Risk Factors for Failure Following Avascular Necrosis After Slipped Capital Femoral Epiphysis

Background: Slipped capital femoral epiphysis (SCFE) is the most common hip disorder affecting adolescents. Delay in the diagnosis of SCFE is frequent and is associated with higher rates of complications, including avascular necrosis (AVN) of the femoral head. AVN is often a predictor of joint failure, leading to poor functional outcomes and degeneration, which may require total hip arthroplasty (THA) or fusion. Previous studies have shown that the degree of femoral head involvement is important to consider when treating AVN of various types. We sought to evaluate factors, including necrosis arc, that might affect outcomes in patients with post-SCFE AVN.

Methods: This is a retrospective case series of patients presenting to our institution from 1991 to 2016 with a diagnosis of AVN after SCFE. Sufficient clinical follow-up with available records and a diagnosis of AVN after SCFE was necessary for inclusion. Lack of imaging of original SCFE or at time of AVN, and lack of clinical follow-up warranted exclusion. Medical records were reviewed for patient demographic variables. Operative reports were reviewed to identify surgical procedures performed. Functional outcomes were calculated from the most recent clinic notes using the modified-Merle D’Aubigné Postel (MDP) score.

Results: Thirty-seven patients treated for SCFE who developed AVN met inclusion criteria. The mean age at initial SCFE treatment was 12 years (range, 9 to 17 years) and the cohort was 54% male. Patients were followed for a minimum of 1 year with a median of 4.5 years follow-up or median of 2.9 years to failure. Failure was defined as having a fusion, THA or Tönnis grade <3. Twenty patients had a necrosis arc of >90°, the remaining 17 patients had a necrosis arc of ≤90º. There was no difference in patient age, sex, SCFE severity, stability, or SCFE procedure type across the two necrosis groups. Our results show that patients with >90° of necrosis had more than 20 times the odds of failure (OR=20.7; 95% CI=4.5 to 126.5; p<0.001). There was no association between failure and patient sex, age, stability, or procedure type. At most recent follow-up, patients who resulted in failure had significantly lower MD scores compared to the non-failure group (median 11 versus median 14; p=0.002). Kaplan-Meier analysis determined that hips with >90 degrees necrosis of the femoral head had significantly lower likelihood of ‘survival’ (median, 2.8 years) compared to those with ≤90º necrosis (median, 10.9 years; p<0.001).

Conclusion: AVN after SCFE can be challenging to treat and success of the hip is highly dependent upon the degree of head involvement. A necrosis arc of >90° on the AP pelvis radiograph may be predictive of failure of attempted joint preserving surgery. For patients with more extensive head necrosis, arthroplasty or fusion may be warranted as the initial treatment.