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We developed novel trunk musculoskeletal models with detailed muscle paths for predicting the thoracolumbar load, and validated the developed models under dynamic loading and various postures. Two types of musculoskeletal models with different paths of the trunk muscles were constructed: a Via-Point type (with linear muscles) and Wrapping type (with curved muscles along ellipsoids). We predicted the intradiscal pressure (IDP) with the models and compared the results with literature values. The IDP predicted using the wrapping-type model had an extremely strong correlation with IDP measurements from the thoracic spine. The results demonstrate the effectiveness of more accurate muscle paths in musculoskeletal models for predicting the thoracolumbar load.

In this study, we constructed a novel three-dimensional trunk musculoskeletal model that included thoracolumbar intervertebral using data from computed tomography (CT) and magnetic resonance imaging (MRI). Characteristics of the model are as follows. Firstly, the thoracolumbar structure was modeled in detail (i.e., skeleton，muscle paths and muscle cross-section areas) from CT and MRI data. Secondly, new factors were included in this model such as intra-abdominal pressure and physiological trunk range of motion to calculate internal biological forces more accurately than in previous models. Thirdly, this musculoskeletal trunk model is an aid to analyzing dynamic motion. The aims of this study was to analyze detailed three-dimensional motion in healthy adults using this model, and to estimate internal biological forces, including spinal moment and muscle force in a standing position. The validation of this model used the calculated intradiscal pressure for the L4/L5 disc according to previous reports. This model is able to analyze spinal moments and trunk muscle force during static motions. The present study confirms that the moment curve of spinal can be generalized in the various postures. The model has been validated, and was able to analyze three-dimensional motion (i.e., combinational factors of rotation and flexion). As a result, this model is expected to have clinical applications.

The restoration of motor functions of patients with spinal cord injury (SCI) is one of important subjects for study. For this purpose, methods of functional neuromuscular stimulation (FNS) have been investigated in medical science and practice during these three decades. However, we have not achieved complete restoration of motor functions in SCI patients. On the other hand, we have achieved useful devices in human-scaled transportation by using power assist technology. Thus, applying power assist technology to the problem of restoring motor functions is one of possible solutions and sounds practical. In this paper, we propose a new hybrid system to combine power assist technology and FNS for restoring motor functions of lower extremity in SCI patients. Both powered orthosis and FNS are used to generate and control the joints moments of lower extremity in the proposed hybrid system. The main role of powered orthosis to compensate the joints moments generated by FNS and to enhance the controllability of FNS with the actuators. The proposed hybrid control system has been experimentally evaluated in gait motions by measuring the angle trajectories and generated moments around the knee and hip joints in the cases when only actuators are used and both FNS and actuators of the orthosis are used. The results prove that the control method for the hybrid system is useful to restore motor functions of lower extremity in SCI patients.

This paper presents an adaptive simulator for a manual wheelchair to reduce the user's upper limb load during wheelchair manipulation and to increase the efficiency of wheelchair propulsion. The proposed simulator provides an optimal position of the handrim/lever and the desired angular position of the seat and backrest of the wheelchair based on the user's body function.

Patients with adult spinal deformity have various standing postures. Although several studies have reported a relationship between sagittal alignment and exacerbation of hip osteoarthritis, information is limited regarding how spinopelvic sagittal alignment changes affect hip joint loading. This study aimed to investigate the relationship between sagittal spinopelvic-lower limb alignment and the hip joint contact force (HCF) using a novel musculoskeletal model. We enrolled 20 women (78.3±6.7 years) from a single institution. Standing lateral radiographs were acquired to measure thoracic kyphosis, lumbar lordosis, the pelvic tilt, sacral slope, sagittal vertical axis (SVA), femur obliquity angle, and knee flexion angle. In the model simulation, the Anybody Modeling System was used, which alters muscle pathways using magnetic resonance imaging data. Each patient’s alignment was entered into the model; the HCF and hip moment in the standing posture were calculated using inverse dynamics analysis. The relationship between the HCF and each parameter was examined using Spearman’s correlation coefficient (r). The patients were divided into low SVA and high SVA groups, with a cutoff value of 50 mm for the SVA. The HCF was 168.2±60.1 N (%BW) and positively correlated with the SVA (r = 0.6343, p<0.01) and femur obliquity angle (r = 0.4670, p = 0.03). The HCF were 122.2 and 214.1 N (75.2% difference) in the low SVA and high SVA groups, respectively (p<0.01). The flexion moment was also increased in the high SVA group compared with that in the low SVA group (p = 0.03). The SVA and femur obliquity angle are factors related to the HCF, suggesting an association between adult spinal deformity and the exacerbation of hip osteoarthritis. Future studies will need to assess the relationship between the hip joint load and sagittal spinopelvic parameters in dynamic conditions.

Joint contractures decrease the patient's ability to walk, but usually other parts of the body compensate the affected joint contractures. When we restore the gait performance in paraplegic patients by means of functional electrical stimulation, however, we cannot expect complications of compensation. A computer simulation was done to clarify how the contractures affect the gait pattern when no complications of compensation were expected. A seven-segment link mechanical model was used for simulation of human walking in the sagittal plane. In turn, using a personal computer stance and swing-leg joint contractures of the ankle, knee, and/or hip were simulated. When stance-leg contracture was simulated, step length became short with increasing hip flexion contracture. The trunk was tilted backward during knee flexion or ankle plantarflexion contracture simulation. When the swing-leg contracture was simulated, step length became short with increasing knee flexion contracture. We found that hip or knee flexion contracture of < or = 15 degrees, or ankle plantarflexion contracture of < 0 degrees was required to maintain positive step length and forward movement of the center of gravity. These findings suggest that 15 degrees of hip and knee flexion contracture, and 0 degrees of ankle plantarflexion contracture are critical when gait restoration is performed by functional electrical stimulation.

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