Journal of Mechanics in Medicine and Biology

Measurement of fetal femur length is crucial for the estimation of fetal age and growth pattern. Due to the noisy nature of ultrasound images and the variation in image acquisition and measurement techniques, manual measurements are subject to interobserver and intraobserver variability. The motivation of this paper is to study the efficiency of automated methods used in the femur endpoint detection module of our proposed computer-assisted processing and analysis system, which is employed to determine the gestational age for promoting the standardization of fetal femur measurements, thus resulting in more reliable age estimates. The proposed methods are based on the morphological operators methods⁵ and the morphological watershed segmentation method. We applied these methods on a set of 100 digitized fetal femur images of size 287 × 224 pixels with 256 gray-level images and a resolution of 100 pixels per inch (ppi) horizontally and vertically. The results showed that the watershed method was the more efficient one and gave reliable results for every femur image tested.

Backpack carrying is a considerable daily "occupational" load among schoolchildren. Most of the research on children's backpacks have focused on gait pattern and trunk forward lean; only a few researches have investigated the impact of backpack carrying on children using the measurements of static posture and gait kinetics. This study investigated the changes in ground reaction force (GRF) and trunk inclination among primary students when carrying heavy backpacks. A randomized controlled experimental study was conducted on seven boys aged between 9 and 11 years old with a similar body mass index. Observations were done when the boys were carrying school bags of 0% (as control), 10%, 15%, and 20% of their own body weight while walking normally. Data acquisition was carried out using force platforms and a 3D motion analysis system. A significant difference in GRF at a load of 20% of body weight was found: the vertical GRF increased almost three times when loads increased up to 20% of body weight compared to 10% of body weight. The anterior–posterior GRFs were asymmetrical when loads were increased. When carrying a load of 15% of body weight, all of the seven subjects adopted a compensatory trunk inclination. The emphasis on GRF and trunk inclination suggests that the safest load applied does not exceed 15% of body weight.

Both sensory information and mechanical properties of the musculoskeletal system are necessary for fast and appropriate reactions of humans and animals to environmental perturbations. In this paper, we focus on the musculoskeletal system and study the stability of a human elbow in an equilibrium state. We derive a biomechanical model of the human elbow, including an antagonistic pair of muscles, and investigate the stability analytically based on the theory of Ljapunov. Depending on the elbow angle and the level of coactivation, we obtain the following three qualitatively different behaviors: unstable, stable with real eigenvalues, and stable with complex eigenvalues. If the eigenvalues are real, then the system is critically damped; for complex eigenvalues, solutions near the equilibrium are oscillating. Based on experimental data, we found that in principle real and complex behaviors may occur in human arm movements. The experiments support the analytical predictions. Furthermore, in agreement with the simulations, we found differences in the experimental results among the subjects. The results of this study support the assumption that arm movements around an equilibrium point may be self-stabilized without sensory feedback or motor control, based only on mechanical properties of musculoskeletal systems.

RNA silencing (also known as RNA interference) suppresses the expression of genes posttranscriptionally. We propose a time delay model of RNA silencing through a system consisting of double-stranded RNA (dsRNA), RNA-induced silencing complex (RISC), messenger RNA (mRNA), and RISC–mRNA complex. The time delay model is based on the consideration that the regeneration (or degradation) of the RISC–mRNA complex needs a finite time τ. The model equations are analyzed using nonlinear dynamics methods, in particular the Hopf bifurcation theorem, and they are solved numerically. From the accomplished analytical and numerical calculations, it becomes clear that time delay τ is a key factor in the behavior of the model. In this case, it has a destabilizing effect on the silencing process.

In this work, the assessment of the mechanical strength of human femur trabecular bone and its classification into normal or abnormal are carried out using digital image processing and neural networks. The mechanical strength components of femur trabeculae, such as primary compressive (PC), primary tensile (PT), secondary tensile (ST), and Ward's triangle (WT), are delineated by the semiautomatic image processing procedure from the planar radiographic images (N = 90) of subjects that are acquired under controlled clinical settings. Parameters such as apparent mineralization and total area of the individual mechanical strength components are calculated for normal and abnormal samples. The data are trained with neural networks and validated. The classifications are carried out using feed-forward neural networks trained with the standard backpropagation algorithm. The abnormal and normal outputs are validated by sensitivity and specificity measurements. The observation shows that the investigation of bone mechanical strength at the various strength components is useful in classifying normal and abnormal human femur trabeculae from conventional radiographs. Furthermore, the results confirm the effectiveness of the neural network–based classification of femur trabeculae into normal and abnormal conditions. The sensitivity and specificity are found to be 100% and 80%, respectively. In this paper, the methodology, data collection procedures, and neural network–based analysis and results are discussed in detail.

Although venipuncture is one of the most common clinical procedures and is performed by trained medical staff, difficulties arise in 5% of insertion procedures. An instrument that guarantees the insertion of a needle into a vein in a single approach is expected to be beneficial to both medical staff and patients. The next step towards automatic venipuncture is to determine if insertion force feedback can be used, irrespective of insertion speed, insertion angle, or vein depth and diameter. Needle insertion experiments are performed on phantom and porcine tissues to study the interaction between the needle and tissue. A prototype instrument is developed to perform automatic venipuncture on the phantom. From the experiments, we conclude that an increased insertion speed of the needle leads to an increase in insertion force and tissue deformation. Furthermore, distinct force peaks are observed at the penetration of phantom skin and vein, thus enabling automatic detection of phantom vein puncture.

A mathematical model is developed in this paper for studying blood flow through a stenosed arterial segment by taking into account the slip velocity at the wall of the artery. Consideration of the non-Newtonian character of blood is made, where a constitutive relation of blood is described by the Herschel–Bulkley equation. The effect of slip at the arterial wall in the presence of mild, moderate, and severe stenosis growth at the lumen of an artery is investigated. Analytical expressions for skin friction, flow resistance, and the flow rate are derived by using the model. The derived expressions are computed numerically by considering an illustrative example. The study provides an insight into the effects of slip velocity on the volumetric flow rate of blood, flow resistance, and skin friction.