Musculoskeletal modeling and simulation techniques have been used to gain insights into movement disabilities for many populations, such as ambulatory children with cerebral palsy (CP). The individuals who can benefit from these techniques are often limited to those who can walk without assistive devices, due to challenges in accurately modeling these devices. Specifically, many children with CP require the use of ankle-foot orthoses (AFOs) to improve their walking ability, and modeling these devices is important to understand their role in walking mechanics. The purpose of this study was to quantify the effects of AFO mechanical property assumptions, including rotational stiffness, damping, and equilibrium angle of the ankle and subtalar joints, on the estimation of lower-limb muscle forces during stance for children with CP. We analyzed two walking gait cycles for two children with CP while they were wearing their own prescribed AFOs. We generated 1000-trial Monte Carlo simulations for each of the walking gait cycles, resulting in a total of 4000 walking simulations. We found that AFO mechanical property assumptions influenced the force estimates for all the muscles in the model, with the ankle muscles having the largest resulting variability. Muscle forces were most sensitive to assumptions of AFO ankle and subtalar stiffness, which should therefore be measured when possible. Muscle force estimates were less sensitive to estimates of damping and equilibrium angle. When stiffness measurements are not available, limitations on the accuracy of muscle force estimates for all the muscles in the model, especially the ankle muscles, should be acknowledged.

The goal of this pilot study was to characterize the effects of gait training on the capacity of muscles to produce body accelerations and relate these changes to mobility improvements seen in children with cerebral palsy (CP). Five children (14 years ± 3 y; GMFCS I-II) with spastic diplegic CP participated in a 6-week gait training program. Changes in 10-m fast-as-possible walking speed and 6-minute walking endurance were used to assess changes in mobility. In addition, musculoskeletal modeling was used to determine the potential of lower-limb muscles to accelerate the body's center of mass vertically and forward during stance. The mobility changes after the training were mixed, with some children demonstrating vast improvements, while others appeared to be minimal. However, the musculoskeletal results revealed unique responses for each child. The most common changes occurred in the capacity for the hip and knee extensors to produce body support and the hip flexors to produce body propulsion. These results cannot yet be generalized to the broad population of children with CP, but demonstrate that therapy protocols may be enhanced by modeling analyses. The pilot study results provide motivation for gait training emphasizing upright leg posture, mediolateral balance, and ankle push-off.

The salience network is responsive during a range of conditions requiring immediate behavioral responses, including pain processing. Resting-state functional connectivity of the salience network to the sensorimotor cortex is altered in chronic pain. However, little is understood about their fundamental communication in the absence of pain. In this study, we mapped salience network resting-state functional connectivity across sensorimotor cortex in healthy individuals. Using electromyography and task-based functional magnetic resonance imaging (fMRI), we first localized distinct regions-of-interest across sensorimotor cortex in medial (gluteal), intermediate (shoulder), and lateral (hand) areas. We then used resting-state fMRI for two cohorts (primary and replication) of healthy individuals from public repositories to map salience network resting-state functional connectivity across sensorimotor cortex. Both the primary and replication cohorts exhibited significant heterogeneity in salience network resting-state functional connectivity across the sensorimotor regions-of-interest. Using a cortical flatmap to visualize the entire sensorimotor surface, we observed similar heterogeneity in both cohorts. In general, the somatotopic representation of proximal body regions (trunk/face) had higher salience network resting-state functional connectivity compared to distal body regions (upper/lower limbs). We conclude that sensorimotor cortex is spatially heterogeneous in its interaction with the salience network in healthy individuals.

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