The fracture lines were found to be mainly located in the middle and lower areas of the anterior and superior regions of the femoral neck, while in the middle region of the posterior and inferior regions. Patients under 10 years old, fractures mainly occurred at the base of the femoral neck, whereas for patients over the age of 10 fractures predominantly was located in the middle region of the femoral neck. Furthermore, most children had Pauwels angle III type of fracture (63%), especially in those over 10 years old.
The results from adults studied by Wu et al.[13] on fracture mapping of femoral neck displaced fractures in middle-aged and elderly was different from the present study, as they found fracture lines concentrated mainly in the superior region of the femoral neck. It may attributed that with aging bone microstructure in the superior femoral neck of adults decrease, weakening the region's supportive capacity[17]. However, for children, the incomplete development of bone trabeculae and the limited tensile strength of bone tissue may contribute to the dispersion of fracture lines in superior region of femoral neck[18]. That may be why the superior fracture area is more concentrated in the elderly adults than in children. In this study, the fracture line in the inferior of femoral neck demonstrated a relatively concentrated pattern. This phenomenon may be contribute to the thicker cortex in inferior of the femoral neck in children[18], higher cortical porosity of the superior neck[19], and lower levels of habitual stress[20]. Therefore, in pediatric FNF, most fracture lines will concentrate in inferior of the femoral neck.
Most research on pediatric FNF have shown that Delbet type II of fracture is the predominant subtype, followed by Delbet type III, collectively accounting for approximately 65–85% of all the pediatric FNF[21, 22]. It was consistent with our finding. However, we also found that Delbet type was related to age of children, Delbet type III of fracture was more common in patients under 10 years of age, while Delbet type II more in patients over 10 years of age.
In this study, the majority (63.04%) of femoral neck fractures were unstable fracture according to Pauwels angle type, especially in patients aged over 10 years (P < 0.05). The majority of FNF in adolescents may be attributed to high-energy trauma[23]. Consequently, young FNF commonly result from high-energy vertical shear forces and predominantly manifest as Pauwels type III fractures[24]. It is plausible that with increasing age, these children are more likely to develop high-energy injuries and lead to unstable fractures.
Pauwels type III fractures present a significant challenge for achieving stable fixation due to substantial shear forces. To enhance the stability of fracture fixation, internal fixation devices should distribute stress along the fracture line at the fracture site. Additionally, it is not advisable for an internal fixator with a large diameter to cross epiphyseal plate of femoral head in children [25]. Ranajit et al.[15] recommended using smooth pins crossing the epiphyseal plate for fixation of fracture. The fracture mapping of FNF in this study revealed a predominant concentration of fracture areas in zone 2, 3 and zone 4 of femoral neck, with fewer occurrences of fracture lines observed in zone 1 adjacent to the epiphyseal plate. To ensure stability during fixation, it is recommended to select thin smooth pins through involved zone 1 of femoral neck.
There are also some limitations of this study that should be taken into account. Firstly, due to the rarity of pediatric FNF, the sample size in the present study was small and weaken our findings. Therefore, multi-center studies should be conducted in the future. Secondly, for those compression fractures, the accuracy of reduction and determination of fracture line may be disturbed. To address the deviation, the reduction took the uninjured side as standard. Finally, due to variations in proximal femur morphology associated with age, each patient's proximal femur may not perfectly align with a standard template. Consequently, some deviation is inevitable when delineating the fracture line using current technology.