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Relative foot position estimation is important for rehabilitation, sports training and functional diagnostics. In this paper an extended Kalman filter fusing ultrasound range estimates and inertial sensors is described. With this filter several gait parameters can be estimated ambulatory. Step lengths and stride widths from 54 walking trials of three healthy subjects were estimated and compared to an optical reference. Mean (\pm standard deviation) of absolute difference was 1.7 cm (\pm1.8 cm) and 1.2 cm (\pm1.2 cm) for step length and stride width respectively. Walking with a turn and walking around in a square area were also investigated and resulted in mean absolute differences of 1.7 cm (\pm2.0 cm) and 1.5 cm (\pm1.5 cm) for step lengths and stride widths. In addition to these relative positions, velocities, orientations and stance and swing times can also be estimated. We conclude that the presented system is low-cost and provides a complete description of footstep kinematics and timing. [ABSTRACT FROM AUTHOR]

The prerequisites for stable crutch supported standing were analyzed in this paper. For this purpose, a biomechanical model of crutch supported paraplegic stance was developed assuming the patient was standing with extended knees. When using crutches during stance, the crutches will put a position constraint on the shoulder, thus reducing the number of degrees of freedom. Additional hip-joint stiffness was applied to stabilize the hip joint and, therefore, to stabilize stance. The required hip-joint stiffness for changing crutch placement and hip-joint offset angle was studied under static and dynamic conditions. Modeling results indicate that, by using additional hip-joint stiffness, stable crutch supported paraplegic standing can be achieved, both under static as well as dynamic situations. The static equilibrium postures and the stability under perturbations were calculated to be dependent on crutch placement and stiffness applied. However, postures in which the hip joint was in extension (C postures) appeared to the most stable postures. Applying at least 60 N · m/rad hip-joint stiffness gave stable equilibrium postures in all cases. Choosing appropriate hip-joint offset angles, the static equilibrium postures changed to more erect postures, without causing instability or excessive arm forces to occur. Index Terms—Biomechanics; control systems; data processing; modeling; orthosis; paraplegic standing; simulation. [ABSTRACT FROM AUTHOR]

Paraplegic persons can stand with hip-knee-ankle-foot orthoses (HKAFO) and crutches. However, current HKAFOs restrict body movement extensively, which may impede functional upper-body movements. A more compliant body support using a more compliant orthosis or well-controlled functional electrical stimulation system may increase freedom of movement to the user, but should not impede stability and required arm support. In the current study, we investigated the consequences of varying stiffness applied at the hip to postural stability and required crutch force during paraplegic stance. Experiments were performed on five paraplegic persons with spinal cord lesions varying from T1 to T12. Static postures and dynamic responses to perturbations were tested for varying hip stiffness and crutch placements. The minimal hip-joint stiffness for stable stance appeared to depend on lesion level. In contrast to the predictions of a previous modeling study, no statistically significant influences of hip-joint stiffness or crutch-to-foot distance on posture and applied crutch forces were found. It is hypothesized that the main reasons of this discrepancy are the active upper-body efforts the paraplegic HKAFO users are still able to exert and the remaining flexibility of the upper trunk and shoulder region, which is present despite the restrictions of the orthosis. Index TermsαBiomechanics; control systems; data processing; orthosis; paraplegic standing. [ABSTRACT FROM AUTHOR]