U.S. patent application number 12/599123 was filed with the patent office on 2010-09-30 for surgically implantable knee prosthesis with captured keel.
Invention is credited to Barry M. Fell, Richard H. Hallock.
Application Number | 20100249941 12/599123 |
Document ID | / |
Family ID | 40122134 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100249941 |
Kind Code |
A1 |
Fell; Barry M. ; et
al. |
September 30, 2010 |
SURGICALLY IMPLANTABLE KNEE PROSTHESIS WITH CAPTURED KEEL
Abstract
A unicompartmental knee prosthesis for implantation in a knee
joint between a femoral condyle and a corresponding tibia plateau
is provided including a generally elliptical body having opposed
femoral and tibial face, the body having an anterior end and a
posterior end. A keel is provided on the tibial face having a
generally anterior-posterior orientation, the keel having an
anterior end and a posterior end, where the keel posterior end
includes a distal posterior portion that extends farther toward the
body posterior end compared with a proximal posterior portion of
the keel posterior end.
Inventors: |
Fell; Barry M.;
(Hummelstown, PA) ; Hallock; Richard H.;
(Hummelstown, PA) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER, TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Family ID: |
40122134 |
Appl. No.: |
12/599123 |
Filed: |
May 15, 2008 |
PCT Filed: |
May 15, 2008 |
PCT NO: |
PCT/US08/63712 |
371 Date: |
November 6, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60938012 |
May 15, 2007 |
|
|
|
Current U.S.
Class: |
623/20.28 |
Current CPC
Class: |
A61F 2002/30884
20130101; A61F 2002/30125 20130101; A61F 2/389 20130101; A61F
2002/30878 20130101; A61F 2002/3895 20130101; A61F 2/3836 20130101;
A61F 2/3886 20130101 |
Class at
Publication: |
623/20.28 |
International
Class: |
A61F 2/38 20060101
A61F002/38 |
Claims
1. A unicompartmental knee prosthesis for implantation in a knee
joint between a femoral condyle and a corresponding tibia plateau,
the prosthesis comprising: a generally elliptical body having
opposed femoral and tibial faces, the body having an anterior end
and a posterior end; and a keel provided on the tibial face having
a generally anterior-posterior orientation, the keel having an
anterior end and a posterior end, wherein the keel posterior end
includes a distal posterior portion that extends farther toward the
body posterior end compared with a proximal posterior portion of
the keel posterior end.
2. The prosthesis according to claim 1, wherein the distal
posterior portion of the keel posterior end is rounded.
3. The prosthesis according to claim 1, wherein the keel posterior
end is step-shaped to form an approximately 90.degree. angle at the
keel posterior end.
4. The prosthesis according to claim 1, wherein a distal end of the
keel is longer than a proximal end of the keel.
5. The prosthesis according to claim 1, wherein the keel anterior
end includes a proximal anterior portion that extends farther
toward the body anterior end compared with a distal anterior
portion of the keel anterior end.
6. The prosthesis according to claim 5, wherein the distal anterior
portion of the keel anterior end is rounded.
7. The prosthesis according to claim 5, wherein the distal anterior
portion of the keel anterior end is chamfered.
8. The prosthesis according to claim 1, wherein the keel anterior
end includes a distal anterior portion that extends farther toward
the body anterior end compared with a proximal anterior portion of
the keel anterior end.
9. The prosthesis according to claim 8, wherein the keel anterior
end is step-shaped to form an approximately 90.degree. angle at the
keel anterior end.
10. The prosthesis according to claim 1, wherein the keel posterior
end is hook-shaped to form an obtuse angle at the keel posterior
end.
11. The prosthesis according to claim 1, wherein the keel anterior
end extends longer distally compared with the keel posterior
end.
12. The prosthesis according to claim 1, wherein the keel posterior
end extends longer distally compared with the keel anterior
end.
13. The prosthesis according to claim 1, wherein the keel tapers
such that a proximal end of the keel is wider than a distal end of
the keel.
14. The prosthesis according to claim 1, further comprising a
surfacing component provided on at least one of the tibial and
femoral faces.
15. The prosthesis according to claim 1, further comprising a
cross-keel having a generally medial-lateral orientation.
16. The prosthesis according to claim 15, wherein the keel extends
longer distally compared with the cross-keel.
17. The prosthesis according to claim 15, wherein the cross-keel
extends to approximately the same distal depth as the keel.
18. The prosthesis according to claim 15, wherein a distal portion
of the cross-keel extends farther toward the body posterior end
compared with a proximal portion of the cross-keel.
19. The prosthesis according to claim 15, wherein the cross-keel
extends distally generally orthogonally from the tibial face.
20. The prosthesis according to claim 15, wherein the cross-keel
extends distally along the keel anterior end.
21. The prosthesis according to claim 1, the keel further
comprising at least one barb member protruding therefrom and having
a generally medial-lateral orientation, the barb member having a
distal portion that extends farther toward the body anterior end
compared with a proximal portion of the barb member.
22. The prosthesis according to claim 21, wherein the at least one
barb member tapers such that an end adjacent the keel is wider
compared with an end removed from the keel.
23. The prosthesis according to claim 1, further comprising a tab
extending distally from the posterior end of the body.
24. The prosthesis according to claim 1, wherein the keel includes
a portion which is expandable in a generally medial-lateral
direction.
25. The prosthesis according to claim 24, wherein the expandable
portion is provided adjacent the keel anterior end.
26. The prosthesis according to claim 1, wherein the body is
arranged to receive a fastener.
27. The prosthesis according to claim 1, wherein the keel is
constructed from a deformable material.
28. The prosthesis according to claim 1, wherein the prosthesis
includes a biologically or pharmaceutically active material
associated therewith.
29. The prosthesis according to claim 28, wherein the biologically
or pharmaceutically active material is a vasodilator associated
with the keel.
30. The prosthesis according to claim 28, wherein the biologically
or pharmaceutically active material is a nerve-targeting agent
associated with the keel.
31. The prosthesis according to claim 1, further comprising an
internal conduit from the body to the keel.
32. A unicompartmental knee prosthesis for implantation in a knee
joint between a femoral condyle and a corresponding tibia plateau,
the prosthesis comprising: a generally elliptical body having
opposed femoral and tibial faces, the body having an anterior end
and a posterior end; and a keel provided on the tibial face having
a generally anterior-posterior orientation, the keel having an
anterior end and a posterior end, wherein the keel posterior end
includes a distal posterior portion that extends farther toward the
body posterior end compared with a proximal posterior portion of
the keel posterior end, and wherein the keel anterior end includes
a proximal anterior portion that extends farther toward the body
anterior end compared with a distal anterior portion of the keel
anterior end.
33. A method of implanting a unicompartmental knee prosthesis in a
knee joint between a femoral condyle and a corresponding tibia
plateau, the method comprising: providing a generally elliptical
body having opposed femoral and tibial faces, the body having an
anterior end and a posterior end, the prosthesis including a keel
provided on the tibial face having a generally anterior-posterior
orientation, the keel having an anterior end and a posterior end,
wherein the keel posterior end includes a distal posterior portion
that extends farther toward the body posterior end compared with a
proximal posterior portion of the keel posterior end; and creating
a cut in the tibial plateau arranged to at least partially receive
the keel.
34. The method according to claim 33, wherein a majority of
subchondral bone of the tibial plateau is left intact.
35. The method according to claim 33, further comprising
positioning the keel to reach below an underside of subchondral
bone of the tibial plateau, thus capturing the prosthesis.
36. The method according to claim 33, further comprising
associating a biologically or pharmaceutically active material with
the prosthesis.
37. The method according to claim 36, further comprising filling
the prosthesis with the active material via an internal conduit
between the body and the keel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
application Ser. No. 60/938,012 filed May 15, 2007, which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a prosthesis which is surgically
implantable into a body joint, such as the knee.
[0004] 2. Background Art
[0005] Current knee arthroplasties typically involve replacement of
the arthritic joint surfaces and are known for their use of metal
and plastic components. They are usually embedded in a
polymethylmethacrylate (PMMA) cement mantle to adhesively and
mechanically bond the components to the area of bone exposed during
the course of surgery.
[0006] Typically, this area of exposed bone is 2-3 mm below the
area of existing eroded bone surface and generally requires removal
of the entire subchondral bone in the area of implant location. In
all cases, the subchondral (SC) bone of the tibial plateau, which
is attached to the remaining articular surface, is removed as
standard practice for both the total knee (TKR) and partial or
unicompartmental knee (UKR) replacement procedures.
[0007] Further, FDA guidelines generally dictate that when
polyethylene (PE) is used as a bearing surface, whether in
conjunction with a metal support plate or not, at least 6 mm of PE
thickness must be used to prevent fracturing of the PE during use.
When the PE is used on the tibial side of these implant designs,
this requirement leads to bone resections of the tibial plateau
generally greater than 7 mm. The subchondral bone thickness on a
typical tibial plateau is generally 2-3 mm. Thus, a typical TKR or
UKR implant will require resection of the entire SC bone present on
the tibial plateau, leaving only cancellous bone.
[0008] The PE is typically held in place by an interference fit or
by melt infusion to a metal backing plate known as the tibial
baseplate. This baseplate, in turn, is held in place on the now
exposed cancellous bone of the tibia by screws, keels, posts, or
combinations of some or all of these devices. The screws and keels
generally provide immediate fixation, but these are usually
enhanced by the addition of the PMMA cement. In the case of
perforated keels, tapered and hourglass shaped posts, when these
projections are set in uncured cement, the cement forms around and
through them and, once hardened, provides an almost indestructible
bond between the PMMA cement and the tibial baseplate. The cement
also permeates the open cellular structure of the cancellous bone,
thus resulting in the same type of bond between the bone and the
tibial baseplate. In some unique cases, the metal tibial baseplate
is not used and an all-PE design is bonded directly to the
cancellous bone with the PMMA cement utilizing a roughened PE
surface or molded posts to facilitate the bond with the PMMA
cement.
[0009] A new generation of tibial hemiarthroplasty (THA) implant
designs has been introduced which do not require significant
resection of the SC bone of the tibial plateau to function
properly. Examples of this are the U.S. Pat. Nos. 6,206,927;
6,558,421; 6,966,928; 6,866,684; and 7,341,602, each of which is
incorporated by reference herein. These THA designs maintain their
proper location in the joint by interference with preexisting or
prepared anatomical shapes present in the knee joint, and none
require PMMA-cemented protrusions or screws for proper
function.
[0010] Previous keel designs, whether utilized for THA, UKR, or TKR
implants, typically utilize an anteriorly-oriented keel. For
example, the Zimmer Sbarbaro "skate" implant has a keel aligned in
the anterior-posterior (AP) direction, with the posterior portion
being rounded and sharpened and the anterior portion having an
anterior (forward) pointing distal tip. In order to insert this
particular shaped keel into a tibia with a cut to accept the keel,
the length of the saw cut needed to insert the bottommost portion
of the keel would be significantly longer the length of the keel at
the base of the implant, thus allowing the implant to be able to
slide in an anterior fashion upon implantation in an anterior to
posterior insertion direction.
[0011] Other previous keel designs, such as the DePuy
"Preservation" UKR, utilize a keel which extends the majority of
the length of the baseplate. In this implant, the keel also
comprises an hourglass shape in medial-lateral (ML) section. Due to
the length of the keel and the hourglass design along its length,
this implant cannot be inserted into the tibia without first making
a substantial femoral cut to provide access to the tibia, or
otherwise inserting the implant via a lengthwise insertion from the
most anterior portion of the tibial plateau. In other words, the
tibial plateau, rather than receiving a simple angle saw cut in
order to receive the implant, must have a milled hourglass shape
cut in the plateau which extends through the most anterior cortical
bone in order for the keel to be inserted into the joint. If such a
milled cut is not prepared, then a cut equal to the largest width
of the keel must be made, which would not provide positive locking
with the keel unless a mantle of cement is used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a side elevational view of a prosthesis according
to the present invention including a keel with angled anterior and
posterior ends;
[0013] FIG. 2 is a bottom perspective view of the prosthesis of
FIG. 1;
[0014] FIG. 3 is a side elevational view of a prosthesis according
to the present invention including a keel with a rounded anterior
end and angled posterior end;
[0015] FIG. 4 is a bottom perspective view of the prosthesis of
FIG. 3;
[0016] FIG. 5 is a bottom perspective view of a prosthesis
according to the present invention including a keel with rounded
anterior and posterior ends;
[0017] FIG. 6 is a bottom perspective view of a prosthesis
according to the present invention including a keel with rounded
anterior and posterior ends;
[0018] FIG. 7 is a side elevational view of a prosthesis according
to the present invention including a keel with rounded anterior and
posterior ends shown with reference to a cross-section of the
tibia, wherein a representative thickness subchondral and cortical
bone are represented;
[0019] FIG. 8 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and chamfered anterior end;
[0020] FIG. 9 is a bottom perspective view of the prosthesis of
FIG. 8;
[0021] FIG. 10 is a side elevational view of the prosthesis of FIG.
8 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0022] FIG. 11 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and oppositely angled anterior end;
[0023] FIG. 12 is a bottom perspective view of the prosthesis of
FIG. 11;
[0024] FIG. 13 is a side elevational view of the prosthesis of FIG.
11 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0025] FIG. 14 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and a step-shaped anterior end;
[0026] FIG. 15 is a bottom perspective view of the prosthesis of
FIG. 14;
[0027] FIG. 16 is a side elevational view of the prosthesis of FIG.
14 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0028] FIG. 17 is a side elevational view of a prosthesis according
to the present invention including a keel with a step-shaped
posterior end and a rounded anterior end;
[0029] FIG. 18 is a bottom perspective view of the prosthesis of
FIG. 17;
[0030] FIG. 19 is a side elevational view of the prosthesis of FIG.
17 shown with reference to a cross-section of a tibia wherein a
representative thickness subchondral and cortical bone are
represented;
[0031] FIG. 20 is a side elevational view of a prosthesis according
to the present invention including a keel with a step-shaped
posterior end and a curved anterior end;
[0032] FIG. 21 is a bottom perspective view of the prosthesis of
FIG. 20;
[0033] FIG. 22 is a side elevational view of the prosthesis of FIG.
20 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0034] FIG. 23 is a side elevational view of a prosthesis according
to the present invention including a keel with a step-shaped
posterior end and a chamfered anterior end;
[0035] FIG. 24 is a bottom perspective view of the prosthesis of
FIG. 23;
[0036] FIG. 25 is a side elevational view of the prosthesis of FIG.
23 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0037] FIG. 26 is a side elevational view of a prosthesis according
to the present invention showing generic keel dimensions;
[0038] FIG. 27 is a bottom plan view of a prosthesis according to
the present invention showing generic keel dimensions;
[0039] FIG. 28 is a side elevational view of a prosthesis according
to the present invention showing exemplary keel dimensions;
[0040] FIG. 29 is a bottom plan view of a prosthesis according to
the present invention showing exemplary keel dimensions;
[0041] FIG. 30 is a side elevational view of a prosthesis according
to the present invention including a keel with a hooked posterior
end and a relatively longer, angled anterior end;
[0042] FIG. 31 is a bottom plan view of the prosthesis of FIG.
30;
[0043] FIG. 32 is a front elevational view of the prosthesis of
FIG. 30;
[0044] FIG. 33 is a rear perspective view of the prosthesis of FIG.
30;
[0045] FIG. 34 is a side elevational view of the prosthesis of FIG.
30 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0046] FIG. 35 is a top perspective view of a tibial cut which may
be utilized for receiving the prosthesis of FIG. 30;
[0047] FIG. 36 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and a relatively longer, rounded anterior end;
[0048] FIG. 37 is a bottom perspective view of the prosthesis of
FIG. 36;
[0049] FIG. 38 is a side elevational view of the prosthesis of FIG.
36 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0050] FIG. 39 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and a relatively shorter, rounded anterior end;
[0051] FIG. 40 is a bottom perspective view of the prosthesis of
FIG. 39;
[0052] FIG. 41 is a side elevational view of the prosthesis of FIG.
39 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0053] FIG. 42 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and a relatively shorter, rounded anterior end, the prosthesis
including a cushioning component on a tibial face thereof;
[0054] FIG. 43 is a bottom perspective view of the prosthesis of
FIG. 42;
[0055] FIG. 44 is a side elevational view of the prosthesis of FIG.
42 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0056] FIG. 45 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end and a relatively shorter, rounded anterior end, the prosthesis
including a cushioning component on a femoral face thereof;
[0057] FIG. 46 is a bottom perspective view of the prosthesis of
FIG. 45;
[0058] FIG. 47 is a side elevational view of the prosthesis of FIG.
45 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0059] FIG. 48 is a bottom perspective view of a cushioning
component according to the present invention;
[0060] FIG. 49 is a top perspective view of a femoral face of the
prosthesis of FIG. 45 which is prepared to receive a cushioning
component thereon;
[0061] FIG. 50 is a side elevational view of a prosthesis according
to the present invention which may be utilized for a lateral
compartment implantation, the prosthesis including a keel having an
angled posterior end and a relatively longer, angled anterior
end;
[0062] FIG. 51 is a bottom perspective view of the prosthesis of
FIG. 50;
[0063] FIG. 52 is a top perspective view of the prosthesis of FIG.
50;
[0064] FIG. 53 is a front elevational view of the prosthesis of
FIG. 50;
[0065] FIG. 54 is a rear elevational view of the prosthesis of FIG.
50;
[0066] FIG. 55 is a side elevational view of the prosthesis of FIG.
50 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0067] FIG. 56 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
edge, a rounded anterior edge, and an angled cross-keel member;
[0068] FIG. 57 is a bottom perspective view of the prosthesis of
FIG. 56;
[0069] FIG. 58 is a side elevational view of the prosthesis of FIG.
56 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0070] FIG. 59 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end, a rounded anterior end, and an angled cross-keel member
extending the depth of the keel;
[0071] FIG. 60 is a bottom perspective view of the prosthesis of
FIG. 59;
[0072] FIG. 61 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end, a rounded anterior end, and a cross-keel member extending
along the depth of the keel;
[0073] FIG. 62 is a bottom perspective view of the prosthesis of
FIG. 61;
[0074] FIG. 63 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end, an angled anterior end, and an angled cross-keel member
extending along the depth of the keel at the anterior end;
[0075] FIG. 64 is a bottom perspective view of the prosthesis of
FIG. 63;
[0076] FIG. 65 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end, an anterior end generally orthogonal to a bottom face of the
prosthesis, and a cross-keel member extending along the depth of
the keel at the anterior end;
[0077] FIG. 66 is a bottom perspective view of the prosthesis of
FIG. 65;
[0078] FIG. 67 is a side elevational view of a prosthesis according
to the present invention including a keel with an angled posterior
end, a rounded, angled anterior end, and a plurality of angled barb
members oriented toward the anterior end;
[0079] FIG. 68 is a bottom perspective view of the prosthesis of
FIG. 67;
[0080] FIG. 69 is a bottom plan view of the prosthesis of FIG.
67;
[0081] FIG. 70 is a side elevational view of the prosthesis of FIG.
67 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0082] FIG. 71 is a side elevational view of a prosthesis according
to the present invention including a keel with a hooked posterior
end, a rounded, angled anterior end, and an angled barb member
oriented toward the anterior end;
[0083] FIG. 72 is a bottom perspective view of the prosthesis of
FIG. 71;
[0084] FIG. 73 is a side elevational view of a prosthesis according
to the present invention including a keel with a hooked posterior
end, a rounded, angled anterior end, and an angled barb member
oriented toward the anterior end, wherein the keel tapers at a
distal end thereof;
[0085] FIG. 74 is a bottom perspective view of the prosthesis of
FIG. 73;
[0086] FIG. 75 is a rear elevational view of the prosthesis of FIG.
73;
[0087] FIG. 76 is a bottom plan view of the prosthesis of FIG.
73;
[0088] FIG. 77 is a side elevational view of the prosthesis of FIG.
73 shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0089] FIG. 78 is a bottom perspective view of a prosthesis
according to the present invention including a posterior tab,
wherein the keel is omitted for clarity;
[0090] FIG. 79 is a top perspective view of the prosthesis of FIG.
78;
[0091] FIG. 80 is a side elevational view of the prosthesis of FIG.
78 including a keel similar to FIG. 73 and shown with reference to
a cross-section of a tibia, wherein a representative thickness
subchondral and cortical bone are represented;
[0092] FIG. 81 is a side elevational view of a prosthesis according
to the present invention including a keel with an expandable
portion in the medial-lateral direction, wherein the prosthesis is
shown with reference to a cross-section of a tibia, wherein a
representative thickness subchondral and cortical bone are
represented;
[0093] FIG. 82 is a bottom perspective view of the prosthesis of
FIG. 81;
[0094] FIG. 83 is a bottom perspective view of the prosthesis of
FIG. 81 with the expandable portion actuated;
[0095] FIG. 84 is a rear elevational view of the prosthesis of FIG.
83;
[0096] FIG. 85 is a side elevational view of a prosthesis according
to the present invention including a keel and a screw for
additional fixation;
[0097] FIG. 86 is a bottom perspective view of the prosthesis of
FIG. 85;
[0098] FIG. 87 is a front elevational view of the prosthesis of
FIG. 85;
[0099] FIG. 88 is a cross-sectional view of the tibia showing a
tibial cut therein and interaction of the flexed femur with the
tibia;
[0100] FIG. 89 is a side elevational view of the prosthesis of FIG.
73 as it is inserted into the tibial cut illustrated in FIG.
88;
[0101] FIG. 90 is a side elevational view of the prosthesis of FIG.
73 upon further insertion into the tibial cut illustrated in FIG.
88;
[0102] FIG. 91 is a side elevational view of the prosthesis of FIG.
73 upon complete insertion into the tibial cut illustrated in FIG.
88;
[0103] FIG. 92 is a schematic representation of a tibia, wherein
the lighter volume shown in cross-section represents a typical
amount of bone resection required for a prior art unicompartmental
knee replacement procedure;
[0104] FIG. 93 is a schematic representation of a tibia, wherein
the total volume represents a typical amount of bone resection
required for a prior art unicompartmental knee replacement
procedure, and the upper, lighter volume represents a typical
amount of bone resection utilized for implanting a prosthesis
according to the present invention;
[0105] FIG. 94 is a top plan view of an instrument according to the
present invention which may be utilized for creating a tibial cut
in order to implant a prosthesis according to the present
invention;
[0106] FIG. 95 is a top perspective view of the instrument of FIG.
94;
[0107] FIG. 96 is a side elevational view of the instrument of FIG.
94;
[0108] FIG. 97 is a bottom plan view of the instrument of FIG.
94;
[0109] FIG. 98 is a top perspective view of a modular instrument
according to the present invention which may be utilized for
creating a tibial cut in order to implant a prosthesis according to
the present invention;
[0110] FIG. 99 is a top perspective view of the instrument of FIG.
98 where one portion of the tibial cut guide has been removed;
[0111] FIG. 100 is a side elevational view of the instrument of
FIG. 98;
[0112] FIG. 101 is a top plan view of the instrument of FIG.
98;
[0113] FIG. 102 is a bottom plan view of the instrument of FIG.
98;
[0114] FIG. 103 is a bottom perspective view of an instrument
according to the present invention for sizing a prosthesis;
[0115] FIG. 104 is a side elevational view of the instrument of
FIG. 103;
[0116] FIG. 105 is a top perspective view of the instrument of FIG.
103;
[0117] FIG. 106 is a side elevational view of an impactor according
to the present invention in contact with a prosthesis according to
the present invention shown with reference to a cross-section of a
tibia, wherein a representative thickness subchondral and cortical
bone are represented;
[0118] FIG. 107 is a top perspective view of the impactor of FIG.
106;
[0119] FIG. 108 is a side elevational view of the impactor of FIG.
106 further illustrating a handle thereon;
[0120] FIG. 109 is a top perspective view of the impactor and
handle of FIG. 108; and
[0121] FIG. 110 is a wireframe representation of a prosthesis
according to the present invention including an internal conduit
and portal.
DETAILED DESCRIPTION OF THE INVENTION
[0122] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale, and some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for teaching one skilled in the art to variously employ the present
invention.
[0123] The present invention includes a prosthesis with a captured
keel design which provides for positive interlocking that resists
unintended dislodgement of the implant without the need for PMMA
cement. The prosthesis according to the present invention may be
used in conjunction with a tibial preparation that removes much of
the remaining cartilage but leaves the majority of the SC bone of
the tibial plateau intact. In accordance with the present
invention, and differentiated from prior keel designs, the keel
disclosed herein incorporates a notched, angled, or other design
wherein the most distal, posterior portion of the keel may extend
more posteriorly than the most proximal, posterior portion of the
keel, thus providing a keel shape of negative draft. In addition,
the distal end of the keel may be longer in an AP direction than
the proximal end of the keel, giving a recessed or hooked
appearance. The keel may be of sufficient depth such that while the
bottom of the prosthesis sits predominantly on the existing SC
bone, the extended portion of the keel may reach below the
underside of the SC bone, thus capturing the prosthesis with the
remaining SC bone.
[0124] By leaving the majority of the SC bone intact and
undisturbed in accordance with the present invention, the risk over
time of prosthesis subsidence into the tibia, the primary failure
mode of present day UKR implants, may be largely eliminated. This
may be of great significance to patients who have unicompartmental
disease but are contra-indicated for UKR or TKR procedures because
of gross obesity. Further, unlike other THA implants, the captured
keel prosthesis according to the present invention may provide for
significantly reduced motion against the tibia because of the
interlocking keel design.
[0125] One function of the prosthesis according to the present
invention may be to effectively replace the articular material that
has been lost due to the effects of osteoarthritis by spanning the
diseased area and supporting the prosthesis by intimate contact
with the surrounding healthy tissue. An advantage of this approach
is that the combination of removing healthy articular material and
replacing that same material with the prosthesis allows for a
minimal thickness prosthesis to be utilized which does not need to
disturb the meniscal function or location. This approach may result
in an area under the prosthesis where the prosthesis is barely in
contact with the area of osteoarthritis (where SC bone has been
deformed or eburnated). The prosthesis according to the present
invention may not disturb SC bone, thus reducing the chance of any
prosthesis subsidence into cancellous bone like a UKR baseplate
often does.
[0126] In accordance with the present invention, unlike previous
THA and UKR methods, it is not necessary that the tibial plateau
have an absolutely flat surface after surgical preparation. Rather,
the majority of the plateau, once the remaining articular material
has been largely removed, may provide an adequate peripheral
shoulder on which the prosthesis can be supported. Thus, if the
area of the osteoarthritis defect were still lower than the SC bone
once the majority of the plateau has been flattened, the prosthesis
may simply bridge this area while the keel may pass through the
defect to the underside of the SC bone in that area, providing an
interlocking behavior.
[0127] The keel of the prosthesis according to the present
invention is arranged to be at least partially received within a
cut prepared on the tibial plateau. According to one aspect of the
present invention, the tibial cut may be of a size substantially
equal to the size of a proximal end of the keel right underneath
the prosthesis, such that little or no give exists between the
tibial cut and keel, such that use of cement may be avoided. The
desired location and size of the tibial cut may be matched with a
particular prosthesis selected from a library of prostheses having
different locations and sizes of keels. The tibial cut may be
prepared with an appropriate milling device or the like which may
be accurately located via temporary fixation, computer guidance, or
other means.
[0128] The surgical procedure may involve resection (flattening) of
the remaining articular material on the tibial plateau in the area
where the prosthesis will reside using an oscillating saw or other
tool, sizing the plateau for the proper length, width and thickness
and, utilizing a cutting guide, making a saw or rasp cut at the
proper angle and direction with the oscillating saw. This vertical
saw cut may ultimately determine the final position of the
prosthesis. The keel of the prosthesis may be positioned into the
guided saw cut location with the knee flexed and once in position,
gently hammered into place. In addition to not requiring the
removal of SC bone, the prosthesis according to the present
invention does not require femoral resection to implant.
[0129] While the prosthesis according to the present invention is
shown and described herein as being implanted in a knee joint,
specifically as a unicompartmental knee prosthesis implantable in a
knee joint between a femoral condyle and a corresponding tibial
plateau, it is understood that the prosthesis could be utilized in
joints other than the knee such as, but not limited to, the hip,
shoulder, wrist, ankle, or elbow, or other small joints of the foot
or hand.
[0130] With reference to the figures, the prosthesis according to
the present invention, designated generally by reference numeral
10, comprises a body 12 which may be generally elliptical and which
includes a bottom, or tibial, face 14 and an opposed top, or
femoral, face 16. Body 12 includes an anterior end 18 and a
posterior end 20, corresponding to the anatomical location of these
ends 18, 20 of body 12 upon implantation into the knee joint,
wherein the prosthesis shape may generally cover the majority of
the medial or lateral tibial plateau T. To restrain movement of the
prosthesis, a keel 22 may be provided on the bottom face 14, and
may have a generally AP orientation as depicted herein. According
to the present invention, the keel 22 can have any location on the
bottom face 14 and can be of any size suitable for insertion. Keel
22 has an anterior end 24 and a posterior end 26, again according
to the anatomical location of these ends 24, 26 upon implantation.
Keel posterior end 26 may include a distal posterior portion 28
that extends farther toward the body posterior end 20 compared with
a proximal posterior portion 30 of the keel posterior end 26,
creating a posterior keel design which is relieved, undercut,
hooked, or similar. The keel designs according to the present
invention provide inherent stability to the prosthesis 10 because
femoral loading on the prosthesis 10 cannot reproduce motion of the
prosthesis 10 required to dislodge it from the tibial plateau T. In
addition to the embodiments depicted herein, it is understood that
any keel having a distal posterior portion extending further toward
the body posterior end than does the proximal posterior portion of
the keel is fully contemplated according to the present
invention.
[0131] The top face 16 could be of uniform shape or could have a
combination of sloped and flat surfaces. The entire top face 16 or
portions thereof may range from generally convex to generally
concave or combinations of those surfaces, and range from generally
conformal to non-conformal, depending on the compartment for
implantation, the condition of the ligaments and other soft tissue
structure at the time of surgery, and how much stability the knee
will require. The femoral face 16 shape may be characterized as an
aspect ratio defined by the chord line and the thickness above or
below this chord line as a function of distance from a defined
point on the chord line, such as the leading edge or midpoint, much
like an airfoil can be described. It is understood that the terms
"concave" and "convex" as used herein are not restricted to
describing surfaces with a constant radius of curvature, but rather
are used to denote the general appearance of the surface.
[0132] According to one aspect of the present invention, the
remainder of the bottom face 14, excluding the keel 22, may
include, for example, a generally flat surface which does not
require "seating." However it is understood that other contours of
the bottom face 14 are fully contemplated in accordance with the
present invention. For example, depending upon the compartment of
implantation, the condition of the ligaments and other soft tissue
structure at the time of surgery, and how much stability the knee
will require, the bottom face 14 may be generally concave, flat, or
convex, or anywhere within the range from concave to convex or
combinations of those surfaces. Again, it is understood that the
terms "concave" and "convex" as used herein is not restricted to
describing a surface with a constant radius of curvature, but
rather is used to denote the general appearance of the surface.
[0133] The body 12 further includes a peripheral edge 32 extending
between the bottom face 14 and the top face 16. Edges along the
periphery of the prosthesis 10 can be rounded. Any thickness of the
prosthesis 10 or variation of thickness within the prosthesis 10
may be utilized, and may be determined so as to provide proper
joint tensioning throughout the range of motion of the knee. The
prosthesis 10 according to the present invention may have length
and width proportions roughly similar to any of the current UKR
tibial base plates, whereas its thickness may generally be 2-3 mm
less than the UKR overall baseplate/PE thickness since the SC bone
is not being removed. Of course, prosthesis 10 is not limited to
these dimensions. The prosthesis 10 according to the present
invention may be used in conjunction with the remaining meniscus or
meniscal replacement by having a relieved thickness along the
periphery where the meniscus is located. Additionally, the
posterior end 20 of the femoral face 16 may be tapered, and two
different femoral and tibial surface profiles utilized. Thinning of
the posterior end 20 may be helpful in deep flexion to eliminate a
lever which could tip the prosthesis 10 upward and potentially out
of engagement with the tibial plateau T, and also to relieve
possible impingement and pain.
[0134] It is understood that the term "generally elliptical" is
intended to include all construction methods which yield a
generally planar shape which is longer in one direction than in the
transverse direction and has generally rounded corners, and that
the prosthesis 10 is not otherwise limited to any particular
shape.
[0135] With reference first to FIGS. 1-2, a prosthesis 10 according
to the present invention is depicted including a keel 22 with
anterior and posterior ends 24, 26 which are angled toward the body
posterior end 20 such that the distal posterior portion 28 of the
keel 22 extends farther toward the body posterior end 20 compared
with the proximal posterior portion 30 of the keel 22. This creates
an undercut portion at the keel posterior end 26 which may then
engage underneath the SC bone upon insertion of the prosthesis 10.
Insertion of the prosthesis 10 may be facilitated by rounding of a
distal anterior portion 34 of the keel as shown in FIGS. 3-4, or
rounding of both the distal anterior 34 and distal posterior
portions 28 of the keel 22 as depicted in FIGS. 5-7. Alternatively,
solely the distal posterior portion 28 of the keel may be
rounded.
[0136] As shown in FIGS. 5-6, keel 22 may be embodied as having
different lengths along tibial face 14 and be positioned
differently on tibial face 14. For example, FIG. 5 depicts a keel
22 having a length that extends along approximately half the length
of the tibial face 14, positioned toward body anterior end 18,
whereas FIG. 6 depicts a keel 22 having a length that extends along
approximately 20% of the length of the tibial face 14. Of course,
it is understood that any length, depth, and positioning of keel 22
with respect to tibial face 14 is fully contemplated.
[0137] In accordance with another embodiment of the present
invention, FIGS. 8-10 depict a prosthesis including a keel with an
angled posterior end 26 and chamfered distal anterior portion 34.
FIGS. 17-25 illustrate keel embodiments according to the present
invention wherein the keel posterior end 26 includes a notched or
step-shaped configuration, such as to form an approximately
90.degree. angle at the keel posterior end 26, and the keel
anterior end 24 is angled, rounded, chamfered, or a combination
thereof.
[0138] With reference to FIGS. 11-16, in addition to the angled
posterior end 26 described above, the keel 22 according to the
present invention could also incorporate an oppositely angled,
notched, or step-shaped anterior end 24 wherein the keel anterior
end 24 includes a proximal anterior portion 36 that extends farther
toward the body anterior end 18 compared with a distal anterior
portion 34 of the keel anterior end 24. Thus, once engaged with the
underside of the SC bone, the prosthesis 10 may be secured both
anteriorly and posteriorly to preventing tipping or accidental
dislodgement of the prosthesis 10.
[0139] Turning now to FIGS. 26-27, a prosthesis 10 according to the
present invention is illustrated with generic keel dimensions for a
left medial knee prosthesis. The keel position may be described as
a percentage of the length ahead of or behind the prosthesis
centerline. The depth may be measured at the longest point as
measured from the bottom face 14 of the prosthesis 10. A
relationship table for the dimensions shown is provided below,
where it is understood a change in these ratios by +/-25% or more
is fully contemplated according to the present invention.
D188=Length
D29=0.367*D188
D76=0.224*D188
D95=0.510*D188
D97=0.694*D188
D103=0.061*D188
D104=0.061*D188
D176=0.204*D188
D177=0.510*D188
D178=0.735*D188
D181=0.041*D188
D182=0.061*D188
D189=0.551*D188
D183=0.429*D188
D186=0.429*D188
D175=0.200*D188
[0140] These ratios may describe the relative placement of the keel
22 on the prosthesis 10 (along the anterior-posterior and
medial-lateral directions) and may apply to all keel embodiments
shown and described herein, wherein the variations in the design of
the keel itself are depicted in the drawings. FIGS. 28-29
illustrate possible dimensions for an exemplary prosthesis
according to the present invention having a 49 mm length and 2 mm
thickness. It is understood, of course, that the prosthesis 10 is
not limited to this configuration.
[0141] U.S. Pat. No. 6,966,928, incorporated by reference herein,
describes a keel having a depth which tapers from one end of the
prosthesis to another, such that the taper may be used to
facilitate the insertion of the prosthesis. Such a tapered design
may also be utilized with the prosthesis 10 according to the
present invention. In particular, FIGS. 30-34 illustrate a
prosthesis 10 including a keel 22 with a hooked posterior end 26
and a relatively longer, angled anterior end 24 such that the keel
anterior end 24 extends longer distally compared with the keel
posterior end 26. FIG. 35 is a top perspective view of a tibial cut
68 which may be utilized for receiving the prosthesis 10 of FIG.
30. FIGS. 36-38 depict a prosthesis 10 according to the present
invention including a keel 22 with an angled posterior end 26 and a
relatively longer, rounded anterior end 24. FIGS. 39-41 depict a
prosthesis 10 according to the present invention including a keel
22 with an angled posterior end 26 and a relatively shorter,
rounded anterior end 24, such that the keel posterior end 26
extends longer distally compared with the keel anterior end 24. In
addition, the keel 22 in any embodiment depicted herein may taper
in width from an end proximal to the prosthesis bottom face 14 to
an end distal from the prosthesis bottom face 14 such that a
proximal end 38 of the keel 22 is wider than a distal end 40 of the
keel 22, creating a sort of knife edge which may facilitate
insertion.
[0142] In accordance with the present invention, a thinner
prosthesis may be used where the final intent is to cover at least
one face of the base prosthesis with a load-absorbing, cushioning,
or other surfacing component 42. As shown in FIGS. 42-44, one
embodiment may utilize a hard articulating surface bearing material
like metal, ceramic, or certain polymers (e.g., pyrolytic carbon or
PEEK) which may include a surfacing component 42 provided on a
bottom face 14 thereof wherein the surfacing component 42 then
contacts the tibial plateau T, or alternatively is sandwiched
between the outer articulating surface and an anchoring implant
base. The load absorbing material may be a polymer or other
material, such as a metallic sponge or springs. Biologically
compatible urethanes, various hydrogels, and/or polymers that
contain biologic components can also be utilized. It is also
possible that one material can perform both the articulating
function and the load absorbing function. According to one aspect
of the present invention, the prosthesis configuration may allow
for volume expansion of the surfacing component 42 while under
load. The prosthesis 10 and the surfacing component 42 may be
mechanically linked at the time of surgery to allow for surgeon
selection of polymer thickness and material properties such as
water content, durometer, viscoelastic behavior, and others.
However, such a linkage is not necessary.
[0143] With reference to FIGS. 45-47, a prosthesis 10 according to
the present invention is illustrated which includes a load
absorbing, cushioning, or surfacing component 42 on a top face 16
thereof. In both this embodiment and that described above, a
surface of the prosthesis 10 may be prepared mechanically and/or
chemically to receive the surfacing component 42. For example, FIG.
48 illustrates a bottom perspective view of a surfacing component
42 according to the present invention, and FIG. 49 illustrates a
top perspective view of a top face 16 of the prosthesis of FIG. 45
which is prepared to receive a surfacing component 42 thereon. In
addition, the keel 22 itself could have a load absorbing,
cushioning, or surfacing component associated therewith, such as to
provide strain isolation.
[0144] With reference now to FIGS. 50-55, a prosthesis 10 according
to the present invention is illustrated which may be utilized for a
lateral compartment implantation. The prosthesis depicted includes
a keel 22 having an angled posterior end 26 and a relatively
longer, angled anterior end 24, although any of the keel 22
embodiments shown or described herein could alternatively be
utilized. As shown, a posterior slope 44 may be provided on both
the femoral and tibial faces 14, 16 of the prosthesis 10.
[0145] The prosthesis 10 according to the present invention may
also include a cross-keel 46 provided generally in the
medial-lateral (ML) direction, wherein cross-keel 46 may have a
shorter length in the ML direction than does keel 22 in the AP
direction. Such a cross-keel 46 may enhance the stability of the
prosthesis 10 once inserted. The cross-keel 46 may be generally
rectangular in shape, but is not limited as such. FIGS. 56-58
illustrate a prosthesis 10 according to the present invention
including a keel 22 with an angled posterior end 26, a rounded
anterior end 24, and a cross-keel 46 positioned at approximately
the midpoint of the keel 22 in the AP direction, wherein the
cross-keel 46 extends approximately 1/2 the depth of the keel 22.
In this case, cross-keel member 46 has an angle which is similar to
the angle of the keel posterior end 26, wherein a distal portion 48
of the cross-keel 46 extends farther toward the body posterior end
20 compared with a proximal portion 50 of the cross-keel 46. Of
course, other depths and orientations of cross-keel 46 as compared
with keel 22 are also contemplated. FIGS. 59-60 depict a prosthesis
10 according to the present invention including a keel 22 with an
angled posterior end 26, a rounded anterior end 24, and an angled
cross-keel 46 extending to approximately the same distal depth as
the keel 22. FIGS. 61-62 illustrate a prosthesis 10 according to
the present invention including a keel 22 with an angled posterior
end 26, a rounded anterior end 24, and a cross-keel member 46
extending along the depth of the keel 22 generally orthogonal to
the prosthesis bottom face 14. FIGS. 63-64 depict a prosthesis 10
according to the present invention including a keel 22 with an
angled posterior end 26, an angled anterior end 24, and an angled
cross-keel member 46 extending along the depth of the keel 22 at
the anterior end 24. FIGS. 65-66 illustrate a prosthesis 10
according to the present invention including a keel 22 with an
angled posterior end 26, an anterior end 24 extending distally
generally orthogonal to bottom face 14, and a cross-keel member 46
extending along the depth of the keel 22 at the anterior end 24
generally orthogonal to the prosthesis bottom face 14.
[0146] The prosthesis 10 according to the present invention may
also include shorter cross-keels or barb members 52 protruding from
keel 22 generally in the ML direction. For example, FIGS. 67-70
illustrate a prosthesis 10 according to the present invention
including a keel 22 with an angled posterior end 26, a rounded,
angled anterior end 24, and a plurality of angled barb members 52
having an orientation generally orthogonal to the angle of the
posterior end 26, where each barb member 52 has a distal portion 54
that extends farther toward the body anterior end 18 compared with
a proximal portion 56 of the barb member 52. Barb members 52 may be
tapered such that an end 58 adjacent the keel 22 is wider compared
with an end 60 removed from the keel 22. In another embodiment, a
single angled barb member 52 may be utilized as in FIGS. 71-77. In
this example, the prosthesis 10 may include a keel 22 with a hooked
posterior end 26 and a rounded, angled anterior end 24, although it
is understood that barb members 52 may be used with any keel design
shown or described herein. As illustrated in FIGS. 73-77, the keel
22 may taper so as to be more narrow at an end 40 thereof distal
from the prosthesis bottom face 14 such that the bottommost portion
of the keel 22 may be sharpened, which may be helpful in the
downward and backward motion used to insert the prosthesis 10. The
hooked posterior end 26 may also taper to a three-sided point. This
configuration may help facilitate securing the prosthesis 10 and
capturing SC bone. According to one aspect of the present
invention, the more proximal portion 30 of the posterior end 26 may
remain flat in order to avoid an upward cutting capability of the
prosthesis 10 once inserted.
[0147] In further accordance with the present invention, FIGS.
78-80 illustrate a prosthesis 10 including a posterior tab 62
provided at body posterior end 20 and extending distally beyond
tibial face 14 which may be used to provide further stability to
the prosthesis 10 once seated on the tibial plateau T. It is
understood that the posterior tab 62 may have any shape or depth
suitable for implantation, and is not limited to the configuration
depicted herein.
[0148] The gap between the femoral condyle and the tibial plateau,
after the plateau has been prepared, determines the allowable size
and particular shape of the prosthesis that can be fit into this
space. The location of the keel on the prosthesis, the angle of the
keel, and the overall length and/or depth of the keel may determine
the allowable insertion angle and thus the overall thickness of the
prosthesis, where too large a keel or too posterior a keel location
may prevent insertion of the prosthesis. To solve this problem, a
deformable keel 22 could be utilized. Alternatively, a short depth
(e.g., 2-3 mm) keel 22 could be used. In this case, once the
prosthesis 10 is located in position, screws may be placed down
through the interior of the keel 22 for final fixation.
[0149] As described above, a keel that is integral with the
prosthesis body may be limited in length due to insertion issues. A
post or screw may be added to the prosthesis, such as by threading
it through the prosthesis body, once the prosthesis is in position.
"Captured" screws have a lower tapered threaded portion for
grabbing the bone and an upper portion with a machined thread for
attaching to the prosthesis body during the last portion of travel
of the screw into the bone, allowing for additional stability for
the prosthesis. Strain isolation bushings may be added between the
prosthesis and the screw to further isolate the screw from any
strain induced by micromotion of the prosthesis. According to one
aspect of the present invention, a modular keel assembly could be
implemented, where a greater depth keel may be inserted once a
short depth keel prosthesis is in place. This approach has the
added advantage of customized fits for an individual patient's
needs. In yet another embodiment, the prosthesis 10 may include an
expandable keel portion 64 such as, but not limited to, an anterior
portion as depicted in FIGS. 81-82. Once the prosthesis 10 is in
place, a push pin or other actuator could be advanced through an
internal slot in the prosthesis 10 to flare out the expandable keel
portion 64 in the ML direction for additional capture as depicted
in FIGS. 83-84.
[0150] According to the present invention, at least a portion of
the keel 22, especially those portions that will ultimately reside
in cancellous bone, can be coated to promote bony in-growth or left
smooth to discourage it. The keel 22 may include one or more
openings therein. The prosthesis 10 according to the present
invention could be screwed in, or have any type of fixation (e.g.,
cement) for additional stability. For example, with reference to
FIGS. 85-87, a screw 66 or other fastener may be provided at the
anterior-lateral corner of the prosthesis 10, and may be angled
roughly 30 degrees downward off of the plane of the tibial plateau
and 30 degrees from the AP direction of the keel 22, laterally
(towards the tibial eminence). Of course, a screw or screws 66 are
not limited to this position or orientation with respect to the
prosthesis 10.
[0151] FIG. 88 is a cross-sectional view of the tibia T showing a
tibial cut 68 therein and interaction of the femur with the tibia
T, and FIGS. 89-91 illustrate the prosthesis of FIG. 73 as it is
inserted into the tibial cut 68. As shown, the prosthesis 10 may be
inserted at approximately a 45 degree angle and, in theory, could
only be potentially dislodged via the same path. However, were the
prosthesis 10 to come upward and forward, the femur in extension
would push the prosthesis back into place, thus providing inherent
stability.
[0152] The prosthesis 10 according to the present invention can be
a monolithic design or may be made of two or more separate
components. By utilizing a modular design, the physician may be
able to draw from a library of components at the time of surgery
that may adhesively, mechanically, magnetically, or otherwise
cooperate with each other to yield an assembled prosthesis
particularly suited for that particular patient's knee geometry,
and also maintain a desired balance between the extension and
flexion gap throughout the range of motion. An additional benefit
of such a prosthesis may be that the components could be assembled
in the joint space. This modularity of the prosthesis of the
present invention may also allow the physician to implant a more
standard first component while providing flexibility in the
selection of a corresponding second component that may be best
suited for each individual patient.
[0153] The prosthesis 10 according to the present invention may
comprise a relatively hard, relatively high modulus, low friction
material. Suitable materials include, for example, metals such as
steel or titanium, metal alloys, ceramics, and reinforced and
non-reinforced thermoset or thermoplastic polymers. The material of
construction may be chosen such that the top face spans defects in
the femur without deforming into the defects, allowing for the
provision of recessed or non-contacting areas of the prosthesis to
encourage articular regeneration. In the case of a modular
prosthesis, the components need not be formed of the same material.
For example, a first component may be relatively hard, whereas a
conformal second component may be constructed from a relatively
lower modulus material to allow for some deformation. Furthermore,
the prosthesis 10 need not be made only of a single material.
Rather, the prosthesis 10 or components thereof may each have areas
of lower or higher modulus material, and composite structures of
steel/thermoplastic, steel/ceramic, ceramic/polymer, or others may
be used.
[0154] In greater detail, materials of construction could include,
but are not limited to, elastomeric polymers such as nylon,
silicone, polyurethane, polypropylene, polyester, or the like,
optionally fiber-reinforced, or viscous-elastic materials such as
PVA hydrogels, as well as other hydrophilic materials or
hydrophobic materials. Polymers capable of containing living cells
could also be utilized. Still other possible materials are those
which can replicate the function of naturally occurring cartilage
or meniscus. A surface coating can be employed, such as for the
reduction of friction between the prosthesis and the femoral
condyle. Generally, the areas of the prosthesis 10 expected to have
the most wear may be made of stronger, more abrasion resistant
material than the remainder of the prosthesis when composite
structures are used. As such, it is understood that particular
areas may be softer than the material used for constructing the
majority of the prosthesis 10.
[0155] In accordance with the present invention, the prosthesis 10
may be manufactured so as to substantially contain, or have
deposited thereon, a biologically or pharmaceutically active
material such as, for example, one that promotes tissue regrowth,
retards tissue degeneration, or decreases inflammation. This may be
particularly suitable when the prosthesis functions to bridge a
defective area of bone or articular cartilage. The active material
may be provided in the form of a coating anywhere on the prosthesis
10, or may be contained within the prosthesis in the form of a
solid, liquid, gel, paste, or soft polymer material. Such active
materials may be designed to be delivered at once or in a
timed-release manner.
[0156] It is known that the erosion of articular cartilage that
occurs in an osteoarthritic patient exposes the subchondral bone,
often known as eburnation. Nociceptor endings of small diameter
axons (nerve endings) that are present in the bone via the bone
marrow are now subject to activation by biomechanical forces
associated with weight bearing. Further, higher than normal
intraosseous pressure (fluid pressure present in the cancellous
(trabecular) and highly mineralized (subchondral) bone) are known
to exist in a large percentage of OA patients. The combination of
these events is considered a likely source of a large amount of the
pain felt by a patient with OA.
[0157] Biomechanical forces causing pain would likely occur during
activity. In a procedure known as percutaneous vertebroplasty, bone
cement, usually PMMA, is injected into the cavitated vertebral body
that has partially or is at risk of collapsing. The injected cement
hardens and increases the mechanical strength of the bone. As
expected, bone deformation under load is decreased and reduces the
mechanical forces applied to the nociceptive nerve endings and
further, the PMMA is known to be toxic for nerve tissue and this
procedure causes at least a partial denervation of the bone matrix,
yielding immediate pain relief for the patient.
[0158] Higher than normal fluid pressure in the bone is suspected
as the cause for the "bone-throbbing" pain often felt at night by
these patients. Transplant patients taking cyclosporine, a known
vasoconstrictor, are subject to severe, episodic knee pain in the
absence of any apparent articular pathology. This phenomenon is
readily controlled, however, by administration of a vasodilator,
nifedipine.
[0159] According to the present invention, when the subchondral
bone is perforated in preparation for the keel 22, immediate
reduction of intraosseous pressure may be noted because of the
obvious bleeding that occurs. If the keel 22 and perhaps the bottom
face 14 are coated with a vasodilator such as nifedipine or similar
acting pharmaceutical agents, one can expect continued reduction of
the intraosseous pressure. Time delay of this medication may be
utilized so that short term healing of the bone lesion can occur
without continued bleeding and, once healed, maintain the
vasodilation activity for an extended period of time.
[0160] Further, if additional nerve-targeting agents that are known
to be toxic to nerve fibers (i.e., PMMA) or have the ability to
desensitize the nerve endings through overstimulation (i.e.,
capsaicin) can also be added to the prosthesis 10, especially in
that area of the prosthesis 10 with the most direct access to these
fibers, such as the keel 22. These agents would be intended to
disperse or leach out of the prosthesis 10 itself via a coating
added to the prosthesis 10 or held in a pocketed reservoir within
the prosthesis 10. Combinations of such agents would be the likely
methodology, whether mixed together, applied to separate regions of
the prosthesis 10, or having dual functionality.
[0161] Finally, with reference to FIG. 110, the prosthesis 10, at
some point after the initial implantation, having expended its
reservoir of such agents, can also contain at least one internal
conduit 90 that would allow for a surgeon to reapply the agents via
a portal 92 that is accessible from the exposed edge of the
prosthesis 10 and leads to that region of the keel 22 below the
topmost surface of the subchondral bone and perhaps to the
underside of the prosthesis 10 that rests on the subchondral bone.
Applications of such active agents to any keeled or posted implant
as used in the hip, thumb, big toe, vertebra and other joints in
the body would have similar function and pain relieving
purpose.
[0162] Turning now to FIG. 92, a schematic representation of a
tibia T is depicted wherein the lighter volume shown in
cross-section represents a typical amount of bone resection
required for a prior art unicompartmental knee replacement
procedure. FIG. 93 is a schematic representation of a tibia T,
wherein the total volume represents a typical amount of bone
resection required for a prior art unicompartmental knee
replacement procedure, and the upper volume shown in white
represents the lesser amount of bone resection utilized for
implanting a prosthesis 10 according to the present invention.
[0163] FIGS. 94-97 depict an instrument 70 according to the present
invention which may be utilized for creating a tibial cut in order
to implant a prosthesis 10 according to the present invention. The
instrument 70 shown may be placed on top of the flattened tibial
plateau and may be pinned or otherwise secured in place, such as
using the illustrated hole 72. The instrument 70 also includes a
tibial cut guide 74 having a slot 76 which may be formed at an
angle that corresponds to the angle of the keel of the prosthesis
to be implanted. FIGS. 98-102 illustrate a modular instrument 70
according to the present invention which may be utilized for
creating a tibial cut in order to implant a prosthesis according to
the present invention. In particular, FIG. 99 is a top perspective
view of the instrument of FIG. 98 where one portion of the tibial
cut guide 74 has been removed. The modular instrument 70 may then
be assembled with different guide components for generating cuts
for different sizes and locations of a keel to be inserted. FIGS.
103-105 depict an instrument 78 according to the present invention
for sizing a tibial cut, so as to ensure that the cut has been made
correctly for the prosthesis to be implanted. Lastly, FIGS. 106-109
depict an impactor 80 according to the present invention in contact
with a prosthesis 10 according to the present invention shown with
reference to a cross-section of a tibia T. In accordance with one
aspect of the present invention, the impactor 80 may be configured
to engage the prosthesis 10 toward the middle thereof, and the
handle 82 may have the ability to pivot as the prosthesis 10 is
being inserted.
[0164] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *