Clinical characteristics of children with atypical and idiopathic slipped capital femoral epiphysis: description of the age-weight test and implications for further diagnostic investigation.

SUMMARY: Slipped capital femoral epiphyses (SCFEs) can be idiopathic or atypical (associated with renal failure, radiation therapy, and endocrine disorders). The demographics of 433 children (285 idiopathic, 148 atypical) with 612 SCFEs were studied to define predictors of atypical SCFEs. Multiple logistic regression analysis showed that age and weight were predictors. For two patients of equal weight, those younger than 10 or older than 16 years of age were 4.2 times more likely to have an atypical SCFE; for two patients of equal age, those <50th percentile weight were 8.4 times more likely. The age-weight test was defined as negative when age younger than 16 years and weight > or = 50th percentile and positive when beyond these boundaries. The probability of a child with a negative test result having an idiopathic SCFE was 93%, and the probability of a child with a positive test result having an atypical SCFE was 52%. An evaluation of the child's age and weight is useful when considering the cause of an SCFE.