Device for interconnecting an elastic nail and a cross screw

A device for interconnecting an elastic nail and a cross screw for the fixation of bone fractures. The device comprises as a separate element a coupling piece with a plate portion which can be mounted to the outside of the bone by means of one or more cross screws. A coupling hook projects from the plate portion, which forms a cross head and can be brought to engage lockingly the elastic nail by the cross head being passed through a slot in one end of the nail and being rotated.

The present invention relates to a device for interconnecting an elastic 
nail and a cross screw in the fixation of bone fractures. It has come 
about particularly for the fixation of fractures in the lower third of the 
femur. 
From a surgical point of view the femur can be divided into three parts. As 
far as the upper and intermediate thirds are concerned there are today in 
most cases good possibilities of fixation while the lower third, however, 
presents problems as to the fixation of the fractures that can occur 
therein, viz. unicondylar fractures wherein one condyle has been burst 
off, bicondylar fractures wherein both condyles are displaced, and 
supracondylar fractures wherein the fracture does not extend 
intercondylarly. In the lower third of the femur pre-drilling and 
Kutscher-nailing no longer provides a stable fixation. For fixation in 
this part of the femur so-called angle condylar plates are used which 
function well in a stable skeleton but on the other side do not provide a 
satisfactory fixation when the skeleton is weakened (fragile). This is 
most often the case as far as older persons are concerned where this 
fracture most frequently occurs and the fixation by means of angle 
condylar plates will be too rigid; a fragile skeleton calls for a more 
flexible fixation. 
In an effort to provide an improved fixation in the lower part of the femur 
the Zickel-nail has been used. This nail is a medullary nail formed as a 
leaf spring, which has a rigid distal end, formed with openings, which can 
be fixed in the condylar portion by means of a cross screw also the 
condyle of the other side being fixed. Owing to the cross screw the nail 
is prevented from changing the position thereof. However, it has been 
found that this nail in the fixation of supracondylar fractures may cause 
further fractures and that it is difficult to provide a satisfactory 
fixation due to the leaf spring form of the nail. The convex side of the 
nail is in fact turned slightly backwards while the natural curvature of 
femur is convex forwards. Moreover, the rather rigid nail may keep the 
condylar portion apart to a greater extent than that desired. As a 
consequence thereof this portion may be projected in relation to the 
proximal fragment an the separate condyles may be twisted. 
On the basis of the experiences thus obtained when available means for the 
fixation of bone fractures have been used in case of fractures in the 
lower third of the femur the following objects desired can be listed as 
far as patients with bone fragility are concerned. 
1. Medullary nails should be used instead of an angle condylar plate with 
screws. 
2. The nail should have a sufficient elasticity and a round cross-sectional 
form in order to avoid stress dislocation or further fractures. 
3. It should be possible to utilize the total length of the medullary 
cavity. 
4. It should be possible to lock the bone fragments at the upper end of the 
femur against twisting by means of two nails, one from each condyle, in 
connection with fractures in the lower part of the femur. 
5. Where an artificial bone has been inserted previously or a fracture 
fixation in the upper part of the femur has been made earlier it should be 
possible to use also shortened nails. 
6. There should be the possibility of locking against twisting also in the 
condylar portion in the lower end of the femur. 
7. The nail should be prevented from disengaging the lower part of the 
femur. 
8. It should be possible to keep together displaced condyles. 
In order to achieve these objects in treating fractures in the lower third 
of the femur with the aim of attaining an early mobilization of the 
patient from bed and possibly also a rapid weight-bearing while providing 
a fixation which is less rigid than that obtained by means of an angle 
condylar plate but is more stable than that obtained only by an external 
fixation with plaster or other articulated bandage, it is proposed 
according to the invention a device for interconnecting an elastic nail 
and a cross screw in the fixation of bone fractures comprising as a 
separate element a coupling piece forming a plate portion to be fixed by 
means of at least one cross screw, and a coupling hook projecting from 
said portion and forming a cross head to be inserted through a slot in the 
end portion of the nail and be rotated so as to lockingly engage the 
elastic nail. 
Preferably, the elastic nail is of a type similar to the Ender-nail as 
presently constructed since this nail satisfies the objects according to 
items 1 to 4 listed above. It has a moderate elasticity and a favourable 
form. Moreover, the use thereof in the upper part of the femur of older 
persons having bone fragility, is well experienced. The nail can be 
shortened without any inconvenience so as to satisfy the object of item 5. 
The objects of the other items are satisfied by the nail being anchored by 
means of the coupling piece according to the invention. 
An important advantage of the device according to the invention is also to 
be seen in the fact that the elastic nails as well as the cross screws, 
screwed into the spongy porous part of the bone (cancellous screws) 
already today are used in most departments for fracture surgery. 
Therefore, the device can be used by applying surgical utensiles now 
available.

With reference to FIG. 1 a femur 10 having a bicondylar fracture 11 at the 
lower end of the femur is shown. In order to fix this fracture an elastic 
nail 12 of a construction known per se is driven from the side into the 
femur from the lower end thereof through one condyle and then through the 
medulla into th eupper end of the femur. The nail 12 is anchored in the 
lower end of the femur by means of a coupling piece 13 connected to said 
one condyle by means of cancellous screws 14 of a type known per se, which 
at the same time keep the displaced condyles together. Another elastic 
nail shall be driven into the femur from the other condyle and shall be 
fixed in the manner described, but this is not shown in FIG. 1 in order 
not to make the drawing unnecessarily complicated. 
The coupling piece 13 is shown in more detail in FIGS. 2 and 3 to which 
reference is made. It is formed as an integral element of stainless steel 
and comprises a rectangular plate 15 having two circular openings 16 
countersunk at one side of the plate, to receive therein the screws 14. 
From the centre of one of the longer edges of the plate a coupling hook 17 
extends in the plane of the plate and then curves outwards at 90.degree. 
to terminate at the outer end thereof in a cross head 18. When the elastic 
nail has been driven into the femur the cross head can be passed through a 
longitudinal slot 19 in a flattened end portion 20 of the projecting lower 
end of the nail when the coupling piece 13 is in the position indicated by 
dash-and-dot lines 13' in FIG. 2. Then, by rotating the coupling piece 13 
to the position shown by solid lines in FIG. 2, i.e. over 90.degree., the 
coupling hook is brought to engage lockingly the nail so as to fixedly 
retain the nail, the cross head 18 being positioned transversely of the 
slot 19. The coupling piece can now be fixed by means of the cancellous 
screws 14 on the outside of the femur as shown in FIG. 1. When this is 
done there are generous possibilities of adjusting the location of the 
coupling piece such that it will be located in the best manner considering 
the actual fracture, and the screws will be oriented as desired. It is 
particularly advantageous that the coupling piece if desired can be 
located on the condyle above the knee joint proper. It is also 
advantageous that the nail first can be driven into the femur and the 
coupling piece then can be mounted such that the mounting to a minor 
extent will be dependent on the location of the nail in the femur. A 
further advantage is that a further nail 12' can be anchored in the lower 
end of the femur by means of a single coupling piece 13 as shown in FIG. 
4. 
With two elastic nails inserted one from each condyle, the bone fragments 
can be locked against twisting at the upper end of the femur by the two 
nails. The nail provides a flexible fixation of the fracture and is 
prevented from sliding out of the femur by the coupling piece which also 
locks against twisting in the lower fragment.