara · J. Oda · K. Tomita · H. Higaki ·
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    ABSTRACT: Mechanical stress analysis of vertebral bone is required to determine compressive strength of vertebra for osteoporosis patients in clinical situation of orthopedics. Stress occurred in vertebrae depend on condition of musculoskeletal system of spine. Spine structure is mainly constructed of many vertebrae and flexible intervertebral disks, and it is unstable by itself under standing condition. Supporting by erector muscles and ligaments keep the spine standing condition, so that loading condition of each vertebra depend on the muscle and ligament forces. Biomechanical simulation of musculoskeletal model taking into account of muscle and ligament forces and intervertebral joint forces is necessary to determine the loading condition for vertebral stress analysis. Commercial software to deal with the musculoskeletal system, e.g. AnyBody Modeling System (AnyBody Technology Inc.), is available nowadays, and it has been applied to clinical, ergonomic or sport biomechanics problem. Spine kyphosis is often caused by compression fracture of osteoporotic vertebra, because shape of the fractured vertebra is sphenoidal with sharp anterior side of vertebral body. Spine kyphosis makes gravity center of trunk shift to anterior side, and then intervertebral joint moment due to trunk weight increase. Additional compression fracture is concerned at adjoining vertebrae to the fractured one in the kyphotic spine. In this study, musculoskeletal simulation model with spine kyphosis was created by using AnyBody Modeling System considering compensation posture due to kyphosis. Kyphosis patient used to have compensation posture to recover body balance and face up. Intervertebral joint forces and muscle forces of the model were computed, and then influence of the kyphosis on the intervertebral joint force at adjoining joints was discussed comparing between kyphosis and intact model. Furthermore, influence of the compensation posture on muscle forces related to spine was considered.
    IFMBE proceedings 01/2009; 23. DOI:10.1007/978-3-540-92841-6_393
  • Shinobu SAKAI · Juhachi ODA · Shigeru YONEMURA · Jiro SAKAMOTO ·

    Journal of Computational Science and Technology 01/2008; 2(4):609-619. DOI:10.1299/jcst.2.609
  • J. Sakamoto · Y. Umemoto · T. Kabata · D. Sakagoshi · J. Oda · K. Tomita ·

    Journal of Biomechanics 12/2007; 40. DOI:10.1016/S0021-9290(07)70181-1 · 2.75 Impact Factor
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    ABSTRACT: Closing-opening correction (COC) osteotomy is a useful procedure for severe angular kyphosis. However, there is no previous research on the reconstructed vertebrae with kyphotic malalignment in the presence of osteoporosis. Finite-element (FE) analysis was performed to estimate the biomechanical stress with both osteoporotic grades and corrective kyphotic angles during COC osteotomy for osteoporotic angular kyphosis. FE models of COC osteotomy were created by changing three major parameters: (1) grade of osteoporosis; (2) kyphotic angle; and (3) compensated posture when standing still. Osteoporosis was graded at four levels: A, normal (nonosteoporotic); B, low-grade osteoporosis; C, middle-grade osteoporosis; D, high-grade osteoporosis. The kyphotic angle ranged from 0 degrees as normal to 15 degrees and 30 degrees as moderate and severe kyphosis, respectively. FE analyses were performed with and without assumed compensated posture in kyphotic models of 15 degrees and 30 degrees . Along each calculated axis of gravity, a 427.4-N load was applied to evaluate the maximum compressive principal stress (CPS) for each model. The CPS values for the vertebral element were the highest at the anterior element of T10 in all FE models. The maximum CPS at T10 increased based on the increases in both the grade of osteoporosis and the kyphotic angle. Compensated posture made the maximum CPS value decrease in the 15 degrees and 30 degrees kyphotic models. The highest CPS value was 40.6 MPa in the high-grade osteoporosis (group D) model with a kyphotic angle of 30 degrees . With the normal (nonosteoporotic) group A, the maximum CPS at T10 was relatively low. With middle- and high-grade osteoporosis (groups C and D, respectively), the maximum CPS at T10 was relatively high with or without compensated posture, except for the 0 degrees model. Lack of correction in osteoporotic kyphosis leads to an increase in CPS. This biomechanical study proved the advantage of correcting the kyphotic angle to as close as possible to physiological alignment in the thoracolumbar spine, especially in patients with high-grade osteoporosis.
    Journal of Orthopaedic Science 08/2007; 12(4):354-60. DOI:10.1007/s00776-007-1144-z · 0.94 Impact Factor
  • Shinobu Sakai · Juhachi Oda · Shigeru Yonemura · Jiro Sakamoto ·
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    ABSTRACT: In the United States and Japan, baseball is a very popular sport played by many people. However, the ball used is hard and moves fast. A professional baseball pitcher in good form can throw a ball at up to 41.7 m/s (150km/hr). If a ball at this speed hits the batter, serious injury is quite likely. In this paper we will describe our investigations on the impact of a baseball with living tissues by finite element analysis. Baseballs were projected at a load cell plate using a specialized pitching machine. The dynamic properties of the baseball were determined by comparing the wall-ball collision experimentally measuring the time history of the force and the displacement using dynamic finite element analysis software (ANSYS/LS-DYNA). The finite element model representing a human humerus and its surrounding tissue was simulated for balls pitched at variable speeds and pitch types (knuckle and fast ball). In so doing, the stress distribution and stress wave in the bone and soft tissue were obtained. From the results, the peak stress of the bone nearly yielded to the stress caused by a high fast ball. If the collision position or direction is moved from the center of the upper arm, it is assumed that the stress exuded on the humerus will be reduced. Some methods to reduce the severity of injury which can be applied in actual baseball games are also discussed.
    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 01/2007; 73(734):1177-1182. DOI:10.1299/kikaia.73.1177
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    ABSTRACT: Bisphosphonate prevents the fracture by controlling the function of osteoclasts and inhibiting bone absorption powerfully for osteoporosis. It is shown clinically that both alendronate and risedronate reduce postmenopausal osteoporosis patient's vertebral and nonvertebral fractures. Recently it became clear that bisphosphonate not only reduces bone absorption, but also improves bone quality such as bone microarchitecture and material properties. Furthermore, we showed using finite element analysis that internal use of bisphosphonate reduces strain of the cancellous bone inside vertebral body within one year, and notably decreases the region of high strain which is easy to break. Internal use of bisphosphonate improves the bone density distribution inside vertebral body, and strengthens the structure of load support of the spine. The structural improvement of spine leads to prevention of fracture.
    Nippon rinsho. Japanese journal of clinical medicine 10/2006; 64(9):1651-6.
  • Juhachi Oda · Jiro Sakamoto · Kenichi Sakano ·
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    ABSTRACT: A woodpecker strikes its beak toward a tree repeatedly. But, the damage of brain or the brain concussion doesn't occur by this action. Human cannot strike strongly the head without the damage of a brain. Therefore, it is predicted that the brain of a woodpecker is protected from the shock by some methods and that the woodpecker has the original mechanism to absorb a shock. In this study, the endoskeltal structure, especially head part structure of woodpecker is dissected and the impact-proof system is analyzed by FEM and model experiment. From the results, it is obvious that the woodpecker has the original impact-proof system as the unique states of hyoid bone, skull, tissue and brain. Moreover it is considered that woodpecker has the advanced impact-proof system relating with not only the head part but also with the whole body.
    JSME International Journal Series A 07/2006; 49(3):390-396. DOI:10.1299/jsmea.49.390 · 0.29 Impact Factor
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    ABSTRACT: Osteoporosis is serious medical issue to be solved in aging society. There are no less than 10 million osteoporosis patients in Japan. Osteoporosis causes frequently bone compressive fracture in lower vertebrae. It is important to estimate a fracture risk and provide adequate treatment in early stage of osteoporosis. However, bone mineral density is quantified by Dual Energy X-ray Absorptiometry (DEXA) in current clinical diagnosis of osteoporosis, mechanical factor such as bone strength, which is essential to evaluate bone fracture risk, is not considered. In this study, we evaluated the fracture risk of osteoporosis patient's vertebrae by patient-specific finite-element (FE) analysis in static loading condition. We used "Mechanical Finder (RCCM, Co., LTD.)" that was computer software for bone strength analysis considering individual bone shape and density distribution based on Computer Tomography (CT) images. Furthermore, we also tried to evaluate the fracture risk by dynamic FE analysis to reflect more severe loading conditions. Availability of dynamic analysis was investigated in comparison with the results of the static analysis. At last, efficiency of proposed mechanical evaluation method for vertebral osteoporosis was discussed.
    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 02/2006; 72(714):255-262. DOI:10.1299/kikaia.72.255
  • D. Tawara · J. Sakamoto · H. Murakami · N. Kawahara · J. Oda · K. Tomita ·

    Journal of Biomechanics 01/2006; 39. DOI:10.1016/S0021-9290(06)84936-5 · 2.75 Impact Factor
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    ABSTRACT: A finite-element study of posterior alone or anterior/posterior combined instrumentation following total spondylectomy and replacement with a titanium mesh cage used as an anterior strut. To compare the effect of posterior instrumentation versus anterior/posterior instrumentation on transmission of the stress to grafted bone inside a titanium mesh cage following total spondylectomy. The most recent reconstruction techniques following total spondylectomy for malignant spinal tumor include a titanium mesh cage filled with autologous bone as an anterior strut. The need for additional anterior instrumentation with posterior pedicle screws and rods is controversial. Transmission of the mechanical stress to grafted bone inside a titanium mesh cage is important for fusion and remodeling. To our knowledge, there are no published reports comparing the load-sharing properties of the different reconstruction methods following total spondylectomy. A 3-dimensional finite-element model of the reconstructed spine (T10-L4) following total spondylectomy at T12 was constructed. A Harms titanium mesh cage (DePuy Spine, Raynham, MA) was positioned as an anterior replacement, and 3 types of the reconstruction methods were compared: (1) multilevel posterior instrumentation (MPI) (i.e., posterior pedicle screws and rods at T10-L2 without anterior instrumentation); (2) MPI with anterior instrumentation (MPAI) (i.e., MPAI [Kaneda SR; DePuy Spine] at T11-L1); and (3) short posterior and anterior instrumentation (SPAI) (i.e., posterior pedicle screws and rods with anterior instrumentation at T11-L1). The mechanical energy stress distribution exerted inside the titanium mesh cage was evaluated and compared by finite-element analysis for the 3 different reconstruction methods. Simulated forces were applied to give axial compression, flexion, extension, and lateral bending. In flexion mode, the energy stress distribution in MPI was higher than 3.0 x 10 MPa in 73.0% of the total volume inside the titanium mesh cage, while 38.0% in MPAI, and 43.3% in SPAI. In axial compression and extension modes, there were no remarkable differences for each reconstruction method. In left-bending mode, there was little stress energy in the cancellous bone inside the titanium mesh cage in MPAI and SPAI. This experiment shows that from the viewpoint of stress shielding, the reconstruction method, using additional anterior instrumentation with posterior pedicle screws (MPAI and SPAI), stress shields the cancellous bone inside the titanium mesh cage to a higher degree than does the system using posterior pedicle screw fixation alone (MPI). Thus, a reconstruction method with no anterior fixation should be better at allowing stress for remodeling of the bone graft inside the titanium mesh cage.
    Spine 01/2006; 30(24):2783-7. DOI:10.1097/01.brs.0000192281.53603.3f · 2.30 Impact Factor
  • Daisuke Tawara · Jiro Sakamoto · Juhachi Oda ·
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    ABSTRACT: Mechanical property of bone is inhomogeneous and its variation depends on individual. It influences on the total stiffness and stress condition of the bone. Therefore, mechanical analysis considering inhomogeneous property is necessary for patients oriented evaluation of bone in clinic. If the finite element method is used, the inhomogeneous analysis is possible by giving a material property to an element one by one. So that, extreme fine meshing is required. In this study, we improved the ``ADVENTURE system'', which had developed by JSPS (Japan Society for the Promotion of Science) as a large-scale finite element analysis system, to be applicable to stress analysis of inhomogeneous bone problems. We applied the improved program to a composite beam model with graded material property and ensured its validity by comparing between the theoretical and calculated results. Furthermore, it was applied to stress analysis of proximal femur based on CT images and its efficiency was discussed.
    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 06/2005; 48(2):292-298. DOI:10.1299/jsmec.48.292
  • Juhachi Oda · Jiro Sakamoto · Kenichi Sakano ·

    Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 01/2005; 71(701):89-94. DOI:10.1299/kikaia.71.89

  • Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 01/2004; 70(697):1186-1192. DOI:10.1299/kikaia.70.1186

  • Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A 01/2004; 70(690):177-182. DOI:10.1299/kikaia.70.177
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    ABSTRACT: The stresses exerted on the instrumentation and adjacent bone were evaluated for three reconstruction methods after a total sacrectomy: a modified Galveston reconstruction (MGR), a triangular frame reconstruction (TFR), and a novel reconstruction (NR). To perform finite-element analysis of reconstruction methods used after a total sacrectomy. When a sacral tumor involves the first sacral vertebra, a total sacrectomy is necessary. It is mandatory to reconstruct the continuity between the spine and the pelvis after a total sacrectomy. However, no previous reports have described a biomechanical study of the reconstructed lumbosacral spine. A finite-element model of the lumbar spine and pelvis was constructed. Then three-dimensional MGR, TFR, and NR models were reconstructed, and a finite-element analysis was performed to account for the stresses on the bones and instrumentation. With excessive stress concentrated at the spinal rod in MGR, there is a strong possibility that the rod between the spine and the pelvis may fail. Although there was no stress concentration on the instruments in TFR, excessive stress on the iliac bones around the sacral rod was above the yield stress of the iliac bone. Such stress may cause a loosening of the sacral rod from the iliac bone. In NR, excessive stress concentration was not detected in the rod or the bones. This reconstruction has a low risk of instrument failure and loosening. If the patient were to stand or sit immediately after MGR or TFR instrumentation, failure or loosening may occur. The NR has a low risk of instrument failure and loosening after a total sacrectomy.
    Spine 08/2003; 28(14):1567-72. DOI:10.1097/01.BRS.0000076914.32408.85 · 2.30 Impact Factor