U.S. patent application number 11/075840 was filed with the patent office on 2016-10-20 for methods and apparatus for conformable prosthetic implants.
The applicant listed for this patent is Timothy G. Haines. Invention is credited to Timothy G. Haines.
Application Number | 20160302933 11/075840 |
Document ID | / |
Family ID | 35717493 |
Filed Date | 2016-10-20 |
United States Patent
Application |
20160302933 |
Kind Code |
A9 |
Haines; Timothy G. |
October 20, 2016 |
Methods and apparatus for conformable prosthetic implants
Abstract
A biomechanical optimization (BMO) prosthetic implant utilizes a
thin cross-section of metallic material that is conformable.
Preferably, the BMO prosthetic implant is conformable both at the
time of implant in response to manipulation and fixation by the
surgeon, as well as during the life of the implant in response to
stresses and loads experienced by the implant and thereby
communicated and responded to by living bone tissue. For most
metallic alloys, the BMO prosthetic implant will have an effective
cross-sectional thickness of 4 mm or less, and preferably 3 mm or
less. In one embodiment, the BMO prosthetic implant is provided
with one or more fins extending from the fixation surface(s) of the
implant which preferably includes retaining structures, such as
cross-pinned apertures or T-shaped edge ridge.
Inventors: |
Haines; Timothy G.;
(Seattle, WA) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Haines; Timothy G. |
Seattle |
WA |
US |
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20060058882 A1 |
March 16, 2006 |
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Family ID: |
35717493 |
Appl. No.: |
11/075840 |
Filed: |
March 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11036584 |
Jan 14, 2005 |
7815645 |
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11075840 |
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11049634 |
Feb 2, 2005 |
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11036584 |
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60551631 |
Mar 8, 2004 |
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60551080 |
Mar 8, 2004 |
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60551078 |
Mar 8, 2004 |
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60551096 |
Mar 8, 2004 |
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60551307 |
Mar 8, 2004 |
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60551262 |
Mar 8, 2004 |
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60551160 |
Mar 8, 2004 |
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60536320 |
Jan 14, 2004 |
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60540992 |
Feb 2, 2004 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 90/10 20160201;
A61F 2/38 20130101; A61B 17/1757 20130101; A61B 17/1671 20130101;
A61B 17/1675 20130101; A61F 2002/3895 20130101; A61B 2017/1602
20130101; A61F 2/3859 20130101; A61B 17/1764 20130101; A61F
2310/00011 20130101; A61F 2002/30649 20130101 |
International
Class: |
A61F 2/38 20060101
A61F002/38 |
Claims
1. An implantable orthopedic prosthesis for implantation on a bone
during an arthroplasty procedure, the implantable prosthesis
comprising: an implant body formed of a metallic material and
having a fixation surface facing the bone and an articulation
surface adapted to articulate with respect to another surface; and
the implant body having a cross-sectional depth between the
fixation surface and the articulation surface that is less than 3
mm on average over the entire implant body, the metallic material
and the cross-sectional depth being such that the implant body is
conformable, both at a time of implant in response to manipulation
and fixation by a surgeon and during an expected life cycle of the
implantable prosthesis in response to stresses and loads
experienced by the implant body.
2. The implantable orthopedic prosthesis of claim 1, wherein the
implant body further comprises: at least one projection strut
extending inwardly from the fixation surface of the implant body
relative to the bone, the projection structure being adapted to
interface with a corresponding cavity created in the bone, wherein
a depth of the at least one projection structure is not included in
determining the average cross-sectional depth of the implant
body.
3. The implantable orthopedic prosthesis of claim 2, further
comprising: means for laterally retaining the at least one
projection structure such that a preload force is exerted on the
implant body biasing the fixation surface of the implant body
against the bone.
4. The implantable orthopedic prosthesis of claim 3, wherein the
projection structure is a fin structure and the means for laterally
retaining comprises at least one lateral projection structure
extending outwardly from at least one side of the at least one fin
structure, the at least one lateral projection structure adapted to
mate with a corresponding channel created in the bone.
5. The implantable orthopedic prosthesis of claim 4, wherein the at
least one lateral projection structure includes a pair of lateral
projections on opposite sides of the at least one fin structure
that together with the at least one fin structure define a
generally T-shaped structure.
6. The implantable orthopedic prosthesis of claim 3, wherein the
means for laterally retaining comprises at least one retention
aperture defined in the at least one projection structure and a
corresponding cross pin adapted to mate with the at least one
retention aperture.
7. The implantable orthopedic prosthesis of claim 6, wherein the
means for laterally retaining comprises at least two retention
apertures defined in the at least one fin structure and a
corresponding cross pin adapted to mate with each retention
aperture.
8. The implantable orthopedic prosthesis of claim 2, wherein the
projection structure is comprised of a porous metal capable of
lateral fluid communication between generally opposing sides of the
projection structure to permit tissue in growth through the
projection structure post operatively.
9. The implantable orthopedic prosthesis of claim 2, wherein a
depth of the projection structure extends inwardly from the
fixation surface of the implant body a distance at least as large
as the cross-sectional depth of the implant body.
10. The implantable orthopedic prosthesis of claim 1, wherein the
preload force induces compressive strains in the fixation surface
of the implant body along an axis normal to an axis normal to the
fixation surface of the implant.
11. The implantable orthopedic prosthesis of claim 1, wherein the
other surface is selected from the set consisting of: another bone,
another implantable prosthesis, and an intermediary structure
adjacent another bone.
12. An implantable orthopedic prosthesis for implantation on a bone
during an arthroplasty procedure, the implantable prosthesis
comprising: an implant body having a fixation surface facing the
bone and an articulation surface adapted to articulate with respect
to another surface, the implant body being a composite of a porous
bulk construct that forms the fixation surface and a thin layer of
a material having a smooth, lubricious bearing surface that forms
the articulation surface, such that the implant body is
conformable, both at a time of implant in response to manipulation
and fixation by a surgeon and during an expected life cycle of the
implantable prosthesis in response to stresses and loads
experienced by the implant body.
13. The implantable orthopedic prosthesis of claim 12, wherein the
implant body further comprises: at least one projection structure
extending inwardly from the fixation surface of the implant body
relative to the bone, the projection structure being adapted to
interface with a corresponding cavity created in the bone.
14. The implantable orthopedic prosthesis of claim 13, further
comprising: means for laterally retaining the at least one
projection structure such that a preload force is exerted on the
implant body biasing the fixation surface of the implant body
against the bone.
15. The implantable orthopedic prosthesis of claim 14, wherein the
projection structure is a fin structure and the means for laterally
retaining comprises at least one lateral projection structure
extending outwardly from at least one side of the at least one fin
structure, the at least one lateral projection structure adapted to
mate with a corresponding channel created in the bone.
16. The implantable orthopedic prosthesis of claim 15, wherein the
at least one lateral projection structure includes a pair of
lateral projections on opposite sides of the at least one fin
structure that together with the at least one fin structure define
a generally T-shaped structure.
17. The implantable orthopedic prosthesis of claim 14, wherein the
means for laterally retaining comprises at least one retention
aperture defined in the at least one projection structure and a
corresponding cross pin adapted to mate with the at least one
retention aperture.
18. The implantable orthopedic prosthesis of claim 17, wherein the
means for laterally retaining comprises at least two retention
apertures defined in the at least one fin structure and a
corresponding cross pin adapted to mate with each retention
aperture.
19. The implantable orthopedic prosthesis of claim 13, wherein the
projection structure is comprised of a porous metal capable of
lateral fluid communication between generally opposing sides of the
projection structure to permit tissue in growth through the
projection stature post operatively.
20. The implantable orthopedic prosthesis of claim 13, wherein a
depth of the projection structure extends inwardly from the
fixation surface of the implant body a distance at least as large
as a cross-sectional depth of the implant body at a location other
than a location of the projection structure.
21. The implantable orthopedic prosthesis of claim 12, wherein the
other surface is selected from the set consisting of: another bone,
another implantable prosthesis, and an intermediary structure
adjacent another bone.
22. The implantable orthopedic prosthesis of claim 12, wherein the
porous bulk construct is a porous metal and the material having a
smooth, lubricious bearing surface is a non-porous metal.
23. The implantable orthopedic prosthesis of claim 12, wherein the
implant body has a bulk volume calculable by integrating a surface
area of a cross sectional outline of the implant body about a
length of the implant body that is normal to the cross sectional
outline, and wherein a ratio of an actual displacement volume of
the implant body to the bulk volume of the implant body is no more
than 1 to 4.
24. The implantable orthopedic prosthesis of claim 12, wherein a
depth of the porous bulk construct measured normal to the
articulation surface is greater than a depth of the thin layer of
the material measured normal to the articulation surface at a
location on the implant body that is the same as a location of the
depth of the porous bulk construct.
25. An implantable orthopedic prosthesis for implantation on a bone
during an arthroplasty procedure, the implantable prosthesis
comprising: an implant body having a fixation surface facing the
bone and an articulation surface adapted to articulate with respect
to another surface, the implant body being a composite of a porous
metal forming the fixation surface and a thin layer of a non-porous
metal forming the articulation surface, such that the implant body
is conformable, both at a time of implant in response to
manipulation and fixation by a surgeon and during an expected life
cycle of the implantable prosthesis in response to stresses and
loads experienced by the implant body.
Description
CLAIM TO PRIORITY
[0001] The present invention claims priority to U.S. Provisional
Application No. 60/551,631, filed Mar. 8, 2004, entitled, "METHODS
AND APPARATUS FOR CONFORMABLE PROSTHETIC IMPLANTS," and U.S.
Provisional Application No. 60/551,080, filed Mar. 8, 2004,
entitled, "METHODS AND APPARATUS FOR PIVOTABLE GUIDE SURFACES FOR
ARTHROPLASTY," and U.S. Provisional Application No. 60/551,078,
filed Mar. 8, 2004, entitled, "METHODS AND APPARATUS FOR MINIMALLY
INVASIVE RESECTION," and U.S. Provisional Application No.
60/551,096, filed Mar. 8, 2004, entitled, "METHODS AND APPARATUS
FOR ENHANCED RETENTION OF PROSTHETIC IMPLANTS," and U.S.
Provisional Application No. 60/551,307, filed Mar. 8, 2004,
entitled, "METHODS AND APPARATUS FOR IMPROVED CUTTING TOOLS FOR
RESECTION," and U.S. Provisional Application No. 60/551,262, filed
Mar. 8, 2004, entitled, "METHODS AND APPARATUS FOR IMPROVED
DRILLING AND MILLING TOOLS FOR RESECTION," and U.S. Provisional
Application No. 60/551,160, filed Mar. 8, 2004, entitled, "METHODS
AND APPARATUS FOR IMPROVED PROFILE BASED RESECTION," and U.S.
patent application Ser. No. 11/036,584, filed Jan. 14, 2005,
entitled, "METHODS AND APPARATUS FOR PINPLASTY BONE RESECTION,"
which claims priority to U.S. Provisional Application No.
60/536,320, filed Jan. 14, 2004, and U.S. patent application Ser.
No. 11/049,634, filed Feb. 3, 2005, entitled, "METHODS AND
APPARATUS FOR WIREPLASTY BONE RESECTION," which claims priority to
U.S. Provisional Application No. 60/540,992, filed Feb. 2, 2004,
entitled, "METHODS AND APPARATUS FOR WIREPLASTY BONE RESECTION,"
the entire disclosures of which are hereby fully incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to methods and apparatus
for prosthetic implant devices. More particularly, the present
invention relates to prosthetic implants for joints that are
conformable, preferably both at the time of implant and over the
life of the implant.
[0004] 2. Background Art
[0005] The replacement or augmentation of joints with artificial or
prosthetic implants is well known in the field of orthopedics.
Total knee arthroplasty (TKA) procedures involving the replacement
of the knee joint are a good example. U.S. Publ. Appl.
2003/0028196A1 and the PFC RP Knee Replacement manual provide a
good background for the techniques and devices used as part of
these arthroplasty procedures.
[0006] The prosthetic implant devices for use in arthroplasty
procedures are typically metallic devices or devices that have a
combination of metallic and plastic components. Because of the high
loads and strains that these devices must endure for years, almost
invariably the design of these prosthetic implant devices relies on
the rigid structure and durability of the metallic components to
support the loads and strains. While the rigid structure and
durability of metallic implants is beneficial in most regards,
these features make the fit or interface between the metallic
implant and the resected bone surface critical to the long term
viability of an implant.
[0007] In total knee replacements, for example, a series of planar
and/or curvilinear surfaces, or "resections," are created to allow
for the attachment of prosthetic or other devices to the femur,
tibia and/or patella. In the case of the femur, it is common to use
the central axis of the femur, the posterior and distal femoral
condyles, and/or the anterior distal femoral cortex as guides to
determine the location and orientation of distal femoral
resections. The location and orientation of these resections are
critical in that they dictate the final location and orientation of
the distal femoral implant. It is commonly thought that the
location and orientation of the distal femoral implant are critical
factors in the success or failure of the artificial knee joint.
Additionally, with any surgical procedure, time is critical, and
methods and apparatus that can save operating room time, are
valuable. Past efforts have not been successful in consistently
and/or properly locating and orienting distal femoral resections in
a quick and efficient manner.
[0008] Over the years, alternatives to metallic prosthetic implants
have been proposed. U.S. Pat. Nos. 3,906,550 and 4,693,721 describe
a porous metallic fabric for use as a medical implant. U.S. Pat.
No. 5,986,169 describes a porous nickel-titanium metal alloy for
use as a medical implant. European Publ. Appl. 0 761 242 A1
describes a molded polymer orthopedic implant with a bearing
surface formed of a porous metal layer. PCT Publ. Appl. WO 02/34310
A2 describes a shape memory polymer material that is used as a
connective tissue replacement material for orthopedic applications.
These alternatives have met with little success or acceptance in
the orthopedic implant field.
[0009] It would be desirable to provide for an orthopedic
prosthetic implant that could be implanted more consistently and
effectively, yet provided or exceeded the ideal long term wear and
stability of current rigid metallic implants.
SUMMARY OF THE INVENTION
[0010] The present invention is a biomechanical optimization (BMO)
prosthetic implant that utilizes a thin cross-section of metallic
material that is conformable. Preferably, the BMO prosthetic
implant is conformable both at the time of implant in response to
manipulation and fixation by the surgeon, as well as during the
life of the implant in response to stresses and loads experienced
by the implant and thereby communicated and responded to by living
bone tissue. For most metallic alloys, the BMO prosthetic implant
will have an effective cross-sectional thickness of 3 mm or less.
In one embodiment, the BMO prosthetic implant is provided with one
or more fins extending from the fixation surface(s) of the implant
which preferably includes retaining structures, such as
cross-pinned apertures or T-shaped edge ridge.
[0011] In another embodiment of the present invention, the BMO
Prosthetic implant is a composite of porous metal or `Trabecular
Metal` bone interface features joined to a thin layer of articular
surface material such as cobalt chrome or titanium. This embodiment
of the present invention is particularly advantageous as much of
the literature available on both Actipore.TM. (a porous nitinol,
which forms a TiNi intermetallic molecule marketed by Biorthex,
Inc.) and Trabecular Metal (chemical vapor deposition of tantalum
on a porous carbon matrix manufactured by Implex, Inc. and
distributed by Zimmer, Inc.) cites that the modulus of elasticity
or stiffness of these materials is similar to that of living bone.
As a result, the composite structure of the present invention
creates an interfacial mechanical environment motivating a highly
favorable biological response from the living bone while the
articular surface of the present invention will providing for
excellent articular function.
[0012] Additionally, this embodiment of the present invention may
allow for the prosthesis, for example, a femoral or tibial
component for use in knee replacement, to have a linear or
curvilinear fixation profile of flexible porous material that is
substantially thicker (at least 10% thicker, and in one preferred
embodiment closer to 500% thicker) than the thickness of the
composite articular surface, for intraoperative attachment to
condylar cuts having a linear cutting profile of sufficient
interfacial area to avoid subsidence of the implant into bone
leading to failure. This embodiment can significantly improve the
arthroplasty continuum of care for a given patient, as surgeons
performing revision procedures will commonly remove necrotic tissue
to a depth sufficient to reveal bleeding bone prior to implantation
of the revision prostheses. Because these porous metals are capable
of accommodating healthy living bone within their interstices, this
ensures that this embodiment of the present invention will require
a minimum of bony material removal both intraoperatively during
primary intervention and intraoperatively during revision
intervention. Another alternate embodiment would further have the
fin and/or keel and/or crosspin be constructed of such porous
material.
[0013] The present invention provides for embodiments of prosthetic
implant designs facilitating intraoperative and postoperative
efficacy and ease of use. The present invention utilizes a number
of embodiments of prosthetic implants, or prosthetic implant
features to facilitate clinical efficacy of arthroplasty
procedures. The overriding objects of the embodiments are to
facilitate short and long term fixation of the implant with respect
to the bone, enable bone preservation to facilitate ease and
efficacy of revision, and/or to take advantage of the natural
physiological phenomenon determining bone growth response to load
stimuli. Specifically, science is beginning to understand the
manner in which bone responds to mechanical stimuli to an extent
that allows for at least first order prediction of the clinical
performance of prosthetic implants attached to bone. Certain
theories regarding bone response to prosthetic implant load
transfer to bone are postulated herein and prosthetic implant
design embodiments proposed to take advantage of these
biomechanical characteristics in facilitating clinical performance
are disclosed.
[0014] It should be clear that applications of the present
invention is not limited to Total Knee Arthroplasty or the other
specific applications cited herein, but are rather universally
applicable to any form of surgical intervention where the resection
of bone is required. These possible applications include, but are
not limited to Unicondylar Knee Replacement, Hip Arthroplasty,
Ankle Arthroplasty, Spinal Fusion, Osteotomy Procedures (such as
High Tibial Osteotomy), ACL or PCL reconstruction, and many others.
In essence, any application where an expense, accuracy, precision,
soft tissue protection or preservation, minimal incision size or
exposure are required or desired for a bone resection and/or
prosthetic implantation is a potential application for this
technology. In addition, many of the embodiments shown have unique
applicability to minimally invasive surgical (MIS) procedures
and/or for use in conjunction with Surgical Navigation, Image
Guided Surgery, or Computer Aided Surgery systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other important objects and features of the invention will
be apparent from the following detailed description of the
invention taken in connection with the accompanying drawings in
which:
[0016] FIGS. 32-34 and 98-127 show various depictions of
embodiments and methods in accordance with alternate embodiments of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] It should be noted that, in many of the figures, the cut
surface created by the cutting tool are shown as having already
been completed for the sake of clarity. Similarly, the bones may be
shown as being transparent or translucent for the sake of clarity.
The guides/pins, cutting tool, bones, and other items disclosed are
may be similarly represented for the sake of clarity or
brevity.
[0018] FIGS. 99 through 127 FIGS. 99 through 127 generally
represent prosthesis and prosthesis fixation feature embodiments of
the present invention.
[0019] FIGS. 99 through 102 show representations of a tongue in
groove fixation feature applied to a Unicondylar femoral component
enabling anterior insertion of one tongue element into a `t-slot`
style groove formed in bone and a progressively increasing press
fit obtained by forcing the implant posteriorly, as is represented
in comparing FIGS. 99 and 100. The t-slot feature, or groove,
formed in the femur is easily formed by, in one embodiment,
providing a trial component possessing a contoured groove and slot
for guiding a t-slot cutter along its length. Such a contour groove
would be responsible for controlling the depth of the t-slot in the
bone with respect to the cut surface to which the implant fixation
surface is attached, while the slot in the trial would dictate the
mediolateral location of the t-slot style groove. It is preferable
to include an aperture in the slot and/or contour groove in the
trial component to allow for insertion and plunging of the wider T
cutting surfaces prior to sweeping.
[0020] Alternatively, FIGS. 103 through 112 represent combinations
of finned and/or crosspinned implants. It should be noted that the
AP Fin Profile of the fin may be linear as shown in FIG. 106 (in
other words, the fin may be may be planar), or it could be slightly
tapered to achieve an interference fit with the walls of the groove
as the implant fixation surfaces are forced into contact with the
cut surfaces to which they are mated (see FIGS. 107 through 109),
or in could be curved as looked at from the viewpoint of FIG. 106
to further provide stability of fixation. Interestingly, the
fixation aperture created to fix a cutting guide to the bone could
be utilized to cross pin a flange or fin of a femoral prosthesis.
It should be noted that although the embodiment shown is a
Unicondylar femoral prosthesis, this concept could be applied to
tibial, femoral, or patellofemoral prostheses in any application,
or in other joint, trauma, spine, or oncology procedures, as is
generally represented in FIGS. 120 through 127.
[0021] In FIGS. 105 through 112, a tapered pin is used to engage
the cross pin hole in the fin of the prosthesis. The tapered pin
may be utilized to facilitate a resulting press fit between the pin
and the fixation surfaces of the implant and/or ease of introducing
the pin into the hole in the fin. The pin could be of any known
material, but resorbable materials are especially interesting as
they are `consumed` by the body leaving minimal hardware within the
body after a fairly predictable amount of time has passed. PLA/PGA
compositions, Tricalcium Phosphate, allograft and autograft bone,
bone substitutes, and the aforementioned slurry type compositions
may serve well. Additionally, as the apertures shown in FIG. 109
resides close to the natural articular surface and extends through
cortical and very robust dense subcondylar bone, a very thin walled
coring saw can be used to create the aperture and simultaneously
form the crosspin that will be used to facilitate fixation of the
implant. Alternatively, bone cement or other liquid or semi-liquid
material may be injected into the portals/apertures to achieve
intimate interdigitation, and the crosspins optionally inserted
thereafter, but prior to complete hardening or curing.
Alternatively, the crosspin(s) could be hollow with radially
extending holes allowing the pins to be inserted and then have bone
cement injected into them and up under the implant. Alternatively,
the cross pin could be threaded to engage threads in the fin, or to
engage the bone (both for short term stability and to facilitate
removal) or both. Alternatively, the crosspin(s) could be formed of
bone cement for use in cemented procedures.
[0022] These embodiments hold significant promise in both providing
for intraoperatively stable cemented or cementless fixation as well
as facilitating long term biological ingrowth. It should be noted
that the use of multiple holes, pins, and apertures in the
prosthesis could be used and that the holes in the bone need not be
fixation holes to which guides are attached. It also should be
noted that such crosspins used in conjunction with the mating
features of the present invention will act to cause the prosthesis
to conform to the bone surface about the fixation path of the
prosthesis (i.e.; in an anterioposterior direction along the
implant fixation surface), but that it may leave something to be
desired in its ability to induce similar conformity of implant bone
interfaces along the fixation profile of the prosthesis. For
clinical applications of embodiments of the present invention where
this is a factor, apertures may be present in the implant about
more medial or lateral locations that allow the crosspins to mate
with said apertures to create the aforementioned intimate fit or
conformability in either or both of the ML and AP directions. Also
it should be noted the condylar sections, and patellofemoral
sections of the implant could be wholely separate, modularly
joined, be composed of a dual condylar prosthesis and separate
patellofemoral prosthesis, or any combination of the above as
generally indicated in FIGS. 120 through 127. Although the
bone/implant interface shown is curved in two planes, these
concepts apply to implants with 3 planar curved geometry (where the
cutting path and cutting profiles of the resected surface geometry
and therefore the fixation surface geometry do not remain in two
planes through the entirety of the cutting path, or where the
cutting path is contained within multiple or single curved
surfaces), entirely planar geometries, or anything in between.
[0023] FIGS. 107 through 112 demonstrate another embodiment of the
present invention allowing for benefits well above and beyond those
of the prior art. This will be referred to herein as a BMO
Prosthesis or BMO Cortical type implant (Biomechanical Optimization
Prosthesis). This embodiment has several applications. For
instance, if the resected surfaces will to vary significantly from
the fixation surface geometries, as may be seen in unguided
kinematic resection, it may be advantageous to implement fixation
surface geometries that can conform to variation in resection
geometry. Most implant materials in joint replacement are thought
of as being rigid, and that their rigidity is a desirable
characteristic for achieving stable fixation. In the case of
surface replacement, that is not necessarily the case. Anecdotally,
picture a bar of aluminum 2 inches square and 5 inches long--now
picture trying to manually bend it. At these dimensions, aluminum
is rigid; however, it is obvious that aluminum foil is not so
rigid. The point to this is that very thin (less than 3 mm thick,
probably closer to a range of 1.5 to 0.01 mm thick) sections of
many metals, including implant grade metals and alloys cobalt
chrome, titanium, zirconium, and liquid metal, can be processed
into very thin forms capable of conforming to variations in the
resected surface and yet still have bearing surfaces that are
highly polished and provide significant contact area, where
desirable, for bearing against the bearing or articular surfaces of
the opposing implant. The construct or prosthesis resulting from
applying the present invention to a femoral component in
Unicondylar knee replacement, for example, may start out being a
1'' wide be 3'' long strip of 1.5 mm thick material curved in a
manner to generally look like the curved cutting path and curved
cutting profile of a natural, healthy femur. A process such as
Tecotex from Viasys Healthcare of Wilmington, Mass. is used to
remove material from the strip down to a nominal thickness of
perhaps 0.1 mm thick while leaving multiple protruding `hooks`
(almost like the hook and eye concept of Velcro) emerging from the
thin fixation surface to engage the bone. One or more fins can be
attached or be made a continuous part of this construct as shown in
FIG. 107. During insertion, the anterior most cross pin could lock
that portion of the prosthesis in place, then the prosthesis could
be wrapped around the remaining, more posteriorly resected surfaces
and the posterior cross pin inserted (see FIG. 111). Alternatively,
the fins can be located about the periphery of the articular
surfaces of the condyle in the form of tabs and the cross pins or
screws or tapered dowels, etc. known in the art inserted through
holes in the tabs and into bone to fix the cortical implant. The
combination of fins and tabs may also be useful. In using the tabs
it is critical to keep all features of the implanted device
ultralow profile to avoid irritating the surrounding soft tissues
(perhaps creating recesses in the bone underlying the tabs would be
desirable to allow for a form of countersinking of the tabs and/or
the pins or screws or other fixation devices).
[0024] The flexibility of the implant in accordance with the
present invention allows the implant to conform to the resection
surface and the stability of the crosspin fixation would assist in
reducing interfacial micromotion known to inhibit bone ingrowth and
fixation (this concept could be used with PMMA, but it is also
desirable to avoid the tissue necrosis and bone preservation for
revision issues associated with the use of bone cement if the
patients health/comorbidities/indications allow). This kind of
implant has some very interesting clinical benefits beyond simple
bone preservation. Given how well this kind of conformable implant
impart load to underlying bone, thus avoiding stress shielding, it
is possible not only to promote healthy bone ingrowth into and
around the interfacial features, but the bearing contact and
strains/stresses imparted to the bone could motivate the bone to
change its shape (and therefore the shape of the conformable
implant also changes over time because of the flexibility) to
ideally conform to the tibial component bearing surface such that
bearing stresses are carried through the broadest desirable contact
area (just like modeling/remodeling in a healthy unmodified
joint).
Biomechanically Optimized Implants
[0025] The manner in which bone may be motivated to change shape
needs to be explained in more detail and is derived from
extrapolations of Wolff's Law. One of the modern interpretations of
Wolff's Law is that bone `seeks` a uniform stress state under load
through the addition or subtraction of bone material and/or changes
in density of bony material. In considering Mattheck's "Axiom
Uniform Stress" ("Design in Nature--Learning from Trees" published
by Springer-Verlag Berlin, Heidelberg, N.Y., copyright 1998.
Mattheck's publications are included herein by reference) which may
be paraphrased as "the ideal shape of a given mechanical component
is that which results in the component experiencing uniform
external stresses during use". Mattheck further provided empirical
evidence that the external shape of human and animal bones (and
even things like tiger claws and tree limbs) reflect this `design
paradigm` in nature.
[0026] The concept of BMO depends on the concept that not only do
human bones and articular surfaces in healthy patients seek uniform
stresses in bearing, but that bone continues to seek this uniform
state despite the pathologies of osteoarthritis. If an implant
design is properly designed to allow for localized load transfer to
underlying living bone, given that bone will seek an ideal, uniform
stress state, it is believed that the bone will adapt its geometry
and shape as per the loading it experiences and thus change the
shape of the articular surfaces of the BMO implant to reflect ideal
or uniform contact stress bearing between the implant articular
surfaces. This change in articular geometry would be based on the
kinematics of that particular patient's knee joint and the geometry
of the articulating surface of the opposing tibial implant (whether
it be UHMWPE or any other bearing material) and thereby the stress
experienced by living tissues resulting in ideal tibiofemoral
articular constraint and conformity. It is believed this
biomechanical optimization of articular geometry would yield ideal
tibiofemoral contact area and kinematics that are tuned to an
individual patient in a manner which standard rigid implants could
not hope to match. The debate over what ideal tibiofemoral and
patellofemoral prosthesis articular geometries should be has been
the topic of heated debate for decades with no clear winner or
universally accepted scientific model. The present invention avoids
this debate by allowing Mother Nature to cast her vote.
[0027] Another interesting embodiment of the present invention is
to make both opposing implants BMO Cortical type implants and allow
the bone to modify the geometry of both to reach an ideal `state`
for that patient (utilizing Liquid Metal as a metal on metal
bearing in this scenario could yield phenomenal results not to
mention unheard of bone preservation). The primary objectives of
this embodiment of the present invention are to preserve viable
bone, to increase prosthesis survival durations, to promote optimal
joint kinematics, load transfer, articulation contact areas, and
patient satisfaction, reduce intraoperative trauma and patient
recovery time, reduce or eliminate proprioceptive compromise,
reduce intraoperative time, and generally make the art of joint
arthroplasty cheaper, better, and faster in all ways. Further, and
perhaps most importantly, the ability to preserve bone to the
extent made possible by BMO Cortical type prostheses would enable a
given patient who, at younger than normal ages, experiences the
debilitating or crippling effects of Osteoarthritis or
Post-Traumatic arthritis to be able to be treated by arthroplasty
over a period of decades, and a series of revisions that is simply
not attainable today given the monolithic nature of conventional
implants.
[0028] The use of bone morphogenic proteins, bone graft, or other
means of promoting or accelerating healing, fixation, and/or
ingrowth of devices derived from this concept could be beneficial.
Also, application of these inventions to all joint arthroplasty
procedures including TKA, hip, ankle, metatarsul, metacarpal,
wrist, spine, elbow, shoulder, mandible, or finger or any other
joint or bone or bone feature identified in Gray's Anatomy or
effected in the aforementioned procedures is likely to provide
significant clinical and economic benefit. Implantation of these
devices could also be performed via standard surgical approaches or
more exotic methods in the art including arthroscopic means or by
what has been described as the Transosseous Core approach in the
patent literature. Given that properly compacted morselized
cancellous bone graft approaches 80% of the Modulus of Elasticity
of cortical bone (in compression as per the work of Bonutti, et
al), this impaction of graft could actually lend some initial
rigidity to the implant. Actually, blood loss from bone surfaces
into the joint space has been referred to as problematic in press
fit knees, and packing morselized bone graft into living bone and
the implant at the bone/implant interface could act as an effective
form of tamponade. The process of `packing` the bone could be
affected by simply reducing the joint and allowing the compression
across the joint to pack the bone, by injection of osteoslurries
into the interfacial area after placement of the implant, or by
other currently known methods or those methods to be
discovered.
[0029] The work of Frost, et al and Lanyon, et al may also have
identified several of the characteristics needed for successful
replication of bone mechanics. Specifically, it has been identified
that living bone tissue experiencing strain states between 50
microstrain to 4,000 microstrain achieves steady state growth
balancing out consumption of bone by osteoclast activity and
creation of new bone by osteoblast activities. As this strain range
is effective in maintaining living tissue, it is likely very
beneficial to assume that the healing of interfacial tissues in the
postoperative recovery and recuperation periods would be
facilitated by ensuring that the fixation apparatus and methods of
the present invention be implemented in a manner that maintains the
healing interfacial tissues within the aforementioned strain range
to facilitate healing and ingrowth of living tissue into the
bone-implant interface and avoid the formation of
fibrocartilageneous tissue associated with excessive micromotion at
this interface (which is known to lead to implant loosening).
Fibrocartilagenous tissue is analogous to scar tissue formed by
skin after a cut, abrasion, or burn in that it is not generally
suited to stable fix a bone-implant interface. Generally, it is
known in art of arthroplasty that the formation of
fibrocartilagenous tissue at a bone implant interface results in
significant pain, sometimes elicited by resulting soft tissue
inflammation, for the patient which is something that must be
avoided or eliminated for any prosthetic system to be considered
successful.
[0030] FIGS. 113 through 115 are an embodiment of the present
invention that may prove to be a very usefully alternative to
conventional rectilinear based referencing techniques. In essence,
conventional alignment techniques, once having established
appropriate flexion extension angulation and varus valgus
angulation of desired implant location, reference the anterior
cortex, distal most femoral condylar surface, and posterior most
condylar surface (indicated in FIG. 114 by stars) to dictate the
anterior posterior location, proximal distal location (otherwise
known as distal resection depth), and appropriate implant size in
determining the `perfect` location and orientation for the
appropriately sized implant (mediolateral location is normally
`eyeballed` by comparison of some visual reference of the
mediolateral border surrounding the distal cut surface and some
form of visual guide reference). These conventional techniques fail
to directly reference the distinctly different anatomic bone
features that dictate the performance of distinctly separate, but
functionally interrelated, kinematic phenomena, and they also
attempt to reference curvilinear articular surfaces by way of
rectilinear approximations. The embodiment of the present invention
is an alternative alignment technique with an object to overcome
the errors inherent in prior art. As shown in FIG. 115, the femur
possesses two distinct kinematic features and functions that lend
themselves to physical referencing; the patellofemoral articular
surface and the tibiofemoral articular surfaces, both of which are
curved, more specifically these surfaces represent logarithmic
curves. The one codependency between the two articular functions,
and therefore any geometric approximation made of them in
referencing, is that they must allow for smooth kinematically
appropriate articulation of the patella as it passes from its
articulation with the trochlear groove (shown in blue in FIG. 115)
to its articulation with intercondylar surfaces between the femoral
condyles (shown in red in FIG. 115). Thus, knowing that three
points define an arc and may be used to approximate a curve or
sections of a curve, what is proposed is to use a referencing
device which contacts at least one femoral condyle at three points
to determine both an approximation of arc radius and centerpoint
location, while independently or simultaneously referencing the
trochlear groove at three points to determine both an approximation
of arc radius and centerpoint location. The referencing system
would further need to provide for the need of the articular
surfaces of the trochlear articular surfaces to smoothly transition
to those of the intercondylar surfaces. Armed with this
information, a surgeon may most appropriately determine appropriate
implant location and orientation.
[0031] This embodiment of the present invention is especially
useful in determining the proper location, orientation, and implant
size for the modular tricompartment components shown in FIGS. 120
through 124, the non-modular implants shown in FIGS. 125 through
127, and standard implants where the appropriate size, location,
and orientation would be determined by that which best mimics
existing articular bone surfaces thus resulting in optimal
postoperative kinematic function. FIG. 123 represents one method of
fixing the patellofemoral implant with respect to the condylar
implant(s) so as to maintain smooth transitional articulation. It
should be noted that this crosspin method of interconnecting the
separate components could be augmented by tongue and groove
interlocking between the medial side of the condylar component
shown and the lateral side of the patellofemoral component shown.
What is critical is that the transition between the patellofemoral
component and the condylar component surfaces responsible for
patellofemoral articulation are and remain tangent at least one
point.
[0032] FIGS. 32 through 34
[0033] An implant design embodying fixation geometries for mating
with such tibial cut surfaces as are shown in FIGS. 32 through 34
is highly desirable. In one embodiment of such a tibial prosthesis
design, the fixation surfaces would be intended to mate, directly
or indirectly, with cut surfaces represented in FIG. 33 and/or 34
(the tibia in the right side of the FIG. 34). In essence, the
tibial implant would possess a planar or gently curvilinear `rim`
for contacting the `cortical skim cut` surface (represented in FIG.
32), and convex fixation surfaces for direct or indirect fixation
to the concave tibial cuts represented in FIGS. 33 and 34. Direct
fixation to such surfaces could be achieved by high precision
resection of both the cortical rim, for attachment of the rim of
the tibial prosthesis, and the concave surface(s), for intimate
apposition to the convex implant surfaces. Such fixation,
specifically of the concave bone cuts to the convex implant
surfaces, could be achieved by way of an interference fit between
the cuts and the implant along one axis (for instance, a front to
back--AP--axis or direction), or along two axes (for instance, AP
and Side to Side--ML--axes), or circumferentially (in other words a
bit like a pin of a given diameter being forced into a hole of a
lesser diameter), or both circumferentially and along an axis at
roughly a 90 degree angle or normal to the skim cut surface when
viewed in one or two orthogonal planes (an "up and down axis" or
superior-inferior or proximal distal direction). It should be noted
that an interference fit in a roughly superior-inferior direction
may call for a textured surface on the bottom most surface of the
convex fixation surfaces presenting a small surface area of contact
at initial contact with the bottom of the concave cut to allow the
implant to compact a reduced area of cancellous bone as the implant
is impacted in a superior to inferior direction until it reaches
its desired superior-inferior location and/or contact between the
rim of the implant and the skim cut of the cortices. As compared to
previous methods of achieving implant fixation, these embodiments
of the present invention yield superior stability of implant
fixation to bone to an extent reminiscent of the difference between
riding a horse wearing a deeply dished saddle and riding a very
sweaty horse bareback.
[0034] An alternative fixation paradigm allows for less intensive
demands for the precision of the fit between concave tibial cuts
and convex fixation surface. In essence, the concave surface may be
`excavated` in any desired manner (such as the Cutting Trials shown
in FIG. 31 which cut the proximal tibia while the tibia is moved
through at least a portion of its range of motion about the femur),
and a morselized or granular osteobiological substance, perhaps
tricalcium phosphate, HATCP, or other substances generally
described as `bone substitutes` or autograft or allograft
cancellous or cortical bone (it would be very useful to use the
bone which was removed from the tibia or other patient bone during
the creation of the cut(s) in that it is readily available and
completely avoids the issues of disease transmission or immune
response), is then impacted into the concave surface using a `form`
to create a surface of impact material (referred to herein as the
"Impacted Surface") of specific shape and location/orientation with
respect to the cortical skim cut and/or the tibia or femur. This
form is beneficially shaped in a manner related to the shape of the
convex implant fixation surface shape so as to create a specific
geometric relationship between the implant fixation surfaces and
the Impacted Surface geometry. In one embodiment of the present
invention, the fit between the implant and the Impacted Surface
would be an interference fit or press fit. As properly impacted
morselized cancellous bone is known to achieve stiffnesses (or
modulus of elasticity) that approach as much as 80% of the
stiffness of cortical bone in compression, robust intraoperative
fixation may be achieved in this manner. In another embodiment, the
fit would leave a significant gap, perhaps 0.2 mm to 4.0 mm in
width, between portions or all of the convex fixation surfaces of
the implant and the convex cut(s), into which bone cement or other
substance would then be injected or impacted achieving
interdigitation with both the surfaces of the prosthesis and the
material of the Impacted Surface. This results in what could be
described as composite interface of both biologically active and
non-living but structurally robust materials to facilitate both
immediate intraoperative stability by way of simple mechanics and
long term stability by way of improved load transfer between the
implant and the bone eliciting a beneficial biological response by
the bone to said loading resulting in intimate and mechanically
robust apposition between the composite interface and living tissue
over time. It should be noted that such a method prevents excessive
micromotion or strain at the interface between the implant (and/or
the composite interface) and living tissue during the postoperative
healing process, which, in essence, gives the bone a chance to
further stabilize its fixation to the implant by way of bone
modeling or remodeling in response to load transfer. Specifically,
it is highly beneficial to maintain the strain state within living
bone at and/or beneath and/or in the general vicinity of the bone
implant interface within a range of 50 microstrain to 4000
microstrain so as to elicit the formation of bone tissue at and
around the interface--strain levels in excess of 4000 microstrain
or less than 50 microstrain are very likely to elicit the formation
of fibrocartilagenous tissues at the interface which may lead to
aseptic loosening of the implant. In the embodiment where the bone
cement is injected, a small hole located at or beneath the skim cut
allows for the injection of the material beneath the implant to
achieve intimate and controlled interdigitation. Alternatively, the
implant could be seated `over` the freshly cut concave surfaces,
and a slurry of biologically active and/or mechanically robust
material(s) injected into the gaps between the implant and the bone
under controlled pressure. Injection could be achieved via the
portal shown in FIG. 34. Such a slurry may comprise a mixture of
substances such as morselized patient bone and bone cement, but
alternative or additional materials including bone substitutes,
osteobiologicals such as bone morphogenic proteins, antibiotics, or
even living cells such as T cells known to promote post-operative
healing and long term implant fixation. Beneficially, a fin feature
may be added to these embodiments to facilitate additional
mechanical stability, and said stem feature could beneficially
possess an aperture for cross-pin fixation as described below for
use in conjunction with the cross pins represented in FIG. 111.
[0035] Importantly, it is an objective of the embodiments of the
present invention to preserve living, structurally viable bone
tissue to facilitate the efficacy of any subsequent revision
procedures. Further, the location and geometry of the concave
tibial cut allows for the use of a bearing insert (conventionally
made of materials such as polyethylene or other materials capable
of `whetting` or mimicking the benefits of `whetting` during
bearing contact; mimicking constituting, in one embodiment, the
absence or mitigation of wear debris generation despite the
application of significant bearing forces, in TKA in excess of 200
lbs and often as much as 500 lbs or more) whose `underside` is
convexly shaped to mate with a concavely shaped mating or
accommodating surface in the upper surface of the tibial implant or
`baseplate` as it is sometimes referred to. This allows for a
tibial insert(s) whose thickness, in the areas beneath where the
femoral implant bears against the tibial insert, may be equal to or
greater than those insert thicknesses used in the past (those
associated with predominantly planar tibial cuts) while require
removal of significantly less structurally viable bone from the
cortical rim of the proximal tibia than past efforts. Determination
of the geometry and location of the baseplate's concave surface and
therefore the areas of greatest insert or bearing surface are
easily determined by analysis of the wear patterns of retrieved
tibial inserts. These embodiments of the present inventions also
facilitate significant clinical benefits when applied to meniscal
or rotating platform TKA designs as a high degree of conformity may
be achieved while constraint is mitigated while preserving
significantly more bone than prior art devices. Further, the
reproducibility of the methods and apparatus described herein
enable independent attachment of single compartment implants to
bone to achieve Unicondylar, Bicondylar, Bicondylar and
Patellofemoral, or Unicompartmental and Patellofemoral replacement
of damaged bone surfaces while achieving the objectives of bone
preservation, robust immediate and short and long term fixation,
reproducibility of implant fixation and resulting location and
orientation, and intraoperative ease of use.
[0036] The complete disclosures of the patents, patent applications
and publications cited herein are incorporated by reference in
their entirety as if each were individually incorporated. Various
modifications and alterations to this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention. It should be understood that
this invention is not intended to be unduly limited by the
illustrative embodiments and examples set forth herein and that
such examples and embodiments are presented by way of example only
with the scope of the invention intended to be limited only by the
claims set forth herein.
* * * * *