Journal of Mechanics in Medicine and Biology

In this study, the optimized structure of a femoral prosthesis for a patient was determined by biomechanical analysis, and the materials that match the model of the prosthesis were determined by multi-objective comprehensive evaluation using a fuzzy matter-element method. The suitable material for the ellipsoidal femoral head of the prosthesis was determined to be a carbon-fiber-enhanced polyether-ketone (CF/PEK) composite, and that for the stem was determined to be a zirconium–niobium alloy (Zr–Nb alloy). The study successfully demonstrated the potential of the developed method for use in selecting the best structure and materials for fabricating a customized prosthesis.

Traditional pelvis fracture reduction suffers from some disadvantages. Robot-assisted pelvis fracture reduction offers some promise in solving these problems. However, the reduction reference to guide robot motion is a key issue that must be resolved. In this paper, we propose a physical symmetry and virtual plane-based reduction reference and adopt the method of registration to calculate the virtual plane for the reference, which were verified via experiments. The results of the position symmetry experiments of the original pelvis and virtual plane-based position symmetry experiments were similar; both showed that the symmetry errors of the pelvis were less than 4mm and 2.5${}^{\circ }$. The results indicated that the proposed method could be used as a reference for robot-assisted pelvis fracture reduction.

Coronary stents are used to prop open blocked arteries in order to restore normal blood flow. A major setback in this technology is in-stent restenosis (ISR), which gravely limits the clinical success of stents, especially in tapered vessels. The present study used the finite element method to study the effects of arterial tapering on the biomechanical behavior of both stents and vessels during stent deployment inside tapered arteries. The effect of arterial tapering was demonstrated by a combination of corresponding tapered arteries with various tapering angles, including a straight artery case for comparison. Results indicated that an increase of vessel tapering led to an increase in stent radial recoil, stent tapering following expansion, and von Mises stresses on vessels. However, an increase of vessel tapering also led to a decrease in stent foreshortening. The analysis provides suggestions for clinical application in tapered vessels. The finite element method evaluated mechanical stent behavior in tapered vessels, and can help designers to optimize the design of stents for tapered vessels.

In recent years, virtual surgical simulation has been one of the hot direction of digital medical research, it is mainly used in teaching, training, diagnosis, preoperative planning, rehabilitation and modeling and analysis of surgical instruments. The modeling of soft tissue of human organs is the basis to realize the virtual surgical simulation. The quasi-linear viscoelastic (QLV) theory has been proposed by Fung, and it was widely used for modeling the constitutive equation of soft tissues. The purpose of this study is to determine the mechanical characterization of the liver soft tissue based on the PHANTOM Omni Haptic devices. Five parameters are included in the constitutive equation with QLV theory, which must be determined experimentally. The specimens were obtained from fresh porcine liver tissues in vitro. The liver tissues were cut into 14mm$\times$14mm$\times$14mm cubes. Two types of unconfined compression tests were performed on cube liver specimens. Puncture tests were performed on the complete liver. The material parameters of the QLV constitutive equation were obtained by fitting the experimental data. These parameters will provide the references for the computational modeling of the liver in the virtual surgical simulation.

The articular cartilage in the human knee plays an important role to ensure a lifetime knee function for an individual. Due to damage of the cartilage in the knee, the coefficient of friction (COF) increases even after treatments for the cartilage, due to the poor self-healing ability of the cartilage, resulting in decreased knee life. As the mechanism of the function of the knee joint is similar to a bearing, a model based on the regression model of cylindrical bearing life has been developed. The model is used to evaluate the effect of the COF on the lifetime of the knee. The results show the correlation between the life of the knee and the COF of the knee cartilage. The knee lifetime depends on the ratio of the COF of the healthy cartilage to the damaged cartilage. The results demonstrate the effect of the COF on the knee lifetime, which is an exponential decrease in the life of the knee for both males and females.

This study deals with free fall accident analysis involving adults, and their numerical replications using a finite element model of the human thorax. The main purpose is to determine the role of body position at impact in the thorax injury risk appearance. For this study, cases of real-world free-fall provided by an emergency department were selected and investigated. These cases involved both male and female with an age range of 20 to 63 years, who sustained accidental free-fall with both injured and uninjured cases. The examination of the patients' medical record provided helpful information to accurately perform numerical replications with the finite element model HUByx (Hermaphrodite Universal Biomechanical yx model) which was already validated for various experimental tests in the field of automobile, ballistic impacts and blast. The results of simulations at different impact location allowed highlighting the crucial influence of the body orientation in the risk of thoracic injury occurrence.

Dynamic soft tissue characterization is of importance to robotic-assisted minimally invasive surgery. The traditional linear regression method is unsuited to handle the non-linear Hunt–Crossley (HC) model and its linearization process involves a linearization error. This paper presents a new non-linear estimation method for dynamic characterization of mechanical properties of soft tissues. In order to deal with non-linear and dynamic conditions involved in soft tissue characterization, this method improves the non-linearity and dynamics of the HC model by treating parameter $p$ as independent variable. Based on this, an unscented Kalman filter is developed for online estimation of soft tissue parameters. Simulations and comparison analysis demonstrate that the proposed method is able to estimate mechanical parameters for both homogeneous tissues and heterogeneous and multi-layer tissues, and the achieved performance is much better than that of the linear regression method.

The newly developed open superconducting magnetic resonance imaging (MRI) system, which combines the advantages of the high magnetic fields of superconducting MRI systems and open characteristics of permanent MRI systems, has great potential in clinical and research applications. However, few pulse sequences are applicable to this system. In addition, further testing on this system is needed. Therefore, in this paper, an inversion recovery gradient echo (IR-GE) pulse sequence was developed based on the features of the 0.7 Tesla open superconducting MRI system. An MR Solutions spectrometer was used to control the IR-GE pulse sequence. The developed IR-GE pulse sequence was applied to a pure water phantom using different inversion recovery times (TI). The results of the theoretical analysis and experiments indicate that the developed IR-GE pulse sequence could be effectively applied to the 0.7 Tesla open superconducting MRI system.

Knee joint is the hub of human lower limb movement and it is also an important weight-bearing joint, which has the characteristics of load-bearing and heavy physical activities. So the knee joint becomes the predilection site of clinical disease. Once people have the cartilage lesions, their daily life will be affected seriously. The simulation of the knee joint lesions could provide help for clinical knee-joint treatment. Based on the complete model of knee joint, this paper use the finite element method to analyze the biomechanical characteristics of the defective knee joint. The results of simulation show that the stress of cartilages when standing on single leg is approximately doubled than that of standing on two legs. When standing on single leg, the 8-mm diameter osteochondral defect in femur cartilage can generate maximal changes in von-mises stress (by 36.74%), while the von-mises stress on tibia cartilage with 8-mm defect increase by 87%. The stress distribution of cartilages is almost the same, there is no obvious stress concentration when in defect. Increasing the defective diameter, femoral cartilage, meniscus and tibial all present an increasing trend towards stress. When increasing the applied load, the stress of the femoral cartilage, the meniscus and the tibial cartilage all increased.

In order to study the movement characteristics of three rotational freedoms of pelvic motion during walking on the ground for middle-aged and elderly people, a mathematical model of pelvis motion was established according to the data measured. Pelvic motion parameters were studied by the Assessment of Biomechanics Functional (FAB) for 21 participants when walking at slow, normal, and fast speeds. In the experiment, multiple trajectories of the pelvis in three directions were measured, and the data were statistically analyzed with respect to the different conditions of height and walking speed. A mathematical model was established to fit the curve associated with walking speed and height. This mathematical model has practical significance for rehabilitation equipment and evaluation.

Patients who suffer from stroke have motion function disorders. They need rehabilitation training guided by doctors and trainers. Nowadays, robots have been introduced to help the patients regain their motion function in rehabilitation training. In this paper, a novel multi degree of freedom (DOF) exoskeleton robot, with light weight, including (6$+$1) DOFs, named as Rehab-Arm, is proposed and developed for upper limb rehabilitation. The joints of the robot are equipped with micro motors which are capable of actuating each DOF respectively and simultaneously. The medial/lateral rotation of shoulder is realized by a semi-circle guide mechanism for convenience consideration and safety. The robot is used in sitting posture which is attached to a custom made chair. Hence, the robot can be used to assist patients in passive movement with 7 DOFs of the upper limb for rehabilitation. Five adult healthy male subjects participated in the experiment to test the joint movement accuracy of the robot. Finally, subjects can wear Rehab-Arm and move their upper limb, led by micro motors of the robot, to perform task assigned with specific trajectory.

Human liver biomechanical responses associated with frontal impacts, lateral impacts were studied using a simplified Chinese human body Finite Element Model (FEM) with more geometrical-accurate liver model for an average Chinese adult male from high resolution CT data. The developed model in this paper was composed by geometrically detailed liver model, simplified models of thoracic-abdominal organs, and the human skeleton model. Then, the whole model was validated at various velocities by comparing simulation outcomes with Post Mortem Human Subjects (PMHS) experimental results in frontal and lateral pendulum impacts. The force–deflection and force–time characteristics were in good agreement with the test results. The validated model was then applied for studying liver dynamic responses and injuries in simulations. Pressure, tensile stress and peak strain that may induce hepatic injuries was computed from model simulations and were analyzed about the correlation with the global parameters, like thoracic deflection, viscous criterion value, contact force. This study demonstrated that the method of developing a simplified finite element thorax-abdomen model with detailed liver model could be effective of hepatic injury assessment in various impacts reported in literature.

The aim of this study was to investigate the effects of Parkinson's disease (PD) on upper body acceleration patterns during level walking. Twenty-three patients with PD and 29 controls of similar age participated in this study. Subjects walked along a 12 m linear walkway at self-selected comfortable speeds. Upper body accelerations were measured using three-axis accelerometers located at the pelvis, shoulder, and head. Acceleration magnitude, stride-to-stride irregularity, and degree of coupling among three body parts were derived from the acceleration signals. In the vertical (supero-inferior) direction, PD patients exhibited a smaller acceleration magnitude, a more irregular pattern, and less coupling of acceleration among body parts compared to the controls ($p<0.05$). In the anterio-posterior (AP) direction, acceleration magnitude at the pelvis in PD patients was smaller than that in the controls ($p<0.05$). In addition, the phase lag of AP head acceleration from shoulder and pelvis was smaller in PD patients than in the controls ($p<0.05$). These results suggest that PD patients walk with reduced ankle power generation and a more rigid upper body in the AP direction and with more irregular muscle force generation in the SI direction.

Essential tremor (ET) is the most common movement disorder that includes postural tremor and action tremor. This study investigates whether sensory electrical stimulation (SES) is effective on the action tremor in patients with ET. One task in the clinical testing of action tremor, “Archimedes spiral drawing”, was performed in 18 patients for three sessions, which were named as pre-stimulation (PRE), stimulation on (ON), and 5min after stimulation (POST). SES (sub-motor threshold) was applied on the muscles of the elbow and wrist only at ON session. Three-dimensional (3D) angular velocities were measured on three segments (index finger, hand, and forearm) from which movements of metacarpophalangeal (MP) and wrist joints were derived. Average tremor intensity in each session was represented by root mean square of the vector sum of 3D angular velocities. Tremor intensities in ON session were smaller than in PRE session in one segment (finger) and two joints (MP and wrist) ($p<0.05$). Tremor intensities in POST session were even smaller than in ON session in all segments and one joint (wrist) ($p<0.05$). The results indicate that SES suppresses action tremor and the effect continues and even improves 5min after the termination of stimulation. The findings of this study may contribute to the improvement of the quality of life in patients with ET.

The purpose of this study was to investigate the effects of age and gender on the biomechanical features of sit-to-stand (STS) movement. Twenty young subjects and 20 elderly subjects participated in this study. Nine events during STS movement were defined where joint angles and joint moments were extracted for further analyses. Two-way repeated measures ANOVA was performed for joint angles and joint moments with age and gender as independent factors. Major gender differences were shown in joint angles. Women used a sliding forward strategy more than men (more flexion of ankle and knee joint) during mid-phases of STS movement ($p<0.01$) and men used an exaggerated trunk flexion strategy more than women (more hip flexion) in later phases of STS movement ($p<0.01$). Age differences were shown in joint moments. Elderly subjects showed smaller knee extension moment (normalized by body weight) but greater ankle plantar flexion moment than young subjects in mid-to-late phases of STS movement ($p<0.001$). More anterior positioning of center of mass (COM) in the elderly might be the reason for the strategy difference. That is, the shorter distance of COM from the knee joint would require less knee extension moment, and likewise, the more forward displacement of COM with respect to the ankle joint would need more plantar flexion moment. More anterior positioning of COM in the elderly, compared to the young was reflected on center of pressure (COP), and the forward displacement of COP was correlated well with the higher body mass index (BMI) and shorter thigh length ($r=0.359-0.66;p<0.01$).

Background: While advanced motion analysis systems can provide accurate kinematic information, the majorities of motion analysis systems are stationary, expensive and time consuming. Image J is a Java-based image processing program that was originally developed at the National Institutes of Health and has rapidly gained widespread acceptance among rehabilitation specialists as a portable and affordable alternative motion analysis system. However, the validity and reliability of the Image J program have not been well established. Objective: The purpose of this study was to investigate the validity and test–retest reliability of the Image J kinematic analysis system. The Image J kinematic analysis system is designed to produce precise kinematic evidence during normal and pathological static and dynamic movement patterns. Methods: The Image J motion analysis system was concurrently compared with the electrogoniometer system as a reference standard measure by obtaining sagittal kinematic knee joint angle data. Results: Image J motion analysis system measurement revealed outstanding validity ($R^2=0.976,r=0.988$ and $p<0.01$). The test–retest reliability for kinematic knee angle data showed remarkable consistency (Cronbach’s $\mathrm{\text{alpha}}=0.994$). Conclusions: This study provides the first evidence highlighting the Image J kinematic analysis system’s excellent validity and reliability for evaluating human kinematic movements in elderly people with hemiparetic stroke.

While the Walkbot-K robotic-assisted gait training systems have rapidly gained widespread acceptance for pediatric locomotor training in children with cerebral palsy, the validity and reliability for the Walkbot-K system have not been well established. The aim of this study is to investigate the validity and test-retest reliability of the innovative exoskeletal Walkbot-K system which is designed to help the active development and learning of fundamental locomotor skills in children with locomotor impairments. The electrogoniometer was used concurrently to compare the sagittal kinematic angular displacement data with that of the Walkbot-K system as a reference standard measure. Neuromechanical data obtained from kinematic measurement produced an excellent validity ($R^2=0.974$). The test-retest reliability for kinematic knee angle data showed a remarkable consistency ($ICC=0.997$). This study provides the first compelling evidence of the children’s robotic gait-assisted Walkbot-K system’s validity and reliability, indicating that the system is a highly valid and reliable robotic-assisted gait training system to evaluate and treat locomotor dysfunction.

The objective of this research is to evaluate the biomechanical effect of zygomatic implant-supported obturator prostheses in unilateral maxillary defect. Based on CT data, four 3D numerical models were built. One model was a normal craniofacial complex (model 1) and other three models were structures with unilateral maxilla defect reconstructed using clasp-retained obturator prosthesis (model 2), one zygomatic implant-supported and clasp-retained prosthesis (model 3), two zygomatic implant-supported and clasp-retained prosthesis (model 4). Bilateral vertical loads of 300N were imposed and the stress and displacement distribution were calculated, analyzed and compared. The bilateral occlusal forces dispersed along the three-mechanical-pillar of the maxillofacial region and the displacement distributed symmetrically in model 1. Because of mechanical pillars break on the affected side, all occlusal forces were transferred by clasps and abutment teeth in model 2, which induced the increase in stress and displacement level. The zygomatic implant restored mechanical pillars and greatly reduced the stress and displacements levels in models 3 and 4. The stress and displacement distributions on clasps, bones, teeth and periodontal ligaments were more reasonable with the support of zygomatic implants. Therefore, the zygomatic implant-supported and clasp-retained prostheses were found to be more effective for unilateral maxillary defect reestablishment.

Preoperative rehearsal is very important before the operation, because of its particularity and difficulty, traditional printing can hardly achieve it, and thus a new kind of fixture for the 3D printing of pelvis model is critical. Fixture design in manufacturing system is very important and directly affects the processing quality, production efficiency and manufacturing costs. As a new method of manufacturing, the alternative style of additive and subtractive manufacturing is potential in market prospect. New requirements on the performance and structure of the fixture were put forward due to the high complexity of product surface in alternative manufacturing, as well as the force characteristics of numerical control (NC) processing. In this paper, we propose a novel type of fixture which is capable of completing printing tasks in preoperative rehearsal. An experiment is performed to validate the rationality and universality of the fixture. A 3D printing practical case of pelvis model before pelvic correction surgery is used to demonstrate the effectiveness of the present fixture.

In recent years, a robust increasing interest has been observed in wearable devices featuring smart health, smart fitness, and human–machine interaction applications. While we gained some advances on use of surface electromyography (sEMG) signals recorded from upper extremities for controlling external devices, only limited attempt has been made to track the status of targeted muscles and forecast muscle fatigue onset. In this study, we address use of sEMG signals acquired from upper extremities to predict onset of muscle fatigue using deep belief networks (DBNs) as a learning mechanism. We demonstrate that a deep architecture can learn from raw data and provide comparable performance to feature-based approaches. Experimental results show that the DBNs model investigated in this study achieves an average classification accuracy of 85.3% without any subject-oriented calibration and achieves a best case accuracy of 97.60%. A transient-to-fatigue state is introduced before the fatigue onsets as an early warning state. The aim of this paper is to evaluate the performance of the popular deep models in real fatigue detection applications. The model provides a promising result compared with state-of-art works without any feature selection process, which could potentially generate better features while reducing the requirement for expertise in data.