A muscle synergy-based method to estimate muscle activation patterns of children with cerebral palsy using data collected from typically developing children.

Preparing children with cerebral palsy prior to gait analysis may be a challenging and time-intensive task, especially when large number of sensors are involved. Collecting minimum number of electromyograms (EMG) and yet providing adequate information for clinical assessment might improve clinical workflow. The main goal of this study was to develop a method to estimate activation patterns of lower limb muscles from EMG measured from a small set of muscles in children with cerebral palsy. We developed and implemented a muscle synergy extrapolation method able to estimate the full set of lower limbs muscle activation patterns from only three experimentally measured EMG. Specifically, we extracted a set of hybrid muscle synergies from muscle activation patterns of children with cerebral palsy and their healthy counterparts. Next, those muscle synergies were used to estimate activation patterns of muscles, which were not initially measured in children with cerebral palsy. Two best combinations with three (medial gastrocnemius, semi membranous, and vastus lateralis) and four (lateral gastrocnemius, semi membranous, sartorius, and vastus medialis) experimental EMG were able to estimate the full set of 10 muscle activation patterns with mean (± standard deviation) variance accounted for of 79.93 (± 9.64)% and 79.15 (± 6.40)%, respectively, using only three muscle synergies. In conclusion, muscle activation patterns of unmeasured muscles in children with cerebral palsy can be estimated from EMG measured from three to four muscles using our muscle synergy extrapolation method. In the future, the proposed muscle synergy-based method could be employed in gait clinics to minimise the required preparation time.

Dynamic muscle-tendon length following zone 2 calf lengthening surgery in two populations with equinus gait: Idiopathic Toe Walkers and Cerebral Palsy.

BACKGROUND: Two populations commonly presenting with equinus gait are Idiopathic Toe-Walkers and children with Cerebral Palsy. Surgical intervention to treat equinus is defined by three zones. Zone three surgery, performed at the Achilles tendon, is most commonly used clinically. There is however, evidence from simulation studies that zone two surgery, performed at the muscle belly, might provide better functional outcomes. The purpose of this study was to investigate the effect of zone two calf-lengthening on post-operative gait in these populations. METHODS: A retrospective audit of the Queensland Children's Motion Analysis Service database identified 17 toe-walkers (mean age 10.13 (SD 2.625)) and 11 Cerebral Palsy (mean age 9.72 (SD 4.04)) participants that received calf-lengthening surgery for plantarflexion contracture and had pre- and post-surgery 3D gait analysis. Inverse kinematics, dynamics, and muscle analysis were performed in OpenSim (v3.3) using a modified gait2392 model. Pre to post-surgery comparisons were performed in MATLAB using statistical parametric mapping. Dependent variables included ankle kinematics, powers and muscle-tendon length estimates. FINDINGS: The primary outcome of this study was that ankle dorsiflexion increased in both Idiopathic Toe Walking and Cerebral Palsy groups post-calf lengthening across 90% and 85% of the gait cycle respectively. There was an increase in modelled muscle-tendon lengths, specifically in the medial gastrocnemius, of 78% (toe-walkers), and 100% (Cerebral Palsy) of the gait cycle. Power generation during push-off was not affected. INTERPRETATION: Overall, the results appear to support the efficacy of zone 2 calf-lengthening for children with Cerebral Palsy and Idiopathic Toe Walking.

Non-negative matrix factorisation is the most appropriate method for extraction of muscle synergies in walking and running.

Muscle synergies provide a simple description of a complex motor control mechanism. Synergies are extracted from muscle activation patterns using factorisation methods. Despite the availability of several factorisation methods in the literature, the most appropriate method for muscle synergy extraction is currently unknown. In this study, we compared four muscle synergy extraction methods: non-negative matrix factorisation, principal component analysis, independent component analysis, and factor analysis. Probability distribution of muscle activation patterns were compared with the probability distribution of synergy excitation primitives obtained from the four factorisation methods. Muscle synergies extracted using non-negative matrix factorisation best matched the probability distribution of muscle activation patterns across different walking and running speeds. Non-negative matrix factorisation also best tracked changes in muscle activation patterns compared to the other factorisation methods. Our results suggest that non-negative matrix factorisation is the best factorisation method for identifying muscle synergies in dynamic tasks with different levels of muscle contraction.

Medial gastrocnemius and soleus muscle-tendon unit, fascicle, and tendon interaction during walking in children with cerebral palsy.

AIM: This study investigates the in vivo function of the medial gastrocnemius and soleus muscle-tendon units (MTU), fascicles, and tendons during walking in children with cerebral palsy (CP) and an equinus gait pattern. METHOD: Fourteen children with CP (9 males, 5 females; mean age 10y 6mo, standard deviation [SD] 2y 11mo; GMFCS level I=8, II=6), and 10 typically developing (6 males, 4 females; mean age 10y, SD 2y 1mo) undertook full body 3D gait analysis and simultaneous B-mode ultrasound images of the medial gastrocnemius and soleus fascicles during level walking. Fascicle lengths were analysed using a semi-automated tracking algorithm and MTUs using OpenSim. Statistical parametric mapping (two-sample t-test) was used to compare differences between groups (p<0.05). RESULTS: In the CP group medial gastrocnemius fascicles lengthened during mid-stance gait and remained longer into late-stance compared to the typically developing group (p<0.001). CP medial gastrocnemius fascicles shortened less during stance (1.16mm [SD 1.47mm]) compared to the typically developing group (4.48mm [SD 1.94mm], p<0.001). In the CP group the medial gastrocnemius and soleus MTU and tendon were longer during early- and mid-stance (p<0.001). Ankle power during push-off (p=0.015) and positive work (p<0.002) and net work (p<0.001) were significantly lower in the CP group. INTERPRETATION: Eccentric action of the CP medial gastrocnemius muscle fascicles during mid-stance walking is consistent with reduced volume and neuromuscular control of impaired muscle. Reduced ankle push-off power and positive work in the children with CP may be attributed to reduced active medial gastrocnemius fascicle shortening. These findings suggest a reliance on passive force generation for forward propulsion during equinus gait.