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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/47839

### **1. Introduction**

The femoral neck fracture is subjected to powerful shearing forces due to the angular, spirallike architecture of the proximal femur. Under the conditions of severe *osteoporosis*, the *femoral neck* consists of cortical walls, enveloping soft cancellous bone, having unimportant mechanical significance, and the neck can often be looked at as a hollow cylinder. If the condition of patient is not appropriate for total hip replacement (mental diseases or other risks), and a decision is made for a screw fixation, the implanted screws must be solidly fixed in the distal fragment in at least two points in order to provide resistance to the shearing forces in case of osteoporosis. The traditional screw fixation methods, however, do not meet the above-named requirement. Present-day popular *traditional methods* of femoral neck fixation, which are performed by three cancellous screws, placed parallel to each other and parallel to the femoral neck axis, are associated with poor results in 20 to 42% [1,2,3,4,5]. The high failure rate of traditional screw fixation methods can be explained by the presence of a number of related biomechanical imperfections. (1) *Instability of the construction regarding varus stress.* The entry points of the three screws in traditional screw fixation methods are located at the thin, fragile cortex of the greater trochanter or close to it. The screws are often placed in the soft cancellous bone near the axis of the femoral neck, with no cortical support [6]. Even if one or two of the distal screws are placed close to the distal cortex of the femoral neck, they lack any second solid point of support. A second point of support for them is the thin and fragile lateral cortex of the greater trochanter – their entry point. Such a construction can rely only on the interfragmental compression, generated by the intraoperative tightening of the screws, but the achieving of compression depends on the

© 2012 Filipov, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### 82 Injury and Skeletal Biomechanics

solidity of the cancellous bone. This circumstance results in high failure rate in cases of osteoporosis. (2) *Lack of sliding phenomenon*. Upon body weight loading, in the process of the subsequent wedging of the osteoporotic cancellous bone in the fracture site, the screws of traditional methods of fixation, which lack two-point cortical support, cannot effectively slide distally and laterally keeping unchanged their angle towards the axis of diaphysis, and rather have expressed tendency to displace in varus, with fixation failure. (3**)** *Inability to move the entry point of the screws distally into the solid diaphyseal cortex, and simultaneous placing of three parallel screws*. In 1961 Garden [7], like other authors before, further developed the concept that the implants must have more vertical placement, similar to the direction of the medial compression lamellae of the femoral neck internal trabecular system, in order to provide resistance to the shearing forces. However, when developing this concept, the classic authors used only one implant (a nail). Thus the implant successfully provided resistance to the shearing forces, but it did not create compression between the fragments, because it is not a screw and it is also not able to ensure reliable rotational stability of the head fragment, being only one [8,9,10].

Biomechanics of the Fractured Femoral Neck –

The New BDSF-Method of Positioning the Implant as a Simple Beam with an Overhanging End 83

**2. Biplane double-supported screw fixation method - Operative** 

primary joint replacement may be contraindicated.

*Implants:* 7.3 mm self-tapping cannulated screws

anatomical reduction is acceptable.

diaphysis at 6-7 cm is performed.

the ventral oblique plane (Fig.1-b.).

into the dorsal third of the femoral head.

distal one-third of the femoral head.

*Indications:* Fractures of the Garden types from I to IV. The indications and contraindications for application of the BDSF-method are generally the same as of the conventional methods for fixation of the femoral neck fractures. The BDSF-method significantly expands the indications for application of screw fixation in terms of the bone, changed by osteoporosis. The method is most useful and has no reasonable alternative in adult patients above 80 years with a high cardiopulmonary risk, as in patients with severe concomitant diseases, inclusively some mental diseases, patients with senile dementia, and others, for which the

*Reduction:* Mild traction, slight abduction and internal rotation of the limb are applied. Only

*Approach*. A straight lateral incision, starting at the level of the lower border of the greater trochanter, with distal length of 6 to 10 cm. A stripping of the periosteum of the lateral

*Placement of the implants.* When applying the BDSF-method, the three cannulated screws are placed in the frontal plane at a highly increased angle. Both the distal and the middle screws touch tangentially on the curve of the distal femoral neck cortex (Fig.1-a.). At internal rotation of the leg, in anteroposterior view, the projection of the distal screw usually crosses the projections of the other two screws, thus forming the letter F (F-technique). Via the concept of *biplane positioning*, developed by the BDSF-method, the three screws are placed in two vertical oblique planes (in lateral view). The two planes diverge towards each other in the direction of the femoral head, and are oblique towards the frontal plane. The distal screw is laid in the dorsal oblique plane. The middle and the proximal screws are placed in

First of all, we lay the guiding wire for the distal cannulated screw. Its tip is placed at 5-7 cm distally from the lower border of the greater trochanter in the anterior one-third of the surface of the stripped off diaphysis. It is directed proximally at an angle of 150 – 165° towards the diaphyseal axis, with inclination from anterodistally to posteroproximally, so that after it touches tangentially on the curve of the distal femoral neck cortex, the wire goes

The middle guiding wire is placed secondly. The entry point is at 2 to 4 cm proximally from the entry point of the distal wire, but in the dorsal one-third of the stripped off surface of the diaphysis. This wire is placed at an angle of 135-140° towards the diaphyseal axis and inclined from posterodistally to anteroproximally, so that after it touches tangentially on the curve of the distal femoral neck cortex, the wire goes into the front one-third of the femoral head. In the frontal plane (anteroposterior view) the tip of this guiding wire goes into the

**technique** 

The anatomy of proximal femur does not allow simultaneous placing of three screws, which are parallel to each other, and lie near the cortex in the periphery of the femoral neck and, at the same time, have their entry points positioned distally, in the solid cortex of the diaphysis, in order to avoid the fragile lateral metaphyseal cortex.

When applying the *conventional* methods of positioning three parallel screws, in case movement of the screw entry point distally is attempted, the screws will be placed at a very obtuse angle towards the diaphysis and obliquely to the femoral neck. By increasing the angle of penetration, the surface of the femoral neck cross-section decreases geometrically, and in practice the placement of more than one or two screws is hard to be accomplished. However, a two-screw fixation does not provide reliable stability in all planes [10]. Both problems are resolved by the newly introduced method of *Biplane Double-supported Screw Fixation* trough the concept of biplane positioning of the implants.

The *Biplane Double-supported Screw Fixation Method in femoral neck fractures (BDSF-method)*, developed by O. Filipov, is a new method of screw fixation in femoral neck fractures, based to *an original concept of the establishment of two supporting points for the implants and their biplane positioning* in the femoral neck and head. The console-like proximal femur requires the fixation screws to have to support the weight-bearing head fragment, acting like a *beam with an overhanging end*, which must have two points of support in the distal fragment. The concept of the Biplane Double-supported Screw Fixation (BDSF) method is based on this principle. This method is original with the three screws being laid in two planes, which aspect allows the entry points of two of the implants to be placed much more distally, in the solid cortex of the proximal diaphysis, and also to lean onto the strong femoral neck distal cortex. Thus, we establish two points of support. The achieved by this method position of the distal screw and the middle screw as well, in view of statics, turns them into *a simple beam with an overhanging end, loaded by a vertical force*. This beam with an overhanging end successfully supports the head fragment, bearing the body weight and transferring it to the diaphysis.
