Walking age does not explain term versus preterm difference in bone geometry.

OBJECTIVE: To elucidate the relationship between bone geometry and onset of walking in former term and preterm children. STUDY DESIGN: We conducted a cross-sectional study of 128 preschool children aged 3 to 5 years who underwent peripheral quantitative computerized tomography measures of bone size at the distal tibia. Linear models were developed, stratifying by sex, to determine whether bone differences between children born term and preterm were caused by differences in walking age. RESULTS: Children with a history of preterm birth walked later than children born at term (12.4 +/- 0.5 versus 10.9 +/- 0.2 months; P = .004); however, gestation-corrected walking age (11.4 +/- 0.5 for children born preterm) did not differ. In multiple regression analysis, boys born preterm had larger periosteal and endosteal circumferences and smaller cortical thickness and area than boys born term (least square means, 49.7 +/- 1.3 mm, 43.0 +/- 1.8 mm, 1.1 +/- 0.11 mm, and 49.3 +/- 3.2 mm2 versus 47.0 +/- 0.5 mm, 38.5 +/- 0.7 mm, 1.4 +/- 0.04 mm, and 56.9 +/- 1.2 mm2, respectively; all P < .05). Preterm birth remained statistically significant after adding the age of walking to the models, but no longer significant when current activity levels were included. CONCLUSION: Greater periosteal and endosteal circumferences, with smaller cortical bone thickness and area, were found in former preterm boys, but not girls, and were explained by differences in current activity levels, not age of walking.

Bone measurements by peripheral quantitative computed tomography (pQCT) in children with cerebral palsy.

OBJECTIVE: To use peripheral quantitative computed tomography (pQCT) to determine bone measurements in patients with cerebral palsy (CP) age 3 to 20 years and compare them with control subjects. STUDY DESIGN: A total of 13 (5 male) patients with CP, along with 2 sex- and age-matched controls for each, were included in a mixed-model analysis with matched pairs as random effects for pQCT bone measurements of the 20% distal tibia. RESULTS: Tibia length was similar in the CP and control groups (P = .57). Weight was marginally higher in the control group (P = .06). Cortical bone mineral content (BMC), area, thickness, polar strength-strain index (pSSI), and periosteal and endosteal circumferences were greater in the control group (P < .05 for all). Relationships between bone measurements and weight showed that cortical BMC, area, periosteal circumference, and pSSI were greater at higher weights in the control group (group-by-weight interaction, P < .05 for all). Cortical thickness was greater in the control group and was correlated with weight. Cortical volumetric bone mineral density (vBMD) was greater with higher weights in the CP group (group-by-weight interaction, P = .03). CONCLUSIONS: Bone strength, as indicated by pSSI, is compromised in children with CP due to smaller and thinner bones, not due to lower cortical bone density.

Factors associated with physical activity in preschool children.

OBJECTIVE: Our purpose was to identify factors associated with the physical activity in young children. STUDY DESIGN: Participants were 214 children (aged 3-5 years) enrolled in 10 childcare centers who were monitored for physical activity with an accelerometer during 2 continuous days (48 hours). Mean daily activity counts, activity counts between 9 AM and 5 PM, and percentage of time spent in vigorous activity were determined. The factors investigated were age, childcare center, season, sex, body mass index (BMI), history of preterm birth, participation in organized activities, parental BMI, and parental educational level. Regression analyses were used to identify factors associated with each of the activity measures. RESULTS: A statistical model including sex, history of preterm birth, childcare center, and father's BMI accounted for 22%, 37%, and 23% of the variance in total daily counts, counts between 9 AM and 5 PM, and percentage of time spent in daily vigorous activity, respectively. Childcare center was the highest individual predictor of activity. Boys were more active than girls in all activity measures except counts between 9 AM and 5 PM. Children born preterm were less active than children born at term, and high activity levels in the child were associated with a low BMI in fathers. CONCLUSION: The findings indicate that sex, history of preterm birth, childcare center, and father's BMI influence the daily physical activity of young children.