In CCS, three cannulated screws apply pressure to the fracture and promote fracture healing. In addition, they occupy a relatively small area in the femoral neck and interfere less with femoral head and neck blood flow. Triangular distribution can form a three-dimensional skeleton and bone tissue, which can decrease the stress of femoral head rotation. It can enhance the intraoperative and postoperative compressive stress between fracture ends, promote close contact between fracture ends, and facilitate fracture healing. However, there is no correlation between the three cannulated screws, and the screw position is easily affected by the subjective and objective factors of the surgeon. Therefore, its ability to resist vertical shear and torsion is poor, which may lead to fracture end loosening and displacement, femoral head necrosis and nonunion, and femoral neck shortening [
11,
12]. A biomechanical study showed that FNS and DHS have shown similar results in fracture fixation for parameter cycles to failure and femoral neck shortening [
5]. These devices allow for a controlled collapse of the fracture site, leading to an increased stimulus for remodeling. For displaced or unstable fracture patterns, a DHS or FNS offers greater mechanical stability to resist the increased shear forces generated [
5,
13]. In our study, there was no statistical difference in the incidence of FNF nonunion (12.5% vs. 10.0%,
p = 0.795) and femoral head necrosis (12.5% vs. 5.0%,
p = 0.389) between the CCS and FNS groups. However, the incidence of femoral neck shortening and screw cut-out was significantly higher in the CCS group than in the FNS group (37.5% vs 10.0%,
p = 0.036). Previous studies have shown that femoral neck shortening after CCS treatment in patients with FNFs may even cause hip dysfunction [
14,
15]. Weil et al. [
16] showed that the quality of reduction of FNFs had a direct effect on the occurrence of postoperative femoral neck shortening. Osteoporosis can lead to a decrease in fixation grip and resistance to stress at the fracture site, resulting in a decrease in stability and a greater likelihood of femoral neck shortening [
17,
18]. In our study, the incidence of femoral neck shortening in the FNS group was significantly lower than that in the CCS group, which may be related to the better mechanical stability and shear resistance of FNS. A previous study also reported that cut-out was a common complication and occurred in 14.5% of patients [
19]. The study also implied that a nonparallel and widely spread screw trajectory might interfere with shortening of the osteoporotic femoral neck during fracture healing, leading to the screws possibly cutting out from the femoral head [
19]. However, due to the locking mechanism of the plate and screw, there were no patients with screw cut-out in the FNS group. In this study, both the CCS and FNS groups achieved relatively satisfactory functions, and there was no statistically significant difference in postoperative HHSs between the two groups. Our meta-analysis was conducted to analyze the clinical outcomes of two implants (CCS and slide DHS) and concluded that two different types of internal fixation could achieve similar clinical outcomes in terms of the HHS [
20]. Factors that affect the clinical outcome after fixation of FNFs primarily depend on the condition of the patients, the degree of fracture displacement, adequacy of internal fixations, and quality of surgical reduction. In our study, the operation time in the FNS group was longer than that in the CCS group, which may be related to the surgical instruments and proficiency. Therefore, it is very important to use the FNS skilfully to shorten the operation time. According to the surgeon’s experience, FNS is significantly better than CCS in applying pressure to the fracture site (Fig.
5).
There are also several limitations in our study: (1) Due to the short clinical application time of FNS, a small number of cases were included in this study; (2) this study only compared the FNS and CCS groups, and the results might be more convincing if the DHS group and the FNS group were compared at the same time.