Introduction: In the United States, access to microprocessor-controlled prosthetic ankles is limited to patients with lower-limb loss classified as unlimited community ambulators or greater. However, the potential benefits of these devices have not been evaluated among patients classified as household or limited community ambulators. This study examined the benefit of hydraulic-and microprocessor-controlled prosthetic ankles for patients classified as limited community ambulators. Materials and Methods: Four different treatment configurations were evaluated using a randomized crossover study design. These four configurations included the participant's current flexible keel (FK) prosthetic foot, an energy-storage-and-return foot (ESAR), a hydraulic ankle (HA), and a microprocessor ankle (MPA). After a 2-week accommodation period, both patient-reported and performance-based outcome measures were recorded for each ankle foot system. A StepWatch activity monitor and two-dimensional video motion analysis were also used to evaluate each system. Results: A single participant meeting the inclusion criteria was recruited. The patient-reported mobility and socket fit instruments were greatest with the HA system. When assessed on slopes and stairs, the MPA demonstrated benefits on hill ascent and stair descent. In considering the walking speed and perceived exertion jointly, the HA system allowed similar walking speed but lower exertion compared with fixed-ankle systems. The patient-reported low back pain and balance confidence instruments did not provide useful data for interpretation. Two-dimensional video motion analysis showed that the HA and MPA contributed to improved ankle and knee postures when ascending and descending a slope. The step activity data showed the greatest activity with the HA. Discussion: The results from the outcome measures showed a varying level of benefit across all four of the treatment configurations. Both the HA and MPA had favorable scores in varying performance-based outcome measures, but the HA scored the most favorable in a majority of the patient-reported outcome measures. Conclusion:The results show varying benefits of the microprocessor-and hydraulic-controlled prosthetic components over fixed-ankle ESAR and FK feet, based on both performance-based and patient-reported outcome measures. Further studies are needed to fully evaluate these benefits in larger sample sizes. (
Objective: During dynamic injury scenarios, such as motor vehicle crashes, neck biomechanics contribute to head excursion and acceleration, influencing head injuries. One important tool in understanding head and neck dynamics is computational modeling. However, realistic and stable muscle activations for major muscles are required to realize meaningful kinematic responses. The objective was to determine cervical muscle activation states for 6-year-old, 10-year-old, and adult 50th percentile male computational head and neck models. Currently, pediatric models including muscle activations are unable to maintain the head in an equilibrium position, forcing models to begin from nonphysiologic conditions. Recent work has realized a stationary initial geometry and cervical muscle activations by first optimizing responses against gravity. Accordingly, our goal was to apply these methods to Duke University's head-neck model validated using living muscle response and pediatric cadaveric data.Methods: Activation schemes maintaining an upright, stable head for 22 muscle pairs were found using LS-OPT. Two optimization problems were investigated: a relaxed state, which minimized muscle fatigue, and a tensed activation state, which maximized total muscle force. The model's biofidelity was evaluated by the kinematic response to gravitational and frontal impact loading conditions. Model sensitivity and uncertainty analyses were performed to assess important parameters for pediatric muscle response. Sensitivity analysis was conducted using multiple activation time histories. These included constant activations and an optimal muscle activation time history, which varied the activation level of flexor and extensor groups, and activation initiation and termination times.Results: Relaxed muscle activations decreased with increasing age, maintaining upright posture primarily through extensor activation. Tensed musculature maintained upright posture through coactivation of flexors and extensors, producing up to 32 times the force of the relaxed state. Without muscle activation, the models fell into flexion due to gravitational loading. Relaxed musculature produced 28.6-35.8 N of force to the head, whereas tensed musculature produced 450-1023 N. Pediatric model stiffnesses were most sensitive to muscle physiological cross-sectional area.Conclusions: Though muscular loads were not large enough to cause vertebral compressive failure, they would provide a prestressed state that could protect the vertebrae during tensile loading but might exacerbate risk during compressive loading. For example, in the 10-year-old, a load of 602 N was produced, though estimated compressive failure tolerance is only 2.8 kN. Including muscles and time-variant activation schemes is vital for producing biofidelic models because both vary by age. The pediatric activations developed represent physiologically appropriate sets of initial conditions and are based on validated adult cadaveric data.
The models are less stiff in dynamic anterioposterior bending than the ATDs; the secant stiffness of the 6- and 10-year-old models is 53 and 67 percent less than that of the HIII ATDs. The ATDs exhibit nonlinear stiffening and the models demonstrate nonlinear softening. Consequently, the models do not remain within the Mertz scaled flexion bending corridors. The more compliant model necks suggest an increased potential for head impact via larger head excursions. The pediatric anterioposterior bending corridors developed in this study are extensible to any frontal loading condition through calculation and sensitivity analysis. The corridors presented in this study are the first based on pediatric cadaveric data and provide the basis for future, more biofidelic, designs of 6- and 10-year-old ATD necks.
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