Note: Descriptions are shown in the official language in which they were submitted.
~ 1 1 33068~
MODULAR JOINT PR08T~E8I~ TOOL
BACRGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to prosthetic
joints and, more particularly, to a tool for removal
from the bone of one component of or for separating the
two components of a modular prosthetic joint
construction which enables the revision of components
having a broad range of sizes for long bones with a
minimum inventory of prosthetic components.
2. Description of the Prior Art
While the present invention is applicable for use with
implants of various types and in numerous applications
in human and animal joints, it will be described herein,
for purposes of example only, as being specifically
adapted for use in regard to a knee joint prosthesis.
The knee joint basically consists of the bone interface
of the distal end of the femur and the prsximal end of
the tibia. Appearing to cover or at least partially
protect this interface is the patella which is a
sesamoid bone within the tendon of the long muscle
(quadriceps) on the front of the thigh. This tendon
inserts into the tibial tuberosity and the posterior
surface of the patella is smooth and glides over the
femur.
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The femur is configured with two knob like
processes (the medial condyle and the lateral
condyle) which are substantially smooth and
articulate with the medial condyle and the~lateral
s condyle of the tibia, respectively. The condyles
of the tibia are substantially smooth and slightly
cupped thereby providing a slight receptacle for
receipt of the femoral condyles.
When the knee joint is injured whether as a result
of an accident or illness, cartilage covering the
natural bones may become damaged to the extent
that they are unable to function (articulate)
properly: If the bones are affected beyond the
level or degree where natural healing and new
growth will remedy the damage, then a prosthetic
replacement of the damaged portion is called for
in order to relieve pain and to restore normal use
to the joint. Typically the entirs joint is
replaced by means of a surgical procedure which
involves removal of the ends of the corresponding
¦ damaged bones and replacement of these ends with
prosthetic implants. A typical such implant would
be for the hip joint wherein a metal implant could
be anchored in the intramedullary canal of the
femur and would provide a generally spherical
protuberance extending outwardly therefrom. The
mating prosthetic portion would be a polyethylene
socket mem~er suitably anchored into the
acetabulum. While prosthetic devices of this
type, normally including a physiologically inert
metal member and an engaging high density
~, polyethylene member, are well known in the art,
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these types o~ devices are of a fixed and
unchanging nature once they are inserted
(implanted) into the patient and anchored there,
whether by pinning or by acrylic bone cement or
both.
Due in part to the fact that the size, shape and
anatomy of virtually every patient is different,
great care must be taken by the orthopedic surgeon
in order to select properly sized and shaped
prosthetic members for implanting. In order to
achieve a suitable fit and size compatibility, an
extensive number of a variety of each type of
prosthet~ic implant must be available to the
orthopedic surgeon from which he may choose. As a
result, the cost of inventory as well as the
logistics of ordering and storing a wide variety
¦ of prosthetiG implants is cumbersome. Therefore,
I it would be an improvement to this present
situation if prosthetic devices could be
structured with removable portions such that there
would be a reduction in inventory without a
corresponding compromise as to the number and
variety of different prosthetic combinations which
I i 25 can be created. In order to provide such an
j improvement, it is necessary that the prosthetic
¦ portions which are to be mixed and matched into a
variety of combinations be suitably secured
together so that the prosthetic member, which they
in combination create, is not weaker nor more
likely to fail than would be a similar prosthetic
member constructed as a single integral piece.
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A further concern involves the procedure when a
prosthetic device becomes worn or damaged and a
replacement must be made. While this is posslble,
it oftentimes involves elaborate surgery depending
upon the particular portion of anatomy ~nvolved
and the extent or nature of the damage to the
prosthetic device. Furthermore, certain portions
of the anatomy such as knee joints may be more
susceptible to wear due to the surface area of
lo articulation, the nature of the anatomy and the
typical loads and forces which are encountered by
this particular joint. Repair and/or replacement
may also be desired when interfacing portions of
the anatomy change and the contacting portion of
the prosthesis needs to be revised as to its shape
or size.
By structuring a prosthetic implant such that the
portion most likely to wear or desired to be
changed is quickly and easily replaceable from the
remaining portion of the prosthetic implant,
significant amounts of surgical time can be saved
i and the prosthesis can be more closely tailored to
I the patient's needs. Equally important is the
fact that the portion of the prosthesis which is
~ anchored into the patient, such as a tapered shaft
? inserted into the intramedullary canal of the
~, tibia or of the femur, does not have to be
surgically removed in order to make a replacement
of a worn or damaged tibia articulation portion.
Such a replaceable concept, in order to be
effective r must securely hold the anchored portion
and the replaceable portion together so as to act
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as an integral member regardless of the nature or
complexity of the forces and loads acting thereon.
With a design which achieves the requisite
strength and durability, it is then possible to
mix and match the replaceable portion with various
anchored portions and vice versa such that, for
example, an inventory of five relatively large and
expensive replaceable portions and five
relatively small and inexpensive anchoring
portions for a tibial or femoral implant would be
able to provide 25 different combinations of each
to the orthopedic surgeon rather than having to
inventory and stock 25 separate complete
relativel~y large and expensive portions.
Tibial and femoral primary or revision prostheses
that are presently being marketed have a fixed
central stem, located on the distal plane of the
tibial tray, or component, and on the proximal
portion of the femoral component's anterior/
posterior box. This stem is used primarily for
purposes of stabilization and strength, both
during installation and after the joint has been
rebuilt. It is difficult to determine prior to
surgery, even by x-raying, the size of the stem to
be used. As a result, it is often necessary to
wait until the bone structure is personally viewed
I by the surgeon during the implant operation before
¦ selecting the proper size of the implant and,
particularly, the stem.
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In the past, it has been neCessar; ~or hospitals
to maintain a large inventory of sizes of
prosthetic ~oint components in order to
accommodate different sizes of patients. However,
the cost of maintaining s~ch a large inventory is
substantial. This expense sometimes becomes so
great that a hospital will maintain no inventory,
but will order a particular prosthesis only when
needed. As a result, if elective surgery is to be
performed, oftentimes components are ordered
specially for the surgery to be performed which
includes one size larger and one size smaller than
is expected to be used. Revision surgery in cases
of traumatic injury could not be performed since
there would be no inventory on hand to provide
prompt availability for all possible patients.
Typical of the prior art known to the inventor
which is broadly of interest when considering the
invention are the U.S. Patents to Noiles, No.
~ 4,219,893 and to Volz, No. 4,257,129. The Noiles
3 patent discloses a prosthetic knee joint of the
hinged type which permits rotation of the bones in
two planes. In respect to the tibial component, a
tibia stem whose upper part is rotatably engaged
with the femoral component has a lower vertically
depending rod which is rotatably received within a
tibia sleeve which, in turn, is adapted to be
implanted in the intramedullary canal of the
tibia. The Volz patent is merely representativa
of a wide range of patents which disclose a tibial
component having a downwardly extending stem for
anchoring it to the tibia. A plastic bearing
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member is dove-tailed into receptive engagement on
the upper surface of a support shelf and is held
against further movement, once installed, by means
of a vertical pin member which is received jthrough
the bearing and into a longitudinal bore formed
in the stem and extending longitudinally in an
axial direction. In neither patent is there a
suggestion that the construction would enable the
provision of various lengths and diameters of
stems.
It is also known, in the instance of hip
prostheses, for hospitals to inventory a number of
~ femoral ~omponents for a hip prosthesis having a
range of different sized heads for articulation in
associated acetabular bearing components having a
similar range of sizes. In some instances, stem-
extensions have been utilized in order to more
readily accommodate a wide range of body sizes.
Although the foregoing devices have generally
satisfied the goals for which they were intended,
none offered the simplicity and economy which
represent goals which have been achieved by the
present invention.
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81JMNARY OF TIIE INVBNTION
To this end, the invention relates to a tool for
separating the two components of or to a tool for the
removal of a modular joint prosthesis intended for
implantation in a body. One component of the prosthesis
is adapted to be fixed to a long bone having an
intramedullary canal includes an elongated male stem
having a uniformly tapered outer surface. In order to
accommodate the particular size of long bone to which
the component is to be fixed, another component, namely,
a properly sized female stem is attached to the male
stem before the male stem is implanted into the long
bone. The female stem is adapted to be received in the
intramedullary canal for fixation thereto, and has a
uniformly tapered inner surface, the angle of the taper
being substantially similar to the angle of taper of the
outer surface of the male stem. As a result, the male
stem and female stem become locked together when the
inner surface of the female stem engages the outer
surface of the male stem. The proper size of female
stem is obtained by selecting it from a family of female
stems having a graduated sequence of different external
dimensions.
A specialized tool is disclosed which can be used to
remove the female stem of such a modular joint
prosthesis whenever it should become necessary or
desirable to do so. The novel tool is of simpli~ied
construction and can be readily attached to the female
stem or disengaged from the female stem in the course of -~
the surgical procedure.
Also disclosed is a specialized tool which can be used
to separate the male stem from the female stem of such a ~;
modular joint prosthesis whenever it should become
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necessary or desirable to do so. The novel tool is of
simplified construction and can be readily attached to
the prosthesis or disengaged from the prosthesis in the
course of the surgical procedure.
Other aspects of this invention are as follows:
In combination:
a modular joint prosthesis for implantation in a
body comprising:
a component adapted to be affixed to one end of a
long bone, said component including a support plate,
said support plate having a lower surface adapted to
engage and bear against and be substantially coextensive
with a complementary resected surface of the long bone
and an elongated male stem integral with and extending
transversely away from said support plate, said male
stem having a longitudinal axis and an outer surface
which is uniformly tapered relative to the longitudinal
axis and having a maximum outer diameter at a proximal
end adjacent the lower surface and a minimum outer
diameter at a distal end distant from said lower
surface; and
a female stem adapted to be affixed within an
intramedullary canal of a long bone, said female stem
having a longitudinal axis and extending between a
closed distal end and an open proximal end, a portion of
said female stem having a bore extending from said open
proximal end a predetermined distance distally thereof,
said bore defining an inner surface which is uniformly
tapered relative to said longitudinal axis and having a
maximum inner diameter at said proximal end and a
minimum inner diameter distant therefrom;
whereby said male stem and said female stem are
configured to be locked together upon engagement of said
inner surface of the female stem and said outer surface
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of the male stem enabling said male stem and said female
stem to be received as a unit in the intramedullary
canal of the long bone for fixation thereto to a depth
at which said support shelf bears against the resected
surface of the long bone; and
a tool for separating said male stem and said
female stem when they become locked together upon mutual
engagement of the inner surface of said female stem with
the outer surface of said male stem, said tool
comprising:
a handle and a shank fixed to said handle and
extending therefrom to a tip end receivable in the
longitudinal bore of said male stem, said shank being
threaded intermediate said handle and said tip end, said
shank being threadedly engaged with said male stem for
disengaging said male stem from said female stem upon
rotation of said tool to advance said tip end of said
shank into engagement with said terminal`surface of said
female stem and, with continued rotation of said tool,
to cause said male stem to be disengaged from said
female stem.
~ In combination:
¦ a modular joint prosthesis for implantation in a
I body comprising~
¦ a component adapted to be affixed within an
intramedullary canal of a long bone, said component
including a support plate, said support plate having a
lower surface adapted to engage and bear against and be
substantially coextensive with a complementary resected
surface of the long bone and an elongated male stem
integral with and extending transversely away from said :~:
~ support plate, said male stem having a longitudinally
¦ axis and an outer surface which is uniformly tapered
. relative to the longitudinal axis and having a maximum :
outer diameter at a proximal end adjacent the lower
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9b
surface and a minimum outer diameter at a distal end
distant from said lower surface; and
a female stem having a longitudinal axis and
extending between a closed distal end and an open
proximal end, a portion of said female stem having a
bore extending from said open proximal end a
predetermined distance distally thereof, said bore
defining an inner surface which is uniformly tapered
relative to said longitudinal axis and having a maximum
inner diameter at said proximal end and a minimum inner
diameter distant therefrom, said inner surface of said
female stem and said outer surface of said male stem
generally forming an angular divergence within the range
of +/-3 minutes of arc;
whereby said male stem and said female stem are
configured to be locked together upon engagement of said
inner surface of the female stem and said outer surface
of the male stem enabling said male stem and said female
stem to be received as a unit in the intramedullary
canal of the long bone for fixation thereto to a depth
at which said support shelf bears against the resected
surface of the long bone; and
a tool for separating said male stem and said
female stem when they become locked together upon mutual
engagement of the inner surface of said female stem with
the outer surface of said male stem, said tool
comprising:
a handle and a threaded shank fixed to the handle
and extending therefrom to a tip end receivable in the
longitudinal bore of said male stem and threadedly
engaged with said male stem for disengaging said male
stem from said female stem upon rotation of said tool to
advance said tip end of said shank into engagement with
said terminal surfa¢e of said female stem and, with
continued rotation of said tool, to cause said male stem
to be disengaged from said female stem.
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Other and further features, advantages, and
benefits of the invention will become apparent in
the following description taken in conjunction
with the following drawings. It is to be
understood that the foregoing general description
and the following detailed description are
exemplary and explanatory but are not to be
restrictive of the invention. The accompanying
~ drawings which are incorporated in and constitute
!~ 10 a part of this invention, illustrate one of the
embodiments of the invention, and, together with
the description, serve to explain the principles
of the invention in general terms. Like numerals
refer to ~ike parts throughout the disclosure. ~;
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a front elevation view, partly in
section, of a knee joint prosthesis which embodies
the invention;
Fig. 2 is an exploded view, certain parts being
cut away and in section illustrating tibial
components embodying the invention:
Fig. 3 is a perspective view of certain of the
tibial components illustrated in Figs. 1 and 2;
~r
Fig. 4 is a side elevation view, certain parts cut
away and shown in section, to illustrate an
extraction tool for disengaging a male stem from a
female stem;
Fig. 5 is a side elevation view, certain parts cut
away and shown in section, to illustrate a
different extraction tool for removing a female
stem from the bone; and
Figs. 6, 7, and 8 are perspective, side elevation,
and top plan views, respectively, of femoral
components embodying the invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
~ Turn now to the drawings and initially to Fig. 1
h which illustrates a knee prosthesis 18 empodying
the invention. One component of the knee
prosthesis i5 a tibial implant 20 which, as more
clearly seen in Fig. 2, includes a tibial tray 22,
a replaceable bearinq member 24, a vertical pin
member 26, and a horizontal clip member 28.
References to the terms "vertical" and
"horizontal" are used in the normal context of
3 such words wherein the tibia of an individual
standing upright extends in a vertical direction.
It is noteworthy that FIG. 2 is an exploded view
and that the assembly of these four component
parts into a single prosthetic implant involves
anteriorly/posteriorly sliding the bearing member
24 into supporting engagement on the tibial tray
by reason of their corresponding dovetail
surfaces. Once this engagement is achieved, the
pin member 26 is inserted downwardly in a vertical
direction through a suitable hole in the bearing
member and into a longitudinal bore 29 in the tray
22. The final assembly step is to insert the clip
member 28 into a suitable slot in the bearing
member enabling the prongs of the clip member to
engage a reduced diameter groove 30 of the pin
member and thereby prevent its unintended removal.
Referring to FIGS. 1-3, the tibial tray 2~ is seen to ;~
include a tapered male stem 32 and a support shelf
or plate 34. The stem 32 i8 integrally joined to the
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support shelf and extends downwardly therefrom.
The support shelf has a somewhat heart shaped
¦ configuration (see FIG. 3), generally conforming
to the proximal end of the tibia 35 and defining
a posterior depression 36 which provides a
significant benefit to the implant in that this
depression provides clearance for ligaments to pass
therethrough without interference. When the tibial
tray 22 is fully implanted, a lower surface of the
support shelf or plate 34 engages and bears against
and is substantially coextensive with a complementary
resected surface of the tibia 35.
While the material choice for the tibial tray 22
and for the other prosthetic components discussed
herein may vary, it is important that a relatively
durable and strong material be used. Preferable
material6 are titanium, titanium alloy, or cobalt
chrome although stainless steel, or even ceramics
or composites could be employed. It is also
important that the material selected be
biologically and physiologically inert and that it
be properly sterilized and prepared prior to
implantation. Inasmuch as one aspect of the
subject invention is the interchangeability of the
prosthetic components, the shape and size
characteristics of a female stem 40 may vary in a
manner to be described. It is important, however"
that the size and shape of the male stem 32 be
standardized so that proper fit and engagement
with any one of a family of female stems 40 can be
achieved. The selection of a particular stem
~3 length and a particular tibial tray configuration
is to be governed by the size, shape and anatomy
of the particular patient as well as the nature
and extent of the damaged bones.
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As especially well seen in Fig. 1, the female stem
40 iS, in effect, an extension member for the male
stem 32. It may be fabricated from titanium bar
stock or from cast cobalt chrome. Stainless steel,
ceramics and composites are other suitable materials.
Additionally, the male stem 32 and the female stem 40
can be of different materials so long a~ no galvanic
reaction would occur as, for example, between
stainless steel and cast cobalt chrome. In any event,
the female stem 40 extends between a nose-or closed
distal end 42 and an open tail or proximal end 44 to
allow for insertion of the male stem 32 into a
reception region 46 which is defined by an inner
surface 48 uniformly tapered from the tail end 44
and extending a substantial distance in the
direction of the nose end 42. The reception
region 46 has a maximum inner diameter at the tail
end 44 and a minimum inner diameter at the
terminus of the inner surface 48 nearer to the
nose end 42. The angle of taper of the inner
surface 48 with respect to a longitudinal axis of
the female stem 40 is substantially similar to the
angle of taper of an outer surface 50 of the male
stem 32. Similar to the inner surface 48, the
outer surface 50 is uniformly tapered from a
maximum outer diameter at a proximal end adjacent
the support shelf 34 and a minimum outer diameter
at a distal end 52 thereof.
The angular divergence between the inner surface
48 and the outer surface 50 lies generally within
the range of + 3 minutes of arc. In this manner,
when the female stem 40 is moved relative to the
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1 3306~8
.
male stem 32 so that the surfaces 48 and 50
engage, the two components thereby achieve a
locking engagement which cannot be broken except
with the application of substantial force tjo again
separate them. Indeed, substantially the entire
surface 48 engages substantially the entire outer
surface 50. This construction is referred to as a
locking taper. Accordingly, once engaged, the
male stem and the female stem operate as a single
unit and have all of the attributes of a single
stem of a similar size.
Although the outer shape of the female stem 40 is
generally unimportant for purposes of the present
invention, it may be desirable to interrupt its
normally smooth surface with one or a plurality of
flats 53. These serve to prevent rotation of the
stem in the bone or in bone cement and, further,
to reduce hoop stresses in the cement at the
proximal tibia. The flats may be regularly or
irregularly sized and spaced, as desired. While
the outer shape may indeed be important for its
reception and retraction within the intramedullary
canal of the tibia, it otherwise has no effect on
the ability of the female stem to matingly join
with the male stem 32 and thereby achieve the
benefits which have earlier been mentioned.
. .
It was previously noted that a primary feature of
the invention lay in its modularity. This feature
-~ arises by reason of the fact that a family or
group of female stems 40 having a graduated
sequence of different external dimensions are
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1 33068~
16
provided for locking engagement with the male stem
32 of a single prosthetic implant 20. It may be
that the implant 20 is universally sized.
However, even if two or more sizes of prQsthetic
implants 20 were to be used to accommodate
different sizes of bodies, according to the
invention, the male stem 32 would remain unchanged
in size and shape as would the reception region 46
for a plurality of female stems 40. In this
manner, a group of female stems 40 may be provided
to accommodate the particular size of long bone to
which the implant is to be fixed.
A typical family or group of female stems 40 of
circular cross section might have the following
relative dimensions:
.
LENGTH tmm) DIAMETER(Sl ~mm~
10, 14
110 10, 14
In this typical family, the outer diameter of the
female stem 40 at its tail end 44 remains constant
for all the different sizes of stems. This
dimension may typically be 20 mm. Those diameters
noted above are the diameters at the rounded, or
spherical, nose end 42. Although the foregoing
dimensions are those for a stem 40 having a
circular cross section, the particular cross
sectional shape is arbitrary and need not be
circular, just so long as the reception region 46
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17
and, specifically, the inner surface 48,
congruently matches that of the outer surface 50.
Of course, a circular cross section would be
desirable from the fabrication standpoint.
Another benefit which accrues from the
construction just described arises when it is
desired to remove the tibial implant 20 from the
tibia for subsequent revision of the joint. In
this instance, the tibial tray 34 and its
associated male stem 32 can be removed from the
female stem 40 without significant bone loss by
use of a specialized extraction tool 54.
Subsequently, if necessary, another specialized
extraction tool 56 can be insérted into the
reception region 46 of the stem 40 to remove the
stem itself, if ne~essary. Of course, it might be
desirable to allow the stem 40 to remain in place
and reinsert the same tibial tray 34 or another
one, as the case may be, again with minimum
disruption of the surrounding bone.
The construction and operation of the extraction
tool 54 for causing the male stem 32 to be
disengaged from the female stem 40 will now be
discussed with the aid of Fig. 4. As seen in Fig.
4, and as previously described, the tibial tray 22
is formed with a longitudinal bore 29 which
extends through the support shelf 34 and through
the male stem 32. The upper regions of the bore
29, those regions generally coextensive with the
support shelf 34, are threaded as indicated at 60.
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18 1 330688
The extraction tool 54 has a handle 6z and a shank
64 f ixed to the handle and extending to a tip end
66. The shank 64 is threaded, as at 68,
intermediate the tip end 66 and the handlej62. In
order to perform the extraction operation, as seen
in Fig. 4, the shank 64 is inserted into the bore
29 until the threads 68 engage with the threads
60. The handle 62 is caused to rotate on the
longitudinal axis of the shank 64 until the tip
end 66 advances into engagement with the female stem
40 proximate to the nose end 42, specifically, a
terminal surface 67. With continued rotation of the
handle 62, the male stem is caused to be disengaged
from the female stem whereupon the shank 64 can be
unscrewed from the tibial tray 22 and the latter
manually lifted away from the tibia.
Turn now to Fig. 5 for a description of the
construction and operation of the extraction tool
56. Once the tibial tray 22 has been removed, the
way is clear for the removal of the female stem 40
from the intramedullary canal 51 of the tibia.
The extraction tool 56 includes a handle 70 and a
shank 72 fixed to the handle and extending to a
tip end 74. The shank 72 is threaded adjacent the
tip end 74 as at 76. Also, an annular collar 78
is fixed to the shank 72 and lies in a plane
transverse to the longitudinal axis of the shank
at a location intermediate the handle 70 and the
tip end 74. The collar 78 is formed with an outer
peripheral surface 80 which is tapered to
generally conform to the inner surface 48 of the
female stem 40. For purposes of extraction, the
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19
female stem 40 is provided with a threaded bore 82
intermediate the inner surface 48 and the nose
end 42. Thus, in order to extract the female
stem 40 from the tibia, the shank 72 is inserted
into the reception region 46 until the threads 76
at the tip end of the shank engage the threaded
bore 82. The shank 72 is then rotated by means of
a handle 70 so as to engage the threads 76 and 82.
When this occurs, the outer peripheral surface 83
lightly engages the inner surface 48 to thereby
stabilize the tool 56 relative to the stem 40.
The handle 70 continues to be rotated until the
threads 76 are firmly engaged with the threads 82.
Thereupon, force is applied to the handle 70
generally along the longitudinal axis of the stem
40, that-is, in a direction away from the bone,
until extraction has been achieved. By pulling
along the longitudinal axis of the stem 40 and by
reason of the stability provided by the collar 78,
the stem 40 is extracted with minimum disruption
of the surrounding bone.
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While the foregoing description has been directed
toward the prosthetic implant 20 utilized in
conjunction with the tibia 35, the concept of the
invention is just as applicable to a prosthetic
implant 84 for a knee applied to the femur 85 as
also seen in Fig. 1. Thus, as more clearly seen
with reference to Figs. 4 6, the implant 84
comprises a U-shaped patella flange 86 which, in
turn, includes a base 88 and a pair of condylar
I runners 90, 92 which extend between a higher
I anterior sidewall 94 and a lower posterior
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e~ sidewall 96. A patella groove 98 between the
' condylar runners 90, 92 is provided for receiving
and guiding the patella (not shown~ in a known
manner as the leg is caused to flex. A male stem
100 is integral with and upstanding from the base.
At its lowermost regions, the stem 100 may be
uniformly shaped and sized along its length, but
at its uppermost regions is tapered in the manner
of the stem 32. As with the stem 32, the cross
~ sectional shape is arbitrary so long as it matches
- with that of the female stem 40 to be matingly
engaged therewith. What is important is that an
outer surface 102 is uniformly tapered in
congruent fashion with the inner surface 48 of the
female stem 40. As in the instance of the tibial
implant 20, the female stem 40 is applied to the
male stem 100 until their mutually facing surfaces
engage and cause them to become locked together.
Thereupon, the implant 84 is applied to the femur
with the ~oined stems 40 and 100 received within
the intramedullary canal 104 at the distal end of
the femur.
Although the foregoing descriptions have
concentrated on the application of the invention
for purposes of knee prostheses, it need not be so
limited, but has application in any instance -
involving joints between long bones and permits
the accommodation of a wide range of sizes of long
bones by providing a family of relatively
inexpensive female stems which can be universally-
joined with a single size, or small number of
'"'
....
