U.S. patent application number 13/933474 was filed with the patent office on 2013-10-31 for interlocking reverse hip and revision prosthesis.
The applicant listed for this patent is Hip Innovation Technology LLC. Invention is credited to Zafer Termanini.
Application Number | 20130289734 13/933474 |
Document ID | / |
Family ID | 44532007 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130289734 |
Kind Code |
A1 |
Termanini; Zafer |
October 31, 2013 |
Interlocking Reverse Hip and Revision Prosthesis
Abstract
A reverse hip prosthesis comprising an acetabular cup for
implanting in an acetabular socket. The acetabular cup is secured
to the acetabular socket of the pelvis using fasteners. The
acetabular cup has a stem extending from the center of a concave
portion thereof and an acetabular ball is attached to the stem,
preferably by means of a Morse taper. A femoral implant is provided
with a femoral cup attached to the proximal end thereof. The
femoral cup has a stem which can be constructed in a modular
fashion with several stem lengths in order to accommodate the
various sizing requirements of different patients. After
implantation of the acetabular cup and ball and the femoral cup,
the members are assembled together so that the femoral cup can
articulate on the acetabular ball. The prosthesis of the invention
has a wide range of motion and substantially improved tribology. As
the femoral cup is articulated, the edge of the femoral cup moves
into a space located between the acetabular cup and the acetabular
ball and thereby becomes restrained, thus reducing the likelihood
of dislocation during extreme ranges of motion.
Inventors: |
Termanini; Zafer; (Boca
Raton, FL) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Hip Innovation Technology LLC |
Boca Raton |
FL |
US |
|
|
Family ID: |
44532007 |
Appl. No.: |
13/933474 |
Filed: |
July 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13024381 |
Feb 10, 2011 |
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13933474 |
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12799609 |
Apr 28, 2010 |
8313531 |
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13024381 |
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61339680 |
Mar 8, 2010 |
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Current U.S.
Class: |
623/22.18 |
Current CPC
Class: |
A61F 2/3609 20130101;
A61F 2/40 20130101; A61F 2002/4011 20130101; A61F 2002/30616
20130101; A61F 2002/30614 20130101; A61F 2002/3401 20130101; A61F
2002/3615 20130101; A61F 2002/3069 20130101; A61F 2002/30784
20130101; A61F 2002/30649 20130101; A61F 2002/30245 20130101; A61F
2002/3483 20130101; A61F 2/34 20130101; A61F 2002/4022 20130101;
A61F 2002/4085 20130101; A61F 2/3607 20130101; A61F 2/32 20130101;
A61F 2002/4033 20130101; A61F 2002/30332 20130101; Y10S 623/908
20130101 |
Class at
Publication: |
623/22.18 |
International
Class: |
A61F 2/34 20060101
A61F002/34 |
Claims
1-17. (canceled)
18. A hip prosthesis having increased stability at extreme ranges
of motion comprising a unitary acetabular cup having a
non-articulating surface for attachment to an acetabular socket in
a pelvic bone and a concave surface located opposite to the
non-articulating surface, the concave surface having an acetabular
cup stem firmly affixed therein and projecting outwardly therefrom,
a spherical acetabular ball firmly affixed to the acetabular cup
stem, the spherical acetabular ball having a surface, the concave
surface of the acetabular cup and the surface of the spherical
acetabular ball are spaced from one another, thereby defining a gap
therebetween, a femoral implant for implantation in a medullary
canal of a proximal end of a femur, and a femoral cup firmly
affixed to a proximal end of the femoral Implant, the femoral cup
being sized for articulation in the gap, such that the femoral cup
has a concave surface sized for articulation on the surface of the
spherical acetabular ball and a convex surface opposite the concave
surface of the femoral cup sized for articulation on the concave
surface of the acetabular cup, the spherical acetabular ball and
the concave surface of the femoral cup comprising a reverse ball
and socket, the gap being sized and configured to permit said
articulation while constraining the femoral cup within the gap
throughout an entire range of said articulation of the femoral cup
as it articulates within the gap, thereby reducing the risk of
dislocation.
19. The prosthesis of claim 18 wherein the concave surface of the
femoral cup is hemispherical and the concave surface of the
acetabular cup is hemispherical.
20. The prosthesis of claim 18 wherein the concave surface of the
acetabular cup has a center and the acetabular cup stem is affixed
to and in the center.
21. The prosthesis of claim 18 wherein the acetabular ball has an
acetabular ball recess sized to receive the acetabular cup
stem.
22. The prosthesis of claim 18 wherein the femoral cup has a
femoral cup stem projecting outwardly therefrom in a direction
opposite the concave surface thereof and the femoral implant has at
its proximal end a recess sized to receive the femoral cup
stem.
23. The prosthesis of claim 18 wherein the femoral implant has a
femoral implant stem extending proximally therefrom and the femoral
cup has a recess sized to receive the femoral implant stem.
24. The prosthesis of claim 21 wherein the acetabular ball has a
center, the acetabular cup stem has a longitudinal center line and
the acetabular ball recess has a longitudinal center line, both
longitudinal center lines being colinear and passing through the
center of the acetabular bail.
25. The prosthesis of claim 22 wherein the femoral cup has a
concave hemispherical portion having a center line, the femoral cup
stem has a longitudinal center line and the femoral implant recess
has a longitudinal center line wherein all of the center lines are
colinear.
26. The prosthesis of claim 23 wherein the femoral cup has a
concave hemispherical portion having a center line, the femoral
implant stem has a longitudinal center line and the femoral cup
recess has a longitudinal center line wherein all of the center
lines are colinear.
27. The prosthesis of claim 18 wherein the acetabular cup further
comprises a circumferential groove in the convex surface, said
circumferential groove located in proximity to a circumferential
edge of the acetabular cup.
28. The prosthesis of claim 18 further comprising a hemispherical
protective shield moveably disposed in the gap, the protective
shield having a retaining ring for engagement with a
circumferential outer edge of the femoral cup whereby articulation
of the femoral cup on the acetabular ball causes movement of the
protective shield.
29. The prosthesis of claim 18 wherein the concave surface of the
femoral cup is fully in contact with the surface of the acetabular
ball during articulation of said concave surface on the actetabular
ball.
30. A method of implanting in a patient a hip prosthesis having
increased stability at extreme ranges of motion comprising a
unitary acetabular cup having a non-articulating surface for
attachment to an acetabular socket in a pelvic bone and a concave
surface located opposite to the non-articulating surface, the
concave surface having an acetabular cup stem firmly affixed
therein and projecting outwardly therefrom, a spherical acetabular
ball firmly affixed to the acetabular cup stem, the spherical
acetabular ball having a surface, the concave surface of the
acetabular cup and the surface of the acetabular ball are spaced
from one another, thereby defining a gap therebetween, a femoral
implant for implantation in a medullary canal of a proximal end of
a femur, and a femoral cup firmly affixed to a proximal end of the
femoral implant, the femoral cup being sized for articulation in
the gap, such that the femoral cup has a concave surface sized for
articulation on the surface of the spherical acetabular ball and a
convex surface opposite the concave surface of the femoral cup
sized for articulation on the concave surface of the acetabular
cup, the spherical acetabular ball and the concave surface of the
femoral cup comprising a reverse ball and socket, the gap being
sized and configured to permit said articulation while constraining
the femoral cup within the gap throughout an entire range of said
articulation of the femoral cup as it articulates within the gap,
thereby reducing the risk of dislocation, comprising preparing an
acetabular socket in a pelvis and firmly affixing the acetabular
cup therein, preparing a medullary canal at the proximal end of a
femur and affixing the femoral implant therein, affixing the
acetabular ball to the acetabular cup stem, affixing the femoral
cup to the proximal end of the femoral implant and aligning the
concave surface of the femoral cup with the acetabular ball so that
the concave surface of the femoral cup will articulate on the
acetabular ball.
31. The method of claim 30 further comprising disposing a
protective shield in the acetabular cup prior to affixing the
acetabular ball to the acetabular cup stem.
32. A revision surgery method of implanting in a patient a hip
prosthesis having increased stability at extreme ranges of motion
comprising a unitary first acetabular cup having a non-articulating
surface for attachment to an acetabular socket in a pelvic bone and
a concave surface located opposite to the non-articulating surface,
the concave surface having an acetabular cup stem firmly affixed
therein and projecting outwardly therefrom, a spherical acetabular
ball firmly affixed to the acetabular cup stem, the spherical
acetabular ball having a surface, the concave surface of the first
acetabular cup and the surface of the acetabular ball are spaced
from one another, thereby defining a gap therebetween, a femoral
implant for implantation in a medullary canal of a proximal end of
a femur, and a femoral cup firmly affixed to a proximal end of the
femoral implant, the femoral cup being sized for articulation in
the gap, such that the femoral cup has a concave surface sized for
articulation on the surface of the spherical acetabular ball and a
convex surface opposite the concave surface of the femoral cup
sized for articulation on the concave surface of the acetabular
cup, the spherical acetabular ball and the concave surface of the
femoral cup comprising a reverse ball and socket, the gap being
sized and configured to permit said articulation while constraining
the femoral cup within the gap throughout an entire range of said
articulation of the femoral cup as it articulates within the gap,
thereby reducing the risk of dislocation, the patient having an
implant in need of revision, the implant comprising a hip joint
prosthesis with an implanted second acetabular cup and a femoral
stem having an articulating femoral ball affixed to the proximal
end thereof, the implanted second acetabular cup having a concave
articulating surface, the method comprising removing the femoral
stem and articulating femoral ball, firmly affixing to the concave
articular surface of the implanted second acetabular cup the first
acetabular cup, preparing a medullary canal at the proximal end of
the femur and affixing the femoral implant therein, affixing the
acetabular ball to the acetabular cup stem, affixing the femoral
cup to the proximal end of the femoral implant and aligning the
concave surface of the femoral cup with the acetabular ball so that
the concave surface of the femoral cup will articulate on the
acetabular ball.
33. The method of claim 32 further comprising disposing a
protective shield in the acetabular cup prior to affixing the
acetabular ball to the acetabular cup stem.
34. A kit comprising the prosthesis of claim 22 and further
comprising one or more additional femoral cups, wherein the femoral
cup stems have different lengths.
35. A kit comprising the prosthesis of claim 23 wherein the femoral
cup recess is disposed in a neck projecting outwardly from the
femoral cup in a direction opposite the concave surface thereof,
further comprising one or more additional femoral cups, wherein the
femoral cup necks have different lengths.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of application
Ser. No. 12/799,609 filed Apr. 28, 2010 which claims the benefit of
U.S. Provisional Patent Application Ser. No. 61/339,680 filed on
Mar. 8, 2010 and entitled "INTERLOCKING REVERSE HIP PROSTHESIS,"
and the entirety of both are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to hip prostheses
and more specifically to an interlocking reverse hip prosthesis
allowing increased range of motion and stability during excessive
range of motion.
[0004] 2. Description of the Prior Art
[0005] It can be appreciated that several hip implants have been in
use for years. Typically, conventional hip implants comprise a
femoral component having an articular femoral ball attached to a
stem. A femoral stem is inserted into the medullary canal of the
femur after preparation and reaming using appropriate reamers by
the operating surgeon. The stem can be secured with bone cement or
press fit. An acetabular component having the shape of a cup is
inserted into an acetabular socket after preparation and
appropriate reaming and secured with cancellous screws through
holes in the cup. It can also be secured with bone cement or press
fit or a combination thereof.
[0006] The acetabular cup is metallic and it is internally lined
with high-density polyethylene or ceramic. Said lining is secured
into the acetabular cup by a press-fit mechanism.
[0007] The main problem with conventional hip implants is the
instability of the prosthesis at the extreme range of motion,
thereby allowing the articular femoral bail to dislodge and
dislocate. Prior art teaches constrained and preassembled ball and
cup devices or devices wherein the ball and cup members are
implanted separately whereupon the ball element is forced into a
resilient opening in the cup and thereafter held in place by the
resilient material. Other constrained acetabular cups may include a
locking ring such as the one described by Albertorio et al. U.S.
Pat. No. 6,527,808. In the case of cup elements having retaining
rings, the ball member is forcefully inserted into the cup after
the two elements are implanted. This constitutes a weak link where
forces exerted on the prosthesis by ambulatory motion may exceed
the forces used to assemble the implant thereby causing the ball to
be separated from the cup.
[0008] While these devices may be suitable for the particular
purpose which they address, they do not provide an interlocking
mechanism as in the reverse hip implant design of the present
invention. The very nature of applicant's design allows increased
range of motion and increased stability at extreme ranges of motion
thereby reducing the risk of dislocation.
[0009] In these respects, the interlocking reverse hip prosthesis
according to the present invention substantially departs from the
conventional concepts and designs of the prior art because the
articular femoral ball of the prior art is replaced with an
articular femoral cup and the acetabular cup is provided with an
acetabular ball. Thus an apparatus is provided which is primarily
developed for the purpose of reducing the risk of dislocation of
hip implants at extreme ranges of motion.
[0010] Furthermore, since the articular surface of the femoral cup
of the invention is fully in contact 100% of the time with the
surface of the acetabular ball, it is clear that this will improve
tribology because the weight bearing distribution is improved on
the articular surfaces, thus decreasing the wear of the surfaces in
contact and reducing the risk of wear particles being released in
the joint. The later, being very detrimental to the proper function
of the joint.
SUMMARY OF THE INVENTION
[0011] The present invention provides a new interlocking reverse
hip prosthesis construction wherein an acetabular ball is solidly
and concentrically attached to a central protrusion or stem of the
acetabular cup via Morse taper. A metallic acetabular cup is used
in the preferred embodiment. A femoral cup, also referred to herein
as a hemispherical femoral cup or an articular femoral cup, is
preferably solidly attached to a femoral implant by means of a
Morse taper. Other means of attachment known to those in the art
can be used. And whenever a Morse taper is referred to herein, it
is intended to describe a preferred embodiment. The Morse taper can
be replaced by other suitable means of attachment as will be
apparent to those having skill in the art.
[0012] The acetabular cup is implanted in an acetabular socket
constructed by the surgeon in the pelvic bone to which it is firmly
secured by one or more fasteners through one or more openings in
the acetabular cup. The fasteners can be cancellous screws or
biocompatible resorbable studs of variable number. The femoral
implant is then inserted and impacted into the femoral medullary
canal which has been prepared and hollowed by the surgeon using
appropriate reamers. During ambulation, the articular femoral cup
edge or lip will glide conformably and concentrically into a space
located between the acetabular ball and the acetabular cup. As will
be apparent to those having skill in the art, the geometrical
configuration of applicant's invention makes it very difficult for
the femoral cup to dislocate when the range of motion increases
since it becomes constrained in the locking space between the
acetabular cup and the acetabular ball.
[0013] As noted above, the articular surface of the femoral cup is
fully in contact at all times with the articular surface of the
acetabular ball. This improves the weight distribution, decreases
the wear of the surfaces in contact and reduces the risk of wear
particles being released in the joint.
[0014] In an optional embodiment of the invention, applicant has
addressed the rare possibility that soft tissue may get lodged in
the implant in the space between the acetabular cup and the
acetabular ball. A protective sheath can be used to avoid this
possibility. As discussed in more detail below, the sheath is
disposed in the space between the acetabular cup and the acetabular
ball and is allowed to glide freely therein.
[0015] There has thus been outlined the more important features of
the invention in order that the detailed description may be better
understood, and so that the present contribution to the art may be
better appreciated. A novel feature of this invention is that the
location of the articular surfaces of the hip joint, namely the
ball and socket, is reversed. This results in a new reverse hip
implant which is not anticipated, rendered obvious, suggested or
even implied by any prior hip prosthesis when considered alone or
in any combination.
[0016] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not committed in its application to the details of
construction and arrangements of the components set forth in the
following description or illustrated in the drawings. The invention
is capable of other embodiments and of being practiced and carried
out in various ways as will be apparent from the description herein
to those having skill in the art. Also, it is to be understood that
the terminology employed herein are for the purpose of the
description and should not be regarded as limiting.
[0017] To the accomplishment of the above and related objects, this
invention may be embodied in the form illustrated in the
accompanying drawings. However, the drawings are elicited only and
changes may be made into any specific construction illustrated
without departing from the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Various other objects, features and advantages of the
present invention will become fully appreciated as the same becomes
better understood when considered in conjunction with the
accompanying drawings, in which like reference characters designate
the same or similar elements throughout the several views, and
wherein:
[0019] FIG. 1 is a perspective view of the interlocking reverse hip
prosthesis of the invention.
[0020] FIG. 2 is a section view of the interlocking reverse hip
prosthesis.
[0021] FIG. 3 is a section view of the interlocking reverse hip
prosthesis in extension and external rotation.
[0022] FIG. 4 is a section view of the interlocking reverse hip
prosthesis in flexion and internal rotation.
[0023] FIG. 5 is a perspective view of the prosthesis of the
invention illustrating an optional soft tissue protective
sheath.
[0024] FIG. 5A is a perspective view of the protective sheath by
itself.
[0025] FIG. 6 is a section view of the embodiment of FIG. 5.
[0026] FIG. 7 is a section view illustrating a femoral cup having a
recess instead of a stem for connection to a femoral implant.
[0027] FIG. 8 is a section view of the embodiment of FIG. 7 which
has been articulated to an extreme position.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Turning now to the drawings, in which the reference
characters denote the same or similar elements throughout the
several views, FIGS. 1-4 illustrate an interlocking reverse hip
prosthesis, which comprises an acetabular cup (11) having a smooth
concave surface and a convex nonarticular surface. The convex
non-articular surface abuts a socket in the pelvic bone when the
acetabular cup is implanted in a patient and provides a porous
surface with multiple asperities and micro-voids to allow bone
ingrowth. Furthermore, the acetabular cup (11) provides one or more
holes (12) at different locations for the purpose of using one or
more fasteners (14). The fasteners (14) can be screws or resorbable
nonmetallic and biocompatible studs of different diameters and
lengths. The studs, which can be called orthobiologic resorbable
studs, will secure the acetabular cup (11) during the initial phase
of bone ingrowth and will resorb within one year, being replaced by
newly generated bone and become part of the host pelvic bone.
During that period, the acetabular cup (11) becomes solidly
attached to the acetabular socket in the pelvic bone (4) by bone
ingrowth. The acetabular cup (11) has a concave hemispherical
surface in which a large acetabular cup stem (9) is disposed. The
acetabular cup stem (9) has a male Morse taper for assembly to the
acetabular ball (8) by means of the acetabular ball recess (10)
which has a female Morse taper. Referring to FIGS. 2-4 and 6, the
femoral cup (6) has a femoral cup stem (7) with a male Morse taper
while the femoral implant (1) has a cooperating femoral implant
recess (5) having a female Morse taper located in neck (3). FIGS. 7
and 8 illustrate a femoral cup (20) with a neck (22) and a femoral
cup recess (21) having a female Morse taper. This cooperates with a
femoral implant stern having a male Morse taper (not shown). In a
preferred embodiment, a modular system is used in a kit according
to the Invention wherein the femoral cup stern (7) or neck (22) can
come in different lengths to accommodate the sizing needs of a
patient. Therefore, in a kit of the invention, two or more femoral
cups are provided having different stem lengths. In a less
preferred embodiment, the length of the neck (3) of femoral implant
(1), or the femoral implant stem (not shown) can also have various
lengths to accommodate patient sizing needs and in a kit comprising
this embodiment two or more neck or stem components having
different lengths will be included. Other variations on the design
to meet different sizing needs will be apparent to those having
skill in the art.
[0029] An important advantage of the present invention is that the
greater the interdigitation the more stability of the implant as
opposed to conventional ball and socket hip implants, where
increased range of motion is usually associated with increased risk
of dislocation.
[0030] Referring to FIG. 2, the proximal femoral bone (2) is reamed
in the usual fashion to accept a femoral implant (1) that can be
cemented or press fitted in the femoral medullary canal. The
acetabular socket in the pelvic bone (4) is reamed to the
appropriate size to accept the acetabular cup (11), which is
impacted for press fit at the correct angle of inclination and
anteversion. Fasteners (14) in the form of fixation screws or
biocompatible resorbable studs are then inserted in piece to secure
the acetabular cup (11). The acetabular ball (8) is then affixed
onto the acetabular cup stem (9), FIG. 2 also illustrates center
line (C-C). In the position shown, the center fine (C-C) passes
through the center of the acetabular cup (11), the longitudinal
center line of the acetabular cup stem (9), the center of
acetabular bail (8), the longitudinal center fine of femoral cup
stern (7) and the longitudinal center line of femoral implant
recess (5). Obviously, when the femoral cup is articulated on the
ball the center line associated with the femoral components will
not be colinear with the center line of the acetabular components.
The fine is simply illustrated in this way for convenience.
[0031] Referring to FIGS. 3, 4 and 8, when the femoral cup (6) or
(20) articulates on the acetabular ball (8), the edges of the
femoral cup (6) or (20) move into and out of hemispherical space
(16) and the articular surface of the femoral cup (6) or (20)
maintains the same area of contact with the acetabular ball (8)
over the entire range of motion. In other words, 100% of the
articular contact area of the femoral cup (6) or (20) is maintained
over the entire range of motion. FIG. 3 illustrates the prosthesis
of the invention in extension and external rotation. FIG. 4
illustrates the prosthesis in flexion and internal rotation and
FIG. 8 illustrates an extreme articulation position of the femoral
cup (20) on the acetabular ball (8).
[0032] In one embodiment, the articular surface of the femoral cup
(6) or (20) contains a high molecular weight polyethylene lining of
varying thickness, but no less than 4 mm. In a different embodiment
the lining could be porcelain, ceramic or a metallic alloy.
[0033] An important feature of the present invention is the ability
to place acetabular ball (8) in a position that minimizes or
eliminates tortional forces on the acetabular cup and acetabular
stem. This is illustrated in FIG. 3 wherein the acetabular ball (8)
is affixed on acetabular cup stem (9) in a position wherein the
equatorial plane (P-P) of the acetabular cup passes through the
center (15) of the acetabular ball.
[0034] An optional embodiment of the invention illustrated in FIGS.
5-8 adds a soft tissue protective sheath (17) to the embodiments
described above. The protective sheath, also illustrated by itself
in perspective in FIG. 5A, addresses the rare cases wherein soft
tissue might get lodged in the space (16) as a result of
articulation of the prosthetic joint of the invention.
[0035] Referring to FIGS. 6-8, the sheath (17) extends beyond the
circular outer edge of the acetabular cup (11) and has a retaining
ring (18). The sheath (17) is installed by placing it into the
acetabular cup (11) before the acetabular ball (8) is installed.
The sheath (17) can have a solid surface as illustrated or it can
be perforated with holes, slots or the like having the same or
different shapes and dimensions as may be desired.
[0036] As can be seen from FIGS. 6-8, the sheath (17) is allowed to
move freely within the space (16), restrained only by the
acetabular ball (8) and acetabular cup stem (9). The sheath (17)
also is moved by contact of retaining ring (18) with the outer edge
of femoral cup (6) or (20). The retaining ring (18) will, for
example, contact the outer edge of femoral cup (6) or (20)
particularly in positions of extreme articulation of the prosthetic
joint as illustrated in FIG. 8.
[0037] In another embodiment of the present invention, also
illustrated in FIGS. 6-8, the acetabular cup (11) is designed for
use in revision surgery of the hip. Revisions are surgical
procedures where the existing implant is removed. This most
frequently requires removal of the acetabular cup and it is
associated with a high level of morbidity. The removal of a
previously implanted acetabular cup may be quite difficult
surgically, especially when the cup has metallic beads for bone
ingrowth. In these cases, the removal is also associated with
iatrogenic bone loss leading to difficulty in inserting another
conventional acetabular cup.
[0038] There are instances where the acetabular cup was not
implanted correctly or where the lining of the existing implant
becomes worn out and needs to be replaced. Recurrent dislocations
of the hip implant are usually secondary to surgical misplacement
of a conventional acetabular cup. For example, if during the
initial procedure, the cup was placed either too vertical or
retroverted (e.g., facing backward instead of forward).
[0039] To remedy the above cited complication, there are times
where the surgeon simply cements a conventional revision cup into
the previously implanted acetabular cup using conventional bone
cement. However, problems arise if the initial position of the
previously implanted acetabular cup is too vertical or retroverted,
preventing a conventional revision cup from being glued in the
previously implanted acetabular cup. As a result, removal of the
previously implanted acetabular cup becomes necessary--entailing
significant risk and possible morbidity to the patient as described
above.
[0040] Another important advantage of the present invention is that
the angle of inclination and retroversion are not critical since
the interlocking mechanism of applicant's implant will compensate
for the misalignment of a previously implanted acetabular cup.
[0041] The acetabular cup (11) of applicant's interlocking reverse
hip prosthesis can optionally be provided with a thin
circumferential groove (19) located in proximity of the equatorial
plane of said cup as illustrated in FIGS. 6-8.
[0042] In revision surgery using the hip prosthesis of applicant's
invention, the plastic polyethylene insert of the previously
implanted acetabular cup is removed. The circumferential groove
(19) of the interlocking reverse hip prosthesis will host a
retaining "o-ring" of the previously implanted acetabular cup being
revised thereby providing solid fixation of applicant's revision
interlocking reverse hip prosthesis to the previously implanted
acetabular cup.
[0043] The components of the reverse hip prosthesis of the
invention are made from biocompatible materials commonly used in
the art and suitable materials will be apparent to those skilled in
the art based upon the disclosures herein. Metals or metallic
alloys such as titanium or cobalt chrome are suitable. For some
components, such as the acetabular ball, metals or ceramics can be
used. High density polyethylene is also suitable for some
components, for example the protective sheath or an optional lining
for the concave portion of the femoral cup. Other biocompatible
materials or combinations thereof can be used for various
components as will be apparent to those having skill in the
art.
[0044] The dimensions of the various components of the reverse hip
prosthesis of the invention can be readily determined by those
skilled in the art based upon the disclosures herein. For the
acetabular cup, which is hemispherical, an outer diameter from
about 35 millimeters (mm) to about 65 mm will be suitable for most
applications. The spherical acetabular ball should have a diameter
from about 28 mm to about 45 mm. The diameter of the acetabular
ball should be from about 7 mm to about 12 mm smaller than the
inner diameter of the acetabular cup, thus creating a hemispherical
space or gap having a width from about 7 mm to about 12 mm to allow
articulation of the femoral cup therein. Of course, the concave,
hemispherical, articular surface of the femoral cup will be sized
compatibly with the acetabular ball to allow for smooth
articulation. Highly polished cobalt chrome is an excellent
material for the articular surface of the femoral cup but other
materials such as biocompatible metallic alloys can be used. The
femoral cup also may contain a lining fabricated from high-density
polyethylene, ceramic or biocompatible metallic alloys.
[0045] It is therefore the object of the present invention to
provide a new and improved interlocking and restrained reverse hip
prosthesis system, where two conventional articular surfaces of the
hip joint are reversed and interlocked. The system described in the
present invention, which has all of the advantages of the prior art
designs, none of the disadvantages, and numerous improvements over
the prior art, particularly in respect of remarkably increased
range of motion and reduced risk of wear particles being released
into the joint.
[0046] With respect to the above description then, it is to be
realized that the optimum dimensional relationships for the parts
of the invention, to include variations in size, materials, shape,
form, function and manner of operation, assembly and use, are
deemed readily apparent to those skilled in the art, and all
equivalent relationships to those illustrated in the drawings and
described in the specification are intended to be encompassed by
the present invention. Therefore, the foregoing is considered as
illustrative only of the principles of the invention. Further,
since numerous modifications and changes will readily occur to
those skilled in the art, it is not desired to limit the invention
to the exact construction and operation shown and described, and
accordingly, all suitable modifications and equivalents may be
resorted to, falling within the scope of the invention.
* * * * *