Note: Descriptions are shown in the official language in which they were submitted.
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~EMIARTHROPLA8TY APPLICATION OF
ZIRCONIU~ O~ID~ COATED PR08TH~8I8
The present invention relates to implants for use in
hemiarthroplasty and, in particular, implants coated with
zirconium oxide.
BA~RGROUND OF TH~ INVENTION
Hemiarthroplasty is a surgical procedure where~y a
portion of a joint is replaced by a prosthetic device.
This surgical procedure is most commonly performed in
joints of the hands, wrists, ankles, feet and shoulders,
although it can be performed with knee and hip joints.
The implants used in hemiarthroplasty heretofore are
most commonly fabricated of silicone elastomers. The
elastomeric ~aterials are durable and provide good
performance. There have been improvemente in the design of
the implants, coupled with the high-performance, durable
elastomeric materials. However, the implant becomes
abraded and deformed because of intrinsic properties of
silicone. The gradual erosion of the implant results not
only in poorly fitting joints, but also in particulate
debris in the joint which can lead to inflammation of the
joint (O. Eiken et al., Scand. J. Plast. Reconstr. Surg.
19, 1985, 295-304) or bone cysts (T. Telaranta et al.,
Skeletal Radiol 10, 1983, 247-249)~
Problems associated with the shearing and abrading of
the silicone elastomer implants has led to the use of
titanium to resist breakdown of the joint. A study
reported by K. M. Leavitt et al. (Jour. of Foot Surgery 3Q,
1991, 289-293) reports positive results over a 30-month
post-operative period with a titanium hemi-great toe
implant. However, the oxide that forms in titanium is
prone to galling and seizing. The present invention
provides a solution to this problem by using implants
coated with zirconium oxide which virtually eliminates all
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the problems associated with shearing and erosion of the
implant used in hemiarthroplasty. U.S. 5,037,438 describes
the use of zirconium oxide-coated orthopedic implants or
protheses made of zirconium or zirconium- containing metal
alloys or a thin coating of zirconium or zirconium alloy on
conventional orthopedic implant materials. The '438 patent
deals with total joint replacement, such as a hip or knee
~oint replacement, wherein both joint surfaces are
replaced. One side is zirconium coated and the other side
is a polyethylene material. The coating is intended to
minimize the wear of the polyethylene. In these
environment~, the problem addressed is the capability of
maintaining the surfaces of both surfaces of the joint
under high-load conditions. The solution provides
compensation for the high stresses in the applied coating.
The pre~ent invention relates to the above-mentioned
problems dealing with hemiarthroscopy wherein lower loads
are experienced, i.e., joints in the hands and feet.
Herein, one joint surface may deteriorate due to a diseased
state, while the other surface remains functionally intact.
The problems in this environment are significantly
different than those at high-load joints, such as a hip
~oint.
The present invention provides for the first time a
prosthetic device for use in hemiarthroscopy which resists
wear and abrasion from natural bone and minimizes the
abrasion on the opposing cartilaginous surface in the joint
and resists erosion due to body fluids.
~NMARY OF THB INVENTION
The present invention provides an improved low-wear
implant for use in hemiarthroplasty wherein the implant is
coated with zirconium oxide. The implant can be made
entirely of zirconium and oxidized or can be made o~
zirconium-containing metal alloys. When the implant
contains a metal alloy, the alloy should contain at least
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80~ zirconium and preferably at least 95% zirconium.
The implant of the present invention can be used to
replace a bone or to repair a bone in low-load joints.
The implant is useful in joints of the wrist, hand,
ankles and feet, as well as the shoulders and elbows. The
implant may incorporate anatomical features of the bone
being repaired or replaced. When the hemiarthroplasty
procedure involves joints comprising long bones, preferably
the bone is resurfaced with an implant of the present
invention, and one end of the implant would be designed to
interact with the cartilage and other bone(s) of the ~oint
and the other end of the implant would be designed to fit
into the long bone when the hemiarthroplasty procedure
involves the carpals, metacarpals, tarsals, metatarsals or
phalanges, the implant can be designed for use in
resurfacing the bone or can be designed for replacemént of
the bone.
DEE~CRIPTION OF FIGURE8
Figure 1 shows the bones of the left hand and a
trapezial implant.
Other advantages of the present invention will be
readily appreciated as the same becomes better understood
by reference to the following detailed description when
considered in connection with the accompanying drawing.
DETAILBD DE~3CRIPTION OF INVE~ ON
The implants of the present invention are fabricated
of zirconium or zirconium- containing metal alloys as
generally described in U.S. 5,037,438 (see column 5, lines
15 to 34). The implants are cast or machined to the
required shape by conventional means known in the art after
which they are oxidized to form a black or blue-black oxide
according to the procedure of U.S. 2,987,352 and as further
elaborated in U.S. 5,037,438 (see column 5, lines 50 to 68
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and column 6, lines 1 to 44). ~he relevant portions of
U.S. 5,037,438 and U.S. 2,987, 352 are incorporated herein
by reference.
Although the implants of the present invention can
contain alloys of zirconium, including titanium, niobium,
hafnium, and other metals known to form stable alloys with
zirconium, it is preferred that the implant be formed
substantially of zirconium.
The implant~ or prothesis are prepared by using a mold
lo which has the appropriate configuration to interact with
other bones and cartilage of the joint being repaired. The
present invention can be used in the 6ame manner as
silicone elastomer implants which are in common use today
for hemi-implants.
Most typically, the implants of the present invention
are used in joints which are considered low load bearing
joints. Nevertheless, the implant of the present invention
finds particular use in the hand, ankle, and foot. The
implant described and claimed herein is useful in
hemiarthroplasty in bunion surgery and can be placed in the
great toe or can be used to replace other bones of the
phalanges, as well a~ the metatarsal, tarsal, carpal, and
metacarpal bones. The implants of the present invention
also find use in shoulder joints and elbow joints.
In using the implant of the present invention, either
the entire bone can be replaced or a portion of the bone
can be replaced, in which case the zirconium implant is
shaped in such a manner as to fit into the bone being
repaired. For example, when the implant is used to replace
a portion of a bone (i.e., to resurface the bone), the
implant can be equipped with spikes or other protrusions
such as a stem that can fit into the bone being repaired
such that one end of the implant would be configured to
interact with the other bone of the joint and the other end
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of the implant would be flat except for the spikes or other
protrusions which would fit into the bone being repaired.
Replacement of a portion of the bone would find a
particular use when repairing joints of the upper extremity
involving long bones, but also would be useful in the short
bones of the wrists, hands, ankles and feet. The implant,
or the portion of the implant which articulates with the
other bone of the joint, can be anatomical (i.e., shaped
similarly to the natural bone). When an entire bone is
being replaced, it is preferred that the entire bone be
anatomical. However, the present invention can be utilized
with non-anatomical prostheses.
The implant of the present invention is abrasion
resistant and capable of interacting with the cartilage of
apposing bone of the joint being repaired. The zirconium
oxide coated implant or prothesis of the present invention
provides very good resistance to the wear imparted by the
apposite bone and cartilage. Additionally, the zirconium
oxide coated implant minimizes wear on the opposing
cartilaginous surface. The zirconium oxide coating is
preferably about 1-5 microns in thickness.
Figure 1 is illustrative of the use of an implant of
the present invention wherein only a portion of the bone is
replaced. In this particular example, the trapezium is
resurfaced with an anatomical implant generally shown at
~10). The left hand is depicted and it is apparent to one
skilled in the art that the configuration of the implant
would be reversed for a right hand implant. The surface
~12) of the implant which interacts with the first
metacarpal i~ non-symmetrical and has a complex radii with
the lateral edge ~14) of the implant elevated more than the
medial edge ~lC).
The implant depicted in Figure 1 illustrates a
resurfacing technique wherein the tip of the trapezium i8
replaced. Such a technique can be applied to other bones
:.:
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as described above. In a resurfacing procedure of the
smaller bones, it is useful to preserve as much of the bone
being repaired as possible. In a bone such as the
trapezium, an implant having spikes (18) as depicted in
Figure 1 is particularly useful, enabling one to preserve
as much of the trapezium as possible. In a larger bone
(e.g., of the elbow), the implant could have a stem for
insertion into the long bone which would provide added
strength to the repaired joint.
~he invention has been descrlbed in an illustrative
manner, and it is to be understood that the terminology
which has been used is intended to be in the nature of
words of description rather than of limitation.
Obviously many modifications and variations of the
present invention are possible ln light of the above
teachings. It is, therefore, to be understood that within
the scope of the appended claims wherein reference numerals
are merely for convenience and are not to be in any way
limiting, the invention may be practiced otherwise than as
specifically described.
