Probability analysis of sequential SCFE (PASS score)

PURPOSE: The study aimed to develop a scoring system based on clinical and radiological findings to predict the risk of a sequential slipped capital femoral epiphysis (SCFE). METHODS: Paediatric patients with unilateral SCFE and at least two years of radiographic follow-up were screened for inclusion. Medical records were reviewed for multiple variables including age, gender, body mass index (BMI), stability of SCFE, and time to sequential presentation. Radiographic analysis included triradiate physeal status, Risser staging, superior epiphyseal extension ratio (EER), posterior epiphyseal angle (PEA), posterior sloping angle (PSA) and slip severity. RESULTS: In total, 163 patients (88 male, 54%, 75 female, 46%) met inclusion criteria. Of those, 65 (40%) with a mean age of 11.9 ± 1.3 years developed sequential SCFE at a mean of 9.8 ± 6.4 months after the initial slip. Eight independent variables were statistically different (p < 0.05) between unilateral and sequential groups. Following multivariate analysis, Risser stage and triradiate status were no longer significant and did not influence the strength of the final model (overall area under the curve (AUC) = 0.954) and were consequently excluded. We developed the PASS score using three radiographic parameters using chosen cut-off values that were close to their maximized value and weighted the point value assigned to each parameter based on the strength of predictor. CONCLUSION: A PASS score of three or higher predicts a high probability of sequential SCFE with 95% confidence and may warrant prophylactic screw fixation. PASS score calculation can be used to predict a sequential SCFE and provide an objective method to determine the utility prophylactic screw fixation. LEVEL OF EVIDENCE: II