Research Advances in Musculoskeletal Biomechanical Modeling in 2021 / 医用生物力学

Biomechanical model of musculoskeletal system has accurate human anatomy and good biological fidelity. It can accurately and effectively reveal the biomechanical state and predict the internal mechanical response of musculoskeletal system. Therefore, it has been widely used in biomechanical study of musculoskeletal system, diagnosis and treatment of bone diseases, implant optimization design and preoperative planning. In 2021, the latest advances in biomechanical modeling method of musculoskeletal system mainly included three aspects, i.e., individualized finite element modeling, statistical model modeling and musculoskeletal system modeling. On this basis, the latest relevant literatures were summarized in this review to illustrate the progress and main applications of the above modeling method, and the future development direction of musculoskeletal modeling was discussed.

Establishment of normal foot and common foot disease models using three-dimensional finite element method and biomechanical analysis / 中国组织工程研究

BACKGROUND: In the field of trauma orthopedics, three-dimensional finite element analysis is only a routine means of biomechanical evaluation and internal fixator design and optimization in the treatment of internal fixation of fractures, but also provides new directions for the basic and clinical researches of trauma orthopedics. OBJECTIVE: To establish a three-dimensional finite element model of normal foot, flatfoot, equinus, and foot fracture and to undergo biomechanical analysis. METHODS: One healthy volunteer and patients with flatfoot, equinus, and foot fracture were selected. Their feet were scanned by CT. Three-dimensional finite element modeling and biomechanical analysis were performed by using computer three-dimensional imaging technology according to the CT data. The stress distribution and stress values of each model were then obtained for comparative analysis. The study was approved by the Ethics Committee of Mindong Hospital Affiliated to Fujian Medical University. RESULTS AND CONCLUSION: The three-dimensional finite element models of normal foot, flatfoot, equinus, and foot fracture were established and biomechanical analysis was performed. In the patients with flatfoot, the stress values of the metatarsus and tarsus were significantly increased compared with the normal values. The stress of the equinus was mainly concentrated around the ankle joint, especially on the talus surface. The simple metatarsus fracture had little effect on the stress changes in the tarsus area. The stress in the tarsus area of the Lisfranc injured patients was increased more obviously than in the normal feet. In this study, the three-dimensional finite element modeling and biomechanical analysis of the foot combines computer technology with clinical practice, which provides reference for biomechanical research of human foot. The numericalization of the mechanical data of different foot conditions by mechanical analysis provides important mechanical basis for the clinical treatment of the foot.

Low power consumption structure design of an incus-stimulating middle ear implant based on piezoelectric stack / 医用生物力学

Objective To design an improvement plan of piezoelectric actuator with displacement magnification structure, so as to reduce power consumption of the existing incus-stimulating piezoelectric actuator for middle ear implant. Methods First, based on anatomical structure of human ear, the piezoelectric actuator with displacement magnification structure and the one just composed of piezoelectric stack were designed, respectively, and the corresponding coupled mechanical models of the middle ear and the piezoelectric actuator were established. By comparing the calculation results from the two types of coupling mechanical models, the hearing compensation property and power consumption of the actuator before and after the implantation of displacement magnification structure were analyzed. Results After adding the displacement magnification structure, the sound pressure level (SPL) at 1 kHz frequency was increased from 100 dB to 113 dB, when the piezoelectric actuator was stimulated by 10.5 V effective voltage. In addition, when the actuator was stimulated by the piezoelectric stack, its power consumption at the frequency of 1, 2 and 4 kHz were 6.42, 1.56 and 0.28 mW, respectviely; after introducing the displacement magnification structure, power consumption at the above-mentioned 3 frequencies decreased to 0.39, 0.09 and 0.01 mW, resepectively. Conclusions Piezoelectric actuator with displacement magnification structure in this study can improve hearing compensation ability of the incus-stimulating middle ear implant and effectively reducing the power consumption. The research findings will help to further improve the structure design of middle ear implant, thus achieving better hearing compensation effect.

Primary blast waves induced brain dynamics influenced by head orientations

There is controversy regarding the directional dependence of head responses subjected to blast loading. The goal of this work is to characterize the role of head orientation in the mechanics of blast wave-head interactions as well as the load transmitting to the brain. A three-dimensional human head model with anatomical details was reconstructed from computed tomography images. Three different head orientations with respect to the oncoming blast wave, i.e., front-on with head facing blast, back-on with head facing away from blast, and side-on with right side exposed to blast, were considered. The reflected pressure at the blast wave-head interface positively correlated with the skull curvature. It is evidenced by the maximum reflected pressure occurring at the eye socket with the largest curvature on the skull. The reflected pressure pattern along with the local skull areas could further influence the intracranial pressure distributions within the brain. We did find out that the maximum coup pressure of 1.031 MPa in the side-on case as well as the maximum contrecoup pressure of −0.124 MPa in the back-on case. Moreover, the maximum principal strain (MPS) was also monitored due to its indication to diffuse brain injury. It was observed that the peak MPS located in the frontal cortex region regardless of the head orientation. However, the local peak MPS within each individual function region of the brain depended on the head orientation. The detailed interactions between blast wave and head orientations provided insights for evaluating the brain dynamics, as well as biomechanical factors leading to traumatic brain injury.

The optimal element size, material property distributions and modeling methods for finite element modeling of lumbar vertebra / 医用生物力学

Objective To investigate the effects of element size and type, material property distributions of vertebral cancellous bone and simulation methods of cortical bone structure on the finite element (FE) results during the finite element modeling of lumbar vertebral body. Methods Based on QCT images of lumbar spine, 22 FE models of L2 without posterior structure were built by 6 element sizes (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 mm), 2 heterogeneous material distribution methods of cancellous bone (300, 150) and 2 cortical bone modeling methods. The maximum displacement, strain energy, average stress and axial stiffness of these models were obtained to analyze and verify the results. Results When the element size was 0.5 mm, the axial stiffness of models with 10, 150 and 300 kinds of heterogeneous materials showed obvious differences; for the vertebral cancellous bone with 150 kinds of materials, the variation of average stress was not distinct under different element sizes; the average stress of the model using the outermost hexahedral elements to simulate the cortical bone structure was larger than that appending the skin to the outmost of the model. Conclusions It is more reasonable and effective to build the FE model of lumbar vertebral body with the method by 0.5 mm element size, 8-noded hexahedral elements, 150 kinds of heterogeneous materials, and using the outermost hexahedral elements to simulate the cortical bone structure. The research findings will lay a foundation for building subject-specific FE models of lumbar vertebral body on a large scale in future.

The Etiology of Residual Symptoms after Hip Arthroscopic Treatment of Femoroacetabular Impingement: Analysis Using Finite Element Modeling / 대한정형외과학회잡지

PURPOSE: To analyze, using finite element model analysis, the causes of postoperative pain in patients who had arthroscopic treatment for femoroacetabular impingement (FAI). MATERIALS AND METHODS: Ten patients with FAI treated by arthroscopic surgery between July 2004 and July 2007 were selected. Five cases whose condition improved to a pain score of 3 postoperatively were assigned to comparative group A and 5 cases who had a second operation done due to a pain score of 1 were assigned to experimental group B. Finite element model analysis was done for the impingement test position. Femoral offset and alpha angle were measured to compare with contact pressure or von Mises stress. RESULTS: Preoperative von Mises stress and contact pressure were all higher in group B than group A. Maximal stress and pressure location was the anterolateral surface of the femoral head and neck, and this location was removed more accurately in group A. CONCLUSION: Finite element model analysis of FAI indicated that incomplete removal of a bump was the cause of pain, and that accurate location of the lesion and adequate bump removal are the definitive factors in reducing pain.

MODELACIÓN POR ELEMENTOS FINITOS EN UN MODELO DE ANEURISMA

En un modelo con características geométricas y un comportamiento mecánico de la pared arterial generalizado para aneurismas periféricos, se realiza una modelación por elementos finitos (MEF) del efecto de la presión arterial y del espesor de la pared arterial en el saco de un aneurisma. Se analizan los esfuerzos de Von Misses, los esfuerzos tensores transversales y el desplazamiento en el saco del aneurisma. Se encuentra que el lugar más propenso a la ruptura para esta geometría de aneurismas es la región circundante a la arteria eferente y opuesta al flujo aferente. Se propone un proceso para realizar MEF en cualquier geometría de aneurisma y condiciones de presión, para analizar el riesgo y el lugar más probable de la ruptura.

Considering a model with generalized geometry and mechanical properties of the arterial wall for the peripheral vasculature aneurisms, a finite element modeling (FEM) is developed for analyzing the effects of arterial blood pressure and the arterial wall thickness in the aneurismal sac. The von Misses stresses, the transversal tensor stresses and the displacement in the aneurismal sac wall are analyzed. The possible site of rupture for this aneurism geometry is found surrounding the efferent artery and opposed to the flow inlet. A method for applying FEM to any aneurism geometry and blood pressure conditions is proposed for analyzing the risk of rupture and possible rupture site.