PROSTHETIC HIP IMPLANTS

IMPLANTS DE HANCHE PROTHETIQUES

English Abstract

Prosthetic hip stems for use in prosthetic hip joints are designed to achieve
more optimized
outcomes with certain types of patient anatomy, such as the anatomy of female
patients and/or
patients having osteoporosis. For these optimized outcomes, each hip stem in a
family or set of
hip stems has diaphyseal width, metaphyseal width, offset, and head height
dimensions. In a set
of hip stems of increasing nominal size, the diaphyseal width dimension
increases substantially
non-proportionally to the corresponding increase of the metaphyseal width,
offset, and head
height dimensions, thereby providing a family or set of hip stems that is
particularly adapted for
patients having osteoporosis, in which the cortical bone of the diaphysis of
the femur becomes
thinner with progression of the osteoporosis.

French Abstract

Publié sans précis

Claims

WHAT IS CLAIMED IS:
1. A set of prosthetic hip stems, comprising:
a plurality of hip stems of increasing nominal size, each said hip stem having
a distal
width dimension x between 12 and 21 mm; a medial side, and a central axis;
said hip stems each having a metaphyseal width dimension y1 measured between
the
medial side and the central axis and defined as a function of x falling within
a conceptual
boundary defined between the following lines:
y1 = 0.053x + 19.17 mm and
y1 = 0.031x + 24.61 mm;
said hip stems each having an offset dimension y2 defined as a function of x
falling
within a conceptual boundary defined between the following lines:
y2= 31 mm and
y2 = 1.46x + 19.86 mm; and
said hip stems each having a head height dimension y3 defined as a function of
x falling
within a conceptual boundary defined between the following lines:
y3 = 0.57x + 10.54 mm and
y3 = 1.21x + 11.82 mm.
2. The set of prosthetic hip stems of Claim 1, wherein said hip stems with
a distal width
dimension x between 13 and 21 mm each have an offset dimension y2 defined as a
function of x
falling within a conceptual boundary defined between the following lines:
y2 = 0.36x + 26.40 mm and
y2 = 1.07X + 24.82 mm.
3. The set of prosthetic hip stems of Claim 1, wherein said hip stems with
a distal width
dimension x between 13 and 21 mm each have an offset dimension y2 defined as a
function of x
falling within a conceptual boundary defined between the following lines:
y2= 0.93X + 19.21 mm and
y2 = 1.07x + 24.82 mm.
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4. The set of prosthetic hip stems of Claim 1, wherein said hip stems with
a distal width
dimension x between 13 and 21 mm each have an offset dimension y2 defined as a
function of x
substantially according to the following line:
y2 = 1.07x + 24.82 mm.
5. The set of prosthetic hip stems of Claim 1, wherein said hip stems each
have an offset
dimension y2 defined as a function of x substantially according to the
following line:
y2 = 1.07x + 20.82 mm.
6. The set of prosthetic hip stems of Claim 1, wherein each hip stem has a
uniform cross-
sectional width dimension along between 35% and 65% of a distance between said

metaphyseal width dimension and a distal end of said hip stem.
7. The set of prosthetic hip stems of Claim 1, wherein each hip stem
further comprises:
a core;
a polymer matrix layer covering at least a portion of said core; and
a porous metal layer substantially covering said polymer layer.
8. A set of prosthetic hip stems, comprising:
a plurality of hip stems of increasing nominal size, each said hip stem having
a distal
width dimension x between 13 and 18 mm, a medial side, and a central axis,
said hip stems each having a metaphyseal width dimension y1 measured between
the
medial side and the central axis and defined as a function of x falling within
a conceptual
boundary defined between the following lines:
y1 = 0.053x + 19.17 mm and
y1 = 0.031x + 24.61 mm;
said hip stems each having an offset dimension y2 defined as a function of x
falling
within a conceptual boundary defined between the following lines:
y2 = 31 mm and
y2 = 1.46x + 19.86 mm; and
said hip stems each having a head height dimension y3 defined as a function of
x falling
within a conceptual boundary defined between the following lines:
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y3 = 0.57x + 10.54 mm and
y3 = 1.21x + 11.82 mm.
9. The set of prosthetic hip stems of Claim 8, wherein said hip stems each
having an offset
dimension y2 defined as a function of x falling within a conceptual boundary
defined between
the following lines:
y2 = 0.36x + 26.40 mm and
y2 = 1.07x + 24.82 mm.
10. The set of prosthetic hip stems of Claim 8, wherein said hip stems each
have an offset
dimension y2 defined as a function of x falling within a conceptual boundary
defined between
the following lines:
y2 = 0.93x + 19.21 mm and
y2 = 1.07x + 24.82 mm.
11. The set of prosthetic hip stems of Claim 8, wherein said hip stems each
have an offset
dimension y2 defined as a function of x substantially according to the
following line:
y2 = 1.07x + 24.82 mm.
12. The set of prosthetic hip stems of Claim 8, wherein said hip stems each
have an offset
dimension y2 defined as a function of x substantially according to the
following line:
y2 = 1.07x + 20.82 mm.
13. The set of prosthetic hip stems of Claim 8, wherein each hip stem has a
uniform cross¨
sectional width dimension along between 35% and 65% of a distance between said

metaphyseal width dimension and a distal end of said hip stem.
14. The set of prosthetic hip stems of Claim 8, wherein each hip stem
further comprises:
a core;
a polymer matrix layer covering at least a portion of said core; and
a porous metal layer substantially covering said polymer layer.
15. A set of prosthetic hip stems, comprising:
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a plurality of hip stems of increasing nominal size, each said hip stem having
a distal
width dimension x between 13 and 18 mm; and
said hip stems each having an offset dimension y1 defined as a function of x
falling
within a conceptual boundary defined between the following lines:
y1 =31 mm and
y1 = 1.46x + 19.86 mm.
16. The set of prosthetic hip stems of Claim 15, wherein said hip stems
each have an offset
dimension y1 defined as a function of x falling within a conceptual boundary
defined between
the following lines:
y1 = 0.36x + 26.40 mm and
y1 = 1.07x + 24.82 mm.
17. The set of prosthetic hip stems of Claim 15, wherein said hip stems
each have an offset
dimension y1 defined as a function of x falling within a conceptual boundary
defined between
the following lines:
y1 = 0.93x + 19.21 mm and
y1 = 1.07x + 24.82 mm.
18. The set of prosthetic hip stems of Claim 15, wherein said hip stems
each have an offset
dimension y1 defined as a function of x substantially according to the
following line:
y1 = 1.07x + 24.82 mm.
19. The set of prosthetic hip stems of Claim 15, wherein said hip stems
each having an
offset dimension y1 defined as a function of x substantially according to the
following line:
y1 = 1.07x + 20.82 mm.
20. The set of prosthetic hip stems of Claim 15, wherein each hip stem has
a metaphyseal
width dimension, and has a uniform cross-sectional width dimension along
between 35% and
65% of a distance between said metaphyseal width dimension and a distal end of
said hip stem.
21. The set of prosthetic hip stems of Claim 15, wherein each hip stem
further comprises:
a core;
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a polymer matrix layer covering at least a portion of said core; and
a porous metal layer substantially covering said polymer layer.
22. The set of prosthetic hip stems of Claim 1, wherein each hip stem
includes a stem
portion and a neck portion, the metaphyseal. width dimension of each hip stem
measured
medially from the central axis of the hip stem to an intersection between the
stem portion and
the neck portion.
23. The set of prosthetic hip stems of Claim 6, wherein the distal width
dimension of each
hip stem is measured at an area of the hip stem having the uniform cross-
sectional width
dimension.
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Description

CA 02674288 2014-12-05
PROSTHETIC HIP IMPLANTS
BACKGROUND
1. Field of the Invention.
[0001] The present invention relates to prosthetic hip implant components,
which
generally include a hip stem for implantation in the proximal femur and an
acetabular cup for
implantation in the acetabulum. In particular, the present invention relates
to prosthetic hip
stems and acetabular cups which include improved features designed to achieve
more optimized
outcomes with certain types of patient anatomy, such as the anatomy of female
patients and/or
patients having osteoporosis.
2. Description of the Related Art.
[0002] Orthopedic implants are commonly used to replace some or all of a
patient's hip
joint in order to restore the use of the hip joint, or to increase the use of
the hip joint, following
deterioration due to aging or illness, or injury due to trauma. In a hip
replacement, or hip
arthroplasty procedure, a femoral component is used to replace a portion of
the patient's femur,
including the femoral neck and head. The femoral component is typically a hip
stem, which
includes a stem portion positioned within the prepared femoral canal of the
patient's femur and
secured via bone cement, or by a press-fit followed by bony ingrowth of the
surrounding tissue
into a porous coating of the stem portion. The hip stem also includes a neck
portion adapted to
receive a prosthetic femoral head. The femoral head is received within a
prosthetic acetabular
component, such as an acetabular cup received within the prepared recess of
the patient's
acetabulum.
[0003] One known hip stem includes a core formed of either a cobalt-
chromium-
molybdenum alloy or titanium, and a porous surface layer in the form of a
matrix of small
metallic beads or a wire mesh. Typically, the porous surface layer is sintered
to the core by
heating the core and the porous surface layer to a high temperature in order
to cause the porous
surface layer and core to fuse, melt, or bond together along their interface.
U.S. Patent Nos.
6,395,327, 6,514,288, and 6,685,987, each assigned to the assignee of the
present invention,
disclose various methods of enhancing the fatigue strength and the connection
between the
core and the porous surface layer of the foregoing types of hip stems.
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[0004] Some medical device manufacturers may manufacture a single custom
implant
prosthesis to accommodate the anatomy of a specific patient. Also, although
prosthetic hip
implants in a line of mass manufactured prostheses are provided in a range of
varying sizes and
are selected by surgeons to best fit the anatomy of a particular patient,
improvements in the
design of prosthetic hip implants are desired.
SUMMARY
[0005] The present invention provides prosthetic hip stems for use in
prosthetic hip joints
and, in particular, provides prosthetic hip stems that are designed to achieve
more optimized
outcomes with certain types of patient anatomy, such as the anatomy of female
patients and/or
patients having osteoporosis. Each hip stem in a family or set of hip stems
has diaphyseal width,
metaphyseal width, offset, and head height dimensions. In a set of hip stems
of increasing
nominal size, the diaphyseal width dimension increases substantially non-
proportionally to the
corresponding increase of the metaphyseal width, offset, and head height
dimensions, thereby
providing a family or set of hip stems that is particularly adapted for
patients having
osteoporosis, in which the cortical bone of the diaphysis of the femur becomes
thinner with
progression of the osteoporosis.
[0006] In one form thereof, the present invention provides a set of
prosthetic hip stems,
including a plurality of hip stems of increasing nominal size, each hip stem
having a distal width
dimension x between 12 and 21 mm; the hip stems each having a metaphyseal
width dimension
yi defined as a function of x falling within a conceptual boundary defined
between the following
lines: yi = 0.053x + 19.17 and yi = 0.031x + 24.61; the hip stems each having
an offset
dimension y2 defined as a function of x falling within a conceptual boundary
defined between the
following lines: y2 = 31 and y2 = 1.46x + 19.86; and the hip stems each having
a head height
dimension y3 defined as a function of x falling within a conceptual boundary
defined between the
following lines: y3 = 0.57x + 10.54 and y3 = 1.21x + 11.82.
[0007] In another form thereof, the present invention provides a set of
prosthetic hip
stems, including a plurality of hip stems of increasing nominal size, each hip
stem having a distal
width dimension x between 13 and 18 mm, the hip stems each having a
metaphyseal width
dimension yi defined as a function of x falling within a conceptual boundary
defined between the
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following lines: yi = 0.053x + 19.17 and yi = 0.031x + 24.61; the hip stems
each having an
offset dimension y2 defined as a function of x falling within a conceptual
boundary defined
between the following lines: y2 = 31 and y2 = 1.46x + 19.86; and the hip stems
each having a
head height dimension y3 defined as a function of x falling within a
conceptual boundary defined
between the following lines: y3 = 0.57x + 10.54 and y3 = 1.21x + 11.82.
[0008] In a further form thereof, the present invention provides a set of
prosthetic hip
stems, including a plurality of hip stems of increasing nominal size, each hip
stem having a distal
width dimension x between 13 and 18 mm; the hip stems each having an offset
dimension yi
defined as a function of x falling within a conceptual boundary defined
between the following
lines: yi = 31 and yi = 1.46x + 19.86.
[0009] In another form thereof, the present invention provides a set of
prosthetic hip
stems, each hip stem having a metaphyseal width dimension and a uniform cross
section along
between 35% and 65% of a distance between said metaphyseal width dimension and
a distal end
of said hip stem.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above-mentioned and other features of this disclosure, and the
manner of
attaining them, will become more apparent and will be better understood by
reference to the
following description of embodiments taken in conjunction with the
accompanying drawings,
wherein:
[0011] Fig. 1 is a first isometric view of a hip stem according to the
present invention;
[0012] Fig. 2 is a second isometric view of the hip stem of Fig. 1;
[0013] Fig. 3 is a first isometric view of the core of the hip stem of
Figs. 1 and 2;
[0014] Fig. 4 is a second isometric view of the core of the hip stem of
Figs. 1 and 2;
[0015] Fig. 5 is a sectional view through the hip stem, taken along line
5-5 of Fig. 2;
[0016] Fig. 6 is a side view of the proximal end of the hip stem, showing
the contoured
neck portion and the version indicator feature;
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[0017] Fig. 7 is an isometric view of the proximal end of the hip stem,
showing the
contoured neck portion;
[0018] Fig. 8 is a side view of the proximal end of the hip stem, shown
with a femoral
head thereof fitted within an acetabular cup which is in turn positioned
within an acetabulum,
and illustrating the relatively large degree of articulating movement possible
therebetween;
[0019] Fig. 9 is a schematic top view of the hip stem, showing relative
neutral and
anteversion positions of the hip stem with respect to a patient in solid and
dashed lines,
respectively;
[0020] Fig. 10 is an isometric view of the proximal end of the core of
the hip stem,
showing the curved groove therein;
[0021] Fig. 11 is an isometric view of a portion of the distal end of the
core of the hip
stem, showing the distal boss of the core, including a plurality of dimples
around the boss and a
plurality of ridges in the stem portion of the core;
[0022] Fig. 12 is a schematic proximal end view of several hip stems each
having an
integral stem portion and neck portion and showing a range of possible
anteversion angles for the
neck portions;
[0023] Fig. 13 is a proximal end view of components of a modular hip stem
system,
including a hip stem portion and a plurality of anteverted modular neck
portions which may be
used with the hip stem portion;
[0024] Fig. 14 is a proximal end view of components of a modular hip stem
system,
including an integral stem portion and neck portion, and a plurality of
anteverted modular
femoral heads which may be used with the hip stem;
[0025] Fig. 15 is an end view of a modular femoral head taken along line
15-15 of Fig.
14;
[0026] Fig. 16 is an exploded, partially sectioned proximal end view of
components of a
modular hip stem system showing a hip stem portion, an anteverted modular neck
portion, and
an anteverted modular femoral head;
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[0027] Fig. 17 is an assembled, partially sectioned proximal end view of
the components
of the modular hip stem system of Fig. 16;
[0028] Fig. 18 is an anterior/posterior schematic view of several hip
stems each having
an integral stem portion and neck portion and showing a range of possible
neck/shaft angles for
the neck portions;
[0029] Fig. 19 is a partially sectioned anterior/posterior view of
components of a modular
hip stem system including a hip stem portion and a plurality of modular neck
components having
various neck/shaft angles which may be used with the modular hip stem portion;
[0030] Fig. 20 is a cross-sectional view of a portion of a hip stem
within the diaphysis of
a femur, further illustrating an embodiment of a distal end fixation mechanism
in a non-
expanded condition;
[0031] Fig. 21 is a cross-sectional view of a portion of the hip stem of
Fig. 20, further
illustrating the distal end fixation mechanism in an expanded condition;
[0032] Fig. 22 is a cross-sectional view of a portion of a hip stem
within the diaphysis of
a femur, further illustrating an alternative embodiment of a distal end
fixation mechanism in a
non-expanded condition;
[0033] Fig. 23 is a cross-sectional view of a portion of the hip stem of
Fig. 22, further
illustrating the distal end fixation mechanism in an expanded condition;
[0034] Fig. 24 is an exploded view of a flexible acetabular cup and
liner, and a pelvic
region of a patient's anatomy;
[0035] Fig. 25 is a sectional view of an acetabular cup according to
another embodiment;
[0036] Fig. 26 is a partial sectional view of an acetabular cup according
to a further
embodiment;
[0037] Fig. 27 is a sectional view of a hip stem according to a further
embodiment;
[0038] Fig. 28 is an anterior/posterior view of a hip stem according to a
further
embodiment, showing portions of the posterior femur in phantom;
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[0039] Fig. 29 is a medial/lateral view of the hip stem of Fig. 28,
showing portions of the
posterior femur in phantom;
[0040] Figs. 30A, 30B, and 30C are partial sectional views of femurs
illustrating Type A,
Type B, and Type C bone, respectively;
[0041] Figs. 31A, 31B, and 31C are partial anterior elevational views of
three exemplary
hip stems of increasing nominal size;
[0042] Fig. 31D is a partial sectional view of a resected proximal femur
having a hip
stem fitted therein;
[0043] Figs. 32A, 32B, and 32C are partial anterior elevational views of
three hip stems
of increasing nominal size in accordance with the present invention;
[0044] Fig. 32D is a full anterior elevational view of a hip stem in
accordance with the
present invention;
[0045] Fig. 32E is a sectional view taken along line 32E-32E of Fig. 32D;
and
[0046] Figs. 33A, 33B, and 33C are graphs of diaphyseal width vs.
metaphyseal width,
offset, and head height, respectively, of exemplary sets of hip stems in
accordance with the
present invention.
[0047] Corresponding reference characters indicate corresponding parts
throughout the
several views. The exemplifications set out herein illustrate embodiments of
the disclosure, and
such exemplifications are not to be construed as limiting the scope of the
invention in any
manner.
DETAILED DESCRIPTION
[0048] Referring to Figs. 1-5, a prosthetic hip stem 20 according to the
present invention
is shown, which generally includes stem portion 22, and neck portion 24
extending at a generally
obtuse angle from stem portion 22 and including a tapered femoral head fitting
26. Stem portion
22 of hip stem 20 is received within a prepared femoral canal of a patient's
femur to anchor hip
stem 20 within the patient's femur. As discussed below, a femoral head
component is fitted on
femoral head fitting 26, and is in turn received within a prosthetic
acetabular component, such as
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an acetabular cup seated within a prepared recess in the patient's acetabulum,
to thereby provide
an articulating, prosthetic hip joint. Hip stem 20 further defines proximal
end 28, distal end 30,
lateral side 32, medial side 34, as well as opposing anterior and posterior
sides depending upon
whether hip stem 20 is used with a patient's right or left femur.
[0049] Referring particularly to Figs. 3-5, hip stem 20 generally
includes a substrate or
core 36 generally defining stem portion 22 and neck portion 24 and, as best
seen in Fig. 5, a
polymer matrix layer 38 substantially covering stem portion 22 of core 36, and
a porous metal
layer 40 substantially covering polymer matrix layer 38. Polymer matrix layer
38 and porous
metal layer 40 may cover substantially all of stem portion 22 of core 36, or
alternatively, may
cover only selected portions thereof, as desired. In one embodiment, stem
portion 22 has a
length L (Fig. 1) extending generally from proximal end 28 to distal end 30,
and, in one
embodiment, stops slightly short of each end 28, 30 by approximately 0.3
inches. Porous metal
layer 40 extends along length L from approximately 10, 20, 30% thereof or as
much as 70, 80,
90, or 95% thereof. In one embodiment, porous metal layer 40 extends along
stem portion 22 for
approximately 33% of the length thereof. In another embodiment, porous metal
layer 40 covers
approximately 33% of proximal end 28 of stem portion 22, i.e., a midcoat
porous stem.
[0050] Core 36 may be made from a cobalt-chromium-molybdenum alloy or a
titanium
alloy, for example, via a forging or casting process, followed by machining to
achieve a desired
shape or profile. Polymer matrix layer 38 may be formed of an inert
polyaryletherketone
("PAEK") polymer such as, for example, polyetheretherketone ("PEEK"). Porous
metal layer 40
may be a metal wire mesh of titanium fibers, or alternatively, may also
comprise a metal bead
matrix or other porous metal structures produced in accordance with Trabecular
MetalTM
technology of Zimmer, Inc. of Warsaw, Indiana, for example.
[0051] Hip stem 20 may be manufactured as follows. First, core 36 is
forged, followed
by machining core 36 after forging to form a desired shape or profile for core
36. Core 36 is
then grit blasted to sufficiently roughen its surface, and then is heat
treated to facilitate polymer
flow across core 36 during the injection molding process. Thereafter, core 36
is positioned
within an injection molding machine with stem portion 22 of core 36 positioned
within porous
metal layer 40, with a gap provided therebetween. Thereafter, polymer matrix
layer 38 is
injected into the space between core 36 and porous metal layer 40 through
suitable gates, with
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polymer matrix layer 38 permeating into porous metal layer 40 and into the
surface of stem
portion 22 of core 36 via grooves 52, dimples 56, ridges 58, and/or flats 60.
Upon cooling of
polymer matrix layer 38, porous metal layer 40 is firmly bonded or secured to
stem portion 22 of
core 36. Advantageously, core 36 is not subjected to a sintering process to
apply porous metal
layer 40, thereby maintaining the fatigue strength of core 36.
[0052] Referring to Figs. 6-8, neck portion 24 of hip stem 20 is contoured
to allow for
increased articulating movement of hip stem 20 with respect to an acetabular
component in a
prosthetic hip joint, as illustrated in Fig. 8. As shown in Figs. 6 and 7,
neck portion 24 of hip
stem 20 includes a neck section 42 which extends between stem portion 22 and
femoral head
fitting 26. Neck section 42 is shaped with a relatively thin or slender
profile, having a diameter
along a substantial portion thereof which is less than the maximum diameter of
femoral head
fitting 26. In particular, neck section 42 may include a plurality of
scalloped recesses 44
therearound which may be formed by removal of material from the original
forging of core 36 by
machining. As shown in Fig. 8, the thin or slender profile of neck section 42
allows for an
increased degree of angular, articulating movement of hip stem 20 with respect
to the acetabular
component in a prosthetic hip joint when a prosthetic femoral head 43 is
fitted on fitting 26 of
stem 20 and received within the acetabular component, which is shown in Fig. 8
as an acetabular
cup 46 positioned within a prepared recess in the surrounding acetabulum.
Also, as shown in
Figs. 2 and 4, neck portion 24 of core 36 of hip stem 20 may include an
instrument engagement
fitting 47 in proximal end 28 thereof within which an instrument (not shown)
may be engaged to
aid in driving hip stem 20 into the prepared femoral canal of a patient's
femur.
[0053] Referring to Figs. 6 and 7, neck portion 24 of hip stem 20 also
includes a version
indicator feature 48, which is shown herein as a bump or protrusion 50
projecting from medial
side 34 of neck portion 24 of hip stem 20. As explained below, version
indicator feature 48 is a
tactile feature on hip stem 20 which may be felt by a surgeon during
implantation of hip stem 20
to aid the surgeon in positioning hip stem 20 according to a desired version
or alignment. U.S.
Patent No. 6,676,706, assigned to the assignee of the present invention,
discloses a method
for performing a "non-open", or minimally invasive, total hip arthroplasty. In
the foregoing
method, a small anterior incision is made for preparing a recess or seat in
the acetabulum for
receiving an acetabular cup, which is inserted and positioned within
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the acetabulum through the anterior incision. A small posterior incision is
also made for
preparing the femur and for receiving a hip stem, such as hip stem 20, which
is positioned within
the prepared femoral canal of the femur. During this and other minimally
invasive procedures,
the insertion of the hip stem into the prepared femoral canal may not be
directly viewable by the
surgeon, or may be only partially viewable by the surgeon, such as through the
anterior incision.
[0054] Referring to Fig. 9, upon insertion of hip stem 20 into the
prepared femoral canal
through a posterior incision, a surgeon may feel protrusion 50 of version
indicator element 48 by
inserting the surgeon's fingers through the anterior incision, for example, to
position hip stem 20
in an anteversion alignment, shown in dashed lines in Fig. 9, in which neck
portion 24 of hip
stem 20 is rotated approximately 12 to 14 anteriorly with respect to stem
portion 22 from the
neutral version, or direct medial/lateral, alignment shown in solid lines in
Fig. 9. Optionally,
according to some surgical procedures, the surgeon may tactilely align
protrusion 50 of version
indicator element 48 with respect to one or more grooves which are cut in the
medial calcar of
the prepared femur in order to position hip stem 20. Protrusion 50 of version
indicator element
48 may also be used by the surgeon to position hip stem 20 in a position other
than in an
anteversion alignment if needed. Thus, protrusion 50 of version indicator
element 48
advantageously allows the surgeon to position hip stem 20 according to a
desired alignment
during a minimally invasive hip arthroplasty procedure without direct
visualization of hip stem
20.
[0055] Although version indicator feature 48 is shown herein as bump or
protrusion 50,
other tactile elements may be used, such as a recess, a group of recesses, or
a ridge or a group of
ridges, for example, in medial side 34 of neck portion 24 of hip stem 20, or
at another location or
locations on neck portion 24 of hip stem 20.
[0056] Referring to Figs. 10 and 11, core 36 includes a plurality of
features for enhancing
the mechanical interconnection between core 36 and polymer matrix layer 38. As
shown in Fig.
10, proximal end 28 of stem portion 22 of core 36 includes a curved, generally
"candy cane"-
shaped or "number 7"-shaped groove 52 on one or both of the anterior and
posterior sides
thereof. During manufacture of hip stem 20, in which the material of polymer
matrix layer 38 is
injected into the space between core 36 and porous metal layer 40, the
material of polymer
matrix layer 38 flows into and substantially fills grooves 52 to form a robust
mechanical
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interconnection between core 36 and polymer matrix layer 38 upon curing of the
material. The
mechanical interconnection resists relative movement between core 36 and
polymer matrix layer
38, such as rotational movement, responsive to torsional and/or other types of
loading which may
be imposed upon core 36 when hip stem 20 is used in a hip joint, and in
particular, after porous
metal layer 40 becomes substantially fused to the surrounding femoral bone
tissue.
[0057] Referring to Fig. 11, distal end 30 of core 36 includes a boss 54
which provides a
rigid leading surface for insertion of hip stem 20 into a prepared femoral
canal. Boss 54 also
includes a plurality of dimples 56 formed circumferentially therearound.
During manufacture of
hip stem 20, in which the material of polymer matrix layer 38 is injected into
the space between
core 36 and porous metal layer 40, the material of polymer matrix layer 38
flows into and
substantially fills dimples 56 to form a robust mechanical interconnection
between core 36 and
polymer matrix layer 38 upon curing of the material. The mechanical
interconnection also
resists relative movement, such as relative rotational movement, between core
36 and polymer
matrix layer 38 responsive to torsional and/or other types of loading upon
core 36 after hip stem
20 is implanted.
[0058] Still referring to Fig. 11, stem portion 22 of core 36 may
additionally include
further features to enhance the mechanical interconnection between core 36 and
polymer matrix
layer 38, such as ridges 58 and/or flats 60, or other projecting or recessed
features in core 36
such as grooves, cavities, bores, dimples, bumps, protuberances, protrusions,
or other features
which may be formed in core 36 by forging or post-forging machining, for
example. Ridges 58
and flats 60 extend longitudinally along core 36 and resist relative movement,
such as relative
rotational movement, between core 36 and polymer matrix layer 38 responsive to
torsional
and/or other types of loading which may be imposed upon core 36 as described
above.
[0059] As discussed in further detail below, the present inventors have
developed a
number of improvements to hip stems and acetabular cups in order to provide
more optimized
results with certain types of patient anatomy, such as female anatomy.
[0060] The hip stems and acetabular cups described herein may be
implanted according
to surgical techniques described in U.S. Patent No. 6,676,706, issued January
13, 2004; U.S.
Patent No. 6,860,903, issued March 1, 2005; U.S. Patent No. 6,953,480, issued
October 11,
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2005; U.S. Patent No. 6,991,656, issued January 31, 2006; abandoned U.S.
Patent Application
Serial No. 10/929,736, filed August 30, 2004; abandoned U.S. Patent
Application Serial
No. 2005-0043810, filed September 28, 2004; issued U.S. Patent Application
Serial No.
7,833,275, filed September 26, 2005; and issued U.S. Patent Application Serial
No.
7,780,673, filed April 13, 2005, all titled METHOD AND APPARATUS FOR
PERFORMING
A MINIMALLY INVASIVE TOTAL HIP ARTHROPLASTY and all assigned to the assignee
of the present application.
[0061] Known hip stems typically have an anteversion angle between the neck
portion of
the hip stem and the anatomical medial/lateral plane of from 1 to 12 degrees,
for example. The
present inventors have observed that for many patients, particularly certain
female patients, a
greater anteversion angle between the neck portion of the hip stem and the
anatomical
medial/lateral plane, and/or an anteversion angle between the femoral head
portion and the neck
portion of the hip stem, would provide more optimum anatomical benefits.
[0062] Referring to Fig. 12, a top view of proximal end 28 of hip stem 20
is shown
including stem portion 22 and neck portion 24 integrally formed with one
another. Typical
known hip stems include neck portion 24a with femoral head fitting 26, shown
in dashed lines in
Fig. 12, whose central longitudinal axis 68c coincides and is aligned with
medial/lateral plane
61, i.e., neck portion 24a is angled approximately 00 anteriorly with respect
to the anatomical
medial/lateral plane 61 and therefore has a neutral version and lacks
anteversion. Hip stem 20
also includes instrument engagement fitting 47 in proximal end 28 thereof
within which an
instrument (not shown) may be engaged to aid in driving hip stem 20 into the
prepared femoral
canal of a patient's femur. Although illustrated throughout as the
intersection point between
medial/lateral plane 61 and central longitudinal axis of the neck portion,
fitting 47 may be
located at any location on hip stem 20 to aid in driving hip stem 20 into the
prepared femoral
canal. As illustrated, however, fitting 47 provides a convenient location for
the intersection of
plane 61 with the central longitudinal axis of each neck portion.
[0063] In order to facilitate greater anteversion, hip stem 20 may include
a neck portion
24 which is angled with respect to the anatomical medial/lateral plane 61. For
example, hip stem
20 is shown in an anteversion alignment in solid lines in Fig. 12, in which
neck portion 24c
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having femoral head fitting 26 is angled approximately 25 anteriorly with
respect to stem
portion 22 from the neutral version, or direct medial/lateral alignment.
Central longitudinal axis
68c of neck portion 24c defines a 25 angle with medial/lateral plane 61. In
another
embodiment, hip stem 20 may include neck portion 24b with femoral head fitting
26, shown in
dashed lines in Fig. 12, which is angled approximately 20 anteriorly with
respect to stem portion
22 from the neutral version alignment, i.e., central longitudinal axis 68b of
neck portion 24b
defines a 20 angle with plane 61. Advantageously, the surgeon may choose a
hip stem 20 from
a plurality of hip stems 20 in a system to have a desired anteversion
alignment corresponding to
the patient-specific anatomy. The angle of anteversion may be selected to have
neck portion 24
angled with respect to medial/lateral plane 61 between 0 and 25 or more and,
more
particularly, the hip stem may be selected from a plurality of hip stems in a
system including hip
stems having respective anteversion angles of as little as 13 , 14 , or 16 or
as great as 21 , 23 ,
or 25 or more, for example, or any angle therebetween. In particular, many
female patients may
require a larger degree of anteversion alignment of neck portion 24 with
respect to the
anatomical medial/lateral plane 61 than is provided by known hip stem systems.
As discussed
above, a larger anteversion angle between the neck portion and the
medial/lateral plane may
provide more optimum anatomical benefits in certain patients, including
certain female patients.
[0064] Referring to Fig. 13, a top view of components of a modular hip
stem system are
shown. Proximal end 78 of stem portion 72 of an alternative hip stem 70 is
shown wherein,
except as described below, hip stem 70 and stem portion 72 are substantially
similar to hip stem
20 and stem portion 22 of Figs. 1-5 described above. Proximal end 78 of stem
portion 72
includes tapered recess 74 for mating engagement with a selected one of a
plurality of modular
neck portions 80. Each modular neck portion 80 includes tapered fitting
portion 82 for mating
with recess 74 upon assembly. Each modular neck portion 80 may also include an
optional anti-
rotation feature, shown as key 81, for engagement with another anti-rotation
feature of hip stem
70, shown as groove 83 in recess 74 of stem portion 72, to prevent rotational
movement between
neck portion 80 and stem portion 72. Alternatively, each modular neck portion
80 and stem
portion 72 may be provided with an oval engagement profile therebetween to
provide anti-
rotation. A substantially spherical femoral head 43 may be integrally formed
with each modular
neck portion 80 as shown in Fig. 13 or alternatively, each modular neck
portion 80 may be
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coupled with a modular femoral head separately formed and attached to modular
neck portion 80
via a tapered bore/fitting connection, for example, as described below.
[0065] Each neck portion 80 is oriented in an alignment which is
anteriorly angled with
respect to stem portion 72 from a neutral version as defined by medial/lateral
plane 76. For
example, as shown in Fig. 13, modular neck portion 80a may be angled
approximately 15
anteriorly with respect to medial/lateral plane 76, i.e., central longitudinal
axis 79a of modular
neck portion 80a defines a 15 angle with plane 76. In another embodiment,
modular neck
portion 80b may be angled approximately 20 anteriorly with respect to
medial/lateral plane 76,
i.e., central longitudinal axis 79b of modular neck portion 80b defines a 20
angle with plane 76.
In yet another embodiment, modular neck portion 80c may be angled
approximately 25
anteriorly with respect to medial/lateral plane 76, i.e., central longitudinal
axis 79c of modular
neck portion 80c defines a 25 angle with plane 76. In a modular system, a
plurality of neck
portions 80 may be provided, wherein the anteversion angle between central
longitudinal axis 79
and medial/lateral plane 76 for a given modular neck portion 80 may be from
approximately 0
to 25 or more, for example, the anteversion angle may be as small as 13 , 14
, or 16 , and as
large as 21 , 23 , or 25 , for example, or any angle therebetween.
[0066] Referring to Fig. 14, components of another modular system are
shown, wherein
neck portion 24 of hip stem 20 is integrally formed therewith, and is shown
with a plurality of
modular femoral heads 84. In the manner described above, neck portion 24 may
be oriented in a
desired anteversion alignment, for example, neck portion may be angled
approximately 15
anteriorly with respect to stem portion 22 from medial/lateral plane 61,
similar to neck portions
24a, 24b, 24c of Fig. 12, i.e., central longitudinal axis 68 of neck portion
24 defines a 15 angle
with medial/lateral plane 61. Each modular femoral head 84 includes tapered
recess 88 for
mating engagement with femoral head fitting 26 of neck portion 24. Each
modular femoral head
84 also includes an optional anti-rotation feature, shown as groove 87, for
engagement with
another anti-rotation feature of neck portion 24, shown as key 85 on femoral
head fitting 26, to
prevent rotational movement between neck portion 24 and each femoral head 84.
Alternatively,
each modular femoral head 84 and neck portion 24 may be provided with an oval
engagement
profile therebetween to provide anti-rotation. As described below, each
modular head 84 is itself
anteverted with respect to neck portion 24 of hip stem 20.
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[0067] In particular, the recess 88 of each modular femoral head 84
defines a central axis
86 which is offset from the center of head 84 and from central axis 68 of neck
portion 24 such
that recess 88 of each head 84 is eccentric with respect to the center of the
head 84. Central axis
86 may be angled anteriorly with respect to central longitudinal axis 68 of
neck portion 24 such
that each modular femoral head 84 is offset from central longitudinal axis 68
upon assembly.
For example, modular femoral head 84a may be angled approximately 5
anteriorly with respect
to longitudinal axis 68, i.e., central axis 86a of femoral head 84a defines a
5 angle with axis 68.
In another embodiment, femoral head 84b may be angled approximately 10
anteriorly with
respect to longitudinal axis 68, i.e., central axis 86b of femoral head 84b
defines a 10 angle with
axis 68. In yet another embodiment, femoral head 84c may be angled
approximately 15
anteriorly with respect to longitudinal axis 68, i.e., central axis 86c of
femoral head 84c defines a
15 angle with axis 68. In a modular system, a plurality of femoral heads 84
may be provided
wherein the angle between central longitudinal axis 68 and axis 86 of same may
vary from
approximately 1 to 25 or more and, in particular, may be as small as 1 , 3 ,
5 , and as large as
21 , 23 , or 25 or more, for example, or any angle therebetween. As discussed
above, a larger
anteversion angle between the femoral head and the neck portion may provide
more optimum
anatomical benefits in certain patient, including certain female patients.
[0068] Referring to Fig. 15, a view of modular femoral head 84a taken
along the line IS-
IS in Fig. 14 is shown including central longitudinal axis 68 of neck portion
24 (Fig. 14) and
central axis 86a of recess 88 of femoral head 84a. As shown in Fig. 15, axis
86a is offset from,
i.e., not coaxial with, axis 68 to provide an offset modular femoral head 84a
to achieve an added
amount of anteversion alignment of hip stem 20. The offset of axes 86a and 68
provides a larger
amount of mass of femoral head 84a on the right side of Fig. 15 as compared to
the left side,
thereby providing the added anteversion component to enhance the performance
of the hip stem.
If no offset between femoral head 84 and neck portion 24 was necessary, axis
68 would coincide
with central axis 86 of a modular femoral head 84.
[0069] As shown in Figs. 16-17, exemplary components of a modular hip
stem system
are shown which includes a modular neck portion and a modular femoral head. In
Figs. 16 and
17, the proximal end 78 of modular hip stem 90 is shown which, except as
described below, is
substantially similar to hip stem 20 (Figs. 1-5) and hip stem 70 (Fig. 13)
described above. The
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modular hip system shown in Figs. 16-17 combines the modularity of the systems
shown in Figs.
13 and 14 described above. Hip stem 90 may include modular femoral head 84
having tapered
recess 88. Upon assembly, recess 74 of stem portion 72 engages with tapered
fitting portion 82
of modular neck portion 80 and recess 88 of modular femoral head 84 engages
with femoral head
fitting 26 of modular neck portion 80. Modular femoral head 84 includes an
optional anti-
rotation feature, shown as groove 87, for engagement with another anti-
rotation feature of neck
portion 80, shown as key 85 on femoral head fitting 26, to prevent rotational
movement between
neck portion 80 and femoral head 84. Further, neck portion 80 includes a
further optional anti-
rotation feature, shown as key 81 on tapered fitting portion 82, for
engagement with another anti-
rotation feature of stem portion 72, shown as groove 83 in recess 74, to
prevent rotational
movement between neck portion 80 and stem portion 72. Alternatively, each of
the foregoing
components may be provided with oval engagement profiles therebetween to
provide anti-
rotation.
[0070] Stem portion 72 defines an anatomical medial/lateral plane 91,
neck portion 80
defines central longitudinal axis 79, and modular femoral head 84 defines
central axis 86.
Advantageously, a surgeon may choose any combination of modular components to
ensure an
adequate degree of anteversion is included in hip stem 90. For example, as
shown in Figs. 16-
17, modular femoral head 84 may be angled at an angle a anteriorly with
respect to longitudinal
axis 79, i.e., central axis 86 of femoral head 84 defines an angle a with axis
79. Also, neck
portion 80 may be angled at an angle 0 anteriorly with respect to
medial/lateral plane 76, similar
to neck portions 80a, 80b, 80c described above, i.e., central axis 79 of neck
portion 80 defines an
angle 0 with axis 76. Angle a may be chosen to be between approximately 1 and
25 or more
and, in particular, may be as small as 13 , 14 , or 16 , and as large as 21 ,
23 , or 25 , for
example, or any angle therebetween. Angle 0 may be chosen to be between
approximately 1
and 25 or more and, in particular, may be as small as 13 , 14 , or 16 , and
as large as 21 , 23 ,
or 25 , for example, or any angle therebetween.
[0071] The angle between the neck and the shaft of the femur in certain
patients,
including many female patients, is typically more varus than the angle between
the neck and the
shaft of the male femur which is relatively more valgus. Known hip stems are
not shaped with a
sufficiently varus neck/shaft angle which would provide optimum results in
certain female
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patients. Also, in order to accommodate a hip stem having a more varus
neck/shaft angle
without the need to lengthen leg length, it is typically necessary to
osteotomize a greater portion
of the metaphysis of the femur in female patients than in male patients.
Specifically, in certain
females, the femur is osteotomized at a location near the lesser trochanter.
This results in less of
the metaphysis being available for hip stem fixation in many female patients
as compared to
male patients, thereby increasing the importance of diaphyseal fixation of the
hip stem in female
patients.
[0072] Referring to Fig. 18, several embodiments of hip stem 100 are
shown which,
except as described below, are substantially similar to hip stem 20 (Figs. 1-
5), described above.
Each hip stem 100 includes integral stem portion 22 and neck portion 104. Hip
stem 100 defines
central longitudinal axis 106 extending through stem portion 22 and includes a
neck portion 104
having a central longitudinal axis 102. Central longitudinal axis 106 and each
central
longitudinal axis 102 define an angle therebetween which may be chosen
depending on the
anatomy of the patient. For example, neck portion 104a, shown in solid lines
in Fig. 18, may
have central longitudinal axis 102a which defines an angle of approximately
110 with axis 106.
If more valgus neck/shaft angle is desired, a surgeon may choose hip stem
100b, shown in
dashed lines in Fig. 18, including neck portion 104b having central
longitudinal axis 102b which
defines an angle of approximately 120 with axis 106. Alternatively, if less
valgus (more varus)
neck/shaft angle is desired, a surgeon may choose hip stem 100c, shown in
dashed lines in Fig.
18, including neck portion 104c having central longitudinal axis 102c which
defines an angle of
approximately 90 with axis 106. In a system of hip stems 100 having various
neck/shaft angles,
a particular hip stem may be selected having a neck/shaft angle corresponding
to the anatomy of
a particular patient. In this system, the neck/shaft angle may range from
approximately 90 to
approximately 145 , and in particular, may be as small as 90 , 110 , or 120
or any increments
therebetween, for example. Advantageously, hip stem 100 may be chosen to have
more varus
orientation without increasing the leg length of the hip implant system. Hip
stem 100 may allow
a surgeon to select from a sufficient variation of hip stems having various
neck/shaft angles to
optimize results in certain female patients.
[0073] Referring to Fig. 19, a modular hip stem system includes hip stem
110 which,
except as described below, is substantially similar to hip stem 20 (Figs. 1-
5), described above.
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Hip stem 110 may include stem portion 112 and a plurality of modular neck
portions 120 each
having tapered fitting portion 122 for mating engagement in tapered recess 114
in proximal end
118 of stem portion 112 and femoral head fitting 26 for acceptance of a
modular femoral head.
Each neck portion 120 includes an optional anti-rotation feature, shown as key
121 on tapered
fitting portion 122, for engagement with another anti-rotation feature of stem
portion 112, shown
as groove 119 in recess 114, to prevent rotational movement between each neck
portion 120 and
stem portion 112. Alternatively, each neck portion 120 and stem portion 112
may be provided
with oval engagement profiles to provide anti-rotation. Each modular neck
portion 120 defines a
central longitudinal axis 116 forming an angle with central longitudinal axis
111 of stem portion
112. In one embodiment, modular neck portion 120a may have central
longitudinal axis 116a
which forms an angle of approximately 110 with axis 111.
[0074] If a surgeon desires a larger neck/shaft angle, modular neck
portion 120b may be
chosen which defines central longitudinal axis 116b which forms an angle of
approximately 120
with axis 111 and an angle of approximately 10 with central longitudinal axis
116a, i.e., a +100
change in neck/shaft angle from modular neck portion 120a. If a surgeon
desires a smaller
neck/shaft angle, modular neck portion 120c may be chosen which defines
central longitudinal
axis 116c which forms an angle of approximately 90 with axis 111 and an angle
of
approximately 20 with central longitudinal axis 116a, i.e., a ¨20 change in
neck/shaft angle
from modular neck portion 120a. Various values for the neck/shaft angle may be
chosen
depending on the varus/valgus anatomy of a particular patient. For example,
the neck/shaft angle
may range from approximately 90 to approximately 145 , and in particular, may
be 90 , 110 ,
or 120 , or any increment therebetween. Hip stem 110 advantageously allows a
surgeon to select
from a variety of modular neck portions to vary the neck/shaft angle to
optimize results in certain
female patients.
[0075] The present inventors have also observed that as certain patients
age, particularly
females, the cortex of bone in the metaphysis and in the diaphysis of the
proximal femur
typically becomes thinner, particularly from the level of the lesser
trochanter downwardly. The
thinning cortex of the metaphysis and diaphysis results in a "stovepipe" shape
of the cortex in the
metaphysis and a pronounced widening of the intramedullary canal in the
diaphysis, respectively.
These effects are more pronounced with women who have osteoporosis, which
results in further
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thinning of the cortex and consequent widening of the intramedullary canal,
and in particular, a
reduction of bone stock in the proximal diaphysis.
[0076] When cementless prostheses are used, the widened intramedullary
canal of certain
patients, particularly aging females, promotes a tendency for using a wider
hip stem to more
completely fill the intramedullary canal and achieve initial fixation. In many
existing hip stems,
stiffness increases with increasing width, such that use of wider hip stems of
increased stiffness
could result in stress shielding around the hip stem. Advantageously, the hip
stems described
herein which include a core, a polymer matrix intermediate layer, and porous
metal outer layer,
have a stiffness modulus which more closely approximates the stiffness modulus
of cortical
bone. This allows relative motion between the hip stem and the femur to be
minimized, and
allows more loading to be distributed to the cortical bone to reduce the
potential for stress
shielding as opposed to known, more stiff hip stems which have only a core and
a porous metal
coating.
[0077] Additionally, the inventors have observed that in females, the
intramedullary
canal tends to widen relatively more in the anterior/posterior plane, as
viewed with a lateral x-
ray, for example, than in the medial/lateral plane, particularly in females
with osteoporosis,
which commonly causes thinning of the posterior cortex of the diaphysis. Thus,
when the
anterior/posterior and medial/lateral diameters of the intramedullary canal
are typically not equal,
known hip stems which have a substantially cylindrical shape may not achieve
optimal fixation
in the diaphysis.
[0078] Referring to Fig. 20, a portion of hip stem 130 is shown which,
except as
described below, is substantially similar to hip stem 20 shown in Figs. 1-5
and described above.
Hip stem 130 may include stem portion 135 with core 36, polymer matrix layer
38, and porous
metal layer 40. Stem portion 135 may further include a distal end fixation
mechanism operable
between a first, non-expanded condition and a second, expanded condition. The
distal end
fixation mechanism may include a plurality of expansion points 140 in porous
metal layer 40,
such as slits, hinges, or weakened areas, for example, which define a
plurality of radially
expandable portions 138. The distal end fixation mechanism may also include
activation
member 148 having a threaded aperture 149 for mating engagement with threaded
end 146 of
shaft 134. Shaft 134 may be a permanent part of hip stem 130 and may be
rotatably positioned
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within throughbore 132 in core 36. Shaft 134 includes proximal end 137 having
suitable
instrument engagement structure, such as a hex fitting, for example, for
engagement with an
actuator device 139 (Fig. 21) for imparting rotational motion to shaft 134.
[0079] In operation and referring to Fig. 21, after hip stem 130 is
initially implanted in
intramedullary canal 145 of the prepared femur 144, shaft 134 may be rotated
by actuator device
39 in the general direction of Arrow A to thread threaded end 146 of shaft 134
into threaded
aperture 149 of activation member 148. Rotation of shaft 134, and the
threading of end 146
thereof into threaded aperture 149 of activation member 148, causes movement
of activation
member 148 towards distal end 133 of hip stem 130 in the general direction of
Arrow B towards
distal end 133 of hip stem 130. Movement of activation member 148 along the
direction of
Arrow B causes activation member 148 to compress expandable portions 138 of
porous metal
layer 40 against a fixed reaction surface provided by abutting portion 136 of
core 36, thereby
causing expansion points 140 in porous metal layer 40 to deform and expand
radially expandable
portions 138 from a first, non-expanded condition to a second, expanded
condition. The
plurality of radially expandable portions 138 cause hip stem 130 to widen and
substantially fill
intramedullary canal gaps 142 (Fig. 20), thereby enhancing distal fixation of
hip stem 130 in the
diaphysis of femur 144.
[0080] The degree of expansion of expandable portions 138 may be
controlled by the
amount of rotation of shaft 134. For example, in one embodiment, a half turn,
or 180 turn, of
shaft 134 with the actuator device provides a limited degree of expansion of
expandable portions
138 to provide initial fixation if the intramedullary canal of femur 144 is
only slightly wider than
hip stem 130. In one embodiment, two complete turns, or a 720 turn, of shaft
134 provides
maximum expansion of expandable portions 138 to provide initial fixation if
the intramedullary
canal of femur 144 is substantially wider than hip stem 130, wherein shaft 134
is rotated until
surface 143 of activation member 148 abuts distal end 133 of hip stem 130 to
limit the travel of
activation member 148. In this manner, the amount of rotation imparted to
shaft 134 may
advantageously allow the surgeon to provide the appropriate amount of
expansion of expandable
portions 138 to ensure adequate diaphyseal fixation of hip stem 130, which may
be verified by
X-ray or other imaging. In one embodiment, expansion points 140 may include a
sliding-
enhancement element, for example, a plastic sheet, to facilitate movement of
porous metal layer
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40 radially outward instead of a potential collapse of porous metal layer 40
in the direction of
Arrow B with no radial expansion. Advantageously, portions 138 in the first,
non-expanded
condition define the original cross-sectional shape of the hip stem. After
implantation,
deformation of portions 138 advantageously allows the hip stem to have a
larger cross-sectional
shape in the distal portion thereof to enhance diaphyseal fixation of the hip
stem in the femur.
[0081] Referring to Figs. 22-23, a portion of hip stem 150 is shown
which, except as
described below, is substantially similar to hip stem 20, shown in Figs. 1-5,
and hip stem 130,
shown in Figs. 20-21. Hip stem 150 may include a distal end fixation mechanism
having
expandable structure 155 which facilitates widening of hip stem 150 near
distal end 152 to
enhance distal fixation of hip stem 150 in the diaphysis of femur 144. Core 36
may be provided
with central throughbore 154. Core 36, polymer matrix layer 38 and porous
metal layer 40 may
include a plurality of passages 153 providing for travel of a filler material
within throughbore
154 into expandable structure 155. Although illustrated as horizontally
oriented, passages 153
may be oriented diagonally or any other orientation to facilitate flow of the
filler material into
expandable structure 155 from throughbore 154. Any number of passages 153 may
be provided
and the width of passages 153 may be varied to regulate the flow of filler
material 156 (Fig. 23)
into expandable structure 155. As shown in Fig. 22, prior to expansion within
intramedullary
canal 145 of femur 144, expandable structure 155 remains substantially flat
and non-expanded
and does not significantly increase the overall diameter of hip stem 150.
Alternatively,
expandable structure 155 may be disposed within a recessed area of porous
metal coating 40 of
hip stem 150 such that expandable structure 155 does not increase the overall
diameter of hip
stem 150.
[0082] As shown in Fig. 23, upon introduction of filler material 156,
e.g., bone cement or
polymethylmethacrylate (PMMA), into throughbore 154 by a tube or other
suitable delivery
device in the general direction of Arrow C, filler material 156 migrates into
passages 153 and
fills expandable structure 155. Expansion of expandable structure 155 widens
distal end 152 of
hip stem 150 to substantially fill any gaps 142 between hip stem 150 and the
intramedullary
canal of femur 144. The filler supply device is gradually proximally removed
from central
throughbore 154 while simultaneously distally filling central throughbore 154
and, consequently,
passages 153 and expandable structure 155 to ensure complete filling of
expandable structure
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155 to the desired expansion state. Expandable structure 155 may be formed of
any suitable
biocompatible material, such as the materials used for the prosthetic implant
described in U.S.
Patent No. 7,485,119, filed October 14, 2005, titled METHOD AND APPARATUS FOR
REDUCING FEMORAL FRACTURES, assigned to the assignee of the present
application.
[0083] In some embodiments, expandable structure 155 may be expanded non-
uniformly
around the circumference of hip stem 150, for example, by varying the number,
relative
locations, and relative cross sections of passages 153 in hip stem 150. This
may allow hip stem
150 to more optimally achieve fixation in the diaphysis because hip stem 150
may expand
further in the anterior/posterior plane than in the mediaUlateral plane, for
example, to provide
optimal fixation in females with osteoporosis wherein the width of the
anterior/posterior plane of
the intramedullary canal may exceed that in the medial/lateral plane. As
discussed above,
osteoporosis in females commonly causes thinning of the posterior cortex of
the diaphysis. The
ability to expand in a non-uniform manner, particularly expanding further
posteriorly than either
medially, laterally, or anteriorly, allows hip stem 150 to achieve optimum
fixation.
[0084] In a total hip arthroplasty, a prosthetic acetabular cup component
is seated within
a patient's acetabulum anteriorly of the medial wall of the pelvis. In certain
patients, loading
from the femoral prosthesis may be transmitted to the pelvis primarily around
the rim of the
acetabular cup, as opposed to being distributed more evenly around the
hemispherical portion of
the acetabular cup, which could potentially result in stress shielding around
the hemispherical
portion of the acetabular cup. Stress shielding of bone around the
hemispherical portion of the
acetabulum may cause resorption of bone in the medial wall of the pelvis
posteriorly of the
acetabulum, potentially resulting in migration of the acetabular cup into the
medial wall of the
pelvis. The present inventors have observed that in female patients, the
medial wall of the pelvis
is often thinner than in most men.
[00851 Referring to Fig. 24, a flexible acetabular cup 160 is shown, which
generally
includes a liner 166 made of ultra high molecular weight polyethylene, for
example, including a
hemispherical articulating surface 168. Liner 166 is fitted within a porous
metal cup portion 170
which may be made from a metal wire mesh of titanium fibers, a metal bead
matrix, or may be a
porous metal layer produced in accordance with Trabecular MetalTM technology
available from
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Zimmer, Inc. of Warsaw, Indiana. Cup portion 170 may be formed relatively
thin, or may
include relief slits therein such that cup portion 170 is generally flexible,
as represented by
dashed lines 172 in Fig. 24, to more evenly distribute acetabular loading
around both the rim and
the hemispherical portions of cup portion 170 to reduce the potential for
stress shielding and, in
turn, to reduce the potential for migration of acetabular cup 160 into the
medial wall 163 of the
pelvis 162.
[0086] Referring to Fig. 25, acetabular cup 180 according to another
embodiment is
shown, which generally includes liner 182 made of ultra high molecular weight
polyethylene, for
example, intermediate layer 184 of a polymer matrix similar to that of hip
stem 20 described
above, which may be formed of an inert polyaryletherketone ("PAEK") polymer
such as for
example, polyetheretherketone ("PEEK"), and porous metal layer 186 which may
be made from
a metal wire mesh of titanium fibers, a metal bead matrix, or may be a porous
metal layer
produced in accordance with Trabecular MetalTM technology available from
Zimmer, Inc. of
Warsaw, Indiana, for example. Liner 182 includes a hemispherical bearing
surface 188 for
articulating receipt of the femoral head component of a hip stem, such as the
various hip stems
described herein. Porous metal layer 186 allows osseointegration of acetabular
cup 180 into the
surrounding bone of the acetabulum. Advantageously, polymer matrix layer 184
allows flexing
movement between liner 182 and porous metal layer 186 to provide a stiffness
for acetabular cup
180 which more closely approximates that of bone than the stiffness of known
acetabular cups.
In this manner, loads from the femoral head component of the hip stem are
distributed more
evenly about the hemispherical portion of the cup to the surrounding bone of
the acetabulum,
thereby reducing the potential for stress shielding and resulting migration of
the cup into the
medial wall of the pelvis.
[0087] Referring to Fig. 26, acetabular cup 190 according to a further
embodiment is
shown which generally includes liner 192 made of ultra high molecular weight
polyethylene, for
example, and porous metal layer 194 which may be a metal wire mesh of titanium
fibers, or
alternatively, may be a metal bead matrix or other porous metal structure
produced in accordance
with Trabecular MetalTM technology available from Zimmer, Inc. of Warsaw,
Indiana, for
example. Liner 192 includes a hemispherical bearing surface 196 for
articulating receipt of the
femoral head component of a hip stem, such as the various hip stems described
herein. Porous
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metal layer 194 allows osseointegration of acetabular cup 190 into the
surrounding bone of the
acetabulum, and advantageously, further includes a loading rib 198 disposed
around the outer
hemispherical portion of porous metal layer 194 which contacts the surrounding
bone of the
acetabulum to transfer loads thereto, such that loads from the femoral head
component of the hip
stem are distributed more evenly about the hemispherical portion of the cup to
the surrounding
bone of the acetabulum, thereby reducing the potential for stress shielding
and resulting
migration of the cup into the medial wall of the pelvis.
[0088] Referring to Fig. 27, hip stem 200 according to a further
embodiment of the
present invention is shown which, except as described below, is similar to hip
stem 20 shown in
Figs. 1-5 and described above. Hip stem 20 generally includes proximal end 28
and distal end
30, wherein proximal end 28 is configured similarly to that of hip stem 20 in
that proximal end
28 of hip stem 200 includes core 36, polymer matrix layer 38, and porous metal
layer 40 as
described above with respect to hip stem 20. However, distal end 30 of hip
stem 200 includes
only core 36 and porous metal layer 40, and lacks polymer matrix layer 38. In
this manner,
distal end 30 of hip stem 200 has a higher stiffness than proximal end 28 of
hip stem 200 to
facilitate initial fixation of distal end 30 of hip stem 200 in the diaphysis
of the femur, wherein
proximal end 28 of hip stem 200 has a stiffness which more closely mimics that
of natural bone
than known hip stems to thereby transfer loading to the surrounding bone of
the metaphysis
around proximal end 28 of hip stem 200 to reduce the potential for stress
shielding. As discussed
above, in certain patients, such as in certain female patients, not only does
the cortex of the
metaphysis thin, but a greater extent of the metaphysis of the femur must be
osteotomized during
a total hip arthroplasty, which results in less of the remaining metaphysis
being available for
fixation. Thus, for these types of procedures, hip stem 200 advantageously
includes a relatively
stiff distal end 30 for enhanced initial fixation in the diaphysis of the
femur, and a relatively
more flexible proximal end 28 to prevent stress shielding and bone resorption
in the metaphysis
of the femur.
[0089] Referring to Figs. 28 and 29, anterior and lateral views of a hip
stem 210
according to a further embodiment are shown, respectively. In Figs. 28 and 29,
hip stem 210 is
shown superimposed on proximal femur "F", shown in ghost lines, to illustrate
features of hip
stem 210 in relation to the proximal femur. Hip stem 210 is particularly
useful in patients, such
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as older female patients, for example, whose proximal femur is characterized
by thinned cortices
"C" in the metaphysis and diaphysis as shown in Fig. 28, perhaps with complete
loss of the
medial and posterior cortices in the metaphysis resulting in the "stovepipe"
shape of the
intramedullary canal seen in Fig. 28, as well as a thinned intramedullary
canal in the diaphysis.
Although anatomical features of the proximal femur, including the greater
trochanter "GT",
lesser trochanter "LT", femoral neck "FN", and femoral head "FH" are shown in
ghost lines in
Figs. 28 and 29 in order to illustrate features of hip stem 210 in relation
thereto, it is to be
understood that the femoral neck and head, as well as portions of the greater
trochanter, are
osteotomized during a total hip arthroplasty to accommodate insertion of
femoral stem 210 into
the prepared intramedullary canal of the femur.
[0090] Hip stem 210 generally includes a proximal, or metaphyseal,
portion 212 and a
distal, or diaphyseal, portion 214. Hip stem 210 may be constructed in a
similar manner as hip
stem 20 described above with respect to Figs. 1-5, wherein hip stem 210 may
include a core 36, a
polymer matrix layer (not shown) disposed over at least a portion of core 36,
and a porous metal
layer 40, such as those described above or a grit-blasted layer, disposed over
the polymer matrix
layer. Proximal portion 212 of stem 210 has a length dimension D1 measured
from stage line
216, which is typically 15 mm from the top of the lesser trochanter, to line
220 at the base of the
lesser trochanter which may be as small as 30 mm or 35 mm to as large as 40 mm
or 45 mm for
example, or any length therebetween. As may be seen from Fig. 28, proximal
portion 212 of
stem 210 is not trapezoidally shaped as are many known hip stems when viewed
in the
anterior/posterior view of Fig. 28, but rather has a "goose neck" profile,
including medially
curved, complementary radiused lateral and medial sides 222 and 224. In
particular, lateral side
222 is curved medially in order to clear the greater trochanter and prevent
loading on any portion
of the greater trochanter which remains after the osteotomy. When viewed in
the lateral view of
Fig. 29, proximal portion 212 of hip stem 210 has a flared shape including
anterior and posterior
sides 226 and 228 which flare slightly outwardly, such as between 1 and 2 mm,
for example, in
the anterior and posterior directions as same approach the proximal end of hip
stem 210.
[0091] The neck portion and the femoral head (not shown) of proximal
portion 212 of hip
stem 210 may be integrally formed with hip stem 210 and may be aligned in
desired
anteversion/retroversion and varus/valgus angles in the same manner as the
other hip stems
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described above with reference to Figs. 12 and 18. Alternatively, the neck
portion and the
femoral head of hip stem 210 may be configured as one or more modular
components to provide
the desired anteversion/retroversion and varus/valgus angles in the manner
described above with
reference to Figs. 13-17 and 19.
[0092] Distal portion 214 of hip stem 210 may have a circular or
trapezoidal cross
section, and is elongated with respect to known hip stems to allow the distal
portion 214 to
engage the cortex of the diaphyseal isthmus, having a length dimension D2
measured from the
from the mid lesser trochanter line 221 to the distal end 230 of the hip stem
210 which may be as
small as 100 mm, 105 mm, or 110 mm and as large as 125 mm, 130 mm, or 135 mm,
for
example, or any length therebetween. Near the distal end 230, the width of hip
stem 210 at
dimension D3 measured laterally-medially may vary from 10 mm to 18 mm and, as
shown in Fig.
29, the width of hip stem 210 at dimension D4 measured anteriorly-posteriorly
may be 1 mm or
more greater than dimension D3, i.e., may vary between 11 mm and 19 mm, in
order to optimally
fit within the intramedullary canal of certain patients, particularly in older
female patients,
wherein the intramedullary canal is slightly wider in the anterior/posterior
dimension and in the
medial/lateral dimension.
[0093] Additionally, distal portion 214 of hip stem 210 may have a
substantially hollow
construction, including an elongated blind cavity 232 extending inwardly from
distal end 230
toward proximal portion 212 of hip stem 210, optionally extending to line 220
at the base of the
lesser trochanter. Cavity 232 allows distal portion 214 of hip stem 210 to
flex, such that the
stiffness modulus of distal portion 214 of hip stem 210 more closely
approximates the stiffness
modulus of the femoral bone surrounding hip stem 210 to aid in prevention of
stress shielding
around distal portion 214 of hip stem 210. Alternatively, distal portion 214
of hip stem 210 may
be formed to include a core/polymer matrix/porous outer layer construction
similar to the other
hip stems disclosed herein to provide a stiffness modulus which more closely
approximates the
stiffness modulus of the femoral bone around distal portion 214 of hip stem
210. In a still further
embodiment, distal portion 214 of hip stem 210 may include a plurality of
grooves, slopes, or
other enervations or weakenings therein to reduce the stiffness modulus
thereof.
[0094] As described in detail below, the present invention provides
prosthetic hip stems
for use in prosthetic hip joints and, in particular, provides prosthetic hip
stems that are designed
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to achieve more optimized outcomes with certain types of patient anatomy, such
as the anatomy
of female patients and/or patients having osteoporosis. Each hip stem in a
family or set of hip
stems has diaphyseal width, metaphyseal width, offset, and head height
dimensions. In a set of
hip stems of increasing nominal size, the diaphyseal width dimension increases
substantially
non-proportionally to the corresponding increase of the metaphyseal width,
offset, and head
height dimensions, thereby providing a family or set of hip stems that is
particularly adapted for
patients having osteoporosis, in which the cortical bone of the diaphysis of
the femur becomes
thinner with progression of the osteoporosis.
[0095] As humans and, in particular females, age, osteoporosis may be of
concern.
Osteoporosis may effect the femur and, in particular, the intramedullary (IM)
canal of the femur.
The present inventors have observed that as certain patients age, particularly
females, the cortex
of bone in the metaphysis and in the diaphysis of the proximal femur typically
becomes thinner,
particularly from the level of the lesser trochanter downwardly. The thinning
cortex of the
metaphysis and diaphysis results in a "stovepipe" shape of the cortex in the
metaphysis, and a
pronounced widening of the intramedullary canal in the diaphysis,
respectively. These effects
are more pronounced with women who have osteoporosis, which results in further
thinning of
the cortex and consequent widening of the intramedullary canal and, in
particular, a reduction of
bone stock in the proximal diaphysis.
[0096] When cementless hip stem prostheses are used, the widened
intramedullary canal
of certain patients, particularly aging females, promotes a tendency for using
a wider hip stem to
more completely fill the intramedullary canal and achieve initial fixation. In
many existing hip
stems, stiffness increases with increasing width, such that use of wider hip
stems of increased
stiffness could potentially result in stress shielding around the hip stem.
Advantageously, the hip
stems described herein which include a core, a polymer matrix intermediate
layer, and porous
metal outer layer, have a stiffness modulus which more closely approximates
the stiffness
modulus of cortical bone. This allows relative motion between the hip stem and
the femur to be
minimized, and allows more loading to be distributed to the cortical bone to
reduce the potential
for stress shielding as opposed to known, more stiff hip stems which have only
a core and a
porous metal coating.
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[0097] Referring to Figs. 30A-30C, proximal femurs are shown in accordance
with the
progression of osteoporosis. The progression of osteoporosis may be
characterized by reference
to Type A, B, and C bone, a classification that is discussed in detail in Dorr
et al., "Structural and
Cellular Assessment of Bone Quality of Proximal Femur", Bone, 14, 231-242
(1993). Type A bone,
illustrated in Fig. 30A, has a generally champagne-fluted intramedullary canal
which defines
relatively thick cortices of bone surrounding the canal and a generally
tapering width of the canal.
As shown in Fig. 30B, Type B bone represents a stage of osteoporosis in which
the cortical wall
begins to decrease in thickness, thereby expanding the canal width. As shown
in Fig. 30C, Type C
bone represents a progressed stage of osteoporosis in which the cortical wall
has decreased in
thickness even further than Type B bone.
[0098] Referring to Figs. 31A-C, three exemplary hip stems 250a-c in a set
of hip stems
of increasing nominal size are shown. The dimensions of these hip stems that
are described
below are as viewed in a generally medial/lateral orientation, it being
understood that when the
hip stems are implanted, same may be oriented with anteversion or retroversion
as described
above. Each hip stem 250 includes a proximal, metaphyseal or head portion 252,
a distal,
diaphyseal or stem portion 254 having a central axis CA, and a neck portion
256 having a neck
portion axis NPA. Distal stem portion 254 has a diaphyseal or distal width
dimension DW,
which may be located at an area of stem portion 254 which has a substantially
uniform width.
[0099] Head portion 252 has a metaphyseal width dimension MW defined with
respect to
central axis CA generally at a location on head portion 252 where the
relatively smooth medial
curve of stem portion 254 begins to transition to neck portion 256, though the
exact location of
metaphyseal width dimension MW may vary slightly across hip stems of different
design. In
many hip stems, metaphyseal width dimension (MW) will be located at the
"osteotomy line", for
example, referring to Fig. 31D, the MW dimension is taken at the section of
the hip stem that
will rest along the proximal femoral osteotomy OS after the hip stem is
implanted. In hip stems
250 and other hip stems having a porous layer or coating 40, metaphyseal width
dimension
(MW) may be located at the location along the medial curve of the hip stem
where the porous
layer or coating 40 ends.
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[00100] Neck portion 256 defines both offset and head or neck height
dimensions OF and
HH, respectively. The offset dimension OF is the horizontal or medial/lateral
distance between
central axis CA and the central point CP which corresponds to the center of
the femoral head
component (not shown) that is attached to the neck taper. The head height
dimension HH is the
vertical or anterior/posterior distance between the metaphyseal width
dimension MW and the
central point CP. The neck angle NA is the angle between central axis CA and
the neck portion
axis NPA of neck portion 256.
[00101] In hip stems 250, as the diaphyseal width dimension DW increases
with greater
nominal size of the hip stems, the increase in the metaphyseal width, offset,
and head height
dimensions MW, OF, and HH is substantially proportional to the increase in the
diaphyseal
width dimension DW. In other words, these four dimensions increase
substantially
proportionally to one another in a given set of hip stems of increasing
nominal size.
[00102] Referring to Figs. 32A-C, three hip stems 300a-c in a set of hip
stems of
increasing nominal size are shown in accordance with the present invention.
The dimensions of
hip stems 300 are described below as hip stems 300 are viewed in a generally
medial/lateral
orientation, it being understood that when the hip stems are implanted, same
may be oriented
with anteversion or retroversion as described above. The dimensions of hip
stems 300 are
defined in the same manner as in hip stems 250 described above though, as set
forth herein as
described below, such dimensions across a given set or family of hip stems 300
are different.
[00103] Each hip stem 300 includes a proximal, metaphyseal or head portion
302, a distal,
diaphyseal or stem portion 304 having a central axis CA, and a neck portion
306. Further, distal
stem portion 304 has diaphyseal or distal width dimension DW, and head portion
302 has a
metaphyseal width dimension MW defined with respect to central axis CA. Neck
portion 306
defines both offset and head or neck height dimensions OF and HH as described
above, and neck
angle NA is the angle between central axis CA and the neck portion axis NPA or
central axis of
neck portion 306, which may be as little as 120 or 125 , or as great as 130 ,
135 , 140 , or 145 .
[00104] In addition, referring to Figs. 32D and 32E, stem portion 304 of a
hip stem 300
has a uniform or substantially uniform cross section along a substantial
extent of stem portion
304. In particular, stem portion 304 is cylindrically shaped, though may have
other cross
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sectional shapes, such as a slight oval cross section. Stem portion 304 of hip
stem 300 may have
a uniform cross section along a percentage of dimension D1 which is defined
from metaphyseal
width dimension MW to the end of stem portion 304 of the stem. Two distances
D2 and D3 are
indicated in Fig. 32D from the most proximal location on stem portion 304
having a circular
cross section (i.e., the location on stem portion 304 where the medial curve
begins) to the distal
most end of the stem 300 and to the end of stem portion 304 adjacent a tip
portion 308,
respectively. In Table 1, these distances are set forth, as well as the values
for the distances D2
and D3 as a percentage of D1.
Table 1
Dimensions of hip stems 300.
Size D1 D2 D3 D2/D1 (%) D3/D1 (%)
13 5.567 3.190 2.760 57.3 49.6
14 5.562 3.135 2.705 56.4 48.6
15 5.565 3.080 2.650 55.3 47.6
16 5.564 3.027 2.597 54.4 46.7
17 5.564 2.971 2.541 53.4 45.7
18 5.568 2.921 2.491 52.5 44.7
19 5.599 2.889 2.459 51.6 43.9
20 5.588 2.816 2.386 50.4 42.7
[00105] Thus, in the specific embodiments set forth above, D2/D1 ranges
from 50.4% to
57.3%, and D3/D1 ranges from 42.7% to 49.6%. However, in other embodiments,
the foregoing
percentages may be as little as 35%, 40%, or 45%, or as great as 55%, 60%, or
65%, indicating
that hip stems 300 have a uniform or substantially uniform cross section along
a substantial
extent of the stem portions 304 thereof.
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[00106] As described in detail below with respect to the data presented in
Tables 1-5 and
Figs. 33A-C, in order to more optimally accommodate patients with osteoporosis
and, in
particular, patients with advanced stages of osteoporosis, such as patients
having Type B (Fig.
30B) and Type C (Fig. 30C) bone, hip stems 300 in accordance with the present
invention are
dimensioned such that the diaphyseal width dimension DW increases non-
proportionally with
respect to the metaphyseal width MW, offset OF, and head height HH dimensions
across a given
family or set of hip stems 300 of increasing nominal size.
[00107] For example, the femur of a patient into which a hip stem is to be
placed may
require a nominal "size 14" stem (i.e., a hip stem having a diaphyseal width
dimension DW of 14
mm) if no osteoporosis were present. However, in various stages of
osteoporosis, the
intramedullary canal width increases at a greater rate than the metaphyseal
region, as discussed
above. Thus, in hip stems 300, the diaphyseal width dimension DW may be sized
at a dimension
equivalent to a greater sized conventional stem, while the metaphyseal width
MW, offset OF,
and head height HH dimensions are sized at dimensions equivalent to a lesser
sized conventional
stem. In this manner, the distal portion of a hip stem 300 can fully occupy
the canal of Type B
or Type C bone at advanced stages of osteoporosis, for example, while the
metaphyseal portion
302 and neck 306 of the hip stems is still dimensioned substantially
equivalent to a non-
osteoporotic bone. Thus, hip stem 300 maintains sufficient contact with the
bone, such that bony
ingrowth is facilitated after implantation, and hip stem 300 substantially
fills the femoral canal
while preventing "hangup" of the hip stem in the metaphyseal region of the
femur during
insertion of the hip stem. Moreover, the offset OF and head height HH of the
hip stem 300
remain properly sized for the anatomy.
[00108] As described herein, as normal, i.e., non-osteoporotic femurs or
femurs with Type
A bone increase in size across a given patient population, the metaphyseal and
diaphyseal
regions of the femur typically increase proportionately and sets of hip stems
250, for example,
have a corresponding proportional rate of increase with respect to the
dimensions of diaphyseal
width, DW, metaphyseal width MW, offset OF and head height HH across a range
of prostheses
of increasing nominal size. However, due to osteoporosis, the canal of the
diaphyseal region of
the femur may have a width which does not correspond to a normal bone, while
the metaphyseal
region may have a width which does correspond to a normal bone. Thus, sets of
hip stems 300
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of the present invention have distal or diaphyseal widths DW that increase at
a non-proportional
rate, sometimes a greater rate, than their corresponding metaphyseal width MW,
offset OF, and
head height HH to accommodate osteoporotic bone.
[00109] In order to provide hip stems 300 in accordance with the above,
the inventors
have designed hip stems 300 having the dimensions discussed below. Tables 2-4
below and their
corresponding charts in Figs. 33A-C show the relationship between the distal
width dimension
DW, and the metaphyseal width dimension MW, offset dimension OF, and head
height
dimension HH for a number of exemplary sets of hip stems 300 of increasing
nominal size. In
Figs. 33A-C, best fit lines have been calculated and shown for each data set.
[00110] The relationship between the distal width dimension DW and the
metaphyseal
width dimension MW is shown in Table 2 below and in Fig. 33A for six exemplary
sets of hip
stems 300 of increasing nominal size.
Table 2
Diaphyseal Width vs. Metaphyseal Width.
MMMMEMMMMM, Metaphyseal Width
(MW) (nna)
Size Diaphyseal
Width
(DW)
(mm) Set 1 Set 2 Set 3 Set 4 Set 5
Set 6
13 13 19.93 21.66 22.2 25.12 26.86 28.43
14 14 19.93 21.66 22.7 25.12 26.86 29.29
15 15 19.93 21.66 23.0 25.12 26.86 29.29
16 16 19.93 21.66 23.4 25.12 26.86 29.74
17 17 19.93 21.66 23.7 25.12 26.86 29.74
18 18 20.3 23.39 24.1 26.86 30.26 30.26
19 19 24.1
20 20 24.1
[00111] The relationship between the distal width dimension DW and the
offset dimension
OF is shown in Table 3 below and in Fig. 33B for eight exemplary set of hip
stems 300 of
increasing nominal size.
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Table 3
Diaphyseal Width vs. Offset.
.....................................
....................................
'.i'.ikrggggggggMNSM Offset (OF)
iN]]]]]]]]]]]]]]]]migigimigigigigim
(mm)
Diaphyseal
Width
Size (mm) Set 1
Set 2 Set 3 Set 4 Set 5 Set 6 Set 7 Set 8
13 13 31
31.52 31.52 35.5 39.5 39.5 44.02 51.52
14 14 31
31.52 31.52 35.5 39.5 39.5 44.02 54.02
15 15 31
31.52 34.02 35.5 39.5 41.52 44.02 54.02
16 16 31
31.52 34.02 38.5 42.5 44.02 46.52 54.02
17 17 31
31.52 34.02 38.5 42.5 44.02 46.52 54.02
18 18 31
34.02 36.52 41.5 45.5 46.52 49.2 56.52
19 19 31 41.5 45.5
20 20 31 41.5 45.5
[00112] The relationship between the distal width dimension DW and the
head height
dimension HH is shown in Table 4 below and in Fig. 33C for five exemplary sets
of hip stems
300 of increasing nominal size.
Table 4
Diaphyseal Width vs. Head Height.
..........................................................,
minggggEggggggggEM Head Height (HH)
...........................................................
.............................................................
inam
Size ,
Diaphyseal
Width
(mm) Set 1 Set 2 Set 3 Set 4 Set 5
13 13 18.56 22.4 23.56 24.9 28.56
14 14 18.56 22.4 23.56 24.9 28.56
15 15 18.56 22.4 23.56 24.9 28.56
16 16 18.56 23.1 23.56 25.6 31.06
17 17 21.06 23.1 23.56 25.6 33.56
18 18 21.06 23.1 26.06 28.6 33.56
19 19 23.1 28.6
20 20 23.1 28.6
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[00113] The relationship between the distal width dimension DW and each of
the
metaphyseal width, offset, and head height dimensions MW, OF, and HH,
respectively, for a
number of exemplary sets of hip stems 300 of increasing nominal size has been
set forth
separately in Tables 2-4 above and in Figs. 33A-C in order to more clearly
illustrate such
relationships. Of course, any given set of hip stems 300 in accordance with
the present invention
will have all four dimensions, wherein each set of dimensions may be selected
from those above
or any dimensions between the extremes of the data sets set forth above. In
Tables 5 and 6
below, these four dimensions are set forth for two exemplary sets of hip stems
300 having neck
angles NA of 125 and 135 .
Table 5
Hip stems 300 - Neck angle 125 .
Size Diaphyseal Width Metaphyseal Width Offset Head Height
(DW) (mm) (MW) (mm) (OF) (mm) (HH) (mm)
13 13 22.2 39.5 22.4
14 14 22.7 39.5 22.4
15 15 23.0 39.5 22.4
16 16 23.4 42.5 23.1
17 17 23.7 42.5 23.1
18 18 24.1 45.5 23.1
19 19 24.1 45.5 23.1
20 20 24.1 45.5 23.1
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WO 2008/098171 PCT/US2008/053423
Table 6
Hip stems 300 - Neck angle 135 .
Size Diaphyseal Width Metaphyseal Width Offset Head Height
(DW) (mm) (MW) (mm) (OF) (mm) (HH) (mm)
13 13 22.2 35.5 24.9
14 14 22.7 35.5 24.9
15 15 23.0 35.5 24.9
16 16 23.4 38.5 25.6
17 17 23.7 38.5 25.6
18 18 24.1 41.5 28.6
19 19 24.1 41.5 28.6
20 20 24.1 41.5 28.6
[00114] In alternate embodiments, the dimensions of metaphyseal or head
portion 302 and
diaphyseal or distal portion 304 of hip stems 300 may be determined with
reference to any
anterior/posterior, medial/lateral, or other suitable dimensions of the
metaphyseal or head portion
302 and diaphyseal or distal portion 304 of hip stems 300 other than the
particular dimensions set
forth and described above. Thus, the hip stems of the present invention are
progressively
dimensioned across a range of increasing nominal sizes to fill the diaphyseal
region of the femur
while properly filling, i.e., not impinging or being obstructed by, the
metaphyseal region of the
femur. Thus, the diaphyseal regions of the present hip stems have widths which
increase at a
rate greater than the metaphyseal regions/widths to provide sufficient contact
and fill of the
diaphyseal region of the femur while simultaneously providing a good fit in
the metaphyseal
region of the femur.
[00115] The present hip stems may also be designed to accommodate for
variation in
medial/lateral (M/L) width of the canal and anterior/posterior (A/P) width of
the canal during
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CA 02674288 2014-12-05
progression of osteoporosis. In this connection, the inventors have observed
that in females, the
intramedullary canal tends to widen relatively more in the anterior/posterior
plane, as viewed
with a lateral x-ray, for example, than in the medial/lateral plane,
particularly in females with
osteoporosis, which commonly causes thinning of the posterior cortex of the
diaphysis. Thus,
the anterior/posterior and medial/lateral diameters of the intramedullary
canal may not be equal.
Generally, the canal begins as circular, then becomes somewhat oval-shaped
during middle
stages of osteoporosis, and then returns to a substantially circular shape at
advanced stages of
osteoporosis. Thus, during middle stages of osteoporosis, the A/P dimension of
the canal loses
bone first to create the oval shape of the canal and the M/L dimension loses
bone at later stages
of osteoporosis to return the canal to substantially the same original
circular cross-sectional
shape. Thus, the present hip stems may be designed to have greater A/P
dimensions than M/L
dimensions to accommodate for this variation in the canal during progression
of osteoporosis.
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