Note: Descriptions are shown in the official language in which they were submitted.
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TIBIAL PROSTHESIS
The present invention relates to orthopedic prosthetic devices
and more particularly to an improved prosthesis for replacing a
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portion of a patient's knee joint. Even more particularly, the present
~ invention relates to an improved tibia! prosthesis that is modular,
having a removable metaphyseal stem portion that includes a
cylindrical section and a tapering section, and wherein parallel fins
extend continuously from the proximal to the distal end of the
metaphyseal stem, tracking first the cylindrically shaped section and
then the tapering section.
A number of tibia! components have been patented that relate
to tibia! components having a tray, and a stem portion that provides
initial fixation when the prosthesis is implanted.
An example of a modular tibia! support is seen in the Elias
Patent 5,246,459 entitled "Modular Tibia! Support Pegs for the
Tibia! Component of a Prosthetic Knee Replacement System". The
Elias Patent discloses a modular tibia! support peg operable to
secure a tibia! component of a knee joint prothesis to a tibia having
a groove. The modular tibia! support peg includes a cylindrical body
with a ridged outer surtace operable to engage the groove in the
tibia. The modular tibia! support peg further includes a plurality of
spikes extending inferiorly from the cylindrical body. The spikes are
operable to engage the tibia at the inferior end of the groove.
U.S. Patent 5,137,536 issued to Tomihisa Koshino describes a
tibia! component for an artificial knee joint. The tibia! component
includes a plate section having an upper surface and a pair of
bearing surfaces parts that are adapted to be in sliding contact with
a femoral component. A stem portion extends downwardly from a
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lower surface of the plate section. A pair of blade like members
extend obliquely and posteriorly from the stem. The plate section
has a lower surtace with a plurality of elongated grooves for
improving affinity with respect to the surrounding bone, the grooves
including a first group of grooves and a second set of group of
grooves extending perpendicularly to the first group of grooves.
A British Patent 2,192,543A discloses a peg for use in
prosthetic devices. A peg of metal or ceramics is defined as being
suitable for use as a fixator andlor a bone strengthener in
connection with a prosthetic device. The peg has a portion of
generally tapered form that increases in cross section from an
insertion end. The surtace of the tapering end portion has
alternating ridges along its length extending therearound, each
successive ridge as one moves away from the insertion end having
an outer surtace spaced by a comparatively small amount at a
greater distance from the axis of the peg then the outer surface of
the preceding ridge. The peg may be discrete or form a part of a
prosthetic device.
U.S. Patent 4,938,769 issued to James Shaw discloses an end
bone anchorage assembly for a tibia! prosthesis that includes an
axially elongated central stem and a plurality of elongated fixation
pegs spaced from the stem. The stem and the pegs have proximal
and distal ends. The proximal ends of the stem define an
attachment table. A plurality of structural links interconnect the
pegs and the stem. Means is provided for removably attaching a
tibia! tray to the assembly wherein each of the pegs is connected to
the stem by the structural link.
The Bolesky et al. patent 4,479,271 entitled "Prosthetic Device
Adapted to Promote BoneITissue Ingrowth" discloses a tibia!
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component that includes a table and at least one porous metal stem
protruding from the lower base surface of the bottom base layer of
the table wherein the outer surtace of the protruding stem is
adapted to be in direct contact with the prepared bone surface to
promote the ingrowth of bone and/or tissue and wherein each of the
protruding porous metal stems includes a bore therethrough which
extends from the distal end of the stem through the upper surface of
the bottom base layer of the table.
The Murray patent 4,016,606 discloses a knee prosthesis that
includes a tibial component with a tray and with a stem adapted to
be received in a longitudinal bore in the patient's femur. The stem
has one end that is integral with a depending generally spheroidal
surface having generally the same radius as the radius of the
spheroidal depression in the insert.
When implanting a tibial tray (eg. porous or cemented), it is
extremely important to get excellent initial fixation. The implant must
be able to resist forces that rotate, shear, or tilt the component. The
present invention provides an improved stem, for use with a tibial
component and which provides the ability to resist the forces of
rotation, shear, and tilt.
According to the invention, a tibial prosthetic knee component
comprises a tibial tray for replacing a portion of the patient's
proximal tibia; a stem portion having proximal and distal end
portions, the stem defining a projection from the tray, forming an
angle therewith, for anchoring the tibial tray to the proximal tibia; the
stem comprising a generally cylindrically shaped proximal portion, a
tapered distal portion and a plurality of generally parallel
circumferentially spaced fins extending substantially the length of
the stem.
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Thus, the present invention provides an improved tibial prosthesis
with excellent initial fixation. The metaphyseal tibial stem of the
present invention provides rotational, shear and tilting resistance for
an implanted tibial component.
The apparatus of the present invention includes a tibial tray for
replacing a portion of the patient's proximal tibia. The stem has
proximal and distal end portions and defines a projection from the
under surface of the tray, forming an angle therewith. The stem is
provided for anchoring the tibial tray to the proximal tibia.
The stem may include a connection for attaching the stem to
the tray in modular fashion. This allows multiple stems of differing
size to form a kit that allows the surgeon to select a particular sized
stem for connection to the tibial tray that fits the patient best.
The stem includes a generally cylindrically shaped proximal
portion and a gradually tapering distal portion. A plurality of
longitudinally extending, generally parallel and circumferentially
spaced fins extend along the stem and substantially the full length
of the stem. Thus, each of the fins tracks the cylindrically shaped
proximal portion and then angles to track the gradually tapering
portion. In a preferred embodiment, the gradually tapering distal
portion of the stem is conically shaped. The stem may have a
hollow cylindrical portion with a generally tubular inner bore. .
The proximal and distal sections of the stem are integrally
joined at a transition portion of the stem in the preferred
embodiment. Each of the fins then has an outer edge that includes
first and second linear sections that define an obtuse angle '
therebetween. In the preferred embodiment, this angle is greater
than 90 and less than 180 degrees.
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The stem preferably provides a generally flat distal tip that
defines the lower end of the stem and the end of the conically shaped
portion.
5 The fins are preferably equally spaced apart around the
circumference of the stem.
The fins may be separated by a longitudinal, generally U-shaped
channel.
Each of the fins preferably includes a pair of surfaces extending
longitudinally between the proximal and distal ends. The fins are
preferably generally triangularly shaped in transverse cross section. As
each fin extends along the tapered section, the pair of surfaces of each
fin preferably become narrower, resulting in a sharp edge prior to
reaching the flat distal tip of the stem which edge may be less sharp
proximally than distally. At least one circumferential portion of the stem
may be without fins.
The tibial prosthesis is preferably supplied in modular form so
that a suitable prosthesis may be assembled to suit an individual
patient. Thus, in this form, the tibial tray and stem portion may be
supplied separately and the stem is provided with a means for
removably attaching it to the tibial tray. Such means may comprise a
taper locking arrangement.
According to an aspect of the present invention, there is
provided a tibial prosthetic knee component comprising (a) a tibial
prosthetic tray for replacing a portion of a patient's proximal tibia; (b) a
stem portion having proximal and distal end portions, the stem defining
a projection from the tray, forming an angle therewith, for anchoring the
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Sa
tibial tray to the proximal tibia; (c) the stem comprising a generally
cylindrically shaped proximal portion and a tapered distal portion; (d) a
plurality of generally parallel circumferentially spaced fins which extend
substantially the length of the stem; wherein each of the fins tracks the
cylindrically shaped proximal portion and then angles to track the
gradually tapering portion.
For a further understanding of the nature and embodiments of
the present invention, reference should be had to the following detailed
description, which is given only as an example of the present invention,
taken in conjunction with the accompanying drawings, in which like
parts are given like reference numerals, and wherein:
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FIGURE 1 is a perspective exploded view of the preferred
embodiment of the apparatus of the present invention;
FIGURE 2 is a fragmentary end view of the stem portion of the ,
preferred embodiment of the apparatus of the present invention;
FIGURE 2A is a cross section through the conical section of
the stem portion taken along lines 2A-2A of Figure 1;
FIGURE 2B is a cross section taken along lines 2B-2B of
Figure 1 and including an overlay of Figure 2A, thus illustrating the
tapering of the stem and the changing thickness of the fins;
FIGURE 3 is fragmentary sectional view of the preferred
embodiment of the apparatus of the present invention illustrating the
stem portion thereof;
FIGURE 4 is a perspective view of the preferred embodiment
of the apparatus of the present invention;
FIGURE 5 is a perspective view of the preferred embodiment
of the apparatus of the present invention;
FIGURE 6 is a sectional view taken along lines 6-6 of Figure 5;
FIGURE 7 is a partial perspective cutaway view of the
preferred embodiment of the apparatus of the present invention
illustrating the stem portion thereof;
FIGURE 8 is another partial perspective cutaway view of the
preferred embodiment of the apparatus of the present invention
illustrating the stem portion thereof;
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FIGURE 9 is a partial elevational view of the preferred
embodiment of the apparatus of the present invention illustrating
various sized and shaped stem portions thereof; and
FIGURES 10-12 are schematic elevational views that
demonstrate the surgical method of implanting the preferred
embodiment of the apparatus of the present invention.
FIGURES 1-6 illustrate the preferred embodiment of the
apparatus of the present invention designated generally by the
numeral 10. Tibia! prosthesis 10 includes a transversely extending
tibia! tray 11 having a proximal surtace 12 and a distal surface 13.
As is known in the art, the distal surface 13 faces the proximal end
of the patient's tibia after the proximal end of the patient's tibia has
been surgically prepared with a transverse cut. The tibia! tray 11
provides a peripheral surface 14 that is shaped to conform to the
prepared surface of the proximal tibia.
A plurality of openings 15 can be placed through the tray 11,
communicating with both the proximal 12 and distal 13 surfaces.
Openings 15 are receptive of one or more bone screws for attaching
the prosthesis 10 to the patient's proximal tibia. A plurality of bone
spikes 16 extend from distal surface 13 forming an angle therewith,
preferably about ninety degrees (90°).
Distal surface 13 can provide a bone attachment surface 17
such as for example a beaded surtace. At the central portion of
distal surtace 13, post 18 extends therefrom at an angle of about
ninety degrees (90°). Post 18 includes a larger diameter section 19
and a smaller diameter section 20 that has a taper. An annular
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conical shoulder 21 defines a transition between larger diameter
section 19 and smaller diameter tapered section 20.
Post 18 has a flat surface 22 portion on the outer surtace of
larger diameter section 19, and extending to annular shoulder 21 as
shown in Figure 1. As will be described more fully hereinafter, flat
surtace 22 cooperates with a similar flat surtace of a modular
metaphyseal stem 25 to prevent incorrect assembly of the
metaphyseal stem 25 relative to post 18.
Post 18 has a flat circular end portion 23 that defines the distal
end of post 18. Post 18 attaches to tibial tray 11 at joint 24 that can
be welded for example or post 18 and tray 11 can be machined as
one piece. The bone attachment surface 17 can extend over joint
24, and partially to larger diameter section 19.
Metaphyseal stem 25 (Figures 1, 2, 2A-2B, 3, 4 and 7-9)
provides a proximal end 26 and a distal end 27. Stem 25 has a
closed end bore 28. Bore 28 has a closed end portion 29 and an
open portion 30. Bore 28 is similarly sized and shaped to post 18
for receiving post 18 upon assembly of metaphyseal stem 25
thereto. Thus, bore 28 provides a larger diameter section 31, an
annular shoulder 35 defining a transition section, a small tapered
diameter section 32, an annular shoulder 32A defining a transition
section, and a conical end portion 33. Internal threads can be
provided to closed end portion 29.
The corresponding flat surfaces 22, 34 ensure proper
assembly of stem 25 relative to post 18. The corresponding smaller
diameter sections 20 and 32 are annular wedge shaped sections
that engage upon assembly so that a Wedge lock or morse taper
lock fit is achieved between stem 25 and post 18 when stem 25 is
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placed over post 18 and loaded onto post 18 with an impact driver
for example. In use, the impact driver would be used to transfer
load to metaphyseal stem 25 at flat distal surtace 36.
In the preferred embodiment, there can be multiple
metaphyseal stems 25A-25C of differing size as shown in Figure 9.
The flat distal surface 36 of the metaphyseal stems 25A-25B shown
in Figure 9 are of a larger diameter than the flat distal surtace 36A
for the metaphyseal stem 25C shown in Figure 9.
Each of the flat metaphyseal stems 25 have a longitudinally
extending flat surface 37 that begins at proximal end 26 of
metaphyseal stem 25 and extends to an annular transition portion
38 of stem 25 as shown in Figures 5-6. The annular transition
portion 38 is positioned between a generally cylindrical section 39 of
metaphyseal stem 25 and a tapering section 40 of metaphyseal
stem 25. The tapering section 40 can be frustroconically shaped as
shown in Figures 1, 3-9.
By providing a cylindrical section 39 of generally constant
diameter, the surgeon can drill a cylindrically shaped opening in the
patient's cancellous bone tissue to receive stem 25 that is smaller in
diameter than the outer diameter of cylindrical section 39. The
tapering section 40 first enters the surgically formed opening,
registering the metaphyseal stem 25 in the proper location.
Thereafter, continued driving of the prosthesis 10 into the patient's
tibia causes the plurality of fins 41 to cut into the cancellous bone.
A plurality of channels 42 (Figures 2, 2A, 2B, 5, 7 and 8) are
defined between the plurality of fins 41. Fins 41 are
circumferentially spaced and generally parallel to one another. In
the preferred embodiment the channels are generally U-shaped,
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extend longitudinally, and are generally parallel to one another.
The fins 41 and channels 42 are circumferentially spaced about the
central longitudinal axis 43 of metaphyseal stem 25. In Figures 2A-
2B fins 41 can be seen as having sharp edges 44 at frustroconical
5 tapering section 40 and blunt edges 45 at cylindrical section 39.
The bone is prepared to receive the metaphyseal stem by
punching a plug into the bone (perpendicular to the plane of the cut)
that creates a hole 46 that is for example 12-14 mm in diameter and
10 40-50 mm deep. The device is then driven into this hole as shown
in Figures 10-12. Notice in Figure 11 that the hole 46 has a
diameter smaller than the diameter of stem cylindrical section 39.
This allows the fins 41 to bite into surrounding bone tissue that is
adjacent hole 46.
The following table lists the parts numbers and parts
descriptions as used herein and in the drawings attached hereto.
PARTS LIST
Part Number Description
10 tibial prosthesis
11 tibial tray
12 proximal surface
13 distal surface
14 peripheral surFace
15 openings
16 bone spikes
17 bone attachment surface
18 post
19 larger diameter section
20 smaller diameter tapered section
21 annular shoulder
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22 flat surface
23 circular end
24 joint
25 metaphyseal stem
25A metaphyseal stem
25B metaphyseal stem
25C metaphyseal stem
26 proximal end
27 distal end
28 bore
29 closed end of bore
30 open end of bore
31 larger diameter section
32 smaller diameter tapered section
32A flat annular surface
33 conical section
34 flat surface
35 flat annular surface
36 flat distal surface
36A flat distal surface
flat longitudinal surface
38 annular transition portion
39 cylindrical section
40 tapering section
41 fins
42 channels
43 central longitudinal axis
44 sharp edges
45 blunt edges
46 . surgically formed opening
tibia
