Single Screw vs. Double Screw Device for Use in Treating Femoral Bone Fractures

Proximal femur fractures commonly occur between the head of the femur and the femoral shaft. As the third most common injury encountered in orthopedic clinics, these fractures are typically treated with medical implants creating internal stabilization of the bone. Over 100 different implants are available for this application. Although the optimal choice for the implants is still controversial, traditional devices which include a single cylindrical screw, such as SHS (Sliding Hip Screw) and IMHS – CP (Intramedullary Hip Screw, Clinically Proven), are widely used to repair the bone fracture. However, the application of the single screw device still suffers technical problems. The head of the femur has the potential to rotate about the screw and the fracture surfaces have potential to slide over each other. In addition, force relaxation can occur, leading to inadequate contact between the fracture surfaces. To attack these problems and prevent possible complications, a new device has been developed. The new device consists of one long screw interlocked with one short screw, creating a cross-sectional figure-eight pattern and offering an integrated, interlocking screw option. The objective of the current study is to compare biomechanical characteristics within the bone caused by the new double screw device verses the traditional single screw device. Experiments were preformed to compare the torsional stiffness of the two devices. 2D and 3D finite element analysis methods were carried out to obtain macroscopic and microscopic responses of each device’s interaction with the fractured bone. The modeled results show a significant difference between the two geometries. The single screw geometry has higher maximum total deformation, equivalent strain, equivalent von Mises stress, and maximum principle stress. The improved rotational stability of the new double screw device may reduce the complication rate of instability of the fracture fragments.