No matter which treatment method is chosen, FNF has a significant impact on the quality of life of these patients, and brings a greater economic burden to society and families. Compared with hip replacement, internal fixation has become the main treatment method for FNF due to its advantages of less trauma, short operation time, less bleeding and low early mortality. The choice of surgical method should consider patient-related factors such as mobility, life expectancy, comorbidities and other fracture related factors such as fracture location, direction, and comminution . The prognosis of FNF is uncertain. Bone nonunion and necrosis of femoral head are recognized as serious complications after internal fixation of FNF, which often require reoperation. The type of fracture and improper treatment are considered to be the main factors leading to nonunion and necrosis of femoral head . However, there is still a lack of consensus on which internal fixation method can better maintain the stability of fracture end, promote fracture healing, avoid and reduce postoperative femoral head necrosis, internal fixation failure and other complications.
Three cannulated screws can be used for compression fixation of the fracture, but they do not lock each other to form a frame structure. The resistance of the three cannulated screws to vertical shear force and rotation force is reduced, which could lead to the loosening and displacement of the fracture end, thereby increasing the risk of femoral head necrosis, femoral neck nonunion or malunion [18–20]. The distribution pattern of cannulated screws was greatly affected by the subjective effect of the surgeon, so the clinical efficacy of cannulated screws in the treatment of FNF was significantly different between related studies. Previous studies have found that the DCLS treatment of FNF is superior to the three cannulated screws, with the advantages of small surgical trauma, good stability, early healing time, high fracture healing rate, early postoperative functional rehabilitation, low complication of fracture healing, and good recovery of hip function .
DHS fixation has the dual function of dynamic and static compression, so the fracture ends can contact closely. DHS can withstand twice the compressive stress of cancellous bone screws and have a higher fixation success rate. The lateral steel plate provides good angulation stability. The sliding mechanism of lag screws transforms the shear force into compressive stress, which is beneficial to fracture healing. However, it has been pointed out in the literature that its large trauma, long force arm, stress concentration and eccentric fixation may lead to fracture of locking plate and screw, fracture of femur, femoral head cutting and varus of hip . Poor rotational stability, especially when the hip screw is screwing in the femoral head, is easy to cause poor rotational alignment of the femoral head and neck . DHS require greater soft tissue exposure and hip screw placement causes greater damage to the cancellous bone of the femoral head and neck, which disrupts the blood supply to the femoral head and neck and affects the healing of FNF.
DCLS is a new method of FNF fixation, which is in the initial clinical application stage. The main features are as follows. ① The positions of the three parallel cannulated screws are distributed on the triangular carina of the section of the axial screw placement of the femoral neck. These screws are close to the bone cortex at the highest and second highest bone density of the femoral neck, which conforms to the principle of "cortical support". Therefore, these screws have the characteristics of maximum screw dispersion and holding force with good biomechanical stability . ② When the system inserts three cannulated screws, the three cannulated screws can apply axial and uniform pressure to the fractured end through the lateral plate. ③ The system forms a triangular frame structure with good shear and torsion resistance. ④ There is no thread in the middle of these screws of the system, so as to realize the dynamic compression of the fracture end after operation and promote the healing of the fracture. Therefore, synthesizing the functions of the DCLS system, it is found that DCLS is the integration of three cannulated screws and DHS, which is further optimized and improved.
This study found that the operation time, blood loss, incision length, number of fluoroscopy, and shortening of the femoral neck in the DCLS group were significantly less than those in the DHS group, indicating that the DCLS group had simpler intraoperative procedures, less trauma, and better control of femoral neck shortening than those in the DHS group. The DCLS is equipped with an intraoperative guide. After the first guide needle is placed in the femoral neck in a good position, the remaining guide needles can be operated with the guide, which simplifies the surgical process and improves the accuracy of screw placement. At the same time, the trauma and the number of intraoperative fluoroscopy are reduced, so the operation time and intraoperative radiation exposure of patients are reduced. Previous studies also found that femoral neck shortening was a common complication of FNF in the DHS group [23–25]. DCLS is locked into a triangular frame structure, which has good postoperative stability and can axially and evenly compress the fracture end. On the one hand, it can promote fracture healing. On the other hand, the degree of shortening of the femoral neck is controlled so that it will not be excessively shortened.
In this study, 1 patient (3.8%) in the DCLS group had femoral head necrosis and 1 patient (3.8%) had nonunion. In the DHS group, 3 cases (12.5%) had femoral head necrosis and 1 case (4.2%) had nonunion. Although the complications in the DHS group were slightly higher than those in the DCLS group, there was not statistical significance (P > 0.05). The Harris score in the DCLS group was significantly higher than that in the DHS group, but there was not significant change in postoperative mobility between the two groups. A previous study found that about 11.3% of the cases of FNF in the DHS group had femoral head necrosis, and 9.4% of the cases had nonunion . The rate of osteonecrosis of the femoral head in our study was similar to that of previous studies, but the nonunion rate was significantly lower than that in previous studies, which may be related to the study population, fracture type, reduction quality, and operators. Several studies have also found that DHS combined with anti-rotation screws for displaced FNF can prevent rotational displacement of the femoral head during hip screw placement, which could increase biomechanical stability, with better mechanical support, shorter operative time, less radiation exposure, and higher hip Harris score [22, 23]. DHS technique and cannulated cancellous screws technique are the two main fixation techniques for the treatment of FNF. The Meta-analysis study found that the nonunion rate of the cannulated cancellous screws group was significantly higher than that of the DHS group, but there was no difference in the incidence of femoral head necrosis between the two groups. For vertically oriented FNF, the DHS technique is more favorable than the cannulated cancellous screws technique, with a lower risk of nonunion . The DCLS group had a higher Harris score, a lower incidence of femoral head necrosis and nonunion than those in the DHS group, which may be related to the excellent characteristics such as the better stability of the "cortical support", triangular frame structure, intraoperative uniform compression and postoperative uniformly dynamic pressure.