Intramuscular fat in children with unilateral cerebral palsy

Human lower leg muscles grow asynchronously

Muscle volume must increase substantially during childhood growth to generate the power required to propel the growing body. One unresolved but fundamental question about childhood muscle growth is whether muscles grow at equal rates; that is, if muscles grow in synchrony with each other. In this study, we used magnetic resonance imaging (MRI) and advances in artificial intelligence methods (deep learning) for medical image segmentation to investigate whether human lower leg muscles grow in synchrony. Muscle volumes were measured in 10 lower leg muscles in 208 typically developing children (eight infants aged less than 3 months and 200 children aged 5 to 15 years). We tested the hypothesis that human lower leg muscles grow synchronously by investigating whether the volume of individual lower leg muscles, expressed as a proportion of total lower leg muscle volume, remains constant with age. There were substantial age-related changes in the relative volume of most muscles in both boys and girls (p < 0.001). This was most evident between birth and five years of age but was still evident after five years. The medial gastrocnemius and soleus muscles, the largest muscles in infancy, grew faster than other muscles in the first five years. The findings demonstrate that muscles in the human lower leg grow asynchronously. This finding may assist early detection of atypical growth and allow targeted muscle-specific interventions to improve the quality of life, particularly for children with neuromotor conditions such as cerebral palsy.

In vivo imaging of skeletal muscle form and function: 50 years of insight

Skeletal muscle form and function has fascinated scientists for centuries. Our understanding of muscle function has long been driven by advancements in imaging techniques. For example, the sliding filament theory of muscle, which is now widely leveraged in biomechanics research, stemmed from observations made possible by scanning electron microscopy. Over the last 50 years, advancing in medical imaging, combined with ingenuity and creativity of biomechanists, have provide a wealth of new and important insights into in vivo human muscle function. Incorporation of in vivo imaging has also advanced computational modeling and allowed our research to have an impact in many clinical populations. While this review does not provide a comprehensive or meta-analysis of the all the in vivo muscle imaging work over the last five decades, it provides a narrative about the past, present, and future of in vivo muscle imaging.

Ex vivo adult stem cell characterization from multiple muscles in ambulatory children with cerebral palsy during early development of contractures

Cerebral palsy (CP) is one of the most common conditions leading to lifelong childhood physical disability. Literature reported previously altered muscle properties such as lower number of satellite cells (SCs), with altered fusion capacity. However, these observations highly vary among studies, possibly due to heterogeneity in patient population, lack of appropriate control data, methodology and different assessed muscle. In this study we aimed to strengthen previous observations and to understand the heterogeneity of CP muscle pathology. Myogenic differentiation of SCs from the Medial Gastrocnemius (MG) muscle of patients with CP (n = 16, 3-9 years old) showed higher fusion capacity compared to age-matched typically developing children (TD, n = 13). Furthermore, we uniquely assessed cells of two different lower limb muscles and showed a decreased myogenic potency in cells from the Semitendinosus (ST) compared to the MG (TD: n = 3, CP: n = 6). Longitudinal assessments, one year after the first botulinum toxin treatment, showed slightly reduced SC representations and lower fusion capacity (n = 4). Finally, we proved the robustness of our data, by assessing in parallel the myogenic capacity of two samples from the same TD muscle. In conclusion, these data confirmed previous findings of increased SC fusion capacity from MG muscle of young patients with CP compared to age-matched TD. Further elaboration is reported on potential factors contributing to heterogeneity, such as assessed muscle, CP progression and reliability of primary outcome parameters.

Body Fat Distribution in Children and Adolescents With Cerebral Palsy

To evaluate the body fat distribution in children with cerebral palsy (CP). The present study focusses on a monocentric retrospective analysis of body fat distribution from children diagnosed with CP. The children participated in a rehabilitation program. Reference centiles were calculated based on data from the National Health and Nutrition Examination Survey (NHANES, 1999-2004). Z-scores for trunk-to-leg fat ratio were calculated. Further, fat mass index (FMI) was evaluated based on percentiles that have already been published. 237 males and 194 females with CP were considered (mean age: 11 years and 11 months [SD 3 years]). These were compared to 1059 males and 796 females from the NHANES (mean age: 14 years and 7 months [SD 3 years and 4 months]). The z-scores for trunk-to-leg fat ratio showed the following values: mean -0.47 (SD 1.50) for males, -0.49 (SD 1.11), for females, -0.48 (SD 1.34) for all. The z-scores for FMI showed the following values: mean -0.29 (SD 0.70) for males, -0.88 (SD 2.0) for females, -0.55 (SD 1.46) for all. The results showed rather a gynoid fat distribution and a lower FMI in children with CP than in the reference population (NHANES 1999-2004).

The Contributions of Extracellular Matrix and Sarcomere Properties to Passive Muscle Stiffness in Cerebral Palsy

Cerebral palsy results from an upper motor neuron lesion and significantly affects skeletal muscle stiffness. The increased stiffness that occurs is partly a result of changes in the microstructural components of muscle. In particular, alterations in extracellular matrix, sarcomere length, fibre diameter, and fat content have been reported; however, experimental studies have shown wide variability in the degree of alteration. Many studies have reported changes in the extracellular matrix, while others have reported no differences. A consistent finding is increased sarcomere length in cerebral palsy affected muscle. Often many components are altered simultaneously, making it difficult to determine the individual effects on muscle stiffness. In this study, we use a three dimensional modelling approach to isolate individual effects of microstructural alterations typically occurring due to cerebral palsy on whole muscle behaviour; in particular, the effects of extracellular matrix volume fraction, stiffness, and sarcomere length. Causation between the changes to the microstructure and the overall muscle response is difficult to determine experimentally, since components of muscle cannot be manipulated individually; however, utilising a modelling approach allows greater control over each factor. We find that extracellular matrix volume fraction has the largest effect on whole muscle stiffness and mitigates effects from sarcomere length.

Quantity versus quality: Age-related differences in muscle volume, intramuscular fat, and mechanical properties in the triceps surae

With aging comes reductions in the quality and size of skeletal muscle. These changes influence the force-generating capacity of skeletal muscle and contribute to movement deficits that accompany aging. Although declines in strength remain a significant barrier to mobility in older adults, the association between age-related changes in muscle structure and function remain unresolved. In this study, we compared age-related differences in (i) muscle volume and architecture, (ii) the quantity and distribution of intramuscular fat, and (iii) muscle shear modulus (an index of stiffness) in the triceps surae in 21 younger (24.6 ± 4.3 years) and 15 older (70.4 ± 2.4 years) healthy adults. Additionally, we explored the relationship between muscle volume, architecture, intramuscular fat and ankle plantar flexion strength in young and older adults. Magnetic resonance imaging was used to determine muscle volume and intramuscular fat content. B-mode ultrasound was used to quantify muscle architecture, shear-wave elastography was used to measure shear modulus, and ankle strength was measured during maximal isometric plantar flexion contractions. We found that older adults displayed higher levels of intramuscular fat yet similar muscle volumes in the medial (MG) and lateral gastrocnemius (LG) and soleus, compared to younger adults. These age-related higher levels of intramuscular fat were associated with lower muscle shear modulus in the LG and MG. We also found that muscle physiological cross-sectional area (PCSA) that accounted for age-associated differences in intramuscular fat showed a modest increase in its association with ankle strength compared to PCSA that did not account for fat content. This highlights that skeletal muscle fat infiltration plays a role in age-related strength deficits, but does not fully explain the age-related loss in muscle strength, suggesting that other factors play a more significant role.

Combination of Quantitative MRI Fat Fraction and Texture Analysis to Evaluate Spastic Muscles of Children With Cerebral Palsy

Background: Cerebral palsy (CP) is the most common cause of physical disability in childhood. Muscle pathologies occur due to spasticity and contractures; therefore, diagnostic imaging to detect pathologies is often required. Imaging has been used to assess torsion or estimate muscle volume, but additional methods for characterizing muscle composition have not thoroughly been investigated. MRI fat fraction (FF) measurement can quantify muscle fat and is often a part of standard imaging in neuromuscular dystrophies. To date, FF has been used to quantify muscle fat and assess function in CP. In this study, we aimed to utilize a radiomics and FF analysis along with the combination of both methods to differentiate affected muscles from healthy ones. Materials and Methods: A total of 9 patients (age range 8-15 years) with CP and 12 healthy controls (age range 9-16 years) were prospectively enrolled (2018-2020) after ethics committee approval. Multi-echo Dixon acquisition of the calf muscles was used for FF calculation. The images of the second echo (TE = 2.87 ms) were used for feature extraction from the soleus, gastrocnemius medialis, and gastrocnemius lateralis muscles. The least absolute shrinkage and selection operator (LASSO) regression was employed for feature selection. RM, FF model (FFM), and combined model (CM) were built for each calf muscle. The receiver operating characteristic (ROC) curve and their respective area under the curve (AUC) values were used to evaluate model performance. Results: In total, the affected legs of 9 CP patients and the dominant legs of 12 healthy controls were analyzed. The performance of RM for soleus, gastrocnemius medialis, and gastrocnemius lateralis (AUC 0.92, 0.92, 0.82, respectively) was better than the FFM (AUC 0.88, 0.85, 0.69, respectively). The combination of both models always had a better performance than RM or FFM (AUC 0.95, 0.93, 0.83). FF was higher in the patient group (FFS 9.1%, FFGM 8.5%, and FFGL 10.2%) than control group (FFS 3.3%, FFGM 4.1%, FFGL 6.6%). Conclusion: The combination of MRI quantitative fat fraction analysis and texture analysis of muscles is a promising tool to evaluate muscle pathologies due to CP in a non-invasive manner.