Prediction of contralateral slipped capital femoral epiphysis using the modified Oxford bone age score.

BACKGROUND The purpose of the present study was to determine whether the modified Oxford bone score can be used as a predictor for the risk of developing contralateral slipped capital femoral epiphysis (SCFE) in children who present with a unilateral slip. METHODS We identified 260 patients treated for unilateral SCFE between 1980 and 2002 and followed them up to skeletal maturity or until development of contralateral slip. Exclusion criteria included patients with endocrine or metabolic disorder, Down syndrome, and those with radiographs inadequate to determine the modified Oxford bone score. The initial radiographs were given a score ranging from 16 to 26. Statistical analysis was used to determine whether the modified Oxford bone score was predictive of future development of contralateral slip. A linear regression model was used to estimate the probability of future development of a contralateral slip as related to the modified Oxford bone score. RESULTS Of the 260 patients, 64 (24%) developed a contralateral slip, at an average of 10 months after initial presentation. Race, sex, age, and weight at initial presentation were not predictive of the development of contralateral slip. The modified Oxford score and a triradiate score of 1 were found to be significant (P<0.0001) predictors, with the modified Oxford score a better overall predictor. CONCLUSIONS The modified Oxford bone age score is the best predictor of the risk of development of a contralateral SCFE in patients presenting with a unilateral slip. Controversy exists regarding prophylactic pinning of a normal hip in patients presenting with unilateral SCFE. The benefits of prophylactic pinning must outweigh risk. This study provides probability data for predicting a contralateral slip based on the modified Oxford bone maturity score that can be shared with families and allows physicians to decide their threshold for prophylactically pinning the contralateral hip in patients presenting with a unilateral slip. LEVEL OF EVIDENCE Therapeutic level IV, Case series.