The most important finding of this study was that the FNS resulted in less trauma and better hip joint function at the last follow-up than the DHSb for the treatment of FNF in young patients. In addition, femoral neck shortening was lower in the FNS group than in the DHSb group. Other postoperative complications, including nonunion, screw pull-out, and femoral head necrosis, showed no statistical difference between the two groups.
In the present study, the FNS group had significantly shorter operation duration, less blood loss, and shorter incision length than the DHSb group. Thus, FNS resulted in less trauma than DHSb. Because of its smaller plate, with a compact design and customized operation device, the FNS had a reduced implant footprint on the bone. In addition, the bolt design could control the femoral head depth and thus avoid protrusion; lateral protrusion can result in thigh pain, which can reflect a theoretical remission. Furthermore, less insertional torque was produced during insertion. These advantages contributed to less intraoperative X-ray irradiation and simplified operative processes, reducing the operation duration and complication occurrence. However, use of this newly designed device incurred a higher cost, leading to a more expensive hospitalization charge in the FNS group than in the DHSb group.
FNF treatment in young patients is focused on five key aspects, including fracture reduction maintenance, femoral neck shortening prevention, femoral head necrosis prevention, better healing promotion, and FNF prevention . Among these, a durable and rigid internal fixation is the primary factor in treating the fracture. Young patients normally have a high hip joint function demand, but are not ideal candidates for arthroplasty. Although young patients have a better blood supply and potential healing ability than older patients, appropriate fixation methods are still essential to promote better healing. As with many other medical conditions, the treatment must be adapted to the unique features of this population. Accordingly, effective internal fixation can delay and even avoid arthroplasty in young patients.
Various internal fixation methods have been compared in several recent studies. A finite element analysis showed that both cannulated screws and DHS could resist shearing and rotational forces . Kuan et al. suggested that compression hip screw fixation was superior to both the modified cross-screw fixation method and the inverted triangle fixation method for Pauwels III FNFs . The DHSb has been reported to have better resistance to pushout and rotational stability compared to that with dynamic hip screw in a biomechanical cadaveric test . Another study showed that DHS combined with fibula bone had better clinical outcomes than cannulated screws in Pauwels type III FNF . However, Stoffel et al. demonstrated that the FNS had greater axial stiffness than the DHSb and cannulated screws based on 20 pairs of cadaveric femora . The outcomes of the finite element and biomechanical analyses are not exactly consistent, and a clinical trial is still needed.
Some studies have aimed to determine the superior method. In a study with an average follow-up of 27 months, DHSb showed better clinical outcomes than cannulated compression screws in preventing femoral neck shortening, screw migration, and cut-out; however, there was no significant difference in postoperative fracture union . In addition, Hu et al. reported that only the occurrence of femoral neck shortening was significantly less with the FNS than with cannulated compression screws; no statistical difference was observed in femoral head necrosis and fracture nonunion between the two groups . However, to date, no clinical trial has investigated the clinical outcomes of FNS and DHSb in young patients. In our study, although both methods achieved satisfactory clinical outcomes, the FNS group had better hip joint function than the DHSb group. This may have resulted from less trauma and better biomechanical properties with the FNS than with the DHSb.
The postoperative complications of FNF have become one of the biggest reasons for the choice of internal fixation. Femoral head necrosis, nonunion, fixation failure, and femoral neck shortening are the most common postoperative complications . A previous study reported the non-union rate of Pauwels type-3 vertical FNFs as 19% when treated with calcaneal screws and 8% when treated with a fixed-angle device . Stockton et al. reported that 32% of young patients with FNF experienced neck shortening of >1 cm when treated with cancellous screws or sliding hip screws . The characteristics of the FNF itself determine the high incidence of complications. A high shear force and varus instability could result in fixation failure and nonunion . Cancellous screws can only provide limited resistance to vertical shear forces at the fracture site . Comparing with the cancellous screws and DHSb, the FNS was designed for more bone retention and fracture fixation properties increasing. Screw-locking into the bolt may contribute to two fracture components sliding together for dynamic fixation; this design can reduce the occurrence of complications. In our study, 4 patients (9.3%) in the FNS group and 8 patients (15.4%) in DHSb group had non-union, screw pull-out, or femoral head necrosis. Although there was no significant difference between the two groups, these methods still showed better clinical prospects than cancellous screws based on previous data. In addition, femoral neck shortening was significantly better in the FNS group than in the DHSb group, rendering it possible for young patients to have better hip function.
There are some limitations to the present study. First, in this retrospective study, patients were not randomly assigned to the two treatment groups. The physician’s preference for FNS or DHSb and the preoperative conversation may influence the patients’ psychology, thus affecting their recovery. Therefore, a random, multi-center, prospective study is required to further prove the present outcomes. Second, the average follow-up duration was somewhat short in the present study. The final destination of the femoral head remains to be observed. Furthermore, although we intended to investigate the superior method for young patients; the average age was still approximately 48–50 years. As the present study is limited by a small sample size for younger patients, the collection of more cases and additional stratification analyses on age could provide more convincing conclusions for the treatment of younger patients.