Bone Mineral Density of Cervical Spine Vertebrae Using Quantitative Computed Tomography

While numerous studies exist quantifying the bone mineral content of the human lumber vertebrae, such information is not available for the cervical spine. This study determined the bone mineral densities of cervical vertebrae. Adult healthy human volunteers, ages ranging from 18 to 40 years, underwent quantitative computed tomography scanning of the neck. BMD data were divided according to subject weight (above and below 50th percentile, termed low and heavy mass) and gender. Low-mass subjects did not consistently have higher bone mineral density at all levels of the cervical column. Bone mineral were higher (259 ± 6 mg/cc) for females than males (247 ± 8 mg/cc); for the entire ensemble the mean density was 253 ± 9 mg/cc. Altered strength of cervical vertebrae coupled with the increased mobility of the disc at the inferior levels of the neck may explain regional biomechanical differences and subsequent physiologic effects secondary to aging. This study quantifies BMD of the human neck vertebrae and offers explanations to the biomechanical behaviors of the human cervical spine.

Multiphasic Finite Element Analysis of Physical Signals and Solute Transport in the Human Intervertebral Disc

A 3D finite element model for charged hydrated soft tissue containing charged/uncharged solutes was developed based on the multi-phasic mechano-electrochemical mixture theory [1–2]. This model was applied to analyze the mechanical, chemical and electrical signals within the human intervertebral disc under mechanical loading. The effects of tissue composition and material property on the physical signals and the transport of fluid, ions and nutrients were investigated. This study is important for understanding disc biomechanics, disc nutrition and disc mechanobiology.

Characterization of Myoelectric Signals Using System Identification Techniques

Human muscle motion is initiated in the central nervous system where a nervous signal travels through the body and the motor neurons excite the muscles to move. These signals, termed myoelectric signals, can be measured on the surface of the skin as an electrical potential. By analyzing these signals it is possible to determine the muscle actions the signals elicit, and thus can be used in manipulating smart prostheses and teleoperation of machinery. Due to the randomness of myoelectric signals, identification of the signals is not complete, therefore the goal of this project is to complete a study of the characterization of one set of hand motions using current system identification methods. The gripping motion of the hand and the corresponding myoelectric signals are measured and the data captured with a personal computer. Using computer software the captured data are processed and finally subjected to several system identification routines. Using this technique it is possible to construct a mathematical model that correlates the myoelectric signals with the matching hand motion.

Hydrodynamics of Cerebrospinal Fluid in Spinal Canal With Chiari Malformation and Syringomyelia

Magnetic resonance imaging (MRI) is has great potential as a tool for diagnosis of neurological diseases such as Chiari malformation (CM) and syringomyelia (SM). Its extended capability to obtain in-vivo velocities of blood or cerebrospinal fluid (CSF) allowed engineers to perform studies with engineering analysis applications such as computational fluid dynamics and physical modeling. Recently, a new MR technique called balanced steady-state free procession (bSSFP) cine imaging was developed for analysis of geometrical changes during the cardiac cycle due to compliance [1]. This study used MRI utilities to investigate hydrodynamic environment of CSF in the sub-cranial subarachnoid space (SAS). A model was constructed to simulate fluid dynamics of CSF in SAS. This model will allow investigation of detailed pressure and velocity using laser Doppler anemometry and pressure transducers. The MRI data from patient, healthy volunteers, the flow model were compared.

Simulation of the Residual Stresses Generated Due to Cement Polymerization in a THA

A personalized 3D model of the proximal femur is reconstructed from medical CT-scan images. The mechanical properties of the cortical and spongious bones are extracted from the medical images. A finite element model of a personalized total hip arthroplasty is developed to investigate the effect of residual stresses due to cement curing in the load transfer during simplified heel strike.

Proprioception Evaluation of Patients Undergoing Anterior Shoulder Stabilization

This paper presents the initial data from the first clinical usage of a 2nd generation device to measure proprioception of the shoulder or knee. The device was used to evaluate the surgical stabilization of subjects with anterior shoulder instability. Two types of shoulder proprioception were evaluated: Threshold to Detection of Passive Motion (TTDPM) and Reproduction of Passive Position (RPP). Data is presented for 12 subjects 1 year post-surgery. The data demonstrated that the involved limb TTDPM and RPP approached that of the uninvolved limb, and that the values improved as the shoulder was rotated upwards. Both results point to the efficacy of the repair method and the ability of the device to evaluate proprioception.

Evaluation of Possible Stress Distributions in Abdominal Aorta on the Basis of Physiologically Loading Data

It is highly desired to establish a method of estimating the stress state and mechanical properties in blood vessels numerically using diagnosis data. To obtain the mechanical state, it is necessary to evaluate the reliability of results from numerical simulation. In the current study, we investigate the possibility of stress distribution in a circular cylindrical shape of vascular wall based on the pressure-diameter relationship in the physiological pressure range with assumptions of a hyperelastic material and no residual stress. As another case, we simulate wall stress in an axisymmetric vessel at a mean pressure level. Results form the former case show that one has many solutions which reproduce the pressure-diameter (p-d) relationship and that more information is required to determine the mechanical properties. Results form the latter case show that a pair of Laplace equation and force equilibrium in the axial direction provides a wall stress for an axisymmetric shape of vessel.

RF Ablation in a Reconstructed Hepatic Geometry With an Electrical Heat Source

This research aims to develop a methodology for modeling three-dimensional radiofrequency (RF) ablation using a reconstructed hepatic vasculature geometry with an electrical heat source. Coupled mass, momentum, heat transfer, and electric field, including voltage potential, equations are solved. The effects of heat convection through the nearby arteries and elevated level of blood perfusion through the tissue on the temperature distribution near the tumor zone is studied. The results show that for an arterial inlet velocity of 13.8 cm/s and 27.6 cm/s the peak tumor temperature drops by 7% and 10%, respectively, whereas the temperature along the outer periphery of the tumor close to the arteries drops by 50% and 75%, respectively. Asymmetries in the temperature profile indicate that the ablation procedure elevates the temperature to the required level only at localized regions. In the other regions the heat energy is not adequate for tumor destruction thereby permitting possible tumor recursion.

Trabecular Bypass: Effect of Schlemm’s Canal and Collector Channel Dilation

An ocular outflow model is proposed to theorize the effect of Schlemm’s canal (SC) and/or collector channel (CC) dilation combined with a trabecular bypass on elevated intraocular pressure (IOP) in glaucomatous eyes. The dilated height of the elliptic SC is largest at the bypass and linearly deceases to the non-dilated height over the dilated circumferential length. The CC dilation is modeled with a reduced outflow resistance of second order polynomial. Equations governing the pressure and flow in SC are solved numerically. The model predicts that the IOP is reduced substantially with moderate dilation from the normal 20 μm to 40 μm at the bypass. SC dilation is more effective for eyes with smaller SC. The dilation of CC can also significantly lower the IOP. With the trabecular bypass alone, the elevated IOP is expected to drop to the mid-to-high teens. The IOP can be further reduced by another 3 to 6 mmHg with moderate SC and CC dilation.

Stress Distributions Along the Inner Wall of the Femoropopliteal Bypass Graft Anastomoses

The distal junction of a femoral or femoropopliteal artery bypass graft has a predilection for failure due to restenosis. However neither the initiation nor proliferation process of atherosclerotic plaque is completely understood. Presently it is hypothesized that the process of atherosclerosis initiates as a result of damage or ‘insult’ to the endothelium. The cause of this initial damage is unknown, although it is widely believed that wall shear stresses are a contributing factor. The primary cause of plaque proliferation has not yet been identified, however it is our belief that intramural pressure plays a significant role. In this study numerical models of the proximal and distal junctions were used to determine both the location and magnitude of the stresses caused by intramural pressure. The simulated artery bypass graft was examined under both static and dynamic conditions.