U.S. patent application number 16/836124 was filed with the patent office on 2020-07-16 for intermedullary devices for generating and applying compression within a body.
The applicant listed for this patent is Arthrex, Inc.. Invention is credited to Robert Devaney, Matthew Fonte, Matthew Palmer.
Application Number | 20200222090 16/836124 |
Document ID | / |
Family ID | 52626273 |
Filed Date | 2020-07-16 |
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United States Patent
Application |
20200222090 |
Kind Code |
A1 |
Palmer; Matthew ; et
al. |
July 16, 2020 |
INTERMEDULLARY DEVICES FOR GENERATING AND APPLYING COMPRESSION
WITHIN A BODY
Abstract
An intramedullary device includes a central bridge region having
a first end and a second end. The intramedullary device also
includes a bone engaging feature at both the first end and the
second end. At least one of the bone engaging features includes a
first barb and a second barb which, in an unbiased condition, flare
outwardly from a longitudinal axis of the central bridge region and
which are capable of being elastically constrained to a constrained
condition such that the first end of the central bridge region may
be advanced into a hole in a first bone fragment when the first
barb and second barb are elastically constrained. The first barb
and second barb are prevented from being withdrawn from the hole in
the first bone fragment when the first barb and the second barb are
not constrained. The intramedullary device i) is cannulated, ii)
generates a compressive load, and iii) comprises nitinol.
Inventors: |
Palmer; Matthew; (Medford,
MA) ; Fonte; Matthew; (Concord, MA) ; Devaney;
Robert; (Auburndale, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Arthrex, Inc. |
Naples |
FL |
US |
|
|
Family ID: |
52626273 |
Appl. No.: |
16/836124 |
Filed: |
March 31, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15653902 |
Jul 19, 2017 |
10603088 |
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16836124 |
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14541017 |
Nov 13, 2014 |
9724138 |
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15653902 |
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13624643 |
Sep 21, 2012 |
9283006 |
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14541017 |
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61537766 |
Sep 22, 2011 |
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61570091 |
Dec 13, 2011 |
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61903820 |
Nov 13, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 2017/00867
20130101; A61B 2017/00946 20130101; A61B 17/7291 20130101; A61B
17/7266 20130101 |
International
Class: |
A61B 17/72 20060101
A61B017/72 |
Claims
1. An intramedullary device comprising: a) a central bridge region
having a first end and a second end, wherein the central bridge
region is cylindrical; and b) a bone engaging feature at both the
first end and the second end, wherein at least one bone engaging
feature comprises a first barb and a second barb which, in an
unbiased condition, flare outwardly from a longitudinal axis of the
central bridge region and which are capable of being elastically
constrained to a constrained condition such that the first end of
the central bridge region may be advanced into a hole in a first
bone fragment when the first barb and second barb are elastically
constrained, and the first barb and second barb are prevented from
being withdrawn from the hole in the first bone fragment when the
first barb and the second barb are not constrained, wherein the
first barb and the second barb of the at least one bone engaging
feature combine to form a substantially continuous extension of the
central bridge region when the first barb and the second barb are
elastically constrained, wherein movement of the first barb of the
at least one bone engaging feature from the constrained condition
to the unbiased condition occurs within a first plane, and movement
of the second barb of the at least one bone engaging feature from
the constrained condition to the unbiased condition occurs within a
second plane, and the first plane intersects the second plane, and
wherein the device i) is cannulated, ii) generates a compressive
load, and iii) comprises nitinol.
2. An intramedullary device comprising: a) a central bridge region
having a first end and a second end; and b) a bone engaging feature
at both the first end and the second end, wherein at least one bone
engaging feature comprises a first barb and a second barb which, in
an unbiased condition, flare outwardly from a longitudinal axis of
the central bridge region and which are capable of being
elastically constrained to a constrained condition such that the
first end of the central bridge region may be advanced into a hole
in a first bone fragment when the first barb and second barb are
elastically constrained, and the first barb and second barb are
prevented from being withdrawn from the hole in the first bone
fragment when the first barb and the second barb are not
constrained; wherein the device i) is cannulated, ii) generates a
compressive load, and iii) comprises nitinol.
3. The intramedullary device according to claim 2 wherein the
central bridge region is cylindrical.
4. The intramedullary device according to claim 2 wherein the
central bridge region is malleable.
5. The intramedullary device according to claim 4 wherein movement
of the first barb of the at least one bone engaging feature from
the constrained condition to the unbiased condition occurs within a
first plane, and movement of the second barb of the at least one
bone engaging feature from the constrained condition to the
unbiased condition occurs within a second plane.
6. The intramedullary device according to claim 5 wherein the first
plane intersects the second plane.
7. The intramedullary device according to claim 4 wherein the at
least one bone engaging feature includes a third barb.
8. The intramedullary device according to claim 7 wherein movement
of the first barb and the third barb of the at least one bone
engaging feature from the constrained condition to the unbiased
condition occurs within a first plane, and movement of the second
barb of the at least one bone engaging feature from the constrained
condition to the unbiased condition occurs within a second
plane.
9. The intramedullary device according to claim 8 wherein the first
plane intersects the second plane.
10. The intramedullary device according to claim 4 wherein the at
least one bone engaging feature includes a fourth barb.
11. The intramedullary device according to claim 10 wherein
movement of the first barb and the third barb of the at least one
bone engaging feature from the constrained condition to the
unbiased condition occurs within a first plane, and movement of the
second barb and the fourth barb of the at least one bone engaging
feature from the constrained condition to the unbiased condition
occurs within a second plane.
12. The intramedullary device according to claim 11 wherein the
first plane intersects the second plane.
13. The intramedullary device according to claim 12 wherein the
first plane is perpendicular to the second plane.
14. The intramedullary device according to claim 2 wherein the at
least one bone engaging feature is laterally aligned the
longitudinal axis of the central bridge region.
15. The intramedullary device according to claim 2 wherein the at
least one bone engaging feature is laterally offset from the
longitudinal axis of the central bridge region.
16. The intramedullary device according to claim 2 wherein the
first barb and the second barb of the at least one bone engaging
feature combine to form a substantially continuous extension of the
central bridge region when the first barb and the second barb are
elastically constrained.
17. The intramedullary device according to claim 2 including a
removable retaining tab for elastically constraining the first barb
and the second barb of the at least one bone engaging feature,
wherein the removable retaining tab slides relative to the
longitudinal axis of the intramedullary device to allow the first
barb and the second barb of the at least one bone engaging feature
to move from the constrained condition to the unbiased
condition.
18. The intramedullary device according to claim 17 wherein the
first removable retaining tab and the second removable retaining
tab are separately detachable from the intramedullary device.
19. The intramedullary device according to claim 2 wherein an end
of at least one of the first barb and the second barb of the at
least one bone engaging feature includes an edge.
Description
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 15/653,902 filed Jul. 19, 2017, now U.S. Pat.
No. 10,603,088 granted on Mar. 31, 2020; which is a continuation of
U.S. patent application Ser. No. 14/541,017 filed Nov. 13, 2014,
now U.S. Pat. No. 9,724,138 granted on Aug. 8, 2017; which is a
continuation-in-part of U.S. patent application Ser. No. 13/624,643
filed Sep. 21, 2012, now U.S. Pat. No. 9,283,066 granted on Mar.
15, 2016; which claims the benefit of prior U.S. Provisional Patent
Application No. 61/537,766, filed Sep. 22, 2011, and U.S.
Provisional Patent Application Ser. No. 61/570,091, filed Dec. 13,
2011. U.S. application Ser. No. 14/541,017 claims priority to U.S.
Provisional Patent Application No. 61/903,820 filed Nov. 13,
2013.
FIELD OF THE INVENTION
[0002] The present invention relates to devices and methods for
generating, applying, and maintaining compression to a site in a
human or animal body in order to effect healing of diseased or
damaged tissue. The invention finds particular utility in the field
of orthopedics and specifically for generating and maintaining
compression between bone fragments that are to be fused. While the
invention has application throughout the body, its utility will be
illustrated herein in the context of the repair of injured bone
tissue, such as the proximal and distal interphalangeal joint of
the second, third, or fourth toe and/or fingers. Additionally, the
invention has application to aid in the fusion of broken ribs,
etc.
BACKGROUND OF THE INVENTION
[0003] In the field of orthopedic surgery it is common to rejoin
broken bones. The success of the surgical procedure often depends
on the successful re-approximation of the bone fragments, the
amount of compression achieved between the bone fragments, and the
ability to maintain that compression between the bone fragments. If
the surgeon is unable to bring the bone fragments into close
contact, a gap will exist between the bone fragments and the bone
tissue will need to fill that gap before complete healing can take
place. Furthermore, gaps between bone fragments that are too large
allow motion to occur between the bone fragments, disrupting the
healing tissue and thus slowing the healing process. Optimal
healing requires that the bone fragments be in close contact with
each other, and for a compressive load to be applied and maintained
between the bone fragments. Compressive strain between bone
fragments has been found to accelerate the healing process in
accordance with Wolf's Law.
[0004] Broken bones can be rejoined using screws, staples, plates,
pins, intramedullary devices, and other devices known in the art.
These devices are designed to assist the surgeon with reducing the
fracture and creating a compressive load between the bone
fragments. Intramedullary devices are often used for fractures of
the long bones; however, they are also frequently used in the
phalanges and specifically for the treatment of "hammer toe", which
is a deformity of the proximal interphalangeal joint of the second,
third, or fourth toe causing the toe to be permanently bent.
Typical intramedullary devices used in the phalanges have opposing
ends that are adapted to grip against the wall of the
intramedullary canal. These intramedullary devices are typically
made of titanium alloys, stainless steel alloys, Nitinol and other
materials, e.g., PEEK. The titanium alloy devices and stainless
steel alloy devices often have barbs or threaded regions at their
opposing ends to grip the wall of the intramedullary canal. The
Nitinol devices typically have a pair of radially extending "legs"
at their opposing ends that expand outward when warmed to body
temperature, with the pair of legs at each end being disposed in a
common plane.
[0005] While these intramedullary devices are designed to bring the
bone fragments into close contact and to generate a compressive
load between the bone fragments, these devices do not always
succeed in accomplishing this objective. It is widely reported that
the compressive load dissipates rapidly as the bone relaxes and
remodels. Furthermore, gripping the bone with only a pair of
co-planar legs does not provide significant torsional stability to
the fusion site.
[0006] Thus there exists a clinical need for intramedullary devices
that are better able to bring bone fragments into close proximity
with each other, generate a compressive load, and maintain that
compressive load for a prolonged period of time while healing
occurs.
SUMMARY OF THE INVENTION
[0007] The present invention comprises the provision and use of
novel intramedullary devices that are better able to bring bone
fragments into close proximity with each other, generate a
compressive load, and maintain that compressive load for a
prolonged period of time while healing occurs.
[0008] In one preferred form of the invention, there is provided
apparatus for securing a first bone fragment to a second bone
fragment, the apparatus comprising: a fusion device, the fusion
device comprising: a shaft having a first end and a second end; a
first bone-engaging feature formed on the shaft at a first
location, the first bone-engaging feature comprising at least one
barb which, in its unbiased condition, flares outwardly from the
longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, such that the first end of the
shaft may be advanced into a hole in the first bone fragment when
the at least one barb is elastically constrained to a position
substantially parallel to the longitudinal axis of the shaft but is
prevented from being withdrawn from the hole in the first bone
fragment when the at least one barb is in its unbiased condition;
and a second bone-engaging feature formed on the shaft at a second
location, the second bone-engaging feature comprising at least one
barb which, in its unbiased condition, flares outwardly from the
longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, such that the second end of the
shaft may be advanced into a hole in the second bone fragment when
the at least one barb is elastically constrained to a position
substantially parallel to the longitudinal axis of the shaft, but
is prevented from being withdrawn from the hole in the second bone
fragment when the at least one barb is in its unbiased
condition.
[0009] In another preferred form of the invention, there is
provided a method for securing a first bone fragment to a second
bone fragment, the method comprising: providing a fusion device,
the fusion device comprising: a shaft having a first end and a
second end; a first bone-engaging feature formed on the shaft at a
first location, the first bone-engaging feature comprising at least
one barb which, in its unbiased condition, flares outwardly from
the longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, such that the first end of the
shaft may be advanced into a hole in the first bone fragment when
the at least one barb is elastically constrained to a position
substantially parallel to the longitudinal axis of the shaft but is
prevented from being withdrawn from the hole in the first bone
fragment when the at least one barb is in its unbiased condition;
and a second bone-engaging feature formed on the shaft at a second
location, the second bone-engaging feature comprising at least one
barb which, in its unbiased condition, flares outwardly from the
longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, such that the second end of the
shaft may be advanced into a hole in the second bone fragment when
the at least one barb is elastically constrained to a position
substantially parallel to the longitudinal axis of the shaft but is
prevented from being withdrawn from the hole in the second bone
fragment when the at least one barb is in its unbiased condition;
elastically constraining the at least one barb of the first
bone-engaging feature to a position substantially parallel to the
longitudinal axis of the shaft, and elastically constraining the at
least one barb of the second bone-engaging feature to a position
substantially parallel to the longitudinal axis of the shaft;
advancing the first bone-engaging feature into a hole in the first
bone fragment, and advancing the second bone-engaging feature into
a hole in the second bone fragment; and releasing the constraint on
the at least one barb of the first bone-engaging feature and
releasing the constraint on the at least one barb of the second
bone-engaging feature, whereby to generate and maintain compression
between the first bone fragment and the second bone fragment.
[0010] In another preferred form of the invention, there is
provided apparatus for securing a first bone fragment to a second
bone fragment, the apparatus comprising: a fusion device, the
fusion device comprising: a shaft having a first end and a second
end; a first bone-engaging feature formed on the shaft at a first
location, the first bone-engaging feature comprising at least one
barb which, in its unbiased condition, flares outwardly from the
longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, the at least one barb being
configured so that the first end of the shaft may be advanced into
a hole in the first bone fragment but prevents the first end of the
shaft from being withdrawn from the hole in the first bone
fragment; and a second bone-engaging feature formed on the shaft at
a second location, the second bone-engaging feature comprising at
least one barb which, in its unbiased condition, flares outwardly
from the longitudinal axis of the shaft and which is capable of
being elastically constrained to a position substantially parallel
to the longitudinal axis of the shaft, the at least one barb being
configured so that the second end of the shaft may be advanced into
a hole formed in the second bone fragment but prevents the second
end of the shaft from being withdrawn from the hole in the second
bone fragment; wherein at least a portion of the shaft disposed
between the first bone-engaging feature and the second
bone-engaging feature is capable of being elastically stretched;
and a holding element connectable to the fusion device for
releasably holding the at least a portion of the shaft in a
stretched condition.
[0011] In another preferred form of the invention, there is
provided a method for securing a first bone fragment to a second
bone fragment, the method comprising: providing a fusion device,
the fusion device comprising: a shaft having a first end and a
second end; a first bone-engaging feature formed on the shaft at a
first location, the first bone-engaging feature comprising at least
one barb which, in its unbiased condition, flares outwardly from
the longitudinal axis of the shaft and which is capable of being
elastically constrained to a position substantially parallel to the
longitudinal axis of the shaft, the at least one barb being
configured so that the first end of the shaft may be advanced into
a hole in the first bone fragment but prevents the first end of the
shaft from being withdrawn from the hole in the first bone
fragment; and a second bone-engaging feature formed on the shaft at
a second location, the second bone-engaging feature comprising at
least one barb which, in its unbiased condition, flares outwardly
from the longitudinal axis of the shaft and which is capable of
being elastically constrained to a position substantially parallel
to the longitudinal axis of the shaft, the at least one barb being
configured so that the second end of the shaft may be advanced into
a hole formed in the second bone fragment but prevents the second
end of the shaft from being withdrawn from the hole in the second
bone fragment; wherein at least a portion of the shaft disposed
between the first bone-engaging feature and the second
bone-engaging feature is capable of being elastically stretched;
longitudinally stretching the fusion device so that the fusion
device is in a longitudinally stretched condition; holding the
fusion device in its longitudinally stretched condition; inserting
the fusion device into a hole in the first bone fragment while the
fusion device is in its longitudinally stretched condition, and
inserting the fusion device into a hole in the second bone fragment
while the fusion device is in its longitudinally stretched
condition; and releasing the fusion device from its longitudinally
stretched condition so as to apply compression between the first
bone fragment and the second bone fragment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other objects and features of the present
invention will be more fully disclosed or rendered obvious by the
following detailed description of the preferred embodiments of the
invention, which is to be considered together with the accompanying
drawings wherein like numbers refer to like parts, and further
wherein:
[0013] FIGS. 1-4 are schematic views showing an intramedullary
fusion device formed in accordance with the present invention;
[0014] FIG. 4A is a schematic view showing removable retaining tabs
which may be used to hold the first and second barbed end regions
of the intramedullary fusion device of FIGS. 1-4 in their radially
constrained condition;
[0015] FIGS. 5-15 are schematic views showing the novel
intramedullary fusion device of FIGS. 1-4 being used to treat a
hammer toe condition;
[0016] FIG. 15A is a schematic view showing another intramedullary
fusion device formed in accordance with the present invention;
[0017] FIG. 15B is a schematic view showing another intramedullary
fusion device formed in accordance with the present invention;
[0018] FIGS. 16-18 are schematic views showing another
intramedullary fusion device formed in accordance with the present
invention;
[0019] FIGS. 19-25 are schematic views showing an intramedullary
fusion system formed in accordance with the present invention;
[0020] FIGS. 26-36 are schematic views showing the novel
intramedullary fusion system of FIGS. 19-25 being used to treat a
hammer toe condition; and
[0021] FIG. 37 is a schematic view showing another intramedullary
fusion device formed in accordance with the present invention and
which may be used with the intramedullary fusion system shown in
FIGS. 19-25.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention comprises the provision and use of
novel intramedullary devices that are better able to bring bone
fragments into close proximity with each other, generate a
compressive load, and maintain that compressive load for a
prolonged period of time while healing occurs.
[0023] Looking first at FIGS. 1-4, there is shown an intermedullary
fusion device 5 manufactured from a shape memory material (e.g., a
material capable of exhibiting superelasticity and/or a
temperature-induced shape change). The shape memory material may be
a metal alloy (e.g., Nitinol) or a polymer (e.g., appropriately
processed PEEK). Intramedullary fusion device 5 comprises a first
barbed end region 10, a second barbed end region 15, and a central
bridge region 20 connecting first barbed end region 10 to second
barbed end region 15. Intramedullary fusion device 5 is preferably
cannulated so as to allow the intramedullary fusion device to be
installed over a k-wire if desired, while also allowing a k-wire to
be passed through the intramedullary fusion device following
implantation if the surgeon desires to fuse a distal or proximal
joint. The first and second barbed regions flare outward in
multiple planes, preferably engaging the surrounding bone about the
full circumference of the intramedullary fusion device, thereby
providing excellent torsional stability to the fusion site.
[0024] First barbed end region 10 comprises a plurality of barbs 25
which, in their unbiased condition, flare outward from the
longitudinal axis of intramedullary fusion device 5 in the manner
shown in FIG. 1. The flare may increase linearly over the length of
the barb, or it may increase non-linearly over the length of the
barb to enable first barbed end region 10 to better engage the
"hourglass-shaped" intramedullary canal. The better that first
barbed end region 10 engages the intramedullary canal, the more
even the pressure distribution will be. However, barbs 25 can be
strained to a position parallel to the longitudinal axis of
intramedullary fusion device 5 and constrained in that position
(e.g., via a removable retaining tab 30, FIGS. 2 and 4A) so as to
reduce the cross-sectional profile of first barbed end region 10,
whereby to allow for insertion into a drilled hole in bone, as will
hereinafter be discussed. Barbs 25 can be constrained in a state
where they partially occupy the cannulation of intramedullary
fusion device 5 (i.e., where barbs 25 are strained to a point past
parallel to the longitudinal axis of intramedullary fusion device
5), thereby further reducing the cross-sectional area of first
barbed end region 10. This is beneficial for accessing the
intramedullary canal through a small drilled hole.
[0025] While FIG. 1 illustrates a device with four barbs 25 on
first barbed end region 10, it should be appreciated that first
barbed end region 10 can be made with more or fewer barbs. Upon
removing retaining tab 30, barbs 25 are allowed to flare outward
again, whereby to grip the side wall of the drilled hole and
intramedullary canal receiving first barbed end region 10, whereby
to lock first barbed end region 10 to a bone fragment via an
expansive force on the intramedullary canal, as will also
hereinafter be discussed.
[0026] In one preferred form of the invention, barbs 25 of first
barbed end region 10 are separated from one another by relatively
small longitudinal gaps when barbs 25 are strained to a position
parallel to the longitudinal axis of intramedullary fusion device
5, such that barbs 25 collectively provide a substantially full
circumferential structure for first barbed end region 10 (i.e.,
when barbs 25 are strained to a position parallel to the
longitudinal axis of intramedullary fusion device 5, barbs 25
collectively provide a substantially continuous extension of
central bridge region 20 of intramedullary fusion device 5). See
FIGS. 3 and 4.
[0027] Second barbed end region 15 comprises a plurality of barbs
35 which, in their unbiased condition, flare outward from the
longitudinal axis of intramedullary fusion device 5 in the manner
shown in FIG. 1. The flare may increase linearly over the length of
the barb, or it may increase non-linearly over the length of the
barb to enable second barbed end region 15 to better engage the
"hourglass-shaped" intramedullary canal. The better that second
barbed end region 15 engages the intramedullary canal, the more
even the pressure distribution will be. However, barbs 35 can be
strained to a position parallel to the longitudinal axis of
intramedullary fusion device 5 and constrained in that position
(e.g., via a removable retaining tab 40, FIGS. 2 and 4A) so as to
reduce the cross-sectional profile of second barbed end region 15,
whereby to allow for insertion into a drilled hole in bone, as will
hereinafter be discussed. Barbs 35 can be constrained in a state
where they partially occupy the cannulation of intramedullary
fusion device 5 (i.e., where barbs 35 are constrained to a point
past parallel to the longitudinal axis of intramedullary fusion
device 5), thereby further reducing the cross-sectional area of
second barbed region 15. This is beneficial for accessing the
intramedullary canal through a small drilled hole.
[0028] While FIG. 1 illustrates a device with four barbs 35 on the
second barbed end region 15, it should be appreciated that second
barbed end region 15 can be made with more or fewer barbs. Upon
removing retaining tab 40, barbs 35 are allowed to flare outward,
whereby to grip the side wall of the drilled hole and
intramedullary canal receiving second barbed end region 15, whereby
to lock second barbed end region 15 to a bone fragment via an
expansive force on the intramedullary canal, as will also
hereinafter be discussed.
[0029] In one preferred form of the invention, barbs 35 of second
barbed end region 15 are separated from one another by relatively
small longitudinal gaps when barbs 35 are strained to a position
parallel to the longitudinal axis of intramedullary fusion device
5, such that barbs 35 collectively provide a substantially full
circumferential structure for second barbed end region 15 (i.e.,
when barbs 35 are strained to a position parallel to the
longitudinal axis of intramedullary fusion device 5, barbs 35
collectively provide a substantially continuous extension of
central bridge region 20 of intramedullary fusion device 5). See
FIGS. 3 and 4.
[0030] It should be appreciated that first barbed end region 10 and
second barbed end region 15 may have different numbers of barbs,
e.g., first barbed end region 10 may comprise four barbs 25 and
second barbed end region 15 may comprise three barbs 35. However,
it should be appreciated that regardless of the number of barbs 25
provided on first barbed end region 10, and regardless of the
number of barbs 35 provided on second barbed end region 15, the
barbs 25 of first barbed end region 10 preferably engage the
surrounding bone about the full circumference of the intramedullary
fusion device, and the barbs 35 of second barbed end region 15
preferably engage the surrounding bone about the full circumference
of the intramedullary fusion device.
[0031] Central bridge region 20 preferably comprises a generally
cylindrical shape and is preferably sized so as to have an outer
diameter somewhat less than the major diameters of first barbed end
region 10 and second barbed end region 15 when their barbs 25, 35,
respectively, have been strained to a position parallel to the
longitudinal axis of intramedullary fusion device 5.
[0032] Intramedullary fusion device 5 may be used to secure
together two bone fragments under compression. By way of example
but not limitation, and looking now at FIGS. 5-15, intramedullary
fusion device 5 may be used to treat a hammer toe deformity (FIG.
5).
[0033] First the distal end of the metatarsal 50 is cut off to
correct the deformity and create a bone face 55 suitable for fusion
(FIGS. 6 and 7). Then the proximal end of the phalange 60 is
removed to correct the deformity and create a bone face 65 suitable
for fusion (FIGS. 7 and 8). With these two cuts complete, the bones
of the metatarsal-phalange joint can be properly aligned (FIG. 8)
for subsequent fusion, as will hereinafter be discussed.
[0034] Next, the surgeon inserts a k-wire 70 through the distal end
of the toe, phalange 60 and into the metatarsal 50 (FIG. 9).
Preferably k-wire 70 passes down the intramedullary canals of
phalange 60 and metatarsal 50. Removal of k-wire 70 leaves a canal
75 (i.e., the opened intramedullary canal) in phalange 60 and a
canal 80 in metatarsal 50, with canal 75 in phalange 60 being
aligned with canal 80 in metatarsal 50 when phalange 60 is aligned
with metatarsal 50 (FIG. 10). Canals 75 and 80 receive
intramedullary fusion device 5 as will hereinafter be
discussed.
[0035] Following removal of k-wire 70, phalange 60 is flexed
downward so as to expose the prepared metatarsal face 55 (FIG.
11).
[0036] Next, with retaining tabs 30, 40 constraining barbs 25, 35,
respectively, of first barbed end region 10 and second barbed end
region 15, respectively, to their "inboard" position (i.e., as
shown in FIG. 2), intramedullary fusion device 5 has its first
barbed end region 10 advanced into canal 80 of metatarsal 50 (FIG.
12). Then removable retaining tab 30 is removed, allowing barbs 25
of first barbed end region 10 to expand outwardly and grip the side
wall of canal 80, whereby to securely fasten intramedullary fusion
device 5 to metatarsal 50 through an expansive force against the
intramedullary surface (FIG. 13). Phalange 60 is then pressed over
second barbed region 15 of intramedullary fusion device 5, with
second barbed region 15 being received in canal 75 of phalange 60
(FIG. 14). This action brings face 65 of phalange 60 against face
55 of metatarsal 50, with just enough room being left for retaining
tab 40 to extend from intramedullary device 5 to a region outside
of the bone.
[0037] Next, retaining tab 40 is removed so that barbs 35 of second
barbed end region 15 are allowed to expand outwardly and grip the
side wall of canal 75 of phalange 60 (FIG. 15). At this point barbs
25 of first barbed end region 10 are securely engaging metatarsal
50, and barbs 35 of second barbed end region 15 are securely
engaging phalange 60, with central bridge region 20 extending
across the fracture line. A force can be applied to reduce any gap
left after removing retaining tab 40.
[0038] It should be appreciated that novel intramedullary fusion
device 5 can first be implanted into phalange 60 and then implanted
into metatarsal 50 if the surgeon so chooses.
[0039] If desired, and looking now at FIG. 15A, central bridge
region 20 may have an enlargement 83 intermediate its length to act
as a stop, limiting how far intramedullary fusion device 5 can be
pushed into either side of the intramedullary canal during
implantation.
[0040] In FIGS. 1-4, barbs 25 of first barbed end region 10 are
shown as being circumferentially offset from barbs 35 of second
barbed end region 15, i.e., barbs 25 and barbs 35 are not axially
aligned with one another. However, if desired, and looking now at
FIG. 15B, barbs 25 of first barbed end region 10 may not be
circumferentially offset from barbs 35 of second barbed end region
15, i.e., barbs 25 and barbs 35 may be axially aligned with one
another in the manner shown in FIG. 15B.
[0041] If desired, and looking now at FIGS. 16-18, intramedullary
fusion device 5 can have a slight bend from central bridge region
20 to one or both of its first barbed end region 10 and second
barbed end region 15. By way of example but not limitation, in the
metatarsal-phalange fusion shown in FIGS. 5-15, it may be desirable
to provide a slight bend to second barbed end region 15 so as to
facilitate the restoration of the normal anatomy. In this form of
the invention, intramedullary fusion device 5 may be bent after
machining and during the working of the shape memory material,
e.g., it may be shape-set at the desired angulation through heat
treatment.
[0042] It should also be appreciated that the central bridge region
20 can be processed so as to be malleable (i.e., to take a set). At
body temperature, the barb regions 10 and 15 can be superelastic
while central bridge region 20 can be fully annealed Nitinol or
martensitic Nitinol, such that central bridge region 20 is
malleable and can take a set. This allows the surgeon to deform
central bridge region 20 at the time of surgery so that it assumes
the bend desired.
[0043] Looking next at FIG. 19, there is shown an intramedullary
fusion system 85 which generally comprises an intramedullary fusion
device 90, an internal restrainer 95 and a locking pin 100.
[0044] Intramedullary fusion device 90 is manufactured from a shape
memory material (e.g., a material capable of exhibiting
superelasticity and/or a temperature-induced shape change). The
shape memory material may be a metal alloy (e.g., Nitinol) or a
polymer (e.g., appropriately processed PEEK). Looking now at FIGS.
20 and 21, intramedullary fusion device 90 comprises a first barbed
end region 105, a second barbed end region 110, and a central
bridge region 115 connecting first barbed end region 105 and second
barbed end region 110. Intramedullary fusion device 90 is
preferably cannulated so as to allow the intramedullary fusion
device to be installed over a k-wire if desired, while also
allowing a k-wire to be passed through the device following
implantation if the surgeon desires to fuse a distal or proximal
joint. The first and second barbed regions flare outward in
multiple planes, preferably engaging the surrounding bone about the
full circumference of the intramedullary fusion device, thereby
providing excellent torsional stability to the fusion site.
[0045] First barbed end region 105 comprises a plurality of barbs
120 which, in their unbiased condition, flare outward from the
longitudinal axis of intramedullary fusion device 90 in the manner
shown in FIG. 20. The flare may increase linearly over the length
of the barb, or it may increase non-linearly over the length of the
barb to enable first barbed end region 105 to better engage the
"hourglass-shaped" intramedullary canal. The better that first
barbed region 105 engages the intramedullary canal, the more even
the pressure distribution will be. While FIG. 20 illustrates a
device with four barbs 120 in first barbed end region 105, it
should be appreciated that the device can have more or fewer barbs.
Barbs 120 can be strained to a position parallel to the
longitudinal axis of intramedullary fusion device 90, e.g., during
insertion into a hole drilled in bone. Once inserted into the
intramedullary canal, barbs 120 flare outwardly so as to engage
with the side wall of the drilled hole receiving first barbed end
region 105. By angling barbs 120 relative to the longitudinal axis
of intramedullary fusion device 90, i.e., with an arrowhead
configuration, barbs 120 can ensure that first barbed end region
105 is insertable into a hole in a bone but not withdrawable from
the hole in the bone. In this way barbs 120 can selectively lock
first barbed end region 105 to a bone fragment, as will hereinafter
be discussed.
[0046] Second barbed end region 110 comprises a plurality of barbs
125, which, in their unbiased condition, flare outward from the
longitudinal axis of intramedullary fusion device 90 in the manner
shown in FIG. 20. The flare may increase linearly over the length
of the barb, or it may increase non-linearly over the length of the
barb to enable second barbed end region 110 to better engage the
"hourglass-shaped" intramedullary canal. The better that second
barbed region 110 engages the intramedullary canal, the more even
the pressure distribution will be. While FIG. 20 illustrates a
device with four barbs 125 in second barbed end region 125, it
should be appreciated that the device can have more or fewer barbs.
Barbs 125 can be strained to a position parallel to the
longitudinal axis of intramedullary fusion device 90, e.g., during
insertion into a hole drilled in bone, with barbs 125 flaring
outwardly so as to remain in constant engagement with the side wall
of the drilled hole receiving second barbed end region 110. By
angling barbs 125 relative to the longitudinal axis of
intramedullary fusion device 90, i.e., with an arrowhead
configuration, barbs 125 can ensure that second barbed end region
110 is insertable into a hole in a bone but not withdrawable from
the hole in the bone. In this way barbs 125 can selectively lock
second barbed end region 110 in the intramedullary canal of a bone
fragment, as will hereinafter be discussed.
[0047] Note that barbs 120 of first barbed end region 105 are
flared in a direction which is opposite to that of barbs 125 of
second barbed end region 110.
[0048] Central bridge region 115 preferably comprises a generally
cylindrical shape and is configured so that it can be selectively
strained (i.e., stretched) longitudinally and constrained in that
position (e.g., via the aforementioned internal restrainer 95 and
locking pin 100). As will hereinafter be discussed, upon removing
locking pin 100, internal restrainer 95 will release the constraint
on central bridge region 115, whereupon central bridge region 115
will attempt to foreshorten. As will also hereinafter be discussed,
this foreshortening can be harnessed to apply compression between
two bone fragments.
[0049] In order to allow central bridge region 115 to be
constrained in its longitudinally stretched state, intramedullary
fusion device 90 preferably comprises cutouts 130, disposed in
first barbed end region 105 and second barbed end region 110, that
allow central bridge region 115 to be constrained in its
longitudinally stretched state by internal restrainer 95, as will
hereinafter be discussed.
[0050] Internal restrainer 95 is shown in further detail in FIG.
22. Internal restrainer 95 may comprise a shape memory material if
desired. Internal restrainer 95 generally comprises a cannulated
cylindrical body 140 terminating in a pair of fingers 145 at each
end of cylindrical body 140. Each pair of fingers 145 are normally
biased together, however, they may be elastically forced apart so
that they extend outboard beyond the circumference of cylindrical
body 140, whereby to allow fingers 145 of internal restrainer 90 to
lock to cutouts 130 of intramedullary fusion device 90 when
intramedullary fusion device 90 is in its longitudinally stretched
state, as will hereinafter be discussed.
[0051] As noted above, central bridge region 115 of intramedullary
fusion device 90 can be strained (i.e., longitudinally stretched),
locked in that position via internal restrainer 95 and locking pin
100 and, upon removing locking pin 100, internal restrainer 95 will
release the constraint on central bridge region 115 of
intramedullary fusion device 90, whereupon central bridge region
115 will attempt to foreshorten. More particularly, and looking now
at FIGS. 23-25, central bridge region 115 is stretched using a
stretching mechanism (not shown) of the sort which will be apparent
to those skilled in the art in view of the present disclosure, and
internal restrainer 95 is inserted into intramedullary fusion
device 90. As internal restrainer 95 is inserted into
intramedullary fusion device 90, the pairs of fingers 145 disposed
at each end of internal restrainer 95 are aligned with cutouts 130
in first barbed end region 105 and second barbed end region 110.
Locking pin 100 is then inserted into internal restrainer 95,
whereby to cause the pairs of fingers 145 disposed at each end of
internal restrainer 95 to project through cutouts 140 of
intramedullary fusion device 90, whereby to lock central bridge
region 115 of intramedullary fusion device 90 in its strained
(i.e., longitudinally stretched) state. The external load
stretching central bridge region 105 (i.e., via the aforementioned
stretching mechanism, not shown) can now be removed, and central
bridge region 115 of intramedullary fusion device 90 will remain in
its strained (i.e., stretched) state due to the action of internal
restrainer 95 and locking pin 100. However, when locking pin 100 is
thereafter removed from the interior of internal restrainer 95, the
pairs of fingers 145 disposed at each end of internal restrainer 95
retract from cutouts 130 by virtue of their inward bias, allowing
central bridge region 115 of intramedullary fusion device 90 to
foreshorten, whereby to generate compression between the bone
fragments, as will hereinafter be discussed.
[0052] Intramedullary fusion system 85 may be used to secure
together two bone fragments and apply compression to the fracture
line. By way of example but not limitation, and looking now at
FIGS. 26-36, intramedullary fusion system 85 may be used to treat a
hammertoe deformity (FIG. 26).
[0053] First, the distal end of metatarsal 50 is cut off to correct
the deformity and create a bone face 55 suitable for fusion (FIGS.
27 and 28). Then the proximal end of phalange 60 is removed to
correct the deformity and create a bone face 65 suitable for fusion
(FIGS. 28 and 29). With these two cuts complete, the bones of the
metatarsal-phalange joint can be properly aligned (FIG. 29) for
subsequent fusion, as will hereinafter be discussed.
[0054] Next, the surgeon inserts k-wire 70 through the distal end
of the toe, then through phalange 60 and into metatarsal 50 (FIG.
30). Preferably k-wire 70 passes down the intramedullary canals of
phalange 60 and metatarsal 50. Removal of k-wire 70 leaves a canal
75 (i.e., the opened intramedullary canal) in phalange 60 and a
canal 80 in metatarsal 50, with canal 75 in phalange 60 being
aligned with canal 80 in metatarsal 50 when phalange 60 is aligned
with metatarsal 50 (FIG. 31). Canals 75 and 80 receive
intramedullary fusion system 85 as will hereinafter be
discussed.
[0055] Following removal of k-wire 70, phalange 60 is flexed
downward so as to expose the prepared metatarsal face 55 (FIG.
32).
[0056] Intramedullary fusion device 90, which has previously been
strained (i.e., its central bridge region 115 longitudinally
stretched) and locked in this state with internal restrainer 95 and
locking pin 100, is then implanted into canal 75 in phalange 60
(FIG. 33), i.e., by advancing the free end of locking pin 100 and
second barbed end region 110 of intramedullary fusion device 90
into canal 75 of phalange 60. Note that the flare on barbs 125 of
second barbed end region 110 is such that intramedullary fusion
device 90 can be advanced into canal 75 of phalange 60 but not
withdrawn. Note also that the free end of locking pin 100 extends
completely out of phalange 60 and any adjacent bone structure(s) so
that it is graspable by the surgeon and able to be retracted when
desired through the distal end of the toe.
[0057] Phalange 60 is then reoriented so that first barbed end
region 105 is aligned with canal 80 in metatarsal 50, and then
phalange 60 is advanced towards metatarsal 50 so that first barbed
end region 105 enters canal 80 of metatarsal 50 (FIG. 34). Note
that the flare on barbs 120 of first barbed end region 105 of
intramedullary fusion device 90 is such that intramedullary fusion
device 90 can be advanced into canal 80 of metatarsal 50 but not
withdrawn.
[0058] Phalange 60 is advanced towards metatarsal 50 until face 65
of phalange 60 engages face 55 of metatarsal 50. At this point
barbs 120 of first barbed end region 105 and barbs 125 of second
barbed end region 110 prevent phalange 60 and metatarsal 50 from
moving apart.
[0059] With intramedullary fusion device 90 firmly secured to both
phalange 60 and metatarsal 50, locking pin 100 is then removed from
internal restrainer 95 (FIG. 35), i.e., by being retracted through
the distal end of the toe. This allows the pairs of fingers 145
disposed on each end of internal restrainer 95 to retract from
cutouts 130 of intramedullary fusion device 90, which allows
central bridge region 115 of intramedullary fusion device 90 to
foreshorten, whereby to generate compression between metatarsal 50
and phalange 60 (FIG. 36).
[0060] If desired, internal restrainer 95 may be left in place
within intramedullary fusion device 90 or, more preferably,
internal restrainer 95 may be removed from intramedullary fusion
device 90 after intramedullary fusion device 90 has been set, e.g.,
by grasping internal restrainer 95 with a grasping tool and drawing
internal restrainer 95 longitudinally out of intramedullary fusion
device 90 and then out canal 75 of phalange 60. Alternatively,
internal restrainer 95 can be automatically removed from
intramedullary fusion device 90 when locking pin 100 is removed
from internal restrainer 95, e.g., by providing the distal end of
locking pin 100 and the proximal end of internal restrainer 95 with
an appropriate "catch mechanism" so that the retreating locking pin
100 engages internal restrainer 95 and carries internal restrainer
95 out of intramedullary fusion device 90 and then out canal 75 of
phalange 60.
[0061] If desired, and looking now at FIG. 37, intramedullary
fusion device 90 can have a slight bend at one or both of its first
barbed end region 105 and second barbed end region 110. By way of
example but not limitation, in the metatarsal-phalange fusion shown
in FIGS. 26-36, it may be desirable to provide a slight bend to
second barbed end region 110 so as to facilitate restoration of the
normal anatomy. In this form of the invention, intramedullary
fusion device 90 may be bent after machining and during the working
of the shape memory material, e.g., it may be shape-set at the
desired angulation through heat treatment.
[0062] Intramedullary fusion device 90 is specifically engineered
so not to "tear through" the bone tissue when central bridge region
115 foreshortens. The compressive forces of intramedullary fusion
device 90 can be controlled by modulating the material properties
of the intramedullary fusion device and/or the geometry of the
intramedullary fusion device.
[0063] The percentage of cold work in the shape memory material
forming intramedullary fusion device 90 affects the compressive
force generated by the intramedullary fusion device. As the
percentage of cold work increases, the compression force declines.
The intramedullary fusion device should, preferably, have between
about 15% and 55% cold work to control the recovery force of the
intramedullary device.
[0064] Another material property that affects the intramedullary
fusion device's compression force is the temperature differential
between the body that the intramedullary fusion device will be
implanted into (assumed to be 37.degree. C., which is the
temperature of a human body) and the austenite finish temperature
of the shape memory material forming intramedullary fusion device
90. A smaller temperature differential between the two will result
in the intramedullary fusion device generating a small compressive
load; conversely, the larger the temperature differential between
the two will result in the intramedullary device generating a
larger compressive load. The shape memory material that the
intramedullary fusion device is made out of should, preferably,
have an austenite finish temperature of greater than about
-10.degree. C., resulting in a temperature differential of less
than about 47.degree. C. when the intramedullary fusion device is
implanted (assuming that the intramedullary fusion device is
implanted in a human body).
[0065] The geometry of the intramedullary fusion device also
affects the compression force generated. The cross-sectional area
of the hollow central bridge region 115 affects the compression
force. As the cross-sectional area increases, so does the
compression force that the intramedullary fusion device 90 will
generate. In this respect it should be appreciated that it is
beneficial for the compression force generated by the
foreshortening of intramedullary fusion device 90 to be constant as
the bone relaxes and remodels. Thus, the cross-section of hollow
central bridge region 115 of intramedullary fusion device 90
preferably has a constant cross-section over its entire length.
Cross-sections that are not uniform over the length of hollow
central bridge region 115 can result in an increase or decrease in
compression as the intramedullary fusion device foreshortens.
[0066] The barbs 120, 125 are important for transmitting the
compression force to the bone without "tearing through" the bone.
The height, width, and number of barbs 120, 125 on the
intramedullary device 90 are all important to the intramedullary
device's ability to not "tear through" the bone.
[0067] It should also be appreciated that shape memory material can
be processed to exhibit two-way shape memory. The intramedullary
fusion device 90 can be trained to have an austenitic shape (i.e.,
barbs expanded) and a martensitic shape (i.e., barbs extending
parallel to the longitudinal axis of intramedullary fusion device
90). In this case, the barbs can be in their austenitic shape at
about body temperature. The barbs can be deformed via the creation
of stress induced martensite to implant the intramedullary fusion
device. If the intramedullary fusion device thereafter needs to be
removed, the intramedullary fusion device may be cooled (e.g., with
cold saline) to a temperature below the austenite start temperature
of the shape memory material, and more preferably below the
martensite start temperature of the shape memory material, and most
preferably below the martensite finish temperature of the shape
memory material. When cooled, the intramedullary fusion device 90
will take on its martensitic shape (i.e., the barbs laying parallel
to the longitudinal axis of the intramedullary fusion device), and
the surgeon can easily remove the intramedullary fusion device.
[0068] Additionally, the intramedullary fusion device can be made
such that central bridge region 115 of intramedullary fusion device
90 has one austenite start temperature, and such that barbs 120,
125 have a lower austenite start temperature. Thus, the
intramedullary fusion device can be stretched at a temperature less
than the austenite start temperature of central bridge region 115
but above the austenite start temperature of barbs 120, 125. Thus
barbs 120, 125 will be in the austenite phase and able to undergo a
stress induced martensite transformation during insertion of
intramedullary fusion device 90 into a bone canal. Maintaining the
intramedullary fusion device at a temperature below the austenite
start temperature of central bridge region 115 allows the
intramedullary fusion device to remain in its elongated state. The
intramedullary fusion device can then be advanced into a bone canal
as discussed above. When the central bridge region 115 warms
(either to body temperature, or to a temperature above body
temperature, e.g., through the application of warm saline), central
bridge region 115 will foreshorten, generating and maintaining
compression across the fracture line.
[0069] It should also be appreciated that central bridge region 115
of intramedullary fusion device 90 can be processed so as to be
malleable (i.e., to take a set). At body temperature, first barbed
end region 105 and second barbed end region 110 can be superelastic
while central bridge region 115 can be fully annealed Nitinol or
martensitic Nitinol. This allows the surgeon to deform the implant
at the time of surgery to the bend desired.
MODIFICATIONS OF THE PREFERRED EMBODIMENTS
[0070] It should be understood that many additional changes in the
details, materials, steps and arrangements of parts, which have
been herein described and illustrated in order to explain the
nature of the present invention, may be made by those skilled in
the art while still remaining within the principles and scope of
the invention.
* * * * *