Fractures of the femoral shaft are common high-energy injuries of the lower extremities . Because of the thick tissue envelope surrounding the femur, iatrogenic muscle injury and adhesion can be caused by conventional open reduction and internal fixation with the plate system . The IM nail system makes it possible to achieve minimally invasive internal fixation and has become the gold standard in the management of fractures of the femoral shaft because it is associated with a high rate of union and a low complication rate [4, 13]. However, if the minimally invasive procedure cannot be achieved during the reduction process, minimally invasive internal fixation with an IM nail is not useful. The challenges associated with minimally invasive reduction result from there being numerous and powerful muscles attached to the femur, including the hip abductors and iliopsoas, which are attached proximally; the adductors, which are attached medially; and the gastrocnemius, which is attached distally , which generate different displacement patterns of femoral shaft fractures. Neutralizing the deforming forces of these muscles percutaneously and finally achieving minimally invasive reduction and fixation of femoral shaft fractures are the goals of surgeons.
Surgeons should not rely heavily on assistants; rather, they should be prepared to use instrumentation and positioning aids to facilitate reduction . Fracture tables can be quite helpful in restoring the length of the lower limb by longitudinal traction but cannot restore the alignment directly; studies have shown that IM nailing of the femoral shaft performed without the use of a fracture table is significantly faster than that performed with a fracture table [3, 13]. Therefore, invasive tools that may facilitate reduction intraoperatively have been adopted, including the finger reduction tool  and Schanz pin [4, 5]. In our experience, the finger reduction tool can be used to control the proximal fragment but is challenging to aim at the entry site of the distal fragment; hence, fast and accurate reduction cannot usually be achieved. Moreover, the more distal the fracture site is, the more difficult the finger reduction tool is to manipulate. When used as a “joystick”, the Schanz pin is theoretically associated with a risk of iatrogenic neurovascular injury and fibrosis or quadriceps contractures in the thigh . In addition, with the aforesaid technique, the powerful muscles of the thigh have to be overcome manually, which can result in an obviously laborious reduction process and difficulty maintaining the reduction. Furthermore, people involved in the operation, especially medical staff members, will be exposed to radiation during the whole process of reduction.
Various closed reduction devices have been developed for the treatment of femoral shaft fractures. Shezar et al.  established an external support device for the closed reduction of femoral shaft fractures but was unable to control the fragments in the coronal plane. Gao et al.  reported the application of a fracture-sustaining reduction frame for the closed reduction of femoral shaft fractures, but muscle swelling was observed because of compression of the frame. The “double reverse traction repositor” was developed by Zhang et al.  and is a kind of rapid closed redactor that can function as the fracture table and has many advantages, but the alignment of the fracture should be restored by other techniques. Additionally, the structure of the device was complex, and the assembly was time consuming [8, 9]. Zhu et al.  developed a teleoperated robot-assisted surgical system for the minimally invasive treatment of displaced femoral shaft fractures, but it is still an experimental model, which is predictably expensive and not ready for practical use . Therefore, because of these technical difficulties, many surgeons continue to consider open reduction and internal fixation  but do not consider the advantages of IM nailing.
The lever principle is an ancient theory of mechanics that was proposed by Chinese scientist Mozi and Greek scientist Archimedes as early as 3rd century BC . Levers can be used to exert a large force over a short distance at one end and only a small force over a longer distance at the other end. In the present study, we used the lever principle. After the shortened limb was lengthened by the fracture table, a labour-saving lever structure was assembled, with the long, curved haemostatic forceps serving as the lever arm and the soft tissue serving as the fulcrum (Figure 4). All the manipulations were performed percutaneously. Only a small force exerted by a surgeon can counteract the retracting force of the thigh muscles to easily achieve closed reduction of femoral shaft fractures. The technical points are as follows: (1) sufficient traction and restoration of the limb length need to be achieved first, as they are prerequisites for the subsequent steps. In our study, these steps were achieved by the fracture table. (2) Moderate adduction of the affected lower limb on the fracture table can partially neutralize the deforming forces of the adductors, which allows femoral shaft fractures to be reduced laterally and the antegrade IM nail to be inserted. (3) The tension resulting from the traction makes the soft tissue envelope rigid enough to serve as a lever fulcrum, and this process cannot be achieved when the muscles are relaxed. Moreover, the closed soft tissue envelope can compact the fragments and restrict their movement with the tension of the muscles, which is conducive for reduction. (4) Because femoral shaft fracture cases differ across individuals, the displacement patterns of the fracture site vary after traction on the fracture table. Nevertheless, regardless of the displacement pattern, there is a C-arm fluoroscopic projection plane (plane a) in which the X-ray view shows that the fragments at the proximal and distal ends are nearly aligned and a second plane (plane b) that is perpendicular to plane a and follows the anatomical axis of the femur. The line intersecting plane b and the skin of the lateral thigh is the reference line. The 2 haemostatic forceps were inserted on either side of the reference line (Figure 5a). In our study, most cases were nearly reduced laterally after longitudinal traction. For these patients, plane a was the approximate sagittal plane, plane b was the approximate coronal plane, and the reference line was the approximate midline of the lateral thigh (Figure 5a). (5) We chose to use 26-cm curved haemostatic forceps because haemostatic forceps of this size are thick and rigid enough to serve as excellent lever arms. Moreover, they are of a sufficient length, as shorter forceps would not be able to serve as a lever arm and thus could not reduce the labour required, and surgeons would not be able to control the fragment as well if the forceps are too long. Furthermore, the curved blunt tip of the forceps restricts the fragment from slipping during the reduction process and allows the surgeon to make small adjustments to determine the best position for reduction.
In terms of the 20 patients with femoral shaft fractures who underwent reduction with long, curved haemostatic forceps, reduction was successful, and the results were satisfactory. Long, curved haemostatic forceps are readily available and inexpensive. The labour-saving lever structure constituted by fragments, haemostatic forceps and a soft tissue envelope can facilitate reduction. Because the resistance from the proximal and distal fragments are in opposing directions, when reduction is completed by lowering the proximal fragment and elevating the distal fragment, the 2 haemostatic forceps can interlock with each other, neutralizing the resilience force and reducing the risk of reduction loss, leading to an automatically stable construct that can maintain the reduction effect without manual operations (Figures 5e and 7), and allowing the surgeon to stand at a distance during the fluoroscopic monitoring of the fracture site. In contrast to when the Schanz pin is used as a “joystick”, the bone structure will not be injured, and iatrogenic secondary fractures may be avoidable. Ideally, the haemostatic forceps penetrate the muscle fibres rather than sever them through just two 0.5-cm incisions. The degree of muscle injury is slight, and complete minimally invasive closed reduction can be achieved. Although perfect alignment cannot be achieved in most cases, it is sufficient to allow the insertion of an IM nail. This is a simple technique with a high operative speed, a short operative time, a short radiation exposure time, and a short learning curve, and it can be mastered by most surgeons in a short time. In the present study, the average reduction time, operative time, fluoroscopy time and blood loss were 6.7±1.9 minutes, 69.1±13.5 minutes, 8.7±2.7 seconds and 73.5±22.5 mL, respectively, which were lower than the values reported in studies on other minimally invasive techniques, such as the “double reverse traction repositor”  and fracture-sustaining reduction frame techniques .
The best indications of this technique are fracture patterns with mainly anterior-posterior and lateral displacement and a small degree of rotation. Because of the external rotation, abduction, and flexion displacement of the proximal fragment in subtrochanteric fractures, it is difficult to achieve reduction by this technique alone, and the use of a second reduction tool, such as a ball spike, the Schanz pin and a periosteal elevator, may be necessary. Heterotopic ossification was observed during the follow-up period (Figure 6), which may be related to the local haematoma at the fracture site that could not be debrided during the closed reduction and fixation procedures. Nonetheless, limb function is not affected by heterotopic ossification distant from the joint.
The small sample size and the absence of a control group for the comparison of outcomes are the limitations of this study. However, there is no recognized gold standard for the minimally invasive reduction of femoral shaft fractures, so it is difficult to design an appropriate control group.
In conclusion, displaced femoral shaft fractures in adults can be treated by lever principle-assisted closed reduction and IM nail fixation. The labour-saving lever structure constituted by fragments, 2 haemostatic forceps and a soft tissue envelope can both reduce displaced femoral shaft fractures and maintain reduction in an anatomical position, which enables IM nailing fixation to be successfully achieved. This technique is easy to perform; reduces blood loss, the fluoroscopy time and the surgical time for intraoperative reduction; and leads to excellent fracture healing.