Note: Descriptions are shown in the official language in which they were submitted.
CA 02839599 2014-01-20
Bone nail with smooth trailing end
FIELD OF THE DISCLOSURE
The invention relates to an implant. In particular, the invention relates to a
bone implant
like a bone nail.
BACKGROUND INFORMATION
An implant and particularly a bone implant includes a portion or section or
end which is
adapted to be first introduced into a body during an implantation. In this
specification,
such a portion or section or end is referred to as leading portion or leading
section or
leading end. Consequently, an opposite portion or section or end of the
implant is
adapted to be introduced last, wherein this portion or section or end may
additionally be
configured for an engagement of a tool for inserting the implant into the
body. Below,
such a portion or section or end is referred to as trailing portion or
trailing section or
trailing end.
A bone implant may be a pin or a nail or screw. A bone nail may be an
intramedullary
=
nail, for example a femur nail, a humerus nail or a tibia nail. A bone screw
may be a
screw for fixing fragments of a bone fracture or may be a locking screw for
locking a
bone nail in the bone.
However, due to the anatomical variation of bones it may happen that the
trailing end of
a bone implant protrudes above the bone surface. The trailing end of the
implant may
act as an interface towards a target or aiming device. In order to create a
solid fixation
nails may be provided with grooves in order to fit pegs on a post of a target
device for
accurate alignment, for sufficient fixation, and for controlling the forces
applied during
implant insertion and removal. It may occur that patients complain about pain
after
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surgery in this area, especially when the implant trailing end is sticking out
of the bone.
This pain may be caused by sharp edges at the trailing end of the implant.
Such edges
may cause irritation and/or injury to the surrounding soft tissue.
US 7,763,022 discloses a typical prior art intramedullary nail.
US 6,443,954 B1 describes an intramedullary nail for securing portions of a
bone
together. A lag screw may extend through a radial bore in the nail.
Furthermore, a cap
screw may be screwed into the trailing end of the nail for holding the lag
screw, wherein
this lag screw has a spherical head portion.
SUMMARY OF THE INVENTION
One aspect of the invention may be defined as providing an implant causing
less
irritations of surrounding tissue when being implanted.
This is achieved by the subject-matter of the independent claim. Further
embodiments
are described in the dependent claims.
In general, an implant, in particular a bone nail comprises a shaft with a
leading section
and a trailing section, wherein the trailing section includes an end surface
having at least
one depressed portion and at least one elevated portion, wherein a transition
between
one of the depressed portions and the adjacent elevated portion is smooth. The
end
surface is formed so as to transmit rotational forces as well as translational
forces from a
medical device to the shaft of the implant, when the medical device is coupled
at the
end surface to the trailing section of the implant. The medical device may be
a targeting
device as shown in US 5,176,681 but with a shape adapted to mate with the end
of the
nail of the present invention.
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It will be understood that "smooth" refers to a shape without any edges, in
particular
without any sharp edges. That is, the end surface is formed without any
discontinuities.
The edge between the end surface and an circumferential outer surface of the
implant
may be provided with a chamfer or may be rounded so as to be also smooth, i.e.
so as to
not form any edge at which irritations of soft tissue may occur when the
tissue is in
contact with the trailing section of the implant including the end surface.
According to an embodiment, the end surface describes a waveform along the
circumference of the shaft, wherein the waveform may be a sinusoidal waveform.
The
waveform extends in the direction of a longitudinal axis of the nail trailing
end. The
outer circumference at the targeting end may be generally cylindrical.
It is noted that the waveform may have only one depressed portion and one
elevated
portion so that the end surface may be formed like a bevel or a slanted
surface relative
to a longitudinal axis of the implant.
According to an embodiment, the end surface includes two or more depressed
portions
with elevated portions between the two or more depressed portions,
respectively.
The following advantages may be achieved by an end surface having a waveform:
= Impingement of the surrounding tissue may be reduced.
= A contour may be formed which fits to the surface of the bone.
= Stress may be reduced in the region between implant and tool, allowing
for a
metal to plastic material interface which permits smaller dimensions and
possibly cost reduction.
= During assembly, the implant and tool may be easily selfcentering.
= An accurate play-free interface is possible.
According to another embodiment, the end surface corresponds to a shape of an
outer
bone surface at an intended implantation site so that the end surface of the
implant may
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be flush with the bone surface surrounding the end surface when the implant is
inserted
into the bone. Depending from the intended implantation site, for example the
femur
head, the end surface may have a complex waveform with differing depressed
portions
and differing elevated portions.
An exemplary bone implant may be an intramedullary nail comprising a through
bore
for receiving a locking screw, the through bore extending through the shaft in
a
direction transverse but also inclined relative to a longitudinal axis of the
shaft. The
depressed portion of the end surface may have a deepest or lowest point,
wherein the
deepest or lowest point may be aligned with the axis of the through bore.
The bone implant may also be a bone screw. For example, the bone screw may be
a
locking screw which may be received in a transverse through bore in the shaft
of an
intramedullary nail. As the bone screw may be inserted with an inclined angle
(being
not perpendicular) to an axis of the bone, or at least angled relative to the
outer surface
of the bone, the trailing end of the bone screw may comprise an end surface
with a
waveform or undulating form corresponding to the shape of the outer surface of
the
bone at the point or area of introduction of the screw. Thus if the bone outer
surface is
cylindrical then the screw receiving end would have high and low points
matching the
bone surface.
According to a further embodiment, the implant further comprises a bore formed
at least
in the trailing end section, with the bore extending in a longitudinal
direction of the
shaft. The longitudinal bore may include an inner thread for releasably fixing
a medical
device like a driving tool for manipulating the implant during an implantation
or like a
targeting device.
Alternatively, the implant may further comprise a longitudinal bore in the
trailing end
section including a feature of a bayonet connector for releasably fixing a
medical device
like a driving tool or a targeting device. Accordingly, one or more grooves
may be
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provided in the inner surface of the longitudinal bore each being configured
for
receiving a pin-like structure. It will be understood that the trailing end of
the implant
may also comprise pin-like structures for an engagement in bayonet grooves
formed at a
medical device. Such a structure is shown in US 7,901,410 and US 8,337,505.
According to an embodiment, a system is provided having the implant as
described
above and a medical device with an implant engagement portion having a contact
surface which corresponds to the end surface at the trailing section of the
implant. The
medical device may be an aiming or targeting device for assisting an
introduction of a
locking screw and/or a driving tool for manipulating the implant during an
implantation
of the implant.
According to another embodiment, the system may further have an adapter
element
having a first end adapted to be coupled to the end surface at the trailing
end of the
implant and a second end adapted to be coupled to the medical device. With an
adapter
element, it is possible to utilize a usual aiming device or driving tool with
an implant
having a smooth end surface.
It is noted that a person skilled in the art will gather from the above and
the following
description that, unless otherwise notified, in addition to any combination of
features
belonging to one embodiment, also any combination of features relating to
another
embodiment is considered to be disclosed with this application.
These and other objects, features and advantages of the exemplary embodiments
of the
present invention will become apparent upon reading the following detailed
description
of exemplary embodiments, when taken in conjunction with the appended claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be detailed by way of exemplary embodiments with
reference to
the attached drawings.
Figure 1 shows a medical device coupled to a trailing end section of a bone
nail.
Figure 2 is a section view of the combination of figure 1.
Figure 3 is an isometric view of a trailing end section of a bone nail
according to a first
embodiment.
Figure 4 is an isometric illustration of an intramedullary nail in a femur.
Figure 5 is a side view of an intramedullary nail in a femur.
Figure 6 is an isometric view of a trailing end section of a bone nail
according to a
second embodiment.
It is noted that the illustration in the drawings is only schematically and
not to scale.
Throughout the drawings, the same reference numerals and characters, unless
otherwise
stated, are used to denote like features, elements, components, or portions of
the
illustrated embodiments. Moreover, while the present invention will now be
described
in detail with reference to the figures, it is done so in connection with the
illustrative
embodiments and is not limited by the particular embodiments illustrated in
the figures,
as defined by the appended claims.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Figures 1 and 2 show a trailing section 10 of an implant together with a
coupling section
of a medical device like a targeting device or a driving tool, or of an
adapter element
to be placed between the medical device and the implant. The coupling section
30
includes an implant engagement portion 31. The implant engagement portion
includes
an end surface with a waveform which is complementary to the waveform of the
end
30 surface at the trailing section of the implant.
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The coupling section further comprises an inner through bore with a first bore
section
33 and a second bore section 35. The first bore section has a first diameter
and the
second bore section has a second diameter, wherein the second diameter is
smaller than
the first diameter. The transition of the first diameter to the second
diameter is formed
by a shoulder 34. An axial bore 11 is formed in the trailing section 10 of the
implant,
wherein this axial bore includes an inner threaded portion.
As shown in figure 2, the coupling section 30 may be firmly connected to the
trailing
section 10 of the implant by means of a fixing screw 40. The fixing screw 40
comprises
a screw head 41 and a screw thread 42. The outer diameter of the screw head
may fit to
the first diameter of the first bore section 33 of the coupling section, i.e.
may be slightly
smaller, and the outer diameter of the threaded portion 42 may fit to the
second diameter
of the second bore portion 35 of the coupling section 30, i.e. may be slightly
smaller, so
that the fixing screw 40 may be received in the bore of the adapter with the
screw head
41 resting on the shoulder 34.
The fixing screw has a length so that the fixing screw protrudes out of the
coupling
section 30 and into the trailing section 10 of the implant so that the screw
thread 42 may
engage the threaded portion of the axial bore 11 in the trailing section 10.
By means of
the fixing screw 40, the end surface at the implant engagement portion 31 of
the
coupling section 30 and the end surface at the trailing section 10 of the
implant may be
pressed together. By way of this, the coupling section and thus a medical
device can be
fixed to the implant in a predetermined orientation and the waveform of the
fitting end
surfaces allow a transmission of forces both in translational direction and in
rotational
direction. The force affected in axial direction by the fixing screw permits
that the end
surfaces slide onto each other. In such a configuration, no edges for a force
transmission
are necessary.
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Figure 3 shows an isometric view of the trailing end section 10 of a bone
nail, and
particularly an embodiment of an end surface 20. The end surface 20 is the
ring-like
surface extending between the inner surface of the axial bore portion 11 and
the outer
surface 14. In figure 3, the end surface 20 includes two depressed portions or
valleys 21
and two elevated portions or peaks 22. Each of the transitions 23 between the
depressed
portions 21 and the elevated portions 22 is smooth. By smooth it is meant
there are no
sharp corners and, for example, the end surface 20 may be continuously curved.
In this
embodiment, the depressed portions differ from each other with respect to the
width. It
will be understood that the portions may also differ from each other with
respect to the
depth. The end surface 20 is defined by a waveform (for example a sine wave)
running
on the circumference of the trailing end section of the bone nail, around an
opening of
an axial bore 11. The end surface 20 can have three or four elevated and
depressed
portions. One embodiment of an end surface with three depressed and elevated
portions
is shown in figure 6. The distance from the peaks to the valleys may be 2. To
3.8 mm.
In a three peak design the peaks may be between 100 degree and 130 degree
apart. In a
15.5 mm proximal diameter nail with three peaks, for example, the peaks would
be
spaced about 16.23 mm (120 degree) which is Pi+15.5mm/3.
As further depicted in figure 3, the trailing section 10 includes a transverse
bore 13
defining an axis. The deepest point of the depressed portion 21 may be aligned
with the
axis of the transverse bore 13. Thus, the coupling section 30 has a
predetermined
orientation relative to the trailing end section of the bone nail. This may in
particular be
of interest when an aiming or targeting device should be coupled to the bone
nail.
Figures 4 and 5 illustrate embodiments in which the implant is an
intramedullary femur
nail already implanted from the proximal end of the femur into the medullary
channel of
the femur, wherein a locking screw 50 is inserted through the transverse bore
13 of the
nail and into the femur head.
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The locking screw 50 comprises a threaded portion 51 adapted to be screwed
into a
bone and a trailing end 52 for an engagement with a driving tool. In these
embodiments,
the trailing end 52 has a crown-like shape with slots, wherein a corresponding
driving
tool may have a structure for engaging this crown to substantially rotate the
screw while
screwing in the screw into the bone. It will be understood that the trailing
end of the
. locking screw may comprise a trailing end with a smooth end surface as
described
herein.
Further illustrated in figures 4 and 5 is the aspect that the smooth end
surface 20 at the
trailing section 10 of the femur nail has a contour which substantially
corresponds to the
contour of the bone at the point of introduction of the nail, i.e. at the
greater trochanter
of the femur.
While the invention has been illustrated and described in detail in the
drawings and
foregoing description, such illustration and description are to be considered
illustrative
or exemplary and not restrictive. The invention is not limited to the
disclosed
embodiments. Other variations to the disclosed embodiments can be understood
and
effected by those skilled in the art in practising the claimed invention, from
a study of
the drawings, the disclosure, and the appended claims.
In the claims, the word "comprising" does not exclude other elements, and the
indefinite
article "a" or "an" does not exclude a plurality.
The mere fact that the certain measures are recited in mutually different
dependent
claims does not indicate that a combination of these measures cannot be used
to
advantage. Any reference signs in the claims should not be construed as
limiting the
scope.
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LIST OF REFERENCE SIGNS
trailing section of shaft
11 axial bore portion with inner thread
5 12 axial bore portion
13 transverse bore
14 outer surface
end surface
21 depressed portion
10 22 elevated portion
23 transition
coupling section
31 implant engagement portion
32 tool engagement portion
15 33 first bore section
34 shoulder
second bore section
fixing screw
41 screw head
20 42 screw thread
locking screw
51 locking screw thread
52 tool engagement portion of locking screw
