U.S. patent application number 11/777872 was filed with the patent office on 2008-10-30 for conformable intramedullary implant with nestable components.
This patent application is currently assigned to Osteolign, Inc.. Invention is credited to Daniel F. Justin.
Application Number | 20080269746 11/777872 |
Document ID | / |
Family ID | 39887873 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080269746 |
Kind Code |
A1 |
Justin; Daniel F. |
October 30, 2008 |
CONFORMABLE INTRAMEDULLARY IMPLANT WITH NESTABLE COMPONENTS
Abstract
The present invention provides a bone fixation device for
implantation into the intramedullary canal of a bone. The bone
fixation device may include a support structure and a
thermo-chemically activated matrix. The support structure may be
radially expandable and contractible, and sufficiently flexible to
be inserted into the intramedullary canal through an opening which
is not parallel to the intramedullary canal. The matrix may attain
a first thermo-chemical state via the addition of energy, and a
second thermo-chemical state via the dissipation of energy. While
in the first thermo-chemical state, the matrix is deformable and
can conform to a shape matching the contours of the intramedullary
canal of the bone. As the matrix attains the second thermo-chemical
state, it may crystallize and becomes relatively hardened. An
implant deformation apparatus may be used to expand the device
within the intramedullary canal. The device may include a series of
nested telescoping components.
Inventors: |
Justin; Daniel F.; (Logan,
UT) |
Correspondence
Address: |
MEDICINELODGE INC.
180 SOUTH 600 WEST
LOGAN
UT
84321
US
|
Assignee: |
Osteolign, Inc.
Duluth
GA
|
Family ID: |
39887873 |
Appl. No.: |
11/777872 |
Filed: |
July 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60913696 |
Apr 24, 2007 |
|
|
|
Current U.S.
Class: |
606/62 ;
128/898 |
Current CPC
Class: |
A61L 27/18 20130101;
A61L 27/50 20130101; A61B 2017/00004 20130101; A61F 2/82 20130101;
A61B 17/866 20130101; A61F 2250/0052 20130101; A61F 2220/0075
20130101; A61B 17/7233 20130101; A61L 2430/02 20130101; A61B
17/7208 20130101; A61L 2400/06 20130101; A61B 17/7064 20130101;
A61F 2/915 20130101; A61B 17/7275 20130101; A61F 2/91 20130101;
A61B 17/72 20130101; A61B 17/7071 20130101; A61F 2/0077 20130101;
A61M 29/02 20130101; A61B 17/7044 20130101; A61L 2400/16 20130101;
A61B 17/80 20130101; A61B 17/7059 20130101; A61B 17/864
20130101 |
Class at
Publication: |
606/62 ;
128/898 |
International
Class: |
A61B 17/58 20060101
A61B017/58; A61B 19/00 20060101 A61B019/00 |
Claims
1. A device for stabilization of a fractured bone, the device
comprising: a first component configured to be sufficiently
flexible to be introduced into an intramedullary canal of the bone
along a path nonparallel to the intramedullary canal; and a second
component configured to be sufficiently flexible to be introduced
into the intramedullary canal of the bone along the path; wherein
the first and second components are configured to be coupled
together to provide an assembly that is collapsible within the
intramedullary canal such that, in the collapsed state, the
assembly is sufficiently rigid to stabilize the fractured bone.
2. The device of claim I, wherein the first and second components
are each substantially equal in length to the assembly in the
collapsed state.
3. The device of claim 1, wherein the first component is configured
to nest inside the second component when the assembly is in the
collapsed state, the assembly having an extended state in which the
second component is telescopically extended from the first
component to facilitate flexure of the assembly, thereby
facilitating insertion of the assembly into the intramedullary
canal.
4. The device of claim 1, wherein the first and second components
are formed substantially of metallic materials.
5. The device of claim 1, wherein the first and second components
each comprise metallic material embedded in thermo-chemically
activated thermoplastic material.
6. The device of claim 1, wherein the first and second components
are threadibly engaged together.
7. The device of claim 1, further comprising a third component
configured to be sufficiently flexible to be introduced into the
intramedullary canal of the bone along the path, wherein the second
and third components are configured to be coupled together.
8. The device of claim 1, wherein the path is at an angle of 10 to
90 degrees relative to the intramedullary canal.
9. A device for stabilization of a fractured bone, the device
comprising: a first component; a second component; and a third
component; wherein the first, second, and third components are
configured to be telescopically assembled to form an assembly that
is collapsible within an intramedullary canal of the bone to
stabilize the fractured bone.
10. The device of claim 9, wherein the first, second and third
components are each substantially equal in length to the assembly
in the collapsed state.
11. The device of claim 9, wherein the first, second and third
components are formed substantially of metallic materials.
12. The device of claim 9, wherein the first, second and third
components each comprise metallic material embedded in
thermo-chemically activated thermoplastic material.
13. The device of claim 9, wherein the first, second and third
components are each sufficiently flexible to be introduced into the
intramedullary canal of the bone along a path that is at an angle
of 10 to 90 degrees relative to the intramedullary canal.
14. The device of claim 9, wherein the second component is
threadibly engaged to the first component and the third component
is threadibly engaged to the second component.
15. The device of claim 9, wherein the first, second and third
components are each substantially tubular in configuration.
16. A method for stabilizing a fractured bone, the method
comprising: inserting a first component into an intramedullary
canal of the bone along a path nonparallel to the intramedullary
canal by flexing the first component; inserting a second component
into the intramedullary canal along the pathway by flexing the
second component, wherein the second component is configured to be
coupled to the first component to form an assembly; and collapsing
the assembly within the intramedullary canal such that, in the
collapsed state, the assembly is sufficiently rigid to stabilize
the fractured bone.
17. The method of claim 16, wherein the first and second components
are each substantially equal in length to the assembly in the
collapsed state.
18. The method of claim 16, wherein collapsing the assembly
comprises nesting the first component inside the second
component.
19. The method of claim 16, wherein the second component is
threadibly engaged to the first component, wherein collapsing the
assembly comprises rotating the second component relative to the
first component.
20. The method of claim 16, further comprising inserting a third
component into the intramedullary canal along the pathway by
flexing the third component, wherein the third component is
configured to be coupled to the second component.
21. The method of claim 16, further comprising introducing
hardenable bone cement into the intramedullary canal of the bone
such that it surrounds the collapsed assembly.
22. The method of claim 16, wherein the path is at an angle of 10
to 90 degrees relative to the intramedullary canal.
23. A method for stabilizing a fractured bone, comprising:
inserting a first component into an intramedullary canal of the
bone; inserting a second component into the intramedullary canal;
inserting a third component into the intramedullary canal, wherein
the first, second, and third components are telescopically
assembled to form an assembly; and collapsing the assembly within
the intramedullary canal to such that the assembly is able to
stabilize the bone.
24. The method of claim 23, wherein the first, second and third
components are each substantially equal in length to the collapsed
assembly.
25. The method of claim 23, wherein the first, second and third
components are each substantially tubular in configuration.
26. The method of claim 23, further comprising inserting the first,
second and third components into the intramedullary canal along a
path which is at an angle of 10 to 90 degrees relative to the
intramedullary canal.
27. The method of claim 23, wherein collapsing the assembly
comprises nesting the first component inside the second component
and nesting the second component inside the third component.
28. The method of claim 23, wherein collapsing the assembly
comprises rotating the second component relative to the first
component and rotating the third component relative to the second
component.
29. The method of claim 23, further comprising introducing
hardenable bone cement into the intramedullary canal of the bone
such that it surrounds the collapsed assembly.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of the following, which
is incorporated herein by reference:
[0002] Pending prior U.S. Provisional Patent Application No.
60/913,696, filed Apr. 24, 2007, which carries Applicants' docket
no. OST-1 PROV, and is entitled THERMO-CHEMICALLY ACTIVATED
INTRAMEDULLARY BONE STENT.
BACKGROUND OF THE INVENTION
[0003] 1. The Field of the Invention
[0004] The present invention relates generally to orthopedic
devices for the surgical treatment of bone fractures and, more
particularly, to the fixation and stabilization of fracture sites
with an intramedullary device that is deformable and conforms to
the shape of the intramedullary canal.
[0005] 2. The Relevant Technology
[0006] Orthopedic medicine provides a wide array of implants that
can be attached to bone to repair fractures. External fixation
involves the attachment of a device that protrudes out of the skin,
and therefore carries significant risk of infection. May fractures
in long bones can be repaired through the use of bone plates, which
are implanted and attached to lie directly on the bone surface. The
bone plate then remains in the body long enough to allow the
fractured bone to heal properly. Unfortunately, such bone plates
often require the surgical exposure of substantially the entire
length of bone to which the plate is to be attached. Such exposure
typically results in a lengthy and painful healing process, which
must often be repeated when the implantation site is again exposed
to allow removal of the plate. There is a need in the art for
implants and related instruments that do not require such broad
exposure of the fractured bone, while minimizing the probability of
infection by avoiding elements that must protrude through the skin
as the bone heals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Various embodiments of the present invention will now be
discussed with reference to the appended drawings. It is
appreciated that these drawings depict only typical embodiments of
the invention and are therefore not to be considered limiting of
its scope. The drawings may not be to scale.
[0008] FIG. 1 is a perspective view of an intramedullary bone
fixation device according to one embodiment of the invention,
comprising a support structure which includes a cage and a
plurality of rods, and a thermo-chemically activated thermoplastic
matrix;
[0009] FIG. 2 is a perspective view of the cage of FIG. 1;
[0010] FIGS. 3A-3I are perspective views of various embodiments of
stent portions suitable for incorporation into the support
structure of FIG. 2;
[0011] FIG. 4 is an enlarged perspective view of a first end of the
cage of FIG. 2;
[0012] FIG. 5 is a perspective view of the rods of FIG. 1;
[0013] FIG. 6 is a perspective view of the thermoplastic matrix of
FIG. 1;
[0014] FIG. 7 is a longitudinal cross-sectional view of a bone with
an alternative embodiment of an intramedullary bone fixation device
partially inserted into the intramedullary canal;
[0015] FIG. 8 is a longitudinal cross-sectional view of a bone with
the intramedullary bone fixation device of FIG. 7 implanted inside
a second intramedullary bone fixation device;
[0016] FIG. 9A is an enlarged cross-sectional view of one section
of the bone and intramedullary bone fixation devices of FIG. 8;
[0017] FIG. 9B is an enlarged cross-sectional view of another
section of the bone and intramedullary bone fixation devices of
FIG. 8;
[0018] FIG. 9C is an enlarged cross-sectional view of another
section of the bone and intramedullary bone fixation devices of
FIG. 8;
[0019] FIG. 10 is a perspective cutaway view of an alternative
embodiment of an intramedullary bone fixation device comprising a
cage, rods, sutures and a thermoplastic matrix;
[0020] FIGS. 11A-11E are cross-sectional views of the
intramedullary bone fixation device of FIG. 10, illustrating radial
expansion of the device from a contracted state in FIG. 11A to a
fully expanded state in FIG. 11E.
[0021] FIGS. 12A-12E are cross-sectional views of an alternative
embodiment of an intramedullary bone fixation device, illustrating
radial expansion of the device from a contracted state in FIG. 12A
to a fully expanded state in FIG. 12E.
[0022] FIG. 13A is a perspective view of a support structure in a
contracted state according to one alternative embodiment of the
invention;
[0023] FIG. 13B is a perspective view of the support structure of
FIG. 13A in an expanded state;
[0024] FIG. 14A is a perspective view of a cage in a contracted
state;
[0025] FIG. 14B is an end view of the cage of 14A in a contracted
state;
[0026] FIG. 14C is a perspective view of a cage in an expanded
state;
[0027] FIG. 14D is an end view of the cage of 14C in an expanded
state;
[0028] FIG. 15 is a perspective view of a slotted support
structure;
[0029] FIG. 16A is a perspective view of a shaft portion of a
mechanical expansion apparatus suitable for use with the device of
FIG. 1;
[0030] FIG. 16B is a perspective view of the complete mechanical
expansion apparatus of FIG. 16A;
[0031] FIG. 17 is a longitudinal cross-sectional view of a bone
with an intramedullary bone fixation device in a contracted state
and a balloon expansion apparatus in the intramedullary canal of
the bone, and a regulator apparatus;
[0032] FIG. 18 is a longitudinal cross-sectional view of a portion
of the bone of FIG. 17, with the intramedullary bone fixation
device in a contracted state and a balloon expansion apparatus of
FIG. 17;
[0033] FIG. 19 is a longitudinal cross-sectional view of the bone,
intramedullary bone fixation device and balloon expansion apparatus
of FIG. 17, with the balloon in an inflated state and the
intramedullary bone fixation device in an expanded state;
[0034] FIG. 20A is an enlarged cross-sectional view of one section
of the bone and intramedullary bone fixation device of FIG. 19;
[0035] FIG. 20B is an enlarged cross-sectional view of another
section of the bone and intramedullary bone fixation device of FIG.
19;
[0036] FIG. 20C is an enlarged cross-sectional view of another
section of the bone and intramedullary bone fixation device of FIG.
19;
[0037] FIG. 21 is a longitudinal cross-sectional view of the bone,
intramedullary bone fixation device and balloon expansion apparatus
of FIG. 17, with the balloon in a deflated state and the and
intramedullary bone fixation device in an expanded state, with the
balloon expansion apparatus partially removed from the
intramedullary bone fixation device;
[0038] FIG. 22A is a perspective view of a telescoping bone
fixation device in an extended state according to one alternative
embodiment of the invention;
[0039] FIG. 22B is a longitudinal cross-sectional view of a
connection between two nesting components of the telescoping bone
fixation device of FIG. 22A;
[0040] FIG. 23 is a perspective view of a telescoping bone fixation
device with mesh-like components and a thermoplastic matrix
according to another alternative embodiment of the invention, in an
extended state;
[0041] FIG. 24 is a perspective view of a helically threaded
telescoping bone fixation device according to yet another
alternative embodiment of the invention, in a partially extended
state;
[0042] FIG. 25A is a perspective view of one nesting component of
the helically threaded telescoping bone fixation device of FIG. 24;
and
[0043] FIG. 25B is a perspective view of another nesting component
of the helically threaded telescoping bone fixation device of FIG.
24.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Referring to FIG. 1, a perspective view illustrates an
embodiment of an intramedullary bone fixation composite device 10.
The composite device 10 comprises a support structure 11 and a
thermo-chemically activated thermoplastic matrix 16. The support
structure 11 comprises a cage 12, and at least one stiffening rod
14. The composite device 10 is generally tubular in form and has a
longitudinal axis 24 and a transverse axis 26. A hollow central
core 18 extends the length of the device 10, surrounded by the cage
12 and rods 14, which are embedded in the thermoplastic matrix 16.
An outer perimeter 22 bounds the outer surface of the composite
device 10. The composite device 10 is an implant which is able to
transition from a contracted and flexible state for introduction
into the intramedullary canal, to an expanded and hardened state
providing rigid support and alignment for fixation of the
surrounding bone, once implanted and allowed to expand to the
perimeter of the canal. The thermoplasticity of the matrix 16
allows the composite device 10 to conform to the shape of the
surrounding intramedullary canal at a first state, and harden in
its conformed shape at a second state providing torsional, axial,
and bending reinforcement of the bone fragments during bone
healing. When contracted for insertion (or removal), a diameter 20
along the transverse axis 26 of the device is reduced, and the
length along the longitudinal axis 24 of the device may be constant
or increased. When expanded within the intramedullary canal, the
diameter 20 is increased, and the length may be constant or
decreased.
[0045] As seen in FIG. 2, the cage 12 is an elongated, generally
web-like tube which allows radial expansion and contraction over at
least part and preferably all of its length, and bending
flexibility as bending loads are applied. The cage 12 has a first
end 30, a second end 32 and a sleeve 34 which extends between the
ends. The sleeve 34 has an attachment portion 36 and a web-like
stent portion 38. The cage is hollow and generally circular in
cross-sectional shape, although the web-like construction allows
the cross-sectional shape to vary to conform to the contours of the
surrounding intramedullary canal. The shape of the intramedullary
canal varies along its length, and its cross-sectional shape may be
substantially circular, generally triangular or another shape. The
cage 12 may comprise a tubular woven or braided cage, a laser cut
tubing cage, a machined cage, or a chemically etched tubing cage
made from materials such as Nitinol, stainless steel, Co--Cr,
Titanium alloys, Tantalum, plastic, polymer or other biocompatible
materials, among others. In the embodiment depicted, the stent
portion 38 comprises a majority of the sleeve 34. However, in other
embodiments the stent portion may be a smaller proportion of the
sleeve, or comprise the entire sleeve. Attachment portions 36 may
be located at one, both, or neither of the ends of the sleeve, or
intermittently along the sleeve length.
[0046] Referring to FIG. 3, possible configurations of the web-like
structure of the stent portion 38 are shown, comprising examples of
commercially available stent shapes. These figures show the
approximate pattern of the web-like structure. These patterns are
adaptable to a variety of lengths, diameters, density of repeatable
patterns, wire thicknesses, web areas, and other structural
characteristics such that the general stent shape can be configured
to a particular bone morphology and size. FIG. 3A is representative
of a Johnson and Johnson Palmaz-Schatz.TM. Version 2 stent. FIG. 3B
represents a Medtronic Wiktor.TM. stent. FIG. 3C represents the
general shape of a Schneider "Magic" Wallstent.TM. stent. FIG. 3D
represents a Scimed NIR.TM. stent. FIG. 3E represents an Arterial
Vascular Engineering (AVE.TM.) Microstent. FIG. 3F is
representative of a Biotronik Stent.TM.. FIG. 3G is meant to
represent the general shape and construct of a Johnson and Johnson
Palmaz-Schatz.TM. stent. FIG. 3H represents a Global Therapeutics
Freedom.TM. stent. FIG. 31 is drawn to represent the adaptable
structure of a Scimed Radius.TM. stent which like all the
previously presented representative figures can be configured to
the length, diameter and size needed to conform to the
intramedullary shape of a particular bone. The stent portion may
also be configured with more than one pattern along its length or
diameter if needed to better conform to the desired geometry. The
stent portion need not be a commercially available stent; it may
also have a unique configuration which is constructed from wire,
woven, machined, laser cut, or chemically etched.
[0047] FIG. 4 is an enlarged view of the first end 30, the
attachment portion 36 and part of the stent portion 38 of the cage
12. The attachment portion 36 comprises struts 40 which extend from
the stent portion 38 and terminate at loops 42, which allow for the
attachment of instruments for device placement, adjustment and
removal. Other fasteners such as holes or hooks, among others, may
be used instead of loops. Between the struts 40 at the first end
30, linkages 44 connect each strut to the adjacent strut. The
linkages allow for radial and longitudinal contraction and
expansion of the struts 40 and therefore the first end 30, as the
device is contracted and expanded during implantation and removal.
The web-like configuration of the stent portion 38 allows for
radial and longitudinal contraction and expansion of the remainder
of the cage 12.
[0048] Referring to FIG. 5, at least one, and optionally, a
plurality, of stiffening rods 14 are oriented parallel to the
longitudinal axis of the cage 12 and are contained by the cage in
such a way as to allow the stiffening rod(s) to move radially with
the cage as the cage contracts and expands. Each rod 14 has a first
end 50, a second end 52 and a shaft 56. Each rod 14 may have loops,
holes, hooks or other attachment structures at the second end 52 to
connect to second end 32 of cage 12. The rods 14 may be threaded
loosely or otherwise linked into the stent portion 38 of the cage
12. Holes (not shown) may extend transversely through the rods, and
individual webs of the stent portion may pass through the holes to
retain the rods. The rods 14 may extend the full length of the cage
12, or preferably from the second end 32 of the cage to the upper
end of the stent portion 38. The stiffening rods 14 can be made
from any biocompatible material such as stainless steel, cobalt
chromium alloys, tantalum, zirconium alloys, titanium or titanium
alloys, particularly beta titanium alloys. The stiffening rods 14
can also be made from non-metal biocompatible materials such as
PEEK, Acetal, bioabsorbable materials, ceramics and biocomposites.
Each stiffening rod 14 is sufficiently flexible to temporarily bend
as the device (in a contracted state) is introduced into the
intramedullary canal. Additionally, the rods may be knurled,
threaded or otherwise treated to provide adhesion and
interdigitation of the matrix and cage. Once the device 10 is
inserted and expanded radially, the rods 14 are aligned parallel to
the longitudinal axis of the bone and line the inner surface of the
canal, within the cage and matrix of the device.
[0049] The ratio of longitudinal contraction to radial expansion of
the composite device 10 varies depending upon the configuration of
the stent portion of the cage, the length of the linkages, and the
length and placement of the rods. Some embodiments have a low
ratio, in which a small decrease in the length of the cage results
in a large increase in the radial expansion (as measured by change
in the core diameter 20). Other embodiments have a 1:1 ratio (a
contraction in cage length results in an equal measurement of
radial expansion), or a higher ratio, in which a large decrease in
longitudinal contraction produces a small increase in radial
expansion. The choice of embodiment will depend upon factors such
as the length and diameter of the particular bone to be fixed,
accessibility to the bone, and severity of the fracture, among
others.
[0050] Referring to FIG. 6, the thermoplastic matrix 16 may be
thermo-chemically activated, and may surround the support structure
11 of FIG. 2, or the support structure of any of the embodiments
described below. The matrix 16 comprises a material which has
physical properties that change between a first and second state.
For example, the material may be flexible and deformable at a first
state and hard and more rigid at a second state. This can be
accomplished by changing factors such as the molecular structure of
chemical components of the matrix 16 from one state to another.
Methods of changing the molecular structure of a material, and thus
the physical properties of the material, include changing the
temperature of the material, exposing the material to gamma
radiation and altering the crosslinking bonds between molecular
chains in the material, exposing the material to ultraviolet
radiation causing the material to cure and harden, exposing the
material to a second material allowing cross-linking and molecular
bonding, allowing the material to harden over time by increasing
the crystallinity within the molecular structure, and other methods
that alter the bonding between the molecules in the matrix 16
material and correspondingly alter its material properties.
[0051] The matrix 16 may comprise a thermoplastic biocompatible
polymer or polymer blend comprising polymers such as polylactic
acid (PLA), poly .epsilon.-caprolactone (PCL), trimethylene
carbonate (TMC), polyglycolic acid (PGA), poly-lactic acid (PLLA),
poly d-l-lactide (PDLLA), poly-D,L-lactic acid-polyethyleneglycol
(PLA-PEG) or other biocompatible polymers. Each of these polymers
has a glass transition temperature T.sub.g such that when raised to
a temperature above its T.sub.g, the polymer is rubbery, flexible
and deformable. When lowered to a temperature below its T.sub.g,
the polymer is crystallized and substantially rigid. Each of these
polymers or blends is capable of being transformed by the
application of energy to a first thermo-chemical state, in which it
is at a temperature above its glass transition temperature T.sub.g.
When, through dissipation of energy, the temperature is reduced to
below T.sub.g, the polymer or blend is at a second thermo-chemical
state. These thermoplastic properties of the polymers allow them to
be repetitively heated to above T.sub.g, and subsequently cooled to
below T.sub.g, moving repeatedly between the first and second
thermo-chemical states.
[0052] Preferred polymers have a glass transition temperature
T.sub.g that is above body temperature, but below the temperature
known to cause thermal necrosis of tissues. A preferred blend is
crystallized and substantially rigid at human body temperature, and
has a T.sub.g which ranges from about 10.degree. C. above body
temperature to about 35.degree. C. above body temperature. This
acceptable T.sub.g range is between about 50.degree. C. and about
80.degree. C., and preferably between about 55.degree. and about
65.degree. C. Preferably, the thermoplastic matrix 16 comprises a
blend of polymers such as PCL and PLA, or PCL and PGA. Table 1
displays the melting points (T.sub.m), glass transition
temperatures (T.sub.g) and thermal decomposition temperatures
(T.sub.dec) of selected synthetic absorbable polymers.
TABLE-US-00001 TABLE 1 Melting, glass transition and thermal
decomposition temperatures of selected synthetic absorbable
polymers. Polymer T.sub.m (.degree. C.) T.sub.g (.degree. C.)
T.sub.dec (.degree. C.) PGA 230 36 260 PLLA 170 56 240 PLA -- 57 --
PCL 60 -62 -- Polyglactin910 200 40 250 Polydioxanone 106 <20
190 Polyglyconate 213 <20 260
[0053] Additional biocompatible polymers which may be included in
the matrix 16, individually or in a blend, comprise aliphatic
polyesters including polyglycolide, poly(dl-lactide),
poly(l-lactide), poly(6-valerolactone), polyhydroxybutyrate;
polyanhydrides including poly[bis(p-carboxyphenoxy) propane
anhydride], poly(carboxy phenoxyacetic acid), poly(carboxy
pheoxyvaleric acid); polyphosphazenes including aryloxyphosphazene
polymer and amino acid esters; poly (ortho esters);
poly(p-dioxane); poly(amino acids) including poly(glutamic
acid-co-glutamate); erodable hydrogels; and natural polymers
including collagen (protein) and chitosan (polysaccharide).
[0054] The thermoplastic matrix 16 may further include at least one
bioactive material to promote growth of bone material and
accelerate healing of fractures. These bioactive materials include
but are not limited to hydroxylapatite, tetracalcium phosphate,
.beta.-tricalcium phosphate, fluorapatite, magnesium whitlockite,
.beta.-whitlockite, apatite/wollastonite glass ceramic, calcium
phosphate particle reinforced polyethylene, bioactive glasses,
bioactive glass ceramics, polycrystalline glass ceramics, and
polyethylene hydroxylapatite.
[0055] The support structure 11 may be embedded in the
thermoplastic matrix 16 through insert molding, pulltrusion, by
dipping the support structure into the thermoplastic matrix
material while it is at a temperature above T.sub.g, or by other
coating methods. A variety of different methods may alternatively
be used to assemble the thermoplastic matrix 16 and the support
structure 11.
[0056] Referring to FIG. 7, a longitudinal cross-section of a bone
illustrates implantation of an intramedullary bone fixation
composite device 710. The method illustrated in FIG. 7 may also be
used for implantation of composite device 10 and other devices
according to alternative embodiments. Composite device 710
comprises a support structure 711 and a thermo-chemically activated
thermoplastic matrix 716. The support structure 711 comprises a
stent-like cage 712 (not shown) and a plurality of rods 714 (not
shown).
[0057] A percutaneous portal 60 is created into the intramedullary
canal 2, preferably in the proximal or distal metaphysial region of
the bone. The opening may not be parallel to the longitudinal axis
of the bone; it may be transverse or at an acute angle relative to
the longitudinal axis of the bone. If necessary to open the canal
space and prepare it for the implant, the canal is evacuated using
a sequence of pulse lavage, brushing, and suction. A delivery tube
62 may be advanced into the percutaneous portal 60. The composite
device 710, in a lengthened and contracted state, is heated
immediately prior to implantation to a first thermo-chemical state,
so that the thermoplastic matrix 716 is above its glass transition
temperature and is therefore plastic and rubbery enough to be
flexed as it is introduced through the percutaneous portal and into
the intramedullary canal. Heating of the composite device 710 to
reach the first thermo-chemical state may be accomplished by means
including soaking the implant in a hot saline bath, application of
ultrasonic vibratory energy, application of radiant heat energy,
use of a local radiation emitter (including ultraviolet, visible
light, and/or microwave energy), use of a laser energy emitter, use
of inductive heat energy, electrical resistive heating of the cage
or the delivery instrument, or heating of an expansion apparatus,
among others.
[0058] The composite device 710 is inserted into the delivery tube
62, pushed through the tube and advanced into the intramedullary
canal 2 until the composite device 710 is contained within the
confines of the canal. Optionally, the composite device 710 may be
inserted directly through the percutaneous portal 60 without
passing through a delivery tube 62. A portion of the composite
device 710 may be surrounded by a protective sheath 749, which is
positioned so that it covers the device 710 at the point of the
bone fracture. The device 710 is then expanded radially. As the
support structure 711 expands, the stiffening rods 714, the cage
712 and thermoplastic matrix 716 move radially outward and are
eventually aligned along the wall of the intramedullary canal,
parallel to the longitudinal axis of the bone. The composite device
710 is allowed to cool to below the low glass transition
temperature T.sub.g, thus attaining the second thermo-chemical
state, and the matrix 716 crystallizes. As the matrix crystallizes
it conforms to the shape of the surrounding intramedullary canal,
and the cage 712 and stiffening rods 714 are fixed in the
thermoplastic matrix 716 along the wall of the canal. The shape of
the intramedullary canal can vary along the length of the bone,
with the canal being generally circular in the diaphysial region
near the midpoint of the bone and irregular in the metaphysial
regions near the ends of the bone. Although the thermoplastic
matrix 716 is in a generally tubular shape as the composite device
710 is inserted, the thermoplastic qualities of the matrix allow it
to conform to the shape of the intramedullary canal around it, and
it crystallizes in that shape, thus providing torsional strength
and support to the surrounding bone. The ability of the
thermoplastic matrix 716 to conform to the irregularities in the
intramedullary canal allows the device 710, and the stabilized
bone, to withstand greater torsional forces than would a device
with a constant circular shape which did not conform to the
canal.
[0059] Deformation and/or radial expansion and of the composite
device 710 to conform to the intramedullary canal can be
accomplished in several ways. A deformation apparatus (such as
those shown in FIGS. 16 and 17) may be introduced into the central
core of the composite device 710 before or after it has been
inserted into the intramedullary canal. The deformation apparatus
is expanded, and forces expansion of the composite device 710 until
it fills the confines of the canal. The deformation apparatus may
comprise a heat source to raise the temperature of the
thermoplastic matrix 716. Alternatively, the cage 712 may be
constructed with an outward spring bias, introduced into the
intramedullary canal and allowed to expand. In another embodiment
which is described in detail below, a balloon apparatus (such as
that shown in FIG. 17) is introduced into the central core of the
composite device 710. As the balloon is inflated with heated gas or
liquid, it expands, and consequently induces expansion of the
composite device 710. Once the device is expanded, the balloon can
be deflated and removed. It is appreciated that these deformation
and expansion techniques and apparatuses may also be employed with
composite device 10 and other embodiments of intramedullary bone
fixation devices disclosed herein.
[0060] Referring to FIG. 8, a longitudinal cross-section shows two
composite devices 710, 750 implanted in a bone. Deploying two bone
fixation devices nested in this manner may provide additional
strength, rigidity and resistance to torsion than would be
available from one bone fixation device. Twice the thermoplastic
matrix material and twice the support structure are present to
provide additional stabilization.
[0061] Composite device 750 comprises a thermoplastic matrix 756,
which surrounds a support structure which includes a cage 752 and a
plurality of rods 754. The configuration of matrix 756, cage 752
and rods 754 may be identical to that of composite device 710.
Prior to implantation, the composite device 750 is partially
radially expanded. The composite device 710 is contracted, and slid
into a hollow central core 758 of the composite device 750.
Together, the two devices 710, 750 are heated until the
thermoplastic matrices 716, 756 reach the first thermo-chemical
state. The two devices 710, 750 are introduced as a unit into the
intramedullary canal. The inner disposed composite device 710 is
expanded using one of the techniques previously described. As the
inner composite device 710 expands, it pushes radially against the
outer disposed composite device 750, forcing it to expand radially
until it contacts and conforms to the wall of the surrounding
intramedullary canal.
[0062] Alternatively, composite devices 710, 750 may be introduced
individually into the intramedullary canal. Composite device 750
may be introduced first, heated and expanded. Composite device 710
is then introduced into the hollow central core 758 of composite
device 750 after is it in the intramedullary canal. After both
devices 710, 750 are in the canal, composite device 710 is heated
and expanded, pushing radially against the outer composite device
750.
[0063] The thermoplastic matrix 716 surrounding the composite
device 710 may contact and conform to the thermoplastic matrix 758
of the composite device 750. The two devices 710, 750 are allowed
to cool to the second thermo-chemical state and harden.
[0064] Referring to FIGS. 9A-9C, three cross-sectional views along
different parts of the bone depicted in FIG. 8 are shown, with
devices 710, 750 implanted in the intramedullary canal. In FIG. 9A,
the intramedullary canal 2 is relatively wide and circular in
shape, resulting in a wide, circular central hollow core 718. Also,
the thermoplastic matrices 716, 756 are relatively thin, and the
rods 714, 754 are spaced relatively far apart, as the devices 710,
750 had to expand radially farther to contact the wall of the
intramedullary canal at that point. As seen in FIG. 9B, at this
point along the bone the intramedullary canal is smaller in
diameter and more irregular in shape. The thermoplasticity of the
matrices 716, 756 allows the devices 710, 750 to match the size and
shape of the canal. As seen in FIG. 9C, at this point along the
bone the intramedullary canal is narrow in cross-section and
substantially triangular in shape. According, the thermoplastic
matrices 716, 756 are thicker and the rods 714, 754 are closer
together, since the devices 710, 750 are relatively less
expanded.
[0065] Referring to FIG. 10, an alternative embodiment of an
intramedullary bone fixation composite device is shown in a cutaway
view. Composite device 810 comprises support structure 811 and a
thermo-chemically activated thermoplastic matrix 816. Support
structure 811 comprises a cage 812, a plurality of rods 814, and a
plurality of sutures 815 which connect the cage to the rods. The
thermo-chemically activated matrix 816 surrounds the cage 812, rods
814 and sutures 815 such that they are embedded in the matrix. The
sutures 815 are interwoven around and between the cage 812 and the
rods 814 to connect the cage 812 to the rods 814 in a manner that
allows regulated movement of the cage 812 and the rods 814 relative
to one another.
[0066] Alternately, the sutures may be knit into a sleeve that
holds the array of rods and surrounds the cage. The interweaving
may be constructed in such a way as to allow radial expansion of
the cage 812 and the rods 814 from a contracted position in which
the cage 812 is lengthened and the rods 814 are tightly packed
together, to an expanded position in which the cage 812 is
shortened, radially expanded and the rods 814 are arrayed around
the cage with relatively more space between each rod. The cage 812
may comprise web-like stent material similar to stents depicted in
FIGS. 3A-3I, or may comprise another woven or laser cut stent-like
material. The rods 814 may be similar to the rods 14 depicted in
FIG. 5. The thermo-chemically activated thermoplastic matrix 816
may be similar to the thermo-chemically activated thermoplastic
matrix 16 described previously and depicted in FIG. 6. The sutures
may comprise any of several commercially available sutures,
including Dyneema Purity) Ultra High Molecular Weight Polyethylene
(UHMWPE), or bioabsorbable multifilament polylactic acid (PLA)
sutures such as PANACRL.TM., among others.
[0067] Composite device 810 may be introduced into the
intramedullary canal in the same manner as previously described for
composite device 710. Energy is applied to composite device 810,
heating it until the thermo-chemically activated matrix 816 reaches
the first thermo-chemical state, and is flexible and rubbery. The
composite device 810 is contracted so that it is sufficiently
flexible to be inserted into the intramedullary canal through an
opening in the bone, an opening which may not be parallel to the
intramedullary canal. The composite device 810 is inserted into the
canal and expanded by one of the expansion methods previously
described. When the device is expanded within the intramedullary
canal, the thermo-chemically activated matrix 816 contacts and is
conformed to the walls of the intramedullary canal. The device 810
is allowed to cool and the thermo-chemically activated matrix 816
attains the second thermo-chemical state, and hardens sufficiently
to fix the support structure 811 in its expanded position within
the intramedullary canal.
[0068] Referring to FIGS. 11A-11E, a series of five cross-sectional
views illustrate the expansion of composite device 810 from a
contracted position to a fully expanded position. Beginning with
FIG. 11A, a hollow central core 818 of composite device 810 is
substantially circular. As composite device 810 expands, the cage
812 and the hollow central core 818 increase in diameter and the
thermoplastic matrix 816 stretches to fit around the cage 812. At
the most expanded state illustrated in FIG. 11E, the thermoplastic
matrix 816 is substantially thinner than at the most contracted
state. In FIG. 11A, the array of rods 814 are relatively closely
packed near one another; in FIG. 11E they are spread apart and are
substantially equidistantly arrayed about the hollow central core
818.
[0069] FIGS. 12A-12E illustrate an alternative embodiment of a
composite device in five cross-sectional views. Similar to
composite device 810, composite device 910 comprises a support
structure 911 with a cage 912, a plurality of rods 914, and a
plurality of sutures 915 which connect the cage to the rods. A
thermo-chemically activated thermoplastic matrix 916 surrounds the
cage 912, rods 914 and sutures 915 such that they are embedded in
the matrix. As most clearly seen in FIG. 12C, in this embodiment,
the thermoplastic matrix 916 is configured in a series of folds
917, as compared to the circular configuration seen for
thermoplastic matrix 816 in FIG. 11C. The folded configuration of
the thermoplastic matrix 916 results in a star-shaped hollow
central core 918. The star-shaped hollow central core 918 is
smaller in terms of cross-sectional open space, as much of the
space is taken up by the folds of the thermoplastic matrix 916.
Therefore, the thermoplastic matrix 916 is thicker in this
embodiment than in other embodiments such as device 810. Thus, as
seen in FIG. 12E, the fully expanded composite device 910 has a
thicker thermoplastic matrix, which may result in additional
support for the surrounding bone during the healing process.
[0070] Composite device 910 may be introduced into the
intramedullary canal in the same manner as previously described for
composite devices 710 and 810. Energy is applied to composite
device 910, heating it until the thermo-chemically activated matrix
916 reaches the first thermo-chemical state, and is flexible and
rubbery. The composite device 910 is contracted into the deeply
folded position seen in FIG. 12A, so that it is sufficiently
flexible to be inserted into the intramedullary canal through an
opening in the bone. The composite device 910 is inserted into the
canal and expanded by one of the expansion methods previously
described. A specifically configured implant expander such as a
star-shaped balloon expansion device (not shown) may be used to
expand the device 910. When the device is expanded within the
intramedullary canal, the thermo-chemically activated matrix 916
contacts and is conformed to the walls of the intramedullary canal.
The device 910 is allowed to cool and the thermo-chemically
activated matrix 916 attains the second thermo-chemical state, and
hardens sufficiently to fix the cage 912 and rods 914 in their
expanded positions within the intramedullary canal. In the case of
a larger bone, two composite devices 910 may be deployed, one
inside the other, to provide additional support to the bone.
[0071] Referring to FIGS. 13A and 13B, one alternative embodiment
of a support structure 71 suitable for use in an intramedullary
bone fixation device has an hourglass shape. In the context of the
present invention, an hourglass shape is a generally longitudinal,
columnar shape in which the two end portions of the column are
wider in diameter than a middle portion of the column. The support
structure 71 comprises a cage 72 and rods 14. In this embodiment,
the diameters of cage ends 74, 76 are greater than the diameter of
a cage sleeve 78. In order to clearly view the configuration of
cage and rods, a thermoplastic matrix is not shown. A matrix
similar to that of the thermoplastic matrix 16 of FIG. 1 may be
used in conjunction with support structure 71, or it may have a
different configuration. The hourglass shape enables the tubular
support structure 71 to conform to the contours of the
intramedullary canal of a long bone, in which the metaphysial
regions at the ends of the bone are irregular and may be greater in
diameter than the diaphysial region near the midpoint of the bone.
In the embodiment depicted, the hourglass shape is achieved by the
particular threading of the rods within the stent portion of the
cage. At the first 74 and second 76 ends, the rods 14 are contained
within the confines of the cage 72; toward the center of the sleeve
78, the cage is contained within the circle of the rods 14. In FIG.
13A, the support structure 71 is shown in the contracted state (for
insertion or removal); in FIG. 13B, the expanded state is shown.
The support structure 71 may be inserted in the same manner as
described previous for support structure 11, and the same expansion
methods described previously may be used to expand the support
structure 71.
[0072] One alternative embodiment of an intramedullary bone
fixation device (not shown) comprises a laser-cut cage which is
constructed with an outward spring bias. In this embodiment, the
device is compressed prior to implantation by holding the rods
steady and pulling longitudinally on the cage. The web-like
configuration of the cage permits the cage to lengthen while
simultaneously its core diameter contracts, enabling the device to
be narrow and flexible enough for insertion. The device is
introduced into the intramedullary canal and the cage is released.
Upon release, the outward spring bias of the cage causes the cage
to expand radially and simultaneously shorten. Radial expansion
continues until the outer perimeter of the device contacts the
inner wall of the intramedullary canal. The web-like configuration
of the cage also allows it to conform to variations in the geometry
of the intramedullary canal. This embodiment may also include the
thermoplastic matrix, wherein prior to the compression step
described above, the thermoplastic matrix is heated to the first
thermo-chemical state, so it is flexible as the device is
compressed, inserted and expanded. After insertion and radial
expansion, the energy is allowed to dissipate and the thermoplastic
matrix attains the hardened second thermo-chemical state.
[0073] Referring to FIGS. 14A through 14D, another alternative
embodiment of the invention comprises a cage with an outward spring
bias, which may be used in conjunction with a thermoplastic matrix
such as that depicted in FIGS. 1 and 6. FIG. 14A is a perspective
view of a cage 112, cut with a plurality of accordion-type folds
114 which unfold as the cage expands radially. Alternating with the
folds 114 are longitudinal ribs 1 16, and a hollow central core I 1
5 extends the length of the cage 1 12. Each rib 1 16 has a
longitudinal channel 1 18 which may hold a stiffening rod. The cage
may be laser-cut or machined from metal, or may comprise a plastic
material or a thermo-chemically activated thermoplastic matrix
material, as described above. The cage 112 may have a straight
shape with a constant diameter, or may have an hourglass shape in
which the two ends are wider than the central section. Other shapes
may alternatively be used for different bone morphologies.
[0074] FIG. 14B is an end view of the cage 112 in a compressed
state, showing the tight compaction of the folds 114 and ribs 116.
FIG. 14C is a perspective view of the cage 112 after radial
expansion, and FIG. 14D is an end view of the expanded cage 112. In
this embodiment, the support structure can be compressed for
implantation by a binding material which is wrapped or tied around
the compressed cage. After insertion into the intramedullary canal,
the cage is released by cutting or removal of the binding material.
Once released, the outward spring bias of the cage 112 causes the
cage 112 to expand radially in the same manner as described for the
previous embodiment.
[0075] In another embodiment the support structure may be
monolithic; that is, formed as a single unit. The cage and rods are
formed together, such as by a machining process and remain
connected together. Referring to FIG. 15, an embodiment of a
monolithic support structure 11 1 is shown in an expanded state.
This embodiment has no channels for rods, but consequently has ribs
117 between the accordion folds 114 which are solid and comprise
more material, thus providing rigidity similar to the rods of other
embodiments. Between the ribs 117, the accordion folds 114 have a
plurality of slots 119. The slots 119 allow for less material and
thus more flexibility of the support structure when compressed.
Additionally, when compressed, the tight packing of the ribs 117
between the accordion folds 114 allows the support structure 111 to
flex sufficiently for insertion into the intramedullary canal. The
monolithic support structure 111 may be used in conjunction with a
thermoplastic matrix. Contraction, insertion and expansion of the
monolithic support structure 111 may be in the same manner as
described previously for the cage 112.
[0076] In another embodiment of the invention, at least two support
structures and/or cages such as those depicted in FIGS. 14 and 15
can be nested, one within the other. A first support structure 111
or cage 112 embedded in the thermoplastic matrix 16 is heated to
the first thermo-chemical state, compressed, inserted into the
intramedullary canal, and expanded. A second support structure 111
or cage 112 embedded in the thermoplastic matrix 16 is similarly
compressed and inserted into the central core 115 of the first
support structure. When the second structure 111 or cage 112
expands, it pushes radially against the first structure 111 or cage
112. As described previously for other embodiments, the
thermoplastic matrix 16 surrounding the first support structure
conforms to the contours of the intramedullary canal. Within the
first support structure, the thermoplastic matrix 16 surrounding
the second support structure conforms to the surrounding first
support structure. The matrix material surrounding both the first
and second structures cools to the second thermo-chemical state and
crystallizes. This double layer of matrix material and support
structures provides enhanced support and rigidity to the
surrounding bone.
[0077] The cage 112 and support structure 111 embodiments depicted
in FIGS. 14 and 15 can alternatively be constructed without an
outward spring bias. The compressed cage 112 or support structure
111 may be surrounded by the thermoplastic matrix 16. As described
previously, the device is heated so the thermo-plastic matrix 16
reaches the first thermo-chemical state and the device is flexed
and inserted into the intramedullary canal. In this case, an
expansion apparatus or balloon mechanism as previously described,
or other expansion mechanism is inserted into the central core 115
and used to expand the device after it is implanted. Once the
device is expanded, energy dissipates into the surrounding tissue,
the matrix attains the second thermo-chemical state, and the cage
112 or support structure 111 is fixed within the cooled,
crystallized matrix 16. The expansion apparatus, balloon mechanism,
or other expansion mechanism may then be removed from the central
core 115.
[0078] One alternative embodiment of an intramedullary bone
fixation composite device (not shown) comprises a thermoplastic
matrix which is not continuous along the entire length of the
corresponding cage or support structure. In this embodiment, the
matrix comprises at least two separate tube-like portions, each of
which surrounds one end of the cage or support structure and
extends partway along the sleeve. This discontinuous configuration
of the matrix contributes to an hourglass shape and allows less
matrix material to be used. This matrix configuration can be used
with either a cage with an outward spring bias, or with a cage with
no outward spring bias.
[0079] Another alternative embodiment of an intramedullary bone
fixation composite device (not shown) comprises a support structure
which comprises at least one rod, and no cage. Prior to
implantation, the matrix is heated to the first thermo-chemical
state and formed into a tubular shape around the rods, which are
subsequently embedded in the matrix. The device is flexed and
inserted into the patient. While the matrix is still in the first
thermo-chemical state, an expansion apparatus or balloon is
inserted into the center of the tubular device and used to expand
the device within the intramedullary canal. As the device expands,
the rods and the matrix material are pushed radially to the inner
wall of the intramedullary canal. After expansion, the device is
allowed to cool to the second thermo-chemical state, and the matrix
hardens, fixing the rods in their positions around the inner wall
of the canal.
[0080] Another alternative embodiment of an intramedullary bone
fixation device (not shown) comprises a support structure which
comprises a cage manufactured of the thermoplastic matrix material,
and rods. During manufacture the matrix material is heated above
its T.sub.g and extruded into a cage-like form. During or after
extrusion the rods are interwoven, braided in, or otherwise
attached as described previously. To implant the device, the device
is heated above the T.sub.g of the matrix to attain the first
thermo-chemical state, contracted, flexed, inserted and expanded as
described previously.
[0081] FIGS. 16A and 16B illustrate an implant expansion device
which may be used to deform and expand several of the
intramedullary bone fixation devices described previously, such as
composite device 10, composite devices 710, 750 and 810, a device
incorporating support structure 71, or other devices which
incorporate a cage or support structure without an outward spring
bias. A mechanical expansion apparatus 500 is longitudinally
insertable into the central core of the intramedullary bone
fixation device. As seen in FIG. 16A, the mechanical expansion
apparatus 500 has a shaft 514, which extends from a first end 510
to a second end 512. An adjustment nut 516 is threaded onto a
threaded portion 515 of the shaft 514, adjacent the first end 510.
A cone-shaped first expander guide 518 is also threaded onto the
threaded portion 515 of the shaft 514, on the opposite side of the
adjustment nut 516 from the first end 510. The second end 512 of
the shaft 514 terminates in a cone-shaped second expander guide
519. The shaft 514 comprises a metallic material, and is
sufficiently thin and flexible to be inserted into the central core
of an intramedullary bone fixation while the device is in the
intramedullary canal of a bone in a patient.
[0082] Referring to FIG. 16B, strung on the central shaft 514 and
listed in their order of occurrence from the first expander guide
518 to the second expander guide 519 are: a first expander segment
520, a plurality of core segments 522, a central segment 524,
another plurality of core segments 522, and a second expander
segment 526. The core segments 522 and the central segment 524
comprise a relatively rigid material, while the expander segments
520, 526 comprise a relatively rubbery, flexible material. The
first expander segment 520 surrounds a portion of the first
expander guide 518 in a sleeve-like manner, and the second expander
segment 526 similarly surrounds a portion of the second expander
guide 519 in a sleeve-like manner. The core segments 522, central
segment 524, and expander segments 520, 526 are initially placed
loosely on the shaft 514 with space between each segment, so that
the apparatus can flex while being inserted into the central core
of the intramedullary bone fixation device.
[0083] After the intramedullary bone fixation device with a
thermoplastic matrix (not shown) is placed in the intramedullary
canal, the mechanical expansion apparatus 500 may be inserted
through the delivery tube 62 (not shown) into the central core of
the intramedullary bone fixation device. Then the adjustment nut
516 is turned, forcing the first expander guide 518 to advance
along the shaft 514 toward the second expander guide 519 at the
second end 512. The first expander segment 520, core segments 522,
central segment 524, and second expander segment 526 are compressed
together as they are held between the first and second expander
guides 518, 519. The rubbery, flexible expander segments 520, 526
expand radially as they are forced farther onto the cone-shaped
expander guides 518, 519. As the expander segments 520, 526 expand
radially, they push the ends of the surrounding intramedullary bone
fixation device outward radially, thus matching the generally
hourglass shape of the intramedullary canal. Expansion is ceased
when the outer perimeter of the intramedullary bone fixation device
contacts the inner walls of the intramedullary canal. The expansion
apparatus 500 may be kept in the central core of the intramedullary
bone fixation device until the thermoplastic matrix cools to the
second thermo-chemical state. The expansion apparatus 500 is
contracted by turning the adjustment nut 516 in the opposite
direction, and the apparatus 500 is then removed from the central
core.
[0084] The expansion apparatus 500 may optionally include a heating
element. In this configuration, it can heat the thermoplastic
matrix of an intramedullary bone fixation device while in a
patient, in order to adjust the conformity of the matrix within the
intramedullary canal.
[0085] Referring to FIGS. 17-21, an alternative method to deform
and expand an intramedullary bone fixation device comprises an
implant deformer which is a balloon expansion apparatus. As seen in
FIG. 17, a balloon expansion apparatus 600 configured to fit within
a composite device 10 in the intramedullary canal of a bone
comprises an elastic bladder 602 with an opening 604. A set of
flexible hoses comprising an input hose 606 and an output hose 608
are configured to extend from a regulator apparatus 610, through
the opening 604 and into the elastic bladder 602. The regulator
apparatus 610 is external to the patient, and comprises a pump to
regulate flow, and a temperature regulator to regulate the
temperature, of liquid which can flow into and out of the elastic
bladder 602. FIG. 17 depicts the hoses adjacent and parallel to one
another; however they may be configured in alternative
arrangements, including a concentric arrangement in which one hose
surrounds the other. The hoses 606, 608 terminate at differing
positions within the bladder 602.
[0086] Referring to FIG. 18, a composite device 710 with a balloon
expansion apparatus 600 already inserted into the central core 718
is introduced into the intramedullary canal of a bone. Introduction
into the bone can be through the method described previously, in
which the composite device (with the balloon apparatus in the
central core) is heated so that the matrix attains the first
thermo-chemical state. The composite device 710 plus balloon
apparatus 600 are flexed and introduced into the intramedullary
canal through the percutaneous portal 60. A delivery tube 62 (not
shown) may optionally be used during the introduction and expansion
procedures. The input 606 and output 608 hoses are inserted through
the balloon opening 604 ideally before the composite device 710
plus balloon apparatus 600 are introduced into the intramedullary
canal, but can optionally be inserted into the balloon opening 604
after introduction into the intramedullary canal. A protective
sheath 49 may surround the composite device 710 at the location of
the bone fracture.
[0087] Referring to FIG. 19, after the composite device 10 plus
balloon apparatus 600 are within the intramedullary canal,
inflation of the bladder 602 may begin. The external regulator
apparatus 610 (not shown) pumps heated liquid such as water or
saline solution, among others, through the input hose 606 into the
elastic bladder 602. The heat of the liquid maintains the
thermoplastic matrix 716 of the composite device 710 at the
deformable first thermo-chemical state. As the heated liquid fills
the bladder 602, the bladder expands. Contained within the
composite device 710, the bladder 602 eventually pushes outward,
inducing radial expansion of the composite device 710. As described
previously, cage and rod components of the support structure 711
are connected in a web-like construction which allows them to
expand radially. The thermoplastic matrix 716 surrounding the
support structure 711 is at the heated first thermo-chemical state
and is pushed radially by the expanding support structure,
conforming to the surrounding intramedullary canal walls. The
flexible, rubbery character of the matrix allows it to fit into the
natural morphological variations in the wall of the intramedullary
canal. A mesh-like end cap 746 on a second end 732 of the composite
device 710 prevents the elastic bladder 602 from escaping or
ballooning out of the second end 732. The output hose 608, which
terminates at a location different from that of the input hose 606,
allows liquid to flow out of the balloon apparatus 600. The
regulator apparatus 610 maintains the flow, temperature and
pressure of the liquid.
[0088] FIGS. 20A-20C display cross-sections of the bone and the
composite device 710 at three different locations along the length
of the bone shown in FIG. 19. At cross-section A-A in FIG. 20A, the
cross-sectional shape of the intramedullary canal is relatively
circular. The device 710 has expanded to the wall of the canal, the
matrix 716 is relatively thin, and the rods 714 are spaced
relatively far apart. At cross-section B-B in FIG. 20B, the canal
is smaller and more rectangular in shape than at cross-section A-A.
However, the deformable nature of the matrix 716 allows the matrix
and the entire composite device 710 to expand differentially and
conform to this variation in shape of the intramedullary canal. At
cross-section C-C in FIG. 20C, the cross-sectional shape of the
intramedullary canal is relatively smaller, and has a triangle-like
shape. Again, the matrix 716 and the composite device 710 can
conform to this irregular shape. The rods 714 are relatively closer
together and the matrix 716 is relatively thicker. The ability of
the composite device 710 to closely conform to the confines of the
intramedullary canal allows the device to withstand greater
torsional forces than would a device with a constant circular shape
which did not conform to the canal.
[0089] Referring to FIG. 21, the balloon expansion apparatus 600 is
depicted being withdrawn from the composite device 710. After
expansion of the elastic bladder 602 is accomplished as described
previously, the liquid in the elastic bladder 602 may be cooled by
pumping cool liquid in through input hose 606 and withdrawing
warmer liquid through output hose 608 until a consistently cooler
liquid is in the bladder 602. The cooler liquid in the bladder
absorbs thermal energy from the matrix 716, allowing it to cool and
transform from the flexible first thermo-chemical state to the
hardened second thermo-chemical state. Once the composite device
710 has thus cooled and hardened, the remaining liquid may be
pumped out of the elastic bladder 602, and the balloon expansion
device 600 is pulled out of composite device 710 through the
percutaneous portal 60.
[0090] A protective, tubular insertion sheath (not pictured) may
surround all or a portion of any of the above-described
intramedullary bone fixation devices during the implantation
procedure, and may optionally be removed following implantation.
The insertion sheath may be very thin, and may prevent portions of
the support structure or matrix from snagging on or scratching the
intramedullary canal, or portions of the fractured bone. Once the
device is inserted, the sheath may be removed by being pulling the
sheath out through the delivery tube, while leaving the device
behind.
[0091] With any embodiment of the device, after insertion of the
device but before conclusion of the implantation procedure, x-ray,
fluoroscopy, or other radiographic methods may be implemented to
assess the alignment of the device relative to the bone. If
alignment is unsatisfactory, a heating element (not shown) or a
heatable expansion device such as the balloon apparatus 600 or
mechanical expansion apparatus 500 as described previously may be
introduced into the central core. The device is heated so the
thermoplastic matrix again reaches first thermo-chemical state, and
the device may then be removed and reinserted or otherwise adjusted
until a satisfactory alignment is achieved. The device is allowed
to cool, so the thermoplastic matrix returns to the second
thermo-chemical state through the natural dissipation of energy
into the surrounding tissue.
[0092] Post-implantation, the device may be removed if desired. The
method of removal will vary, depending on the state of the
decomposition of the biocompatible thermoplastic matrix. If the
thermoplastic matrix is still intact, a percutaneous portal may be
opened and a tube may be inserted. The tube may be the same as or
similar to the delivery tube 62 described previously. A heating
element or heatable expansion apparatus such as the mechanical
expansion apparatus 500 or balloon expansion apparatus 600 is
introduced into the central core, and the device is heated until
the matrix reaches the first thermo-chemical state, above the glass
transition temperature. The heat source is removed; the device may
be contracted by holding the rods steady and pulling longitudinally
on the cage. The device may be removed through the delivery tube,
or directly through the percutaneous portal. If the thermoplastic
matrix has been sufficiently absorbed so that it is no longer
intact, no heating is required; the device is contracted and
removed.
[0093] Another embodiment of the invention (not shown) comprises a
support structure and an alternative form of the thermoplastic
matrix, comprising an injectable form of a synthetic biodegradable
polymer, poly-D,L-lactic acid-polyethyleneglycol (PLA-PEG). This
biodegradable composite is temperature-sensitive so that when it is
heated it takes on a liquid, semi-solid form and following
injection, cools and becomes semi-solid. A structure such as
support structure 11, 711, 811 or 71 is introduced into the
intramedullary canal. The structure may have a protective sheath
surrounding the portion of the structure which will be adjacent to
the fracture location. Following insertion of the support structure
into the intramedullary canal, and radial expansion of the support
structure, heated PLA-PEG is injected through a flexible tube or
catheter which is inserted through the delivery tube 62 into the
central core. The liquid PLA-PEG flows through the web-like support
structure, filling the canal and surrounding the support structure.
The protective sheath prevents the PLA-PEG from contacting the
fractured area of the bone. The PLA-PEG is allowed to cool and
harden, and provides rigid support around the structure.
[0094] Referring to FIG. 22A, a perspective view shows another
embodiment of the invention, comprising a telescoping
intramedullary fixation device 210. This device comprises a central
wire 212 surrounded by a series of five tubular nesting components
213-217. Each tubular nesting component is substantially the length
of the entire device 210 when all components are nested together,
and each successive nesting component is slightly wider in diameter
than the component it surrounds. Other embodiments of the
telescoping intramedullary fixation device 210 may have fewer, or
more, than five nesting components. The central wire 212 may have a
solid core and may not be tubular, but is slender and thus
sufficiently flexible to be inserted into the intramedullary canal.
The nesting components 213-217 may comprise metal, a biocompatible
polymer material, or a mesh-like stent material (such as those
depicted in FIG. 3), and may be embedded in a thermoplastic matrix
material. FIG. 22A displays the telescoping device 210 in a fully
extended or telescoped position; however when completely implanted
in a patient the device 210 is in a collapsed position in which the
nesting components are concentrically nested together.
[0095] The first nesting component 213 surrounding the central wire
212 is slightly wider in diameter than the central wire 212. Each
successive nesting component 214-217 is slightly wider than the
preceding one, and as the nesting components increase in diameter,
the width of the wall of the component may decrease so that each
nesting component is still flexible enough to be inserted into the
canal. The wall thickness of each of the nesting components 213-217
may advantageously be selected such that the nesting components
213-217 are all nearly equally flexible. According to one
alternative embodiment (not shown), the nesting components do not
have solid walls but have slots in the walls to increase
flexibility.
[0096] In a patient, the central wire 212 may first be inserted
into the intramedullary canal. Then, successive nesting components
213-217 with increasing diameters are introduced into the
intramedullary canal. The nesting component 213 with the smallest
diameter is slid in around the central wire 212; the nesting
component 214 with the next largest diameter is slid in surrounding
the first nesting component 213, and the remaining nesting
components 215-217 are inserted in a similar fashion. The largest
nesting component 217 fits just inside the walls of the canal.
After the components are inserted and collapsed together, an
injectable, hardenable polymer such as bone cement or a
biocompatible polymer such as PLA-PEG may be introduced into the
canal to fill any spaces between the largest nesting component 217
and the wall of the canal. The largest nesting component 217 may
have a sheath 219 which prevents the polymer from accessing the
fractured area of the bone, as described previously. The nested set
of nesting components 213-217 has a combined strength and rigidity
which exceeds that of any of the individual nesting components, and
the device 210 provides strength and support during bone
healing.
[0097] FIG. 22B is an enlarged, stylized cross-sectional view of
the connection between nesting components 216 and 217; however the
figure is representative of the connections between each of the
nesting components 213-217. Nesting component 217 has a first end
230 with an inward-projecting first lip 234. The next smallest
nesting component 216 has a second end 232 with an
outward-projecting second lip 236. The projecting lips 234, 236
allow for easy removal of the apparatus. During removal, initially
a slap hammer is used to break the largest nesting component 217
away from the bone cement. Nesting component 217 is pulled out
first, and its inwardly-projecting lip 234 hooks the
outwardly-projecting lip 236 of the next largest nesting component
216, and causes it to be pulled out next, followed by the next
largest nesting component 215, until all the nesting components
213-217 are pulled out. The central wire 212 is removed separately
after all the nesting components are removed.
[0098] Referring to FIG. 23, another embodiment of a telescoping
fixation device is shown in an extended state. In this embodiment,
telescoping fixation device 310 comprises a series of nesting
components 313-317, each of which comprises a mesh-like stent
portion embedded in thermoplastic matrix material 318 similar to
that of the thermoplastic matrix 16 of FIGS. 1 and 6. Each nesting
component 313-317 is substantially the length of the entire device
310 when all components are nested together. Prior to implantation,
the device 310 is heated as described previously so that the
thermoplastic matrix material 318 reaches the first thermo-chemical
state, and is rubbery and flexible. The device 310 is telescoped
out into an extended configuration, and introduced into the
intramedullary canal through an opening transverse to the
longitudinal axis of the bone. The central wire 312 is introduced
first, and the adjacent and smallest nested component 313 is
inserted so it nests around the central wire. The next smallest
nested component 314 is nested about the smallest nested component
313, and so on until all the remaining nested components 315-317
are introduced into the intramedullary canal and nested together.
The device 310 is allowed to cool so that energy dissipates into
the surrounding tissue, and the thermoplastic matrix material 318
of each nesting component 313-317 reaches the second
thermo-chemical state, and hardens.
[0099] Referring to FIG. 24, another alternate embodiment of a
telescoping fixation device is shown, in a partially extended
state. In this embodiment, telescoping fixation device 410
comprises a series of nesting components 413-417, which are
helically threaded so that during implantation each nesting
component is threaded onto the preceding smaller component. The
direction of the threading on each nesting component may alternate,
so that each nesting component is threaded onto the next nesting
component in the opposite direction from the previous one. Each
nesting component 413-417 is substantially the length of the entire
device 410 when all components are nested together. As with devices
210 and 310, five nesting components are described, however in
alternate embodiments the number and size of the nesting components
may vary.
[0100] Similar to the telescoping fixation devices 210 and 310,
device 410 has a central wire 412 which is initially inserted into
the intramedullary canal through a delivery tube 62 or similar
interface. The first nesting component 413 is slid in around the
central wire. The first nesting component 413 is tubular in form
has a clockwise helical protrusion 420 which protrudes on the
outside of the tube, winding in a clockwise direction along the
length of the nesting component 413.
[0101] Referring to FIGS. 25A-25B, two adjacent helically threaded
nesting components have threading configurations which wind in
opposite directions. As seen in FIG. 25A, the second nesting
component 414 has a clockwise helical slot 422 which winds
clockwise along its length, and a counter-clockwise helical
protrusion 421 which winds counter-clockwise along its length. As
nesting component 414 is inserted into the intramedullary canal, it
is twisted clockwise so that its clockwise helical slot 422 fits
over the clockwise helical protrusion 420 on the first nesting
component 413. As seen in FIG. 25B, the third nesting component 415
has a counter-clockwise helical slot 423, and a clockwise helical
protrusion 420. It is inserted and threaded onto the second nesting
component 414 in a counter-clockwise fashion, so that its
counter-clockwise helical slot 423 engages with the
counter-clockwise helical protrusion 421 on the second nesting
component 414. Each remaining nesting component is threaded
clockwise or counter-clockwise to engage with the smaller component
nested inside of it. The outermost nesting component 417 may or may
not have a helical protrusion.
[0102] The helical threading system varies in direction so that the
entire device will not be loosened when the outermost component 417
is turned in one direction. In addition, this bi-directional
threading system adds overall torsional strength to the telescoping
fixation device 410, since a twisting force in one direction will
not disengage all the threading on the nesting components.
[0103] The telescoping fixation device 410 may be used in
conjunction with an injectable hardenable polymer, such as bone
cement or a biocompatible polymer such as PLA-PEG, among others.
The fixation device 410 may be implanted as described previously,
and the injectable polymer may then be injected into the
intramedullary canal around the periphery of the device, to fix the
device in place. The outermost nesting component 417 may have a
protective sheath 419 which prevents the polymer from accessing the
fractured area of the bone, as described previously. Removal of the
device 410 is accomplished by breaking the device away from the
polymer as described previously, then unthreading and removing each
component 413-417 in a clockwise or counter-clockwise direction,
beginning with the outermost component 417 and proceeding
inward.
[0104] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. It is appreciated that various features of the
above-described examples can be mixed and matched to form a variety
of other alternatives. For example, support structure and matrix
materials and configuration features can vary, as can the method
used to expand the device. As such, the described embodiments are
to be considered in all respects only as illustrative and not
restrictive. The scope of the invention is, therefore, indicated by
the appended claims rather than by the foregoing description. All
changes which come within the meaning and range of equivalency of
the claims are to be embraced within their scope.
* * * * *