Simon-Henri Schless

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.

Estimating medial gastrocnemius muscle volume in children with spastic cerebral palsy: a cross-sectional investigation

This cross‐sectional investigation evaluates the reliability of estimating medial gastrocnemius anatomical cross‐sectional area (aCSA) in typically developing and spastic cerebral palsy (SCP) cohorts. It verifies whether muscle volume estimations based on aCSA improve when aCSA is multiplied by muscle–tendon unit (MTU) or muscle length, and whether the resulting errors in volume estimations are smaller than changes after intervention.

Reliability of a clinical 3D freehand ultrasound technique: Analyses on healthy and pathological muscles

BACKGROUND AND OBJECTIVE 3D freehand Ultrasonography is a medical imaging technique that can be used to measure muscle and tendon morphological and structural properties, including volume, lengths and echo-intensity. These properties are clinically relevant in neurological disorders such as spastic cerebral palsy to monitor disease progression and evaluate the effect of treatment. This study presents a methodology for extracting these parameters along with a clinical reliability analysis for the data acquisition and processing. METHODS The medial gastrocnemius muscles and Achilles tendon of 10 typically developing children and 10 children with spastic cerebral palsy were assessed. An open-source in-house software library developed in Python (Py3DFreeHandUS) was used to reconstruct, into one 3D data set, the data simultaneously acquired from an US machine and a motion tracking system. US images were manually segmented and linearly interpolated by means of a new simplified approach which involved sequentially decreasing the total number of images used for muscle border segmentation from 100% to 5%. Acquisition and processing reliability was defined based on repeated measures from different data processers and from different data acquirers, respectively. RESULTS When only 10% of the US images were outlined, there was an average underestimation of muscle volume of 1.1% and 1.6% with respect the computation of all the available images, for the typically developing and spastic cerebral palsy groups, respectively. For both groups, the reliability was higher for data processing than for data acquisition. High inter-class correlation coefficient values were found for processing and acquisition reliability, with worst case values of 0.89 and 0.61, respectively. The standard error of measurement, expressed as a percentage of the average volumes, was smaller than 2.6 ml (4.8%) in all cases. CONCLUSIONS The present analysis demonstrates the effectiveness of applying 3D freehand ultrasonography in a clinical setting for analysing healthy and pathological paediatric muscle.

Can in Vivo Medial Gastrocnemius Muscle–Tendon Unit Lengths be Reliably Estimated by Two Ultrasonography Methods? A Within-Session Analysis

A clinically feasible method to reliably estimate muscle-tendon unit (MTU) lengths could provide essential diagnostic and treatment planning information. A 3-D freehand ultrasound (3-DfUS) method was previously validated for extracting in vivo medial gastrocnemius (MG) lengths, although the processing time can be considered substantial for the clinical environment. This investigation analyzed a quicker and simpler method using the US transducer as a spatial pointer (US-PaP), where the within-session reliability of extracting the muscle-tendon unit (MTU) and tendon lengths are estimated. MG MTU lengths were extracted in a group of 14 healthy adults using both 3-DfUS and US-PaP. Two consecutive acquisitions were performed per participant, and the data processed by two researchers independently. The intra-class correlation coefficients were above 0.97, and the standard error of measurements below 3.6 mm (1.5%). This investigation proposes that the simplified US-PaP method is a viable alternative for estimating MG MTU lengths.

A new strength assessment to evaluate the association between muscle weakness and gait pathology in children with cerebral palsy

Aim The main goal of this validation study was to evaluate whether lower limb muscle weakness and plantar flexor rate of force development (RFD) related to altered gait parameters in children with cerebral palsy (CP), when weakness was assessed with maximal voluntary isometric contractions (MVICs) in a gait related test position. As a subgoal, we analyzed intra- and intertester reliability of this new strength measurement method. Methods Part 1 –Intra- and intertester reliability were determined with the intra-class correlation coefficient (ICC2,1) in 10 typical developing (TD) children (age: 5–15). We collected MVICs in four lower limb muscle groups to define maximum joint torques, as well as plantar flexor RFD. Part 2 –Validity of the strength assessment was explored by analyzing the relations of lower limb joint torques and RFD to a series of kinematic- and kinetic gait features, the GDI (gait deviation index), and the GDI-kinetic in 23 children with CP (GMFCS I-II; age: 5–15) and 23 TD children (age: 5–15) with Spearman’s rank correlation coefficients. Results Part 1 –The best reliability was found for the torque data (Nm), with the highest ICC2,1 (0.951) for knee extension strength (inter) and the lowest (0.693) for dorsiflexion strength (intra). For plantar flexor RFD, the most reliable window size was 300 milliseconds (ICC2,1: 0.828 (inter) and 0.692 (intra)). Part 2 –The children with CP were significantly weaker than the TD children (p <0.001). Weakness of the dorsiflexors and plantar flexors associated with delayed and decreased knee flexion angle during swing, respectively. No other significant correlations were found. Conclusion While our new strength assessment was reliable, intra-joint correlations between weakness, RFD, and gait deviations were low. However, we found inter-joint associations, reflected by a strong association between plantar- and dorsiflexor weakness, and decreased and delayed knee flexion angle during swing.

Medial Gastrocnemius Muscle–Tendon Junction and Fascicle Lengthening across the Range of Motion Analyzed in 2-D and 3-D Ultrasound Images

Ultrasound imaging modalities offer a clinically viable method to visualize musculoskeletal structures. However, proper data comparison between investigations is compromised because of a lack of measurement error documentation and method standardization. This investigation analyzes the reliability and validity of extracting medial gastrocnemius belly and fascicle lengths and pennation angles in different ankle joint positions, across the full range of motion, in a cohort of 11 children with spastic cerebral palsy and 11 typically developed children. Each of these parameters was extracted from two consecutive acquisitions, using both 2-D and 3-D ultrasound images. The findings suggest that the muscle tendon junction extraction in 2-D images can be a suitable parameter for analyzing medial gastrocnemius muscle length in typically developed children and children with spastic cerebral palsy, although averaging over multiple measurements is recommended to reduce variability. More caution should be taken when performing analyses based on fascicle length.

An innovative solution to reduce muscle deformation during ultrasonography data collection

BACKGROUND 3D freehand ultrasound enables the creation of volumetric data. The acquisition of morphological features, such as muscle volume, is influenced by the variations in force applied to the skin with the ultrasound probe. To minimise the deformations, a concave-shaped plastic mount combined with a custom-shaped gel pad was developed for the ultrasound head, named Portico. This study analyses to what extent the Portico reduces muscle deformation and corresponding errors in estimating muscle volume. METHOD Twenty medial gastrocnemius (MG) muscles were assessed (10 from typically developing children; 10 from children with spastic cerebral palsy). Two repetitions were acquired in each of the following approaches: (1) with the lower leg submerged in a water tank as a non-deformed reference; (2) probe-on-skin (PoS) as the conventional approach and (3) the newly introduced Portico. PoS and Portico data were registered with respect to the ones corresponding in a water tank. An in-house software package (Py3DFreeHandUS) was used to process the data and MG volume was estimated using MeVisLab. The minimal detectable change (MDC) was calculated. RESULTS With respect to the PoS approach, the Portico reduced muscle deformation by 46%. For both the typically developing and spastic cerebral palsy cohorts, lower MDCs were found when using the Portico. DISCUSSION Despite the improvements, the Portico did not yield statistically more reliable MG volume estimations than the traditional PoS approach. Further improvement can be attained by optimising the fit between the gel pad and the curvature of the limb, using a larger choice of Portico geometries.

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.

The Relationship Between Medial Gastrocnemius Lengthening Properties and Stretch Reflexes in Cerebral Palsy

Stretch reflex hyperactivity in the gastrocnemius of children with spastic cerebral palsy (CP) is commonly evaluated by passively rotating the ankle joint into dorsiflexion at different velocities, such as applied in conventional clinical spasticity assessments. However, surface electromyography (sEMG) collected from the medial gastrocnemius (MG) during such examination reveals unexplained heterogeneity in muscle activation between patients. Recent literature also highlights altered muscle tensile behavior in children with spastic CP. We aimed to document MG muscle and tendon lengthening during passive ankle motion at slow and fast velocity and explore its interdependence with the elicited hyperactive stretch reflex. The ankle of 15 children with CP (11 ± 3 years, GMFCS 9I 6II, 8 bilateral, 7 unilateral) and 16 typically developing children (TDC) was passively rotated over its full range of motion at slow and fast velocity. Ultrasound, synchronized with motion-analysis, was used to track the movement of the MG muscle-tendon junction and extract the relative lengthening of muscle and tendon during joint rotation. Simultaneously, MG sEMG was measured. Outcome parameters included the angular and muscle lengthening velocities 30 ms before EMG onset and the gain in root mean square EMG during stretch, as a measure of stretch reflex activity. Compared to slow rotation, the muscle lengthened less and stretch reflex activity was higher during fast rotation. These velocity-induced changes were more marked in CP compared to TDC. In the CP group, muscle-lengthening velocity had higher correlation coefficients with stretch reflex hyperactivity than joint angular velocity. Muscles with greater relative muscle lengthening during slow rotation had earlier and stronger stretch reflexes during fast rotation. These initial results suggest that ankle angular velocity is not representative of MG muscle lengthening velocity and is less related to stretch reflex hyperactivity than MG muscle lengthening. In addition, muscles that lengthened more during slow joint rotation were more likely to show a velocity-dependent stretch reflex. This interdependence of muscle lengthening and stretch reflexes may be important to consider when administering treatment. However, muscle and tendon lengthening properties alone could not fully explain the variability in stretch reflexes, indicating that other factors should also be investigated.

Medial gastrocnemius volume and echo-intensity after botulinum neurotoxin A interventions in children with spastic cerebral palsy

This cross‐sectional investigation evaluated whether recurrent botulinum neurotoxin A (BoNT‐A) interventions to the medial gastrocnemius have an influence on muscle morphology, beyond Gross Motor Function Classification System (GMFCS) level.