Background: Traumatic osteonecrosis of the femoral head (TONFH) is the most common and severe complication after femoral neck fracture in teenagers. Despite the rapid progression of hip destruction once femoral head collapse ensues, no clear treatment exists for this condition. The purpose of this study was to evaluate the outcome of adolescents with collapsed-stage TONFH who were treated by non-vascularized bone grafting through a window at the collapsed articular cartilage, which is known as the "trapdoor procedure". Methods: We retrospectively reviewed the medical records of teenagers with TONFH who were treated with the trapdoor procedure or conservative methods between 2003 and 2013. The medical records were extracted from a database. The Harris score was obtained as a clinical evaluation, with less than 80 points defined as clinical failure. The risk of clinical failure, progression of femoral head collapse (PFHC) and secondary hip degeneration (SHD) were compared between the surgical and conservative groups using a Kaplan Meier analysis, and multivariate Cox regression analysis was used to eliminate the effect of demographic and radiographic characteristics. Results: Seventeen teenagers treated with the trapdoor procedure and 20 teenagers treated with conservative methods were included in the study, totaling 27 boys and 10 girls. The mean age was 15.1 years (range: 13 to 18). The mean follow-up period was 44.5 months (range: 24 to 68). The rates of clinical failure, PFHC and SHD were 23.5%, 17.6% and 35.3%, respectively, in the operative group, whereas those in the conservatively treated group were 65.0%, 65.0%, and 60.0%, respectively (log rank test: P-clinical failure= 0.006, P-PFHC = 0.004 and P-SHD = 0.053). Multivariate Cox regression analysis showed that the trapdoor procedure significantly lowered the risk of clinical failure (HR = 0.18; 95% CI: 0.05 to 0.72; P = 0.015) and PFHC (HR = 0.09; 95% CI: 0.02 to 0.47: P = 0.004) compared with the conservative methods. Conclusions: The trapdoor procedure appeared effective in avoiding or forestalling the rapid progression of TONFH in teenagers and provided clinical and radiographic improvement compared with those who were treated conservatively in a short-term follow up.