The Hong Kong Growth Survey 1993 provided data for the construction of reference curves for body mass index (BMI) of Chinese children from birth to 18 years. Data on weight and height was obtained from 11797 boys and 12168 girls. The LMS method was used to smooth the percentile curves. These curves showed a definite physiological rising pattern to a peak at 6 months, then fell to a trough at 6 years, before another rise towards adulthood. Compared to published reports from the US, Britain, France and Sweden, Hong Kong Chinese children, particularly the girls, were less obese. In the first 2 years median curves of Hong Kong Chinese were similar to those of the Japanese.

Introduction Since the beginning of Coronavirus disease 2019 (COVID-19) pandemic, schools in Hong Kong were suspended intermittently as part of the anti-epidemic measure. This study aims to investigate the impact of COVID-19 pandemic on the epidemiology of paediatric fracture and bone health of children. Methods We recruited patients aged 3–17 admitted to tertiary paediatric orthopaedic trauma centres for fractures from 1st February 2020 till 4th March 2021 during COVID-19 period as study group and compared with patients admitted from 1st February 2019 till 31st January 2020 before COVID-19 as control group. Results Total number of admissions due to fracture was reduced by 49% (pre-COVID period: 345, COVID period: 177). Demographic data such as age, age group distribution, sex, location of fractures, energy of injury, prior history of fracture were comparable in the two groups. There was no statistically significant difference in the proportion of patients requiring operative treatment. Significant change was found in injury mechanisms, with injury related to body-powered vehicles (33.7%, n = 58) becoming the leading cause of injury during COVID period ( p < 0.001). There was significant drop in proportion of patient with injury from level ground fall ( p < 0.001) and sports ( p < 0.001). The percentage of obese children increased significantly ( p = 0.009) during the COVID period (32.7%, n = 48) than pre-COVID period (21.0%, n = 67). The proportion of patients with hypocalcaemia was found to be higher ( p = 0.002) during COVID period. Conclusions This study reflects paediatric bone health issues during COVID-19 pandemic. We postulate the reduction in fracture incidence, change in the distribution of injury mechanisms, and more obesity could be related to a more sedentary lifestyle during COVID period. Hypocalcaemia can be associated with reduced sunlight exposure, obesity, and lack of physical activities. If the problem is left neglected, it can lead to long-term bone health problems.