The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform
Meir Shillor - One of the best experts on this subject based on the ideXlab platform.
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A frictional contact problem with wear diffusion
Zeitschrift für angewandte Mathematik und Physik, 2019Co-Authors: Piotr Kalita, Pawel Szafraniec, Meir ShillorAbstract:This paper constructs and analyzes a model for the dynamic frictional contact between a viscoelastic body and a moving foundation. The contact involves wear of the contacting surface and the diffusion of the wear debris. The relationships between the stresses and displacements on the contact boundary are modeled by the normal compliance law and a version of the Coulomb law of dry friction. The rate of wear of the contact surface is described by the differential form of the Archard law. The effects of the diffusion of the wear particles that cannot leave the contact surface on the surface are taken into account. The novelty of this work is that the contact surface is a manifold and, consequently, the diffusion of the debris takes place on a curved surface. The interest in the model is related to the wear of mechanical joints and Orthopedic Biomechanics where the wear debris are trapped, they diffuse and often cause the degradation of the properties of joint prosthesis and various implants. The model is in the form of a differential inclusion for the mechanical contact and the diffusion equation for the wear debris on the contacting surface. The existence of a weak solution is proved by using a truncation argument and the Kakutani–Ky Fan–Glicksberg fixed point theorem.
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quasistatic thermoviscoelastic problem with normal compliance multivalued friction and wear diffusion
Nonlinear Analysis-real World Applications, 2016Co-Authors: Leszek Gasinski, Anna Ochal, Meir ShillorAbstract:Abstract This paper presents and analyzes a model for quasistatic frictional contact between a thermoviscoelastic body and a moving foundation that involves wear of the contacting surface and the diffusion of the wear debris. The constitutive law includes temperature effects and the evolution of the temperature is described by a parabolic equation with a subdifferential heat exchange boundary condition. Contact is modeled with normal compliance together with a subdifferential frictional law. The rate of wear of the contact surface is described by the differential form of the Archard condition. The effects of the diffusion of the wear particles on the contact surface are taken into account. Such situations arise in mechanical joints and in Orthopedic Biomechanics where the wear debris is trapped, diffuses and influences the properties of joint prosthesis and implants. The variational formulation of the problem leads to a system with a time-dependent hemivariational inequality for the displacement, a parabolic hemivariational inequality for the temperature and a parabolic equation on the contact boundary for the wear diffusion. The existence of a unique weak solution is proved by using recent results from the theory of hemivariational inequalities, variational diffusion equation, and a fixed point argument.
Shen Y - One of the best experts on this subject based on the ideXlab platform.
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Which one is more effective for the treatment of very severe osteoporotic vertebral compression fractures: PVP or PKP?
Dove Medical Press, 2018Co-Authors: Wang F, Dong Z, Shen YAbstract:Feng Wang,1,2 Lin-Feng Wang,1,2 De-Chao Miao,1,2 Zhen Dong,1,2 Yong Shen1,2 1Department of Spine Surgery, The Third Hospital of Hebei Medical University, 050051 Shijiazhuang, China; 2The Key Laboratory of Orthopedic Biomechanics of Hebei Province, The Third Hospital of Hebei Medical University, 050051 Shijiazhuang, China Purpose: The purpose of this study was to compare the clinical efficacy and safety of percutaneous vertebroplasty (PVP) and percutaneous kyphoplasty (PKP) in the treatment of the elderly with very severe osteoporotic vertebral compression fractures (vsOVCFs). Methods: From September 2012 to September 2015, 57 patients with vsOVCFs who had undergone PVP and PKP surgeries at our medical center were reviewed retrospectively, at least 2 years follow-up. All patients were divided into PVP group (n=31) and PKP group (n=26). Clinical data including clinical and radiological evaluation results were performed pre- and postoperatively. Results: The operation time of PVP group (29.6±3.3 minutes) was less than that of PKP group (37.4±4.2 minutes), with significant differences (P<0.05). Compared with preoperative data, the VAS scores, Oswestry disability index (ODI) scores, and local kyphotic angle were improved with significant differences at 1 day after surgery and the last follow-up in two groups (P<0.05). However, there were no differences in VAS and ODI scores between the two groups (P>0.05). The local kyphotic angle of PVP group was more than that of PKP group after surgery, with significant differences (P<0.05). At 1 day after surgery and the last follow-up, the anterior height of vertebrae fractured was significantly improved compared with preoperative in PKP group (P<0.05), and there was no statistical difference compared with preoperative in PVP group (P>0.05). However, there were no significant differences between the two groups in the leakage rate of bone cement (P>0.05) and incidence of adjacent-level vertebra fracture (P>0.05). Conclusion: Both PVP and PKP can significantly relieve the pain of the patients with vsOVCFs. Restoring the vertebral height and local kyphotic angle corrections of PKP are comparatively better than those of PVP. However, the operation time of PKP is significantly longer than that of PVP and PKP is not superior in the leakage rate of bone cement and incidence of adjacent-level vertebra fracture compared to PVP. Keywords: percutaneous vertebroplasty, percutaneous kyphoplasty, osteoporosis, vertebral compression fractures, cement leakag
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Characteristics of Modic changes in cervical kyphosis and their association with axial neck pain
Dove Medical Press, 2017Co-Authors: Li J, Shen YAbstract:Yonghui An,1,2 Jia Li,1,2 Yongqian Li,1,2 Yong Shen1,2 1Department of Orthopaedic Surgery, The Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China; 2The Key Laboratory of Orthopedic Biomechanics of Hebei Province, The Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China Background: The purpose of this study was to evaluate characteristics of Modic changes in cervical kyphosis (CK) and their association with axial neck pain. Methods: Study participants included 286 asymptomatic or symptomatic patients with CK (mean age = 54.2 ± 12.2 years) who were consecutively enrolled from March 2009 to October 2015. Clinical and radiographic evaluations were performed at a university outpatient department. CK was classified as global type, reverse sigmoid type, or sigmoid type. Results: There were 138 participants with global type CK, 103 with reverse sigmoid type CK, and 45 with sigmoid type CK. Of the 286 participants, 102 had Modic changes (Modic-1 in 38 segments and Modic-2 in 75 segments). Spinal cord compression grade and disc degeneration occurred more frequently in the group with axial neck pain compared to the group without pain. Angular motion was decreased in those with axial neck pain (mean ± standard deviation [SD] 7.8°±4.6°) compared to those who were asymptomatic (mean ± SD 8.9°±5.1°; P<0.001). In multivariate logistic regression analysis, Modic changes were associated with axial neck pain (odds ratio =5.356; 95% confidence interval =1.314–12.800; P<0.001). Conclusion: Modic changes occur most commonly in association with CK global type and less commonly with reverse sigmoid type and sigmoid type. Modic changes are associated with axial neck pain in patients with CK. Keywords: cervical kyphosis, axial neck pain, Modic change, kinematic analysis, magnetic resonance imagin
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Modic changes of the cervical spine: T1 slope and its impact on axial neck pain
Dove Medical Press, 2017Co-Authors: Li J, Qin S, Li Y, Shen YAbstract:Jia Li,1,2* Shuhui Qin,1,2* Yongqian Li,1,2 Yong Shen1,2 1Department of Orthopaedic Surgery, The Third Hospital of Hebei Medical University, Shijiazhuang, Peoples Republic of China; 2The Key Laboratory of Orthopedic Biomechanics of Hebei Province, The Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China *These authors contributed equally to this work Background: The purpose of the research was to evaluate cervical sagittal parameters on magnetic resonance imaging (MRI) in patients with Modic changes and its impact on axial neck pain. Methods: This study consisted of 266 consecutive asymptomatic or symptomatic patients with Modic changes, whose average age was 50.9±12.6 years from January 2015 to December 2016. Cervical sagittal parameters included sagittal alignment of the cervical spine (SACS), T1 slope, thoracic inlet angle (TIA), and neck tilt (NT). The Modic changes group was compared with an asymptomatic control group of 338 age- and gender-matched adults. Results: In the Modic changes group, T1 slope was significantly higher (25.8º±6.3º) compared with that in the control group (22.5º±6.8º) (P=0.000). However, there was no significant difference of the NT, TIA, and SACS between the two groups. Patients in the Modic changes group were more likely to have experienced historical axial neck pain compared with the control group (P=0.000). With regard to the disc degeneration, it indicated that the disc in the Modic changes group had more severe disc degeneration (P=0.032). Conclusion: T1 slope in the Modic changes group was significantly higher compared to that of the control group. The findings suggested that a higher T1 slope with broken compensation of cervical sagittal mechanism may be associated with the development of Modic changes in the cervical spine. Keywords: Modic changes, T1 slope, axial neck pain, cervical spine
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Impact of T1 slope on surgical and adjacent segment degeneration after Bryan cervical disc arthroplasty
Dove Medical Press, 2017Co-Authors: Yang P, Li J, Li Y, Shen YAbstract:Peng Yang,1 Yongqian Li,2,3 Jia Li,2,3,* Yong Shen2,3,* 1Department of Neurosurgery, Affiliated Hospital of North China University of Science and Technology, Tangshan, 2Department of Orthopedic Surgery, 3Key Laboratory of Orthopedic Biomechanics of Hebei Province, the Third Hospital of Hebei Medical University, Shijiazhuang, People’s Republic of China *These authors contributed equally to this work Background: This retrospective study investigated an association between preoperative T1 slope and surgical and adjacent segment degeneration (SASD) after Bryan cervical disc arthroplasty (BCDA) in patients with cervical degenerative disc disease.Methods: Based on preoperative standing lateral radiographs, 90 patients were classified according to T1 slope that was higher or lower than the 50th percentile (high T1 or low T1, 28 and 62 patients, respectively). Patients were also classified as SASD or non-SASD (38 and 52 patients, respectively) determined by radiographs at final follow-up. Visual analog scale (VAS) and Neck Disability Index (NDI) scores for neck and arm pain were noted, and changes in the sagittal alignment of the cervical spine (SACS), functional spinal unit (FSU) angle, and FSU range of motion (ROM) were also noted. Univariate and multivariate logistic regression analyses were performed to determine the risk factors for SASD.Results: The overall rate of SASD was 42.2% (38/90). The SACS, FSU angle, FSU ROM, and SASD rates of the high T1 and low T1 slope groups were significantly different at the last follow-up. The NDI and VAS scores of the high T1 slope group were significantly greater than those of the low T1 slope. The multivariate logistic regression analysis showed that high T1 slope and endplate coverage discrepancy (ie, residual space behind the prosthesis) were significant risk factors for SASD after BCDA.Conclusion: High T1 slope and endplate coverage discrepancy were associated with SASD after BCDA. Patients with a high preoperative T1 slope have a smaller FSU angle and more neck pain after BCDA. Keywords: Bryan cervical disc arthroplasty, surgical and adjacent segment degeneration, T1 slope, endplate coverage discrepancy, risk factor, clinical outcome
Leszek Gasinski - One of the best experts on this subject based on the ideXlab platform.
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quasistatic thermoviscoelastic problem with normal compliance multivalued friction and wear diffusion
Nonlinear Analysis-real World Applications, 2016Co-Authors: Leszek Gasinski, Anna Ochal, Meir ShillorAbstract:Abstract This paper presents and analyzes a model for quasistatic frictional contact between a thermoviscoelastic body and a moving foundation that involves wear of the contacting surface and the diffusion of the wear debris. The constitutive law includes temperature effects and the evolution of the temperature is described by a parabolic equation with a subdifferential heat exchange boundary condition. Contact is modeled with normal compliance together with a subdifferential frictional law. The rate of wear of the contact surface is described by the differential form of the Archard condition. The effects of the diffusion of the wear particles on the contact surface are taken into account. Such situations arise in mechanical joints and in Orthopedic Biomechanics where the wear debris is trapped, diffuses and influences the properties of joint prosthesis and implants. The variational formulation of the problem leads to a system with a time-dependent hemivariational inequality for the displacement, a parabolic hemivariational inequality for the temperature and a parabolic equation on the contact boundary for the wear diffusion. The existence of a unique weak solution is proved by using recent results from the theory of hemivariational inequalities, variational diffusion equation, and a fixed point argument.
Anna Ochal - One of the best experts on this subject based on the ideXlab platform.
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quasistatic thermoviscoelastic problem with normal compliance multivalued friction and wear diffusion
Nonlinear Analysis-real World Applications, 2016Co-Authors: Leszek Gasinski, Anna Ochal, Meir ShillorAbstract:Abstract This paper presents and analyzes a model for quasistatic frictional contact between a thermoviscoelastic body and a moving foundation that involves wear of the contacting surface and the diffusion of the wear debris. The constitutive law includes temperature effects and the evolution of the temperature is described by a parabolic equation with a subdifferential heat exchange boundary condition. Contact is modeled with normal compliance together with a subdifferential frictional law. The rate of wear of the contact surface is described by the differential form of the Archard condition. The effects of the diffusion of the wear particles on the contact surface are taken into account. Such situations arise in mechanical joints and in Orthopedic Biomechanics where the wear debris is trapped, diffuses and influences the properties of joint prosthesis and implants. The variational formulation of the problem leads to a system with a time-dependent hemivariational inequality for the displacement, a parabolic hemivariational inequality for the temperature and a parabolic equation on the contact boundary for the wear diffusion. The existence of a unique weak solution is proved by using recent results from the theory of hemivariational inequalities, variational diffusion equation, and a fixed point argument.
Syumpei Miyakawa - One of the best experts on this subject based on the ideXlab platform.
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Optical Stress Imaging for Orthopedic Biomechanics – Comparison of Thermoelastic Stress Analysis and Developed Mechanoluminescent Method
IFMBE Proceedings, 2010Co-Authors: Koji Hyodo, Hajime Mishima, Syumpei MiyakawaAbstract:Thermoelastic stress analysis, which utilizes the thermoelastic properties of materials, is a full-field, noncontact technique for surface stress mapping of materials and structures. Unlike the conventional technique such as strain gauge method, the unique advantage of the method is its ability to image whole-surface stress (Δ(σ1 + σ2)) distribution in specimens. An experimental system using the thermoelastic stress analysis method and a synthetic femur was utilized to perform reliable and convenient mechanical biocompatibility evaluation of hip prosthesis design. In addition, the mechanoluminescent materials, the author (Xu) developed, are novel inorganic materials that can luminesce in response to applied mechanical energy. A prosthetic device in which these mechanoluminescent materials are applied to a synthetic bone is a “mechanoluminescent synthetic bone.” Since the region subjected to load emits high intensity light in the visible region, the device has allowed high-definition and high-speed visualization of the mechanical dynamic environment using conventional image sensors such as CCDs. Thermoelastic stress analysis and mechanoluminescent method have mutual, supplementary advantages. It is confirmed that they are very effective techniques in vitro Biomechanics research and to contribute to a variety of biomechanical analyses and thus support the practical implementation of prosthetic devices.
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optical stress imaging for Orthopedic Biomechanics comparison of thermoelastic stress analysis and developed mechanoluminescent method
2010Co-Authors: Koji Hyodo, Hajime Mishima, Syumpei MiyakawaAbstract:Thermoelastic stress analysis, which utilizes the thermoelastic properties of materials, is a full-field, noncontact technique for surface stress mapping of materials and structures. Unlike the conventional technique such as strain gauge method, the unique advantage of the method is its ability to image whole-surface stress (Δ(σ1 + σ2)) distribution in specimens. An experimental system using the thermoelastic stress analysis method and a synthetic femur was utilized to perform reliable and convenient mechanical biocompatibility evaluation of hip prosthesis design. In addition, the mechanoluminescent materials, the author (Xu) developed, are novel inorganic materials that can luminesce in response to applied mechanical energy. A prosthetic device in which these mechanoluminescent materials are applied to a synthetic bone is a “mechanoluminescent synthetic bone.” Since the region subjected to load emits high intensity light in the visible region, the device has allowed high-definition and high-speed visualization of the mechanical dynamic environment using conventional image sensors such as CCDs. Thermoelastic stress analysis and mechanoluminescent method have mutual, supplementary advantages. It is confirmed that they are very effective techniques in vitro Biomechanics research and to contribute to a variety of biomechanical analyses and thus support the practical implementation of prosthetic devices.
