We associate cortical sensorimotor (cortical proprioception) impairments with peripheral motor disorders (spasticity) at the ankle joint. The cortical proprioception is quantified by using evoked fields to passive movements recorded with magnetoencephalography (MEG), whilst biomechanical evaluation consists of spasticity assessments. The cortical proprioceptive processing is evaluated by following the proprioceptive stimulation paradigms and analysis tools developed by Dr. Piitulainen, which are already well established in adults and elderly people24, and recently successfully applied in children with cerebral palsy. The cortical proprioceptive processing is primarily reflected by corticokinematic coherence (phase locked between limb kinematics and MEG). The MEG data are already recorded within the EXECP project.
With regard to motor disorders, spinal-level mechanisms are assessed by H-reflexes and M-waves from soleus muscle by percutaneous electrical stimulation of the tibial nerve while the participants are lying prone on a table. Spasticity of soleus and medial gastrocnemius is being assessed utilizing the tonic stretch reflex threshold. The participants are seated with the knee joint fully extended and an ankle dynamometer will induce stretches. EMG data is used to determine the joint angle in which the stretch reflex onset occurred. Also this data are already recorded within the EXECP project. We hypothesize to find such an association between spasticity and cortical proprioception.
Ankle resistance is also related to the changes in musculoskeletal properties. These changes occur in muscle composition, with fatty infiltration and an increase in the accumulation of connective and fibrous tissues which replace the contractile elements, impeding the muscle to contract functionally. In addition, muscle morphology is altered, including reduced muscle volume and length compared to age-matched typically developing children. Their combination contributes to muscle contractures, increased stiffness (rigidity), and reduced muscle strength. Current methods for analysing morphology, composition, and stiffness are based on magnetic resonance imaging (MRI). MRI technique can be reliably used for estimating intramuscular content. However, an ultrasound (US) approach would be crucial for frequent clinical applications (ideally for monitoring treatments) since it allows low costs and frequent usage. Yet, US methodologies are not yet well established for extracting these parameters. Once the musculoskeletal technique is established, the 3D US framework will be used in JYU for extracting muscle volume, length, and echo-intensity. Children will also participate in 3D gait analysis with simultaneous 2D US imaging. The US probe will be positioned over the medial gastrocnemius (MG) muscle-tendon junction, and over the MG belly allowing imaging of MG and soleus. Since the final goal in cerebral palsy is to improve gait ability, musculoskeletal properties were recently analysed also during walking. However, the relationship between passive and active musculoskeletal properties is still unclear. This relationship will show how altered passive and active musculoskeletal properties affect gait.
