Seasonal Variation in Slipped Capital Femoral Epiphysis: New Findings Using a National Children's Hospital Database.

BACKGROUND: Slipped capital femoral epiphysis (SCFE) demonstrates seasonal variation in certain latitudes but not others. Is such variation influenced by temperature differences, sunlight exposure and subsequent vitamin D production, or other climate variables? It was the purpose of this study to further investigate the seasonal variation in month of presentation for SCFE.

METHODS: Data for this study originated from the Pediatric Hospital Information System for all children with a diagnosis of SCFE from January 1, 2004 through December 31, 2014. From this database the patient's sex, ethnicity, hospital location, and month of presentation was determined. Only those patients treated primarily for SCFE were included. Geographic and climate data [latitude, average annual temperature, precipitation, climate type (Köppen-Geiger and Liss), horticultural plant zone hardiness, and sunlight exposure] for each of the 49 Pediatric Hospital Information System hospitals was determined. Seasonal variation was analyzed using cosinor analysis. A P<0.05 was considered statistically significant.

RESULTS: There were 10,350 cases of SCFE with an overall peak presentation in mid August. For those living at a latitude of >35-degree N there was single peak, a less prominent double peak for those 31- to 35-degree N, and no variation for those <31-degree N. As the average annual temperature increased there was less seasonal variability. Humid, temperate and cold winter climates demonstrated seasonal variation, whereas other climate types did not. Those living in areas having <2500 hours of sunlight per year demonstrated seasonal variation. Further, areas having a photovoltaic solar production potential <5.0 kWh/m/d also demonstrated seasonal variation.

CONCLUSIONS: We discovered new seasonal variation findings regarding SCFE. These are a double peak pattern for those between 31- and 35-degree N latitude; less variability as the average annual temperature increases; and sunlight exposure correlates with seasonal variability. Potential explanations are a rachitic state due to seasonal variation in vitamin D production, and seasonal variation in physeal growth and strength. These new findings will require further investigation.

LEVEL OF EVIDENCE: Level III.