Muscle morphology of the lower leg in ambulant children with spastic cerebral palsy.

INTRODUCTION: In this study we aimed to determine the lower limb morphological characteristics of skeletal muscle of ambulant children with spastic cerebral palsy (CP) and typically developing (TD) children. METHODS: Seventeen children with spastic diplegic CP (10 boys and 7 girls, 5-12 years of age, Gross Motor Function Classification System [GMFCS] level I or II) and 19 TD children (8 boys and 11 girls, 5-11 years of age) underwent lower limb T1-weighted MRI. Morphological characteristics of the triceps surae, including muscle volume, anatomical cross-sectional area, muscle length, and subcutaneous adipose tissue, were digitally quantified, and the proportional distribution calculated. RESULTS: Children with GMFCS II had significantly reduced muscle volume, cross-sectional area, and muscle length, and increased subcutaneous fat compared with TD children. Children classified as GMFCS II consistently exhibited the greatest deficits in all morphology variables. DISCUSSION: Morphological variables were significantly different between the groups. These alterations have the potential to influence the functional capabilities of the triceps surae muscle group. Muscle Nerve 58:818-823, 2018.

Ultrasound characterization of medial gastrocnemius tissue composition in children with spastic cerebral palsy.

INTRODUCTION: In this study we aimed to characterize muscle composition of the medial gastrocnemius in children with spastic cerebral palsy (SCP) using quantitative ultrasound. METHODS: Forty children with SCP, aged 4-14 years, participated in this study. Children were grouped according to the gross motor function classification system (GMFCS I-V) and compared with a cohort of age- and gender-matched, typically developing children (TD; n = 12). Ultrasound scans were taken of the medial gastrocnemius. Images were then characterized using grayscale statistics to determine mean echo intensity (EI) and the size and number of spatially connected homogeneous regions (i.e., blobs). RESULTS: Significant differences in skeletal muscle composition were found between children with SCP and their TD peers. Children classified as GMFCS III consistently exhibited the highest EI and blob area. CONCLUSIONS: This study demonstrates altered tissue composition in children with SCP visualized using ultrasound. Further work is required to determine the pathophysiology contributing to these alterations in SCP.

Childhood muscle morphology and strength: alterations over six months of growth.

INTRODUCTION: The purpose of this study was to establish the nature and stability of the strength-size relationship for the knee flexors and extensors across a 6-month period of childhood growth. METHODS: Nineteen typically developing children aged 5-11 years underwent lower limb magnetic resonance imaging (MRI) and dynamometry strength assessments on 2 occasions, 6 months apart. Muscle volume (MV) and maximum anatomical cross-sectional area (aCSA) for the knee flexors and extensors were determined using MRI analysis software. Isokinetic dynamometry determined corresponding isometric and isokinetic strength. RESULTS: Strong correlations were found between muscle size and strength for both the knee flexors and extensors (r = 0.84-0.90; P < 0.01). Furthermore, the ratio of strength to muscle size remained consistent across 6 months of prepubescent growth. CONCLUSIONS: Increases in thigh muscle strength were relative to those in muscle size, suggesting that muscle growth may play an important role in the development of strength during childhood.

Does muscle size matter? The relationship between muscle size and strength in children with cerebral palsy.

PURPOSE: To investigate the muscle size-strength relationship of the knee flexors and extensors in children with spastic cerebral palsy (CP) in relation to typically developing children (TD). METHODS: Eighteen children with spastic Diplegia, Gross Motor Function Classification System I-III (mean 7 y 5 mo SD 1 y 7 mo) and 19 TD children (mean 7 y 6 mo SD 1 y 9 mo) participated. Muscle volume (MV) and anatomical cross-sectional area (aCSA) were assessed using MRI. Measures of peak torque (PT) and work of the knee flexors and extensors were assessed isometrically and isokinetically using a Biodex dynamometer, and normalised to bodymass (Bm). RESULTS: Children with CP were weaker than their TD peers across all torque variables (p < 0.05). MV and aCSA of the knee flexors (MV: p = 0.002; aCSA: p = 0.000) and extensors (MV: p = 0.003; aCSA: p < 0.0001) were smaller in children with CP. The relationship between muscle size and strength in children with CP was weaker than the TD children. The strongest relationship was between MV and isometric PT/Bm for TD children (r = 0.77-0.84), and between MV and isokinetic work (r = 0.70-0.72) for children with CP. CONCLUSIONS: Children with CP have smaller, weaker muscles than their TD peers. However, muscle size may only partially explain their decreased torque capacity. MV appears to be a better predictor of muscle work in children with CP than aCSA. This is an important area of research particularly in regard to treatment(s) that target muscle and strength in children with CP. Implications for Rehabilitation This research adds to the evidence that children with CP have smaller, weaker knee flexor and extensor muscles than their TD peers. However, unlike their TD peers, muscle size does not necessarily relate to muscle strength. The weak correlation between MRI-derived muscle volume and isometric peak torque suggests children with CP are underpowered relative to their muscle size. For children with CP, muscle volume appears to be the best predictor of isokinetic muscle torque output. Therefore, when assessing the capacity of a muscle, it appears preferable to measure total muscle volume and torque development through a range of motion (isokinetic strength).