U.S. patent number RE32,488 [Application Number 06/907,594] was granted by the patent office on 1987-09-01 for hip prosthesis.
Invention is credited to Ramon B. Gustilo, Richard F. Kyle.
United States Patent |
RE32,488 |
Gustilo , et al. |
September 1, 1987 |
Hip prosthesis
Abstract
A femoral insert combines bone ingrowth surfaces in the proximal
portion of the shaft which is wide in the medial-lateral direction
and curved in the medial aspect with a distal portion which has a
round cross-section and is curved in the direction of the anterior
bow of the femur. Accordingly, firm fixation of the implant is
initially provided by the distal portion functioning as an
intramedullary rod while long term stabilization is achieved
proximally through bone ingrowth. Also, the neck connecting the
spherical head to the shaft through the collar is anteverted with
respect to the collar at an angle of about 10.degree. to
12.degree.. The prosthesis for the left femur is basically a mirror
image of the prosthesis for the right femur.
Inventors: |
Gustilo; Ramon B. (Minneapolis,
MN), Kyle; Richard F. (Minneapolis, MN) |
Family
ID: |
27026906 |
Appl.
No.: |
06/907,594 |
Filed: |
September 12, 1986 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
426092 |
Sep 28, 1982 |
04546501 |
Oct 15, 1985 |
|
|
Current U.S.
Class: |
623/23.35;
606/62 |
Current CPC
Class: |
A61F
2/30907 (20130101); A61F 2/36 (20130101); A61F
2250/0084 (20130101); A61F 2002/3631 (20130101); A61F
2002/3688 (20130101); A61F 2002/30708 (20130101) |
Current International
Class: |
A61F
2/30 (20060101); A61F 2/36 (20060101); A61F
2/00 (20060101); A61F 002/32 () |
Field of
Search: |
;623/18,19,20,21,22,23 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0016480 |
|
Aug 1980 |
|
EP |
|
0032165 |
|
Jul 1981 |
|
EP |
|
0038902 |
|
Nov 1981 |
|
EP |
|
0038908 |
|
Nov 1981 |
|
EP |
|
2322101 |
|
Nov 1973 |
|
DE |
|
560042 |
|
Mar 1975 |
|
CH |
|
1126961 |
|
Sep 1968 |
|
GB |
|
1285460 |
|
Aug 1972 |
|
GB |
|
1554454 |
|
Oct 1979 |
|
GB |
|
2069340 |
|
Aug 1981 |
|
GB |
|
Other References
Advertisement-Bard Contour Link SP-Prosthesis, Waldemar Link GmbH
& Co. .
Advertisement-Isoelastic Femural Prosthesis Butel..
|
Primary Examiner: Apley; Richard J.
Assistant Examiner: Isabella; David J.
Attorney, Agent or Firm: Sherman and Shalloway
Claims
What is claimed is:
1. In a femoral insert for hip joint prosthesis having a spherical
shaped head member, a neck member connected to the head member and
terminating at a collar, and a shaft member having a proximal
portion connected to the collar and extending approximately half
the extent of the shaft member, and a distal portion extending
therefrom, the improvement comprising
the collar being flush to the anterior and posterior sides of and
extending medially from the shaft member;
the proximal portion having a longitudinal axis and a substantially
straight lateral aspect, an upper half which is broad in the
medial-lateral direction and curved in the medial aspect and having
a generally rectangular cross-section which is widest at the collar
and gradually tapers to a generally square cross-section, and a
lower half which has flat sides and a generally square
cross-section of the upper half;
said neck member being anteverted with respect to the collar and
proximal portion at an angle of about 10.degree. to 20.degree. and
is at angle to said longitudinal axis through said proximal portion
of said shaft member of about 125.degree. to about 140.degree.;
at least one of the anterior and posterior sides of the upper half
of said proximal portion including at least one porous bony
ingrowth surface; and
said distal portion having the curved configuration of an
intramedullary rod and curving in the opposite direction from the
direction of said anteversion of said neck member, and said
proximal portion extending straight in a plane parallel to said
lateral aspect,
whereby firm fixation of the prosthesis is initially provided by
the distal intramedullary rod portion while long term stabilization
is achieved proximally through the bony ingrowth surface.
2. The femoral insert of claim 1 wherein the distal portion has a
generally circular cross-section.
3. The femoral insert of claim 1 or 2 wherein the distal portion is
curved to match the anterior bow of the femur.
4. The femoral insert of claim 3 wherein the distal portion is
fluted.
5. The femoral insert of claim 1 or 2 wherein the distal portion is
fluted.
6. The femoral insert of claim 1 wherein the angle .beta. is about
10.degree. and the angle .alpha. is about 135.degree..
7. The femoral insert of claim 1 wherein said straight lateral
aspect extends in both the upper and lower halves of the proximal
portion.
8. The femoral insert of claim 1 wherein the medial aspect is
curved in the upper half of the proximal portion and is flat in the
lower half of the proximal portion.
9. The femoral insert of claim 5 in which the upper half of the
lateral aspect further comprises an upstanding curved rib which
extends from the underside of the collar and terminates
tangentially into the body of the lateral aspect.
10. The femoral insert of claim 1 which comprises porous bone
ingrowth surfaces on both the posterior and lateral sides
comprising a coating of a sintered titanium metal or alloy having a
pore size in the range of 300 to 400 microns.
11. A femoral insert for hip joint prosthesis which comprises a
spherical shaped head member, a neck member connected to the head
member and terminating at a collar, a long stem member having a
proximal portion connected to the collar and extending
approximately half the extent of the shaft member, and a distal
portion extending therefrom and having the curved configuration of
an intramedullary rod and being curved to match the anterior bow of
the femur, the proximal portion of said long stem having an upper
half which is broad in the medial-lateral direction and curved in
the medial aspect to match the inside contour of the femoral shaft
and having a generally rectangular cross-section which is widest at
the collar and gradually tapers to a generally square
cross-section, said proximal portion having a longitudinal axis
being straight in the anterior and posterior aspects, and a lower
half which has flat sides and substantially the same generally
square cross-section as that of the upper half, said neck member
being anteverted with respect to the collar and proximal portion at
an angle .beta. of about 10.degree. to 20.degree., said distal
portion of said stem member being curved in a direction opposite to
the direction of said anteversion of said neck member, said long
stem member having a length of at least about 200 mm and sufficient
to extend to the intramedullary canal, said neck member forming an
angle to said longitudinal axis through the proximal portion of the
stem member of about 125.degree. to about 140.degree., and porous
bone ingrowth surfaces on both the posterior and lateral sides of
the upper half of the proximal portion of the stem member,
whereby firm fixation of the prosthesis is initially provided
distally by the long curved stem and proximally by the broad upper
half of the proximal portion of the stem member fitting tightly in
the reamed out portion of the femoral canal, including
bone-prosthesis contact area at the curved medial aspect and long
term stabilization is achieved proximally through the growth of
bone into the bony ingrowth surfaces.
12. The femoral insert of claim 11 wherein the distal portion has a
generally circular cross-section and is fluted, and said porous
bone ingrowth surfaces comprise a coating of a sintered titanium
metal or alloy having a pore size in the range of 300 to 400
microns. .Iadd.
13. In a femoral insert for hip joint prosthesis having a spherical
shaped head member, a neck member connected to the head member and
terminating at a shaft member having a proximal portion connected
to the neck member and extending approximately half the extent of
the shaft member, and a distal portion extending therefrom, the
improvement comprising:
the proximal portion having a longitudinal axis and a substantially
straight aspect, an upper half which is broad in the medial-lateral
direction and curved in the medial aspect and having a generally
rectangular cross-section which is widest adjacent the neck member
and gradually tapers to a generally square cross-section, and a
lower half which has flat sides and a generally square
cross-section of the upper half;
said neck member being anteverted with respect to the proximal
portion at an angle of about 10.degree. to 20.degree. and is at an
angle to said longitudinal axis through said proximal portion of
said shaft member of about 125.degree. to about 140.degree.;
at least one of the anterior and posterior sides of the upper half
of said proximal portion including at least one porous bony
ingrowth surface; and
said distal portion having the curved configuration of an
intramedullary rod and curving in the opposite direction from the
direction of said anteversion of said neck member, and said
proximal portion extending straight in a plane parallel to said
lateral aspect,
whereby firm fixation of the prosthesis is initially provided by
the distal intramedullary rod portion while long term stabilization
is achieved proximally through the bony ingrowth surface..Iaddend.
.Iadd.
14. A femoral insert for hip joint prosthesis which comprises a
spherical shaped head member, a neck member connected to the head
member and terminating at a long stem member having a proximal
portion connected to the neck member and extending approximately
half the extent of the shaft member, and a distal portion extending
therefrom and having the curved configuration of an intramedullary
rod and being curved to match the interior bow of the femur, the
proximal portion of said long stem having an upper half which is
broad in the medial-lateral direction and curved in the medial
aspect to match the inside contour of the femoral shaft and having
a generally rectangular cross-section which is widest at the neck
member and gradually tapers to a generally square cross-section,
said proximal portion having a longitudinal axis being straight in
the interior and posterior aspects, and a lower half which has flat
sides and substantially the same generally square cross-section as
that of the upper half, said neck member being anteverted with
respect to the proximal portion at an angle .beta. of about
10.degree. to 20.degree., said distal portion of said stem member
being curved in a direction opposite to the direction of said
anteversion of said neck member, said long stem member having a
length of at least about 200 mm and sufficient to extend to the
intramedullary canal, said neck member forming an angle to said
longitudinal axis through the proximal portion of the stem member
of about 125.degree. to about 140.degree., and porous bone ingrowth
surfaces on both the posterior and lateral sides of the upper half
of the proximal portion of the stem member,
whereby firm fixation of the prosthesis is initially provided
distally by the long curved stem and proximally by the broad upper
half of the proximal portion of the stem member fitting tightly in
the reamed out portion of the femoral canal, including
bone-prosthesis contact area at the curved medial aspect and long
term stabilization is achieved proximally through the growth of
bone into the bony ingrowth surfaces..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a femur prosthetic device. More
particularly, this invention relates to a hip prosthesis adapted
for insertion into the upper medullary canal in the femur of a
patient. The hip prosthesis of this invention is of the type
generally characterized as including a head or ball member, a shaft
member for insertion into the intermedullary canal, and a neck
member connecting the ball and shaft or stem member, and also
including at least one porous metal surface portion which provides
for stabilization by bone ingrowth without requiring any
cement.
2. Description of the Prior Art
Hip prostheses are known in the art and these have included various
design configurations of the various components, including the head
member, neck, collar and shaft. Both straight and curved shafts as
well as fluted shafts are known. Representative of these known hip
prostheses are those described in the following: U.S. Pat. No.
4,279,042--T. P. Andriacchi, et al; U.S. Pat. No. 3,965,490--I. P.
Murray, et al; U.K. Patent Application, G.B. No. 2,069,340A--K.
Hardinge. Known commercial products include the Bard Contour.TM.
and Link SP-femoral hip prosthesis, manufactured by Waldemar Link
Hamburg, West Germany and the Isoelastique Butel hip prosthesis by
Butel, Grenoble, France.
Prosthetic devices provided with porous surfaces for bone ingrowth
are also known, e.g. U.S. Pat. No. 3,906,440--W. Rostoker, et al
and British Pat. Spec. No. 1,554,454--J. C. Bokros.
Nevertheless, further improvements in the total design of hip
prosthesis are required to assure stable fixation of the implanted
prosthesis at the bone/metal interface. Thus, in cemented
prosthetic devices there has not been satisfactory fixation due to
the various stress loads, i.e. compression, shear and torsion, to
which the implanted device is subjected. These mechanical forces,
especially shear and torsion, weaken the bone cement bond. In
addition, it is known that there is a tendency for bone resorption
which also weakens the cement bond between the bone, e.g.
intramedullary canal of the femur, and the femoral prosthesis.
On the other hand, by providing a bone ingrowth surface on the
prosthetic device a more stable fixation would be expected and some
advances along these lines have been made. However, experiments by
the present inventors have shown that bone ingrowth requires the
prosthesis to be stably fixed without movement for at least six
weeks and any relative motion of the prosthesis during that period
prevents or minimizes bony ingrowth.
As a result, an incidence of ten to twenty percent of femoral stem
loosening or failure in total hip arthroplasty patients followed
over 5 or more years, especially in younger patients, has been
reported.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a femoral
hip prosthesis which avoids these problems of prior art
devices.
A particular object of the invention is to provide a femoral hip
prosthesis which combines long term stabilization by bone ingrowth
proximally with initial stable fixation distally.
A further object of the invention is to provide a hip prosthesis
which closely approximates in geometry and curvature the natural
femur, including a curved long stem or shaft having a fluted design
in the distal portion, to obtain maximum torque resistance, which
is wide in the medial-lateral direction and curved medially in the
proximal portion to maximize bone-prosthesis contact area, and
which has a bone ingrowth media on both the anterior and posterior
aspects in the proximal portion of the shaft.
A still further object of the invention is to provide a femoral hip
prosthesis in which the femoral head and neck are anteverted from
the collar at about 10.degree., and at an angle with respect to the
shaft of the prosthesis of about 135.degree., and wherein the
collar extends medially from the prosthesis to allow load (stress)
sharing and distribution with the bone to an extent of about 30% of
the total load, with the remaining 70% being borne by the shaft
(stem).
Generally speaking, these and other objects of the invention, which
will become evident from the following more detailed description
and specific embodiments, are accomplished by a femoral insert for
hip joint prosthesis having a spherical shaped head member, a neck
member connected to the head member and terminating at a collar,
and a shaft member connected at its proximal end to the collar and
including a proximal portion and a distal portion. The proximal
portion has a cross-section which is rectangular at the proximal
end at the collar and gradually tapers to a relatively constant
square cross-section. The distal portion of the shaft member or
stem has the configuration of and functions as an intramedullary
rod, for example, a generally circular cross-section which is
curved to match the anterior bow of the femur. The upper half of
the proximal portion is wide in the medial-lateral direction with
flat anterior and posterior sides, is curved medially, and may be
straight or curved in the lateral aspect. The lower half of the
proximal portion is straight in the medial and lateral aspects as
well as in the anterior and posterior sides. A porous bone ingrowth
surface, such as sintered titanium metal, is provided on at least
one of the proximal anterior and proximal posterior sides. The
collar is flush with the anterior and posterior sides and extends
medially. Accordingly, firm fixation of the prosthesis is initially
provided by the distal intramedullary rod portion while long term
stabilization is achieved proximally through the bony ingrowth
surface.
The neck member may be anteverted with respect to the collar at an
angle of about 10.degree. to about 20.degree. and may be at an
angle to the longitudinal axis through the proximal portion of the
shaft of about 125.degree. to about 140.degree.. The curved distal
portion of the shaft is also preferably fluted.
In one embodiment, the lateral aspect of the shaft is straight in
the entire proximal portion. In an alternative embodiment, the
upper portion of the lateral aspect is curved over about the same
or shorter length as the medial curve but with a slightly smaller
radius of curvature. In this embodiment, the curved upper portion
of the lateral aspect includes an upstanding curved rib which
extends from the underside of the collar and terminates
tangentially into the body of the lateral aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with respect
to specific embodiments thereof with the aid of the accompanying
drawings in which:
FIG. 1 is a front elevation view of an embodiment of the prosthetic
device of the invention shown installed within the intramedullary
of a left femur;
FIG. 2 is a side elevation view of the left leg prosthetic device
of FIG. 1;
FIG. 3 is a top view of the left leg prosthetic device of FIG.
1;
FIG. 4 is a front elevation view similar to FIG. 1 of a right leg
prosthetic device according to the invention;
FIG. 5 is a side elevation view of the right leg prosthetic device
of FIG. 4;
FIG. 6 is a top view of the right leg prosthetic device of FIG.
4;
FIG. 7 is a section view in the direction of line 7--7 of FIG.
4.
FIG. 8 is a section view in the direction of line 8--8 of FIG.
4;
FIG. 9 is a section view in the direction of line 9--9 of FIG.
4;
FIG. 10 is a partial side elevation view of an alternative
embodiment of a left leg prosthetic device according to the
invention.
FIG. 11 is a view, partially in section, in the direction of line
11--11 of FIG. 10; and
FIG. 12 is a section view in the direction of line 12--12 of FIG.
11.
DETAILED DESCRIPTION OF THE INVENTION
Firm implantation of the femoral insert prosthetic device of this
invention is provided by combining a unique configuration of the
component parts, namely spherical head, neck, collar, and shaft
which closely approximate the natural configuration of the normal
femoral shaft, femoral neck and head, and specifically an
anteverted femoral neck, with a shaft which, in the proximal
portion, is wide in the medial-lateral direction, at least
partially straight in the lateral direction and curved in the
medial direction to match the inside contour of the femoral shaft
and in the distal portion is fabricated to the configuration of an
intramedullary rod, preferably it is curved to match the anterior
bow of the femur. Opposite curvatures are provided for each of the
left and right leg femoral prostheses.
In addition, at least one of, and preferably both, the anterior and
posterior aspects are provided with a bone ingrowth surface and,
therefore, the need for cement fixation, which is one of the major
causes of total hip failure, is eliminated.
Accordingly, firm fixation is achieved in the greater trochanter
region by making the upper segment (proximal end) of the shaft
broad in the medial-lateral direction. The bone ingrowth surfaces
on the anterior and/or posterior aspects provide still further
fixation of the proximal portion of the shaft while the
intramedullary rod portion of the shaft at the distal end is firmly
fixed by virtue of its being curved to stimulate the anatomical
configuration of the normal femur. The initial stable fixation of
the distal intramedullary rod portion of the shaft in the
intramedullar of the femoral shaft permits bone ingrowth to occur
proximally to provide an overall secure fit of the entire
prosthesis without requiring any adhesive cement.
Turning now to to the drawings, a left femoral prosthesis is shown
generally at 1 in FIGS. 1-3. The prosthetic device includes
spherical head member 2, neck member 3, collar 4 and shaft member
5. The prosthetic device is preferably fabricated from titanium
metal or titanium alloy, but any other biologically compatible,
inert metal that has sufficient mechanical strength can be
used.
FIGS. 4, 5 and 6 are similar to FIGS. 1, 2 and 3, respectively, but
are for a right femoral prosthesis. In FIGS. 4-9, the spherical
head member, neck member, collar and shaft member are designated by
42, 43, 44 and 45, respectively.
As will be described in greater detail below, the direction of
angulation of the neck member and the direction of the curved bow
of the distal stem portion are in one direction for the left
femoral prosthesis and in the opposite direction for the right
femoral prosthesis. However, the right and left femoral prostheses
are otherwise constructed in the same manner and are, generally
speaking, mirror images of each other.
Head member 2, 42 is generally globular in shape and assumes
somewhat more than a hemisphere. The head member has a highly
polished bearing surface to mate with the hip socket, which may be
the natural hip socket or an artifical prosthesis in the case of
total hip replacement. The femoral head member has a diameter of
about 28 millimeters, although smaller and larger sizes can be
stocked or prepared as needed for individual patients.
The underside 52 of head member 42 is substantially flat (FIG. 7),
although it can also be slightly curved, either convexly or
concavely, to where the neck member joins the underside in
substantially the center portion thereof.
The neck member which connects the head member to the shaft at the
collar, is generally rectangular in cross-section and is broader in
the inferior and superior direction than in the anterior and
posterior direction. The base of the neck at the collar is broader
than its apex where it joins the head to approximate the pyrimidal
configuration of a normal femoral neck. Additional structural
strength is provided by having the base and the apex diverge
outwardly at the juncture with the collar and head member,
respectively.
As best seen in FIG. 2, the longitudinal axis 13 of neck 3,
intersects the longitudinal axis 15, of shaft 5 at an angle .alpha.
in the range of 125.degree. to 140.degree., preferably about
135.degree.. The neck member is also anteverted with respect to the
collar by the angle .beta., between longitudinal axis 13 and line
14 which is an extension of longitudinal axis 15 of shaft member 5
through the upper proximal portion thereof, which ranges from about
10.degree. to about 20.degree., preferably about 10.degree. to
12.degree., especially about 10.degree.. As seen in FIG. 3, line 14
is parallel to and equidistant from the anterior and posterior
edges of collar 4.
Collar 4, 44, extends medially from the shaft member at extension
16, 56 but is otherwise flush with the lateral sides of the shaft
member. As seen in FIG. 7, extension 56 has an arcuate elliptical
periphery 59 which bulges slightly from either of the anterior 57
and posterior 48 lateral sides of shaft member 45. The extended
collar rests on the upper surface of the femoral shaft bone (as
shown in phantom outline in FIG. 1 and FIG. 2) to provide for
medial load transfer and stabilization of the implanted
prosthesis.
The upper proximal portion 6 of shaft member 5 is broad in the
medial-lateral direction with the greatest width occurring at the
juncture with collar 4 and gradually tapering to a substantially
constant width at or near the midpoint thereof. In the widened
upper medial-lateral region of the upper proximal portion bone
ingrowth pads 20 and 60, 61 are provided on the anterior and
posterior lateral sides, respectively. These are preferably formed
from sintered titanium metal of 300-400 microns pore size, although
any other bone ingrowth media or construction can be used.
Preferably, as shown in FIG. 7, the bone ingrowth pads are securely
fitted within the notched undercut portions 62, 63 in the anterior
and posterior lateral faces 57, 58, respectively. The outer
surfaces of the bone ingrowth pads are preferably flush with the
lateral sides 17, 18 and 57, 58, respectively. The configuration of
the bone ingrowth pads is not particularly critical but generally
they will be in the same general configuration as the lateral sides
and should cover the majority of the surface area of the upper
portion, for example, about 50 to about 90%, of the area of the
upper portion, or about 1 to 3 square inches for each pad.
The upper proximal portion has a straight lateral aspect 26 and is
slightly curved in the upper half of the medial aspect 24 to match
the inside contour of the femoral shaft thereby allowing for firm
fixation in the greater trochanteric region. The curve of the upper
medial aspect makes a smooth transition with the lower flat medial
aspect which is substantially parallel to the straight lateral
aspect.
The lower distal portion 7 of shaft member 5 is curved to match the
anterior bow of the femur and is fluted over its entire length
which is about one-half of the total length of the shaft member
from collar 4 to the free end 31. The curved/fluted configuration
enables the distal portion to function as an intramedullary rod to
again provide firm fixation of the prosthesis in the femoral shaft
at the distal end so that bone ingrowth can proceed at the proximal
end.
As can be seen from FIGS. 1 and 4, the curve of the distal portion
of the shaft is in the opposite direction than the direction of
anteversion of neck member 3, 43. This can also be seen in FIGS. 3
and 6 where the free end 31, 71 of the shaft member is "behind"
collar 4, 44 or into the plane of the paper while neck member 3, 43
and head member 2, 42 are "in front of" collar 4, 44 or out of the
plane of the paper. In other words, the right hip prosthesis and
left hip prosthesis are mirror images of each other.
As seen in FIG. 8, the lower half of the upper proximal portion 46
of shaft member 45 has a substantially square cross-section with
slightly rounded corners. The upper half of the upper proximal
portion which includes the curved medial aspect 64 has a
rectangular cross-section (FIG. 7). The fluted distal portion 47
has a substantially circular cruciform cross-section (FIG. 9).
Flutes 8, 48 are cicumferentially spaced at 90.degree. intervals
around the distal portion 7, 47 and their edges merge smoothly into
the rounded ribs 9, 49 which separate them and which are
circumscribed within a circle having a diameter which is
substantially equal to the length of a side of the square
cross-section of the upper proximal portion 6, 46, i.e. the
distance between the medial and lateral aspects and between the
anterior and posterior sides. The width and depth of each of the
four flutes is substantially constant along the length of the
distal portion.
FIGS. 10, 11 and 12 illustrate a slightly modified embodiment of a
hip prosthesis (illustrated for the left hip only) according to the
invention.
In this embodiment, the lateral aspect 126 in the upper region 135
of the upper proximal portion 106 is also curved but with a
somewhat smaller radius of curvature than the radius of curvature
for the curved medial aspect 124. Curved rib 138 is provided in the
central portion of the upper region 135 beginning at the underside
of collar 104 and terminating in the lateral aspect at or near the
transition from the curved upper region 135 to the straight lower
region 136 of lateral aspect 126. As seen in FIGS. 10 and 11, rib
138 blends smoothly and tangentially into the lateral aspect. By
appropriate reaming of the greater trochanteric region of the femur
additional contact area can be provided between the prosthesis and
the femur at the rib 138. Also in this embodiment the extension 116
on collar 104 has a more rounded configuration than the elliptical
configuration of extension 16 and does not bulge beyond the lateral
walls.
It is envisioned that the hip prosthesis can be stocked in several
standard sizes and combinations. For example, the femoral neck can
be stocked in lengths 1 of 28 mm, 30 mm, 34 mm and 40 mm, measured
from the base of the collar to the center of the femoral head.
Standard sizes for the length L of the shaft member, measured from
the base of the collar to the free end, would typically be 200 mm,
220 mm, 230 mm, 250 mm, 260 mm and 270 mm.
For a typical embodiment of the right and left femoral inserts
illustrated in FIGS. 1-9 with a 28 mm diameter spherical head the
neck member will be about 34 mm in length, the overall length of
the collar LC will be about 42 mm, the width W is about 15 mm, the
length L is about 230 mm and the length of the fluted distal
portion is about 125 mm.
Accordingly, the hip prosthesis of the present invention will have
the following advantages:
1. Allows early weight bearing, such as in conventional total hip
arthoplasty, but not present ingrowth systems;
2. Avoids use of cement;
3. Ideal for young patients, need not enlarge acetabulum in
contrast to resurfacing arthoplasty;
4. Does not require any unconventional surgical procedures since
orthopaedic surgeons are familiar with reaming the intramedullary
canal;
5. Reduces loosening by a combination of proximal bony ingrowth and
distal fixation.
* * * * *