Treatment of intertrochanteric fractures have evolved greatly over the last 50 years, particularly with respect to the choice of implante.
Since Smith-Pettersen in 1931 published its preliminary results with the trilaminar nail, several authors turned their attention to the issue of development of synthetic materials for intertrochanteric fractures.
Thus, consecutively appeared the Thornton, Jewett and McLaughlin implants, all based on the Smith-Pettersen nail. However, deficiencies common to all these systems, as the great aggression to the femoral neck by the trilaminar nail and the constant need of association with other synthetic materials, usually in the most unstable fractures, produced a high incidence of complications and later its abandonment. Only in the late 1950s, with the creation of the AO group - Association for the Study of Internal Fixation (Arbeitsgemeinschaft für Osteosynthesefragen), new advances could be made in the field of fastening internal devices.
Specifically for intertrochanteric fractures high performance angular plates or placards blade have been developed. Initially it was thought that the "U" shaped profile of the blade and the presence of fixed angle were associated with increased strength of the implant. However, difficulties in the insertion of the laminar part and early fatigue of these materials led to doubts regarding its uso.
Like what had happened to the Smith-Pettersen nail, the first AO implants have become obsolete after a period of time. Because of these technical difficulties, many implants have emerged since then, almost always presenting the same evolution of its predecessors. Finally, in the 1980s, Regazzone et al.,
of the AO Group, developed the dynamic hip screw (DHS®)
. Unlike the rigid implants, in this new system the introduction of a screw through the sliding plate has made possible to promote continuous compression through the fracture focus, which was never made possible before. In addition, other common devices previously developed were fixed with DHS®
as loss of reduction in the post-operative phase and perforation of the femoral head by the pin.
Currently, the sliding bolt is the method of choice for most intertrochanteric fractures.
The incidence of complications when the system is used correctly is about 5%.
Despite that, poor preoperative planning, technical mistakes and degenerative changes occurring in older patients are often related to poor results.
In addition, we must consider the lack of standardization among manufacturers of the DHS®
systems in our country as a possible cause of treatment failure, according to a previous study.
In this context, little has been discussed about possible errors and complications directly related to the design of the dynamic hip screw. Due to its fixed angle and the impossibility of changing the sliding screw without disassembling the whole osteosynthesis, disastrous consequences can occur, mainly related to the reduction quality and longer surgical exposure. Recently in our service a modification was performed in a sliding hip screw in order to permit the exchange of the sliding pin without the need for the surgeon to remove the plate and disassemble the entire system to reposition the implant.
This implant was called DHS-AF®
This theoretical advantage may not be important in developed countries or even in services in our country that rely on a fluoroscopy unit. However, we believe that the national reality does not allow the easy insertion of the image intensifier in most orthopedics services. Based on this logistical difficulty and on design issues of currently existing sliding screws, we developed the changes proposed in this study.
Thus, the goal of the authors of this study was to evaluate the in vitro
resistance of the DHS-AF®
through static bending test, since the implant structural changes may alter the mechanical properties thereof. We evaluated the flexural strength, stiffness and ductility, as recommended for material testing.
The results obtained were similar to those found in the literature on experiments with underlineament.