To the best of our knowledge, our study consisted of the first data analyzing the factors of children’s height, weight and BMI in association with Cth and we established the reference value of Cth for Asian school age children. In consistence with others, we found that the Cth in girls to be thinner than that of the boys. Besides, we demonstrated that age is the most critical factor in association with Cth in the school ages children as compared to body weight, height and BMI. Grouping children by their height, weight and BMI revealed no difference in the Cth of the evaluated joints. Finally, we established a standard reference of Cth in the knees, ankles, wrists, MCPs and PIPs for the Asian school age children and found that there were no significant differences between Caucasians and Asians.
In the present study, we discovered that the Cth were universally thicker in boys than girls among the evaluated joints. Moreover, the Cth of knees decline faster in girls than boys during their school age period. Similar observation was also reported by Spannow A.H.et al in 2010. Among the 394 Danish children aged 7-16, Spannow discovered gender difference in Cth measurements and the steeper slope of Cth in the knee joints in girls. Although the exact mechanism remain to be clarified, estrogen receptors located on articular chondrocytes may likely play a role. Estrogen has been shown to act on cartilage receptors and subchondral bone as a second messengers like regulatory polypeptides, similar to cartilage inducing factor alpha and transforming growth factor beta, to interfere cartilage turnover[15, 16]. Moreover, considering the differences in Cth between genders also existed in the prepuberty population, others and we hypothesized that physical activities and environmental factors may also contribute to the effects.
In line with Spannow and Moumita’s observation[7, 8], our data on school aged children between age 5 to 13 suggested that the Cth declines as the age advances. Although this linear correlation is true in our study as well as other reports[7, 8], it is not always the case since the measures of Cth in those preschool-aged-children and elder teens have been reported otherwise. In the present study, without the very young children and older teens, we took advantage of the linear correlation and established a formula to calculate the Cth with 95% confident interval in the knees, ankles, wrists, MCPs and PIPs joints among Taiwanese school aged girls and boys. Worthwhile to say, however, extrapolation of our proposed formula in children outside of the targeted age may not be accurate.
In adults, overweight people were found with thinner cartilage in their knees [18, 19]. Interestingly, Meng T et al following 186 participants from their childhood, discovered that the weight and BMI in the childhood were negative associated with the bone area and cartilage thickness in their knees after they reach adulthood. While Meng T assumed that between adolescence and adulthood, obesity affects different part of the knee joints (weight-bearing and non-weight-bearing), the association between body weight and Cth among school age children, however, has not been investigated yet. Moreover, the influence of body height on Cth was also surveyed for the very first time. With our extensive effects in evaluating these potential confounding factors, our data suggested that age is the leading contributor for Cth among school age children. Children with body weight or body height in different growth percentile do not have different Cth in the 5 joints evaluated.
In 2011, Yue B et al reported that the elderly in China have smaller knees as compared to the Caucasians. Nonetheless, among girls with a mean age of 11, Novotny R et al discovered that girls with Asian ethnicity gained body size more slowly than those Caucasian girls without significant difference in the changes of the bone parameters. In consistence with the observation, we also found no differences in the Cth among the five invested joints between the Asian children and the Caucasian population.
In this first study investigating the Cth in pure Asian children, adjusting for weight, height and BMI, our research has several limitations. One of these was the setting of a cross-sectional study. Serial follow up of the Cth from childhood into adolescence provides clearer picture of how Cth is affected by age. Moreover, despite the effects we placed to minimized the observer-dependent measurement bias were inevitable.