U.S. patent application number 09/040700 was filed with the patent office on 2002-01-10 for modular prosthesis and connector therefor.
Invention is credited to WHITE, PATRICK MICHEL.
Application Number | 20020004685 09/040700 |
Document ID | / |
Family ID | 21912443 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020004685 |
Kind Code |
A1 |
WHITE, PATRICK MICHEL |
January 10, 2002 |
MODULAR PROSTHESIS AND CONNECTOR THEREFOR
Abstract
A modular orthopedic prosthesis has a body with a generally
triangular cross-section near one end, allowing its angular corners
to bite or incise into the surrounding bone cavity for rotational
stability. A stem, which may be either unitary or modular in
structure, is received within a through-bore of the body, having a
proximal neck and distal shaft. A connecting sleeve receives the
stem and is, in turn, received within the bore of the body, then
actuated to lock the stem and body together.
Inventors: |
WHITE, PATRICK MICHEL;
(MAHWAH, NJ) |
Correspondence
Address: |
KLAUBER & JACKSON
411 HACKENSACK AVENUE
HACKENSACK
NJ
07601
|
Family ID: |
21912443 |
Appl. No.: |
09/040700 |
Filed: |
March 18, 1998 |
Current U.S.
Class: |
623/23.15 |
Current CPC
Class: |
A61F 2/36 20130101; A61F
2002/30354 20130101; A61F 2220/0025 20130101; A61F 2230/0023
20130101; A61F 2002/4051 20130101; A61F 2002/30332 20130101; A61F
2/30734 20130101; A61F 2002/30738 20130101; A61F 2002/4074
20130101; A61F 2002/4018 20130101; A61F 2220/0033 20130101; A61F
2/367 20130101; A61F 2/40 20130101; A61F 2002/30158 20130101; A61F
2230/0026 20130101; A61F 2002/30112 20130101; A61F 2002/30156
20130101; A61F 2002/30484 20130101; A61F 2002/30339 20130101; A61F
2002/30594 20130101; A61F 2002/4062 20130101; A61F 2230/0004
20130101; A61F 2002/3674 20130101; A61F 2002/30574 20130101; A61F
2002/30474 20130101; A61F 2002/30604 20130101 |
Class at
Publication: |
623/23.15 |
International
Class: |
A61F 002/36 |
Claims
1. A modular orthopedic prosthesis comprising: a stem having one
end with an elongated portion and another, longitudinally opposed
end with a first means presenting a joint motion surface; a body
including a bore defining at least a first axis and having a
generally polygonal cross-section with at least two angular corners
adapted to bite into the bone cavity of a patient to prevent
rotation of the implanted prosthesis relative to the bone; and
means for connecting the stem and body together in a fixed
position.
2. The prosthesis of claim 1 wherein the body has a generally
triangular cross-section.
3. The prosthesis of claim 1 wherein the body has a single
through-bore.
4. The prosthesis of claim 1, the body having first and second ends
longitudinally opposed from one another along the first axis, the
first end being adjacent the first means and the second end being
adjacent the elongated portion, the body having a generally
polygonal cross-section in the region of the first end of the
body.
5. The prosthesis of claim 1, the body having a planar osteotomy
surface oriented at a selected angle relative to the first axis,
such that the distance between the axis and the edge of the surface
increases in a direction from the from the first end of the body
toward the second end of the body.
6. The prosthesis of claim 4, the body having a generally circular
cross-section in the region of the second end of the body.
7. The prosthesis of claim 1, the first means further comprising a
neck operatively connected to the body in the region of the first
end.
8. The prosthesis of claim 1, the elongated portion further
comprising a shaft having a free end with a tip and a fixed end
opposite the tip wherein the bore of the body is adapted to receive
the fixed end for assembly with the body.
9. The prosthesis of claim 1 wherein the stem further comprises a
neck, carrying the joint motion surface, and a shaft opposite the
neck, the shaft being adapted for receipt within the medullary
canal of a bone, the stem passing through the bore and being
attached to the body in a fixed position along the first axis.
10. The prosthesis of claim 1, wherein the neck and shaft each
comprise separate modular articulating components of the stem.
11. The prosthesis of claim 10, the stem further comprising a neck
attached to the body along the first axis.
12. The prosthesis of claim 10 wherein the elongated portion is
attached to the body along the first axis.
13. The prostheses of claim 1 wherein the sleeve comprises a
super-elastic material.
14. The prostheses of claim 13 wherein the super-elastic material
is nitinol.
15. The prosthesis of claim 1 wherein the bore of the body and an
outer surface of the sleeve have mating tapers which, when seated
together, activate the stem and body to lock together in fixed
relative position.
16. The prosthesis of claim 1, the sleeve having an inner bore that
is tapered and the stem having at least one corresponding outer
surface that is tapered wherein the mating tapers, when engaged,
activate the stem and body to lock together in fixed relative
position.
17. A modular orthopedic prosthesis comprising: a stem component
having one end with an elongated portion and another,
longitudinally opposed end with a first means presenting a joint
motion surface; a body component including a bore defining at least
a first axis; and a radially expansible sleeve having opposed ends,
one end received within the bore and the other end projecting
outwardly from the bore, the sleeve connecting the stem and body
together in a fixed position.
18. The prosthesis of claim 17 wherein the body has a polygonal
cross-section with at least two angular corners adapted to bite or
incise into the bone cavity of a patient to prevent rotation of the
implanted prosthesis relative to the bone.
19. The prosthesis of claim 17, the sleeve further comprising a
collet having a bore wherein the stem is received within the bore
of the collet, the stem and collet together being further received
within the bore of the body to lock them together.
20. The prosthesis of claim 19, the sleeve further comprising a
split collet.
21. The prosthesis of claim 19 wherein the collet has a distal
insertion end for receipt within the bore along the first axis and
an opposed, proximal end including an annular flange.
22. The prosthesis of claim 19 wherein the annular flange comprises
a spacer shoulder having a selected thickness.
23. The prosthesis of claim 17 wherein the stem comprises a unitary
member.
24. The prosthesis of claim 17, the first means further comprising
a neck wherein the receives the neck for assembly with the
body.
25. The prosthesis of claim 17, the elongated portion further
comprising a shaft having a free, distal end with a tip and a
fixed, proximal end opposite the tip wherein the receives the fixed
end for assembly with the body.
26. The prosthesis of claim 17 wherein the stem further comprises a
neck, carrying the joint motion surface, and a shaft opposite the
neck, the shaft having a distal tip adapted for receipt within the
medullary canal of a bone, the stem passing through the bore and
being attached to the body in a fixed position along the first
axis.
27. The prosthesis of claim 26, the stem further comprising a neck
attached to the body along the first axis.
28. The prosthesis of claim 27 wherein the elongated portion is
attached to the body along the first axis.
29. The prostheses of claim 17 wherein the neck and the shaft
comprise separate modular components of the stem.
30. The prostheses of claim 17 wherein the body has an upper face
defining an outer periphery of the bore, the sleeve having an end
received within the bore and an opposite end with an annular flange
juxtaposed with the outer periphery.
31. The prostheses of claim 17 wherein the annular flange has a
shoulder with an upper surface and the first means includes a neck
with an abutment surface contacting the upper surface of the
shoulder as the stem is locked within the body.
32. The prostheses of claim 17 wherein the first means of the stem
comprises a separate neck component and the elongated portion a
separate shaft component, the neck having means adjacent the body
for connecting within the bore of the sleeve, the shaft having a
free end and a fixed end, the fixed end passing through the bore of
the body and into the bore of the sleeve.
33. The prostheses of claim 17 wherein the sleeve comprises an
annular collet made of a super-elastic material.
34. The prostheses of claim 33 wherein the super-elastic material
is nitinol.
35. The prosthesis of claim 17 wherein the bore of the body and an
outer surface of the sleeve have mating tapers which, when seated
together, activate the stem and body to lock together in fixed
relative position.
36. The prosthesis of claim 17, the sleeve having an inner bore
that is tapered and the stem having at least one corresponding
outer surface that is tapered wherein the mating tapers, when
engaged, activate the stem and body to lock together in fixed
relative position.
37. A modular orthopedic prosthesis comprising: a stem having one
end with an elongated portion and another, longitudinally opposed
end with a first means presenting a joint motion surface; a body
including a bore defining at least a first axis and having a
polygonal cross-section with at least two angular comers adapted to
bite into the bone cavity of a patient to prevent rotation of the
implanted prosthesis relative to the bone; and a radially
expansible sleeve having opposed ends and a bore, one end of the
sleeve being received within the bore of the body and another end
projecting outwardly from the bore of the body, wherein the stem is
received within the bore of the sleeve, the stem and sleeve
together being further received within the bore of the body to
connect the stem and body together in a fixed position.
38. The prosthesis of claim 37, the first means of the stem
comprising a neck and the elongated portion comprising a shaft, the
bore of the body being a through-bore, wherein the neck and shaft
are a unitary member received in the through-bore.
39. The prosthesis of claim 37, the first means of the stem
comprising a neck and the elongated portion comprising a shaft, the
bore of the body being a through-bore, wherein the neck and shaft
are separate members each received within the through-bore.
40. The prosthesis of claim 37, the body having first and second
ends longitudinally opposed from one another along the first axis,
the first end being adjacent the first means and the second end
being adjacent the elongated portion, the body having a generally
triangular cross-section in the region of the first end of the
body.
41. The prosthesis of claim 40, the body having a generally
circular cross-section in the region of the second end of the
body.
42. The prosthesis of claim 37 wherein the sleeve comprises a split
collet.
43. The prosthesis of claim 37, the body having a pair of ends
longitudinally opposed from one another along the first axis of the
bore with one of the ends presenting a top surface adjacent the
first means and another end being adjacent the elongated portion,
wherein the collet further has an end received within the bore of
the body and an opposed end spaced from the top of the body.
44. The prosthesis of claim 37, wherein the collet has an annular
flange on the end of the collet that is spaced from the top surface
of the body, the flange being of a larger size than the bore of the
body and limiting motion of the collet within the bore.
45. The prosthesis of claim 37 wherein the sleeve comprises an
annular collet made of a super-elastic material.
46. The prosthesis of claim 45 wherein the super-elastic material
is nitinol.
47. The prosthesis of claim 37 wherein the bore of the body and an
outer surface of the sleeve have mating tapers which, when seated
together, activate the stem and body to lock together in fixed
relative position.
48. The prosthesis of claim 37, the sleeve having an inner bore
that is tapered and the stem having at least one corresponding
outer surface that is tapered wherein the mating tapers, when
engaged, activate the stem and body to lock together in fixed
relative position.
49. A modular orthopedic prosthesis comprising: a stem having one
end with a neck presenting a joint motion surface and another,
longitudinally opposed end having a shaft; a body including a
through-bore having at least a tapered portion, defining a first
axis, the body having first and second ends longitudinally opposed
from one another along the first axis, the first end being adjacent
the neck and presenting an upper face, the second end being
adjacent the shaft, the body having a generally triangular
cross-section in the region of its first end with at least two
angular corners adapted to bite and incise into the bone cavity of
a patient to prevent rotation of the implanted prosthesis relative
to the bone, the body having a generally circular cross-section in
the region of the second end; and a radially expansible collet
having opposed ends including an internal bore and a tapered
external surface mating with the tapered portion of the bore, the
collet being received within the bore of the body and projecting
outwardly from the bore of the body, wherein the stem is received
within the bore of the sleeve, the stem and sleeve together being
further received within the bore of the body to lock the stem and
body together in a fixed position as the mating tapers are
engaged.
50. The prosthesis of claim 49 wherein the stem comprises a unitary
member.
51. The prostheses of claim 49 wherein the neck and the shaft
comprise separate modular components of the stem.
Description
TECHNICAL FIELD
[0001] This invention relates generally to orthopedic prostheses,
particularly to those having a modular construction that is
assembled from selected components and implanted during
re-constructive arthroplastic surgery.
BACKGROUND
[0002] It is known that bone matter that is not stressed/loaded
will atrophy and lose viability, a problem which currently persists
in present orthopedic implants.
[0003] One approach others have taken is to provide a collar
intended to correspond in shape and size to the prepared cavity of
a proximal femur, ostensibly to offer rotatory stability to the
implanted device. For example, U.S. Pat. No. 4,790,852 to Noiles
shows a modular hip prosthesis including a collar having a shape
with a keyhole cross-section and terraces surrounding the outer
surface perpendicular to the longitudinal axis of the collar. The
collar has a tapered proximal-to-distal contour. However, the shape
of the collar is instead dictated by the milling instrumentation
used to prepare the proximal femoral cavity. According to the
procedure, a surgeon resects the femoral head (ball) with an
osteotome, thereby exposing the medial aspect of the cavity, then
reams the intramedullary canal to make a space for the collar. The
medial bone cavity is then milled to make it fit set criteria of
the implant. U.S. Pat. No. 5,002,578 to Luman also has transverse
terraces and a supposed cavity conforming cross-section. However,
such terraces, like those of the above Noiles '852 patent, do not
counteract rotary motion of the prosthesis, but rather axial
motion. U.S. Pat. No. 4,549,319 to Meyer has an external geometric
pattern of elongated projections spaced circumferentially on a hip
prosthesis. U.S. Pat. No. 4,624,673 to Meyer discusses a component
for use in a prosthetic joint having a hollow tube with a closed
end and an open end. The area of the external surface adjacent to
the open end is at least twice the area of the external surface
adjacent to the closed. A plurality of terraces, oriented
orthogonal to a distal shaft, are on the external surface. A female
part of self-locking taper is provided to connect the components.
U.S. Pat. No. 4,846,839 to Noiles shows a modular hip with a collar
having an oval cross-section and a terraced external surface,
connecting with a stem. Products have been marketed generally based
upon this approach, e.g., The SROM Hip, of Joint Medical Products,
Inc.
[0004] The aforementioned patents seek to provide rotatory
stability by circumferential contact between the prepared femoral
cavity and an outer surface of a main body or collar member. This
type of contact is actually tangential in nature. The use of an
oval cross-sectional shape often does not allow the outer surface
of the prosthesis collar to effectively engage the intact bone. In
many cases, especially in revision patients, healthy bone can be
problematic to uniformly contact, for example, in the lateral
aspects of the proximal femur, where the greater trochanter is left
largely undisturbed by the surgeon during a primary implantation.
The lack of rotatory stability, needed for uniform stress on such
healthy bone, can cause the intact tissue to weaken and possibly
atrophy, unacceptably, at some point following the initial
implantation of the prosthesis.
[0005] Others, including some of the above approaches, have further
sought to achieve prosthesis-cavity conformance while providing
various modular constructions and ways of connecting the components
of the prosthesis.
[0006] For example, related U.S. Pat. Nos. 5,370,706 and 5,080,685
to Bolesky show a body member having a neck with a base defining a
neck basal plane. A body member includes an upwardly and inwardly
directed portion and a tapered longitudinal bore. A tapered
connector engages a head member with the upwardly and inwardly
directed portion. A problem experienced with this particular design
is its limited strength, due to the location of the interconnecting
components. Thus, the point of connection of the shaft must bear a
load that is often too great, without being able to distribute that
force. In U.S. Pat. No. 4,878,917 to Kranz, et al., there is shown
a modular implant with a tensioning connector rod structurally
designed to break when loaded a selected amount. U.S. Pat. No.
5,201,882 to Paxson discloses indicia for selecting the desired
ante-version of a modular hip stem that is connected via tapered
fittings to a unitary neck/body member, but the neck is not
independently adjustable relative to the body. U.S. Pat. No.
5,725,592, issued to the present inventor, describes a modular hip
prosthesis having a distal stem component that connects with a body
component and a neck component both having tapered
through-bores.
[0007] There is still a need for a modular prosthesis having
independently adjustable components, and for a connector mechanism
allowing the surgeon to visibly adjust them. Also, a prosthesis is
needed, having an adjustable body with a geometry that incisively
engages healthy bone, then securely locks with a stem component
inter-operatively. The prior patents do not show a body shape
capable of adjustably engaging healthy bone tissue in such a
manner.
[0008] Other prior unitary implants have had various shapes, but
the distal shaft and main body portions of these were not
independently adjustable components, allowing surgeons to
inter-operatively achieve optimal engagement of the body with
healthy bone tissue.
[0009] Moreover, a need exists for a prosthesis that allows the
surgeon to independently adjust the implant and realize the aim of
engaging intact bone, as well, for an implant geometry that incises
the intact bone and stresses it.
[0010] There is a further need for a modular implant that is
infinitely adjustable, rotationally and axially, using a relatively
simple array of components, allowing a surgeon flexibility while
reducing the cost of carrying a large inventory of sizes. Such a
need also exists while continuously delivering desired benefits,
via the implant geometry, to a patient's intact bone. A modular
implant design is called for, whose components can be readily
assembled inter-operatively and securely locked together by the
surgeon to achieve these purposes.
SUMMARY OF THE INVENTION
[0011] According to the invention, there is provided a modular
orthopedic prosthesis including a stem having one end with an
elongated portion and another, longitudinally opposed end with a
first means presenting a joint motion surface. The prosthesis has a
body including a bore defining at least a first axis and having a
polygonal cross-section with at least two angular corners adapted
to bite or incise into the bone cavity of a patient to prevent
rotation of the implanted prosthesis relative to the bone. Means
are provided for connecting and locking the stem and body together
in a fixed position.
[0012] In a preferred embodiment of this invention, the body has a
first end with a generally triangular cross-section in the region
of the first end and a generally round cross-section in the region
of its second end, presenting a multi-axial wedge shape.
[0013] According to the invention, in another of its aspects, a
modular orthopedic prosthesis is provided. The prosthesis comprises
a stem component having one end with an elongated portion and
another, longitudinally opposed end with a first means presenting a
joint motion surface. A body component includes a bore defining at
least a first axis. A radially expansible sleeve has opposed ends,
one end received within the bore and the other end projecting
outwardly from the bore, the sleeve adjustably connecting the stem
and body together and locking them in a fixed position.
[0014] In a preferred embodiment of this invention, the joint
motion surface is adjustably spaced from the body.
[0015] An advantage of the present invention is inventory and
manufacturing cost savings, since its modularity allows for economy
in manufacturing, as any number of well-known stem types may be
selected, and also reduces the inventory of pieces needed on-hand
for each surgical procedure.
[0016] Another advantage of the invention is enhanced clinical
benefits, as the wedge shape offers enhanced rotatory stability of
the prosthesis in use, particularly with revision surgery
patients.
[0017] A further advantage of the invention is in providing a
connector mechanism that is highly secure once fixed in place,
meanwhile providing the surgeon inter-operative flexibility to
axially and rotationally adjust the stem independently of the
body.
[0018] A still further advantage of the invention gives a surgeon
the capability to rotationally "dial" the body in order to have its
triangular corners contact and "bite into" or incise as much
available healthy bone as possible. By evenly loading/stressing
such intact bone, wherever found by the surgeon, particularly in
revision patients, it is possible to avoid potential eventual
atrophy of the bone tissue.
[0019] Other objects and advantages will become apparent to those
skilled in the art by reference to the following Description and
Drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of a modular hip prosthesis of
the invention, fully assembled and implanted in a proximal femur,
with the bone longitudinally cut away;
[0021] FIG. 2 is an external side view of the body component of the
present invention, taken from an anterior-posterior aspect;
[0022] FIG. 2A is a cross-section of the proximal portion of the
body of FIG. 2, taken substantially along the lines 2A-2A;
[0023] FIG. 2B is a cross-section of the proximal portion of the
body of FIG. 2, taken substantially along the lines 2B-2B;
[0024] FIG. 2C is a cross-section of the proximal portion of the
body of FIG. 2, taken substantially along the lines 2C-2C;
[0025] FIG. 3 is an external side view of the sleeve component of
the present invention, taken from either an anterior-posterior or
medial-lateral aspect;
[0026] FIG. 3A is a longitudinal section of the body of FIG. 3,
taken substantially along the lines 3A-3A;
[0027] FIG. 3B is an external top view of the proximal portion of
the sleeve of FIG. 3;
[0028] FIG. 4 is a partially exploded perspective view of the
invention, showing the sleeve partially seated in the bore of the
body, prior to insertion of the stem;
[0029] FIG. 5 is a cross-section of the proximal portion of the
body of the invention, implanted in a cadaver bone, showing also
the cross-section of a representative prior art implant for
comparison purposes.
[0030] FIG. 6 is an exploded perspective view of the stem, body and
sleeve of the invention, shown prior to assembly, wherein the stem
has a modular construction with separate neck and distal shaft
components;
[0031] FIG. 7 is an exploded perspective view of the prosthesis of
FIG. 6, showing the distal shaft component of the modular stem
being connected to the body with another independent sleeve;
[0032] FIG. 8 is an exploded perspective view of the prosthesis of
the invention showing a unitary stem with a tapered connection
region, a sleeve with a cylindrical outer surface and a tapered
internal bore, and a body with a linear through-bore;
[0033] FIG. 9 is a top view of the body component having a
generally triangular shape with two sharp corners and a tapered
bore;
[0034] FIG. 10 is a top view of the body component having a
generally polygonal shape, i.e., hemi-hexagonal, with sharp
corners, and a tapered bore;
[0035] FIG. 11 is an external view of the body of a prosthesis of
the invention with a medial osteotomy plane;
[0036] FIG. 12 is a top view of the body component of FIG. 11;
and
[0037] FIG. 13 is a sectional view, taken substantially along lines
13-13 of FIG. 12.
DETAILED DESCRIPTION
[0038] According to the invention, as shown in FIGS. 1-13, there is
provided a modular prosthesis assembly, generally shown at 10,
including a stem component, generally shown at 12, a body
component, generally shown at 14, and means in the form of a
sleeve, generally shown at 16, for affixing the stem and body
together. In FIGS. 1, 4, and 8 the stem 12 is a unitary member,
however, as shown in FIGS. 6-7, the stem can be in a modular form.
In FIGS. 1, 4, 6 and 8, the prosthesis 10 comprises a single
sleeve, however, as shown in FIG. 7, the prosthesis can include a
pair of sleeves 16 in conjunction with a modular stem.
Nevertheless, a single sleeve is preferred. In FIGS. 1, 2, 2-C, 4,
and 6-13, the body has a first or proximal end 15 and a second,
longitudinally opposed or distal end 17. The body 14 functions as a
wedge generally in the anterior-posterior and medial-lateral plane,
as well as the proximal-distal plane, as will be herein
elucidated.
[0039] The body 14 has a bore 18 with a first axis A extending
between the proximal 15 and distal 17 ends, through which stem 12
is received, once the stem has been passed through sleeve 16. The
assembled stem 12 and sleeve 16 are seated in bore 18 and, as they
are urged into the bore fully, the sleeve radially compresses to
pressure-lock the stem and body together in a fixed relative
position.
[0040] The present invention employs a distinctive geometry and
connection technology that variably locks together the three
fundamental components 12, 14 and 16 of the prosthetic hip 10 into
a fixed configuration. In surgery, the proximal femoral bone cavity
is prepared by reaming and then a finish broaching operation,
thereby creating the desired cavity in the bone. In FIG. 4, the
sleeve 16 is placed in the bore 18 (phantom) through a first end 15
of body 14 but left proud, i.e., not fully seated in the bore. Then
stem 12 is passed through the sleeve 16 until the desired neck
height is achieved for restoring the tension of the total
articulated joint. Indicia could be added to allow visual
recognition of the height adjustment by the surgeon. Once the
proper height is achieved, an axial force is applied to the top 24
of sleeve 16, locking it against the bore 18. In a preferred
embodiment, axial force can be applied to the top 26 of neck 22 and
transmitted indirectly, through the bottom 20 of neck 22, to top 24
of sleeve 16. The components are actuated and locked together in
this manner as shown by FIGS. 1 and 4, in the case of a unitary
stem 12, and similarly in the case of a modular assembly. As shown
in FIGS. 6-7, modular neck 22 has a protrusion 27 extending
distally from bottom 20 of the neck for connecting with sleeve 16.
Protrusion 27 may be either straight or tapered, depending upon the
geometry of its interconnecting member.
[0041] The sleeve 16 will now be more particularly described.
Preferably, sleeve 16 is radially flexible by means of a preferred
split collet 28, as shown in FIGS. 3 and 3A-3B, to lock the
components together. The preferred split collet 28 can be made from
titanium, stainless steel or cobalt-chromium alloys. Sleeve 16 has
bottom 25 received within bore 18. The same locking function is
performed by sleeve 16 in the embodiments of FIGS. 6-8 that show a
modular distal shaft 30. Alternatively, a solid construction could
be employed for the sleeve (not shown), using a super-elastic
material that is inherently radially flexible under controlled
temperature conditions, e.g., a nickel-titanium alloy such as
nitinol. Sleeve 16 has an outer surface 31 that engages bore
18.
[0042] The body 14 will now be more particularly described. As
shown is FIG. 2A, taken through the region of first or proximal end
15 of body 14, the body has an outer surface 32 with a "generally
polygonal" cross-sectional shape, although the polygon is
preferably a triangle. Such a shape affords non-tangential contact
with the intact bone, in a plane perpendicular to the longitudinal
axis of the bone. Together with the tapered contour in the
proximal-distal plane, body 14 functions as a three-dimensional
wedge. By the term "generally polygonal", it is meant that one or
more of the sides of the polygon could be either linear or slightly
bowed, in a concave or convex manner. However, substantially linear
sides are preferred. The degree to which the sides may be bowed
should not defeat the function of the angular corners 34 shown in
FIGS. 1, 2, 2A, 2C and 4-10, as well as in FIGS. 11-12 that will be
described below.
[0043] The centroid (not shown) of the proximal polygonal
cross-sectional shape of body 14 need not coincide with axis A of
bore 18. Likewise, the centroid (not shown) of the distal
cross-section (FIG. 2B) which could be polygonal or preferably
round, need not coincide with the axis A of bore 18, although such
coincidence is preferred. Neither of the first 15 and second 17
ends of body 14 need be perpendicular to the axis A of bore 18,
yet, it is preferred that ends 15, 17 are perpendicular to axis A.
As shown in FIGS. 11-13, body 14 has a planar osteotomy surface 35,
oriented at a selected angle relative to axis A, such that the
distance between the axis A and the edge of the outer surface 32
increases in a direction from the first end of the body toward the
second end of the body. The planar surface 35 generally corresponds
to the location of an osteotomy cut. Either of the surfaces 15 or
35 could optionally carry a collar member (not shown) that is meant
to rest on the end of the bone, where clinically indicated, to help
prevent linear subsidence of the body component axially into the
bone cavity. As to the function of the cross-sectional shape,
however, the body geometry shown in FIGS. 11-13 has the same
function as in the other embodiments previously discussed. That is,
the corners 34 incise into the bone to provide rotatory stability
to the implanted prosthesis 10, while effectively loading the
bone.
[0044] Reference is now made to the three views of sleeve 16 shown
in FIG. 3. An outer surface 31 of sleeve 16 contacts bore 18 and
creates a lock between stem 12 and body 14, while an inner bore 36
of the sleeve creates a lock between stem 12 and the body, when
axial force is applied to the assembled components. Sleeve 16 is
radially flexible about axis A of bore 18, by means of collet 28.
As with the first 15 and second 17 ends of body 14, the opposed top
24 and bottom 25 of sleeve 16 need not lie in planes that are
parallel to one another, although such is preferred. As shown in of
FIG. 3A, sleeve 16 may have either a straight or tapered bore 36.
Similarly, the outer surface 31 of sleeve 16 could be tapered or
straight. The sleeve may have bore 36 of different diameters
correspond to the different outer diameters of the stem 12,
respectively. The thickness of the wall defined between the inner
diameter of the bore 36 and outer diameter to the surface 31 may be
varied to accommodate different corresponding diameter sizes of the
stem.
[0045] Although a single through-bore 18 is preferred, separate
bores (not shown) could be used to receive each of the distal shaft
and neck components, as in the case of a modular stem construction
contemplated by FIGS. 6-7. In a modular construction, shaft 30 has
a free end or distal tip 37 that is received within the medullary
canal of the femur, in the case of hip prosthesis 10.
[0046] In the top and external views of FIG. 3, top 24 of sleeve 16
has an optional upper shoulder 38 that is spaced from surface 15 of
body 14. In FIG. 8 an embodiment is shown wherein the optional
shoulder 38 stops the sleeve 16 from falling through the bore 18 in
body 14 which is necessary since the bore 18 and outer surface 31
of sleeve 16 are both straight rather than tapered. When the stem
12 is passed through the sleeve 16 the taper connection region 40
adjacent the bottom 20 of neck 22 spreads the collet 28 of sleeve
16 and locks the components together. Shoulder 38 has an underside
42 that abuts the outer periphery of bore 18 and stops the sleeve
16 from falling through the bore 18. Alternatively instead of the
shoulder 38 limiting axial motion of the sleeve relative to the
bore, the bore could have a counter-sunk inlet (not shown) that
would abut the bottom 25 of sleeve 16 and arrest its downward
motion in the bore. The leg length could be adjusted by using
different height shoulders 38.
[0047] Referring to FIGS. 1, 4, 6 and 7-8, neck 22 carries a joint
motion surface via tapered connector 44 to which a ball (not shown)
may be attached having the acetabular fit needed to ensure proper
articulation and total joint tension. Distal shaft 30 could be
coated, fluted, slotted or the like. The connection region 40,
although shown with a tapered diameter in FIG. 8, as well as in a
unitary stem 12 or modular neck 22 and shaft 30 configuration, can
also have a straight diameter in the other embodiments described.
Region 40 is adjacent a fixed or proximal end 41 of modular shaft
component 30 (FIGS. 6-7), which is longitudinally opposed from
distal tip 37. End 41 is received within sleeve 16.
[0048] Reference is now made to FIG. 5, showing the preferred
triangular proximal cross-sections of the invention versus a
representative prior art collar (oval and keyhole shapes) in an
actual cadaver bone. Superimposed on the prior keyhole shape is the
triangular cross-section of the invention. By contrast, the prior
art relies upon circumferential and, ultimately tangential contact
with the bone and does not present a multi-axial wedged shape that
reaches out and incises into intact bone in the lateral regions of
the proximal femoral cavity, as does the present design. This
structural difference results in a crucial functional
distinction.
[0049] In FIGS. 9-10, two preferred polygonal shapes are shown for
body 14, taken cross-sectionally in the region of first end 15
adjacent neck 22. In FIG. 12, body 14 has a generally triangular
cross-section, with at least two corners 34 on its outer surface
32, whereas, in FIG. 13 there is shown another polygonal shape,
i.e., partially hexagonal, which presents such corners 34. The
necessity for biting into intact bone, in the case of hip
arthroplasty, is most important in the lateral aspect of the
femoral cavity, which is less exposed than the medial aspect. This
is because the femoral head is resected, exposing the entire
proximal medial cavity to the surgeon. This is not so laterally,
hence the geometry of the body of the present invention which can
reach out and bite into the lateral intact bone. An oval shape does
not do this. Bore 18 of body 14 has a tapered portion 46 adjacent
the top or proximal end 15, for mating engagement with either
sleeve 16 or a tapered stem.
[0050] Although the invention has been described with reference to
a prosthesis 10 designed for hip arthroplasty, it must be
understood that this invention may be used in other types of
arthroplasty, e.g., a shoulder joint (not shown), with certain
particular adaptations.
[0051] The above Description should not be construed as limiting
but rather is given for purposes of illustrating the invention.
Obviously, persons skilled in the art could make various
modifications to the embodiments shown, without departing from the
scope of the present invention, as claimed in those claims appended
to this Specification.
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