U.S. patent application number 16/518415 was filed with the patent office on 2019-12-12 for transcutaneous implant for skeletal attachment of external prosthetic devices.
The applicant listed for this patent is Zimmer, Inc.. Invention is credited to Ronald Hugate.
Application Number | 20190374354 16/518415 |
Document ID | / |
Family ID | 50237694 |
Filed Date | 2019-12-12 |
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United States Patent
Application |
20190374354 |
Kind Code |
A1 |
Hugate; Ronald |
December 12, 2019 |
TRANSCUTANEOUS IMPLANT FOR SKELETAL ATTACHMENT OF EXTERNAL
PROSTHETIC DEVICES
Abstract
Provided herein are devices and methods for connecting a
transcutaneous external prosthetic device to a bone, such as a bone
of an amputee. The device is a two-piece transcutaneous implant
device to provide reversible connection for ease of implantation,
reliability, and relatively easy access for removal, while
maximizing tissue ingrowth to reduce risk of infection and
attendant adverse outcomes. The devices provided herein comprise a
prosthetic interface and a bone anchor. A through-hole that
traverses a longitudinal length of the prosthetic interface and at
least a longitudinal portion of the bone anchor receives a fastener
to reversibly connect the prosthetic interface to the bone anchor
implanted in bone. A connector may connect to a failsafe element
which, in turn, connects to an external prosthetic device.
Inventors: |
Hugate; Ronald; (Aurora,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zimmer, Inc. |
Warsaw |
IN |
US |
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|
Family ID: |
50237694 |
Appl. No.: |
16/518415 |
Filed: |
July 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15241180 |
Aug 19, 2016 |
10390975 |
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16518415 |
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14023161 |
Sep 10, 2013 |
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15241180 |
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61698866 |
Sep 10, 2012 |
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61820264 |
May 7, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2002/7887 20130101;
A61F 2/2814 20130101; A61F 2002/30028 20130101; A61F 2002/6845
20130101; A61F 2002/3092 20130101; A61F 2002/30884 20130101; A61F
2/78 20130101; A61F 2002/3093 20130101; A61F 2/30771 20130101; A61F
2002/30011 20130101 |
International
Class: |
A61F 2/78 20060101
A61F002/78; A61F 2/28 20060101 A61F002/28; A61F 2/30 20060101
A61F002/30 |
Claims
1. (canceled)
2. A transcutaneous device to anchor an external prosthetic device
to a bone, the transcutaneous device comprising: a bone anchor
implantable into bone and defining a longitudinal length, the bone
anchor including a male end configured to extend from the bone
along the longitudinal length; a prosthetic interface configured
for implantation external to the bone and configured to receive the
male end of the bone anchor to secure the prosthetic interface to
the bone anchor; and a connector releasably securable to the
prosthetic interface, the connector configured to optionally
connect to a prosthetic and to a failsafe external to the bone and
external to soft tissue.
3. The transcutaneous device of claim 2, wherein the prosthetic
interface and the bone anchor are configured to mate through a
tapered interference fit.
4. The transcutaneous device of claim 3, further comprising: a
fastener securable to the prosthetic interface and the bone
anchor.
5. The transcutaneous device of claim 4, wherein the fastener is
configured to reversibly secure the prosthetic interface to the
bone anchor and is removable from the bone anchor and the
prosthetic interface external to the soft tissue and the bone.
6. The transcutaneous device of claim 4, wherein the fastener is an
axial taper bolt positioned beneath the connector.
7. The transcutaneous device of claim 2, wherein the prosthetic
interface is configured for soft tissue ingrowth and
vascularization after implantation.
8. The transcutaneous device of claim 2, wherein the connector is a
pyramid connector.
9. A transcutaneous assembly to anchor an external prosthetic
device to a bone, the transcutaneous assembly comprising: a bone
anchor implantable into bone and defining a longitudinal length,
the bone anchor including a male end configured to extend from the
bone along the longitudinal length; a prosthetic interface
configured for implantation external to the bone and configured to
receive the male end of the bone anchor to secure the prosthetic
interface to the bone anchor; and a connector releasably securable
to the prosthetic interface and optionally releasably couplable to
a prosthetic external to the bone and external to soft tissue; and
a failsafe optionally releasably couplable to the connector
external to the bone and external to the soft tissue.
10. The transcutaneous assembly of claim 9, wherein the failsafe
includes: a first clamp connectable to the connector; a central
tube connectable to the first clamp, the central tube configured to
fail by bending when a predetermined moment is applied to the
central tube; and a second clamp connectable to the central tube
and to the prosthetic, the first clamp and the second clamp
configured to rotate with respect to the central tube when a
predetermined torque load is applied to at least one of the first
clamp or the second clamp.
11. The transcutaneous assembly of claim 10, wherein the failsafe
includes: a plurality of set screws securable to the first clamp to
couple the first clamp to the connector.
12. The transcutaneous assembly of claim 9, wherein the connector
is a pyramid connector.
13. The transcutaneous assembly of claim 12, wherein the connector
is threadably securable to a threaded interface of a body of the
prosthetic interface.
14. The transcutaneous assembly of claim 13, wherein the threaded
interface of the body of the prosthetic interface is configured to
receive a distraction bolt when the connector is removed.
15. The transcutaneous assembly of claim 9, wherein the prosthetic
interface and the bone anchor are configured to mate through a
tapered interference fit.
16. The transcutaneous assembly of claim 15, further comprising: a
fastener securable to the prosthetic interface and the bone
anchor.
17. The transcutaneous assembly of claim 15, wherein the fastener
is configured to reversibly secure the prosthetic interface to the
bone anchor and is removable from the bone anchor and the
prosthetic interface external to the soft tissue and the bone.
18. The transcutaneous assembly of claim 15, wherein the fastener
is an axial taper bolt positioned beneath the connector.
19. The transcutaneous assembly of claim 9, wherein the prosthetic
interface is configured for soft tissue ingrowth and
vascularization after implantation.
20. A transcutaneous device to anchor an external prosthetic device
to a bone, the transcutaneous device comprising: a bone anchor
implantable into bone and defining a longitudinal length, the bone
anchor including a male end configured to extend from the bone
along the longitudinal length; a prosthetic interface configured
for implantation external to the bone and configured to receive the
male end of the bone anchor to secure the prosthetic interface to
the bone anchor; and a pyramid connector releasably securable to
the prosthetic interface, the pyramid connector connectable to a
prosthetic external to the bone and soft tissue and connectable to
a failsafe external to the bone and the soft tissue.
21. The transcutaneous device of claim 20, further comprising: a
bolt securable to the prosthetic interface and the bone anchor to
reversibly secure the prosthetic interface to the bone anchor, the
bolt removable from the bone anchor and the prosthetic interface
external to the soft tissue and the bone, the bolt positioned
beneath the connector.
22. The transcutaneous device of claim 21, wherein the prosthetic
interface is configured for soft tissue ingrowth and
vascularization after implantation, and wherein the prosthetic
interface and the bone anchor are configured to mate through a
tapered interference fit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit to U.S. Provisional Patent
Application Nos. 61/698,866, filed Sep. 10, 2012 and 61/820,264
filed May 7, 2013, each of which are incorporated by reference to
the extent not inconsistent herewith.
BACKGROUND OF THE INVENTION
[0002] Provided herein are devices and related methods for
mechanically connecting an external prosthetic device to a user's
skeleton via a transcutaneous implant.
[0003] Currently, amputees are most commonly fit with a socket
interface prosthesis, with the socket contoured to fit the
individual's residual limb. In this manner, the socket interface
transmits forces from the appendicular skeleton through the soft
tissues to the prosthesis. There are a number of significant
disadvantages with such a configuration. First, skin breakdown is
common as the soft-tissue/socket interface may create excessive
pressure areas on the skin. The transmission of forces from the
skeleton through the soft tissues is an energy inefficient process.
Users having poorly fitting prostheses with this interface tend to
lack proprioception, particularly as the standard prostheses do not
tend to convey tactile feedback during use. Such feedback is
valuable in dictating one's gait, cadence, etc., during movement
and ambulation. Fluctuations in weight, muscular tone, edema,
hydration, perspiration, level of activity and body habitus all
affect the ability of the soft tissue/socket interface to function
appropriately using standard socket-type prosthesis.
[0004] These problems are addressed herein by directly connecting
the appendicular skeleton to the prosthesis via a transcutaneous
implant. The implant is tailored to integrate with both bone and
soft tissue while providing a means to directly attach a prosthesis
to the skeleton. This avoids unwanted prosthetic physical
interaction with soft tissue and improves energy transfer
efficiency. Not only does the implant provide a durable mechanical
construct, but the integration with both soft and a bone tissue
provides beneficial biologic properties, including infection
resistance.
SUMMARY OF THE INVENTION
[0005] Provided herein are implantable transcutaneous devices and
related methods for connecting an external prosthetic device to
bone. The implantable transcutaneous devices have a number of
special design configurations to provide important functional
benefit. For example, the implant is configured as a two-piece
design with a bone anchor and a prosthetic interface, with the bone
anchor configured for implantation in bone. The prosthetic
interface, in contrast, is generally placed outside the bone
passage, but reliably connected to the bone anchor in a
transcutaneous manner such that a proximal portion is implanted
within soft tissue at and beneath the skin, and a distal portion
that is exposed to receive a prosthetic above the skin. A fastener
can reliably connect the prosthetic interface to the bone anchor.
Alternatively, female and male elements may be provided for a
press-fit connection between the prosthetic interface and the bone
anchor. Alternatively, the connection may comprise a combination of
both fastening and press-fitting. In an embodiment, the connection
between the bone anchor and the prosthetic interface can be
distracted with the use of a distraction bolt to ease extraction of
the components from bone. Such a connection configuration
facilitates ease of extraction should the implant or a part of the
implant need to be removed.
[0006] Furthermore, this two-piece design is compatible with
failure load design, where mechanical failure is designed to occur
at the prosthetic interface (outside of the body), such as at a
failsafe, to minimize risk of damage to the bone-implanted bone
anchor, the bone adjacent thereto, or other tissue or implanted
component. In this manner, the damaged prosthetic portions may be
removed and replaced without necessarily having to replace the
implant, including the prosthetic interface or bone anchor.
[0007] In an embodiment, the invention is a transcutaneous device
to anchor an external prosthetic device to a bone directly, the
transcutaneous device comprising two separate components: a bone
anchor configured for implantation into bone and a prosthetic
interface for connecting an external prosthetic device to the bone
anchor. A through-hole traverses a longitudinal length of the
prosthetic interface and at least a longitudinal portion of the
bone anchor. The through-hole is configured to receive a fastener
that connects the prosthetic interface to the bone anchor, such as
a bone anchor that has been implanted in bone. Alternatively, a
distraction bolt may be inserted into the through-hole to aid in
distraction and separation of the components should that become
necessary. The prosthetic interface is configured for implantation
external to bone and for soft tissue ingrowth and vascularization
after implantation. The bone anchor, in contrast, is substantially
or entirely implanted in bone.
[0008] In an aspect, the fastener provides physical contact between
the prosthetic interface and the bone anchor defined by a contact
region that corresponds to the bone surface, with the
transcutaneous device above the bone corresponding to the
prosthetic interface component and the device within the bone
corresponding to the bone anchor. In an aspect, the contact region
is shaped to provide a stable base for seating of the implant and
for bony ingrowth medium to reduce or prevent infection. The
contact region can include a step-off defined by different
dimension of the prosthetic interface and bone anchor, such as a
prosthetic connecter diameter that is greater than the bone anchor
diameter. The corresponding lip can then rest on the bone surface
surrounding the bone anchor. Of course, the bone anchor may also
include a portion that is not implanted in the bone, such as a male
member, whose function is to reliably connect to the prosthetic
interface portion. One example is a male member that is received by
a passage within the prosthetic interface.
[0009] In an embodiment, the fastener is a bolt that secures the
prosthetic interface to the bone anchor, wherein the bolt is
dropped through the through-passage of the prosthetic interface to
the through-passage of the bone anchor. In an aspect, the bolt is
reversibly connected to the bone anchor, so that the prosthetic
interface can be removed from the bone anchor by removing the bolt
from the bone anchor. The reversible connection is by any means
known in the art, such as an adhesive that may be removed or
exposed to a physical or chemical signal that reduces adhesive bond
strength, such as by electromagnetic radiation, temperature
variation or chemical application that reduces adhesive bond
strength. Another example of a reversible connection is a
mechanical connection, such as threads on a bolt (external
thread--male) and a threaded receptacle positioned in the bone
anchor through-hole (internal thread--female).
[0010] The prosthetic interface may be further described by various
constituent parts or elements. For example, the prosthetic
interface has a distal end to connect to an external prosthetic
device and a proximal end for connecting to the bone anchor and to
rest against bone. A central portion extends between the distal and
proximal ends. The central portion is a particularly significant
aspect of the device and is designed to maximize soft-tissue
ingrowth into the transcutaneous device. "Soft-tissue" refers to
skin, subcutaneous tissue, muscle, blood vessels and other non-bony
biological tissues that surround the prosthetic interface proximal
end and central portion. To maximize soft-tissue ingrowth, the
central portion of the prosthetic interface may have a shaped
three-dimensional surface to maximize surface area for soft-tissue
ingrowth and also to provide implant stability, specifically for
the portion of the implant not within bone. This shaped
three-dimensional surface is also referred to as a "shaped tissue
ingrowth surface" and may refer to a surface that does not have any
sharp edges or corners, thereby maximizing surface area available
for tissue ingrowth and/or vascularization.
[0011] Extending from the distal portion of the shaped surface is a
distal connecting element having at the end opposite to the shaped
surface the distal end to which an external prosthetic can be
attached. A suture ring for attaching skin to the prosthetic
interface may be positioned within the distal connecting
element
[0012] Extending from the proximal portion of the shaped surface is
the proximal connecting element having at the end opposite to the
shaped surface the proximal end that can connect to the bone anchor
and a bone surface in which the bone anchor is connected. The
portion of the prosthetic interface that is subcutaneous, including
the central portion and proximal end and selected portions thereof,
may be a highly porous material, such as a foam metal, to act as a
matrix for biologic ingrowth of various tissues, as desired.
[0013] In an aspect, the distal end of the prosthetic interface
comprises a connector to mate the transcutaneous device to an
external prosthetic device (or a failsafe element that is in turn
connected to the external prosthetic device). The connector may be
interchangeable so that the implant can be connected to any of a
number of different external prosthetic systems. The connector is
then selected based on the anticipated external prosthetic system
selected for use in the individual patient. Examples of connectors
include a pyramid-shaped connector or a male end Morse taper having
a geometry that is cylindrical or oblong.
[0014] In this manner, the transcutaneous device may be configured
to have an external prosthetic device-prosthetic interface failure
load that is less than a bone anchor-bone failure load, or implant
failure load, thereby minimizing or avoiding damage to the bone or
the implant by a force exerted on an external prosthetic device
that in the absence of the external prosthetic device-prosthetic
interface failure load results in bone damage or implant failure.
This ensures that when damaging force is encountered on the
transcutaneous device, such as by the external prosthetic or by the
force on the external prosthetic by the bone, the bone implanted
portion or biological tissue is not damaged. Instead, the break
point or damage point is external to the bone, such as at distal
region of the prosthetic interface, including at the point of
connection between the external prosthetic and the prosthetic
interface. The failure point is configured to occur, in order of
preference, at the external prosthetic, the prosthetic connector,
and finally the bone anchor. In this manner, damage to the bone is
avoided and likelihood of catastrophic implant or bone failure is
minimized. A failsafe may operably connect the prosthetic interface
to the prosthetic, wherein the failsafe ensures damaging forces are
not transferred to the prosthetic interface or the bone anchor.
[0015] In an embodiment, the prosthetic interface further comprises
a shaped tissue ingrowth surface configured for soft tissue
ingrowth and vascularization. The shaped tissue ingrowth surface
may be further described as having an apex region concentrically
positioned on a distal portion of a central body outer surface, a
rounded radial edge portion; and a convex outer-facing surface
extending between the apex region and rounded radial edge portion.
Such a shape maximizes surface area available for soft-tissue
ingrowth and vascularization. In an aspect, the outer-facing
surface is a distal surface and the inner-facing surface is a
proximal surface. The inner-facing surface may be concave in shape,
so that the inner surface and outer surface are somewhat parallel
to each other, but shaped to increase contact surface area with the
surrounding soft tissue without adversely impacting reliable
implantation and unwanted movement. The shape may be characterized
as umbrella-shaped, skirt-shaped or mushroom shaped.
[0016] In another embodiment, the shaped tissue ingrowth surface
has a geometry that is substantially bulbous.
[0017] In an aspect, the shaped tissue ingrowth surface has a
surface area that is selected depending on the anatomy in which the
implant is to be implanted. Because the implant is configured for
use with a wide range of anatomies that may span from bones within
a finger to a thigh, as well as variations in the user such as age
or animal type, the surface area is selected accordingly, such as a
surface area that is between about 1 cm.sup.2 and up to about 200
cm.sup.2 or more, such as up to about 100 cm.sup.2. Given the
curved shape of the shaped surface, the invention optionally
further comprises a structural enhancer element, such as a solid
internal ring, to mechanically stabilize the shaped tissue ingrowth
surface to the central body. The ring may be a solid metal material
placed within the shaped surface that mechanically stabilizes the
shaped surface that is made of a highly porous material. This
configuration minimizes unwanted displacement and motions without
adversely affecting tissue ingrowth. The configuration of the
shaped surface ensures that both the distal and proximal facing
surfaces, and the edge region there between, are accessible for
soft tissue ingrowth. This shape, therefore, further reduces risk
of infection and adverse outcomes post-implantation requiring
implant removal and replacement.
[0018] In an embodiment, the prosthetic interface further comprises
a suture ring positioned at the apex region of the tissue ingrowth
surface to provide an anchoring point for skin upon implantation.
In particular, the suture ring is positioned at an appropriate
longitudinal distance along the prosthetic interface distal region
and central portion to be substantially coincident with the skin
location overlying the bone and sufficiently far from the distal
end to which the external prosthetic interface connects so as to
not interfere with the connection.
[0019] In an embodiment, a distal portion of the bone anchor and a
proximal portion of the prosthetic interface are formed from or
coated with a highly porous material to facilitate ingrowth of soft
tissues and bone. In an aspect, the highly porous material
comprises a ceramic, polymer, tantalum, titanium, or cobalt chrome
steel. The highly porous material may have an initial porosity of
up to 80% that subsequently decreases after implantation as tissue
in growth occurs. In an aspect, the implant is formed from a solid
metal core with foam coating in the regions where biological tissue
ingrowth is desired. In an aspect, the pores are interconnected
pores. Such a configuration enhances mechanical characteristics,
while still taking advantage of the biological properties of the
surrounding tissue, allowing the biologic tissues to more
thoroughly permeate the pores. In an aspect, the target tissue is
soft tissue for the prosthetic interface and bone for the bone
anchor. The highly porous material has a pore density and/or pore
size selected to the desired target tissue. For example, target
tissue that is bone generally has a pore size that is smaller than
for target tissue that is soft tissue. In this aspect, the porosity
may vary with position, such as pore size that varies as the
implant traverses skin, epidermal layers, muscle, highly
vascularized areas, and bone. In an aspect, the highly porous
material may contain antibiotics, anti-infectious chemicals, and/or
morphogenic proteins to reduce the risk of deep infection as well
as to help facilitate and steer the differentiation of tissues that
permeate the implant. In an aspect, the highly porous material
comprises tantalum with dodecahedral interconnecting pores, having
a porosity selected from a range that is greater than 70% and less
than 90%, and an average pore diameter that is selected from a
range that is greater than 150 .mu.m and less than 700 .mu.m.
[0020] In an aspect, the proximal portion of the prosthetic
interface connects to the distal portion of the bone anchor at a
step-off region. In this manner, the step-off region can function
as a base against which the bone outer surface rests, imparting
vertical stability, with the portion of the transplant above the
bone corresponding to the prosthetic interface, and the portion
situated below the bone surface the bone anchor. A fastener that
connects the prosthetic interface to the bone anchor traverses both
the soft tissue and the bone. In an aspect, the proximal portion of
the prosthetic interface and the distal portion of the bone anchor
have a defined outer dimension, such as for a cylinder or ellipse,
and the proximal portion outer diameter is greater than the distal
portion outer parameter. In this manner, a lip functions as a
stable base to seat the prosthetic interface against a surface of
the bone in which the bone anchor is implanted.
[0021] In an embodiment, the bone anchor has a tip end at the
proximal end. The tip end may be rounded to reduce stress on the
bone upon insertion. In this aspect, the bone anchor is a stem,
having a proximal portion that is furthest inserted into bone, and
an upper or distal portion toward the prosthetic interface. The
distal portion of the bone anchor comprises a highly porous
material, such as a coating of highly porous material. This coating
may extend partway down the stem, or may extend substantially to
the tip end. For mechanical integrity, the proximal portion of the
bone anchor may be a solid stem without the porous material. To
avoid or minimize unwanted rotation between the bone anchor and the
bone in which the bone anchor is implanted, the solid stem may
further comprise longitudinal splines. Alternatively, the stem is
smooth and is cemented in place, thereby avoiding or minimizing
unwanted rotational movement.
[0022] In an aspect, the solid stem is configured for press
fitting, cementing, or both, into an intramedullary canal of the
bone.
[0023] In an embodiment, a portion of the solid stem receives the
through-hole, and the through-hole of the solid stem is threaded
for receiving the fastener that connects the prosthetic interface
with the bone anchor. This is one manner in which a reliable but
reversible connection is established between the two pieces of the
transcutaneous implant. Other connection means are provided, such
as a friction-fit or tight-fit between male and female elements, or
both fastener and friction-fit. The male element may be on either
the prosthetic interface or the bone anchor, with the corresponding
receiving passage on either the bone anchor or prosthetic
interface, respectively. Alternatively, a partial threaded
extractor bolt may be inserted into the longitudinal through-hole
to aid in distraction of the elements of the design should that
become necessary to facilitate removal of the bone anchor.
[0024] Alternatively, the invention relates to a method for
implanting or a method of making or a method of using any of the
transcutaneous devices provided herein.
[0025] In an embodiment, provided herein is a method for implanting
a transcutaneous device for connecting an external prosthetic
device to a bone by inserting a bone anchor into an intramedullary
canal of the bone and providing a prosthetic interface. A fastener
is passed through a through-hole of the prosthetic interface and a
through-hole of the bone anchor and fastened to the bone anchor. In
this manner, the prosthetic interface is connected to the bone
anchor and the prosthetic interface is readied for receipt of an
external prosthetic device. In an aspect, the method further
comprises connecting the external prosthetic device to a distal
portion of the prosthetic interface. Alternatively, the two device
portions are tight-fitted to each other, such as be press-fitting
the prosthetic interface to the bone anchor to reliably engage a
male member in a corresponding receiving passage.
[0026] In an aspect, the step of inserting the bone anchor is by
press-fitting, cementing, or both. In an aspect, the bone is within
a residual limb, and the method further comprises opening the end
of the residual limb; and reaming or broaching a bone canal of the
bone. In an aspect, the method further comprises the step of
closing soft tissues around the prosthetic interface by connecting
soft tissues to a suture ring of the prosthetic connector.
[0027] In an aspect, the prosthetic interface is positioned outside
the bone and skin overlaying the bone is attached to the prosthetic
interface, including at a suture ring.
[0028] In an embodiment, the fastener is configured to be removed
to facilitate extraction of the prosthetic interface or the
prosthetic interface and the bone anchor. One example of a
removable connector is a bolt that is threaded for engaging a
threaded receptacle of the bone anchor through-hole. Rotational
motion of the fastener provides means for engaging and disengaging
the prosthetic interface and bone anchor.
[0029] Any of the methods and devices provided herein relate to a
bone from a human or a non-human animal, such as an amputee where
an external prosthetic serves to replace a limb. In an aspect, the
limb is part of the leg, such as a bone that is a femur, or other
bone for another limb, for example, tibia, metacarpal, humerus,
forearm bone, phalanx, phalanges.
[0030] To further maximize tissue ingrowth, vascularization and
tissue differentiation, the method optionally further comprises
impregnating a highly porous coating portion of the bone anchor and
the prosthetic interface that contacts biological tissue when
implanted with antibiotics, anti-infectious chemicals, and/or
morphogenic proteins (e.g., BMP, growth factors, cytokines to
induce formation of a desired phenotype).
[0031] Another embodiment of the invention relates to a method of
making a transcutaneous implant for connecting an external
prosthetic device to bone, including any of the devices provided
herein. In an aspect, the method comprises the steps of forming a
through-hole in a bone anchor and a threaded portion of the
through-hole for fastening a bolt thereto. A through-hole is formed
in a prosthetic interface, wherein the prosthetic interface
through-hole substantially matches the bone anchor through-hole
through which the bolt fastened to the bone anchor passes, so that
the bolt when present connects the prosthetic interface to the bone
anchor. "Substantially matches" refers to the dimensions and
position of the through-holes in each of the two pieces are
functionally equivalent so that movement between the two pieces is
avoided by a fastener that passes and connects the
through-holes.
[0032] Any of the devices and methods provided herein optionally
relate to a failsafe that is positioned between a prosthetic and
the implant, thereby ensuring dangerous loads are not transmitted
to the bone-implanted portion of the implant or to the bone of the
amputee. Accordingly, any of the implantable transcutaneous devices
provided herein may be described as a four piece system, comprising
a stem, an abutment, a prosthetic interface (also referred herein
as a prosthetic interface plug), and a failsafe break-away
mechanism.
[0033] Also provided herein is a method of extracting any of the
transcutaneous implants from a patient by removing the connector
from the prosthetic interface, and distracting the prosthetic
interface by rotation of a distraction bolt to impart a force
against the bone anchor that acts to force the prosthetic interface
away from the bone anchor and facilitate extraction of at least a
portion of the implant. In an aspect, the distraction bolt
corresponds to fastener and has a partially unthreaded portion to
provide an extraction force exerted against the prosthetic
interface. Alternatively, the fastener is different than the
distraction bolt, and the fastener is removed and a distraction
bolt inserted into the through-hole to generate the extraction
force on the prosthetic interface.
DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic illustration of one embodiment of a
two-piece transcutaneous implant device.
[0035] FIG. 2 is a schematic illustration of another embodiment of
a two-piece transcutaneous implant device.
[0036] FIG. 3 is a diagram illustrating various subsystems for an
embodiment relevant for an implanted transcutaneous device,
including the patient (e.g., biological tissue such as a residual
limb comprising bone and soft tissue), the implant, the prosthesis,
and optionally a failsafe for ensuring damaging forces are not
transmitted to the implant that could damage the biological tissue
(e.g., fracture bone).
[0037] FIG. 4 illustrates an experimental process for ground
reaction force capture (A) and corresponding development of a
skeletal model to determine joint loads under loads associated with
various ground reaction forces (B).
[0038] FIG. 5 is a schematic of a two-piece transcutaneous implant
to connect a prosthetic to a patient, such as a lower limb
prosthetic to a femur bone. The two pieces include a soft-tissue
and bone integration component referred herein as prosthetic
interface and bone anchor, respectively.
[0039] FIG. 6 is a transparent view of a taper within the
prosthetic connection to receive a portion of the bone anchor.
[0040] FIG. 7 is a transparent view of a taper within the
prosthetic connection to receive a portion of the bone anchor. The
image on the right is a blown-up view of the area indicated by the
box in the image on the left.
[0041] FIG. 8 is a plot of the pullout force determined for a taper
having: large end diameter 14 mm; small end diameter 11 mm, and
length 40 mm (taper angle of 1.49.degree.) or 60 mm (taper angle of
2.15.degree.) for indicated delta-z (corresponding to the distance
the taper is pressed into the housing when set).
[0042] FIG. 9 is a plot of the loosening torque determined for a
taper having: large end diameter 14 mm; small end diameter 11 mm,
and length 40 mm (taper angle of 1.49.degree.) or 60 mm (taper
angle of 2.15.degree.) for indicated delta-z (corresponding to the
distance the taper is pressed into the housing when set).
[0043] FIG. 10 is a section view of an implant with a fastener
connection between the bone anchor and the prosthetic
interface.
[0044] FIG. 11 is a section view of an implant with a tapered
interference fit between the bone anchor and the prosthetic
interface having male member.
[0045] FIG. 12 is an exploded sectional view of a tapered
interference fit between the bone anchor having male member and the
prosthetic interface.
[0046] FIG. 13 shows the male end of an oblong taper having an oval
shape.
[0047] FIG. 14 illustrates one embodiment of an implant prosthetic
interface.
[0048] FIG. 15 illustrates a porous material that is trabecular
metal (TM) having an overhang.
[0049] FIG. 16 is a transcutaneous device for implantation having a
length of 140 mm and 15 mm diameter.
[0050] FIG. 17 is a straight stem implanted in femur cut 190 mm
distal of femoral head.
[0051] FIG. 18 illustrates straight (left panel) and curved (right
panel) stems for implantation into bone tissue.
[0052] FIG. 19 top panel is a CAD drawing of an implant in a femur
(140 mm implant in 190 mm femur) for FEA. The bottom panel is the
strain distribution of a FEA experiment for a 140 mm implant having
sharp splines in a 250 mm femur.
[0053] FIG. 20 (A) Failsafe having a shear pin that fails at high
torque and controlled breakable material that are notches that fail
under high bending force. (B) Failsafe having mechanical springs
configured to fail at one or more of high torsion, bending,
compression and tension.
[0054] FIG. 21: Photograph of the porous tantalum implant and the
solid titanium implant side by side.
[0055] FIG. 22: Photographs of Implant technique: A. a 9 mm dermal
punch is used to create a full thickness circular skin defect. B.
the circular skin defect is extended using a scalpel 1 cm cephalad
and 1 cm caudad. A pocket is then created by bluntly dissecting
down to the level of the dorsal muscular fascia. C. Once the pocket
is prepared, the implant is placed within the pocket and the edges
approximated with nylon sutures.
[0056] FIG. 23: Photograph of the dorsum of the animal subject
after implants have been placed showing the spacing scheme. They
are each 5 cm off the midline and placed cephalad to the iliac
crest/caudal to the scapulae. Implant centers are spaced apart
longitudinally by 10 cm.
[0057] FIG. 24: Photograph of: A. implanted porous tantalum
implant; and B. implanted solid titanium implant.
[0058] FIG. 25: Photograph of a: A. porous tantalum implant at 42
days; and B. solid titanium implant at 42 days. 3 of the 4 solid
implants extruded prior to necropsy.
[0059] FIG. 26: A. Animal 804, site 4. H&E stain at low power.
A typical porous tantalum implant. The epidermis (E) grew up to the
trabeculae of the post on both sides but did not penetrate into the
pores. Trabecular pores of the base portion of the implant contain
vascularized connective tissue or loosely arranged fibrin-like
material. There was a mild amount of fibrous connective tissue
(FCT) surrounding the implant base, except where portions of the
base contacted the underlying muscle. B. Animal 804, site 4.
H&E stain at high power (100.times.). A higher magnification
photo at the post/base intersection. This shows epidermal contact
with the porous tantalum. C. Animal 806, site 3. H&E stain at
high power (100.times.). A typical cross section near the base/post
interface in an in-grown porous tantalum implant. The epidermis is
in contact with the deep implant post. Vascularized connective
tissue (*) fills the pores of the tantalum implant.
[0060] FIG. 27: A. Animal 805, site 1. H&E stain at low power.
This is the sole surviving solid titanium implant. The implant is
not in direct contact with the epidermis or dermis. The
subcutaneous tissue is in contact with the base portion of the
implant at the superficial corners and along the deep aspect of the
base of the implant. The subcutis contains fibrous connective
tissue (F) and mild inflammation (I). B. Animal 805, site 1.
H&E stain at high power (100.times.). A higher magnification
photo at the interface between the solid titanium and the
surrounding tissues showing accumulation of neutrophils (N) and
mononuclear cells (M) in the subcutis adjacent to the base portion
of the implant. Note the gap (G) between the implant (IM) and the
subcutis.
[0061] FIG. 28: Animal 802, site 1. H&E stain at high power
(100.times.). High magnification photo of the epidermal/dermal
junction with porous tantalum implant post. Note the neutrophils
(N) which are positioned superficial to the epidermis (E) showing a
`barrier` effect against inflammation of the soft tissues along the
post of the implant.
[0062] FIG. 29: Animal 802, site 4. H&E stain at low power.
Some of the porous tantalum implants experience epidermal
down-growth such that the epidermis (E) contacts the base directly
rather than the post. Most of the pores of the base portion of the
implant are filled with vascularized connective tissue. Fibrous
connective tissue (FCT) is present in the dermis adjacent to the
implant on 3 sides.
[0063] FIG. 30: Comparison between alternative implant
configurations, with the right pair of schematics having a pyramid
screw and axial taper bolt to connect to an external prosthetic.
Common components include a soft tissue cap and stem.
[0064] FIG. 31: A. Close-up view of the soft tissue integration
portion (part of the prosthetic interface that receives the
connector for connection to the prosthetic or failsafe) of the
transcutaneous device and exemplary dimensions. B. Top view of the
connector received by the prosthetic interface soft tissue
integration portion with removal passages to facilitate connection
and removal of connector, as desired. The right panel is an example
of a wrench that may be employed during connection or removal.
[0065] FIG. 32: Alternative failsafe design, for accommodating both
bending and torque-induced failure.
DETAILED DESCRIPTION OF THE INVENTION
[0066] "External prosthetic device" refers to a device that
replaces a missing body part, such as a device attached to the body
that remains entirely external relative to the body. One example is
a lower extremity prosthetic used to replace a lower leg that may
have been amputated. The implant and prosthetic in combination may
be transcutaneous in that one portion is within the body and
another portion outside the body.
[0067] "Through-hole" refers to a passage in which a structure may
be positioned, such as a fastener, to reliably connect two
physically distinct components. In this example, the two physically
distinct components are a bone anchor and prosthetic interface of
the transcutaneous device each having a through-hole in which a
single fastener may be positioned to fasten the components to each
other or distract the two components, depending on the
situation.
[0068] "Reversibly connected" refers to the ability to remove two
components that are connected without substantially damaging the
components or the functionality of the components. In an aspect, a
reversible connection provides reliable connection, but is
configured to be removed upon application of a force, such as a
fastener that may be fastened and unfastened, as desired, such as
by clockwise and counter-clockwise rotation of the fastener. A
fastener that is used to distract the components may be referred to
as an extraction bolt or distraction bolt.
[0069] "Distal" refers to a region or portion that is away from the
trunk of the animal or person in which the device is implanted.
"Proximal" refers to the region or portion that is toward or closer
to the trunk of the animal or person in which the device is
implanted.
[0070] "Highly porous material" refers to a surface in which the
porosity facilitates tissue ingrowth of biological tissues. The
level of porosity or parameter related to porosity (size, number,
distribution, density) is selected to maximize tissue ingrowth,
such as soft tissue or hard tissue ingrowth. In an aspect, the
highly porous material has a porosity selected from a range that is
between about 40% and 85%, or about 80%. Generally, higher porosity
may be used for materials that coat a solid substrate, including a
metallic substrate, as the solid substrate can provide mechanical
stability. Generally, these materials comprise inter-connected
pores with open-cell foam configuration.
[0071] The invention may be further understood by the following
non-limiting examples. All references cited herein are hereby
incorporated by reference to the extent not inconsistent with the
disclosure herewith. Although the description herein contains many
specificities, these should not be construed as limiting the scope
of the invention but as merely providing illustrations of some of
the presently preferred embodiments of the invention. Thus, the
scope of the invention should be determined by the appended claims
and their equivalents, rather than by the examples given.
[0072] The implants provided herein provide a number of functional
benefits, including avoiding skin breakdown that can occur for
those prosthetics having a soft-tissue interface with the body.
Instead, the implants provided herein are constructed to transmit
forces directly between bone and prosthetic. This provides
extremely efficient energy transfer, increased proprioceptive
ability, improved tactile feedback and good fit independent of
fluctuations in weight, muscular tone, edema, perspiration, level
of activity, and body habitus.
[0073] There are certain other relevant attributes of the system
that provide functional benefits and attendant improved implant
outcome, including when compared to other devices, including
WO2013/048589. Examples of attributes of the implant provided
herein include the stem having a male end morse taper as well as
the ability to reliably incorporate other connectors of other
shapes, as desired, such as a pyramidal-shaped connector.
Furthermore, the stem does not have a porous surface that abuts the
end of the bone. Instead, the face that abuts the bone is part of
the abutment component (see, e.g., 550 of FIG. 5), thereby making
stem extraction, if necessary, easier. The through hole in the
abutment is used to either screw down the abutment to the stem, or
can be used alternatively to separate the stem and abutment (e.g.,
for a partially threaded bolt), if necessary. In addition, the
surface of the bone anchor portion is uniform in that there are not
recesses (in contrast to WO2013/048589 at element 32). A suture
ring 540 positioned near the apex provides the ability to reliably
intimately contact soft tissue (e.g., skin). Provided with any of
the implants of the instant invention is an intercalary element or
failsafe that connects to the prosthetic interface and controllably
breaks away at forces less than the failure forces of the implanted
components. In a functionally similar manner to a ski binding to
release boot from ski to minimize injury, the failsafe ensures and
implant failure occurs outside the body, including a "controlled"
implant failure so that the implant may be reconnected and/or reset
as desired after failure.
[0074] The shaped tissue ingrowth surface (e.g., bulbous,
umbrella-shaped, skirt-shaped or mushroom shaped) allows more
surface area for ingrowth of soft tissues and decreases the
likelihood that infection will circumvent the implant and infect
the underlying or adjacent bone. In combination with the shaped
tissue ingrowth surface, a structural enhancer element such as
metallic circumferential `rib` or ring is included within the
porous umbrella portion of the abutment to mechanically support
this region.
[0075] A threaded `prosthetic interface plug` can unscrew,
revealing a locking bolt below. This locking bolt can be removed
and replaced by a `distraction bolt` which is partially threaded to
allow dissociation of the abutment and stem if necessary for ease
of extraction.
[0076] In contrast to WO2013/048589 (e.g., FIGS. 7A-C of
WO2013/048589 showing tapered implant), the implant provided herein
does not require a tapered portion of the stem.
Example 1: Two-Piece Transcutaneous Device
[0077] FIGS. 1-2 illustrate a two-piece transcutaneous device
designed to provide a bone anchor in the bone of a residual limb or
digit in an animal (human or non-human) for direct skeletal
attachment of an external prosthetic device. The device uses highly
porous coating along the majority of its length to act as a matrix
for biologic ingrowth of various tissues.
[0078] The biologic ingrowth at the bone interface (in and around 5
of FIG. 1) is bony and facilitates rigid, stable, and durable
fixation of the implant to the bone. The biologic ingrowth in the
soft tissues in and around 2 (skin, subcutaneous tissue, muscle)
provides an effective barrier against infection at the bone/implant
interface due to its vascularity--making available white blood
cells and antibiotic delivery via blood vessels if necessary to
ward off advancing bacteria.
[0079] The device is illustrated as two separate pieces, `A` Piece
("prosthetic interface") and `B` Piece ("bone anchor"). These two
pieces are mated at the elbow labeled 5 in the diagram and is
referred herein as a "stable base". They are held together with a
fastener (not shown) that can be a threaded bolt that slips down
the center of the implant through the through-holes of A and B
pieces as indicated by the dashed lines. One benefit of the two
piece design is ease of extraction should the implant need to be
removed. The extraction process involves removing the locking bolt,
inserting a partially threaded distraction bolt, disengaging piece
`A`, and using a cylindrical trephine to remove piece `B` from the
bone.
[0080] The cross-hatched regions of the implant represent a highly
porous material, such as a coating on a solid substrate. In FIG. 1,
the cross-hatched is on a distal portion of the bone anchor and a
proximal portion of the prosthetic interface. The pore
sizes/diameter may be varied from region to region on the implant
to facilitate ingrowth by the target tissues (i.e. smaller pore
sizes for bone ingrowth, and larger pore sizes for soft tissue
ingrowth). The highly porous coating may be impregnated with
antibiotics, anti-infectious agents/chemicals, or morphogenic
proteins to help reduce risk of deep infection and help
facilitate/steer the differentiation of tissues that permeate the
material. In an aspect, the coating is about 1 mm to about 5 mm
thick and covers a solid substrate, wherein ingrowth does not
substantially occur into the solid substrate. In this manner, only
an outermost layer of the implant has tissue ingrowth.
[0081] Referring to FIG. 1, 1 refers to a distal end of the
prosthetic interface for connecting to an external prosthetic
device (not shown), and can be a male end Morse taper. The end can
be shaped cylindrically or oblong with the purpose of mating the
osseous integration implant provided herein with an external
prosthetic device. Optionally, the external prosthetic device is
designed such that its failure loads are less than that of the
osseous integration device itself--allowing for mechanical failure
of the prosthetic interface before the osseous integration implant
itself fails. A male-end Morse taper system uses a mating interface
so that the prosthetic end such as the female end of the Morse
taper is the weak link in the mechanical system. This avoids
implant failure and minimizes need for revision surgery with
extraction/insertion of the implant.
[0082] Element 2 illustrates a shaped tissue ingrowth surface. The
rounded `shoulder` of porous materials ("rounded radial edge")
facilitates and maximizes soft tissue ingrowth and vascularization.
This rounding is to create an extensive network of vascularized
tissue through which bacteria must circumnavigate to get to the
bone/implant interface. By rounding this and creating an `umbrella`
shape, this creates more of a vascular barrier against infection
and more surface area for the skin to integrate and stabilize on
the implant, thereby improving implant success and long-term
reliability. The apex region corresponds to the region of the
surface furthest from the proximal end. The outer facing surface is
distal-facing and is referred to as convex. The inner facing
surface faces in a proximal direction and is referred to as
concave-shaped. This configuration can maximize surface area
available for soft-tissue ingrowth without unduly sacrificing
mechanical stability. Sharp-edged surfaces, in contrast, have
corners that are not as accessible for ingrowth and may create
stress risers.
[0083] In another embodiment, the shaped tissue ingrowth surface
has a surface shape that is bulbous. Bulbous refers to a generally
bulb shaped surface that does not have any sharp corners or edges,
but instead has a varying curvature depending on the surface
position, such as for a conventionally shaped bulb.
[0084] A structural enhancer such as a solid metal ring 3
(indicated as "solid metal skirt" in FIG. 2; also referred herein
as a "structural enhancer element") helps to mechanically stabilize
the rounded `shoulder` of porous materials.
[0085] A suture ring 4 is placed at the base of the Morse taper and
at the apex of the rounded `shoulder` of porous material to provide
an anchoring point for the skin upon implantation of the device.
This anchor point helps stabilize the skin edge upon implantation
and allows the skin to permeate the porous metals and provide
barrier against deep infection.
[0086] A step-off region 5 of porous material is meant for the bone
face. The implant above this line (piece `A`--prosthetic interface)
is all external to the bone, while piece `B` (bone anchor) is
configured to be intramedullary within the bone. This provides a
stable base for seating of the implant and also provides a bony
ingrowth medium to prevent deep infection.
[0087] Bone anchor distal portion or region 6 having a highly
porous material coating is designed to be intra-medullary and
facilitate bone ingrowth for stabilization of the implant. Note
that the highly porous material may or may not extend to the tip of
the stem. If the patient is deemed at risk for stress shielding
phenomenon, the ingrowth coating here can be shortened such that
the lower stem (e.g., a proximal portion of the bone anchor) is not
coated with highly porous material.
[0088] Solid stem 7 of the bone anchor can have longitudinal
splines to promote rotational stability upon initial implantation
or can be smooth, so long as the press-fit and/or cementing results
in a sufficiently strong fit to avoid unwanted rotation during use.
The cross-sectional shape, dimensions and length of the stem is
anatomy specific at this location. The tip end of the proximal-most
end of the stem can be bullet-shaped or rounded to reduce stress on
the bone upon insertion. This is configured to be press fit or
cemented into the host bone intramedullary canal.
[0089] Through-hole 8 receives a fastener, such as a threaded bolt
that mates piece `A` to piece `B`. In order to separate the pieces
from one another, the bolt is removed and an extraction device that
separates the two is employed. Again, one purpose of this design
feature is to allow for ease of extraction of the implant if
necessary. Threaded receptacle 9 (built into through-hole of piece
`B`) mates the two pieces with fastener such as the drop-through
threaded bolt described above.
Example 2: Prosthesis for Transfemoral Amputees
[0090] An example of a prosthesis for use by transfemoral amputees
is illustrated in FIG. 3. The overall system can be characterized
into different subsystems: the patient 10 (residual limb), implant
20, prosthesis 40 and, optionally, a failsafe 30 that operably
connects the prosthesis 40 to the implant 20, including any of the
two-piece transcutaneous devices disclosed herein. The failsafe
functions as an interface between the prosthesis and the implant
and, therefore, the patient; in particular the bone that surrounds
the bone-implanted portion of the implant. As further discussed
below, system load is empirically measured by force or pressure
transducers, computationally determined such as by finite element
analysis, and/or obtained from the literature. In this manner, the
loads exerted on bone by the implant in various settings are
determined. With such loads known, as well as the strength of
patient's tissue such as bone strength and bone failure of fracture
load, the system is designed to ensure that loads that would
otherwise be potentially damaging are not transmitted to the
patient. This may be achieved via the failsafe 30 which disconnects
the implant from the prosthesis at a defined load, force or
pressure.
[0091] Several studies contribute in assessing loading conditions
for amputees. In most circumstances, loads are measured directly at
the abutment (distal end of the implant) by means of a load
transducer. Some of the examined movements include walking,
ascending and descending stairs, ascending and descending a ramp,
walking in a circle, falling, and running [8] [9]. The
literature-obtained measures may be used to: 1) gain knowledge
regarding the range of loading conditions typical of common
activities, 2) implement loading into preliminary static and future
dynamic FE models to determine implant design, and 3) develop
criteria for the failsafe 30. One study by Lee et al is examined to
set baseline loading profiles during walking. [10] While walking
data are valuable to understand the required loading and can
provide useful model information, other movements are assessed to
better characterize risk. For preliminary static analysis, a peak
loading condition from force and moment profiles is selected.
Examples of loading values obtained from the literature are
provided in Tables 1 and 2, with the forces and moments defined as:
F.sub.AP: Force in the anterior-posterior direction (anterior
positive); F.sub.ML: Force in the medial-lateral direction (medial
positive); F.sub.IS: Force in the inferior-superior direction
(superior/compressive positive); M.sub.AP: Moment in the
anterior-posterior axis (lateral rotation positive); M.sub.ML:
Moment in the medial-lateral axis (anterior rotation positive);
M.sub.IS: Moment in the inferior-superior axis (external rotation
positive). The positive and negative signs reflect the specific
direction along the relevant axis.
[0092] Since the loads corresponding to the subject are dependent
on their body weight, the normalized values are of primary
interest. For finite element analysis (FEA) of the average femur
model and for quantifying daily activities for the failsafe
mechanism, the normalized value is multiplied by body weight and
divided by one-hundred in order to accurately represent the average
male. Further, loads are assessed at the distal end of the implant
of a transfemoral amputee during a forward fall. [9] That study
involved a subject who has an implant, and while the fall did not
cause harm to the subject, the collected loading data is useful for
determining harmful loads. Table 3 below presents the peak forces
and moments that occurred at the abutment during this fall.
[0093] From these peak loading values, the moment in the
inferior-superior direction (M.sub.IS+ and M.sub.IS-) are largely
of interest because this corresponds to the axial torque applied to
the implant and femur.
[0094] The literature-based loading information is further
supplemented, verified and extended by empirical measurements in a
Human Dynamics Laboratory (HDL). Examples of activity and
corresponding measured loads include sit-to-stand, normal gait,
pivots, stairs, getting up from the ground, jog, jump, trip, ankle
roll and turn. The measurement may be performed by an amputee or a
non-amputee. This load determination is illustrated in FIG. 4, with
the left panel illustrating motion and capture, and the right panel
a corresponding skeletal model to resolve joint loads. The results
are compared to published literature with maximal knee loads in six
degrees-of-freedom calculated via inverse dynamics. The loads of
highest risk are confirmed to be axial torque and bending.
[0095] Normalized forces and moments are compared between
literature and HDL collections and ranges obtained. This quantifies
the upper limit associated with daily living (DL). The obtained
data is summarized in Table 4. The data may be further verified and
refined so as to ensure typical and upper-limit load ranges are
accurate for a number of different situations.
[0096] One example of an implant of the present invention is
provided in FIG. 5. The implant or transcutaneous device 500 is
generally referred to as "transcutaneous" because when implanted a
portion (e.g., bone anchor 501) of the device 500 is beneath skin
510 and another portion (e.g., prosthetic interface 502) extends
beyond the skin surface 510. The dashed line 511 indicates the
bone/soft-tissue interface, with the region above the dashed line
corresponding to implant that facilitates soft tissue integration
with the implant, and the region below the line corresponding to
implant that facilitates bone integration with the implant.
Accordingly, the device may be described as having a bone-tissue
ingrowth portion 503 and a soft-tissue ingrowth portion 504.
[0097] The prosthetic interface 502 may have a distal end that is a
male end of a Morse taper 520 to connect the implant directly to an
external prosthesis or, alternatively, to a failsafe (not shown).
The device may have a shaped tissue ingrowth surface 530, such as
an "umbrella" shaped surface made of a porous material or materials
to facilitate soft tissue in-growth and vascularization. A
structural enhancer element (not shown) may be positioned within
the shaped tissue ingrowth surface of the prosthetic interface to
provide mechanical support to the rounded shoulder of the porous
material. In an aspect, the structural enhancer element is a solid
ring, such as a solid metal ring, that is positioned around the
central shaft (not shown) of the device. A suture ring 540 is an
anchoring point for the skin 510 to set implant position relative
to the skin and to promote skin ingrowth into the porous materials
to generate a biologically tight skin-implant interface that
assists in preventing or avoiding infection. In the embodiment of
FIG. 5, the suture ring 540 is positioned at an apex region of the
tissue ingrowth surface 530.
[0098] An elbow or step-off region 550 of porous material may
further assist with implant positioning. The step region 550 also
delineates the bone tissue ingrowth portion 503 from the soft
tissue ingrowth portion 504, as indicated by dashed line 511 where
the portion of the implant below line 511 is within bone 512 and
the implanted portion of the device above the line 511 is within
soft tissue with optionally a portion external to the body. Bone
tissue ingrowth portion 503, similar to soft tissue ingrowth
portion 504, comprises a highly porous material. In an embodiment,
the highly porous materials correspond to each other. In an
embodiment, the highly porous material of the soft tissue ingrowth
portion is different than the highly porous material of the bone
tissue ingrowth portion, such as having porosity, pore sizes,
growth factors and the like tailored to facilitate ingrowth of the
desired cell type (e.g., soft versus hard tissue). Optionally, the
mechanical properties of the implant portions are selected to match
mechanical properties of the surrounding tissue, such as a modulus
including Young's modulus, thereby minimizing compliance mismatch
between implant and surrounding biological tissue.
[0099] Bone tissue ingrowth portion 503 may extend a defined length
of the solid stem 570, up to and including the entire length of the
solid stem 570. FIG. 5 illustrates bone tissue ingrowth portion 503
that extends less than half the longitudinal length of the bone
anchor region 501. Optionally, solid stem 570 has splines 572
running in a longitudinal direction along at least a portion of the
solid stem 570. Splines 572 may help prevent unwanted rotational
motion of the implant relative to surrounding bone. Optionally, the
tip or a distal portion of the bone anchor 501 has a
cross-sectional shape that is elliptical. Optionally, the tip 574,
a portion, or all of the bone anchor has a cross-sectional shape
that is substantially circular or is circular. Optionally, a
distal-most portion of the bone anchor has an elliptical
cross-section that transitions to a circular cross-section 576 in a
direction that is toward the residual limb surface. An elliptical
cross-section toward or at the tip of the implant may reduce stress
when the implant is inserted into bone. Optionally, the tip 574 is
tapered. The modular design outlined herein allows for extraction
of the soft tissue ingrowth or prosthetic interface 502 without
removing the bone-implanted portion, thereby avoiding or minimizing
the need for a more invasive medical procedures.
[0100] FIG. 6 is an illustration focused on the connection features
of the device. Any one or more connection means may be employed.
For example, the taper connection 520 may contain a fastener such
as a locking bolt or screw 600 that connects the bone anchor
portion 503 to the prosthetic interface 502 (including, e.g., the
soft tissue ingrowth portion). Furthermore, the prosthetic
interface 502 may contain a through-hole 610 (e.g., threaded
through-hole) for receiving the screw 600. Similarly, the bone
anchor portion may contain a threaded receptacle or passage 620 for
receiving screw or bolt 600. In addition or in alternative, the two
pieces may mate via a tight-fit connection, such as a tapered
connecting so that the two pieces press-fit with respect to each
other. Referring to FIG. 6, male end 630 of bone anchor 503 may be
received by a passage 640 contained within the interior of
prosthetic interface 502. In an aspect, the connection may be via a
tapered passage 640 and corresponding tapered male end 630. In an
embodiment, the connection is by the combination of a fastener and
press-fit.
[0101] FIG. 7 shows the male member 630 taper set within the Soft
Tissue Integration component (transparent in this image), also
referred herein as prosthetic interface 502 or soft tissue ingrowth
portion. On the right is a blown-up view of the interface between
the two components: the bone anchor and the prosthetic interface.
The structural core of the Soft Tissue Integration component has a
minimum thickness of 5 mm, with the central portion comprising a
passage 640 for receiving the bone anchor male member. There is
also a small clearance between the beginning of the taper and the
Soft Tissue Integration component which allows the taper to further
set under loading, thus strengthening the connection. A structural
enhancer element 700, such as a solid ring, is shown within the
prosthetic interface, and more particularly, within the shaped
tissue ingrowth surface. Optionally, fastener 600 is used to
further fasten two components of the device, such as male member
630 within a receiving passage 640.
[0102] The pullout and loosening torque for different tapers and
distance the taper is pressed into the housing is summarized in
FIGS. 8 and 9.
[0103] The pullout forces shown in FIG. 8 greatly exceeds all
tensile loads the implant encounters discussed above. Loosening
torques of the tapers are relatively close to what is expected to
occur in normal day-to-day activity. The maximum torque is
determined to be approximately 50 Nm (shown as the lower dashed
line in FIG. 9). This value is calculated based on the average male
weight. This torque corresponds to an inferior-superior moment
recorded from the HDL data collection for a non-amputee. As shown
in FIG. 8: Loosening torque calculated for the taper options
indicates the maximum expected day-to-day torque is greater than
the loosening torque for both tapers with a minimum .DELTA.z of
0.05 mm. The loosening torques for the larger values of .DELTA.z
exceeds the maximum day-to-day torque value of 50 Nm. In order to
design for a safety factor of two, the tapers may be assembled with
a .DELTA.z of 0.15 mm or higher.
[0104] These results indicate that the tapered interference fit
does not require an additional feature for rotational stability for
a .DELTA.z of 0.15 mm or higher. Since there is some uncertainty as
to whether a .DELTA.z of 0.15 mm can be reliably achieved during
use, a locking bolt/screw mechanism may be included to serve as an
additional stability feature. This locking bolt or screw may later
be removed if a .DELTA.z of 0.15 mm is reliably and consistently
achieved during the taper assembly.
[0105] Examples of mechanisms to connect the bone anchor and
prosthetic interface are summarized in FIGS. 10-13. FIG. 10 shows a
fastener (long bolt or screw) 600 connection through the
longitudinal axis of the prosthetic interface 502 and bone anchor
501 (compare to the shorter fastener (bolt or screw) 600 of FIG.
6). Accordingly, in an aspect, the fastener extends through and
past shaped tissue ingrowth surface 530 or terminates before the
shaped tissue ingrowth surface 530 (compare, e.g., FIGS. 6 and 10).
The prosthetic interface piece of the transcutaneous device may
then be simply removed by removing the locking bolt 600.
[0106] In contrast to the fastener systems of FIG. 10, FIGS. 11-13
illustrate different systems that employ of tight-fit or press-fit
between the two components of the implant, referred herein as a
"tapered interference fit". The interference fit systems relies on
frictional forces to hold the two components of the implant
together. During prosthetic use, the loads transmitted to the
implant further strengthens the interference fit. If no fastener is
used, no through-hole is required which may further strengthen the
implant, particularly the prosthetic interface 502 portion.
Structural enhancer 700, such as a solid ring, assists with
structural integrity and strength of the shaped tissue ingrowth
surface 530.
[0107] To address concerns related to rotational stability, an
oblong shaped taper of FIG. 13 may be used, where the male member
630 of the bone anchor has a non-circular cross-sectional shape
matched to the counterpart receiving passage 632 in the prosthetic
interface. One suitable cross-sectional shape is elliptical,
wherein the cross-section is defined by a major radius and a minor
radius. Alternative means are available. For example, use of set
screws on different sides of the stem may control concerns
associated with unwanted rotational motion.
[0108] Soft tissue integration: The prosthetic interface 502,
focused on the soft-tissue ingrowth portion 504 and shaped tissue
ingrowth surface 530 is illustrated in FIG. 14. A removal shelf may
be positioned in a more physically-accessible position at the top
portion of the porous material. FIG. 15 shows the solid core of the
prosthetic interface and a porous material (e.g., trabecular metal
or "TM") on the proximal end of the piece along with receiving
passage 640. The overhang allows the entire bone face to fit flush
with the TM allowing for optimum bone in-growth at the
soft-tissue/bone-tissue/implant interface.
[0109] Bone integration: The Bone Integration component (e.g., bone
anchor 501) of the implant includes the stem that is inserted into
the medullar canal of the femur. The shape of this stem is
dependent on the size and shape of the femur in addition to the
location at which the femur is cut during surgery. The stem may be
tailored to a specific individual. The stems described herein
correspond to an "average" femur model.
[0110] Three stems options are provided. These options include a
straight and curved press-fit stem and a straight cemented stem.
These stems are designed for use with different cut lengths within
the femur model. The straight stems are designed for the femur
model cut 240 mm and 180 mm proximal of the lateral epicondyle. The
bent stem is designed for the femur model cut 120 mm and 180 mm
proximal of the lateral epicondyle.
[0111] The straight stem is 140 mm in length and 15 mm in diameter.
This stem is designed for the average femur model cut 240 mm and
180 mm proximal of the lateral epicondyle. FIG. 16 shows the 140 mm
straight stem. The image on the left shows the entire press-fit
stem with the TM. The image in the middle shows the rigid core of
the implant without the TM. The image on the right shows the
geometry of the sharp splines looking down the stem longitudinal
axis. These splines are designed to provide an interference fit of
roughly 0.5 mm with the bone.
[0112] The diameter of this stem is selected to fit within the
medullar canal of the femur model while providing a tight press fit
into the endosteum. FIG. 17 shows the 140 mm length stem within the
femur model cut 240 proximal to the lateral epicondyle. Other
implant parameters that may be varied, depending on the amputation
location and bone morphology, are illustrated in FIG. 18. For
example, the bone implanted stem may be straight (FIG. 18 left
panel) or may be bent or curved (FIG. 18 right panel). The splines
may have a sharp surface for straight stems or may have a smooth
surface to facilitate insertion of the bent stem into bone during a
surgical procedure.
[0113] Further detail of the in silico experiments and methodology
is illustrated in FIG. 19. Bone and implant are subject to FEA,
including under dangerous loading conditions. One example of a FEA
model of a bone with implant is provided in the top panel of FIG.
19, where each element is tetrahedral. Calculated strain and stress
in bone under different loading conditions is used to predict
potential fracture in bone, based on mechanical properties of bone.
FIG. 19 bottom panel shows resultant calculated strain distribution
in the femur for an implant with sharp splines. Other FEA is
conducted for smooth splines for different implant and femur
lengths (see Table 5). Results include the maximum strain that is
seen within the bone. Since strain is directly correlated with pain
and fracture of the bone, it is one of the most important factors
to consider when analyzing the effectiveness of an implant design
within bone. The maximum bone strains are provided in Table 5, with
one representative strain distribution provided in FIG. 19 (bottom
panel). It should be noted that stress within the implant is
another important factor, but according to the data, the implant is
not exposed to stresses that could cause it to yield; the highest
stress observed in the implant for any of the models is below 800
Pa, while Titanium yields at a stress of 880 MPa.
[0114] FIGS. 30-31 illustrate another embodiment of a
transcutaneous device having a threaded pyramid screw or
"connector" 800 for connection to a prosthetic implant (or a
failsafe) at one end and the prosthetic interface 804 at the other
end. A fastener 802, such as an axial taper bolt, may connect the
stem or bone anchor 806 to the prosthetic interface portion 804.
FIG. 30 illustrates the different components of a transcutaneous
implant connected to each other (top middle panel) and separated
from each other (top right panel). A tapered interference fit and
axial bolt provide the locking mechanism between the prosthetic
interface and bone anchor portions of the implant device. This
configuration provides additional connection in the event of wear
of the threads of the fastener that could otherwise compromise
implant durability. Use of a pyramid shaped connector that attaches
to a prosthetic at one end, or a failsafe mechanism element
connected thereto, is compatible with a range of prosthetics,
including commercially available prosthetics. Such a system permits
ease of removal and installation of the prosthetic and failsafe by
the patient.
[0115] FIG. 31A is a close-up view of the soft tissue ingrowth
region of the implant, including the shaped tissue ingrowth
surface. The left panel is a solid surface schematic and the right
panel is a transparent image to further illustrate the placement of
the four components that form the exemplified transcutaneous
device. The connector is a pyramid shaped or may have any other
shape, depending on the shape of the female connection portion of
the prosthetic or the failsafe. The fastener 802 rests beneath the
connector 800 for connection to the failsafe mechanism and external
prosthesis. Exemplary dimensions are illustrated, and typical taper
dimensions may be: 14 mm--large end diameter; 11 mm--small end
diameter; 30 mm--length; taper angle--2.879. The soft tissue
integration portion of the prosthetic interface, as illustrated in
FIG. 31, operably connects with a fastener and a connector. The
connector that is pyramid in shape is advantageous in that it can
connect to the failsafe via a plurality of set screws, including
the four set screws illustrated in the clamp adapter of FIG. 32.
This connection allows for the male exposed end of the connector
800 to be installed and removed easily from either the implant or
from the prosthetic or failsafe. This design allows for ready
replacement of the connector, such as for use with other prosthetic
types or brands, and to replace worn connectors. Optionally, a
plurality of receiving passages provide the ability to stabilize
the implant while another wrench twists the connector. The
plurality of passages may be contained on an exposed surface of the
prosthetic interface, such as two passages on opposed sides
relative to the connector so that a two prong spanner wrench can
stabilize the implant during twisting of the connector by another
wrench (FIG. 31B). This ensures that maximum force can be applied
to the connector without transferring unduly high forces to the
patient or the implant.
[0116] The connector that is a pyramid screw can mate with a
threaded receptacle of 15 mm in diameter within the body of the
prosthetic interface. When the pyramid screw 800 and axial bolt 802
are removed, this threaded receptacle can then be used to remove
the prosthetic interface using a push-out screw (distraction bolt).
The push-out screw has a step to a smaller diameter at its tip to
allow it to fit through the passage for the axial bolt. It can then
be used to apply pressure to the end of the male taper of bone
anchor 806 to lift the prosthetic interface component off of the
stem of the bone anchor 806. The small end of the push-out screw
may have a diameter less than 7 mm. This aspect provides unique
advantages in the event the implant or part of the implant needs to
be removed.
Example 3: Failsafe
[0117] Examples of a failsafe 30 (see FIG. 3) for use between the
prosthesis and the implant is provided in FIGS. 20 and 32. The
failsafe, also referred to as failsafe mechanism or failsafe
element, is designed to ensure that dangerous loads are not
transmitted to the body, thereby avoiding possible harm such as
bone fracture and/or bone anchor damage requiring surgical removal
and replacement. Another example is provided in U.S. Pat. Pub. No.
2008/0058957. The implant provided herein may use any failsafe. The
failsafe is preferably reliable, simple and easy to use. FIG. 20A
shows one option for a failsafe based on controlled material
properties, such as a shear pin and two notches. The shear pin 2000
is designed to fail in torsion while the notches 2010 are designed
to fail in bending, in this case posterior/anterior and/or
medial/lateral directions. Another failsafe option is provided in
FIG. 20B that relies on a mechanical system having a plurality of
springs 2020 connected to mechanical elements 2030, such as
spheres. The springs may be set or adjusted to the desired tension,
thereby tailoring failure to a specific individual. For example,
older bone may have a lower fracture stress than younger bone. One
advantage of the spring-set system of FIG. 20B is that the failsafe
may be reset, whereas the failsafe mechanically breaks in FIG. 20A.
Other examples of failsafe mechanisms include disk and spring,
sphere and spring, and shear pin and shock absorption.
[0118] FIG. 32 is another example, with the failsafe comprising a
central portion 3200 that is a notched tube to accommodate bending
and an end portion 3202 that is a tube clamp adapter for
accommodating torque. The notched tube can fail under a bending
load and the tube clamp adapter can fail under torque, including
under the exemplary torque failure for an average male. Failure
load under bending can be accommodated by varying the relative
depth of the notch to the tube thickness, with larger notches
failing under relative smaller bending loads than smaller notches.
The bottom schematics provide examples of tube clamp adaptors that
may be used to ensure failure above a certain torque. The bottom
right panel is a photograph of a commercial tube claim adapter from
Medex International, Inc. (Kensington, Md.). FIG. 32 is an example
where the failsafe involves material-controlled failures in bending
and torsion. The torque protection is provided by a tube clamp 3202
which may contain four screw receiver and set screws to operably
connect to a connector, such as the pyramid connector 800
illustrated in FIG. 32. The torque failure occurs by means of a
specified interference fit between the clamp and the internal tube.
The torque failure point is selected as desired, such as 50 Nm for
an average male. Preferably, the failsafe has a total height that
is minimal to limit required resection during surgery. For example,
the overall length of the failsafe illustrated in FIG. 32 may be
about 40 mm, with an even shorter effective length since the tube
and pyramid connector both connect internally.
[0119] The bending failure occurs by means of a stress
concentration in a failsafe central portion 3200, such as an
aluminum (Al 2024-T6) tube (FIG. 32). A hollow tube is preferred in
order to lessen the weight of the component. Based on loading
determination and average male statistics, failure should occur
with a bending moment of 220 Nm. Because the tube is axisymmetric,
a bending moment of this magnitude will cause failure of the device
in all transverse axes. The full assembly of the failsafe is
provided in the top right panel of FIG. 32. In this example, the
entire assembled height is about 85 mm, but again, the effective
height is less because of the internal pyramid connector
connections. The assembled failsafe mechanism provides an important
feature to the patient which is the ability for rotational
adjustment. This allows the patient to adjust his/her prosthetic to
the correct angle with relative ease and simplicity. This is done
by loosening the torque screws and rotating the device accordingly
and tightening the screws to the specified torque again.
Example 4: Experimental Results for Transcutaneous Implants of
Highly Porous Tantalum
[0120] Porous tantalum has been used in orthopedics for enhanced
bone in-growth. The purpose of this example is to evaluate and
validate soft tissue integration into transcutaneous porous
tantalum implants. Eighteen porous tantalum and four solid titanium
implants are placed in the subcutaneous tissues of swine. They are
harvested after six weeks and examined microscopically. Epidermal
contact, soft tissue penetration, and inflammation are scored for
each implant.
[0121] Fifteen of sixteen porous implants demonstrate soft and
vascular tissue penetration. Nine of sixteen porous implants
demonstrate epidermal contact. We use a score of 0-4 to describe
tissue ingrowth (0=none and 4=100%). Soft tissue penetration score
averages 1.25 at the post and 2.63 at the base of the implant.
Vascular penetration score average 1.0 at the post and 2.63 at the
base.
[0122] Inflammation is evaluated and scored from 0-4 (0=none and
4=marked inflammation). Acute inflammation is present in six of
sixteen porous implants with an average score of 1.88 at the post
and 0.81 at the base. Chronic inflammation is present in every
porous implant with a mean score of 1.5 at the post and 1.56 at the
base.
[0123] Three of the four solid titanium implants extruded during
the study. The one surviving implant does not demonstrate any
epidermal contact or tissue ingrowth with chronic and acute
inflammation scores of 2 at the base.
[0124] Porous tantalum transcutaneous implants experience
epidermal, soft tissue, and vascularized tissue integration with
minimal inflammation when placed in the subcutaneous tissues of
swine. This finding suggests a means for preventing deep infection
in transcutaneous implants.
[0125] Implantable prosthetic devices have been a mainstay in the
treatment of orthopedic problems. Joint replacements are just one
example. They have improved the quality of life of millions around
the world. The durability and function of these implants are
excellent and the complication rates are relatively low (2,8).
[0126] Efforts in the development of safe and effective
transcutaneous implants however, have not been as successful.
Although implantable transcutaneous prosthetics could be of value
(for example to the world's amputee population), issues with
infection originating at the skin/implant interface that
subsequently permeate proximally into the bone/implant interface
have precluded their routine use in the general population.
Infection rates of up to 18% in healthy selected individuals who
have received transcutaneous prostheses have been reported (16,21,
22).
[0127] A number of strategies have been employed and are under
current investigation as it relates to prevention of infection at
the skin-implant interface with variable results. The use of
topical antimicrobials, surface texturing, mechanical stabilization
of the skin interface, and surface coatings are reported in the
literature (4, 15-19). There have been few reports however, on the
use of highly porous tantalum, and what limited reporting that is
available is in a non-analagous rabbit skin model (19).
[0128] In an attempt to reduce the incidence of deep infection in
transcutaneous implants, this example investigates the use of
highly porous metal as a soft tissue in-growth medium to help
create a `biologic barrier` against infection at the skin/implant
interface. A newer generation of highly porous, open cell `foam`
materials may hold further advantage in creating a vascular
environment at the skin/implant interface.
[0129] One such technology is highly porous tantalum (Trabecular
Metal.TM. material or TM). This material is relatively inert and
can be manufactured up to 80% porosity by volume with open
interconnecting dodecahedral shaped cells, allowing for rapid
ingrowth of tissues. TM has been used reliably on the bone ingrowth
surfaces of orthopedic implants (6,7). An interesting
characteristic of highly porous materials is that when the cells
are filled with living tissues, the implants become more biologic
tissue (80%) than foreign material (20%). The resulting 80% living,
vascularized implant should then theoretically hold an advantage
against its solid metal counterpart in defending against infection
because of this permeating biological tissue acting as both a tight
barrier to foreign material as well as providing access to an
immune response to actively patrol against foreign material, such
as bacteria and virus.
[0130] This example evaluates the interaction of the soft tissues
and the degree of inflammation present when porous tantalum
transcutaneous implants are implanted in the subcutaneous tissues
of swine. The porcine model is selected due to the analogous skin
structure that swine share with humans. Specifically we ask the
questions: Do the soft tissues permeate the porous tantalum
implants, and if so to what degree? If so, do we see chronic and
acute inflammation in or around the implants in the short term and
in what depth patterns? A secondary goal of this study is to
evaluate the soft tissue interaction with similarly sized solid
titanium implants without porous tantalum material.
[0131] The percutaneous porous tantalum implants are expected to
demonstrate soft tissue integration with the cutaneous and
subcutaneous tissues at the interface providing a stable implant
that is infiltrated with biologic materials potentially more
resistant to infection. In addition, we expect that the degree of
inflammation present should decrease with depth relative to the
implant/skin interface because of vascularization that should
confine immune response toward the soft-tissue surface interface of
the animal.
[0132] MATERIALS AND METHODS: Two groups of implants consisting of
18 porous tantalum implants and 4 solid titanium alloy implants are
used. The porous tantalum implants consist of a 10 mm tall
by.times.9 mm diameter cylindrical percutaneous porous tantalum
upright post with a solid 5 mm diameter titanium alloy core atop a
5 mm thick.times.25 mm diameter discoid porous tantalum base. The
structure of the porous tantalum used is 80% porous with
dodecahedral interconnecting cells. The average open pore diameter
is 450 um. Control implants consisted of polished solid titanium
alloy with same outer geometry as the porous tantalum implants (see
FIG. 21).
[0133] Four domestic female Yorkshire Cross-bread Swine, each at
least 12 weeks of age and between 35-45 kg in weight, are used. The
animals are continuously housed at the research facility (MPI
Research Facility, Mattawan Mich.) and supervised by licensed
veterinarians. The animals are each designated as healthy and fit
for participation by the supervisory veterinarians upon arrival at
the facility.
[0134] On day zero of the study, the animals are taken to a sterile
operating theater. Each of the animals receive perioperative
antibiotics (preoperative dose of Cefazolin followed by 3 doses of
IV Ceftiofur post-operatively) and are anesthetized with routine
general anesthetics. Once anesthetized, the animals are placed in
the prone position and the dorsum of the animals shaved, prepared,
and draped in a sterile fashion using Chlorhexadine skin
preparation.
[0135] A total of 18 porous tantalum implants (6 per animal) are
placed in the dorsal subcutaneous tissues of the three test animals
designated 802, 804, and 806. Animal 805 receives the 4 solid
titanium alloy implants. In each animal, transcutaneous implants
are placed at equally spaced intervals parallel to the spine caudal
to the level of the scapulae and cranial to the level of the iliac
crests. Implants are placed at least 5 cm off the midline and
spaced at least 10 cm apart longitudinally.
[0136] First, a circular defect through the skin is created using a
9 mm dermal punch at each pre-designated implant site to permit
transcutaneous penetration of the implant post. Skin incisions are
then created extending away from both ends of the circular defect
by 1 cm in each direction parallel to the spine. A subcutaneous
pocket is created by blunt finger dissection down to the level of
the dorsal muscular fascia. The assigned implant is placed into
each pocket with the base placed deep abutting the fascia and the
post protruding percutaneously (see FIGS. 22-23). Once the implant
is positioned, the incision is closed with full thickness nylon
sutures to approximate the edges of the longitudinal incision and
`cinch up` the skin against the implant post. The implant sites are
dressed in a sterile fashion (see FIG. 24).
[0137] Post-operatively, animals are single housed in runs with
ample Aspen wood shavings and plexi-glass covering the chain link
fencing, to prevent the animals from rubbing the externalized
implants against the caging. Post-operative monitoring of the
implant sites is conducted through Day 10-14, based on healing at
the tissue-implant interface. Implant sites are bandaged Day 0-7
post-operatively with Xenofoam, dry, clean gauze, and VetWrap, or
other suitable covering. Discontinuation of dressings is dependent
on wound closure and healing around the implant post. Implant sites
are cleaned daily. Dirt, debris, and dried exudates are wiped off
the implants using clean gauze. Implant sites are then cleaned with
chlorhexadine solution. Following cleansing, each implant site is
then dried completely with gauze. Implant sites are each
photographed weekly.
[0138] At the termination of the study (Day 42.+-.1), all animals
are euthanized and the implant sites (18 porous tantalum implants
and 4 solid titanium implants) are photo-documented and excised
along with the surrounding soft tissues (see FIG. 25). Each
specimen is sectioned through the approximate longitudinal mid-line
of the defect site and was embedded in plastic (Technovit 7200
VLC). One ground and polished section is created from each plastic
block. All sections are stained with hematoxylin and eosin
(H&E) and assessed microscopically for epidermal contact, depth
of penetration of soft tissues into the implant, acute and chronic
inflammation, and depth of demonstrable vascular invasion by a
veterinary pathologist.
[0139] Microscopic observation of epidermal contact with the
implants is assessed as 0 if no contact is present, 1 if contact
was present on one side of the implant post, and 2 if contact is
present on both sides of the implant post.
[0140] The depth of penetration of soft tissue and vascular tissue
at the implant post is assessed using a `penetration score` of 0-4,
where 0=no penetration; 1=penetration of 1-25% of the distance to
the titanium post; 2=penetration of 26-50% of the distance to the
titanium post; 3=penetration of 51-75% of the distance to the
titanium post; and 4=penetration of 76-100% of the distance to the
titanium post.
[0141] A penetration score is also assigned to each implant at the
implant base. The depth of penetration of soft tissue and vascular
tissues into the implant base is scored on a scale of 0 to 4. No
penetration is given a score of 0; penetration confined to the
periphery of the implant is given a score of 1; penetration to the
center of the implant is given a score of 4; scores of 2 and 3
denote penetration to areas intermediate to the peripheral and
central areas.
[0142] Chronic and acute inflammation are assessed and scored at
both the post and base portions of the implants. Inflammation is
assessed a score of 0-4, where 0=finding not present, 1=minimal,
2=mild, 3=moderate, and 4=marked. Direct observation of bacterial
invasion is impossible to assess based on the methods of fixation
of the specimens in this study and therefore could not be measured
reliably.
[0143] Results: All animals survived to study termination. Sixteen
of the eighteen porous tantalum implants completely integrated with
the surrounding soft tissues and are present in the operative sites
at the time of study conclusion. One of the eighteen porous
tantalum implants partially extruded and one completely extruded
from the operative site Three of the four solid titanium implants
completely extruded during the course of the study with only one
remaining in situ.
[0144] Direct epidermal contact is found to be present in nine of
the sixteen porous implants (56%) at the skin/post interface. Of
the nine implants in which skin contact is observed, seven
exhibited contact with the epidermis on both sides of the implant
post while two showed unilateral contact. Each of the implants that
did not exhibit direct dermal contact, did exhibit soft tissue
ingrowth as described below. At the sites in which epidermis
contacted the post, the epidermis grew to the outer edge of the
trabeculae, but did not penetrate the pores (see FIG. 26). The only
remaining solid titanium implant did not exhibit any dermal contact
features microscopically (see FIG. 27).
[0145] We assess the degree of soft tissue penetration into the
implants. Soft tissues permeate fifteen of the sixteen (94%) porous
tantalum implants. This soft tissue in-growth occurred in the post
portion of the porous tantalum implant in six of sixteen (38%)
implants and in the base portion in fifteen out of sixteen porous
tantalum implants (94%). A soft tissue penetration score is
assigned to each implant based on the scoring scheme described
above. The mean soft tissue penetration score at the porous
tantalum post is 1.25 (Range 0-4, STD 1.81) and for tissues
permeating the base is 2.63 (Range 0 to 4, STD 1.54). Soft tissue
penetration is not seen in the solitary surviving solid titanium
implant.
[0146] Regarding vascular permeation into the implants, fifteen of
sixteen (94%) of the porous tantalum implants exhibit some degree
of vascular permeation. The depth of ingrowth is measured using the
same penetration score as that for soft tissue ingrowth. Most
permeation occurs within the base where 94% of the bases experience
vascular ingrowth with a mean score of 2.63 (Range 0 to 4, STD
1.54). Five of the sixteen porous tantalum implants exhibit
vascular ingrowth at the post level with a mean penetration score
of 1.0 (Range 0 to 4, STD 1.63). There is no vascular permeation
present in the sole solid titanium implant examined (see Table
6).
[0147] Acute Inflammation (AI) is evaluated in the retrieved
implants both at the level of the post and at the level of the
base. The degree of AI is scored on a scale from 0-4 as defined
above by the observing pathologist. Some degree of AI is found at
the post/soft tissue interface in all porous titanium implants with
a mean score of 1.88 (Range 0 to 3, STD 0.72). AI is also found in
six out of sixteen porous tantalum implant bases (38%) with a mean
score of 0.81 (Range 0 to 3, STD 1.22). In the only solid titanium
implant, there is no acute inflammation at the post and the acute
inflammation present at the base is scored 2.
[0148] Chronic inflammation (CI) is scored and recorded in a
similar fashion using the same scheme as that for acute
inflammation by the observing pathologist. Cl is present at the
post implant interface in fifteen of sixteen (94%) porous tantalum
implants with a mean score of 1.5 (Range 0 to 3, STD 0.73). Cl is
also present in every base with a mean score of 1.56 (Range 1 to 3,
STD 0.81). Chronic inflammation is not seen at the post of the sole
solid titanium implant and is scored as a 2 at the base (see Table
7).
[0149] Discussion: The development of safe and effective
percutaneous implants holds the potential to improve the lives of
millions of amputees worldwide. The recent wars in Iraq and
Afghanistan have added to the numbers of young, healthy, and
previously active amputees. With advances in center of mass
protection, battlefield injuries have become more survivable, but
have unfortunately yielded more combatants with loss of limb (1,5).
Many injured combatants wish to return to active duty and continue
the fight despite their injuries.
[0150] The predominant method of prosthetic fitting and attachment
in amputees has long been the molded socket. Using this method, the
residual limb is casted, and a custom molded socket interface is
created and placed around the residual limb with a distal
attachment point for the external prosthetic device. This
technology dates back hundreds of years and (with the exception of
changes in materials and techniques) has changed relatively little
over that time. This is an expensive and perpetual process over the
life of the amputee as their body shape and residual limb go
through constant changes (13). While for some patients, this
provides an acceptable interface, depending on the location of the
amputation and the body type of the individual, socket technology
can have its limitations.
[0151] As an example, energy transfer is extremely inefficient with
the current socket technology--especially in patients with above
the knee amputations (AKA). In this subgroup, it takes a single leg
amputee up to 50% more energy to perform the same task as a
well-bodied individual and up to 250% more energy in double
amputees at this level (7,20). This is mostly due to the depth of
the soft tissues that typically surrounds the femur and the energy
lost in transferring motion from an amputee's femur, through these
soft tissues, and then on to the prosthetic socket and eventually
the prosthesis itself.
[0152] Maintaining fit can also be an issue with the amputee
population using traditional socket technology. The average
individual fluctuates in weight over his adult lifetime by up to
10% (23). Weight fluctuation of this magnitude can make a socket so
loose it will fall off or so tight that it creates pressure and
skin breakdown. In addition, active amputees who perspire can have
difficulty with adherence of their prosthetic sockets. There is
also a subgroup of amputees who have skin breakdown issues related
to anything from skin conditions to underlying heterotopic bone
(6,10,14). Each of these issues would become irrelevant if there
were a safe, reliable, percutaneous skeletal attachment available
to amputees.
[0153] Although percutaneous implants have been used for many years
in the treatment of amputees in Europe, infection remains an issue
(16,21, 22). Unlike traditional prosthetic devices (such as hip and
knee replacements which are implanted completely below the dermal
barrier) transcutaneous prostheses, by definition, are exposed to
the outside world and the exposed portion inevitably becomes
colonized with bacterial flora. When that flora is allowed to
migrate along the implant, it eventually infects the bone/implant
interface causing deep-seated osteomyelitis and implant
loosening.
[0154] Various surface coating and texturing strategies have been
employed in an effort to reduce the transmigration of bacteria
along the implant's skin interface with some success. Puckett et al
(18) have demonstrated that nano-texturing the surface of titanium
alloy results in increase keratinocyte function (adhesion and
spreading). Salinized fibronectin has also been found to promote
adhesive surface cell alignment in vivo alone and when combined
with hydroxyapatite coatings (4).
[0155] Antimicrobials have been investigated as well. The topical
antimicrobial ceragenin was applied via an impregnated pad at the
skin-implant interface of transcutaneous implants in sheep, but
when compared to controls at 24 weeks, there was no advantage
relating to prevention of infection (17). Topical 1% pexiganan
acetate was applied daily to a percutaneous implant in a rabbit
model and was found to reduce incidence of infection by up to 75%
when compared to controls at 24 weeks (19).
[0156] Other authors have advocated mechanical stabilization of the
skin interface as a method to promote skin adhesion and prevent
infection. This has led in part to design elements with porous
subcutaneous flanges which have been used with success in Europe
(9, 15).
[0157] A critical element of this example was to demonstrate that
soft tissues in and below the skin can effectively integrate
themselves into porous tantalum implants. The most effective
defense against infection is biologic tissue adhesion and
apposition. Biologic tissues have an inherent mechanism to defend
against infection: the white blood cell. The vascularity within
biologic tissues can also deliver antibiotics (if necessary) to
sites of potential infection. By introducing vascularity into the
implant, the body's ability to defend against infection at the
skin/implant interface is harnessed, creating an effective barrier
against deep infection, and increasing the likelihood of successful
long-term transcutaneous implant survivability.
[0158] This example demonstrates effective, consistent soft tissue
and vascular penetration into porous tantalum implants with minimal
inflammation in a skin structure model analogous to that of humans.
Rather than being encapsulated and extruded as foreign materials
usually are, the vast majority of the porous tantalum implants
integrated with the tissues, becoming a part of them.
[0159] This example focuses on the soft-tissue and vascular
interface and so does not address a bone/implant interface. Because
there was no bone/implant interface, these implants lacked a stable
base and therefore were subjected to small amounts of motion, which
may have affected their ability to more fully in-grow. The goal of
this example was to focus on the skin-implant interface and prove
the viability of this concept before moving on to add other
elements such as osseous integration.
[0160] We were also unfortunately unable to directly compare the
porous tantalum implants to the solid implants due to the fact that
three of the four solid implants extruded during the study leaving
us only one solid implant to analyze. This made it impossible to
provide meaningful statistical comparison. However, we do believe
that this further demonstrates the advantage of porous materials
over solid materials.
[0161] This example confirms that highly porous tantalum implants
incorporate with soft tissues at the level of the dermis and
subcutis. This finding may be important in improving a
transcutaneous implant's ability to resist retrograde migration of
bacteria and subsequent infection in the long term. Further studies
in an amputee model can provide further understanding of this
process when it is coupled with a strong implant/bone base.
[0162] The terms and expressions which have been employed herein
are used as terms of description and not of limitation, and there
is no intention in the use of such terms and expressions of
excluding any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the invention claimed. Thus, it
should be understood that although the present invention has been
specifically disclosed by preferred embodiments, exemplary
embodiments and optional features, modification and variation of
the concepts herein disclosed may be resorted to by those skilled
in the art, and that such modifications and variations are
considered to be within the scope of this invention as defined by
the appended claims. The specific embodiments provided herein are
examples of useful embodiments of the present invention and it will
be apparent to one skilled in the art that the present invention
may be carried out using a large number of variations of the
devices, device components, methods steps set forth in the present
description. As will be obvious to one of skill in the art, methods
and devices useful for the present methods can include a large
number of optional composition and processing elements and
steps.
[0163] When a group of substituents is disclosed herein, it is
understood that all individual members of that group and all
subgroups are disclosed separately. When a Markush group or other
grouping is used herein, all individual members of the group and
all combinations and subcombinations possible of the group are
intended to be individually included in the disclosure. Specific
names of compounds are intended to be exemplary, as it is known
that one of ordinary skill in the art can name the same compounds
differently.
[0164] It must be noted that as used herein and in the appended
claims, the singular forms "a", "an", and "the" include plural
reference unless the context clearly dictates otherwise. As well,
the terms "a" (or "an"), "one or more" and "at least one" can be
used interchangeably herein. It is also to be noted that the terms
"comprising", "including", and "having" can be used
interchangeably. The expression "of any of claims XX-YY" (wherein
XX and YY refer to claim numbers) is intended to provide a multiple
dependent claim in the alternative form, and in some embodiments is
interchangeable with the expression "as in any one of claims
XX-YY."
[0165] Unless defined otherwise, all technical and scientific terms
used herein have the same meanings as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
any methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are now described.
Nothing herein is to be construed as an admission that the
invention is not entitled to antedate such disclosure by virtue of
prior invention.
[0166] Whenever a range is given in the specification, for example,
a size range, a porosity range, or a composition or concentration
range, all intermediate ranges and subranges, as well as all
individual values included in the ranges given are intended to be
included in the disclosure. As used herein, ranges specifically
include the values provided as endpoint values of the range. For
example, a range of 1 to 100 specifically includes the end point
values of 1 and 100. It will be understood that any subranges or
individual values in a range or subrange that are included in the
description herein can be excluded from the claims herein.
[0167] As used herein, "comprising" is synonymous with "including,"
"containing," or "characterized by," and is inclusive or open-ended
and does not exclude additional, unrecited elements or method
steps. As used herein, "consisting of" excludes any element, step,
or ingredient not specified in the claim element. As used herein,
"consisting essentially of" does not exclude materials or steps
that do not materially affect the basic and novel characteristics
of the claim. In each instance herein any of the terms
"comprising", "consisting essentially of" and "consisting of" may
be replaced with either of the other two terms. The invention
illustratively described herein suitably may be practiced in the
absence of any element or elements, limitation or limitations which
is not specifically disclosed herein.
[0168] One of ordinary skill in the art will appreciate that
starting materials, biological materials, reagents, synthetic
methods, purification methods, analytical methods, assay methods,
and biological methods other than those specifically exemplified
can be employed in the practice of the invention without resort to
undue experimentation. All art-known functional equivalents, of any
such materials and methods are intended to be included in this
invention. The terms and expressions which have been employed are
used as terms of description and not of limitation, and there is no
intention that in the use of such terms and expressions of
excluding any equivalents of the features shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the invention claimed. Thus, it
should be understood that although the present invention has been
specifically disclosed by preferred embodiments and optional
features, modification and variation of the concepts herein
disclosed may be resorted to by those skilled in the art, and that
such modifications and variations are considered to be within the
scope of this invention as defined by the appended claims.
Tables:
TABLE-US-00001 [0169] TABLE 1 Peak Forces and standard deviations
collected from literature involving daily activities presented as
their actual and normalized values with respect to mean body
weight. Mean Peak Forces Reference Force Units F.sub.AP+ F.sub.AP-
F.sub.ML+ F.sub.ML- F.sub.IS+ F.sub.IS- [10] Value (N) 101 137 93 x
769 x S.D. (N) 19 98 39 x 171 x Value (% BW) 12.5 16.9 11.5 x 95.0
x S.D. (% BW) 2.35 12.1 4.82 x 21.1 x [8] Value (% BW) 7.91 14.04
12.57 x 89.32 x S.D. (% BW) 0.123 0.051 0.072 x 0.033 x
TABLE-US-00002 TABLE 2 Moments and standard deviations collected
from literature involving daily activities presented as their
actual and normalized values with respect to mean body weight. Mean
Peak Moments Reference Moment Units M.sub.AP+ M.sub.AP- M.sub.ML+
M.sub.ML- M.sub.IS+ M.sub.IS- [10] Value Nm 27 x 17 30 5.3 6.3 S.D.
(Nm) 9 x 12 20 3.6 2.5 Value (% BW-m) 3.34 x 2.10 3.71 0.65 0.78
S.D. (% BW-m) 1.11 x 1.48 2.47 0.44 0.31 [8] Value (% BW-m) 2.8 x
1.2 2.4 x x S.D. (% BW-m) 9.4 x 55.7 12.1 x x
TABLE-US-00003 TABLE 3 Forces and moments with their respective
standard deviations during a forward fall of a transfemoral
amputee. Values are presented as their actual and normalized (to
body weight) units Peak Forces Force Units F.sub.AP+ F.sub.AP-
F.sub.ML+ F.sub.ML- F.sub.IS+ F.sub.IS- Value (N) 22.73 554.13
37.71 269.63 1144.56 x S.D. (N) 0 0 0 0 0 x Value (% BW) 2.49 60.77
4.14 29.57 125.52 x S.D. (% BW) 0 0 0 0 0 x Peak Moments Moment
Units M.sub.AP+ M.sub.AP- M.sub.ML+ M.sub.ML- M.sub.IS+ M.sub.IS-
Value Nm 20.87 10.46 153.36 11.39 30.01 13.11 S.D. (Nm) 0 0 0 0 0 0
Value (% BW-m) 2.29 1.15 16.82 1.25 3.29 1.44 S.D. (% BW-m) 0 0 0 0
0 0
TABLE-US-00004 TABLE 4 Summary of quantified loading ranges from
literature and HDL data: F.sub.AP F.sub.ML F.sub.IS M.sub.AP
M.sub.ML M.sub.IS Range (% BW) (% BW) (% BW) (% BW-m) (% BW-m) (%
BW - m) DL Upper Limit 215 86 608 25 136 5.8
TABLE-US-00005 TABLE 5 Maximum bone strains for different implants
and bone cuts: Implant Femur Length Spline Length (mm) Design Max
Strain 140 190 Sharp 15.579e-03 140 190 Smooth 10.751e-03 140 250
Sharp 11.464e-03 140 250 Smooth 8.016e-03 190 250 Sharp
4.878e-03
TABLE-US-00006 TABLE 6 Soft tissue and vascular tissue penetration
scores for porous tantalum implants. A measure of penetration to
the solid core of the post or the center of the base. Porous
Tantalum Implants Soft Tissue Penetration Score Vascular
Penetration Score Implant ID Post Level Base Level Post Level Base
Level 802-1 4 4 2 4 802-2 0 1 0 1 802-3 0 1 0 1 802-4 0 4 0 4 802-5
0 2 0 2 802-6 0 1 0 1 804-1 4 4 4 4 804-2 4 4 4 4 804-3 4 4 4 4
804-4 0 1 0 1 804-5 0 1 0 1 804-6 Extruded Extruded Extruded
Extruded 806-1 Extruded Extruded Extruded Extruded 806-2 0 4 0 4
806-3 0 4 0 4 806-4 3 4 2 4 806-5 1 3 0 3 806-6 0 0 0 0 Mean 1.25
2.625 1 2.625 STD 1.807 1.544 1.633 1.544 0 = no penetration, 1 =
25% penetration depth, 2 = 50% penetration depth, 3 = 75%
penetration depth, 4 = 100% penetration depth. The solid titanium
implant did not exhibit any soft tissue or vascular tissue
penetration.
TABLE-US-00007 TABLE 7 Acute and chronic inflammation scores in the
porous tantalum implants. A measure of intensity of inflammation at
the stem and base levels. Porous Tantalum Implants Acute
Inflammation Score Chronic Inflammation Score Implant ID Post Level
Base Level Post Level Base Level 802-1 2 0 1 1 802-2 3 0 1 1 802-3
2 0 2 1 802-4 2 1 2 1 802-5 1 0 0 1 802-6 3 0 1 1 804-1 1 0 1 1
804-2 2 0 2 1 804-3 2 0 1 2 804-4 1 0 1 1 804-5 1 3 3 3 804-6
Extruded Extruded Extruded Extruded 806-1 Extruded Extruded
Extruded Extruded 806-2 3 3 2 2 806-3 2 0 2 1 806-4 2 1 2 2 806-5 1
2 1 3 806-6 2 3 2 3 Mean 1.875 0.8125 1.5 1.5625 STD 0.719 1.223
0.730 0.814 Microscopic findings in the dermis and subcutis were
assessed on a scale of 0-4, where 0 = no inflammation, 1 = minimal
inflammation, 2 = mild inflammation, 3 = moderate inflammation, and
4 = marked inflammation.
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