RADIOGRAPHIC FOLLOW-UP AFTER MILD SLIPPED CAPITAL FEMORAL EPIPHYSIS: WHAT IS THE INCIDENCE OF SUBSEQUENT SURGERY FOR FEMORACETABULAR IMPINGEMENT?

BACKGROUND: Slipped capital femoral epiphysis (SCFE) is characterized by translation of the proximal femoral epiphysis posterior and medial relative to the metaphysis. The gold standard treatment of mild SCFE, defined as a slip angle <30°, remains in-situ pinning (ISP) to stabilize the epiphysis in its current position after slippage. METHODS: 127 hips from 113 individuals met inclusion criteria: mild SCFE (Southwick angle <30°) that underwent ISP with available pre- and post-procedure radiographs. Medical records were reviewed to collect demographic data, preoperative symptoms, surgical details, radiographic measurements, and post-operative follow-up. Six hips were identified as having undergone additional joint preserving surgery of the hip (JPSH) while seven other hips were identified as having undergone screw removal and/or replacement within two years of initial ISP. Anterior-posterior (AP) and frog-leg lateral alpha angles, femoral epiphyseal-metaphyseal offset angle, and Southwick angle were all measured preoperatively, post-operatively, and at final radiographic follow-up. Chi-squared analyses, binary logistic regression models and Kruskal-Wallis tests were used to evaluate the association between clinical and radiographic parameters and the occurrence of additional surgery or screw failure. RESULTS: Demographic variables, including age, body mass index, prodrome pain, sex, laterality, and chronicity were not found to significantly influence the likelihood of additional surgery. Preoperative AP alpha angle, frog-lateral alpha angle, epiphyseal-metaphyseal offset angle, and Southwick angle did not significantly impact the likelihood of additional surgery or screw failure. Radiographic measurements taken after ISP demonstrated that AP alpha angle significantly increased the likelihood of additional surgery. For every one degree increase, the likelihood of additional surgery increased 1.091 times (average 70.264° for no additional surgery and 82.333° for additional surgery, p=0.017). CONCLUSION: Mild SCFE can progress to residual pain and limited hip motion even after initial treatment with ISP. Of our cohort of 127 hips, six (4.72%) went on to have secondary JPSH while an additional seven (5.51%) presented with screw failure within two years of initial ISP. Increased AP alpha angle after ISP was correlated with an increased likelihood of secondary JPSH. This increased AP alpha angle may contribute to intra-articular pathology due to CAM-type morphology which may lead to the necessity of JPSH. These findings suggest that patients with increased AP alpha angle after ISP may need to be followed long-term for the development of further joint symptoms and may need to be counseled after ISP for mild SCFE for the risk of secondary JPSH. TABLES/FIGURES: