Jung-Hong Park

Variability analysis of lower extremity joint kinematics during walking in healthy young adults

The first objective of this study was to determine the kinematic variability of the lower extremity joints using methods from the mathematical chaos theory in a normal walking environment in conjunction with a large population of healthy young adults. The second objective was to test the hypothesis that variability characteristics are different between joints and to further investigate differences between male and female and right and left subgroups. A total of forty young healthy subjects (20 males: 24.1+/-3.1 years; 20 females: 22.5+/-3.2 years) volunteered, and their joint motions were captured while walking on a treadmill for 90 s in order to estimate Lyapunov Exponent (LE) values. Means and standard deviations of the LEs ranged from 0.035+/-0.016 (right ankle) to 0.073+/-0.023 (left knee) for the male subjects and from 0.028+/-0.014 (left ankle) to 0.065+/-0.028 (right hip) for the female subjects. Between the males and females, differences in LEs were observed to be statistically significant only for the left knee. There were no statistically significant differences between the right and left sides of the joints. However, differences between joints were statistically significant except between the hip and knee. These results are the first such comparison of the variability in the lower extremity without the confounding effect of walking speed on the variability of joint motions, and can serve as a normative database.

Biomechanical Analysis of Lumbar Interspinous Process Fixators and Design of Miniaturization and Advanced Flexibility

The intervertebral fusion was reported to increase the degeneration of the neighboring region. Recently, a new technique of inserting an interspinous process fixator has been introduced to minimize the degenerative change in the lumbar spine. This study analyzed biomechanical effects of the fixator in the lumbar spine, and designed a new prototype to improve flexibility of the fixator with a reduced size. The evaluation was based on the displacement, stiffness and von-Mises stress obtained from the mechanical test and finite element analysis. A finite element lumbar model of L1 to L5 was constructed. The finite element model was used to analyze intervertebral fusion, insertion of a commercial fixator and a new prototype. The range of motion of intervertebral segments and pressures at vertebral discs were calculated from FEA. The results showed that the stiffness of the prototype was reduced by 32.9% than that of the commercial one.

Analysis of a Roller Guide Container Stacking System Applicable to the Mobile Harbor

The purpose of this study is to evaluate a simulation model of a stacking guidance system (SGS) with a roller guide applicable to the mobile harbor. The study used a small-scale model (1/20) made of wood with rollers in order to compare the dynamic analysis with experiment results. The law of similarity was applied for the validation of the scaled model. In order to construct a more realistic simulation model, the damping coefficient of the dynamic model was adjusted to 0.5 Ns/mm for the wood-to-wood contact condition based on the experimental results. Using this validated model, dynamic simulations were also carried out for containers of 20, 30, and 40 tons. The results showed that the reaction force of the roller guide was increased from 74.7 kN to 91.2 kN as the weight of container increased. For the design of a roller guide for SGS, the results obtained in this study can be used to reduce the reaction force by employing a rubber roller or a highly damped rotational joint.

Improvement of the Detection of LOB through Reconstruction of an Internal Model

Many researchers have tried to detect the falling and to reduce the injury associated with falling. Normally the method of detection of a loss of balance is more efficient than that of a compensatory motion in order to predict the falling. The detection algorithm of the loss of balance was composed of three main parts: parts of processing of measured data, construction of an internal model and detection of the loss of balance. The internal model represented a simple dynamic motion balancing with two rear legs of a four-legged chair and was a simplified model of a central nervous system of a person. The internal model was defined by the experimental data obtained within a fixed time interval, and was applied to the detecting algorithm to the end of the experiment without being changed. The balancing motion controlled by the human brain was improved in process of time because of the experience accruing to the brain from controlling sensory organs. In this study a reconstruction method of the internal model was used in order to improve the success rate and the detecting time of the algorithm and was changed with time the same as the brain did. When using the reconstruction method, the success rate and the detecting time were 95 % and 0.729 sec, respectively and those results were improved by about 7.6 % and 0.25 sec in comparison to the results of the paper of Ahmed and Ashton-Miller. The results showed that the proposed reconstruction method of the internal model was efficient to improve the detecting performance of the algorithm.

Kinematic Analysis of the Neck and Upper Extremities During Walking in Healthy Young Adults

The objective of this paper is to quantify the local stabilities of the neck and upper extremities (right/left shoulders and right/left elbows), and investigate differences between linear and nonlinear measurements of the associated joint motions and differences in the local stability between the upper and lower extremities. This attempt involves the calculation of a nonlinear parameter, Lyapunov Exponent (LE), and a linear parameter, Range of Motion (ROM), during treadmill walking in conjunction with a large population of healthy subjects. Joint motions of subjects were captured using a three-dimensional motion-capture system. Then mathematical chaos theory and the Rosenstein algorithm were employed to calculate LE of joints as the extent of logarithmic divergence between the neighboring state-space trajectories of flexion-extension angles. LEs computed over twenty males and twenty females were 0.037±0.023 for the neck, 0.043±0.021 for the right shoulder, 0.045±0.030 for the left shoulder, 0.032±0.021 for the right elbow, and 0.034±0.026 for the left elbow. Although statistically significant difference in the ROM was observed between all pairs of the neck and upper extremity joints, differences in the LE between all pairs of the joints as well as between males and females were not statistically significant. Between the upper and lower extremities, LEs of the neck, shoulder, and elbow were significantly smaller than those of the hip (~0.064) and the knee (~0.062). These results indicate that a statistical difference in the local stability between the upper extremity joints is not significant. However, the different result between the ROM and LE gives a strong rationale for applying both linear and nonlinear tools together to the evaluation of joint movement. The LEs of the joints calculated from a large population of healthy subjects could provide normative values for the associated joints and can be used to evaluate the recovery progress of patients with joint related diseases.

Stability of Treadmill Walking Related with the Movement of Center of Mass

The human gait is highly coordinative as to achieve combined movements of extremity joints at a desired speed. The purpose of study is to relate the variability of hip joint motion with the movement of the center of mass (COM) of the whole body in the treadmill walking. Each walking speed was converted to Froude number for normalizing differ- ent subject statures. Flexion-extension angles of the hip and the anterioposterior movement of COM were calculated. The correlation was relatively low (R 2 =0.113) between the move- ment of COM and the normalized walking speed. These results revealed that the movement of COM must be considered as one of important parameters for the analysis of walking stabil- ity on the treadmill

Effect of Data Selection on the Loss of Balance in the Seated Position

A fast and accurate detection of the loss of balance (LOB) can reduce the elderly fall that is one of the most dangerous injuries. Real-time detection of body reactions against a fall will be used to improve the performance of devices for the elderly. The loss of balance is detected by control error anomaly (CEA) that is an unusually large value of the system control error.

Analysis of Isometry of the Anterior Cruciate Ligament for Optimal Ligament Reconstruction

The anterior cruciate ligament (ACL) is liable to a major injury that often results in a functional impairment requiring surgical reconstruction. The success of reconstruction depends on such factors as attachment positions, initial tension of ligament and surgical methods of fixation. The purpose of this study is to find isometric positions of the substitute during flexion/extension. The distance between selected attachments on the femur and tibia was computed from a set of measurements using a 6 degree-of-freedom magnetic sensor system. A three-dimensional knee model was constructed from CT images and was used to simulate length change during knee flexion/extension. This model was scaled for each subject. Twenty seven points on the tibia model and forty two points on the femur model were selected to calculate length change. This study determined the maximum and minimum distances to the tibial attachment during flexion/extension. The results showed that minimum length changes were (average ). The most isometric region was both the posterosuperior and anterior-diagonal areas from the over-the-top. The proposed method can be utilized and applied to an optimal reconstruction of ACL deficient knees.

A Simulation Model of the ACL Function Using MADYMO

A mathematical knee model was constructed using MADYMO. The purpose of this study is to present a more realistic model of the human knee to reproduce human knee motion. Knee ligaments were modeled as line elements and the surrounding muscles were considered as passive restraint elements. A calf-free-drop test was performed to validate the suggested model. A calf was dropped from the rest at about 65 degree flexed posture in the prone position. The motion data were recorded using four video cameras and then three dimensional data were acquired by Kwon3D motion analysis software. The results showed that general shapes of angular quantities were similar in both the experiment and computer simulation. Functional stability of the anterior cruciate ligament was explicitly revealed through this model.

A Study of Adaptive Bone Remodeling by Cellular Automata Method

An adaptive bone remodeling is simulated by using the cellular automata (CA) method. It is assumed that bone tissue consist of bone marrow, osteoclast, osteoblast cell or osteoprogenitor cell. Two types of local rule are adopted; those are the metabolism rule and adaptive bone formation rule. The metabolism rule is based on the interactions of cells and the bone formation rule is based on the adaptation against the mechanical stimulus. The history of load and memory of mechanical stimulus are also considered in the local rules. As a result, the pattern of distribution of the bone tissue is dynamically adequate and it is similar to intact cancellous bone.