Cold Weather as a Risk Factor for Late Diagnosis and Surgery for Developmental Dysplasia of the Hip.

BACKGROUND

Newborn hip screening aims to prevent the late diagnosis of and subsequent surgical procedures for developmental dysplasia of the hip (DDH). Weather may affect how parents swaddle their babies in early life, but weather has never been formally regarded as a risk factor in hip screening. This study investigates the association between the incidence of surgically treated DDH and the outdoor temperature.

METHODS

Surgical procedures for late-diagnosed DDH were investigated in 12 birth-year cohorts (1999 to 2010) using the Taiwan National Health Insurance Research Database. The number of children who underwent a DDH-related surgical procedure between 6 months and 5 years of age per total live births was evaluated as an outcome of hip screening. Trend and regression analyses were used to determine the association between the incidence of surgically treated DDH and birth year, birth month, and the temperature during the birth month and first 3 months of life.

RESULTS

The mean incidence of surgically treated DDH was 0.48 per 1,000 live births (1,296 surgically treated patients per 2,712,002 live births). The incidence of surgically treated DDH among babies born in winter months (0.70 per 1,000) was significantly higher than that among babies born in summer months (0.32 per 1,000), and it was significantly correlated with mean temperature in the first 3 months of life (r2 = 0.91; p < 0.0001) and birth month (r2 = 0.68; p < 0.001). Multivariable regression revealed that external temperature in the first 3 months of life was the most significant factor (β = -0.034 [95% confidence interval, -0.042 to -0.022]; p < 0.001) for the incidence of surgically treated DDH (adjusted r2 = 0.485). The trend of seasonal differences remained the same throughout the study years following implementation of the hip-screening policy.

CONCLUSIONS

As the incidence of surgically treated DDH is the ultimate outcome of newborn hip screening, cold weather should be regarded as a risk factor and should be incorporated into future screening programs. Weather patterns of different geographical areas should be studied to determine if children born in the winter are at an increased risk for requiring a surgical procedure for DDH, and newborn hip-screening programs should be revised accordingly.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.