Slipped capital femoral epiphysis (SCFE) is a condition in which the epiphysis covering the femoral head in pre-adolescence and adolescence slips posterior relative to the femoral neck. The incidence in the US is 10.8 per 100,000 children per year, but varies from as low as 0.71 to 10.8 in different studies.

The overall prevalence in this group is 0.7 to 0.8 per 100,000. The incidence is showing an upward trend, and this is thought to be associated with the rising prevalence of childhood obesity which is a risk factor for it. Supportive findings include the increase in the occurrence of SCFE at earlier ages, and a rise in the number of bilateral SCFE cases. Over 50% of cases have body mass indices over the 95th percentile for their age.

The stable variant is more common in boys than girls, the ratio being 1.5 to 1. Overall, the incidence rates were 13.5 per 100,000 in boys versus 8.07 per 100,000 in girls. However, the unstable type is found to equally affect both sexes.

Age of Onset

The usual age group is between 10-14 years in girls and 12-16 years in boys. This is the most common hip disorder in this age group. The age of onset is trending downward , with the average being 12.7 to 13.5 years in male children, and 11.2 to 12 years in female children.

Uni- or Bilaterality

In most children the left hip is more commonly affected than the right. In anywhere from 20-80% of cases the condition affects both sides. In most of these the slip on the second side occurs within 18 months of the first. African children are the most likely to have bilateral SCFE (34%) compared to 17% for white and Hispanic children, and 18% for Asians.

Bilaterality is more frequent in Africans (34%) than Hispanics (17%), Whites (17%), or Asians (18%).

Racial Differences

Data gathered from the Kids’ Inpatient Database and US Census Bureau is the basis for the following figures regarding idiopathic SCFE. The children in this group were aged between 9 and 16 years. There was a definite tilt in the ratio of black and white children, with black children having 3.94 times and Hispanic children having 2.53 times higher rates of the condition compared to white children Polynesians (5.6 relative racial frequency) and Native Americans also show higher incidence rates.

Regional Differences

The northeast and west of the US shows a higher incidence as compared to the midwestern and southern states. This has been suggested to be due to climatic differences. Latitudinal differences are also noted, with the highest incidence in summer being found in regions north of 40 degrees latitude, but in regions south of 40 degrees in winter.

Epidemiologists suggest that the combination of ethnic, climatic and geographic differences may point to the interplay of environmental and genetic factors in the etiology of the condition. The racial differences are suggested to be due to different prevalence of obesity between races.