Mechanographic analyses in pediatrics: allometric scaling of 'peak jump force' and its relationship to 'maximal isometric grip force' in childhood and adolescence.

BACKGROUND: Kinetic analyses of the neuromuscular system have become an important part in the diagnostics of metabolic bone disorders in pediatrics because of the relevance of the 'Functional Muscle-Bone Unit'. Because muscle function is associated with muscle metabolism, it is suggested that the association of maximal forces with anthropometric variables (e. g., body weight) is characterized by allometric scaling. The present manuscript aims to describe the scaling exponent for the association of maximal forces of mechanography and dynamometry to body weight and exemplarily applies the prediction of 'Peak Jump Force' (PJF) by 'Maximal Isometric Grip Force' (MIGF) for the characterization of the unconditioned neuromuscular system in subjects with congenital heart disease (CHD). SUBJECTS: MIGF was measured in a reference population of 135 school boys and 177 school girls who were not randomized individuals of a German primary and high-school. In addition, data of the neuromuscular system were analyzed in 29 individuals with CHD. METHODS: Participants performed counter-movement jumping on a force plate to measure PJF and v (max). MIGF was determined by dynamometric measurement. RESULTS: PJF scaled (body mass) (0.97) in girls and (body mass) (1.05) in boys. PJF was not different from the scaling exponent=1 in both genders. After having taken the logarithm, MIGF predicted PJF with R (2)(adjusted)=0.774 in boys, R (2)(adjusted)=0.720 in girls (p<0.001 each) and R (2)(adjusted)=0.209 (p=0.007) in patients with CHD. The mean of the predicted PJF was lower than the mean of the measured PJF in subjects with CHD (p<0.001). The difference between the predicted and the measured PJF (DeltaPJF) was associated with v (max) (R (2)(adjusted)=0.113, p=0.042). CONCLUSIONS: PJF scales body weight in an isometric way as recently describe for other vertebrates. MIGF is a good predictor of PJF in healthy children, but not in unconditioned individuals. DeltaPJF indicates conditioning of the individual and may be used to describe inter- and intramuscular coordination in children. HINTERGRUND: Mechanografische Analysen des neuromuskulären Systems haben mittlerweile auch einen diagnostischen Stellenwert in der Pädiatrie erlangt. Ziel der vorliegenden Untersuchung ist die kinetische Analyse des Counter-movement-Sprungs durch die Messung der Bodenreaktionskräfte in Hinblick auf seine allometrische Skalierung und im Vergleich zur Entwicklung der ,Maximalen isometrischen Griffstärke' (MIGF) bei Kindern und Jugendlichen. PROBANDEN: Die Studienpopulation umfasste 135 Schüler und 177 Schülerinnen, die nicht randomisiert wurden und Schüler einer deutschen Grundschule und eines deutschen Gymnasiums waren. Zudem wurden Daten von 29 Patienten mit kongenitalen Herzfehlern analysiert. METHODEN: Die Studienteilnehmer absolvierten Counter-movement-Sprünge auf einer Sprungplatte, sodass die maximale Sprungkraft (Peak Jump Force, PJF) und die maximale Geschwindigkeit des Massenschwerpunktes beim Absprung (v (max)) ermittelt werden konnten. MIGF wurde durch Messung mit einem Dynamometer bestimmt. ERGEBNISSE: PJF-skalierte (Körpermasse) (0,97) bei den Mädchen und (Körpermasse) (1,05) bei den Jungen. Der Skalierungsfaktor von PJF war bei Mädchen und Jungen nicht signifikant vom Faktor=1 verschieden. Nach Lograithmierung sagte die Variable MIGF den Parameter PJF in der Gruppe der Jungen mit R (2)(adjusted)=0,774, in der Gruppe der Mädchen mit R (2)(adjusted)=0,720 (jeweils p<0,001) und in der Gruppe der Herzkranken mit R (2)(adjusted)=0,209 (p=0,007) voraus. Der Mittelwert des vorhergesagten Wertes für PJF war niedriger als der Wert der gemessenen PJF in Patienten mit Herzerkrankung (p<0,001). Die Differenz zwischen vorhergesagter und gemessener PJF (DeltaPJF) stand statistisch mit v (max) (R (2)(adjusted)=0,113; p=0,042) in Zusammenhang. SCHLUSSFOLGERUNGEN: PJF skaliert isometrisch zur Körpermasse, wie es bereits für andere Vertebraten beschrieben wurde. MIGF ist ein guter Prädiktor für PJF bei gesunden Kindern und Jugendlichen, jedoch nicht bei Menschen mit einem unkonditionierten neuromuskulären System. DeltaPJF kann als Marker für die Konditionierung eines neuromuskulären Systems angesehen werden und beschreibt inter- und intramuskuläre Koordination.

The influence of auxology and long-term glycemic control on muscle function in children and adolescents with type 1 diabetes mellitus.

We intended to investigate in this pilot-study if long-term glycemic control stands in close relationship with muscle function in children and adolescents with type 1 diabetes mellitus (T1DM). Muscle function (MIGF, maximal isometric grip force; PJF, peak jump force; PJP, peak jump power) was investigated in 40 children and adolescents (males 20, females 20; age 13.5-/+2.5 yr) affected with T1DM. Muscular parameters were correlated with anthropometric parameters (age, height, weight) and with glycosylated hemoglobin (HbA1c) of the presence and the past. Standard deviation scores (SDSs) of weight and MIGF indicated significantly higher weight (mean 0.75-/+1.83 (SD)) and lower MIGF (mean -1.06-/+1.76 (SD)) in individuals with T1DM. When the study group was divided into two groups by the criteria that the actual HbA1c (HbA1c0) was lower (N=25) or higher (N=15) than 8.5%, the comparison showed significantly higher muscular parameters (PJF-SDS, PJP-SDS and MIGF-SDS) in individuals with higher HbA1c0. Multiple regression analyses demonstrated that body weight and height primarily predicted muscle force (MIGF, PJF) in T1DM. In conclusion, skeletal growth is an important determinant for the development of muscle function in children and adolescents with T1DM.

A cybernetic approach to osteoporosis in anorexia nervosa.

A group of 25 female individuals, who had been admitted to the University Hospital with the diagnosis of anorexia nervosa (AN) 3 to 10 years before, was seen for a follow-up visit in the hospital. These women got a psychiatric exploration to detect a present eating disorder. Moreover, parameters of the muskuloskeletal interaction were determined on the non-dominant forearm. Bone mineral content (BMC) of the radius was measured by pQCT and maximal grip force was evaluated by the use of a dynamometer. Eating disorders were present in 12 females. The mean of BMC standard deviation (SD) score was significantly reduced in comparison with reference values. Furthermore, the mean of BMC SD score was also significantly lower than the mean of grip force in SD score. These results gave the suggestion that the adaptation of bone mass to biomechanical forces is disturbed in AN. The linear regression analyses between the parameters grip force and BMC were compared between the study and the reference group. The comparison delivered a significantly lower constant in the regression equation of the study group. This result can be interpreted on the background of the mechanostat theory. The affection with an eating disorder decreases the set point in the feedback loop of bone modeling. The results offer for the first time the possibility to analyse osteoporosis in anorexic females under the paradigm of muskuloskeletal interaction.

The bone behind a low areal bone mineral density: peripheral quantitative computed tomographic analysis in a woman with osteogenesis imperfecta.

Areal bone mineral density (BMD) is the most widely used densitometric parameter. However, this approach makes it difficult to understand the structural basis of bone diseases, because a large number of bone properties are integrated into a single number. This is exemplified in the present case of a 27-year-old woman with osteogenesis imperfecta type I. Peripheral quantitative computed tomographic analysis at the radial metaphysis and at the radial diaphysis revealed a decreased areal BMD at both sites (z score -3.9 and -3.4, respectively). Yet, the structural basis for this decrease was different for the two locations: At the distal radius areal BMD was decreased because volumetric BMD was very low, whereas bone size was above the mean of the reference range. At the proximal radius areal BMD was decreased, because bone size was very low but volumetric BMD was above average. Bone mineral content of the radial diaphysis was very low for forearm muscle size, a finding which is compatible with Frost's hypothesis that the mechanostat setpoint is increased in osteogenesis imperfecta.

Analysis of the musculoskeletal system in children and adolescents receiving anticonvulsant monotherapy with valproic acid or carbamazepine.

OBJECTIVE: To examine bone development in children and adolescents who have uncomplicated idiopathic epilepsy and had received monotherapy with carbamazepine or valproic acid for at least 1 year. METHODS: Thirty-nine patients from 6 to 19 years of age (18 girls) were studied. Total bone mineral content (BMC) and trabecular volumetric bone mineral density were measured at the distal radius using peripheral quantitative computed tomography. Maximum isometric grip force was determined with a standard dynamometer. Alkaline phosphatase activity and deoxypyridinoline (a marker of bone resorption) were assessed in serum and urine, respectively. RESULTS: Trabecular volumetric bone mineral density was significantly decreased in the entire group (z score mean +/- standard deviation: -0.62 +/- 1.04) and in the subgroup using valproic acid (-0.75 +/- 1.18). In the carbamazepine subgroup, there was a similar but nonsignificant trend (-0.50 +/- 0.90). Total BMC and isometric maximum grip force were normal in the entire study population (0.10 +/- 1.22) and in the 2 subgroups. The relationship between BMC and grip force was similar between patients and healthy participants. Urinary levels of deoxypyridinoline were significantly elevated above normal in the whole study population (1.35 +/- 2.00) and in both the valproic acid and the carbamazepine subgroups. CONCLUSIONS: Bone turnover can be increased, but bone mass is adequate in children and adolescents who have uncomplicated idiopathic epilepsy and who receive monotherapy with carbamazepine or valproic acid.

Peripheral quantitative computed tomography at the distal radius: cross-calibration between two scanners.

Peripheral quantitative computed tomography (pQCT) is an important technique to study the interaction between the muscle and bone systems. We have recently established pQCT reference ranges for children, adolescents and young adults using a recent version (XCT 2000) of the Stratec scanners (Stratec Inc., Pforzheim, Germany). However, the previous version of this type of scanner (XCT 900) is still widely used and cross-calibration is needed to use these reference data. Therefore, both distal radii of 19 healthy subjects (age 21 to 59 years; 11 women) were analyzed at the "4% site" using both the XCT 900 and the XCT 2000. Cross-sectional area, total and trabecular bone mineral density (BMD), total bone mineral content (BMC) and polar Strength-Strain Index (SSI) results from the two scanners were compared using linear regression analysis. To achieve scanner calibration we used the intercept and slope of the correlations. The correlation coefficients between the two devices were 0.82 for the cross-sectional area, 0.81 for total BMD, 0.97 for trabecular BMD, 0.99 for total BMC and 0.86 for polar SSI. In conclusion, these data allow for the conversion of XCT 900 results at the distal radius to XCT 2000 values and vice versa.

Analysis of cancellous bone turnover by multiple slice analysis at distal radius: a study using peripheral quantitative computed tomography.

We compared the results of peripheral quantitative computed tomography (pQCT) measurements (XCT-900; Stratec) at the 4% site of the distal radius (section 1; slice thickness of 2 mm) and in two proximally adjacent sections (sections 2 and 3). The study population consisted of 138 ambulatory patients (age 16.4 +/- 5.6 yr; mean +/- SD; 71 female) who were referred to a pediatric densitometry unit. Total volumetric bone mineral density (BMD) increased, whereas the area of the radial cross-section decreased in a proximal direction. There was a decrease in bone mineral content between sections 1 and 3, which was more pronounced in subjects under age 16. Cancellous BMD significantly decreased from section 1 to 3 only under the age of 16. In 12 patients under age 17 who suffered from increased bone fragility, cancellous BMD decreased about 2.5 times more between sections 1 and 3 than in age-matched patients who received anticonvulsant therapy but had a normal neurologic and musculoskeletal status (-21.4% +/- 16.9 vs -8.1% +/- 6.3; p = 0.02). This suggests that in the bone fragility group, trabeculae were removed faster during longitudinal growth of the radius. In conclusion, multiple slice analysis may provide information on the dynamic turnover of metaphyseal trabeculae during growth.