U.S. patent application number 11/589013 was filed with the patent office on 2007-02-22 for differential porosity prosthetic hip system.
This patent application is currently assigned to Encore Medical Asset Corporation. Invention is credited to Ian Murray.
Application Number | 20070043446 11/589013 |
Document ID | / |
Family ID | 29254192 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070043446 |
Kind Code |
A1 |
Murray; Ian |
February 22, 2007 |
Differential porosity prosthetic hip system
Abstract
A prosthetic femoral implant for use in a hip joint, as a ball
and socket type joint, is disclosed. The implant includes a modular
neck having a variety of adjustable positions to adjust the lateral
offset and version angle of the femoral implant in relation to the
femur. The implant further includes a broad, full collar for
providing a compression force increasing the interdigitation
between the interface of the bone, implant and cement. The implant
also includes a stem having a depression having a roughened porous
surface for resisting the increased torsional loads placed on the
implant due to the increased lateral offset and version angle. The
stem further comprises three distinct zones, each zone having its
own roughened surface creating a tripartite differential
porosity.
Inventors: |
Murray; Ian; (Hunt Valley,
MD) |
Correspondence
Address: |
KARL R CANNON
PO BOX 1909
SANDY
UT
84091
US
|
Assignee: |
Encore Medical Asset
Corporation
|
Family ID: |
29254192 |
Appl. No.: |
11/589013 |
Filed: |
October 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10244149 |
Sep 13, 2002 |
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11589013 |
Oct 26, 2006 |
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09505876 |
Feb 17, 2000 |
6464728 |
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11589013 |
Oct 26, 2006 |
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09059698 |
Apr 14, 1998 |
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09505876 |
Feb 17, 2000 |
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60372390 |
Apr 12, 2002 |
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Current U.S.
Class: |
623/22.12 ;
623/22.42 |
Current CPC
Class: |
A61F 2002/30604
20130101; A61F 2220/0033 20130101; A61F 2/3676 20130101; A61F
2002/30321 20130101; A61F 2002/3631 20130101; A61F 2230/0008
20130101; A61F 2310/00029 20130101; A61F 2002/3071 20130101; A61F
2002/30367 20130101; A61F 2002/3082 20130101; A61F 2002/30795
20130101; A61F 2002/30345 20130101; A61F 2/36 20130101; A61F
2002/3054 20130101; A61F 2250/0024 20130101; A61F 2002/30606
20130101; A61F 2250/0023 20130101; A61F 2/3662 20130101; A61F 2/34
20130101; A61F 2/3607 20130101; A61F 2002/4658 20130101; A61F
2002/3625 20130101; A61F 2002/30171 20130101; A61F 2002/30332
20130101; A61F 2310/00023 20130101; A61F 2002/30616 20130101; A61F
2250/0025 20130101; A61F 2002/3652 20130101; A61F 2002/30339
20130101; A61F 2002/30906 20130101; A61F 2/3609 20130101; A61F
2002/30011 20130101; A61F 2002/30125 20130101; A61F 2/30767
20130101; A61F 2002/365 20130101; A61F 2/367 20130101; A61F
2250/0089 20130101; A61F 2002/30322 20130101; A61F 2002/3611
20130101; A61F 2002/4631 20130101; A61F 2230/005 20130101; A61F
2250/0026 20130101 |
Class at
Publication: |
623/022.12 ;
623/022.42 |
International
Class: |
A61F 2/32 20060101
A61F002/32 |
Claims
1-112. (canceled)
113. A prosthetic device for implantation into a bone comprising: a
head portion configured to articulate with an articulation surface
of a ball and socket joint; a stem portion having a proximal
region, and a distal region, the proximal region having a top
surface with a cavity formed therein, said cavity being defined by
a wall, said stem portion configured for securing the prosthetic
device to the bone; a plurality of modular neck portions, each of
the neck portions comprising an indexable portion, an anteverted
portion, and a proximal end and a distal end separated by a shaft,
the shaft of each of the modular neck portions is provided with a
length differing from the other modular neck portions, wherein a
surgeon selects one of the modular neck portions for insertion into
the cavity of said stem portion such that the selected modular neck
portion laterally offsets the head portion from the stem portion to
thereby aid in restoring the natural biomechanics of the ball and
socket joint; and a means for attaching the selected modular neck
portion to the stem portion; wherein said indexable portion permits
the modular neck portion to be positioned in a plurality of
orientations; and wherein said anteverted portion is configured to
provide differing version angles through varying the orientation of
the modular neck portion for further alteration of the stress
points between the prosthetic device and the fixation material.
114-131. (canceled)
132. A method of implanting a prosthetic device into a bone
comprising the steps of: resecting a portion of a femoral bone
exposing the medullary canal; reaming a canal in the femoral bone;
interposing an amount of bone cement into the canal; implanting a
stem portion of the prosthetic device into the canal, said stem
portion having top portion and a cavity formed in the top portion
thereof; and attaching a modular neck portion to the cavity of the
stem portion using an indexable portion located on a distal end of
the modular neck portion to interact with the cavity and for
altering stress points on an interface between the stem portion and
the bone cement, the modular neck portion having an anteverted
portion for further altering the stress points.
133-143. (canceled)
144. A prosthetic device for implantation into a bone, said device
comprising: a stem having a cavity formed therein; a modular neck
portion comprising an anteverted section and a means for attaching
the modular neck portion to the stem, wherein said means for
attaching comprises a double tapered section and further comprises
an indexable portion providing a plurality of selectable,
predetermined indexable positions of the neck portion relative to
the stem, such that said neck portion produces a plurality of
selectable angles of anteversion corresponding to said plurality of
selectable, predetermined indexable positions.
145. The prosthetic device of claim 145, wherein the double tapered
section comprises an inner portion and an outer portion, and where
said inner portion has a length that is about one to about ten
times a length of the outer portion, wherein the inner portion is
configured and dimensioned so as to avoid bottoming out in the
recess thereby allowing friction fit to occur.
146. The prosthetic device of claim 145, wherein the length of the
inner portion is about three to about four times the length of the
outer portion.
147. The prosthetic device of claim 145, wherein the outer portion
comprises a diameter and the inner portion comprises a diameter,
wherein the diameter of the outer portion is greater than the
diameter of the inner portion.
148. The prosthetic device of claim 145, wherein the outer portion
and the inner portion both taper at an angle relative to a
longitudinal reference axis of the modular neck portion, the angle
being within a range of self-locking taper angles.
149. The prosthetic device of claim 148, wherein the cavity of the
stem comprises a recess formed by at least a first and second
sidewall, and wherein said first and second sidewalls both taper at
an angle relative to a neck axis, the angle being within a range of
taper angles of the self-locking type, such that the inner tapered
sidewall and the second sidewall form a primary self-locking taper
fit, and the outer tapered sidewall and the first sidewall form a
secondary self-locking taper fit that serves as an emergency backup
to thereby support a primary self-locking taper.
150. A prosthetic device for implantation into a bone, said device
comprising: a stem having a cavity formed therein; a plurality of
modular neck portions, each modular neck portion comprising an
anteverted section and a double tapered section, wherein each neck
portion has a different length than the other modular neck portions
such that each neck portion thereby produces a different lateral
offset when attached to the stem than the other neck portions would
produce.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 10/244,149, filed Sep. 13, 2002, entitled
"DIFFERENTIAL POROSITY PROSTHETIC HIP SYSTEM," which claims the
benefit of U.S. Provisional Application No. 60/372,390, filed Apr.
12, 2002.
[0002] Co-pending U.S. patent application Ser. No. 10/244,149 is a
continuation-in-part of U.S. patent application Ser. No.
09/505,876, filed Feb. 17, 2000, entitled "MODULAR NECK FOR FEMUR
REPLACEMENT SURGERY," now U.S. Pat. No. 6,464,728, which is a
continuation-in-part application of U.S. patent application Ser.
No. 09/059,698, filed Apr. 14, 1998, now abandoned.
[0003] All of the above mentioned applications are hereby
incorporated by this reference herein in their entireties,
including but not limited to those portions that specifically
appear hereinafter, the incorporation by reference of all
applications being made with the following exception: In the event
that any portion of the above-referenced applications is
inconsistent with this application, this application supercedes
said portion of said above-referenced applications.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0004] Not Applicable.
BACKGROUND
[0005] 1. The Field of the Invention
[0006] The present disclosure relates generally to prosthetic
implants, and more particularly, but not necessarily entirely, to a
prosthetic hip stem system for enhanced interdigitation between the
prosthetic implant and either bone or cement for increasing the
torsional stability of the prosthetic implant within the femur.
[0007] 2. Description of Related Art
[0008] It is known in the art to replace the natural hip joint with
an artificial hip stem replacement. Numerous artificial implants
are available that can be installed to replace the natural hip
joint with an artificial ball and socket combination. The medullary
canal may be opened using a reamer to create a passage through the
medullary canal in the upper end of the femur where a hip stem may
be implanted. A stem or femoral component of an artificial implant
is inserted into the reamed portion of the medullary canal in a
secure, seated position. Typically, femoral implants include a neck
member that extends outward and away from the stem and terminates
in a spherical knob for insertion into the acetabulum of the hip in
rotational contact therewith about the three major orthogonal
axes.
[0009] There are two major systems to secure the femoral component
of the implant within the medullary canal of the femur. The first
system utilizes the natural tendencies of the bone and allows the
bone to grow into porous sections of the implant without the aid of
cement. The cementless system requires the removal of all
cancellous bone and uses bone ingrowth to form a tight, secure fit
between the implant and the bone, which maintains the implant
within the bone. This system was first introduced nearly forty
years ago and has become the preferred method of installation due
in part to the strength of the connection between the implant and
the bone.
[0010] The second system utilizes bone cement to maintain the
implant within the bone. The use of cement requires the removal of
bone tissue while leaving a layer of cancellous bone tissue to
anchor the implant with the aid of cement. This process was used
extensively during the 1980's and is still used today on a more
limited basis.
[0011] Both systems may be advantageous depending upon a patient's
needs. For example, recovery from an operation using the cementless
system takes an average of about three months before the patient
may return to any activity so that the bone may be permitted to
grow into the pores of the implant, which results in a connection
that has the potential to endure in the patient for a long period
of time. This system is recommended for patients who lead active
lives and is typically used in relatively young patients.
Conversely, the cemented system results in a decrease in pain
compared to the cementless system and an increase in joint
mobility. However, the interface between the bone, the cement and
the implant may not last as long as the cementless system.
Therefore, the cemented system is typically used in less active,
older patients.
[0012] It is a fairly common occurrence for femoral implants to
loosen from the bone or cement over time due in part to the high
stresses placed on the hip joint. Attempts have been made in the
prior art to increase the efficiency of the bond between the
implant and either bone or cement, such that the loosening of the
implant from the bone or cement over time is decreased. One way of
improving the adhesion of the stem of the implant to the bone or
cement is found in U.S. Pat. No. 4,430,761 (granted Feb. 14, 1984
to Niederer et al.). Niederer et al. discloses a femoral prosthesis
having a plurality of parallel grooves formed on the shank or stem
of the implant to improve adhesion of the shank in a prepared bone
cavity.
[0013] However, the system disclosed by Niederer et al. is
disadvantageous for those situations where, for one reason or
another, the implant must be removed and replaced. The location of
the grooves at the distal end of the femoral prosthesis is
disadvantageous because during the removal process in order to
completely loosen the implant from the bone the surgeon must have
adequate access to those portions of the implant where bone
ingrowth has occurred. With grooves located on the distal end of
the implant, the surgeon does not have adequate access to loosen
that portion of the implant from the bone and the implant is,
therefore, very difficult to remove.
[0014] There are many other systems known in the prior art for
improving the adhesion between the implant and the bone or cement,
such as that disclosed in U.S. Pat. No. 4,828,566 (granted on May
9, 1989 to Griss). This patent reference discloses a shank or stem
having a recess in the proximal medial region with a U-shaped wire
mesh disposed in said recess for providing an ingrowth of bone
tissue and an absorption of shear micro movements between the bone
and the implant. However, this system is disadvantageous because
torsional forces may still be exerted on the implant, which may
loosen the implant over time.
[0015] U.S. Pat. No. 3,965,490 (granted Jun. 29, 1976 to Murray et
al.) discloses a femoral implant having one or more shallow
teardrop-shaped depressions disposed in the flat sides of the
curved proximal portion of the stem. These teardrop depressions
provide extra surfaces and directional configuration, which
facilitates retention within the medullary canal of the femur.
However, this system is disadvantageous because there is a tendency
for the implant to loosen from the cement due in part because the
surface of the implant is smooth and does not provide a surface for
interdigitation with the cement.
[0016] It is noteworthy that none of the prior art known to
applicants provides a femoral implant having a tripartite
differential porosity where the distal portion of the stem
comprises the smoothest section, the proximal portion of the stem
comprises a section rougher than the distal portion, and the
teardrop recess comprises the roughest section of the stem and is
rougher than the proximal portion. Applicants have discovered that
it is advantageous for femoral implants used as part of a total hip
replacement system to mimic the natural biomechanics of the hip
through increasing the lateral offset, which is accomplished by
increasing the length of the neck portion of the implant, which
thereby increases the torsional load on the femoral implant.
Applicants have further discovered that the use of differential
roughness on the proximal portion, distal portion and the recessed
portion of the stem opposes and resists the increased torsional
load placed on the femoral implant. There is a long felt but unmet
need, for a tripartite differential porosity femoral implant which
has the ability to resist the increased torsional loads created by
the larger lateral offset. This is accomplished by using a recessed
section that may be advantageously located on both the posterior
and anterior sides of the prosthesis, resulting in an increase in
torsional stability in the connection between the stem and the
femur. The increase in stability is due, at least in part, to the
recessed section located at the posterior and anterior sides of the
prosthesis, but not on the medial or lateral sides of the
prosthesis, such that abrasion wear is not increased on the medial
side.
[0017] The prior art is thus characterized by several disadvantages
that are addressed by the present disclosure. The present
disclosure minimizes, and in some aspects eliminates, the
above-mentioned failures, and other problems, by utilizing the
methods and structural features described herein.
[0018] The features and advantages of the disclosure will be set
forth in the description which follows, and in part will be
apparent from the description, or may be learned by the practice of
the disclosure without undue experimentation. The features and
advantages of the disclosure may be realized and obtained by means
of the instruments and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The features and advantages of the disclosure will become
apparent from a consideration of the subsequent detailed
description presented in connection with the accompanying drawings
in which:
[0020] FIG. 1 is a side view of a prosthetic femoral implant,
specifically illustrating a collar portion, a modular neck portion,
and a stem portion having a plurality of surficial zones, each zone
having a roughness, made in accordance with the principles of the
present disclosure;
[0021] FIG. 2 is a top view of the prosthetic femoral implant of
FIG. 1, specifically illustrating a top surface of the collar
portion, with the modular neck portion removed, having a cavity
formed therein, made in accordance with the principles of the
present disclosure;
[0022] FIG. 3 is a bottom view of the modular neck portion, which
has an indexable portion shaped to correspond with the cavity
formed in the top of the collar, made in accordance with the
principles of the present disclosure;
[0023] FIG. 4 is a side view of a prosthetic femoral implant,
similar to FIG. 1, illustrating a femoral head portion of the
prosthetic femoral implant attached to the modular neck portion and
the stem portion, made in accordance with the principles of the
present disclosure;
[0024] FIG. 5 is a side view of one embodiment of the modular neck
portion made in accordance with the principles of the present
disclosure;
[0025] FIG. 5A is a side view of an alternative embodiment of the
modular neck portion made in accordance with the principles of the
present disclosure;
[0026] FIG. 6 is a schematic view of a human pelvis illustrating
the natural placement of the femur within the hip joint, and the
naturally occurring lateral offset of the femur within the hip
joint;
[0027] FIG. 7 is an exploded side view of the prosthetic implant
illustrating the head portion, the modular neck portion and the
stem portion of the implant, made in accordance with the principles
of the present disclosure;
[0028] FIG. 8 is an enlarged side view of the prosthetic implant
illustrating the lateral offset and the vertical drop of a head and
neck combination;
[0029] FIGS. 9 through 11 are illustrations representing several
examples of the lateral offset and the vertical drop as illustrated
in FIG. 8 using an anteversion angle of eight degrees in the
modular neck portion; and
[0030] FIGS. 12 through 14 are illustrations representing several
examples of the lateral offset and the vertical drop as illustrated
in FIG. 8 using an anteversion angle of twelve degrees in the
modular neck portion.
DETAILED DESCRIPTION
[0031] For the purposes of promoting an understanding of the
principles in accordance with the disclosure, reference will now be
made to the embodiments illustrated in the drawings and specific
language will be used to describe the same. It will nevertheless be
understood that no limitation of the scope of the disclosure is
thereby intended. Any alterations and further modifications of the
inventive features illustrated herein, and any additional
applications of the principles of the disclosure as illustrated
herein, which would normally occur to one skilled in the relevant
art and having possession of this disclosure, are to be considered
within the scope of the disclosure claimed.
[0032] Before the present device and methods are disclosed and
described, it is to be understood that this disclosure is not
limited to the particular configurations, process steps, and
materials disclosed herein as such configurations, process steps,
and materials may vary somewhat. It is also to be understood that
the terminology employed herein is used for the purpose of
describing particular embodiments only and is not intended to be
limiting since the scope of the present disclosure will be limited
only by the appended claims and equivalents thereof.
[0033] Referring generally to FIG. 8, a "focal point," referred to
as item 15, may be defined as a point of convergence of two axes,
namely a long axis, represented by the line Y, of a femoral stem
portion 16 of a prosthetic implant 10, and a neck axis, represented
by the line Z', of the prosthetic implant 10. The phrase "lateral
offset" refers to the horizontal distance relative to a patient in
a standing position from the center of the pelvis to the center of
the femoral canal in the natural hip joint. In the prosthetic
implant 10, "lateral offset" refers to the horizontal distance
between a center 11a of a ball or femoral head portion 11 of the
implant 10 and the long axis Y of the femoral stem portion 16 of
the implant 10. The phrase "vertical drop" refers to the vertical
distance between the center 11a of the head portion 11 and the
focal point 15.
[0034] Designers of hip stem prostheses may choose to increase the
lateral offset by increasing or decreasing the distance between a
center of the ball or femoral head of the implant and the mid-line,
or long axis, of the femur in order to aid in the restoration of
the biomechanics of the natural hip joint, as illustrated in FIG.
6. An increased lateral offset operates to increase the torsional
forces that are exerted on the femoral implant, and such forces
become applied to the cement-implant interface between the implant
and the medullary canal of the femur. There is therefore, in cases
of an increased lateral offset, an increased need for torsional
stability to prevent the implant from loosening from the bone or
cement.
[0035] Applicants have also discovered that torsional forces may be
more effectively opposed by applying a type of differential
porosity to the surface of a femoral implant, to resist the
torsional forces. Applicants have further discovered that the
femoral implant may be more effectively tuned or adjusted after
implantation of the femoral stem into the medullary canal of the
femur, by selectively increasing or decreasing the lateral offset,
and the version angle of the neck, using a modular neck component.
In some instances, it is advantageous to adjust the lateral offset
and the version angle simultaneously.
[0036] Referring now to FIGS. 1 and 7, there is shown a side view
of a femoral prosthetic implant designated generally at 10,
illustrated with a medial side of the implant 10 facing downward in
FIG. 1 and to the right in FIG. 7. The femoral prosthetic implant
10 comprises a substantially spherical femoral head 11 (illustrated
best in FIGS. 4 and 7), which may be attached to a modular
indexable neck portion 12 for use as the ball portion of a ball and
socket joint, a collar portion 14, a stem portion 16 comprising a
proximal stem region 50 and a distal stem region 60, and a
teardrop-shaped depression 18 located between the proximal stem
region 50 and the distal stem region 60. The above components may
be manufactured from titanium for cementless stem applications and
from cobalt chrome molybdenum alloy in cemented stem applications
for interfacing with cement and for providing less risk of fretting
and corrosion at the modular stem neck junction. It should be noted
that other material may be used that are presently known, or which
may become known, in the art for manufacturing the above
components, which can be readily determined by one of skill in the
art. Each of the above components will be more particularly
described below in relation to FIGS. 1, 4 and 7.
[0037] As used herein, the term "fixation material" may be defined
as bone that may grow into the implant, bone cement that may
interdigitate with the implant, or any other substance that one of
skill in the art may use for securing the implant to the bone to
inhibit torsional loads that is presently known, or which may
become known in the future, in the art without departing from the
scope of the present disclosure.
[0038] The present disclosure is directed to utilize a prosthetic
hip having an increased lateral offset between the spherical ball
portion 11, sometimes referred to herein as a head portion
(illustrated in FIG. 4), of the prosthetic implant 10 and the shaft
of the patient's femur (illustrated best in FIG. 6). It should be
noted that any suitable head portion 11, which may be substantially
spherical in shape, either presently known in the art, or which may
become known in the future, may be utilized by the present
disclosure as the ball portion of the ball and socket joint. The
head portion 11 may be configured for articulating with an
articulation surface, which articulation surface may be an
acetabular cup or other surface used to assemble the socket portion
of a ball and socket joint. The head portion 11 may be modular and
attached to the neck portion 12 by a taper lock as illustrated in
FIG. 4, or the head portion 11 may alternatively be integral with
the neck portion 12 (not illustrated in the figures).
[0039] The present disclosure may also utilize a modular neck
portion 12 to create the lateral offset required to aid in
restoring the natural biomechanics of the joint. The natural
biomechanics of the hip joint is demonstrated in FIG. 6. Referring
back to FIG. 1, neck portion 12 may be adjusted by a surgeon after
the prosthetic implant 10 has been implanted within the femur, by
changing the orientation of the neck portion 12 to any one of a
plurality of differing positions as illustrated in FIG. 2. Although
there are twelve such positions shown in FIG. 2, it is to be
understood that the implant 10 may be designed to accommodate more
or fewer than twelve such selectable positions.
[0040] Neck portion 12 may be replaced with various sizes of necks
12, for example by a longer neck or shorter neck than that shown in
the figures, with the size of the neck depending upon the need of
the patient. The neck size may be determined by the surgeon at the
time of surgery. The length of the neck portion 12 may be
configured and dimensioned to correspond with the increased need
for lateral offset. Some exemplary lengths of the modular neck
portion 12 include 32 mm, 35 mm, and 38 mm. It should be noted that
any size neck portion 12 may be used to increase the lateral offset
and one of skill in the art could modify the length of the neck
portion 12 to match the varying needs and anatomies of each
individual patient.
[0041] The neck portion 12 comprises a proximal end 30 and a distal
end 31. The proximal end 30 comprises a smooth surface 32 that may
have a slightly tapered outer edge 33 such that the proximal end 30
may matingly engage a matching opening located within the head
portion 11 such that the head portion may be secured to the neck
portion 12 as illustrated in FIG. 4. It should be noted that one of
skill in the art may modify the shape of the tapered outer edge 33
to increase or decrease the taper angle or to be of any shape,
including no taper, presently known, or which may become known, in
the art to secure the neck portion 12 to the head portion 11. The
above structural features may be referred to herein as a means for
attaching the indexable neck portion to the head portion. As noted
previously, the head portion 11 may alternatively be integrally
attached to the neck portion 12 without departing from the scope of
the present disclosure.
[0042] As illustrated particularly in FIG. 5, a long axis of the
neck portion 12, referred to herein as the reference axis Z, may be
defined as being normal to a plane 35 of the base of the neck
portion 12. An angle .theta., also referred to herein as an
anteversion angle .theta., is also illustrated in FIG. 5, and may
be defined as the angle between the reference axis Z and an
anteverted axis, also referred to herein as the neck axis,
represented by the line Z'. Thus, the angle .theta. of the neck
portion 12 permits the head portion 11 to be located either farther
anteriorly, or farther posteriorly within the hip joint. Exemplary
anteversion angles .theta. may be between the range of about zero
and about twelve degrees. It should be noted that one of skill in
the art could modify the anteversion angle .theta. without
departing from the scope of the present disclosure such that the
anteversion angle .theta. could be greater than twelve degrees,
depending upon the need of the patient and the desired result.
[0043] The neck portion 12 further comprises a shaft 34 separating
the proximal end 30 from the distal end 31. The neck portion 12
comprises a raised portion 36 located near the base of the shaft 34
on the distal end 31, positioned at an angle with respect to the
neck axis Z' creating the anteversion of the neck portion 12 as
illustrated most clearly in FIGS. 5 and 5A, and discussed above. It
should be noted that one of skill in the art may modify the angle
of the raised portion 36 to increase or decrease the anteversion
angle .theta. or may reposition the raised portion 36 to any
position presently known, or which may become known, in the art to
create an anteversion in the neck portion 12. It should further be
noted that one of skill in the art could modify the current
disclosure without departing from the scope of the present
disclosure so as to eliminate the raised portion 36 completely, and
simply angle the shaft 34 of the neck portion 12 to the desired
anteversion angle .theta..
[0044] The surface of the shaft 34 and the distal end 31 of the
neck portion 12 may contain a roughness as illustrated in FIGS. 5
and 5A. It should be noted that one of skill in the art may modify
the surface of the neck portion 12 such that the roughness may be
increased to an even rougher surface, or such that the neck portion
12 may be smooth, instead of rough, without departing from the
scope of the present disclosure.
[0045] The distal end 31 of the modular neck portion 12 may
comprise an indexable portion extending therefrom. The distal end
31 may also comprise a first tapered portion 38 disposed thereon,
sometimes referred to herein as a first insert, and may further
comprise a second tapered portion 39, sometimes referred to herein
as a second insert, extending below and being disposed on the first
tapered portion 38. This combination of tapers may be referred to
herein as a double taper. One embodiment of the first tapered
portion 38 includes a geared section 21 illustrated in FIG. 5
comprising a plurality of male gears 37 for matingly engaging a
corresponding female geared section 21 of the stem portion 16. It
should be noted that the male gears 37 may be tapered as it is a
part of the first tapered portion 38. The male gears 37 function to
act in concert with the female geared section 21 of the stem
portion 16 permitting the modular neck portion 12 to be indexed in
a plurality of positions and orientations, thus altering the angle
of anteversion with respect to the stem portion 16 and permitting
the surgeon the ability to fine tune and adjust the modular neck
portion 12 such that the stress points may be altered or
shifted.
[0046] An alternative embodiment of the first tapered portion 38
comprises a taper without gears and may be fashioned as illustrated
in FIG. 5A. It should be noted that the first tapered portion 38
may be modified by one of skill in the art to be of any length,
either larger or smaller than illustrated in FIGS. 5 and 5A,
presently known, or which may become known in the future, in the
art for securing the neck portion 12 to the stem portion 16, and
may further be modified to increase or decrease the angle of taper
without departing from the scope of the present disclosure.
[0047] The second tapered portion 39 extends below the first
tapered portion 38 and may be between the range of about two to
about five times the length of the first tapered portion 38. It
should be noted that the length of the second tapered portion 39
may be modified, as illustrated in FIGS. 5 and 5A, by one of skill
in the art to provide a taper that does not bottom out and provides
a secure connection between the neck portion 12 and the stem
portion 16. For example, FIG. 5 illustrates one embodiment of the
second tapered portion as being longer than an alternative
embodiment of the second tapered section 39 illustrated in FIG.
5A.
[0048] The second tapered portion 39 functions to provide a primary
self-locking taper for locking and securing the neck portion 12 to
the stem portion 16. Whereas, the first tapered portion 38
functions as a secondary locking taper to secure the neck portion
12 to the stem portion 16, and may act as an emergency backup to
maintain the connection between the neck portion 12 and a cavity 20
such that the stem portion 16 does not separate from the rest of
the prosthetic implant 10, should the primary locking taper fail
for any number of reasons.
[0049] During a hip replacement surgery, it is common for a surgeon
to experience at least the following two problematic scenarios. The
first scenario relates to the patient's anatomy where the stem
portion 16 cannot be surgically placed in an upright orientation
with respect to the medullary canal of the femur (not shown),
causing a skewed orientation of the implant 10. The second scenario
occurs when the surgical technique of the surgeon results in less
than perfect orientation of the stem portion 16 within the
medullary canal of the femur (not illustrated). In either scenario
the result is the same, the orientation of the stem portion 16 is
not aligned with the shaft of the femur causing pain and discomfort
to the patient as well as reducing the longevity of the implant,
which will loosen over time due to the differing forces placed on
the implant. The present disclosure permits the surgeon during
surgery to fine tune and adjust the orientation of the stem with
the shaft of the femur by replacing one neck portion 12 with
another to create the desired lateral offset and create the desired
orientation for each individual patient. The ability to permit
positioning of the modular indexable neck portion 12 independent of
the stem portion 16, by varying the version angle and the offset
angle (and hence the offset itself) simultaneously in order to fine
tune the implant 10 to the patient's needs, whether to match the
original biomechanics of the hip joint or to produce an altered
position that is different from the original biomechanics of the
patient, causes altered stress points to become applied to the
cement-implant interface. There is usually more stress imposed in
comparison to many prior hip stem designs, thus precipitating a
need for increased torsional stability and resistance. One solution
is explained below in connection with the differential porosity, or
roughness, of the stem portion 16.
[0050] The stem portion 16 may be designed such that it may aid in
the restoration of the natural joint mechanics and for allowing the
surgeon a final opportunity to correct for malpositioning of
implants 10 due to surgical technique and bone deformity. The
proximal stem 50 may contain collar portion 14 configured with a
cavity 20 where a self-locking taper and a positive indexing
mechanism may be employed to ensure that the proper head, length,
version and offsets may be obtained. This unique design may feature
provides a plurality of self-locking positions providing several
combinations of neck length version and offset for closely aiding
in the restoration of the natural hip joint mechanics. This
innovative design provides the surgeon with the opportunity to
intervene at the last possible surgical moment and fine tune the
hip joint mechanics without disruption of the implant-cement-bone
interface. In addition, the design of the stem portion 16 provides
for increased opportunity to surgically intervene for certain
post-operative complications, for example, component malposition,
leg length discrepancy, dislocations and replacement of bearing
surfaces, with minimal disruption of the interfaces of the
bone.
[0051] FIG. 2 illustrates a top view of the collar portion 14
having a cavity 20 formed therein. Within the cavity 20 may be a
first sidewall 40 defining a first portion 41 having twelve
different positions denoted by numerals 0-11 situated in a similar
position as a standard clock. The differing orientations may be
established by a female geared section 21, which permits the neck
portion 12 to have differing version angles with respect to the
stem portion 16, which may be adjusted by removing the neck portion
12 from the cavity 20 and rotating the neck portion 12 to the
desired orientation creating the desired version angle. The female
geared section 21 of the cavity 20 may be configured and
dimensioned with slight protrusions 22 extending inwardly into the
cavity 20 from the first sidewall 40 creating a plurality of female
gears to matingly engage the male gears 37 of the modular neck
portion 12 for adjusting the orientation of said modular neck
portion 12.
[0052] FIG. 3 illustrates the corresponding bottom portion of the
modular neck portion 12 having male gears 37 with mating
protrusions 24 for mating with the female gear section and may be
spaced between protrusions 22 such that the two arrays of
protrusions mate with one another forming a matching fit. Mating
protrusions 24 function similarly to protrusions 22 in that the
mating protrusions 24 permit the modular neck portion 12 to be
adjusted into twelve differing version angles. It should be noted
that the number of protrusions and gears may be modified by one of
skill in the art to include more or less than twelve differing
positions in which the neck may be oriented such that differing
version angles may be achieved. For example, by removing two
protrusions 22 or female gears from the cavity 20 and removing the
same number of corresponding mating protrusions 24 or male gears 37
from the first tapered portion 38, ten different positions may be
achieved instead of twelve. The same relationship holds true for
adding protrusions 22 or female gears and mating protrusions 24 or
male gears 37.
[0053] A second sidewall 42 within the cavity 20 defines a second
portion 43 that may be tapered to match the taper of the second
tapered portion 39 of the modular neck portion 12 such that a
secure lock may be achieved between the stem portion 16 and the
modular neck portion 12. The taper of the second portion 43 maybe
of the self-locking type and provides for the primary fixation of
the stem portion 16 to the neck portion 12. The depth of the second
portion 43 may be dimensioned such that the second portion 43 may
be deep enough to avoid "bottoming out" of the taper, ensuring that
the self-locking taper may occur. Thus, the first tapered portion
38 of the modular neck portion 12 may be configured for matingly
engaging the first portion 41 of the cavity 20 forming a secondary
lock or fixation, and the second tapered portion 39 of the modular
neck may be configured for matingly engaging the second portion 43
of the cavity 20 forming a primary lock or fixation of the
self-locking type. The above structural features maybe referred to
herein as a means for attaching the indexable neck portion to the
stem portion.
[0054] The collar portion 14 may be disposed on the stem portion 16
by extending from the proximal region 50 of the stem portion 16 in
a medial, anterior and posterior direction creating a broad, full
collar portion 14. The broad, full collar (i.e. more than just a
medial collar) aids in compression of the bone cement into the
differential surface porosities (described in more detail below),
during implantation to provide a more consistent cement mantel
interface by creating a force for counter-pressure. The force
created by the full collar portion 14 provides for optimal/complete
interdigitation of the cement with the bone as well as with the
implant. Therefore, the collar portion 14 functions to force cement
into the medullary canal of the femur as well as into the porous
depressions on the surface of the prosthetic implant. Additionally,
when the stem portion 16 of the prosthetic implant 10 is seated
within the medullary canal of the femur the collar portion 14
functions as a cap to cover the medullary canal such that wear
debris generated from the prosthetic implant may be prevented from
migrating into the medullary canal.
[0055] Below the collar portion 14 extends the stem portion 16,
which may be configured and dimensioned to be surgically located
within the medullary canal of the femur. As referred to previously
and as illustrated in FIG. 4, the stem portion 16 comprises a
proximal region 50, a distal region 60 and a depression 18 located
between the proximal region 50 and the distal region 60. The
depression 18 may be defined by a boundary with the boundary
defining the overall shape of the depression. The stem portion 16
may be divided into multiple separate and distinct zones, each zone
having its own unique surface porosity or roughness, thereby
creating a differential porosity or differential roughness. FIGS. 1
and 4 illustrate three zones of differing porosity or roughness,
zone A, zone B and zone C. It is to be understand that more or
fewer than three zones of porosity or roughness may be used. The
first zone, designated as A, comprises the distal stem 60 and may
be configured and dimensioned with either a very slight porous
surface or with no porous surface at all creating a smooth surface.
The second zone, designated as B, substantially comprises the
proximal stem 50 and may be configured and dimensioned with a
porous surface that is rougher than zone A. The third zone,
designated as C, comprises a teardrop-shaped depression 18 that may
be configured and dimensioned with an even rougher porous surface
than zone B and provides increased torsional stability for the
implant 10. Therefore, zone A has the smoothest surface, zone B has
a rougher surface than zone A and zone C has the roughest surface
of all three zones, creating a tripartite differential porosity or
roughness.
[0056] The rougher surfaces of zones B and C provide surfaces to
which either the bone may interdigitate with and grow into more
effectively, or to which the bone cement may adhere to more
effectively to thereby secure the implant 10 to the medullary canal
of the femur. The smooth surface of zone A provides a surface that
bone and cement will not adhere to as effectively, such that the
distal portion 60 of the stem portion 16 will be more easily
removable from the medullary canal of the femur, should removal of
the implant 10 become necessary. The benefit of the tripartite
differential porosity or roughness is an increased torsional
stability in the connection between the stem portion 16 and the
femur, at the posterior and anterior sides of the prosthesis, but
not on the medial or lateral sides of the prosthesis, such that
abrasion wear is not increased on the medial side. Such a
differential roughness may sometimes be referred to herein as a
means for resisting torsional loads.
[0057] The distal portion 60 of the stem portion 16 or zone A may
have a finish that has a polished finish between the range of 2-15
RA. The proximal portion 50 of the stem portion 16 or zone B may
have a rougher satin finish between the range of 15-30 RA. The
depression 18 may have an enhanced satin polish that may be between
the range of 30-80 RA, which is rougher than the proximal portion's
50 satin finish.
[0058] It will be appreciated that zones A, B and C may each be
modified, such that the area of the implant 10 that each zone
includes may be increased or decreased. For example, FIG. 1
illustrates the zones A, B and C, with zone A being roughly the
same length on the stem as zone B. However, zone A may be shortened
to include the area covered by zone A', thus decreasing the area of
zone A while increasing the area of zone B to include the area
covered by zone B'. It is evident from FIG. 1, that one of skill in
the art may modify the area of each zone to include a larger or
smaller area and thus proportionally increasing or decreasing the
amount of surficial roughness present in a given zone.
[0059] The stem portion 16 may include roughness depressions 18 of
any suitable shape. For example, the stem portion 16 may include a
single teardrop-shaped depression 18, or the stem portion 16 may
alternatively comprise two opposing teardrop-shaped depressions 18.
Teardrop-shaped depressions 18 maybe located on the anterior and
posterior portions of the stem portion 16 and may extend from a
proximal stem region 50 into a distal stem region 60. The
depressions 18 may be located on the anterior and posterior
portions and aid in securing the stem portion 16 to the
implant-bone cement interface, and which functions to oppose the
torsional forces experienced in the hip joint. Additionally, the
depression(s) 18 located on either the anterior portion, the
posterior portion or on both portions of the stem portion 16 may be
a single depression or may be a series of multiple depressions
effectuating a single depression 18.
[0060] The porosity or roughness of the depression 18 may fill the
entire depression 18 or may fill only a portion of the depression
18, depending upon the desired result. FIGS. 1 and 4 illustrate the
depression 18 having a boundary defining the depression 18 or
recessed surface, in which the boundary of the depression 18 is the
same as the boundary of the porosity or roughness. The surface of
the depression 18 provides for increased interdigitation between
the implant 10 and the cement or bone and causes the implant 10 to
have an increased ability to resist the increased torsional loads
placed on the implant 10 responsive to the increase in lateral
offset and version angle, both of which create an increased need
for torsional resistance. It should be noted that the size of the
teardrop-shaped depression 18 may be modified to be of any suitable
size and accomplish the same results. It should be further noted
that while the shape of the depression(s) 18 has been illustrated
as teardrop-shaped, one of skill in the art may modify the shape of
the depression 18 to be of any shape presently known, or which may
become known, in the art to inhibit torsional forces.
[0061] As stated previously, the surface of the stem portion 16 may
contain a roughness as illustrated in FIGS. 1 and 4. The roughness
may be comprised of a material such as beads that have been bead
blasted onto the surface of the stem portion 16 such that the
surface area of the stem portion 16 may be increased for increasing
the interdigitation between the bone, the implant 10 and the bone
cement such that a more secure fixation of the implant 10 to the
bone maybe achieved. It should be noted that the method of applying
the surficial roughness to the stem portion 16 may be modified by
one of skill in the art using a method presently known, or which
may become known in the future, in the art for adding a surficial
roughness to the stem portion 16. Additionally, the material,
design and shape used to create the roughness may be modified by
one of skill in the art using any suitable material, design and
shape presently known, or which may become known, in the art for
increasing the surface area and interdigitation of the stem portion
16.
[0062] Applying the differential surficial roughness described
above is an advantageous feature of the present disclosure.
Advantageously, it is a feature of the present disclosure to have a
different surficial roughness located within the depression 18 as
opposed to the surficial roughness of the proximal stem region 50
and the distal stem region 60 because as the surface of the stem
portion 16 increases in roughness there is a corresponding increase
in surface area, which increased surface area causes greater
contact between the bone cement or other fixation material and the
stem portion 16. Increased contact between the fixation material
and the stem portion 16 results in increased strength, stability
and resistance to withdrawal forces such that the implant may be
securely fastened to the bone.
[0063] Applying the above surface area principles it will be noted
that zone A has the smoothest surface and has less surface area
than both zone B and zone C. The reason for the decreased surface
area is in large part due to the fact that it is difficult to
remove the distal stem 60 from the femoral bone once the stem
portion 16 has been implanted into the femur and that difficulty is
increased when the surface area of the distal stem 60 is increased.
As noted above, as the surface area of the distal stem 60
increases, the strength of the bond between the bone fixation
material and the distal stem 60 also increases and becomes
extremely difficult to remove the implant 10 from the bone should
it become necessary to remove the implant 10 for revision surgery.
Removal becomes extremely difficult because there is no technique
available, barring drastic resection, for the surgeon to get
instrumentation into the distal portion of the femur that permits
the surgeon to sufficiently loosen and remove the implant 10.
[0064] Zone B, comprising the proximal stem 50, has similar
problems as the distal stem 60 with respect to removal of the stem
portion 16. However, the surficial roughness and hence the surface
area of the proximal stem 50 may be increased because the proximal
stem 50 is more readily accessible to the surgeon as the surgeon
may use instrumentation to pry the stem and ultimately the implant
10 from the bone. In this case, the increased roughness in zone B
is advantageous because it increases the bonding strength, which
results in greater stabilization of the implant 10 within the
femur.
[0065] Zone C, comprising the depression 18, may contain the
greatest roughness and results in the greatest surface area of all
three zones. Therefore, there is a large amount of interdigitation
between the fixation material and the depression 18, which results
in great bonding strength. Additionally, because the depression or
depressions are located on the anterior and posterior portions of
the stem portion 16 the increased roughness and surface area of the
depressions 18 operate to oppose the increased torsional forces
that are experienced as the natural biomechanics of the femur are
simulated by increasing the lateral offset and version angle of the
modular neck portion 12. Further, the increased bonding strength
does not prevent removal of the stem portion 16 from the medullary
canal of the femur because of the tear-drop shape of the depression
18, with the majority of the depression 18 being located in the
proximal stem region 50 and the remainder of the depression 18
being located in the distal stem region 60. Therefore, the
differential roughness of the present disclosure advantageously
utilizes unique, novel design features that increase resistance to
torsional forces.
[0066] Further, the depression 18, while increasing the bonding
strength and hence resisting torsional forces, may be used as a
part of a mechanism to break the bond between the fixation material
and the implant 10. For example, an instrument (not shown in the
figures) may be used to initially uncover the proximal most portion
of the depression 18. The instrument may be used to break the bond
by following the depression 18, which acts as a channel or guide
for the instrument, loosening the implant 10 from the fixation
material.
[0067] Referring now to FIG. 8, wherein an enlarged side view of
the proximal portion of the femoral prosthetic implant 10 with the
neck portion 12 and the head portion 11 secured to the stem portion
16. Specifically, the lateral offset between a center 11a of the
head portion 11 and the mid-line or longitudinal axis, represented
by the line Y, of the femoral implant 10 is illustrated along with
the corresponding vertical drop associated with the size of the
modular neck portion 12 and head portion 11 to be used. The
vertical drop may be determined as the vertical distance between
the center 11a of the head portion 11 of the implant 10 and the
intersection of the longitudinal axis Y and a neck axis Z' at the
focal point 15. The neck axis Z' runs through the center 11a of the
head portion 11 and extends through the neck portion 12. As the
size of the neck portion 12 and the size of the head portion are
changed, the lateral offset as well as the vertical drop will also
change accordingly. For example, as the neck portion 12 increases
in size, the lateral offset will necessarily increase as the center
11a of the head portion 11 is positioned farther away from the
longitudinal axis Y, thus changing the vertical drop as well.
Conversely, as the neck portion 12 decreases in size, the center
11a of the head portion 11 is brought closer to the longitudinal
axis Y, reducing the lateral offset as well as the vertical drop.
Referring now to FIGS. 9-14, wherein specific examples of how the
size of the femoral head portion 11 and size of the neck portion 12
affect the lateral offset and vertical drop of the implant 10.
FIGS. 9-14 are intended as illustrative examples only, and are not
intended to be limiting of the scope of the present disclosure.
[0068] It should be noted that FIGS. 9-11 use an eight degree
anteversion angle .theta. in the neck portion 12, while FIGS. 12-14
use a twelve degree anteversion angle .theta. in the neck portion
12. It should further be noted that FIG. 9 utilizes a 32 mm neck
portion 12, FIG. 10 utilizes a 35 mm neck portion 12, and FIG. 11
utilizes a 38 mm neck portion 12. The same sizes of neck portions
12 are also used in the illustrations of FIGS. 12-14.
[0069] It will be appreciated that one exemplary demonstration of
how to use the illustrations of FIGS. 9-14, may be applicable to
each of the illustrations of FIGS. 9-14. For example, FIG. 9
utilizes a neck portion 12 having an anteversion angle .theta.
equal to eight degrees, and the neck portion 12 is 32 mm in length.
Referring specifically to the circular chart and lateral offset in
FIG. 9, the collar portion 14 is illustrated as having twelve
positions numbered 0-11. Position number 11 will now be used to
demonstrate how the charts may be read. When the neck portion 12 is
located in position number 11, the neck portion 12 has a four
degree anteversion angle .theta.. Further, as labeled, the small
chart associated with position number 11 represents the femoral
head size and the associated lateral offset. As the size of the
femoral head portion 11 is increased or decreased, as noted above
in relation to FIG. 8, the lateral offset may also be increased or
decreased as noted in the chart. Thus, a +5 mm femoral head will
have a corresponding lateral offset of 46 mm. Referring now to the
leg length vertical drop chart of FIG. 9, the +5 mm femoral head
located in position number 11 will also correspond to a 41 mm
vertical drop. Therefore, as demonstrated above, as the length of
the neck portion 12 or the size of the femoral head changes, the
corresponding lateral offset and associated vertical drop will also
change accordingly. It should be noted that the remaining position
numbers may be referred and interpreted in like manner as position
number 11 demonstrated above.
[0070] Those having ordinary skill in the relevant art will
appreciate the advantages provided by the above-described features
of the present disclosure. Current surgical technique requires the
surgeon to expose the proximal portion of the femur and the
acetabular portion of the hip joint, and perform an osteotomy of
the proximal portion of the femur. Such a resection of the proximal
femur causes the bone to bleed. The surgical devices of the prior
art utilize a prosthetic implant having a neck that is integral
with the stem. When using an integral neck, the surgeon is required
to implant the acetabular cup and its component parts into the
acetabulum and then attach the femoral head to the acetabular cup
prior to implanting the femoral component of the prosthesis into
the exposed femoral canal. Implanting the acetabular components
typically takes approximately thirty minutes for a surgeon to
complete. Thus, while the surgeon is preparing the acetabulum and
securing the acetabular cup and other components therein, the
resected proximal femur remains exposed and continues to bleed. The
result is often an unnecessary loss of blood between the range of
200-400 cc in volume.
[0071] Conversely, the advantageous features of the present
disclosure described above permit the surgeon to avoid unnecessary
bleeding in original hip replacement surgeries and aid the surgeon
in subsequent revision surgeries if needed. For example, the
modularity of the neck portion 12 of the present disclosure permits
the surgeon to resect the proximal femur, expose and otherwise
prepare the femoral canal and then implant the stem portion 16 of
the prosthetic implant 10 promptly into the femoral canal without
having to wait for the surgeon to implant the acetabular cup and
its component parts into the acetabulum, which reduces excessive
bleeding in the femur. The implantation of the stem portion 16 into
the femoral canal acts similarly to a plug being inserted into a
hole to stop a leak, and thereby reduces excessive bleeding in the
femur. Thereafter, the surgeon may proceed with the implantation of
the acetabular components without unnecessary blood loss in the
femur. Finally, the surgeon may attach the modular neck portion 12
to the implanted components and finish the remainder of the
surgery.
[0072] Another advantageous feature of the present disclosure may
be realized during the unfortunate occurrence of a revision surgery
to replace damaged components or for any other reason a revision
surgery may be necessary. For example, when a prosthetic device
having an integral neck has been surgically implanted on a previous
occasion, and it becomes necessary for the surgeon to replace the
acetabular cup on the socket side of the joint by implanting a bone
graft, there is a high risk of damaging the femoral component of
the prosthetic implant 10. This is because the head portion 11 and
the neck portion 12 are connected to the acetabular cup in the
acetabulum and may get in the way during removal, making it
difficult to remove the acetabular cup without damaging the femoral
component. In this circumstance, the only other option for the
surgeon, besides potentially damaging other components, is to try
to avoid the integral neck. However, such avoidance compromises the
quality of the surgical procedure.
[0073] Once again the modularity of the neck portion 12 of the
present disclosure advantageously permits the surgeon to detach the
modular neck portion 12 from the remainder of the implant 10. At
that point, the surgeon may expose the needed area to perform the
revision surgery and then reattach the modular neck portion 12
without the need to remove the stem portion 16 from the femur and
posing a risk of damaging the femur or the stem portion 16.
[0074] An additional advantageous feature of the modular neck
portion 12 of the present disclosure may be realized in a revision
surgery when the previously implanted stem and neck are chrome
cobalt or other metallic material, but the prosthetic femoral head
is ceramic. It is a contra-indication to take a ceramic femoral
head off and then reattach it again to the neck in the original
circumferential grip friction-pressure fit, because the ceramic can
split or crack at the tapered connection by the inherent stress
riser that exists in a friction fit involving a circumferential
grip. Therefore, using the integral necks of the prior art causes
the surgeon to replace the entire femoral component in order to
avoid refitting and possibly splitting the ceramic head, which
requires further resection of the femur. However, using the present
disclosure, the surgeon can simply replace the entire head and neck
combination without having to remove the stem portion 16 by simply
detaching the neck 12 from the stem 16. Therefore, the
contra-indication of ceramic is avoided without removing the stem
portion 16 of the implant 10 from the femur, which eliminates
unnecessary bone resection.
[0075] In accordance with the features and combinations described
above, a useful method of attaching a prosthetic femoral implant to
a patient's femur includes the steps of:
[0076] (a) creating a passage into the medullary canal of the femur
by removing at least a portion of the cancellous bone;
[0077] (b) pouring an amount of bone cement into the medullary
canal;
[0078] (c) inserting a femoral prosthetic implant having a modular
neck, a full collar, and stem, said stem comprising a proximal
portion, a distal portion and a teardrop-shaped depression, each
portion of the stem being separate and having distinct porosity
creating a tripartite differential porosity surface, into the bone
cement; and
[0079] (d) providing a compression force on the collar of the
femoral prosthetic implant for shaping the bone cement into a
consistent cement mantle and for creating increased interdigitation
between the bone, bone cement, and implant interface.
[0080] It should be noted that the present disclosure and the
principles taught herein may be used for implanting a prosthetic
device either with or without bone cement without departing from
the scope of the disclosure.
[0081] In the foregoing Detailed Description, various features of
the present disclosure are grouped together in a single embodiment
for the purpose of streamlining the disclosure. This method of
disclosure is not to be interpreted as reflecting an intention that
the claimed disclosure requires more features than are expressly
recited in each claim. Rather, as the following claims reflect,
inventive aspects lie in less than all features of a single
foregoing disclosed embodiment. Thus, the following claims are
hereby incorporated into this Detailed Description by this
reference, with each claim standing on its own as a separate
embodiment of the present disclosure.
[0082] It is to be understood that the above-described arrangements
are only illustrative of the application of the principles of the
present disclosure. Numerous modifications and alternative
arrangements may be devised by those skilled in the art without
departing from the spirit and scope of the present disclosure and
the appended claims are intended to cover such modifications and
arrangements. Thus, while the present disclosure has been shown in
the drawings and described above with particularity and detail, it
will be apparent to those of ordinary skill in the art that
numerous modifications, including, but not limited to, variations
in size, materials, shape, form, function and manner of operation,
assembly and use may be made without departing from the principles
and concepts set forth herein.
* * * * *