Objective:To identify the risk factors for premature proximal femur physeal closure (PPC) in children treated surgically for femoral neck fractures.Methods:Data of 106 children with an open triradiate cartilage who were treated surgically for a femoral neck fracture were retrospectively analyzed. Age, gender, laterality, mechanism of injury, the type of fracture, initial displacement, time to reduction, fixation method, whether the implant crossed the physeal plate, reduction method, reduction quality and development of femoral head avascular necrosis (AVN) were collected. PPC of the proximal femur was assessed through postoperative 6-12 months radiographs.Results:A total of 106 patients with an open triradiate cartilage were followed up, with an average duration of 20.4±13.3 months (range, 6-86 months). The overall rate of PPC following paediatric femoral neck fractures treated surgically was 36.8% (39/106). Among the 39 patients with PPC, 25 were males and 14 were females; the average age at the time of injury was 9.7±3.6 years (range, 3-15 years); 23 patients were involved in left hips and 16 were in right; the mechanisms of injury included motor vehicle accident in 5 fractures, falling injury in 21, sports-related injury in 12 and other causes in 1 fracture; two hips were Delbet type I, and 26 hips and 11 hips were Delbet type II and III, separately; type II and III of initial displacement were involved in 26 and 13 patients, separately; the mean duration from injury to surgery was 3.3±2.8 d (range, 1-14 d); 2 hips were treated with Kirschner wires, 35 hips with screw fixation, and the remaining 2 hips underwent screw and plate fixation; 2 hips had the hardware crossing the proximal femoral growth plate, and the remaining 37 hips didn’t; 15 hips were treated by closed reduction and internal fixation, and the other 24 hips underwent open reduction and internal fixation; anatomical reduction was achieved in 14 patients, acceptable reduction in 24 hips and unacceptable reduction in 1 hip; 24 hips developed AVN at the latest follow-up and the remaining 15 hips didn’t. Statistical analysis indicated that age ( t=3.875, P< 0.001), the severity of initial displacement ( Z=-2.118, P=0.034) and the rate of AVN ( χ2=42.280, P< 0.001) in patients with PPC were significantly higher than those in patients without; Logistic regression analysis confirmed age ( OR=1.288, P=0.011) and AVN ( OR=40.336, P< 0.001) as risk factors for PPC. ROC curve analysis indicated 10 years was the cut off age to significantly increase the rate of PPC. The rate of PPC in patients aged over 10 years (63.6%, 21/33) was significantly higher than that (24.7%, 18/73) in those aged less than 10 years ( χ2=14.848, P< 0.001). Conclusion:Age over 10 years and AVN are risk factors for PPC in children with femoral neck fractures treated surgically.