A device for the fixation of bones is disclosed. The device includes a block, a bone plate integral to the block which has at least one plate hole for accommodating a fastener, a first guide channel on the block for accommodating a first longitudinal carrier, and a second guide channel on the block for accommodating a second longitudinal carrier. The first and second guide channels are parallel to each other and the axes of the guide channels are in a plane which is parallel to the bone-contact surface of the bone plate. A cylinder defined by the first guide channel does not intersect the cylinders defined by the bone plate holes and a cylinder defined by the second guide channel does intersect the cylinders defined by the bone plate holes.

FIELD OF THE INVENTION 
The invention relates to a device for the fixation of bones. 
BACKGROUND 
For the anterior fusion of vertebra segments (fractures, tumors, 
infections, congenital and post traumatic kyphoses, deformities) a wide 
variety of plate- as well as rod-systems are available. 
Some of the advantages of plate systems such as the one disclosed in 
PCT/US93/08433, are the relatively small dimensions and the generally easy 
handling. Important disadvantages of these known plate-system consist 
therein that the area of fusion cannot actively be set under compression, 
a great assortment of expensive plate implants, and in the case of 
deformities no possibilities of correction. 
Rod systems, such as the ones disclosed in PCT/US93/10908 or 
PCT/EP94/01606, do not have the above mentioned disadvantages of the 
plate-systems, but they are naturally larger in their dimensions and more 
difficult to handle. 
U.S. Pat. No. 4,289,123 discloses an orthopedic appliance which includes a 
pair of brackets anchored to bone and connected by a pair of rods. 
However, the disclosed device is bulky and cumbersome to use. 
SUMMARY OF THE INVENTION 
The present invention provides a device which combines the advantages of 
the known plate- and rod-systems easy handling, platelike dimensions, an 
assortment favourable in costs as well as possibilities of compression and 
correction. 
The device according to the present invention comprises a block, a bone 
plate associated with the block and having a bone-contact surface and at 
least one plate hole, and first and second parallel guide channels 
associated with the block for accommodating first and second longitudinal 
carriers. Each of the guide channels has a longitudinal axis lying in a 
plane which is parallel to the bone-contact surface and an imaginary 
cylinder defined by the first guide channel does not intersect an 
imaginary cylinder defined by the bone plate hole while an imaginary 
cylinder defined by the second guide channel intersects the imaginary 
cylinder defined by the bone plate hole. 
The first guide channel extends completely through the block while the 
second guide channel extends partially through the block to form an 
opening in the block opposite the bone plate. At least one of the guide 
channels can extend to the side of the block opposite the bone-contact 
surface to facilitate insertion of a longitudinal carrier. Alternatively, 
at least one of the guide channels can extend to the top of the block to 
facilitate insertion of a longitudinal carrier. 
The bone plate comprises at least two plate holes having centers which lie 
on a common connecting line. In one preferred embodiment, the connecting 
line is disposed at an angle of +10.degree. to +50.degree. with respect to 
the longitudinal axes of the first and second guide channels. In another 
preferred embodiment, the connecting line is disposed at an angle of 
-10.degree. to -50.degree. with respect to the longitudinal axes of the 
first and second guide channels. 
Each guide channel includes a bore hole positioned orthogonal to its 
longitudinal axis to accommodate a fastener for removably securing a 
longitudinal carrier to the guide channel. The bone-contact surface 
includes a cylindrical segment having a cylinder radius of between 25 and 
35 mm and a longitudinal axis which is parallel to the longitudinal axes 
of the first and second guide channels. Preferably, the plate holes have 
longitudinal axes lying in parallel planes which are perpendicular to the 
longitudinal axis of the cylindrical segment of the bone-contact surface. 
The bone plate holes have a multiple-threaded threads preferably having a 
planar thread bottom. In a further preferred embodiment, the planar thread 
bottom forms an angle of between 20.degree. and 40.degree. with respect to 
the thread longitudinal axis. The plate holes can be spherical. 
An apparatus for the fixation of bones according to the present invention 
includes first and second devices each comprising: a block; a bone plate 
associated with the block and having a bone-contact surface and at least 
one plate hole; and first and second parallel guide channels associated 
with the block for accommodating first and second longitudinal carriers, 
and each having a longitudinal axis lying in a plane which is parallel to 
the bone-contact surface so that an imaginary cylinder defined by the 
first guide channel does not intersect an imaginary cylinder defined by 
the bone plate hole while an imaginary cylinder defined by the second 
guide channel intersects the imaginary cylinder defined by the bone plate 
hole. The apparatus also includes first and second longitudinal carriers 
positioned in the first and second guide channels of the first and second 
devices. 
Each guide channel includes a bore hole positioned orthogonal to its 
longitudinal axis to accommodate a fastener for removably securing the 
longitudinal carrier therein. Each bone plate comprises at least two plate 
holes having centers which lie on a common connecting line. At least one 
guide channel of each of the first and second devices can extend to the 
side of the block opposite the bone-contact surface to facilitate 
insertion of the longitudinal carrier. Alternatively, at least one guide 
channel of each of the first and second devices extends to the top of the 
block to facilitate insertion of the longitudinal carrier. 
In use two complementarily shaped devices according to the invention are 
attached to two parallel longitudinal carriers. Each device is connected 
to the respective vertebral body by means of two bone screws. The bone 
screws have both a bone- and a machine thread. The two threads are 
arranged so that they provide the same pitch and pass over to one another 
seamlessly. The plate holes within the two devices provide the same 
machine thread as the bone screws. The geometry of the thread in the bone 
plate part of the device is shaped so that after fastening the screws the 
device and the screws are connected to each other at a stable angle and 
safe against vibrations. 
The longitudinal carriers are directly connected to the two devices 
according to the invention and not to the bone screws. Thereto the block 
parts of the device according to the invention purposefully provide each a 
pocket hole and a through hole, wherein the longitudinal carriers can be 
inserted and fastened by means of adjusting screws. The holes for the 
longitudinal carriers are arranged such that the pocket hole on the block 
part on the one device aligns with the through hole of the other device 
and the bone screws can still be inserted also after the mounting of the 
longitudinal carriers. This particular arrangement and embodiment of the 
holes for the longitudinal carriers lead to all the above mentioned 
advantages of the combination according to the invention as easy handling, 
small dimensions and unlimited distraction/compression in situ. 
The invention and further embodiments of the invention are discussed in 
more detail in the following section by means of the partial schematic 
representations of several embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The device 20 for the fixation of bones according to the invention shown in 
FIG. 1 essentially consists of a block 1 and a bone plate 2 connected 
thereto with a bone-contact surface 3 and two plate holes 4 running 
through the bone plate 2 and having centres lying on a common connecting 
line 12 in order to accommodate a bone fixation means such as a bone 
screw. The block 1 provides a first guide channel 5 in order to 
accommodate a first longitudinal carrier 13 and a second guide channel 6 
in order to accommodate a second longitudinal carrier 14. The two guide 
channels 5;6 run parallel to each other whereby the axes 7;8 of the two 
guide channels 5;6 lie in a plane parallel to the bone-contact surface 3. 
The circular cylinder 9 defined by the first guide channel 5 does not 
intersect the circular cylinders 10 defined each by the plate holes 4 
whilst the circular cylinder 11 defined by the second guide channel 6 
intersects one of the circular cylinders 10 defined each by the plate 
holes 4 (FIG. 1 and 3). 
The first guide channel 5 completely penetrates the block 1 so that a 
longitudinal carrier 13 inserted therein can be pushed in any arbitrary 
axial position. Whereas the second guide channel 6 is formed as a pocket 
hole which opens at the side opposite to the bone plate 2. A longitudinal 
carrier 14 can consequently only be pushed until the maximum depth of the 
pocket hole and can not reach into the area of the circular cylinders 10 
defined by the plate holes 4. The two guide channels 5;6 provide two bore 
holes 17 running perpendicularly to their axes 7;8 in order to accommodate 
fixation means 18 (in the form of adjustment screws) for the longitudinal 
carriers 13;14. 
The connecting line 12 which connects the two plate holes 4 encloses a 
positive angle of +30.degree. with the axes 7;8 of the two guide channels 
5;6. This angle may vary in the range between +10.degree. and +50.degree. 
preferably between +20.degree. and +40.degree.. 
The bone-contact surface 3 forms a cylinder segment having a cylinder 
radius of 30 mm whereby the axis of the cylinder segment runs parallel to 
the longitudinal axes 7;8 of the guide channels 5;6. The cylinder radius 
may vary within a range between 25 and 35 mm preferably between 29-31 mm. 
The longitudinal axes of the plate holes 4 lie in parallel planes that are 
perpendicular to the longitudinal axis of the bone-contact surface 3 
shaped as a cylinder segment. 
In FIG. 2 a device 30 that is complementary to the device 20 is represented 
which differs particularly therein that the connecting line 12 encloses a 
negative angle of -30.degree. with the axes 7;8 of the guide channels 5;6. 
This angle may vary in the range between -10.degree. and -50.degree. 
preferably between -20.degree. and -40.degree.. 
As shown in FIG. 3 the two devices 20 and 30 can be combined to a combined 
device with the longitudinal carriers 13;14, whereby a first longitudinal 
carrier 13 is insertable into the first guide channel 5 of the one device 
20 and into the second guide channel 6 of the other device 30 and a second 
longitudinal carrier 14 is insertable into the second guide channel 6 of 
the one device 20 and into the first guide channel 5 of the other device 
30. 
The distance between the two devices 20;30 to one another is adjustable 
through displacement on the two longitudinal carriers 13;14 and can be 
fastened in any arbitrary position by means of the fixation means 18 in 
the form of adjustment screws. 
As shown in FIG. 4 the device 20 can be modified such that the first guide 
channel 5 is shaped open on the side opposite to the bone-contact surface 
3 so that a longitudinal carrier 13 is insertable from above--in the 
direction of the arrow 15. 
A further embodiment of the device 20 is shown in FIG. 5 and consists 
therein that the first guide channel 5 is shaped open in the direction of 
its adjacent side surface 24 of the block 1 so that a longitudinal carrier 
13 is insertable from the side--in the direction of the arrow 16. 
As shown in FIG. 6 the plate holes 4 can provide a multiple-threaded thread 
19 which can accommodate a respective shaped bone screw--providing a 
external thread in the head area--so that a rigid and axially aligned 
connection between bone screw and bone plate 2 results. The thread 19 
provides a planar thread bottom 22 which forms an angle of 30.degree. 
together with the longitudinal axis 23 of the thread. The angle may vary 
in a range between 20.degree. and 40.degree. preferably between 
29.degree.-31.degree.. 
The plate holes 4 can also be shaped spherical as shown in FIG. 7 in order 
to accommodate a slotted sphere with a conical bore hole for the bone 
screw so that the bone screw can be adjusted under a defined angle to the 
bone plate 2 and can be fastened angular stable. 
In the following the course of the surgical application of the device 
according to the invention is described in more detail. 
For or after the treatment of the anterior lesion the respective vertebral 
bodies are spread by means of a vertebral spreader and bone splinters 
respectively vertebral replacement bodies are inserted into the produced 
defect. Afterwards the length of the longitudinal carriers to be used is 
defined. Into each of the second guide channels 6 which are shaped as 
pocket holes of each device 20;30 according to the invention a 
longitudinal carrier 13;14 is inserted and fastened by means of an 
adjustment screw 18. 
The devices 20;30 each instrumented with a longitudinal carrier 13 
respectively 14 are assembled as shown in FIG. 3 to a combined device. 
This happens that way that the free ends of the longitudinal carriers 
13;14 are pushed in the first guide channel 5 of the respectively other 
device 20 respectively 30 according to the invention and slightly fastened 
with an adjustment screw 18. 
Each of both--now connected to each other--devices 20;30 according to the 
invention is now instrumented with an implant holder (not shown in the 
drawings) e.g. a sleeve of a drill jig with an integrated awl in the plate 
holes 4. The combined device is now pressed with the implant holders 
sidewardly against the vertebral column, the first bore awl is released, a 
bore hole is drilled, the sleeve of a drill jig with the integrated bore 
awl taken away and a bone screw turned into the bore hole drilled into the 
bone through the plate hole 4. Afterwards the second bore awl is released, 
a bore hole drilled, the sleeve of a drill jig with the integrated bore 
awl taken away and a bone screw turned into the drilled bore hole. 
As long as only one bone screw each is turned into the particular vertebral 
bodies it may still be kyphosised or lordosised. 
Now the sleeves of a drill jig with integrated awl are turned into the 
resting plate holes 4 and processed as described above. 
The zone fusioned by means of the combined device may now be compressed so 
that the adjustment screws 18 which fasten the two longitudinal carriers 
13;14 in the first guide channels 5 are loosened and the blocks 1 of the 
both devices 20;30 according to the invention are pushed together by means 
of a compression nippers.