A. Van Campenhout

Instrumented assessment of the effect of Botulinum Toxin-A in the medial hamstrings in children with cerebral palsy

This study examined the sensitivity of an instrumented spasticity assessment of the medial hamstrings (MEH) in children with cerebral palsy (CP). Nineteen children received Botulinum Toxin type A (BTX-A) injections in the MEH. Biomechanical (position and torque) and electrophysiological (surface electromyography, EMG) signals were integrated during manually-performed passive stretches of the MEH at low, medium and high velocity. Signals were examined at each velocity and between stretch velocities, and compared pre and post BTX-A (43 ± 16 days). Average change between pre and post BTX-A was interpreted in view of the minimal detectable change (MDC) calculated from previously published reliability results. Improvements greater than the MDC were found for nearly all EMG-parameters and for torque parameters at high velocity and at high versus low velocity (p<0.03), however large inter-subject variability was noted. Moderate correlations were found between the improvement in EMG and in torque (r=0.52, p<0.05). Biomechanical and electrophysiological parameters proved to be adequately sensitive to assess the response to treatment with BTX-A. Furthermore, studying both parameters at different velocities improves our understanding of spasticity and of the physiological effect of selective tone-reduction. This not only provides a clinical validation of the instrumented assessment, but also opens new avenues for further spasticity research.

European consensus on the concepts and measurement of the pathophysiological neuromuscular responses to passive muscle stretch

To support clinical decision‐making in central neurological disorders, a physical examination is used to assess responses to passive muscle stretch. However, what exactly is being assessed is expressed and interpreted in different ways. A clear diagnostic framework is lacking. Therefore, the aim was to arrive at unambiguous terminology about the concepts and measurement around pathophysiological neuromuscular response to passive muscle stretch.

O 019 - Do Botulinum Toxin-A and lower leg casting alter calf muscle and tendon lengths in children with spastic cerebral palsy?

INTRODUCTION Ankle joint hyper-resistance in children with spastic cerebral palsy (SCP) is commonly treated with Botulinum Toxin-A (BoNT-A) injections in the medial gastrocnemius (MG) combined with lower-leg casting. The overall aim of this combined treatment is to reduce spasticity and increase range of motion (1). Since hyper-resistance assessment mainly focuses on the joint level, whereas the treatment is directed at the muscle, it is worthwhile investigating the individual effects of BoNT-A and casting on MG and tendon lengths, to provide insight into the working mechanisms and to help improving treatment efficacy. RESEARCH QUESTION What are the effects of BoNT-A injections and lower-leg casting on the MG and tendon lengths, at resting position and maximum dorsiflexion, in children with SCP? METHODS Children with SCP were assigned by minimization to receive either two weeks of lower-leg casts (n = 12, mean age 8.27 years; GMFCS-level I-III) or MG BoNT-A injections (n = 11, mean age: 6.75 years; GMFCS-level I-III). Data was acquired by 3D-freehand-ultrasound (2) at baseline and two weeks post-intervention with the knee in flexion (30.9° ± 3.7°) and the ankle in resting position and maximum dorsiflexion (maxDF). The same assessor extracted muscle and tendon lengths from the 3D reconstructions twice, and the standard error of measurement (SEM) was quantified. Muscle tendon unit (MTU) length was calculated as the summation of muscle (ML) and tendon length (TL). The change in ML and TL between rest and maxDF was used to calculate extensibility. Within-group treatment effect was evaluated with Wilcoxon signed rank tests and treatment differences, with Mann-Whitney U tests. Post-treatment changes were considered significant when >SEM and p < 0.05. RESULTS At baseline, groups did not differ for age, joint angles and lengths. Post-casting, resting angle, maxDF, MTU and TL at maxDF significantly increased. While two weeks post-BoNT-A-injection only MTU length and ML at rest significantly increased. There was no treatment effect on the extensibility. The change in maxDF, and ML at rest were significantly larger post-casting compared to post-BoNT-A. Similarly, the post-treatment change in MTU length at maxDF was significantly larger after casting compared to BoNT-A. DISCUSSION The results suggest that two weeks casting resulted in increased maxDF and MTU-length by increased TL (or compliance). This confirms previous research on the effects of ankle foot orthoses on MG morphology (3). BoNT-A on the other hand, affected the muscles resting length, however without gain in extensibility or MTU-length. This emphasizes the requirement to combine both treatments, but also cautions the use of stretching casts for having adverse effects on the tendon. The treatment-effects on the MTU on the long-term and their carry over effect to gait is material for further investigation.

O 107 – Impact of subject-specific musculoskeletal geometry on estimated joint kinematics, joint kinetics and muscle forces in typically developing children

1.. Introduction: Gait analysis together with musculoskeletal modeling can be used to calculate muscle forces and assess pathological gait [1]. No generic, pediatric musculoskeletal models are available and, therefore, linear scaling methods are commonly used to personalize a generic, adult musculoskeletal model to the child’s anthropometry. 2. Research: How different are joint kinematics, joint kinetics and muscle force estimates of generic scaled models compared to medical-imaging based models in typically developing (TD) children? 3. Methods: 3D motion capture data and magnetic resonance images (MRI) of a TD boy (age: 8 years; height: 1.23 m; weight: 20.4 kg) were collected. Two musculoskeletal OpenSim models were created: (1) a scaled generic model (M_gen), and (2) a MRI-based model, which included subject-specific musculoskeletal geometry (M_mri) [2]. Joint kinematics, joint kinetics and muscle forces were calculated for each model using OpenSim 3.3 [3]. Joint kinematics, joint kinetics, muscle force waveforms, as well as femoral anteversion angle, neck-shaft angle and hip joint centre location were compared between both models. 4. Results: Joint kinematics and joint kinetics were surprisingly similar between the M_gen and M_mri with root-mean-square-differences below 2.8° and 0.05Nm/kg for joint angles and moments, respectively (Fig. 1, Fig. 2). Depending on the analyzed muscle, differences in muscle forces varied substantially (up to 230% difference) between the M_gen and M_mri (Fig. 3). Femoral anteversion and neck-shaft angles differed between M_gen and M_mri by 12 and 5 degrees, respectively. The hip joint centre position differed between both models by 5, 15 and 6 mm in the anterior/posterior, superior/inferior and medial/lateral direction, respectively.