U.S. patent application number 17/461851 was filed with the patent office on 2022-02-24 for ankle prosthesis and methods of using the same.
The applicant listed for this patent is DT MEDTECH, LLC. Invention is credited to Zachary C. Christensen, John S. Crombie, Neil Etherington, Andrew R. Fauth, Beat Hintermann, Shawn Thayer Huxel, Justin Hyer, David Koch, Trevor K. Lewis, Nathan O. Plowman.
Application Number | 20220054273 17/461851 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-24 |
United States Patent
Application |
20220054273 |
Kind Code |
A1 |
Huxel; Shawn Thayer ; et
al. |
February 24, 2022 |
ANKLE PROSTHESIS AND METHODS OF USING THE SAME
Abstract
The present disclosure pertains to ankle prostheses. In an
example embodiment, the ankle prosthesis comprises an adjustable
and replaceable intermediate implant that is disposed between a
tibial implant and a talar implant. The intermediate implant is
adjustable relative to the tibial implant and can be interlocked
therewith once adjusted. Methods of using, fitting, and adjusting
the device are also described. Still other embodiments are
described.
Inventors: |
Huxel; Shawn Thayer;
(Seaside Park, NJ) ; Crombie; John S.; (East
Hanover, NJ) ; Hintermann; Beat; (Liestal, CH)
; Fauth; Andrew R.; (North Logan, UT) ; Hyer;
Justin; (Smithfield, UT) ; Christensen; Zachary
C.; (Wellsville, UT) ; Lewis; Trevor K.;
(Lehi, UT) ; Plowman; Nathan O.; (Wellsville,
UT) ; Etherington; Neil; (North Logan, UT) ;
Koch; David; (North Logan, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DT MEDTECH, LLC |
McMinnville |
TN |
US |
|
|
Appl. No.: |
17/461851 |
Filed: |
August 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15707661 |
Sep 18, 2017 |
11103353 |
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17461851 |
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62395781 |
Sep 16, 2016 |
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International
Class: |
A61F 2/30 20060101
A61F002/30; A61F 2/46 20060101 A61F002/46; A61F 2/42 20060101
A61F002/42 |
Claims
1-48. (canceled)
49. A method of adjustably implanting an intermediate implant of an
ankle prosthesis comprising a tibial implant and a talar implant,
the method comprising: implanting an intermediate implant between
the tibial implant and the talar implant, the intermediate implant
comprising a projecting member defining an axis of rotation;
rotating the intermediate implant about the axis of rotation of the
projecting member and relative to the tibial implant while the
tibial implant, the talar implant, and the intermediate implant are
implanted in the ankle; and fixing the position of the intermediate
implant relative to the tibial implant by inserting an implant lock
between the tibial implant and the talar implant, the implant lock
applying a force that is substantially perpendicular to the axis of
rotation of the projecting member.
50. The method of claim 49, the fixing step comprising the implant
lock traversing linearly in a direction substantially perpendicular
to the axis of rotation to engage the projecting member thereby
resisting the rotation of the projecting member
51. The method of claim 49, the fixing step comprising the implant
lock moving in the anterior-posterior direction relative to the
projection member, thereby resisting the rotation of the projecting
member
52. The method of claim 49, wherein the intermediate implant
further comprises a first surface and a second, curved surface
opposite the first surface, the projecting member extending
outwardly from the first surface, wherein the tibial implant
further comprises a recess, and the implanting step comprises
inserting the projecting member into the recess of the tibial
implant.
53. The method of claim 52, wherein during the rotating step, the
projecting member can rotate at least one of 70 degrees, at least
180 degrees, or 360 degrees relative to the tibial implant when
disposed in the recess.
54. The method of claim 49, where the projecting member comprises a
substantially circular transverse cross-section and a cross section
of the projecting member perpendicular to the transverse
cross-section is a quadrilateral.
55. The method of claim 49, wherein the projecting member comprises
a lateral surface that is substantially parallel to the axis of
rotation of the projecting member and comprises one or more
interlocking surface features, and the fixing step further
comprising engaging the implant lock with the one or more
interlocking surface features.
56. The method of claim 49, wherein the projecting member comprises
a lateral surface comprising one or more interlocking surface
features, wherein the implant lock comprises a first end and a
second end opposite the first end, the first end comprising one or
more interlocking surface features, and the fixing step further
comprising engaging the interlocking surface features of the
implant lock with the one or more interlocking surface features of
the lateral surface of the projecting member to resist rotation of
the projecting member relative to the tibial implant.
57. The method of claim 52, wherein the tibial implant comprises a
slot that is in communication with the recess, and during the
fixing step, the inserting of the implant lock comprises inserting
the implant lock into the slot along a direction that is within
10.degree. of an axis perpendicular to the axis of rotation.
58. The method of claim 57, the fixing step further comprising
releasably interlocking the implant lock with a portion of the
tibial implant.
59. The method of claim 58, wherein the implant lock comprises a
protrusion and the slot further comprises a sidewall and a notch in
the sidewall, and the fixing step further comprises engaging the
protrusion with the notch of the slot such that the implant lock is
releasably interlocked with the slot.
60. The method of claim 59, wherein the slot comprises a width and
the implant lock comprises a width that is less than the width of
the slot.
61. The method of claim 49, wherein the implant lock comprises an
insert, the insert comprising a first portion and a second portion,
and the fixing step further comprising moving the first portion
relative to the second portion.
62. The method of claim 61, wherein the first portion of the
implant lock comprises a screw, and wherein the insert comprises a
bore, the fixing step further comprising tightening the screw in
the bore.
63. The method of claim 62, wherein the first portion and the
second portion of the insert of the implant lock are configured to
move away from each other as the screw is rotated in a first
direction and toward each other as the screw is rotated in a second
direction.
64. A method of trialing an intermediate implant of an ankle
prosthesis comprising a tibial implant and a talar implant, the
method comprising: inserting a first intermediate implant into the
ankle prosthesis, the first intermediate comprising a projecting
member; determining, using a measurement tool, an optimal
anteroposterior position of the projecting member for alignment
with the talar implant; removing the first intermediate implant
from the ankle prosthesis; selecting a second intermediate implant
comprising a projecting member defining an axis of rotation, the
second intermediate implant comprising a configuration of the
projecting member that corresponds to the determined optimal
anteroposterior position; inserting the second intermediate implant
into the ankle prosthesis such that the second intermediate implant
can rotate relative to the tibial implant about the axis of
rotation; and fixing the position of the second intermediate
implant relative to the tibial implant by engaging the implant lock
with the tibial implant, the implant lock applying a force that is
substantially perpendicular to the axis of rotation.
65. The method of claim 64, further comprising: before inserting
the first intermediate implant, coupling the measurement tool with
the projecting member of the first intermediate implant.
66. The method of claim 64, wherein the tibial implant comprises a
recess and the measurement tool comprises a bar, the step of using
the measurement tool comprises inserting the bar of the measurement
tool into the recess of the tibial implant, and the implanting of
the second intermediate implant step comprises inserting the
projecting member of the second intermediate implant into the
recess.
67. The method of claim 64, wherein the optimal anteroposterior
location of the projecting member is selected from a group
comprising: posterior, neutral, or anterior.
68. A method of implanting an ankle prosthesis or a portion thereof
from a prosthesis kit, the method comprising: providing a
prosthesis kit comprising a talar implant, a first tibial implant,
a second tibial implant, a first intermediate implant configured to
be coupled in fixed relation to the first tibial implant, and a
second intermediate implant configured to slide or rotate relative
to the second tibial implant; implanting the talar implant into a
patient; selecting either a fixed bearing configuration or a mobile
bearing configuration; if the fixed bearing configuration is
selected: implanting the first tibial implant and the first
intermediate implant, and fixing the position of the first
intermediate implant relative to the first tibial implant by
inserting a first implant lock between the tibial implant and the
talar implant, the first implant lock applying a force that is
substantially perpendicular to the axis of rotation of the
projecting member; if the mobile bearing configuration is selected:
implanting, the second tibial implant and the second intermediate
implant, and constraining the position of the second intermediate
implant relative to the second tibial implant, wherein the second
intermediate implant is configured to rotate relative to the second
tibial implant when constrained, wherein both the first and second
intermediate implants comprise a lower bearing surface that is
shaped to correspond to an upper bearing surface of the talar
implant.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application No. 62/395,781, filed Sep. 16, 2016. The contents of
which are incorporated by reference in their entirety.
TECHNICAL FIELD
[0002] The present application relates to the technical field of
joint prostheses, and more particularly to orthopedic implants
facilitating at least some restoration in anatomical mobility to a
joint, such as an ankle joint.
BACKGROUND
[0003] Joint prostheses can be used to restore a certain amount of
freedom of movement to a joint, after the joint has been damaged
due to injury or disease. For example, ankle joints can be damaged
by arthritis, and an ankle replacement joint prosthesis can bring
such patients a reduction in pain and improvement in mobility.
[0004] Ankle prosthesis are designed to replace the ankle joint and
replicate the anatomic motion of the ankle joint which includes
loadbearing and flexion of the foot through the gait cycle. Flexion
of the foot includes dorsi-flexion, or upward motion of the
forefoot relative to the hindfoot, and plantar-flexion, downward
motion of the forefoot relative to the hindfoot. As the foot
flexes, minor rotation, internal for dorsi-flexion and external for
plantar-flexion must occur between the foot and the tibia. To
account for this complex dynamic motion, optimally, the prosthetic
joint would be located such that the load-bearing central axis of
the tibia is aligned with the apex of the talar dome. In addition,
such a joint would not be cylindrical, but would form the partial
surface of a cone. This frustoconical surface is defined by
locating the smaller radius of the cone on the interior side of the
ankle (the lateral side closer to the median axis of the body) and
the larger radius on the outer side of the ankle (the lateral side
further from the median axis of the body).
[0005] Insertion of an ankle prosthesis includes providing surgical
access to the joint being replaced, preparing the surfaces of the
distal tibia and the talar dome for acceptance of the prosthesis,
and providing just enough space for the prosthesis for fit and
function. Generally, a diseased ankle, even when surgically
prepared to accept a prosthesis, would be mal-aligned to accept the
prosthesis "out of the box". Therefore, certain surgical
intervention would be necessary to balance the ankle joint
including, but not limited to, osteotomies (in order to shorten,
lengthen, or reorient bones), soft tissue excision (in order to
alleviate unwanted tension to the skeletal structure), or the
support or tightening of soft tissue (in order to add tension and
support to the skeletal structure). Even in the best of surgical
hands, the ankle prosthesis would still have to support loading
which may not be matched to the perfect anatomy of the complex
healthy ankle joint. Thus, an ankle prosthesis which is adaptable
to the variations of the anatomy and of the surgical placement of
the fixed components of the prosthesis would be beneficial to
restoring motion of the replaced ankle joint.
[0006] Ankle prostheses are composed of components moveable
relative to each other, such as a talar implant, a tibial implant,
and an intermediate implant interposed between said tibial implant
and said talar implant. The intermediate implant and the talar
implant can move relative to each other. In certain ankle
prostheses, the tibial implant and the intermediate implant are
fixed relative to each other.
[0007] Once surgical access is achieved and the ankle joint is
balanced and prepared to accept the prosthesis, the tibial implant
and the talar implant are fixed to the bones of the tibia and the
talus, respectively. In most surgical instances, the center of the
tibia implant may or may not be aligned with the central axis of
the tibia bone and the talar implant may be rotated, internally or
externally, relative to the central axis of the tibia bone. In
addition, the center of the tibial implant may not be aligned with
the apex of the talar implant to provide and maximize full flexion
of the foot.
[0008] Current ankle prostheses available are either (i) "mobile
bearing" in that the intermediate implant to tibia implant
interface is a planar friction joint allowing for
anterior-posterior and lateral translation, coupled with relatively
free internal and external rotation of the intermediate implant
relative to the tibial implant; or (ii) "semi-constrained"in that
the intermediate implant is fixed to the tibial implant in a
predetermined fashion (referred to herein as "fixed bearing" as
well), regardless of the anatomic placement of the tibial implant
relative to the talar implant.
[0009] The mobile-bearing design, due to its relatively low level
of constraint, accommodates variability in anatomy and surgical
placement of the tibial and talar implants. However, the lack of
constraint introduces circumstances requiring significant surgical
skill in placing the implant while balancing the skeletal and soft
tissue anatomy about the ankle prosthesis. Anatomic balancing is
required in order to prevent subluxation or, sometimes, fracture of
the mobile-bearing intermediate implant when the tibial and talar
components of the prosthesis are loaded in a condition of
mal-alignment. In addition, highly diseased or deformed ankles may
not be candidates for the mobile-bearing design.
[0010] The semi-constrained design, due to its relatively high
level of constraint, does not accommodate variability in anatomy
and surgical placement of the tibial and talar implants. The
intermediate implant is rigidly affixed to the tibial implant
either in vitro, that is while the tibial implant and intermediate
implant are outside the patient or in vivo, where the fixation of
the intermediate implant takes place in the patient after
implantation of the tibial implant. However, the presence of
constraint introduces circumstances requiring significant surgical
skill in placing the implant in that the talar and tibial implants
must be expertly aligned by the surgeon utilizing techniques for
balancing the skeletal and soft tissue anatomy about the ankle
prosthesis. Anatomic balancing is required in order to prevent
abnormal loading and subsequent wear of the fixed intermediate
implant when the tibial and talar components of the prosthesis are
loaded in a condition of mal-alignment. Advantages of this design,
due to the constraint, include use in patients with poor soft
tissue support of the ankle joint or in patients where large
deformity has been corrected by the surgeon. Each of these
instances require a more stable, semi-constrained prosthesis.
SUMMARY
[0011] Embodiments of the invention described herein combine the
advantages of both a mobile-bearing design and a semi-constrained
design to treat a broader spectrum of patients and to better adapt
the implant to the patient anatomy and placement of the talar and
tibial components. Further embodiments of the invention can allow
for adjusting the relative position of the ankle prosthesis
components, particularly, the position of an intermediate implant
relative to a tibial implant, and then securely fixing these
components to each other. Moreover, embodiments of this invention
can allow for components, particularly the intermediate implant, to
be replaced and adjusted when clinically indicated due to, for
example, wear of the component.
[0012] Embodiments of the present disclosure can comprise an ankle
prosthesis having a tibial implant, an intermediate implant, and an
implant lock. The intermediate implant can comprise a first surface
and a second, curved surface opposite the first surface and a
projecting member extending outwardly from the first surface. The
projecting member can be configured to extend into a recess of the
tibial implant and rotate relative to the tibial implant. The
implant lock can be configured to resist rotation of the projecting
member relative to the tibial implant by applying a force that is
substantially perpendicular to the axis of rotation of the
projecting member.
[0013] Other embodiments of the present disclosure can also
comprise an ankle prosthesis having a tibial implant, an
intermediate implant, and an implant lock. The tibial implant can
define a recess and a slot, wherein the slot is in communication
with the recess. The intermediate implant can comprise a first
surface and a second, curved surface opposite the first surface and
a projecting member extending outwardly from the first surface. The
projecting member can be configured to extend into the recess of
the tibial implant and rotate relative to the tibial implant. The
implant lock can be configured to be at least partially disposed
within the slot and to resist rotation of the projecting member
relative to the tibial implant, wherein the slot is configured such
that the implant lock is inserted into the slot along a direction
that is substantially perpendicular to the axis of rotation of the
projecting member.
[0014] Still other embodiments of the present disclosure can also
comprise an ankle prosthesis having a tibial implant, an
intermediate implant, and an implant lock. The intermediate implant
can comprise a first surface and a second, curved surface opposite
the first surface and a projecting member extending outwardly from
the first surface, wherein the projecting member is configured to
be disposed in a recess of the tibial implant and rotate relative
to the tibial implant. The implant lock can be configured to resist
rotation of the projecting member relative to the tibial implant.
The projecting member can comprise a lateral surface, and the
implant lock can be configured to engage with the lateral surface
of the projecting member such that rotation of the projecting
member is resisted.
[0015] Still other embodiments of the present disclosure can
comprise an ankle prosthesis having a talar implant, a tibial
implant, and an intermediate implant. The intermediate implant can
comprise a first surface and a second, curved surface opposite the
first surface and a projecting member extending outwardly from the
first surface. The talar implant can be configured to move relative
to the to the intermediate implant along the second surface, and
the projecting member can be configured to extend into a recess of
the tibial implant and rotate at least 180 degrees relative to the
tibial implant.
[0016] Other embodiments of the present disclosure can comprise an
ankle prosthesis component having an intermediate implant. The
intermediate implant can comprise a base having a first surface and
a second, curved surface opposite the first surface and a
projecting member extending outwardly from the first surface of the
base. The projecting member can have a width and the base has a
width and wherein the projecting member width is 25% to 85% of the
base width.
[0017] Still other embodiments of the present disclosure can
comprise a method of fixing the relative position of an
intermediate implant of an ankle prosthesis, wherein the
intermediate implant is configured to be disposed between a tibial
implant and a talar implant, and the method can comprise rotating
the intermediate implant relative to the tibial implant while the
tibial implant, the talar implant, and the intermediate implant are
implanted in the ankle and fixing the position of the intermediate
implant relative to the tibial implant by applying a force that is
substantially perpendicular to the axis of rotation of the
intermediate implant.
[0018] Yet other embodiments of the present disclosure can comprise
a method of replacing an intermediate implant of an ankle
prosthesis, wherein the intermediate implant is configured to be
disposed between a tibial implant and a talar implant, and the
method can comprise releasing an implant lock of a first
intermediate implant of the ankle prosthesis such that the first
intermediate implant can rotate relative to the tibial implant,
wherein the implant lock is released by removing a force that is
substantially perpendicular to the axis of rotation of the
intermediate implant; hereafter, removing the first intermediate
implant from the ankle prosthesis; and inserting a second
intermediate implant into the ankle prosthesis.
[0019] These and other aspects, objects, features, and embodiments
will be apparent from the following description and the appended
claims. Those skilled in the art may use the components of the
ankle prosthesis together or separate and may apply techniques
provided herein for other applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The drawings illustrate only example embodiments of ankle
prostheses and are therefore not to be considered limiting of its
scope.
[0021] FIG. 1 illustrates an embodiment of an ankle prosthesis
implanted in an ankle in accordance with the present
disclosure.
[0022] FIG. 2 illustrates an anterior, upper perspective view of a
tibial implant coupled to an intermediate implant and an implant
lock in accordance with the present disclosure.
[0023] FIG. 3 illustrates an exploded view of the tibial implant,
the intermediate implant and an implant lock in accordance with the
present disclosure.
[0024] FIG. 4A illustrates a top perspective view of a talar
implant in accordance with the present disclosure and FIG. 4B
illustrates a bottom perspective view of the talar implant shown in
FIG. 4A.
[0025] FIG. 5 illustrates a schematic of a frustoconical
surface.
[0026] FIG. 6A illustrates a lower, perspective view of the tibial
implant shown in FIG. 2.
[0027] FIG. 6B illustrates bottom view of the tibial implant shown
in FIG. 2.
[0028] FIG. 7 illustrates a grasper which can be used for removal
of the implant lock shown in FIG. 2.
[0029] FIG. 8A illustrates a upper, perspective view of the
intermediate implant shown in FIG. 2.
[0030] FIG. 8B illustrates a lower, perspective view of the
intermediate implant shown in FIG. 2.
[0031] FIG. 8C illustrates an exploded view of the intermediate
implant shown in FIG. 2.
[0032] FIG. 9A illustrates a right side view of an embodiment of an
intermediate implant with a posterior alignment.
[0033] FIG. 9B illustrates a right side view an embodiment of an
intermediate implant with a neutral alignment.
[0034] FIG. 9C illustrates a right side view an embodiment of an
intermediate implant with an anterior alignment.
[0035] FIG. 10A illustrates an exploded view of the implant lock
shown in FIG. 2.
[0036] FIG. 10B illustrates a lower, perspective view of the
implant lock shown in FIG. 10A.
[0037] FIGS. 10C and 10D illustrate a cross-sectional view of the
implant lock and the tibial implant shown in FIG. 2. FIG. 10C
illustrates the implant lock in an unlocked position with the
intermediate implant. FIG. 10D illustrates the implant lock in an
interlocking position with the intermediate implant.
[0038] FIG. 11A illustrates an upper perspective view of an
embodiment of a measurement tool in accordance with the present
disclosure.
[0039] FIGS. 11B to 11D illustrate an upper perspective view of a
measurement tool measuring the alignment of the intermediate
implant with respect to the tibial implant in accordance with the
present disclosure.
[0040] FIGS. 12A to 12D illustrates another embodiment of a tibial
implant and an intermediate implant of an ankle prosthesis.
[0041] FIG. 13 illustrates an embodiment of ankle prosthesis
kit.
[0042] FIG. 14 is a graph of the kinematics and load profile which
is an aspect of the wear test parameters described in the Example
section.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0043] An embodiment of an ankle prosthesis according to the
invention is illustrated in FIG. 1. Ankle prosthesis 10 includes a
tibial implant 100, a talar implant 200, an intermediate implant
300, and an implant lock 400. The tibial implant 100 is configured
to be implanted in or on the base of the tibia 30 of a patient. The
talar implant 200 is configured to be implanted in or on the talus
20 of a patient. The intermediate implant 300 is configured to be
disposed between the talar implant 200 and the tibial implant 100.
The implant lock 400 is configured to fix the position (e.g.,
angular position) of the intermediate implant 300 relative to the
tibial implant 100. FIG. 2 depicts an anterior, upper perspective
view of the tibial implant 100 coupled to the intermediate implant
300 and the implant lock 400. FIG. 3 depicts an exploded view of
the tibial implant 100, the intermediate implant 300, and the
implant lock 400. FIG. 4A depicts an upper perspective view of the
talar implant 200 and FIG. 4B depicts a bottom perspective view of
the talar implant 200.
[0044] To facilitate the function of the prosthetic joint, the
intermediate implant 300 and the talar implant 200 are configured
to be moveable relative to each other along a contact interface 250
(FIG. 1) between a lower bearing surface 320 (FIG. 2) of the
intermediate implant 300 and an upper bearing surface 210 (FIGS. 4A
and 4B) of the talar implant 200. To this end, the lower bearing
surface 320 of the intermediate implant is designed to bear against
the upper bearing surface 210 of the talar implant 200 that is of
complementary shape, so that the intermediate implant 300 can move
by sliding relative to the talar implant 200 and vice versa. The
talar implant upper surface 210 and intermediate implant lower
surface 320 are rounded in shape, e.g., substantially spherical,
cylindrical or frustoconical, so as to form a contact interface 250
(FIG. 1) that allows the foot to move in plantar flexion and in
dorsal flexion relative to tibia 30 (FIG. 1).
[0045] In the embodiment shown, the contact interface 250 between
the intermediate implant 300 and the talar implant 200 can be
considered as defining a surface that is a fraction of the surface
of a substantially frustoconical shape (see FIG. 5 as an example of
a fraction of the surface 7 of a substantially frustoconical shape
8). The contact interface 250 can be oriented such that its portion
with larger radius R (FIG. 5) is directed substantially towards the
outer side 45 of the ankle 15, i.e., away from the median axis of
the body, when the prosthesis 10 is in place.
[0046] In the embodiment shown, the intermediate implant 300
comprises a concave lower surface 320, and the talar implant's
upper surface 210, being complementary in shape and dimension to
the lower surface 320, is convex. However, an inverse mechanical
disposition is envisioned where the lower surface of the
intermediate implant 300 is convex while the upper surface 210 of
the talar implant 200 is concave.
[0047] In the embodiment shown, in order to restrain the lateral
movement of the intermediate implant 300, the talar implant 200 can
comprise rails 220, the pair of rails maintaining equal distance
from each other along their length and each extending upwardly on a
corresponding side of the upper surface 210. The rails 220 are
spaced apart a distance that permits the lateral surface 325 of the
intermediate implant base 350 to be disposed between the two rails.
Because of the presence of rails 220, the intermediate implant 300
is guided by bearing on surface 320 against the rails during the
movement of the talar implant 200 relative to the intermediate
implant 300.
[0048] The talar implant 200 can be configured to be affixed to the
talar bone. For example, the talar implant 200 can comprise an
anterior plate 230 (FIGS. 4A and 4B). The anterior plate 230
projects outwardly (in a general posterior-to-anterior direction)
from the anterior edge 201 of the talar implant 200. As shown in
FIG. 1, the anterior plate 230 extends from the anterior edge 201
of the upper surface 210. The anterior plate 230 can contain one or
more holes 240 (FIGS. 4A and 4B) to facilitate fixation with
orthopaedic screws.
[0049] In the embodiment shown, with particular reference to FIGS.
2, 3, 6A, and 6B, the tibial implant 100 comprises a base 110
defining an upper surface 112 and an anterior shield 140. The upper
surface 112 is configured to abut the end of the tibia 30.
Anti-slip elements 115 can project outwardly from the upper surface
112 and are configured to maintain the alignment of the tibial
implant 100 relative to the tibia 30. In an embodiment, the
anti-slip elements 115 can be pointed and configured to penetrate
bone. In the embodiment shown, the upper surface 112 is planar.
Other anti-slip elements maybe also be considered suitable for use
with the invention including elements extending upward past the
sides of the tibia implant that can be secured to the sides thereof
either through pressure or mechanical means including pins or
screws.
[0050] The lower surface 120 of the tibial implant 100, which is
viewable in FIGS. 6A and 6B, is configured to couple with the
intermediate implant 300. At an interior region of the lower
surface 120 is a recess 122. The recess 122 is configured to
receive a portion of the intermediate implant, particularly, a
projecting member 330. The recess 122 is configured to receive the
projecting member 330. A sidewall 124 defines the perimeter of the
recess. The recess 122 is shaped to permit the projecting member
330 to bear against the sidewall 124, and the sidewall 124 is
configured to impede lateral movement of the projecting member 330.
For example, the sidewall 124 extends vertically (e.g., extends in
a plane that is parallel to the Z-Z axis) or may be angled or
curved.
[0051] The recess 122 is sized and shaped to allow for rotation of
the projecting member 330 within the recess 122. For example, the
recess 122 can have a minimum transverse dimension (e.g., the width
or the dimension along the Y-Y axis, shown in FIG. 6B) that is
slightly more than the maximum transverse dimension of the
projecting member 330, as discussed below. Also to facilitate
rotation of the projecting member 330 within the recess 122, the
sidewall 124 of the recess 122 can define a fraction of a circular
shape.
[0052] The tibial implant 100 is also configured to couple with the
implant lock 400 (FIGS. 1, 2, 3, and 10A to 10D). In the embodiment
shown, tibial implant 100 comprises a slot 130 configured to
receive at least a portion of the implant lock 400. Slot 130 is in
communication with the recess 122 such that the implant lock 400 is
able to couple directly with the projecting member 330 when the
projecting member 330 is disposed within the recess 122. In the
embodiment shown, slot 130 has a first end 131 and a second end
132. The first end 131 is closer to the recess 122 than the second
end 132. An exposed surface of the tibial implant 100, such as
anterior face 136, defines the second end 132.
[0053] The tibial implant 100 can be configured such that the
implant lock 400 is inserted into the slot 130 at a direction that
is substantially perpendicular to the Z-Z axis (e.g., the axis of
rotation of the projecting member 330). For example, the slot 130
extends within a plane through which the recess 122 also extends,
and such plane can be substantially perpendicular to the Z-Z axis
(e.g., the axis of rotation of the projecting member 330). In
embodiments, substantially perpendicular can be within 10.degree.,
5.degree., 3.degree., 2.degree., or 1.degree. of the perpendicular.
Implant lock 400 is configured to be inserted into slot 130. In
order to facilitate insertion, the height (e.g. dimension along the
Z-Z axis shown in FIG. 2) of the implant lock 400 can be of a
dimension which is smaller than the height of slot 130.
[0054] The implant lock 400 and the tibial implant 100 can be
configured to interlock with each other. When interlocked, movement
of the implant lock 400 relative to the tibial implant 100 is
constrained. For example, in the embodiment shown, the sidewall 134
defining the slot comprises two notches 136a, 136b. The notches
136a, 136b can be located on opposing sidewall surfaces such that
they face each other. Each notch 136a, 136b is configured to
receive and interlock with a projection 410a, 410b of the implant
lock 400 (FIG. 10A to 10D). The implant lock 400 can be configured
such that the projections 410a, 410b are pushed or snapped into
interlocking engagement with the notches 136a and 136b.
[0055] The slot 130 and the implant lock 400 can be configured such
that the implant lock 400 is retrievable from the slot 130. A tool,
for example a surgical grasper commonly used during surgery, can be
used to retrieve the implant lock. FIG. 7 shows an example of such
a grasper that can be used as grasper 700. To facilitate retrieval,
slot 130 has an overall width (e.g., dimension along the Y-Y axis
shown in FIG. 6B) which is greater than the width of the implant
lock 400. This width at the second end 132 is sufficient to provide
some space 138a, 138b on both sides of the implant lock 400. This
space 138a and 138b (FIG. 2) permits the nose portions 738a and
738b of grasper 700 to be inserted into the slot 130 on both
lateral sides 405a, 405b of the implant lock 400 in order to pull
and retrieve the implant lock 400. The lateral sides 405a, 405b of
the implant lock 400 can each comprise surface contours 437
configured to interlock with the retrieval tool. Similarly, a
roughened surface on lateral sides 405a, 405b and nose portions
738a, 738b can provide sufficient coupling force to facilitate
removal of implant lock 400.
[0056] The tibial implant 100 is likewise provided with an anterior
shield 140 configured to resist the tibial implant 100 from
migrating posteriorly. The anterior shield 140 projects upwardly
from the anterior edge 101 of the implant 100. When said implant is
in place in the patient, the anterior shield 140 would extend
upwards along the tibia bone 30. Thus, as shown in FIG. 1, the
anterior shield 140 extends from the anterior edge 101 of the
implant 100 upward and obliquely relative to upper surface 112. The
anterior shield 140 can define one or more holes 142 for inserting
one or more screws to facilitate fixing the implant to the tibia
bone.
[0057] The tibial implant 100 and the talar implant 200 can be made
of a biocompatible metal alloy, such as cobalt chromium alloy,
titanium alloy, stainless steel or any other material that is
comparably able to withstand the forces in and around the ankle
joint as well as being physiologically tolerated.
[0058] In some embodiments, the tibial implant 100 and/or the talar
implant 200 can comprise a coating of one or more layers on the
surface intended to be in contact and adhere to bone. Such coatings
can facilitate bone apposition, osteointegration and/or
osteoinduction. In some embodiments, a coating of plasma-sprayed
titanium is applied to the talar implant 200 and/or the tibial
implant 100 on the surfaces in contact with bone to promote bone
apposition and osteointegration. The plasma-sprayed titanium
coating can comprise an average thickness between 100 to 800 .mu.m,
such as 200 to 300 .mu.m. In some embodiments, a coating of calcium
phosphate, such as hydroxyapatite, is applied to the talar implant
200 and/or the tibial implant 100 on the surfaces in contact with
bone to promote bone apposition, osteointegration and/or
osteoinduction. The calcium phosphate coating can comprise an
average thickness between 25 to 200 .mu.m, such as 60 to 100 .mu.m.
In some embodiments, a dual coating of plasma-sprayed titanium,
followed by a coating of calcium phosphate is applied to the talar
and/or the tibial implant. The dual coating can comprise an average
thickness between 125 and 1000 .mu.m, such as 260 to 400 .mu.m. A
tibial implant 100 and/or the talar implant 200 can comprise a
titanium coating, a calcium phosphate coating, or both.
[0059] With particular reference to FIGS. 2, 3, and 8A, 8B, and 8C,
the intermediate implant 300 comprises a base 350 and the
projecting member 330. The base 350 defines an upper surface 310
and the curved lower surface 320 opposite the upper surface 310,
and the projecting member 330 extends outwardly from the upper
surface 310. The intermediate implant 300 can be in frictional
contact with the tibial implant 100 and talar implant 200 at the
upper surface 310 and the lower, curved surface 320,
respectively.
[0060] The projecting member 330 is configured to extend into the
recess 122 of the tibial implant 100 and to rotate relative to the
tibial implant 100. In particular, the projecting member 330 is
sized to rotate within the recess 122. As mentioned above, the
projecting member 330 is sized to have a maximum transverse
dimension that is slightly less than the minimum transverse
dimension of the recess 122. In embodiments, the maximum transverse
dimension of the projecting member 330 can be at least 0.1%, 0.2%,
0.3%, 0.4%, 0.5%, 1%, 1.5%, or 2% less than the minimum transverse
dimension of the recess 122. In some embodiments, the projecting
member 330 can rotate at least 70 degrees, at least 180 degrees, or
360 degrees relative to the tibial implant 100 when disposed in the
recess 122. In some embodiments, the projecting member 330 can
freely rotate relative to the tibial implant 100 when disposed in
the recess 122.
[0061] The projecting member 330 can have a transverse
cross-sectional shape that facilitates load distribution along the
lateral surface 335 of the projecting member 330 as it bears
against the sidewall of the recess 122. For example, the transverse
cross-section of the projecting member 330 can define a rounded
shape, such as a substantially circular shape. However, the
transverse cross-sectional shape of the projecting member 330 can
be any shape such as a square, pentagon, star, or other regular or
irregular, convex or non-convex polygonal shape.
[0062] The projecting member 330 is configured to interlock with a
portion of the implant lock 400, such as the first end 402 of the
implant lock 400. For example, in the embodiment shown, the
projecting member 330 comprises a lateral surface 335 having one or
more interlocking surface features, such as cogs 337, which are
configured to interlock with corresponding cog(s) 412 on the first
end 402 of the lock 400.
[0063] The projecting member 330 can be configured to have a
lateral surface 335 that is more wear resistant than the lower
surface 320. For example, the projecting member 330 or a portion
thereof defining the lateral surface 335 can comprise a material
that is tougher, harder, and/or of a higher modulus than the
material of the intermediate implant 300 that defines the lower
surface 320. In the embodiment shown, the projecting member 330
comprises an inner core 332 of a first material and a
circumscribing member 334 of a second material, wherein the second
material is tougher, harder, and/or of a higher modulus than the
first material. In some embodiments, the circumscribing member 334
can be made of a biocompatible metal alloy, such as titanium alloy,
cobalt chromium alloy or stainless steel, or any other material
that is tougher, harder, and/or of a higher modulus than the
material used for the intermediate implant 300. The portion of the
intermediate implant 300 defining the lower surface 320 can be made
of polyethylene, polytetrafluoroethylene, polyether-ether-ketone,
nylon, copolymers or composites thereof, or other suitable material
which can withstand the forces of and about the ankle joint and
provide relatively low friction contact with the talar implant
200.
[0064] Moreover, the circumscribing member 334 can be configured so
that it is coupled in fixed relation to the remainder of the
intermediate implant 300. For example, the inner core 332 and the
circumscribing member 334 are coupled so that the circumscribing
member 334 resists rotation relative to the inner core 332 (see
FIGS. 8A and 8C.) In some embodiments, the inner core 332 has a
non-circular, transverse cross-sectional shape and the
circumscribing member 334 defines an interior opening that has a
transverse cross-sectional shape that is the same as the transverse
cross-sectional shape of the inner core 332. In the embodiment
shown, the transverse cross-sectional shape is a polygonal shape.
Alternatively, or in addition thereto, the circumscribing member
334 can be configured to couple in fixed relation to the base 350
of the intermediate implant 300. For example, the circumscribing
member 334 can interlock with the base 350, such as through one or
more mortise-tenon structures 360.
[0065] The transverse dimension of the projecting member 330 can be
any suitable size. In some embodiments, the transverse dimension of
the projecting member 330 is the same as or less than that of the
base 35. In some embodiments, the maximum transverse dimension of
the projecting member 330 can be between 20% and 85% of the maximum
transverse dimension of the base 350 of the intermediate implant,
such as between 30% to 80% or 40% to 80% or 50% to 80%.
[0066] To facilitate obtaining an ankle prosthesis that has an
alignment which is closer to the specific anatomy of the patient,
an ankle prosthesis kit or an intermediate implant replacement kit
can comprise a plurality of intermediate implants 300 that provide
different configurations to allow varied alignment of the lower,
curved surface 320 relative to the tibial implant 100. In
particular, variance of alignment can be effected by the position
of the projecting member 330 relative to the apex 322 of the lower
curved surface 320. FIGS. 9A, 9B and 9C show three variations in
alignment of the projecting member 330 relative to the apex 322 of
the lower curved surface 320. The three variations shown in the
figures comprise a shift in the position of the projecting member
330 only along an anterior-posterior axis. A first intermediate
implant 300a of the kit can be configured such that a center 338 of
the projecting member 330 be posterior to the apex 322. (FIG. 9A
illustrates an embodiment of the first intermediate implant 300a.)
A second intermediate implant 300b of the kit can be configured
such that a center 338 of the projecting member 330 be disposed
directly above (e.g., vertically aligned or substantially aligned
along an axis that is parallel with the Z-Z axis) the apex 322.
(FIG. 9B illustrates an embodiment of the second intermediate
implant 300b.) A third intermediate implant 300c of the kit 50 can
be configured such that a center 338 of the projecting member 330
be anterior to the apex 322. (FIG. 9C illustrates an embodiment of
the first intermediate implant 300c.). The amount of anterior or
posterior offset, 11, from the apex 322 would be dependent upon the
size of the tibial implant 100. In particular the offset would be a
fraction of the anterior-posterior length dimension of the tibial
implant and can be between 2 to 10% of the anterior-posterior
length, such as 2, 3, 4, 5, 6, 7, 8, 9, or 10%.
[0067] To facilitate obtaining an ankle prosthesis that has an
alignment which is closer to the specific anatomy of the patient,
the intermediate implant 300 can be configured such that the
position of the projecting member 330 on the upper surface of the
intermediate implant is adjustable. (Embodiment not illustrated.)
For example, a plurality of fastening points (e.g., mortise
structures) can be provided on the upper surface of the
intermediate implant to which the projecting member 330 can be
coupled. A clinician can select which fastening points to which the
projecting member 330 should be coupled based on the patient's
anatomy.
[0068] Another factor influencing fit of the ankle prosthesis is
the thickness (or height) of the intermediate implant 300,
particularly the base 350. To account for this variation amongst
patients, an ankle prosthesis kit or an intermediate implant
replacement kit can comprise a plurality of intermediate implants
300 that have different thicknesses. The thickness can be between 5
and 12 mm at the thinnest cross sectional point of the base 350,
such as 5, 6, 7, 8, 9, 10, 11, or 12 mm.
[0069] With particular reference to FIGS. 2, 3, and 10A to 10D, the
implant lock 400 is configured to resist rotation of the projecting
member 330 relative to the tibial implant 100 by applying a force
to the projecting member that is only substantially perpendicular
to the axis of rotation of the projecting member 330 (e.g.,
substantially perpendicular to the Z-Z axis). (In embodiments,
substantially perpendicular can be within 10.degree., 5.degree.,
3.degree., 2.degree., or 1.degree. of the perpendicular.) The
implant lock 400 can also be configured to interlock with the
tibial implant 100. The interlocking can be releasable. [0070] In
the embodiment shown, the implant lock 400 comprises an insert or
main body portion 420, which is formed from two sub-portions,
namely a head portion 430 and a tail portion 440. When inserted
into the slot 130, the tail portion 440 would be closer to the
projecting member 330 than the head portion 430.
[0070] These two portions 430 and 440 are configured to move
relative to each other along an axis that is generally
perpendicular to the axis of rotation of the projecting member 330
or that passes through the first end 402 and the second end 404 of
the implant lock 400. In the embodiment shown, the implant lock 400
further comprises a screw 450 and is configured such that the head
portion 430 and the tail portion 440 move away from each other as
the screw 450 is rotated in a first direction and move toward each
other as the screw 450 is rotated in a second direction. In
particular, each of the head portion 430 and the tail portion 440
comprise a through-bore 431 and 441, respectively, through which
the screw 450 can extend. Through-bore 441 of the tail portion 440
is threaded. The through-bore 431 of the head portion 430 is not
threaded, and the screw 450 is able to freely rotate within the
through-bore 431
[0071] In addition, head portion 430 and screw 450 are configured
such that the axial position of the screw 450 relative to the head
portion 430 does not change as the screw 450 is rotated. For
example, in the embodiment shown, screw 450 comprises a head 452
coupled to a shaft 454 and a collar 456 spaced apart from the head
452 and circumscribing the shaft 454. The through-bore 431 of the
head portion 430 has a transverse dimension that is narrower at an
intermediate section 432 than at the end sections 434 and 436. The
section of the shaft 454 that is disposed within the narrower,
intermediate section 432 of through-bore 431 is the section between
the collar 456 and the head 452. In the embodiment shown, this
narrower intermediate section 432 can be formed by two retaining
pins 466a, 466b pressed into holes 468a, 468b intersecting
through-bore 431 and capturing the shaft 454 above the collar 456.
As the screw 450 is rotated, the collar 456 or the head 452 of the
screw 450 bears against the retaining pins 466a, 466b. This
facilitates the movement of the tail portion 440 away from the head
portion 430.
[0072] Head portion 430 can also be configured to interlock with
the tibial implant 100. For example, in the embodiment shown, head
portion 430 comprises a body 438 coupled to two legs 439a, 439b
projecting from the body 438 such that the legs 439a, 439b flank
the tail portion 440. Each leg 439a, 439b comprises two
projections, a first projection 410a, 410b facing outward and a
second projection 411a, 411b facing inward. The tail portion 440
tapers such that it has a wider transverse dimension nearer the
head portion 430. The tapering of the tail portion 440 facilitates
the sidewall 444 of the tail portion 440 to bear against the inward
facing, second projection 411a, 411b and press projections 410a,
410b into the respective notch 136a, 136b in the sidewall 134
defining the slot 130.
[0073] By rotating the screw 450 in a first direction, such as to
partially withdraw it from the through-bore 441 of the tail portion
440, the tail portion 440 moves away from the head portion 430 and
toward the recess 122 or toward the projecting member 330 disposed
within the recess 122. This motion facilitates the tail portion 440
interlocking with the projecting member 330, such as by the cog(s)
412 of the tail portion 440 interlocking with cogs 337 of the
projecting member 330 (see FIG. 10D). This motion can also
facilitate the head portion 430 interlocking with the tibial
implant 100 through the wedge surface interface of sidewall 444
with second projections 411a and 411b.
[0074] Implant lock 400 can further be configured to bind the screw
450 such that rotation of the screw 450 is impeded when locking the
implant lock 400. For example, to facilitate impeding rotation of
the screw 450 when locking, in the embodiment shown, implant lock
400 can further comprise an abutment pin 470a and a hole 470b
intersecting through-bore 441 of the tail portion 440. As screw 450
is rotated, such as to partially advance it into the through-bore
441 of the tail portion 440, the threads of the screw 450 will abut
the pin 470a, thereby binding the screw by galling and impeding its
rotation.
[0075] By rotating the screw 450 in a second direction, such as to
advance it into the through-bore 441 of the tail portion 440, the
tail portion 440 moves toward the head portion 430 and away from
the recess 122 or away from the projecting member 330 disposed
within the recess 122. This motion facilitates the tail portion 440
unlocking with the projecting member 330, such as by the cog(s) 412
of the tail portion 440 releasing or decoupling from the cogs 337
of the projecting member 330 (see FIG. 10C). This motion can also
facilitate the head portion 430 unlocking with the tibial implant
100 through the freeing of the wedge surface interface of sidewall
444 with second projections 411a and 411b retracting from the
respective notches 136a, 136b in the sidewall 134.
[0076] As mentioned above, there can be different configurations of
the intermediate implant 300 that provide different degrees of
alignment of the lower, curved surface 320 relative to the tibial
implant 100. When a particular configuration of the intermediate
implant 300 is inserted in vivo, its curvature on the lower surface
320 will align with that of the upper surface 210 of the talar
implant 200. Whether or not this particular configuration is
optimal as compared to the other options, with reference to FIGS.
11A to 11D, a measurement tool assembly 600 can be used to indicate
where the projecting member 330 is within the recess 122 or the
slot 130, whether it is anterior, posterior, or generally in
alignment with the apex 222 of upper surface 210 of the talar
implant 200. The measurement tool assembly 600 comprises a bar 610
that is sized to extend through the slot 130 and the recess 122 and
a trial intermediate member 620. In the embodiment shown, the bar
610 defines a hole 615 configured to receive a trial projecting
member 650 coupled to and extending from base 660. The bar 610 also
comprises marking 630 which indicated the distance from the hole
615, thereby indicating the relative anterior position of the apex
222 of upper surface 210 talar implant 200 to that of the anterior
face 136 of tibia implant 100. The markings 630 can comprise
numerical values and/or can comprise symbols or colors which
represent the numerical vales.
[0077] To use the measurement tool assembly 600, a trial
intermediate implant 620 is assembled to bar 610, such as by
disposing the trial projecting member 650 of the trial intermediate
implant 620 in the hole 615. The trial projecting member 650 with
the bar 610 coupled thereto is inserted into position between the
tibial implant 100 and talar implant 200 such that the trial
projecting member 650 and the bar 610 are disposed within the
recess 122 and slot 130. The marking 630 that is visible at the
anterior face 136 of the tibial implant 100 is indicative of
whether the trial intermediate implant 620 is generally in neutral
alignment (FIG. 11B), posterior (FIG. 11C), or anterior (FIG.
11D).
[0078] An embodiment of the trial intermediate implant 620 can be
the same as embodiments of the intermediate implant 300 described
above except that the trial projecting member 650 has smaller
transverse dimensions than that of the intermediate implant 300 and
the trial projecting member 650 is configured to assemble to the
bar 610.
[0079] With reference to FIGS. 12A to 12D, another embodiment of a
tibial implant and an intermediate implant of an ankle prosthesis
is shown. A tibial implant 805 and an intermediate implant 810
shown in FIGS. 12A to 12D are similar to those of described above
for ankle prosthesis 10, except that the projecting member 830 and
the implant lock 850 are different than those of the ankle
prosthesis 10. In particular, the projecting member 830 comprises
an circumscribing member 832 disposed around an inner core 834,
where the circumscribing member 832 is composed of a material
(e.g., stainless steel, titanium and its alloys, cobalt chrome
alloys or any other biocompatible metal) that is capable of being
permanently deformed by the implant lock 850. The circumscribing
member 832 and the inner core 834 are configured such that they
resist rotation relative to each other when coupled. Like in ankle
prosthesis 10, the implant lock 850 can be inserted into a slot 860
in a direction that is perpendicular to the axis of rotation of the
intermediate implant 810.
[0080] The implant lock 850 is configured to press into the
circumscribing member 832 thereby permanently deforming the
circumscribing member 832. For example, the implant lock 850 can
define a threaded bore 855 configured to receive a screw 857.
Rotating the screw 857 into the threaded bore 855 can force a
moveable component 858 to extend and press into the circumscribing
member 832. The pressure applied by the moveable component 858 can
deform the circumscribing member 832, thereby causing the
circumscribing member 832 to impede rotation of the intermediate
implant 820 relative to the tibial implant 805.
[0081] A method of determining the relative position of a talar
implant to a tibial implant while the implants are in the body can
comprise determining whether an apex of the upper surface of the
talar implant is posterior to, anterior to, or aligned with a
center of a recess of the tibial implant. The center of the recess
is the center of curvature of the curve along which the sidewall
defining the recess extends. The method of determining the relative
position of the two implants can comprise inserting a measurement
tool into the recess of the tibial implant. An intermediate implant
can be selected from amongst implants with varied projection member
positions depending on whether the apex of the upper surface of the
talar implant is posterior to, anterior to, or aligned with a
center of a recess of the tibial implant.
[0082] Once an appropriate intermediate implant is selected, the
implant can be inserted between the tibial implant and the talar
implant such that the projecting member is disposed within the
recess of the tibial implant. In some embodiments, the projecting
member while disposed within the recess of the tibia implant is
able to freely rotate within the recess.
[0083] A method of establishing the position of the intermediate
implant relative to a tibial implant can comprise rotating the
intermediate implant relative to the tibial implant and fixing the
position of the intermediate implant relative to the tibial
implant. Fixing the position of the intermediate implant comprises
engaging an implant lock with the intermediate implant such that
the implant lock resists rotation of the intermediate implant by
applying a force that is only substantially perpendicular to the
axis of rotation of the intermediate implant. The implant lock can
be inserted into the ankle prosthesis along a direction that is
substantially perpendicular to the axis of rotation of the
intermediate implant. In some embodiments, only a portion of the
implant lock is advanced toward the projecting member of the
intermediate implant to engage the projecting member. This can
occur while the tibial implant, the talar implant, and the
intermediate implant are implanted in the ankle. In some
embodiments, rotating the screw of the implant lock fixes the
position of the intermediate implant relative to the tibial
implant.
[0084] A method of inserting the ankle prosthesis can comprise
inserting an implant lock into the ankle prosthesis along a
direction that is substantially perpendicular to the axis of
rotation of the intermediate implant (e.g., the axis of rotation
that extends along the Z-Z axis shown in FIG. 2). In some
embodiments, only a portion of the implant lock is advanced toward
the projecting member of the intermediate implant in the
substantially perpendicular direction to engage the projecting
member. In some embodiments, rotating the screw of the implant lock
fixes the position of the intermediate implant relative to the
tibial implant.
[0085] A method of replacing an intermediate implant of an ankle
prosthesis (such as that described above) can comprise accessing an
ankle prosthesis within the patient, releasing a first intermediate
implant from a locked position, removing the first intermediate
implant from the ankle prosthesis, and inserting a second
intermediate implant into the ankle prosthesis. In some
embodiments, releasing the intermediate implant from a locked
position can comprise removing a force that is only substantially
perpendicular to the axis of rotation of the intermediate implant,
such as by releasing/unlocking the implant lock. Unlocking the
implant lock to release the intermediate implant can comprise
rotating the screw of the implant lock. Once the first intermediate
implant is removed and the second intermediate implant is inserted,
the same or a second implant lock can be inserted into the ankle
prosthesis. In some embodiments, the second intermediate implant is
allowed to rotate relative to the tibial implant and then the
position of the intermediate implant can be fixed relative to the
tibial implant.
[0086] Another aspect of the present disclosure pertains to an
ankle prosthesis kit comprising a single talar implant configured
for use in either a mobile bearing device or a fixed bearing
device. Such kits can allow a surgeon to choose intraoperatively
between implanting a mobile bearing device or a fixed bearing
device. In an embodiment, as shown in FIG. 13, the kit can comprise
one talar implant 200, an implant lock 400, and two different types
of intermediate implants and tibial implants, namely, a first
intermediate implant 300 and a first tibial implant 100 as well as
a second intermediate implant 950 and a second tibial implant 900.
The talar implant 200, the implant lock 400, the first intermediate
implant 300, and the first tibial implant 100 are the same as those
described above and shown in FIGS. 3, 4A, 4B, 6A, 6B, 8A to 8C and
10A to 10D. Both the first and second intermediate implants 300,
950 have identical lower bearing surfaces 320, 970, which are
shaped to correspond to the upper bearing surface 210 of the talar
implant 200. However, the upper surface contours 310, 960 of each
intermediate implant 300, 950 are different. The first intermediate
implant 300 is configured to couple in fixed relation to the first
tibial implant 100 as described with respect to the embodiment
shown in FIG. 3. The second intermediate implant 950 is configured
to slide or rotate relative to the second tibial implant 900 and
not couple in fixed relation thereto. As such, the upper bearing
surface 960 of the second intermediate implant 950 is planar, and
the lower bearing surface 920 of the second tibial implant 900 is
also planar.
[0087] A system in which the talar implant 200 can be utilized in
either a mobile-bearing or a fixed-bearing device, such as that
described above and shown in FIG. 13, can also be useful in
scenarios where one style of ankle prosthesis (mobile-bearing or
fixed-bearing) is implanted into a patient but after some time, a
determination is made to use the other style. In such
circumstances, a revision arthroplasty procedure can be conducted
that would leave the talar implant 200 in place but would swap the
intermediate implant 300 or 950 and tibial implant 100 or 900 for
those of the alternative style.
[0088] A method of implanting an ankle prosthesis can comprise
implanting a talar implant 200 into a patient; selecting a tibial
implant for implantation by choosing between a first tibial implant
100 configured to couple in fixed relation to a first intermediate
implant 300 and a second tibial implant 900 being configured to be
mobile bearing in relation to a second intermediate implant 950;
implanting the selected tibial implant 100 or 900; selecting an
intermediate implant for implantation by choosing between the first
intermediate implant 300 and the second intermediate implant 950
based upon the selection of the tibial implant 100 or 900;
implanting the selected intermediate implant 300 or 950, wherein
both the first and second intermediate implants 300, 950 have a
lower bearing surface 320, 970 that is shaped to correspond to an
upper bearing surface 210 of the talar implant 200.
[0089] Embodiments described herein are useful in primary ankle
replacements but can also be used in a revision arthroplasty
procedure, including disarthrodesis.
Example Section
[0090] 1. Ankle Prosthesis Wear Testing
[0091] Materials:
[0092] Four ankle prostheses for a right ankle were constructed in
accordance with the present disclosure. The intermediate implant
was composed of a UHMWPE and had a circumscribing member composed
of Titanium alloy ASTM F136. The talar implant was composed of CoCr
(ISO 5832/ASTM F75), and had a titanium and hydroxyapatite coating.
The bearing surface of the talar implant is an 8 degree
frustoconical-shaped surface. The tibial implant was composed of a
titanium alloy ASTM F136. The implant lock insert was composed of
titanium alloy ASTM F136 and the implant locking screw is composed
of titanium alloy ASTM F136.
[0093] Equipment:
[0094] A servo hydraulic six station joint stimulator (Endolab,
Rosenheim) was used for the wear testing. Three stations and one
load-soak station were used.
[0095] Protocol:
[0096] All tests were performed in accordance with Endolab's
TP-151109-2 (April 2017 as amended May 2017) using the parameters
specified in Table 1 below.
TABLE-US-00001 TABLE 1 Force Curve See FIG. 14 Load direction was
relative to the tibial component Force Maximum Goint reaction
force) 2.3 kN Frequency 1 Hz Dorsiflexion/plantarflexion
+15.degree./-15.degree. internal rotation/external rotation Not
actively controlled but instead defined by the frusto- conical
surface of the talar implant and the intermediate implant
corresponding to +/-2.degree. internal/external rotation
displacement in anterior direction (+)/ 2.5 mm/-2.5 mm displacement
in posterior direction (-) Test fluid temperature 37.degree. +/-
2.degree. C. Number of cycles >9 million Inspection cycles every
millionth cycle
[0097] The test fluid was a calf serum diluted with deionized water
to 20 grams of protein per liter with 2.3 g/l of EDTA, of 10 ml/l
of amphotericin solution (250 .mu.g/ml), and 10 ml/l of gentamicin
solution (10 mg/ml).
[0098] All intermediate implants were presoaked in a test fluid for
a period of 27 days. The test fluid was held at a temperature
between 35.degree. and 39.degree. C.
[0099] For the load-soak control and the test articles, the test
fluid was replaced every 500,000 cycles. The load-soak control
underwent the same joint reaction force as the other samples but
did not undergo any translational/angular motion.
[0100] When installing a sample into the simulator, the
intermediate implant was locked to the tibial implant by tightening
the implant lock screw to a torque of 1 Nm.
[0101] Samples are dismounted, inspected for wear, and cleaned
every 0.5 million cycles, 1 million cycles, and at 1 million cycle
intervals thereafter. The wear of the intermediate implant was
determined according to gravimetric change of the component
according to ISO 14243-2: 2016.
[0102] Results:
[0103] The data collected from the three wear samples was corrected
by the weight loss of the load-soak control. After such correction,
a mean wear rate of 1.38 mg per million cycles was observed between
0 and 9 million cycles for the three samples (SDev=0.08 mg per
million cycles).
[0104] Visual inspection revealed that the teeth on the
circumscribing member and the corresponding implant lock did not
change in appearance throughout testing indicating that the tibial
implant and the intermediate implant remained secure throughout the
testing.
[0105] All three ankle prosthesis samples were still mechanically
sound after 9 million cycles.
[0106] Similar wear testing was conducted on the mobile-bearing
design shown in FIG. 13. The data collected from the three
mobile-bearing wear samples was corrected by the weight loss of the
load-soak control. After such correction, a mean wear rate of 2.62
mg per million cycles was observed between 0.5 and 5 million cycles
for the three samples (SDev=0.17 mg per million cycles).
[0107] All three mobile-bearing ankle prosthesis samples were still
mechanically sound after 5 million cycles.
[0108] 2. Static Torque Testing
[0109] An ankle prosthesis as described in Example I was
constructed. The intermediate implant was coupled to the tibial
implant with the implant lock. Static torque was applied to the
intermediate implant. The amount of torque was well above the
amount that would be encountered during use by the full range of
potential patients. Visual inspection revealed that the teeth on
the circumscribing member and the corresponding implant lock did
not change in appearance throughout testing indicating that the
tibial implant and the intermediate implant remained secure
throughout the testing.
[0110] 3. Dynamic Anterior Force Testing
[0111] An ankle prosthesis as described in Example I was
constructed. The ankle prosthesis as shown in FIG. 1 was assembled
and secured to a stand. A dynamic force in a posterior to anterior
direction was applied to the intermediate implant for 10,000
cycles. The maximum of the dynamic force was well above the amount
that would be encountered during use by the full range of potential
patients. Visual inspection revealed that the teeth on the
circumscribing member and the corresponding implant lock did not
change in appearance throughout testing indicating that the tibial
implant and the intermediate implant remained secure throughout the
testing.
[0112] Although embodiments described herein are made with
reference to example embodiments, it should be appreciated by those
skilled in the art that various modifications are well within the
scope and spirit of this disclosure. Those skilled in the art will
appreciate that the example embodiments described herein are not
limited to any specifically discussed application and that the
embodiments described herein are illustrative and not restrictive.
From the description of the example embodiments, equivalents of the
elements shown therein will suggest themselves to those skilled in
the art, and ways of constructing other embodiments using the
present disclosure will suggest themselves to practitioners of the
art. Therefore, the scope of the example embodiments is not limited
herein.
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