Changes in knee mechanics following anterior cruciate ligament reconstruction (ACLR) have been implicated as a contributor to the development of premature osteoarthritis (OA). However, changes in ambulatory loading in this population have not been well documented. While the magnitude of the external knee moment vector is a major factor in loading at the knee, there is not a comprehensive understanding of the changes in the individual components of the vector following ACL reconstruction. The purpose of this study was to test for differences in the three components of the external knee moment during walking and stair locomotion between ACLR, contralateral and healthy control knees. Forty-five ACLR and 45 healthy control subjects were tested during walking, stair ascent and descent. ACLR knees had a lower first peak adduction moment than contralateral knees during all three activities. Similarly, additional cases of significant differences between ACLR and contralateral knees consisted of lower peak moments for the ACLR than the contralateral knees. These differences were due to both ACLR and contralateral knees as the ACLR knees indicated lower and the contralateral knees greater peak moments compared to healthy control knees. The results suggest a compensatory change involving greater loading in the contralateral knee, perhaps due to lower loading of the ACLR knee. Further, lower knee moments of the ACLR knee suggest that increased joint loading may not be the initiating factor in the development of OA following ACL reconstruction; but rather previous described kinematic or biological changes might initiate the pathway to knee OA.
The results of this study provide an understanding of the relationship between kinematics and kinetics of the ACLD knee and the amount of time since injury. They suggest that elapsed time since injury might be an important factor when the function of ACL-injured knees is interpreted as it relates to osteoarthritis.
Electromyography (EMG) is commonly used to measure electrical activity of the skeletal muscles. As exoskeleton technology advances, these signals may be used to predict human intent for control purposes. This study used an artificial neural network trained and tested with knee flexion angles and knee muscle EMG signals to predict knee flexion angles during gait at 50, 100, 150, and 200 ms into the future. The hypothesis of this study was that the algorithm’s prediction accuracy would only be affected by time into the future, not subject, gender or side, and that as time into the future increased, the prediction accuracy would decrease. A secondary hypothesis was that as the number of algorithm training trials increased, the prediction accuracy of the artificial neural network (ANN) would increase. The results of this study indicate that only time into the future affected the accuracy of knee flexion angle prediction (p < 0.001), whereby greater time resulted in reduced accuracy (0.68 to 4.62 degrees root mean square error (RMSE) from 50 to 200 ms). Additionally, increased number of training trials resulted in increased angle prediction accuracy.
This paper presents a shape memory alloy actuator design using a bimorph structure capable of high-speed actuation and low power consumption. Two active layers of shape memory alloy wires are separated by a passive layer of thermoplastic polyurethane. This structure results in a bending actuator when current is alternated between the two active shape memory alloy layers. Actuators of lengths 20, 25, 30, 35, and 40 mm were tested at peak current input of 110, 120, 130, and 140 mA. The 40-mm actuator was shown to have a natural frequency of 11.4 Hz with a bending displacement of 26.4 mm perpendicular to the neutral position and a power input of 0.78 W (140 mA peak current input). A relationship between the input current and the resulting vibratory characteristics was found. As the current increases, the natural frequency decreases and the damping ratio increases. The experimental results are compared with a finite element method (FEM) vibration analysis and an Euler–Bernoulli cantilever beam equations.
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