U.S. patent application number 12/759455 was filed with the patent office on 2010-08-05 for prophylactic bactericidal implant.
Invention is credited to Thomas A. Fuller, Wayne J. Sebastianelli, Richard A. Wysk.
Application Number | 20100198357 12/759455 |
Document ID | / |
Family ID | 42398367 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100198357 |
Kind Code |
A1 |
Fuller; Thomas A. ; et
al. |
August 5, 2010 |
PROPHYLACTIC BACTERICIDAL IMPLANT
Abstract
A medical implant system is described for inhibiting infection
associated with a joint prosthesis implant. An inventive system
includes an implant body made of a biocompatible material which has
a metal component disposed on an external surface of the implant
body. A current is allowed to flow to the metal component,
stimulating release of metal ions toxic to microbes, such as
bacteria, protozoa, fungi, and viruses. One detailed system is
completely surgically implantable in the patient such that no part
of the system is external to the patient while the system is in
use. In addition, externally controlled devices are provided which
allow for modulation of implanted components.
Inventors: |
Fuller; Thomas A.; (State
College, PA) ; Wysk; Richard A.; (Boalsburg, PA)
; Sebastianelli; Wayne J.; (Boalsburg, PA) |
Correspondence
Address: |
ANDREW J. CORNELIUS, P.C.
305 MT. LEBANON BOULEVARD, SUITE 205
PITTSBURGH
PA
15234
US
|
Family ID: |
42398367 |
Appl. No.: |
12/759455 |
Filed: |
April 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11172138 |
Jun 30, 2005 |
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12759455 |
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Current U.S.
Class: |
623/23.53 ;
607/2; 623/23.54; 623/23.6 |
Current CPC
Class: |
A61B 17/866 20130101;
A61F 2002/3631 20130101; A61F 2310/00155 20130101; A61F 2002/30329
20130101; A61F 2310/00149 20130101; A61F 2310/00395 20130101; A61L
2300/102 20130101; A61F 2/36 20130101; A61F 2310/00113 20130101;
A61F 2310/00467 20130101; A61F 2002/30433 20130101; A61F 2220/0041
20130101; A61F 2310/00107 20130101; A61F 2002/2821 20130101; A61F
2002/30668 20130101; A61F 2002/3625 20130101; A61F 2/0095 20130101;
A61F 2/34 20130101; A61F 2002/30235 20130101; A61F 2002/305
20130101; A61F 2002/30535 20130101; A61F 2310/00455 20130101; A61F
2310/00083 20130101; A61F 2310/00514 20130101; A61N 1/30 20130101;
A61F 2/30 20130101; A61F 2002/30405 20130101; A61F 2230/0069
20130101; A61B 17/86 20130101; A61L 2300/602 20130101; A61F 2/3662
20130101; A61L 2300/404 20130101; A61F 2002/30932 20130101; A61N
1/20 20130101; A61F 2/30767 20130101; A61F 2002/30718 20130101;
A61F 2220/0025 20130101; A61N 1/00 20130101; A61L 2300/104
20130101; A61N 1/205 20130101; A61B 17/864 20130101; A61F 2/3609
20130101; A61F 2310/00029 20130101; A61F 2310/00568 20130101; A61F
2250/0026 20130101; A61F 2310/00562 20130101; A61F 2/0077 20130101;
A61F 2002/30677 20130101; A61F 2002/3611 20130101; A61F 2002/482
20130101; A61F 2002/30593 20130101; A61F 2250/0058 20130101; A61F
2310/00077 20130101; A61F 2/30724 20130101; A61B 2017/00734
20130101; A61F 2310/00449 20130101; A61L 2300/606 20130101; A61F
2310/00473 20130101; A61F 2/367 20130101; A61L 27/54 20130101; A61F
2250/0043 20130101; A61F 2310/00059 20130101; A61F 2310/00413
20130101; A61L 27/306 20130101; A61N 1/18 20130101; A61L 27/30
20130101; A61F 2002/30354 20130101; A61F 2/28 20130101; A61F
2250/0001 20130101; A61F 2002/30322 20130101; A61F 2310/00065
20130101; A61L 2430/02 20130101; A61F 2002/009 20130101; A61F
2310/00461 20130101; A61F 2/3676 20130101; A61F 2002/30795
20130101; A61F 2002/368 20130101; A61F 2220/0033 20130101; A61F
2002/30604 20130101; A61L 2/0082 20130101; A61F 2310/0052 20130101;
A61B 17/8685 20130101; A61B 17/60 20130101; A61F 2/30744 20130101;
A61F 2002/30589 20130101; A61F 2310/00071 20130101; A61F 2/32
20130101 |
Class at
Publication: |
623/23.53 ;
623/23.6; 623/23.54; 607/2 |
International
Class: |
A61F 2/28 20060101
A61F002/28; A61N 1/00 20060101 A61N001/00 |
Claims
1. A medical implant system, comprising: an implant body made of a
biocompatible material, the implant body having an external
surface; a metal component disposed on the external surface of the
implant body; a conduit for electrical current, the conduit in
contact with the metal component; and a power source in electrical
communication with the conduit for electrical current.
2. The medical implant system of claim 1, wherein the implant body
further comprises: an internal cavity, the internal cavity having a
wall and an opening; and a cap removably disposed in the opening of
the internal cavity, wherein the power source is disposed in the
internal cavity and wherein the conduit is the implant body.
3. The medical implant system of claim 1, wherein the implant body
is adapted to be disposed totally within a human body when in
use.
4. The medical implant system of claim 2, further comprising a
metal component disposed on a portion of the internal cavity
wall.
5. The medical implant system of claim 1, wherein the metal
component comprises silver.
6. The medical implant system of claim 1, wherein the metal
component comprises a metal selected from the group consisting of:
gold, zinc, copper, cadmium, cobalt, nickel, platinum, palladium,
manganese, and chromium.
7. The medical implant system of claim 1, wherein the metal
component is a coating disposed on the external surface of the
implant body.
8. The medical implant system of claim 7, wherein the metal coating
ranges in thickness between 1.times.10.sup.-9-5.times.10.sup.-5
meters.
9. The medical implant system of claim 7, wherein the metal coating
is disposed on a portion of the external surface of the implant
body ranging from 1-100% of the external surface of the implant
body.
10. The medical implant system of claim 7 wherein the metal coating
is disposed on a portion of the external surface of the implant
body ranging from 50-99% of the external surface of the implant
body.
11. The medical implant system of claim 7, wherein the metal
coating is disposed as a single region of continuous coating on the
external surface.
12. The medical implant system of claim 7, wherein the implant body
comprises an articular surface having no coating.
13. The medical implant system of claim 7, wherein the metal
component is in the form of a wire disposed on the external
surface.
14. The medical implant system of claim 1, wherein the metal
component is more electrically conductive than the biocompatible
material.
15. The medical implant system of claim 1, further comprising a
resistor in electrical communication with the power source.
16. The medical implant system of claim 1, further comprising a
switch in electrical communication with the power source.
17. The medical implant system of claim 16, further comprising a
controller in signal communication with the switch.
18. The medical implant system of claim 2, wherein the cap is made
of an electrically insulating material.
19. The medical implant system of claim 1, further comprising an
electrically insulating material disposed between the external
surface of the implant body and the metal component.
20. The medical implant system of claim 17, wherein the controller
is external to the body of an individual having an implant body
disposed therein.
21. A method for inhibiting microbial infection associated with an
orthopedic implant, comprising: providing a medical implant system
according to claim 1; delivering a current to a metal component
disposed on an external surface of an implant body, the implant
body located in a human body at a site of potential infection,
wherein the delivery of current to the metal component causes
release of metal ions toxic to an infectious microbe at the site of
potential infection, such that microbial infection is inhibited.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Patent Application Ser. No. 60/585,159, filed Jul. 1, 2004, the
entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to systems and methods for inhibition
of microbial infection related to surgical implant devices. In
particular, the invention relates to systems and methods for
inhibition of microbial infection related to orthopedic
implants.
BACKGROUND OF THE INVENTION
[0003] Joint degeneration is the leading chronic condition in the
elderly; it affects one in every eight Americans and almost half
the population over the age of 65. (Brooks, P. M, Med. J. Aust.,
173:307-308, 2000) The most common form of joint degeneration is
osteoarthritis. Osteoarthritis weakens and breaks down cartilage
and bone, causing pain as bones rub together. Eventually the
constant rubbing of the bony surfaces destroys the surfaces that
are rubbing against one another leading to rough, painful movement.
Total joint replacement, or arthroplasty, represents a significant
advance in the treatment of painful and disabling joint
pathologies. Arthroplasty can be performed on almost any joint of
the body including the hip, knee, ankle, foot, shoulder, elbow,
wrist, and fingers. Total joint replacement: whether hip, knee,
ankle, foot, shoulder, elbow, wrist, and fingers or other, is
typically done as a final stage treatment for a patient who suffers
from some form of joint degeneration.
[0004] In its early stages, many people manage arthritis pain
conservatively by using anti-inflammatory medicines, weight
reduction, lifestyle modification, physiotherapy, or occupational
therapy. However, as the disease progresses the pain intensifies.
When the pain gets to the point where everyday, normal activities
such as putting on shoes and socks or walking up stairs become too
painful, total joint replacement surgery is an attractive option to
restore movement and independence, and to dramatically reduce
pain.
[0005] Although joint replacement is a relatively large field
within orthopedics, the number of fracture fixation devices
utilized around the world far outranks the number of artificial
joints. Fracture fixation is growing daily as the number of
fractures associated with trauma accidents is increasing. Fixation
devices can be internal or external in nature and include devices
such as a plate, wire, screw, pin, rod, nail or staple, which aid
in maintaining fracture fragments in proper position during
healing. Such devices are usually inserted after open reduction of
the fracture and will remain for the entirety of the healing
process, often becoming a permanent structure within the body.
[0006] Joint replacement surgery began in the early 1950's, and its
frequency has grown as surgical techniques and medical care
associated with surgery improves. In the late 1980's between
500,000 and 1 million total hip replacements were performed per
year, while in 2004 it is estimated that approximately 600,000
joint prosthesis and 2,000,000 fracture-fixation devices will be
inserted into patients in the United States.
[0007] Unfortunately, as the number of implant surgeries increases,
the number of associated infections also increases. Any person who
has an implant is at risk for developing an infection associated
with the device. It is estimated that 2% of joint prostheses and 5%
of fixation devices will become infected. Taking 3% as an average
estimate of infected implants, as many as 30 million incidents of
infection may occur.
[0008] The effects of implant infection are expensive as well as a
danger to the health and well-being of the affected individual. For
example, infection results in direct medical and surgical costs and
additionally may cause patient pain, suffering, lost wages, lost
work and decreased productivity. On average an infected hip
prosthesis patient spends six times the number of days in the
hospital when compared to the non-infected prosthetic hip patient.
In 1991, the total cost of an infected patient, both in hospital
and as an outpatient, was $45,000 as compared to the total cost of
$8,600 associated with a non-infected patient. (Bengston, S., Ann.
Med., 25:523-529, 1993)
[0009] Joint replacement implants and fixation devices include a
variety of materials foreign to the human body, such as metals,
plastics, and polymeric substances, all of which have the potential
to serve as substrates for attachment and growth of
microorganisms.
[0010] In particular, certain microorganisms may exude a glycocalyx
layer that protects certain bacteria from phagocytic engulfment by
white blood cells in the body. The glycocalyx also enables some
bacteria to adhere to environmental surfaces (metals, plastics,
root hairs, teeth, etc.), colonize, and resist flushing.
[0011] Once microorganisms colonize an implant, it is often very
difficult to eradicate or even inhibit the infection. For example,
systemic administration of antibiotics is often ineffective due to
limited blood supply to the areas of the implant. Additionally,
many bacterial species today are resistant to antibiotics.
[0012] Where infection cannot be inhibited it may spread and become
even more serious, as in patients who have an infection within the
bone, osteomyelitis. Such patients often must undergo a difficult
and costly treatment involving extended hospitalization, joint
debridement, aggressive antimicrobial therapy, total joint removal
followed by total joint replacement and possible amputation if the
infection can not be eliminated.
[0013] Since implantation of an orthopedic implant device, such as
a joint replacement prosthesis or fixation device, is quite common
and associated infection frequent, there is a continuing need for
new approaches to inhibition of infection. In particular, it would
be very desirable for both the physician as well as the patient to
be able to treat a prosthetic osteomyelitic infection without the
removal of an implant. Further, economical and safe apparatus and
methods of inhibiting implant associated infections are needed.
SUMMARY OF THE INVENTION
[0014] A medical implant system is provided which includes an
orthopedic implant body made of a biocompatible material. In one
option, the implant body is a joint replacement prosthesis implant.
In a further option, the implant body is an orthopedic fixation
device. Optionally, more than one implant body is provided as part
of an inventive system. The implant body has an external surface
and a metal component is disposed on the external surface of the
implant body. An inventive system further includes a conduit for
electrical current wherein the conduit is in contact with the metal
component. A power source is also included which is in electrical
communication with the conduit for electrical current. More than
one power source may be provided, for example, where more than one
implant body is included.
[0015] Optionally, an implant body is a joint replacement
prosthetic implant. In a further option an implant body is a part
of a joint replacement prosthetic implant
[0016] In one embodiment, an internal cavity having a wall and an
opening is included in the implant body and a cap is provided to
close the opening of the internal cavity. A power source is
positioned in the internal cavity. The conduit for electrical
current provided in such an embodiment is optionally the implant
body itself. Thus, a current from the power source may be connected
to the metal component through the biocompatible material of the
implant body.
[0017] In a further option, the implant body is adapted to be
disposed totally within a human body when in use as an implant.
[0018] Also optionally, a metal component disposed on a portion of
the internal cavity wall, preferably such that the portion of the
metal component in the cavity is continuous with the portion of the
metal component disposed on the external surface of the implant
body. Also preferably, the metal component in the cavity has the
same composition as the metal component on the external surface.
Optionally, the form of the metal component in the cavity is the
same or different compared to the form of the metal component on
the external surface. For example, a wire or metal ribbon may be
attached to the metal component on the external surface and to the
cavity wall. In one embodiment, the metal component in the cavity
is in contact with a terminal of a power source disposed
therein.
[0019] In a preferred option, the metal component includes a
transition metal, selected from gold, zinc, copper, cadmium,
cobalt, nickel, platinum, palladium, manganese, and chromium. In a
further preferred option, the metal component includes silver.
[0020] In a further preferred option, the metal component is more
electrically conductive than the biocompatible material of the
implant body.
[0021] One form of a metal component is a coating disposed on the
external surface of the implant body. Such a metal coating ranges
in thickness between 1.times.10.sup.-9-5.times.10.sup.-3 meters,
inclusive.
[0022] Optionally, a metal coating disposed on a portion of the
external surface of the implant body covers a portion of the
external surface ranging from 1-100% of the total external surface
of the implant body. Further optionally, the metal coating disposed
on a portion of the external surface of the implant body covers a
portion of the external surface ranging from 50-99% of the external
surface of the implant body. Preferred is a configuration in which
the metal coating is disposed as a single region of continuous
coating on the external surface.
[0023] In one embodiment of an inventive medical implant system the
implant body includes an articular surface which does not include a
metal component such as a metal coating.
[0024] In another option, metal component is provided in the form
of a wire, ribbon, or foil disposed on the external surface.
[0025] An inventive system may be configured such that the power
source is continuously powering a current conducted to the metal
component for release of metal ions. Alternatively, a system
includes a switch for powering the current on or off. In a further
embodiment, the current is modulated by circuitry adapted to
control the current so as to increase or decrease the amount of
current flowing and the amount of metal ions released. Thus, a
resistor in electrical communication with the power source is
optionally included. In a preferred embodiment, the resistor and
power source are positioned in an internal cavity of the implant
body. Optionally, a switch in electrical communication with the
power source is included to control the power source. Further
optionally, a controller in signal communication with the switch is
provided. Such a controller is operated to send a signal to a
system component adapted to receive the signal and to control the
switch. Preferably, a controller is external to an individual
having the implant, such that activation of the switch may be
performed by a doctor, technician or by the patient.
[0026] Also described is a method for inhibiting microbial
infection associated with an orthopedic implant, which includes
providing an inventive system and delivering a current to a metal
component disposed on an external surface of an implant body, the
implant body located in a human body at a site of potential
infection. Delivery of current to the metal component is associated
with antimicrobial action such as release of metal ions toxic to an
infectious microbe at the site of potential infection, such that
microbial infection is inhibited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a line drawing of an apparatus according to an
embodiment of the invention in the form of a hip joint implant
showing a portion of the exterior of the implant and a cut away
portion;
[0028] FIG. 1A is a line drawing of an apparatus according to an
embodiment of the invention in the form of a hip joint implant
showing an exterior view of the implant;
[0029] FIG. 2 is a line drawing of an apparatus according to an
embodiment of the invention in the form of a hip joint implant
having a power source external to the body of the patient;
[0030] FIG. 3 is a line drawing of a hip joint implant apparatus
according to an embodiment of the invention, showing transmission
of a signal to the apparatus in situ; and
[0031] FIG. 4 is a line drawing of an inventive bone screw implant
body.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention provides methods and apparatus for
prevention and inhibition of implant-associated infection.
[0033] A medical implant system is provided which allows for
release of microbe-inhibiting metal ions in the vicinity of a
temporary or permanent surgically implanted device. In particular,
metal ions are released from a metal component of an implant by
application of an electrical current to the metal component. A
power source for producing the electrical current is provided which
may be external to the implant, or preferably, contained within the
implant.
[0034] A medical implant system is provided which includes an
implant body made of a biocompatible material. A metal component is
disposed on the external surface of the implant body and a power
source is included to power delivery of an electrical current to
the metal component. The electrical current is delivered to the
metal component via an electrical conduit. In a preferred
embodiment, the metal component is different than the biocompatible
material. Thus, where the biocompatible material is a metal, the
metal component differs in composition from the biocompatible
material. For instance, preferably, the metal component has a
higher conductivity than the biocompatible material.
[0035] The term "implant body" as used herein refers to an
orthopedic implant for replacement or repair of a component of the
musculoskeletal system. For example, an orthopedic implant includes
a joint replacement prosthetic implant for joint replacement or
repair. Prosthetic implants include those for replacement or repair
of any joint illustratively including a knee, a hip, an ankle, a
shoulder, a wrist, and a finger or toe joint among others. Further,
an orthopedic implant is an orthopedic fixation device used in
replacement or repair of a component of the musculoskeletal system,
such as a plate, wire, screw, pin, rod, nail or staple. In a
preferred embodiment, an implant body is preferably an implant body
which is wholly contained within a patient's body when in use for
the purpose of the implant.
[0036] The term "biocompatible material" as used herein refers to a
material which is relatively inert in use following surgical
placement into an individual such that adverse reactions such as
inflammation and rejection are rare. The biocompatible material is
sufficiently strong and durable to allow the implant to perform its
intended function, such as joint replacement or fixation. Exemplary
biocompatible materials include metal materials such as surgical
stainless steel, titanium, and titanium alloys; ceramics; plastics;
and combinations of these.
[0037] The metal component includes a metal which inhibits
infection by microbes, such as bacteria, protozoa, viruses, and
fungi. Such antimicrobial metals are typically transition metals
illustratively including silver, gold, zinc, copper, cadmium,
cobalt, nickel, platinum, palladium, manganese, and chromium. A
metal component preferably contains at least 50% by weight of an
antimicrobial metal, further preferably contains at least 75% by
weight of an antimicrobial metal and still further preferably
contains at least 95% by weight of an antimicrobial metal. In
another preferred embodiment, the metal component is substantially
all antimicrobial metal. The antimicrobial properties of silver are
particularly well characterized and a metal component preferably
contains at least 50% by weight silver, further preferably contains
at least 75% by weight silver and still further preferably contains
at least 95% by weight silver. In another preferred embodiment, the
metal component is substantially all silver. In particular, the
metal component is capable of releasing a metal ion when an
electrical current is applied to the metal component.
[0038] In a preferred embodiment, the metal component is in the
form of a coating disposed on the external surface of the implant
body. The coating can be applied by any of various methods
illustratively including dunk coating, thin film deposition, vapor
deposition, and electroplating. The metal component in the form of
a coating ranges in thickness between
1.times.10.sup.-9-5.times.10.sup.-3 meters, inclusive, preferably
1.times.10.sup.-7-4.times.10.sup.-3 meters, inclusive, and more
preferably between 0.5.times.10.sup.-6-5.times.10.sup.-4 meters in
thickness.
[0039] In an example including a silver coating metal component,
the total amount of silver used during the coating process ranges
between 0.016 grams in weight and 8.95 grams in weight. Such a
coating is at least 0.016 grams in weight in order for enough
silver material to be present for the ionization to occur. The
total weight of silver typically does not exceed 8.95 grams in
order to maintain a nontoxic state for the patient.
[0040] In an embodiment including a metal coating disposed on the
external surface of the implant body, a metal coating is preferably
disposed on at least 50% of the external surface of the implant
body, and more preferably a coating is disposed on at least 75% of
the external surface of the implant body. In an embodiment
including a metal coating disposed on the external surface of the
implant body, the coating is optionally disposed on substantially
all of the external surface of the implant body. In a further
option, the implant body is coated with the metal coating on
substantially all of the external surface excluding one or more
articular wear surfaces. An "articular wear surface" is a portion
of an implant body which is exposed to wear during normal use when
implanted. For example, a hip joint implant includes articular wear
surfaces at the interface of the "ball" and "socket" components of
the joint prosthesis, that is, at the acetabular surfaces. Where
the implant body is a fixation device, it is preferred that the
coating is present on at least 50% of the external surface of the
implant body, and more on at least 75% of the external surface of
the implant body, and further preferably on substantially all of
the external surface of the implant body, including threads where
the device is a bone screw.
[0041] A metal coating is preferably disposed on the external
surface as a single continuous expanse of the coating material.
[0042] Optionally, the metal component is in the form of a wire,
ribbon, or foil disposed on the external surface of an implant
body. Such a metal component may be attached to the implant body by
welding, by an adhesive, or the like.
[0043] In order to deliver an electrical current to the metal
component and release antimicrobial metal ions, a power source is
included in an inventive system. A power source may be any of
various power sources such as a battery, capacitor, or connection
to external AC. Such power sources are known in the art.
[0044] In one embodiment of an inventive system, a power source is
implanted in the body of an individual receiving a joint
prosthesis. An implant power source in such an embodiment is
self-contained, that is, requiring no connection to external power.
Illustrative examples include an electrochemical cell such as a
battery and a capacitor. In a preferred embodiment, the implant
body has an internal cavity housing the power source and,
optionally, other components of the system, including circuitry
adapted to modulate a current from the power source.
[0045] An internal cavity in an implant body includes a wall
defining the cavity and an opening for insertion of a power source
and, optionally, other components of the system.
[0046] In general, a preferred power source housed in an implant
body cavity is lightweight and sized to fit in the cavity. In
addition, a power source housed in an implant body cavity is
capable of producing electrical currents in the range of 0.1-200
microamps. A power source housed in an implant cavity may be
selected according to the requirements of a patient. For example, a
temporary implant may not require a power source having as long a
life expectancy as a permanent implant.
[0047] In a further embodiment, circuitry adapted to modulate an
electrical current is included in an inventive system. Metal ions
can be mobilized in greater quantities by increasing the current
that is applied to the implant. If the current is increased a
greater concentration of metal ions, preferably silver ions, will
be provided near the surface of the implant. The greater
concentration of silver ions will create a greater diffusion
constant and provide for a greater distance of penetration by the
ions. Similarly, current may be modulated to decrease ion release
as desired, such as where no infection is believed to be
present.
[0048] For example, a resistor, a switch, a signal receiver, a
relay, a signal transmitter, transformer, a sensor, or a
combination of these or other such components and connectors may be
included, optionally configured as a circuit board arrangement. In
a preferred embodiment, all or part of the circuitry adapted to
modulate an electrical current included in an inventive system is
housed in a cavity in the implant body of an orthopedic
implant.
[0049] Thus, optionally, the internal cavity also contains a
resistor for modulation of the current. For example, a resistor in
series with a battery allows use of a larger size battery with a
greater lifetime. The resistor in series can be used to reduce
current flow to a desired level.
[0050] Once a power source capable of producing the required
current and of the appropriate size is determined, a resistance can
be calculated by using the equation; V=I*R .Where V is the voltage
of the battery that has been selected, I is the current, 1
microampere, and R is the resistance that will allow for the
current to flow from the determined battery. This resistor then can
be placed in series with the power source to yield the required
current. It is noted that neither the current nor the voltage
delivered from a power source will be altered by the size of the
implant.
[0051] In a specific example, a surface mounted chip resistor will
satisfy the requirements of the resistor for use in this
application. Surface mounted chip resistors come in a variety of
resistances, ranging form 1 ohms up to 51 mega-ohms. Surface
mounted chip resistors are manufactured in a variety of sizes which
will meet the size constraints. For example, the Ohmite, thick film
high voltage SMD chip, series MMC08 will easily fit within the
shaft of the redesigned hip implant. The MMCO8 has dimensions of
over all length of 2.0 millimeters and over all width of 1.25
millimeters. This particular resistor is manufactured in resistance
between 100 ohms and 51 mega-ohms.
[0052] An inventive implant system may be configured such that a
desired amount of an antimicrobial metal ion is released over a
specified period of time so as to optimize the inhibitory effects
on undesirable microbes and minimize any unwanted side effects. In
one embodiment, an inventive implant system is configured such that
an included power source is in continuous operation and metal ions
are released continuously.
[0053] In a preferred option, a switch is included in an inventive
system to control current to flow from the power source to the
metal component. A switch allows antimicrobial ions to be released
during specified periods of time by controlling current flow. For
example, the switch is turned on to activate current and release
antimicrobial ions at regular intervals, such as once a week or
once a month, for a time following implantation in order to prevent
infection. Further, where an infection is detected or suspected,
the switch is activated to allow current flow and release of metal
ions to combat the infection. An included switch is capable of
withstanding the current and the voltage transferred across it.
[0054] A switch is optionally and preferably controlled by a
controller external to the body of the individual having an
implanted prosthesis. An external controller may emit a signal
operative to control a switch. In one example, a magnetically
controlled switch, such as a reed switch is used. Magnetically
based switches that are externally controlled by a controller are
currently manufactured and are available from commercial sources.
Such switches are controlled by a controller including a magnet
which is placed in proximity to the switch in order to turn the
switch on or off. For example, a magnet may be positioned in the
vicinity of a patient's hip in order to activate a magnetically
controlled switch in an internal cavity of a hip prosthesis
implant. Thus, the switch is in signal communication of with the
controller.
[0055] Optionally, a transmitter is included in an inventive system
which is in signal communication with receiver circuitry adapted to
operate a switch and modulate current flow. Preferably the
transmitter is activated external to the body of an individual
having an implanted prosthesis as described herein. For example, a
radio frequency transmitter may be used to transmit a radio
frequency signal to receiver circuitry in the internal cavity of
the implant body adapted to operate a switch and modulate current
flow.
[0056] In a further embodiment, microchip circuitry, programmed to
modulate current flow is included in an inventive system.
Preferably, the microchip circuitry is included in a cavity of an
inventive implant body. In a further embodiment, such microchip
circuitry may be implanted at a second location in the implant
patient, such as just under the skin, to remotely control the
current flow.
[0057] A sensor may be included to sense microbial growth, such as
bacterial growth on an external surface of an implant body. Such a
sensor communicates a signal indicating bacterial growth to
circuitry adapted to activate a switch, stimulating release of
metal ions and inhibiting the microbes.
[0058] Preferably, the implant body having a power source in an
internal cavity is adapted to be disposed totally within a human
body when in use. Thus, the implant body preferably has
substantially the same dimensions and shape of a conventional
implant body.
[0059] In a preferred option, a portion of the metal component is
disposed in the internal cavity. For example, in a preferred
option, a metal coating is present on a portion of the wall of the
internal cavity. Such a metal coating is preferably continuous with
a metal component, such as a coating, disposed on the external
surface of the implant body. Optionally, and preferably, a metal
component present in the internal cavity is in electrical contact
with one terminal of a power source present in the cavity. A metal
component present in the cavity may also be in the form of a wire,
ribbon, or foil. Preferably the metal component in the cavity is in
the same form as the metal component present on the external
surface of the implant body and is continuous therewith.
[0060] In a preferred option, a metal component disposed on the
external surface and/or internal cavity wall is more electrically
conductive than the biocompatible material of which the implant
body is made.
[0061] The internal cavity has an opening which can be closed using
a cap which may be attached to the implant body, such as by a
hinge, or completely detachable.
[0062] In a preferred option, the cap is made of an electrically
insulating material.
[0063] In a further option, an electrically insulating material is
disposed between the external surface of the implant body and the
metal component.
[0064] A conduit for conduction of an electrical current from the
power source is included in an inventive system. In one embodiment,
the conduit is the biocompatible material of the implant body. In a
further embodiment, a power source is external to the body of the
individual having the implanted prosthesis and the conduit
traverses the skin of the individual, connecting the metal
component disposed on the implant body with the external power
source.
[0065] FIG. 1 illustrates an exemplary embodiment of an inventive
apparatus 100 in a partial external, partial cut away view. A
drawing illustrating a prophylactic bactericidal hip implant is
shown having a silver coating, depicted as stippling, on the
external surface 120. An internal cavity 170 is shown in cut away
sectional view, shown as the stripe marked region. This cavity
allows for the internal placement of the battery, switch and
resistor components. A switch 130, resistor 140 and battery 150 are
shown, which are contained in the cavity. The remaining end of the
original shaft has been machined to form a cap 160 so that a press
fit of the cap 160 in cavity 170 can be obtained after assembly of
the internal components. In this example, no coating is present on
surfaces tending to wear due to interaction with other implant
parts or natural elements of the body, articular surfaces, shown
without stippling or stripe marks at 180. This allows for a dead
end electrical circuit between the battery and the external silver
surface. Current will flow through the better conductor, the silver
coating, to the external surface and thus avoid the much poorer
conductor, internal residual hardware device.
[0066] FIG. 1A shows an external view of a hip implant body 100
illustrating a metal coating, such as a silver coating, shown as
stippling, present on an external surface 120 of the implant body.
The coating is present on the cap 160 as well in this illustration
but not on articular or wear surfaces as shown at 180.
[0067] A conduit from one terminal of the power source and a metal
component is optionally provided in the form of a wire extending
there-between. As noted above, a further connection between the
metal component and a second terminal of the power source is
optionally provided.
[0068] In a further preferred embodiment of the invention, a metal
component is in removable contact with the implant. For example, a
metal component is in removable contact with an implant may have
the form of a metal wire in contact with an implant surface.
[0069] In another embodiment of an inventive system, a conduit is
provided which extends outside of the body of an individual having
an implant prosthesis according to the invention. For example, a
conduit is provided in the form of a wire such that one end of the
wire may be positioned in proximity to the metal component of an
implanted prosthesis, preferably in contact with the metal
component in order to deliver current and release metal ions from
the metal component. The opposite end of the wire optionally may
extend outside the body to contact a power source. The conduit is
optionally removed when risk of infection is low and may be
repositioned for stimulation of metal ion release as desired.
[0070] FIG. 2 illustrates an inventive system 200 in the context of
a human body including an external power supply 250 and a conduit
270 contacting an implant body 210 having a metal coating, shown as
stippling, on a portion of the surface of the implant body 210. It
will be noted that no coating is present on an acetabular wear
surface of the implant prosthesis. Further shown is the "cup"
portion of a hip replacement implant, marked by stripes.
[0071] Another embodiment of an inventive apparatus is shown in
FIG. 3 which shows an inventive system 300 including a hip
replacement prosthesis 310 in the context of a human body. Also
shown is an external controlling device 390 which may be used to
modulate current flow in an implanted prosthesis by acting on
internal circuitry 380 in order to modulate delivery of metal ions
to inhibit microbes.
[0072] Joint replacement or repair implants include one or more
implantable parts which may be included as an implant body in an
inventive system. For example, a hip joint replacement implant
typically includes a femoral part, replacing the natural femoral
head, and a socket part, or acetabular cup or shell, replacing the
natural acetabulum. While an inventive system is extensively
discussed herein with regard to an implant body which is a femoral
part of a hip joint replacement prosthetic implant, it is
appreciated that the socket part, or cup portion of a hip implant
prosthesis may also be included in an inventive system as an
configured to include an internal cavity containing a power source
and other components as described herein. A further example of
joint replacement implant parts include a wrist implant having a
carpal component, for instance present where a first row of carpal
bones is removed, and a radial part, for instance inserted or
attached to the radius bone. The radial part may provide an
articular surface for interaction with a carpal part. Another
example is a knee joint prosthetic implant, having a femoral part
attached to the femur and a tibial part attached to the tibia, each
having an articular surface for interaction with the other. It is
appreciated that one or more parts of an implant prosthesis may be
configured to include an internal cavity containing a power source
and other components as described herein. Thus, an inventive system
may include more than one implant body. In a further option, each
of the multiple implant bodies may include a cavity and power
source, and may further include other components, preferably a
resistor and switch, as described. In a further option, multiple
switches may be controlled separately, for instance where one
implant body or region in the vicinity of the implant body is more
vulnerable to infection than another, a switch in that implant body
may be activated to turn on current in that implant body without
turning on current in another implant body.
[0073] As noted, an implant may be a temporary implant, intended to
remain implanted for a limited period of time, or a permanent
implant, intended to remain implanted long-term, even as long as
the remainder of the individual's life. One type of temporary
implant is known as a "spacer" implant. A spacer implant typically
has a similar size and shape compared to a permanent or short-term
implant. A spacer implant is typically implanted in order to
maintain the spatial integrity of an area where a permanent joint
replacement implant will be positioned eventually. For example,
where an individual has a badly infected implant which must be
removed, a spacer implant may be implanted while the infection is
being fought. An inventive system is particularly advantageous in
such a situation since a synergistic effect of an inventive
antimicrobial system with a course of systemic or local antibiotics
is achieved. Further, an inventive spacer implant may lessen or
eliminate the need for use of bone cement, currently used in this
situation. The insertion of a spacer implant would allow the
patient to be much more active than if the joint were filled with
bone cement. Further, tissue encroachment at the site is decreased
by placement of a spacer implant.
[0074] FIG. 4 illustrates an implant body in the form of a fixation
device, particularly, a bone screw 10. An external surface 20 of
the implant body includes a metal component in the form of a
continuous metal coating, including coating on screw threads. Also
shown is a switch 30, a resistor 40 and a battery 50 inserted in an
internal cavity 70 shown in the cut away region marked by stripes.
Also shown is a cap 60 for closing the cavity and protecting the
components disposed in the cavity from the external environment, as
well as limiting exposure of cells to the components disposed in
the cavity. Also shown is a metal coating 80 inside the cavity 70.
Also shown is an embodiment in which a metal coating is also
present on the threads 90 of the illustrated bone screw.
[0075] In one embodiment a power source, such as a battery, having
a first terminal, a second terminal, and a potential difference
between the first and second terminals, is provided. Further
provided is a conduit for an electrical connection between the
first terminal and the metal component. Also provided is a conduit
for an electrical connection between the metal component and the
second terminal.
[0076] A method for inhibiting microbial infection associated with
an orthopedic implant is provided which includes providing an
inventive system as described and delivering a current to a metal
component disposed on an external surface of an implant body, the
implant body located in a human body at a site of potential
infection.
[0077] In one embodiment, an inventive method for inhibiting an
infectious organism includes introducing an electrical current into
a metal component of an implanted joint prosthesis to release metal
ions from the component. The metal ions have a biostatic or
biocidal effect on microorganisms such that growth and/or
attachment of microorganisms on the implant and in the vicinity of
the implant are inhibited.
[0078] As noted above, biocidal metals and ions include a
transition metals and ions. Preferred metals and ions include
silver, gold, zinc, copper and combinations thereof. Further,
metals and ions such as cadmium, cobalt, nickel, platinum,
palladium, manganese, chromium, and the like may be included.
[0079] Infectious organisms inhibited by such metals and metal ions
illustratively include bacteria, viruses and fungi.
[0080] Generally, such metal ions inhibit infection at
concentrations ranging between 1.times.10.sup.-3
M-1.times.10.sup.-7 M, inclusive, and is preferably delivered in
amounts sufficient to achieve a concentration in this range.
Optionally, and preferably, metal ions are delivered in amounts
sufficient to achieve a concentration in the range between
5.times.10.sup.-5 M-0.25.times.10.sup.-6 M, inclusive. In
particular, silver ions are delivered in amounts sufficient to
achieve a concentration in the range between 5.times.10.sup.-5
M-0.25.times.10.sup.-6 M, inclusive.
[0081] A metal ion is released from a metal component by
application of an electrical current to the metal component. Bone
and soft tissue cells are affected by electrical current and thus
the amount of current delivered and the length of time for which it
is delivered must be considered in the context of the proximity of
the implant to such cells. The amount of a metal ion released is
dependant on the strength and duration of the electrical stimulus
which is adjusted accordingly.
[0082] Generally, a current in the range of 0.1 microamps to 200
milliamps is delivered to a metal component. In general, a current
is delivered to a metal component for periods of time ranging from
about 1 minute to continuous delivery over the lifetime of the
power source, that is, weeks, months or years. In general weaker
currents are used for longer-term treatments. Thus, in a preferred
embodiment, 0.3-1.5 micro-amperes of current is delivered in order
to ionize a silver surface layer. Also preferred is an embodiment
in which 0.8-1.2 microamps of current is delivered to a silver
coating.
[0083] Small electrical currents in the ranges described are
sufficient to ionize a solid silver coating, producing silver ions.
Without wishing to be bound by theoretical considerations,
according to Faraday's law, under ideal conditions 4 micrograms of
silver will be liberated per hour per micro ampere of current
applied to silver. Calculation 1 below details this.
( 1 AMP ) * ( 1 Coulomb 1 Amps * Sec ) * ( 1 Faraday 96 , 487
Coulombs ) * ( 107.868 gram AG 1 Fraday ) * 1 * 10 6 g 1 g * ( 3600
Sec Hour ) ( Equation 1.0 ) ##EQU00001##
[0084] Assuming the power source is capable of producing a 1
micro-ampere current and that the electrical current should not
exceed 20 micro-amperes at any time, 10 micrograms/milliliter
concentration of silver ions within a couple of hours. Additionally
the maintenance of a 10 micrograms/milliliter concentration of
silver ions is possible with very small electrical current
requirements.
[0085] Additional theoretical considerations indicate that total
lifetime exposure to silver ions advantageously do not exceed 8.95
grams for a person of average size, approximately 70 kilograms, and
having an average life expectancy, about 70 years. This calculation
is based on the assumption that about 0.35 milligrams of silver can
be safely consumed each day, see Newman, J. R., Tuck Silver 100
Safety Report, Jan. 9, 1999. Thus, for a permanent implant, it is
desirable that an inventive system not contain more than about this
amount of silver. Similar calculations may be made for other metal
ions as will be recognized by one of skill in the art.
[0086] In one embodiment, a method of inhibiting bacterial
infection associated with an implant includes administration of a
systemic or local antibiotic and administration of a metal
antibiotic via an inventive implant. A synergistic effect of such
treatment is achieved as a lower dosage of both the systemic or
local antibiotic and the metal antibiotic is necessary to achieve a
therapeutic effect.
[0087] While inventive methods and apparatus are generally
described with reference to use in humans herein, the methods and
apparatus are also used in other animals to inhibit infection. For
example, an inventive apparatus and method is used in animals
illustratively including cats, dogs, cattle, horses, sheep, goats,
rats, and mice.
[0088] The apparatus and methods described herein are presently
representative of preferred embodiments, exemplary, and not
intended as limitations on the scope of the invention. Changes
therein and other uses will occur to those skilled in the art. Such
changes and other uses are encompassed within the spirit of the
invention as defined by the scope of the claims.
Example 1
[0089] An implant body is manufactured by obtaining a hip
replacement prosthesis similar to a DePuy SUMMIT Tapered Hip System
designed to include an internal cavity, about 10 millimeters in
length and about 5 millimeters in width and a cap to close the
opening of the cavity as described herein. Articular surfaces of
the implant body are masked and the remaining external surfaces are
coated with a silver metal film about 1 micron in thickness. A
battery, resistor and switch are chosen to fit in the cavity. A
portion of the cavity wall adjacent to the external surface of the
implant body is also coated with silver metal to a depth adjacent
the positive terminal of the battery.
[0090] A battery with the desired profile is currently in
production by many battery manufacturers. The Energizer battery
number 337 satisfies all of the required size characteristics
needed for implementation within a bactericidal hip implant. When
examining the Energizer 337 battery one can see that the small
size, 1.65 mm in height by 4.8 mm in diameter allow the battery to
easily fit within the 5 mm compartment.
[0091] The 337 size battery provides a voltage of 1.55 volts, which
is much greater than required for the application of ionizing a
solid silver coating. Thus, a resistor is chosen to be placed in
series with the battery. Using a voltage of 1.55 volts and a
required current of 1 micro-ampere one can calculate the required
resistor as shown in Equations 2.1 and 2.2 below
V = IR ( Equation 2.0 ) R = V I = 1.55 volt 1 * 10 - 6 amperes = 15
, 550 , 000 ohms ( Equation 2.1 ) ##EQU00002##
[0092] The required resistor should have a resistance of
approximately 15.5 mega-ohms. Additionally the resistor must
conform to the size requirements as set by the diameter of the
pocket within the shaft of the implant, 5 millimeters.
[0093] Utilizing a resistor with the required 15.5 mega-ohms rating
in series with the 337 battery will provide for approximately 75573
hours of run time. The calculation of the run time for the battery
under with this resistance is show in calculation #3 below. During
this running time the battery will be producing the required 1
micro-ampere current that is required to ionize the solid silver
coating.
run_Time ( New_hip ) MMCO 8 - Resistance = run_Time (
simulated_application simulated - resistance ( Equation 3.0 )
##EQU00003##
[0094] An included switch, like all other components, fits within
the 5 millimeter diameter cavity that has been machined within the
shaft of the original hip implant. Additionally the switch will
have the ability to be turned ON and OFF once implanted within the
human body. In this example, a magnetically based switch is
selected. Coto Technology manufactures a switch, RI-80 Series Dry
Reed Switch that is designed specifically for medical applications
and which meets the design size constraints. The switch has a
maximum dimension of the central tube of 5 millimeters in length
and 1.8 millimeters in diameter. This switch will carry a maximum
current of 0.5 amperes and a has a maximum operating voltage of 200
volts, both of which are satisfactory operating characteristics
needed for a bactericidal hip implant according to the
invention.
[0095] Any patents or publications mentioned in this specification
are incorporated herein by reference to the same extent as if each
individual publication is specifically and individually indicated
to be incorporated by reference. In particular, U.S. Provisional
Patent Application Ser. No. 60/585,159, filed Jul. 1, 2004, is
hereby incorporated by reference in its entirety.
[0096] The compositions and methods described herein are presently
representative of preferred embodiments, exemplary, and not
intended as limitations on the scope of the invention. Changes
therein and other uses will occur to those skilled in the art. Such
changes and other uses can be made without departing from the scope
of the invention as set forth in the claims.
* * * * *