Range of motion (ROM) is an essential index for assessing the effectiveness of therapeutics in clinical practice. Rehabilitation therapists commonly use a goniometer to manually measure the ROM of finger joints. However, the measurement could be time consuming and burdening for patients, particularly when multiple finger joints are required to be measured. The required measurement accuracies of general rehabilitation and hand therapy tests are less than 5° and 2°, respectively. Therefore, in this study, we developed an active ROM digital testing device to reduce the measurement time and ease the burden on both patients and rehabilitation therapists during the measurement. The proposed digital testing device comprises an Intel RealSense depth camera and a computer. Rehabilitation therapists point the camera toward the patient’s finger joints to capture the RGB and depth images. Similar to the measurement principle of the goniometer, the target joint angle can be computed by obtaining the three-dimensional coordinates of the point cloud on the centerline of the finger bones that form the joint and the center point of the joint. The effectiveness of the proposed device was verified by comparing the generated results with those obtained from the goniometer. In 91.7% of the trials conducted in this study, the error of the proposed digital testing device was found to be less than 2° with a mean measurement time of 4.9 s, which is 46.2% less that of the goniometer.

Neural oscillators, which are a mathematical model of a central pattern generator, have been used to investigate human gait and control mobile robots. A typical neural oscillator uses two neurons that mutually inhibit each other’s activity. The exact orbitally-stable conditions of the neural activity of neural oscillators without external signals have been reported. However, the behavior of neural oscillators with external signals is unclear because their neural activity depends on the external signals, which have many types. In this study, for simplicity, external signals were regarded as a sinusoidal wave with a period T_ex and an amplitude A_ex. The connectivity a_ij, ratio for time constants τ_z/τ_x, and fatigue coefficient b were changed for neurons i and j, while T_ex and A_ex were changed for external signals. The orbit-stability of the output signals from a neuron was decided based on the transient time (≦ 3 s) and the duration (≧ 30 s). The period T_out and the amplitude A_out of the output signals were evaluated. T_out had discrete values of T_ex, 2T_ex, or 0.5T_ex or was non-orbitally-stable (value of 0). When A_ex was greater than or equal to u_i, the neural oscillator became synchronized. For a small T_ex, some combinations of τ_z/τ_x and a_ij values led to instability. For a large T_ex, some combinations of b and a_ij values led to instability. In contrast to T_out, the amplitude A_out of the output signal showed continuous changes depending on τ_z/τ_x, b, and a_ij. The amplitude A_out could be expressed as the sum of u_i and A_ex. A_out was not significantly affected by τ_z/τ_x but decreased with decreasing b.

Osteoarthritis (OA) is the most common degenerative joint disease. In the advanced stages of OA, patients suffer from severe pain, functional limitations in the affected joints, and restriction of mobility. In the animal test to develop therapeutic agents of intra-articular injection for knee OA, it is important to understand the functional properties of synovial joints, and to establish precise measurement techniques. The pendulum test can mechanically evaluate the friction properties of joints. In this study, the frictional properties of the synovial joint were measured using a novel system based on the equation of motion for pendulum joint motion. It was hypothesized that the motion during the pendulum test included rotation motion and translation motion and that the instantaneous center of rotation changes occurred. It was also hypothesized that the coefficient of friction would fluctuate within one cycle in response to changes in the instantaneous center of rotation. To test these hypotheses, the motion of a rabbit knee joint was measured using a pendulum test with three laser displacement sensors, and the instantaneous center of rotation was calculated. It considered the fluctuation of the instantaneous center of rotation and measured the fluctuation of the coefficient of friction in one cycle using a novel calculation method. The trajectory of the instantaneous center of rotation was obtained, and changes in the motion phase were observed. The coefficients of friction were not uniform but were dependent on the phase of the joint motion. The coefficients of friction fluctuated significantly with a cycle of half of the joint motion.

To understand adaptive bone remodeling in response to external mechanical stimuli, researchers have elucidated the mechanisms of mechanosensing and mechanoresponse through in vitro experiments targeting subcellular components from molecules to organelles. Such subcellular experiments have been performed by applying mechanical stimuli to mechanosensitive components and by measuring and observing the dynamic behaviors of the mechanosensitive and mechanoresponsive components. For a better understanding of the importance of the subcellular experiments, this article reviews the recent subcellular experiments for osteoblasts and osteocytes. First, we introduce the tools used for the stimulation and measurement/observation, and we discuss how these tools have contributed to the elucidation of the mechanisms. Second, we shed light on how the findings on the behaviors of the subcellular components have enhanced our basic understanding of the underlying mechanisms. Furthermore, we present future perspectives for subcellular experiments. To do this, we discuss the utilization of microscopes with higher spatial resolution and discuss focus points for a clearer understanding of these mechanisms in osteocytes. Future experiments will reveal how osteoblasts and osteocytes sense and respond to external mechanical stimuli in their surrounding environment in bone, and how cellular behaviors finally lead to the regulation of bone resorption and formation in adaptive bone remodeling.

When wearing clothes, one feels pressure, called clothing pressure, and friction. These are considered to be factors of the comfort ableness of wearing clothes. Although the contact pressure on the skin and shear stress due to friction are considered to have an important influence on the wearing comfort, no study has been conducted to simultaneously measure them while wearing clothes because of the difficulty in measuring contact stress on the interface between clothing and skin. In this study, we fabricated a thin and flexible triaxial stress sensor that can simultaneously measure contact pressure and shear stress on the skin. We bonded the sensor on the skin to measure contact pressure and shear stress with wear clothing. The sensor was attached to the subject's proximal part of the right knee joint, and the subject wore a commercially available sports legging. In the measurement experiment, the stress between the clothing and the skin was measured during the squatting motion. Shear stresses in the proximal and medial directions were detected during flexion of the knee joint. The reason is considered to be the friction caused by the sports legging being stretched in the proximal and medial directions on the skin during the knee joint flexion. When the knee was extended, the shear stress was reduced by returning of the legging to its initial position. The thin and flexible sensor fabricated was able to simultaneously detect contact pressure and shear stress between clothing and skin during the squatting motion. The sensor is expected to contribute to the quantification of the comfort ableness.