Slipped capital femoral epiphysis. Prediction of contralateral involvement.

We performed a retrospective review of the medical records and radiographs of fifty children who had had unilateral slipped capital femoral epiphysis. Our purpose was to determine if there were any epidemiological parameters that were associated with the later development of a contralateral slip. The mean duration of follow-up was thirty-four months (range, twenty-four to sixty-eight months). Physiological maturity, determined with a modified form of the Oxford method for assessment of bone age, strongly correlated with the risk of development of a contralateral slip in patients who were initially seen with a unilateral slip (r = 0.59, p < 0.0005). The scores were determined by four raters; the variation in the predictive value of the scores among the raters was not significant (p = 0.5). The relationship between the score as determined with the modified Oxford method and the risk of contralateral involvement had a linear distribution. The four raters performed a total of 442 observations to determine the modified Oxford scores for the fifty hips. The prevalence of a subsequent slip for the hips that had been assigned a score of 16 points was 85 +/- 15 per cent (95 per cent confidence limit) (seventeen of twenty observations). The risk of contralateral involvement when the score was 21 points was 11 +/- 9 per cent (six of fifty-four observations). A slip did not develop in any hip with a score of 22 points or more (sixty-nine observations). For boys, the age at the time of the initial slip was predictive of a contralateral slip. A contralateral slip developed in all four boys who had been eleven years and seven months old or less at the time of the initial presentation; however, a contralateral slip developed in only nine of the twenty-two boys who had been eleven years and eight months to fourteen years and eleven months old. A contralateral slip did not develop in the three boys who had been fifteen years old or more. There was no association between age and the risk of a contralateral slip in girls.