Onset and clinical characteristics of transient synovitis of the hip in 733 children: an eight-year retrospective analysis
Authors: Feng Haoran , Deng Hansheng , Chen Jianlin , Zhu Tianfeng , Huang Zilong , Li Jiahui , Liu Shizhe , Wang Shuaiyin , Gu Zhenkun , Liu Gen , Qiu Xin , Fu Guibing 
Published: July 2024

Purpose
Transient synovitis of the hip (TSH) is the most common cause of acute limp among children. The clinical characteristics and time of onset of TSH in children must be fully understood. As such, this study analyzed the demographic characteristics, preceding factors, positive rates of laboratory values, and association between the number of onsets and climate in children with TSH to provide clues to a deeper understanding of the etiology of TSH.
Methods
A single-center retrospective analysis of demographic information, preceding factors, and laboratory values from hospitalized children diagnosed with TSH at the authors’ hospital between September 1, 2015, and August 31, 2023, was performed. Preceding factors included upper respiratory tract infections, trauma, and strenuous activity. Laboratory values included white blood cell (WBC), neutrophil, eosinophil, and basophil counts, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level. Climate data, including temperature, precipitation, hours of insolation, and relative humidity, were also collected. Children with TSH were divided into 4 groups according to age: infants (< 2 years); preschool (2 to < 6 years); school-age (6 to < 11 years); and adolescents (11 to ≤ 18 years).
Results
Data from 733 children were included. The mean (± SD) age at onset was 6.01 ± 2.17 years, and the greatest number of cases occurred among those 5 years of age. Among the different age groups, the preschool group had the largest proportion of patients, accounting for 52.5% of all children with TSH, whereas the infant group accounted for only 1.2%. There were more males (74.9%) than females (25.1%); the male-to-female ratio was 2.98:1. The most common site of onset was the right hip (42.4%). Among children with TSH, 26.9% had preceding factors, including strenuous activity (12.6%), trauma (8.3%), and upper respiratory tract infections (7.6%). Winter and autumn were the peak seasons for TSH, and especially in December (11.7%). There was no correlation between climatic factors and the number of children with TSH. Among initial laboratory values of children with TSH, the positivity rate of ESR > 20 mm/h was highest (18.9%), followed by neutrophil (17.2%) and WBC (16.2%) counts. CRP had the lowest positivity rate among laboratory values, which was 4.2% when CRP was > 20 mg/L but increased to 8.2% when CRP was > 10 mg/L. When grouped according to symptom duration, positive WBC and neutrophil counts gradually decreased, whereas positive eosinophil and basophil counts gradually increased. Positive rates for ESR and CRP were highest when symptoms lasted 2–7 days, and both decreased after > 7 days.
Conclusion
Children with TSH in various age groups exhibited differences in sex and preceding factors, with strenuous activity the most common among those with TSH. Children should exercise moderately and take protective measures. The relationship between TSH and climate remains controversial and more evidence is required to support the temporal characteristics of TSH onset. The positive rates of laboratory values in children with TSH and symptom durations differed.