Hip Joint Articulotrochanteric Distance Measurements in Children: Articulotrochanteric Distance in Children Aged 5 to 14 Years Does Not Increase With Age.

Background: The articulotrochanteric distance (ATD) has universally been utilized to assess greater trochanter overgrowth in pediatric orthopaedic diseases. However, its overgrowth cannot be detected in a timely manner due to the absence of a normal ATD value. This study is to determine the ATD normal value in hip radiographs of children under the age of 14 and to establish the threshold for overgrowth of the greater trochanter.

Methods: A retrospective analysis of 1787 hip radiographs was conducted, measuring ATD, trochanter-to-trochanter distance (TTD), lesser trochanter-to-articular surface distance (LTA), epiphysis height (EH), and femoral head epiphyseal plate-to-lesser trochanter distance (ELD). The differences in TTD and ELD between adjacent age groups were denoted as ΔTTD and ΔELD, respectively. Data with normal distribution were analyzed using independent sample (tow-tailed student t test) t tests and One-way ANOVA, while data with non-normal distribution were analyzed through nonparametric tests. The range defined by the 95% measurement values (mean±2SD) was considered the normal range.

Results: Among 5-14 year-olds, the mean ATD (mean±2SD) was 23.5±10.0 mm for males and 21.2±9.6 mm (mean±2SD) for females, statistically significant differences in the ATD were observed between sexes (P<0.05), whereas no significant differences were noted among age subgroups within the same sex (P>0.05). The normal range for males was 13.5 to 33.5 mm, while for females it was 11.6 to 30.8 mm. In addition, no significant distinction (P>0.05) was noted in the EH between males and females within this age range. Furthermore, the analysis revealed no significant difference (P>0.05) between the changes in ΔTTD and ΔELD among the hips.

Conclusions: Our findings revealed that in hip radiographs, ATD values of children aged 5 to 14 years differ significantly between males and females, although within each sex group, there was no notable variation across different age groups. We proposed that ATD <13.5 mm in males and <11.6 mm in females might indicate an overgrowth of the greater trochanter, and in such patients, prophylactic greater trochanteric epiphysiodesis may be beneficial. In addition, we believed that the growth rates of the femoral neck and greater trochanter were approximately similar.

Level of evidence: Level IV-diagnostic studies.