A DXA-based mathematical model predicts midthigh muscle mass from magnetic resonance imaging in typically developing children but not in those with quadriplegic cerebral palsy

Cardiometabolic Risk and Its Relationship With Visceral Adiposity in Children With Cerebral Palsy

Context

Adults with cerebral palsy (CP) display a higher prevalence of cardiometabolic disease compared with the general population. Studies examining cardiometabolic disease risk in children with CP are limited.

Objective

The purpose of this study was to determine if children with CP exhibit higher cardiometabolic risk than typically developing children, and to examine its relationship with visceral adiposity and physical activity.

Methods

Thirty ambulatory children with CP and 30 age-, sex-, and race-matched typically developing control children were tested for blood lipids, glucose, and the homeostatic model assessment of insulin resistance (HOMA-IR). Visceral fat was assessed using dual-energy x-ray absorptiometry. Physical activity was assessed using accelerometer-based monitors.

Results

Children with CP had higher total cholesterol, low-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol (non-HDL-C), glucose, prevalence of dyslipidemia, prevalence of prediabetes, and visceral fat mass index (VFMI) and lower physical activity than controls (all P < .05). In the groups combined, non-HDL-C and glucose were positively related to VFMI (r = 0.337 and 0.313, respectively, P < .05), and non-HDL-C and HOMA-IR were negatively related to physical activity (r = -0.411 and -0.368, respectively, P < .05). HOMA-IR was positively related to VFMI in children with CP (r = 0.698, P < .05), but not in controls. Glucose was not related to physical activity in children with CP, but it was negatively related in controls (r = -0.454, P < .05).

Conclusion

Children with CP demonstrate early signs of cardiometabolic disease, which are more closely related to increased visceral adiposity than decreased physical activity.

Greater Visceral Fat but No Difference in Measures of Total Body Fat in Ambulatory Children With Spastic Cerebral Palsy Compared to Typically Developing Children

BACKGROUND

Individuals with cerebral palsy (CP) are at increased risk for obesity and obesity-related complications. Studies of total body fat in those with CP are inconsistent and studies of abdominal fat are lacking in children with CP. The objective of this study was to determine if ambulatory children with spastic CP have greater central adiposity compared to typically developing children.

METHODOLOGY

Eighteen ambulatory children with spastic CP (n = 5 girls; 8.6 ± 2.9 yr) and 18 age-, sex-, and race-matched typically developing children (controls; 8.9 ± 2.1 yr) participated in this cross-sectional study. Children with CP were classified as I or II using the Gross Motor Function Classification System. Dual-energy X-ray absorptiometry assessed body composition, including total body, trunk and abdominal fat mass, fat-free mass, fat mass index (FMI), and fat-free mass index (FFMI).

RESULTS

There were no group differences in fat mass, fat-free mass, FMI, and FFMI in the total body, fat mass, fat-free mass, and FFMI in the trunk, or fat mass, visceral fat mass, and subcutaneous fat mass in the abdomen (p > 0.05). Compared to controls, children with CP had higher trunk FMI, abdominal FMI, and visceral FMI (p < 0.05). Although marginally insignificant (p = 0.088), children with CP had higher subcutaneous FMI.

CONCLUSIONS

Ambulatory children with spastic CP have elevated central adiposity, especially in the visceral region, despite no differences in measures of total body fat. How this relates to cardiometabolic disease progression in those with CP requires further investigation.

Quantifying bone marrow fat using standard T1-weighted magnetic resonance images in children with typical development and in children with cerebral palsy

Excess bone marrow adiposity may have a negative effect on bone growth and development. The aim of this study was to determine whether a procedure using standard T1-weighted magnetic resonance images provides an accurate estimate of bone marrow fat in children with typical development and in children with mild spastic cerebral palsy (CP; n = 15/group; 4-11 y). Magnetic resonance imaging was used to acquire T1-weighted images. It was also used to acquire fat and water images using an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) technique. Bone marrow fat volume and fat fraction in the middle-third of the tibia were determined using the standard T1-weighted images (BMFV_T1 and BMFF_T1, respectively) and the fat and water images (BMFV_IDEAL and BMFF_IDEAL, respectively). In both groups, BMFV_T1 was highly correlated with (both r > 0.99, p < 0.001) and not different from (both p > 0.05) BMFV_IDEAL. In both groups, BMFF_T1 was moderately correlated with (both r = 0.71, p < 0.01) and not different from (both p > 0.05) BMFF_IDEAL. There was no group difference in BMFV_T1 or BMFV_IDEAL (both p > 0.05). BMFF_IDEAL was higher in children with CP (p < 0.05), but there was no group difference in BMFF_T1 (p > 0.05). We conclude that a procedure using standard T1-weighted magnetic resonance images can produce estimates of bone marrow fat volume similar to estimates from the IDEAL technique in children. However, it is less sensitive to variation in the bone marrow fat fraction.

Complicated Muscle-Bone Interactions in Children with Cerebral Palsy

PURPOSE OF REVIEW

The goal of this review is to highlight the deficits in muscle and bone in children with cerebral palsy (CP), discuss the muscle-bone relationship in the CP population, and identify muscle-based intervention strategies that may stimulate an improvement in their bone development.

RECENT FINDINGS

The latest research suggests that muscle and bone are both severely underdeveloped and weak in children with CP, even in ambulatory children with mild forms of the disorder. The small and low-performing muscles and limited participation in physical activity are likely the major contributors to the poor bone development in children with CP. However, the muscle-bone relationship may be complicated by other factors, such as a high degree of fat and collagen infiltration of muscle, atypical muscle activation, and muscle spasticity. Muscle-based interventions, such as resistance training, vibration, and nutritional supplementation, have the potential to improve bone development in children with CP, especially if they are initiated before puberty. Studies are needed to identify the muscle-related factors with the greatest influence on bone development in children with CP. Identifying treatment strategies that capitalize on the relationship between muscle and bone, while also improving balance, coordination, and physical activity participation, is an important step toward increasing bone strength and minimizing fractures in children with CP.

Preferential deficit of fat-free soft tissue in the appendicular region of children with cerebral palsy and proposed statistical models to capture the deficit

BACKGROUND

Cerebral palsy (CP) is a neurological disorder characterized by a profound skeletal muscle deficit. However, whether there is a regional-specific skeletal muscle deficit in children with CP is unknown. The purpose of this study was to determine whether fat-free soft tissue mass (FFST), a commonly used surrogate for skeletal muscle mass, is more compromised in the limbs than in the trunk in children with CP. A second purpose was to determine whether physical characteristics can be used to accurately estimate appendicular FFST (AFFST) in children with CP.

METHODS

Forty-two children with CP (4-13 y) and 42 typically developing children matched to children with CP for sex, age and race were studied. Whole body FFST (FFST_whole), FFST in the upper limbs (FFST_upper), FFST in the lower limbs (FFST_lower), the ratio of AFFST to height (AFFST/ht), the ratio of AFFST to height² (AFFST/ht²) and non-appendicular FFST were estimated from dual-energy X-ray absorptiometry. Statistical models were developed to estimate AFFST, AFFST/ht and AFFST/ht² in both groups of children, and the leave-one-out method was used to validate the models.

RESULTS

Children with CP had 21% lower FFST_whole, 30% lower AFFST, 34% lower FFST_lower, 14% lower non-appendicular FFST, 23% lower AFFST/ht, 19% lower AFFST/ht² and 9% lower AFFST/FFST_whole (all p < 0.05). Statistical models developed using data from typically developing children overestimated AFFST, AFFST/ht and AFFST/ht² by 35%, 30% and 21% (all p < 0.05), respectively, in children with CP. Separate models developed using data from children with CP yielded better accuracy, with the estimated results highly correlated (r² = 0.78, 0.66 and 0.50, respectively; all p < 0.001) and not different from calculated AFFST, AFFST/ht and AFFST/ht² (all p > 0.99). However, when the difference in estimated values and measured values of AFFST, AFFST/ht and AFFST/ht² were plotted against measured values, there was an inverse relationship (r = -0.38, -0.47 and -0.61, respectively, all p < 0.05).

CONCLUSION

Children with CP have a remarkable deficit in FFST that is more pronounced in the appendicular than in the non-appendicular region and more pronounced in the lower than in the upper limbs. Preliminary models developed using data from children with CP can provide reasonable estimates of AFFST and indexes of AFFST relative to height, but further development of the models may be needed.

Statistical Models to Assess Leg Muscle Mass in Ambulatory Children With Spastic Cerebral Palsy Using Dual-Energy X-Ray Absorptiometry

Cerebral palsy (CP) is a movement disorder associated with small and weak muscles. Methods that accurately assess muscle mass in children with CP are scarce. The purpose of this study was to determine whether dual-energy X-ray absorptiometry (DXA) accurately estimates midleg muscle mass in ambulatory children with spastic CP. Ambulatory children with spastic CP and typically developing children 5-11 y were studied (n = 15/group). Fat-free soft tissue mass (FFST) and fat mass at the middle third of the tibia (i.e., midleg) were estimated using DXA. Muscle mass (muscle_MRI) and muscle mass corrected for intramuscular fat (muscle_MRIfc) in the midleg were estimated using magnetic resonance imaging (MRI). Statistical models were created to predict muscle_MRI and muscle_MRIfc using DXA. Children with CP compared to typically developing children had lower FFST (38%), muscle_MRI (40%) and muscle_MRIfc (47%) (all p < 0.05) and a lower ratio of muscle_MRIfc to FFST (17%, p < 0.05). DXA-based models developed using data from typically developing children overestimated muscle_MRI (13%) and muscle_MRIfc (22%) (both p < 0.05) in children with CP. DXA-based models developed using data from children with CP explained 91% of the variance in muscle_MRI and 90% of the variance in muscle_MRIfc in children with CP (both p < 0.05). Moreover, the estimates were not different from muscle_MRI and muscle_MRIfc (both p > 0.99). We conclude that DXA-based statistical models accurately estimate midleg muscle mass in children with CP when the models are composed using data from children with CP rather than typically developing children.

BMI does not capture the high fat mass index and low fat-free mass index in children with cerebral palsy and proposed statistical models that improve this accuracy

Background/Objectives:

Children with cerebral palsy (CP) are at risk for having a misclassified overweight/obesity status based on BMI thresholds due to their lower fat-free mass and similar fat mass compared to typically developing children. The primary objective was to determine if BMI could predict fat mass index (FMI) and fat-free mass index (FFMI) in children with CP.

Subjects/Methods:

Forty-two children with CP and 42 typically developing children matched to children with CP for age and sex participated in the study. Dual-energy x-ray absorptiometry was used to assess body composition. Childrenwith CP who could ambulate without assistance were considered ambulatory (ACP) and the rest were considered nonambulatory (NACP).

Results:

Children with CP had higher percent body fat (%Fat) and FMI and lower fat-free mass and FFMI than controls (p < 0.05) but no difference in fat mass (p = 0.10). When BMI wasstatistically controlled, NACP had higher %Fat, fat mass and FMI and lower FFMI than ACP and controls (p < 0.05). NACP also had lower fat-free mass than controls (p < 0.05). ACP had higher %Fat and FMI and lower fat-free mass and FFMI than controls (p < 0.05). BMIwas a strong predictor of FMI (r² = 0.83) and a moderately-strongpredictor of FFMI (r² = 0.49) in children with CP (both p < 0.01). Prediction of FMI (R² = 0.86) and FFMI (R² = 0.66) from BMI increased (p < 0.05) whenage, sex and ambulatory status were included.

Conclusion:

Compared to typically developing children, children with CP have a higher FMI and lower FFMI for a given BMI which is more pronounced in NACP than ACP. The finding suggests that the prevalence of overweight/obesity status may be underestimated in children with CP.

Muscle volume is related to trabecular and cortical bone architecture in typically developing children

INTRODUCTION

Muscle is strongly related to cortical bone architecture in children; however, the relationship between muscle volume and trabecular bone architecture is poorly studied. The aim of this study was to determine if muscle volume is related to trabecular bone architecture in children and if the relationship is different than the relationship between muscle volume and cortical bone architecture.

MATERIALS AND METHODS

Forty typically developing children (20 boys and 20 girls; 6 to 12y) were included in the study. Measures of trabecular bone architecture [i.e., apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th) and trabecular separation (appTb.Sp)] in the distal femur, cortical bone architecture [cortical volume, total volume, section modulus (Z) and polar moment of inertia (J)] in the midfemur, muscle volume in the midthigh and femur length were assessed using magnetic resonance imaging. Total physical activity and moderate-to-vigorous physical activity were assessed using an accelerometer-based activity monitor worn around the waist for four days. Calcium intake was assessed using diet records. Relationships among the measures were tested using multiple linear regression analysis.

RESULTS

Muscle volume was moderately-to-strongly related to measures of trabecular bone architecture [appBV/TV (r=0.81), appTb.N (r=0.53), appTb.Th (r=0.67), appTb.Sp (r=-0.71); all p<0.001] but more strongly related to measures of cortical bone architecture [cortical volume (r=0.96), total volume (r=0.94), Z (r=0.94) and J (r=0.92; all p<0.001)]. Similar relationships were observed between femur length and measures of trabecular (p<0.01) and cortical (p<0.001) bone architecture. Sex, physical activity and calcium intake were not related to any measure of bone architecture (p>0.05). Because muscle volume and femur length were strongly related (r=0.91, p<0.001), muscle volume was scaled for femur length (muscle volume/femur length(2.77)). When muscle volume/femur length(2.77) was included in a regression model with femur length, sex, physical activity and calcium intake, muscle volume/femur length(2.77) was a significant predictor of appBV/TV, appTb.Th and appTb.Sp (partial r=0.44 to 0.49, p<0.05) and all measures of cortical bone architecture (partial r=0.47 to 0.54; p<0.01).

CONCLUSIONS

The findings suggest that muscle volume in the midthigh is related to trabecular bone architecture in the distal femur of typically developing children. The relationship is weaker than the relationship between muscle volume in the midthigh and cortical bone architecture in the midfemur, but the discrepancy is driven, in large part, by the greater dependence of cortical bone architecture measures on femur length.

Effect of muscle length on voluntary activation level in children and adults

PURPOSE

The aim of the present study was to compare the effect of muscle length on the level of voluntary activation (VA) at short and long muscle lengths between children and adults.

METHODS

Thirteen prepubertal boys (10.2 ± 1.1 yr) and 10 men (23.9 ± 2.9 yr) performed 5-s maximal isometric voluntary contractions of the knee extensor muscles at three muscular angles (20°, 90°, 100°; 0°, full extension) interspersed with at least 60-s passive recovery periods. Single magnetic stimulations were delivered to the femoral nerve during maximal isometric voluntary contractions to determine the level of VA using the twitch interpolation technique. The specific torque was calculated as the absolute torque divided by thigh muscle mass, as assessed using dual-energy x-ray absorptiometry. Finally, the theoretical specific torque that could be produced with a complete (i.e., 100%) activation level (specific torque at 100% VA) was estimated from the values of specific torque and VA.

RESULTS

Results showed a higher specific torque in adults at 90° and 100° but not at 20°. Accordingly, VA was significantly higher in adults at 90° (94% ± 4% vs 88% ± 8%, P < 0.05) and 100° (93% ± 6% vs 86% ± 8%, P < 0.05), whereas no significant difference was observed at 20°. Interestingly, the specific torque at 100% VA was not different between groups whatever the joint angle.

CONCLUSIONS

The lower ability of children to fully activate their motor units at long muscle length could account for their lower specific torque because no difference in theoretical specific torque was observed between groups at 90° and 100°.

The pattern of trabecular bone microarchitecture in the distal femur of typically developing children and its effect on processing of magnetic resonance images

INTRODUCTION

Magnetic resonance imaging (MRI) is used to assess trabecular bone microarchitecture in humans; however, image processing can be labor intensive and time consuming. One aim of this study was to determine the pattern of trabecular bone microarchitecture in the distal femur of typically developing children. A second aim was to determine the proportion and location of magnetic resonance images that need to be processed to yield representative estimates of trabecular bone microarchitecture.

MATERIALS AND METHODS

Twenty-six high resolution magnetic resonance images were collected immediately above the growth plate in the distal femur of 6-12year-old typically developing children (n=40). Measures of trabecular bone microarchitecture [i.e., apparent trabecular bone volume to total volume (appBV/TV), trabecular number (appTb.N), trabecular thickness (appTb.Th) and trabecular separation (appTb.Sp)] in the lateral aspect of the distal femur were determined using the twenty most central images (20IM). The average values for appBV/TV, appTb.N, appTb.Th and appTb.Sp from 20IM were compared to the average values from 10 images (10IM), 5 images (5IM) and 3 images (3IM) equally dispersed throughout the total image set and one image (1IM) from the center of the total image set using linear regression analysis. The resulting mathematical models were cross-validated using the leave-one-out technique.

RESULTS

Distance from the growth plate was strongly and inversely related to appBV/TV (r(2)=0.68, p<0.001) and appTb.N (r(2)=0.92, p<0.001) and was strongly and positively related to appTb.Sp (r(2)=0.86, p<0.001). The relationship between distance from the growth plate and appTb.Th was not linear (r(2)=0.06, p=0.28), but instead it was quadratic and statistically significant (r(2)=0.54, p<0.001). Trabecular bone microarchitecture estimates from 10IM, 5IM, 3IM and 1IM were not different from estimates from 20IM (p>0.05). However, there was a progressive decrease in the strength of the relationships as a smaller proportion of images were used to predict estimates from 20IM (r(2)=0.98 to 0.99 using 10IM, 0.94 to 0.96 using 5IM, 0.87 to 0.90 using 3IM and 0.66 to 0.72 using 1IM; all p<0.001). Using the resulting mathematical models and the leave-one-out cross-validation analysis, measures of trabecular bone microarchitecture estimated from the 10IM and 5IM partial image sets agreed extremely well with estimates from 20IM.

CONCLUSIONS

The findings indicate that partial magnetic resonance image sets can be used to provide reasonable estimates of trabecular bone microarchitecture status in the distal femur of typically developing children. However, because the relative amount of trabecular bone in the distal femur decreases with distance from the growth plate due to a decrease in trabecular number, careful positioning of the region of interest and sampling from throughout the region of interest is necessary.

Are muscle volume differences related to concentric muscle work during walking in spastic hemiplegic cerebral palsy?

BACKGROUND

Individuals with spastic hemiplegic cerebral palsy are typically high functioning and walk without assistive devices. The involved limb is usually smaller and shorter, although it is not clear whether the difference in muscle volume has an impact on walking capacity.

QUESTIONS/PURPOSES

We determined the volume of muscles important for propulsion and related that volume to concentric muscle work during walking on the hemiplegic and noninvolved sides in patients with cerebral palsy.

PATIENTS AND METHODS

We studied 46 patients (mean age, 17.6 years; range, 13-24 years) with spastic hemiplegic cerebral palsy. We assessed muscle volume using MRI and concentric muscle work in the sagittal plane from the hip, knee, and ankle using three-dimensional gait analysis. Patients were classified by Winters' criteria to assess the involvement of cerebral palsy and movement pattern during walking.

RESULTS

On the hemiplegic side, muscles were smaller, except for the gracilis muscle, and concentric muscle work from the ankle plantar flexors, knee extensors, and hip flexors and extensors was lower compared to the noninvolved side. Hip extensor work was higher on the hemiplegic and the noninvolved sides compared to a control group of 14 subjects without cerebral palsy. Hemiplegic to noninvolved volume ratios correlated with work ratios (r = 0.40-0.66). The Winters classification and previous calf muscle surgery predicted work ratios.

CONCLUSIONS

Our observations of smaller muscles on the hemiplegic side and changes in muscle work on both sides can help us distinguish between primary deviations that may potentially be treatable and compensatory mechanisms that should not be treated.

Knee extension strength in obese and nonobese male adolescents

The aim of the present study was to compare "absolute" and "relative" knee extension strength between obese and nonobese adolescents. Ten nonobese and 12 severely obese adolescent boys of similar chronological age, maturity status, and height were compared. Total body and regional soft tissue composition were determined using dual-energy X-ray absorptiometry (DXA). Knee extensors maximum voluntary contraction (MVC) torque was measured using an isometric dynamometer at a knee angle of 60° (0° is full extension). Absolute MVC torque was significantly higher in obese adolescents than in controls. However, although MVC torque expressed per unit of body mass was found to be significantly lower in obese adolescent boys, no significant difference in MVC torque was found between groups when normalized to fat-free mass. Conversely, when correcting for thigh lean mass and estimated thigh muscle mass, MVC torque was significantly higher in the obese group (17.9% and 22.2%, respectively; P <0.05). To conclude, our sample of obese adolescent boys had higher absolute and relative knee extension strength than our nonobese controls. However, further studies are required to ascertain whether or not relative strength, measured with more accurate in vivo methods such as magnetic resonance imaging, is higher in obese adolescents than in nonobese controls.

Effect of a novel procedure for limiting motion on body composition and bone estimates by dual-energy X-ray absorptiometry in children

We studied the effect of using the BodyFIX (Medical Intelligence Inc, Schwabmunchen, Germany) to immobilize children during a dual-energy X-ray absorptiometry scan on body composition and bone estimates. Overestimates of soft tissue and bone introduced by the BodyFIX were avoided by using a modified version of the system or were corrected by using mathematical models developed in this study.