Note: Descriptions are shown in the official language in which they were submitted.
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Device for fixation of bone fractures
BACKGROUND OF THE INVENTION
The invention relates in general to sonic fusion technology, it relates more
particularly to a device and a method for the fixation of fractures, with a
screw for
augmenting within a fractured object, wherein said object might be, for
example, a
bone or a wooden or plastic object like furniture.
Known from US patent 4,653,489 is a system wherein a fixation cement is
introduced through a screw into a portion of a bone afflicted by osteoporosis.
Femural neck fractures as well as distal femural fractures can be fixated by
means of
this device.
The system in accordance with prior art comprises a screw having a flow
cavity, i.e.
an axial through bore through which bone cement can be introduced into the
portion
at the tip of the screw. The bone cement is advanced by a device which is
releasably
attached to the subsequent end of the screw. This device is similar to a
commercially
available syringe in comprising substantially a cylindrical barrel and a
plunger. The
barrel forms a cavity in which the plunger is movable to and fro.
In use of this prior art device the fixation cement is filled into the barrel,
after which
the plunger is urged against the cement. By applying manual compression force
the
fixation cement is jetted into the axial through bore of the screw. Due to the
pressure
the fixation cement is adequately fluidized so that it can pass through the
proximal
end of the screw into the bone, as a result of which the screw is augmented in
the
bone.
This system has the drawback that the manual pressure applied to the fixation
cement
varies, not only basically from application to application but also during the
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application itself so that the distribution of the fixation cement within the
portion of
the bone at the tip of the screw is neither reliable nor even.
SUMMERY OF THE INVENTION
An object of the invention is to define a device and a method by means of
which a
reliable and even augmentation of a screw at an installation site in an object
can now
be assured.
This is achieved by the subject matter of each independent claim. Further
preferred
embodiments read from the dependent claims.
Generally, a device for fixation of a fracture, having a screw comprising a
shank
having a first threaded end and having along its longitudinal center line an
axial
through bore having a first bore portion with a first diameter and a second
bore
portion with a second diameter, wherein the first diameter is larger than the
second
diameter and the second bore portion is adjacent the first shank end, and a
step in the
bore between the first and the second bore portions.
Further, a method for fixation of a fracture comprises the steps of screwing a
screw
having an axial bore therein with transverse passageways connecting the bore
with
an outer surface of the screw into an object across a fracture site; combining
a
polymer pin with a insert; inserting the polymer pin together with the insert
into the
axial through bore in the screw; pressuring and vibrating the polymer pin,
wherein
the polymer pin is supported by the insert which is in turn supported by a
step in the
diameter in the through bore, resulting in the polymer pin being fluidized at
its tip,
the fluidized polymer material being pressed out of the screw.
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This object is achieved in accordance with the invention by the screw having
the
features as recited in the respective independent claims. Further preferred
embodiments read from the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be detailled by way of a preferred embodiments with
reference to the attached drawings in which:
FIG. 1 is a section view of a screw in accordance with the invention.
FIG. 2 is a detail view of the tip of the screw as shown in FIG. 1.
FIG. 3 is a view of a polymer pin in accordance with a first embodiment of the
invention.
FIGs. 4a and 4b are a side view and respectively a plan view of an insert in
accordance with the first embodiment of the invention.
FIG. 5 is a view of a polymer pin in accordance with a second embodiment of
the
invention.
FIG. 6 is a detail view of the tip portion of the polymer pin in accordance
with the
second embodiment of the invention.
FIG. 7 is a side view of an insert in accordance with the second embodiment of
the
invention.
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FIG. 8 is a view of the polymer pin together with the insert in accordance
with the
second embodiment of the invention.
FIG. 9 is a detail view of the tip portion of the polymer pin, together with
the insert
in accordance with the second embodiment of the invention.
FIG. 10 is a section view of a device for fixation of a fracture in accordance
with the
invention, with the screw as shown in FIG. 1 in which the polymer pin as shown
in
FIG 5 and the insert as shown in FIG. 7 are inserted.
FIG. i l is a detail view of the tip of the device as shown in FIG. 10.
DETAILED DESCRIPTION
Referring now to FIG. 1 there is illustrated a screw 10 in accordance with the
invention. The screw comprises a shank and a thread 12 machined in an end
portion
of the shank, wherein the thread may also cover the shank of the screw full
length. In
addition, the screw 10 is canulated. Provided along the longitudinal centre
line of the
screw is a through bore composed of two bore portions 16, 17. The bore portion
16
comprises a first diameter and the bore portion 17 a second diameter, the
first
diameter being larger than the second diameter. In addition the bore portion
16 forms
the main portion of the through bore. Just a small portion adjoining the end
of the
shank of the screw in which the thread 12 is machined is formed by the bore
portion
17. The transition from the bore portion 16 to the bore portion 17 is formed
by a step
18 in the diameter. The step 18 in the diameter forms an annular ridge having
substantially right-angled edges at the wall of the through bore within the
screw.
Each edge of the step 18 in the diameter may be machined flat or rounded or
conical.
Furthermore the position of the step in diameter together with the holes in
the wall
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can be positioned optionally along the longitudinal centre line and thus the
siting of
the augmentation can be determined in accordance with the particular
application and
the desired effect.
In addition, the screw 10 features holes 14 radially configured through the
wall of the
screw. The holes 14 may be configured in differing directions perpendicular to
the
longitudinal centre line of the screw and arranged in the end portion with the
thread
12. Preferably the holes 14 are arranged in a region of the end portion which
also
features the bore portion 16. In the embodiment as shown in FIG. 1 two holes
14
each are configured axially juxtaposed in the bore portion 16 and through the
thread
12. Furthermore, four such pairs of holes are evenly distributed about the
circumference of the screw, in other words, circumferentially spaced by 90 .
It is,
however, just as possible that three, four, five or more holes may be provided
circumferentially and it is not necessary that the holes circumferentially
distributed
are all at same level. It is, the holes might also be distributed
circumferentially along
the thread tum. Apart from this, transverse or longitudinal oblong holes,
slots, or the
like may be provided.
Referring now to FIG. 2 there is illustrated the tip of the screw as shown in
FIG. 1
but on a magnified scale, the step 18 in the diameter between the bore portion
16 and
bore portion 17 now being particularly evident. Apart from this, a few of the
holes 14
are shown which are configured passing through the thread 12 in the bore
portion 16.
Referring now to FIG. 3 there is illustrated a polymer pin 20 according to a
first
embodiment of the invention, elongated in shape and slightly tapered at a
conically
tapered end 22. Provided in the conically tapered end 22 of the polymer pin 20
is a
cavity 24 in the end face. The cavity 24 is substantially cylindrical having a
constant
diameter and a blunt end. The polymer pin 20 may also be made of other
materials
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such as for instance a thermoplastic material suitable for augmenting a screw,
both
resorptive and non-resorptive materials being useful.
Referring now to FIGs. 4a and 4b an insert is shown in a side view and in a
plan
view. The insert features a substantially disk-shaped end 32 and a
substantially pin-
shaped end 34. The disk-shaped end 32 has an outer diameter somewhat smaller
thari
the diameter of the bore portion 16 of the screw 10 and somewhat larger than
the
diameter of the bore portion 17 of the screw 10. The pin-shaped end 34 is
configured
so that it can be inserted into the cavity 24 in the polymer pin 20.
In another embodiment the insert includes instead of the pin-shaped end a
protruding
end suitable for snap mounting, the polymer pin in this case having a snap
mounting
end corresponding to the protruding end. When the insert is snap mounted with
the
polymer pin, both elements can be inserted together into the screw, it being
of
advantage when the snap mount comprises a slight clearance when connected.
This
clearance has the advantage that when the polymer pin ispressurized it can be
better
fluidized at the joint with the insert to thus easier jetted from the screw
into the
object easier, wherein said object might be a bone or a furniture or another
object
made of wood, plastic or another porous material.
In the following, an exemplary embodiment of a snap fit connection between the
insert and the polymer pin will be described.
Referring to FIG. 5 there is illustrated a polymer pin 40 according to a
second
embodiment of the invention, elongated in shape and slightly tapered at a
conically
tapered end 42. As shown in FIG. 6, a cavity is provided in the end face of
the
conically tapered end 42 of the polymer pin 40. The cavity comprises a
cylindrical
portion 44 having a substantially constant diameter, and a ball shaped portion
46.
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The hollow cylindrical portion 44 is orientated substantially in the direction
of the
centre axis of the polymer pin 40 and connects the end surface of the polymer
pin
with the hollow ball shaped portion 46 inside the polymer pin 40.
The pin 40 may also be made of other materials then polymer, for instance of a
thermoplastic material suitable for augmenting a screw, wherein both
resorptive and
non-resorptive materials being useful.
Referring now to FIG. 7 an insert according to a second embodiment is shown in
a
side view. The insert includes a substantially disk-shaped end 52 and a
substantially
pin-shaped portion 54. As for the first embodiment, the disk-shaped end 52 has
an
outer diameter somewhat smaller than the diameter of the bore portion 16 of
the
screw 10 and somewhat larger than the diameter of the bore portion 17 of the
screw
10. However, the insert according to the second embodiment further comprises a
ball
head 561ocated at an end of the pin-shaped portion 54, opposite to the disc-
shaped
end 52.
FIGs. 8 and 9 show a combination of an insert and a polymer pin according to
the
second embodiment of the invention. The ball head 56 together with at least a
part of
the pin-shaped portion 54 are configured so that they can be inserted into the
cavity
in the polymer pin 40, the cavity having a correspondingly dimensioned ball-
shaped
portion 46 and a pin-shaped portion 44.
It is noted that the insert has to be made from a material which is harder
with an
higher melting temperature than the material of the polymer pin such that the
polymer pin will melt at the contact area between the insert and the pin, and
a
suitable augmentation might be achieved. Preferably, the insert is made of a
metal.
The insert may alternatively be made of an alloy or a ceramic material. Also a
plastic
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material is possible, as long as said plastic material of the insert is harder
with an
higher melting temperature than the chosen material of the pin which should be
fluidized.
It is furthermore possible that the insert instead of including a pin-shaped
end or a
snap mounting end, has a through bore into which a corresponding end of the
polymer pin can engage. In this embodiment the polymer material is jetted
axially
from the screw not only through the holes 14 but also through the hole in the
insert.
The proportion of the polymer material emerging from the holes and bores can
be
varied by the size thereof.
Depending on the aspect concerned, a snap mount may also be provided in
combination with axial and/or radial holes, it being just as possible,
however, to
configure the insert integrally with the screw. In this arrangement the step
in the
diameter between two portions of the bore is configured by a larger difference
in
diameter; indeed, even an axial blind hole may be configured instead of the
axial
through bore in the screw.
The following details inserting the screw into a bone. Firstly a K-wire is
powered up
to the site in a bone at which the screw is to be located. Via the K-wire the
screw is
then advanced and ultimately screwed into place until it is sited as desired.
After
insertion of the screw in the bone the K-wire is removed. This procedure makes
it
necessary that the screw features a full length through bore. This is a
popular
operation technique because the operator can best check the position of the
screw.
The K-wire is also used to measure the necessary screw length.
After removal of the K-wire the passageway or through bore along the
longitudinal
centre line of the screw is free to receive the polymer pin together with the
insert, the
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tip of the pin shaped end of the insert being inserted into the concavity of
the
polymer pin.
Referring now to FIGs. 10 and 11, there is illustrated how an insert rests on
the step
formed by the step 18 in the diameter of the bore in the screw 10, when the
polymer
pin together with the insert has been inserted facing the direction of the
tip. It is in
this way that the step 18 in the diameter forms, within the screw, a
counterhold for
the insert which in turn supports the polymer pin when the polymer pin is
pressurized
by an ultrasonic handpiece which, for this purpose, is mounted on the free end
of the
screw. The vibration and pressure generated by the ultrasonic handpiece and
applied
to the polymer pin fluidizes the polymer pin so that the material of the
polymer pin
emerges from the radially arranged holes 14 into the bone. It is in this way
that the
polymer pin furnishes the material for augmenting the screw in the bone.
It is to be noted that the inside-out technology is not just limited to the
indications as
recited above. In other words, all screw applications which can be supplied by
cannulated screws can be potentially supplied by the inside-out technology and
thus
with the device in accordance with the invention.
Although the invention herein has been described with reference to particular
embodiments, it is to be understood that these embodiments are merely
illustrative of
the principles and applications of the present invention. It is therefore to
be
understood that numerous modifications may be made to the illustrative
embodiments and that other arrangements may be devised without departing from
the
spirit and scope of the present invention as defined by the appended claims.
