U.S. patent application number 11/367386 was filed with the patent office on 2006-07-06 for implant for reconstruction of joints.
This patent application is currently assigned to ARTIMPLANT AB. Invention is credited to Bengt Edberg, Anders Nilsson.
Application Number | 20060149261 11/367386 |
Document ID | / |
Family ID | 20282644 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060149261 |
Kind Code |
A1 |
Nilsson; Anders ; et
al. |
July 6, 2006 |
Implant for reconstruction of joints
Abstract
A spacer member (1) is intended to be placed between the ends of
the bones which are to be connected, one end of the spacer member
being designed to form a joint surface against one of the bone ends
(6,7). A joint-stabilizing connection (2,3) is arranged to connect
the bones. The spacer member (1) is made of at least one
tissue-compatible material.
Inventors: |
Nilsson; Anders; (Goteborg,
SE) ; Edberg; Bengt; (Goteborg, SE) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Assignee: |
ARTIMPLANT AB
VASTRA FROLUNDA
SE
|
Family ID: |
20282644 |
Appl. No.: |
11/367386 |
Filed: |
March 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10250310 |
Dec 23, 2003 |
7037342 |
|
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PCT/SE02/00038 |
Jan 11, 2002 |
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11367386 |
Mar 6, 2006 |
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Current U.S.
Class: |
623/18.11 ;
606/77; 623/21.15; 623/21.19; 623/23.58 |
Current CPC
Class: |
A61F 2/30721 20130101;
A61F 2002/30563 20130101; A61F 2002/307 20130101; A61F 2250/0024
20130101; A61L 27/58 20130101; A61F 2002/30576 20130101; A61F
2002/30242 20130101; A61F 2002/30616 20130101; A61B 2017/00004
20130101; A61F 2002/30172 20130101; A61F 2/4225 20130101; A61F
2002/30757 20130101; A61B 17/562 20130101; A61F 2002/30062
20130101; A61B 17/06166 20130101; A61F 2/4241 20130101; A61F
2002/30064 20130101; A61B 17/86 20130101; A61F 2230/0052 20130101;
A61F 2002/30672 20130101; A61F 2002/30235 20130101; A61F 2/30724
20130101; A61F 2230/0071 20130101; A61F 2/30756 20130101; A61F
2002/30011 20130101; A61F 2002/30578 20130101; A61F 2210/0004
20130101; A61F 2002/30245 20130101; A61F 2/08 20130101; A61F
2230/0069 20130101; A61F 2002/30593 20130101; A61F 2/30965
20130101; A61F 2310/00365 20130101; A61F 2002/30754 20130101; A61F
2002/30909 20130101; A61F 2250/0081 20130101; A61F 2002/4258
20130101 |
Class at
Publication: |
606/072 ;
606/077; 623/023.58; 623/021.15; 623/021.19 |
International
Class: |
A61B 17/84 20060101
A61B017/84; A61F 2/30 20060101 A61F002/30; A61F 2/42 20060101
A61F002/42 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2001 |
SE |
0100127-0 |
Claims
1. Implant for reconstruction of joints, which is T-shaped in cross
section and is made entirely of degradable polyurethane urea which
is of one piece construction and at least partly porous.
Description
[0001] This application is a division of co-pending application
Ser. No. 10/250,310, filed on Dec. 23, 2003. Application Ser. No.
10/250,310 is the national phase of PCT International Application
No. PCT/SE02/00038 filed on Jan. 11, 2002 under 35 U.S.C. .sctn.
371, which claims priority of Swedish Application No. 0100127-0
filed Jan. 15, 2001. The entire contents of each of the
above-identified applications are hereby incorporated by
reference.
TECHNICAL FIELD
[0002] The present invention relates to an implant for
reconstruction of joints, preferably of the hands and feet.
PRIOR ART
[0003] Primary wear, arthrosis, of the joints of the hands and
feet, for example the carpometacarpal joints of the thumb, is a
common condition, especially in middle-aged women. Investigations
show that about 12% of all women and 8% of men in their fifties
complain of pain at the base of the thumb. The incidence of wear of
the big toe, hallux rigidus, is probably even greater. These
conditions cause pain at rest and also load-related pain and they
reduce mobility. In the hand, this leads to pain in various types
of grips and thereby reduces the gripping strength.
[0004] In the foot, wear causes pain when walking, with reduced
mobility and freedom of movement in the persons affected.
[0005] Today, arthrosis of the base of the thumb is initially
treated with anti-inflammatory agents, local cortisone injections
and various types of supports. At a more developed stage of
arthrosis of the base of the thumb, surgical methods are employed.
In younger men, and in middle-aged men in work, wear of the joints
is preferably treated by an operation stiffening the joint.
[0006] Today, in middle-aged and older women, the surgical method
employed involves some form of bridging graft with a tendon.
However, tendoplasty requires a long period of rehabilitation. The
reduction in pain and the increase in mobility are only achieved
after 6 to 9 months. Moreover, the persons involved have to live
with a permanent loss of strength in the thumb grip.
[0007] Various types of prostheses have also been produced, for
example for treating arthrosis of the base of the thumb. They are
made of titanium, steel, plastic, carbon or silicone. However, they
fail after a short time on account of luxation of the joint. It has
also been found that when carbon is used, the carbon fibre
structure breaks down mechanically over time and the carbon fibre
fragments tend to migrate within the body. U.S. Pat. No. 4,411,027
proposes surrounding the carbon fibre structure with a shell of a
bioabsorbable polymer for the purpose of protecting the structure
from external mechanical action and keeping the fragments in place,
at least in the early stage of healing. However, it has been found
that carbon fibre fragments from the prosthesis still migrate
within the body.
[0008] SE-B-457,962 describes an implantable prosthesis for
completely or partially replacing a tendon, a ligament or a
cruciate ligament. U.S. Pat. No. 6,007,580 further describes a
prosthesis made of a biodegradable material, which prosthesis is
intended to connect two bones.
[0009] However, no suitable implant for reconstruction of joints
has hitherto been proposed. Preconditions for such an implant to be
able to function well are, first, that it must have properties,
such as the requisite strength and mobility, allowing it to replace
the functions of the damaged joint, and, second, that it is
biocompatible, i.e. that the body is not poisoned or otherwise
harmed by the implant. Joints are particularly complicated since
they involve joint capsules, ligaments, cartilage and synovial
fluid in order to permit natural joint movements.
[0010] It has been stated above that joint damage at the base of
the thumb is extremely common and represents a major problem and
causes suffering and impaired function in those concerned.
[0011] Another common problem is hallux rigidus, which is a form of
arthrosis of the base of the big toe and which mainly affects men
and entails restricted mobility of the metatarso-phalangeal joint
of the big toe. This means that the foot cannot be deployed in the
normal way when walking, and that the person affected suffers pain
when walking and an altered gait pattern with loss of speed.
[0012] The abovementioned method with a bridging tendon graft
means, in the case of treating arthrosis of the base of the thumb,
that a bone, namely the trapezoid bone, is removed in its entirety,
which means that the thumb is shortened by the order of 1 cm and
that the short thumb muscles have an altered range of functioning.
Moreover, the proximal end of the metacarpal loses its stability.
In order to reduce the instability and avoid conflict with the
navicular bone, a bridging graft is formed from a tendon. However,
the technique does not mean that the metacarpal is completely
stable. This, together with the shortening of the thumb, leads to
permanent loss of thumb strength both in the key grip and the
three-point grip.
[0013] As has been mentioned above, the prostheses which have
hitherto been produced are not entirely satisfactory either. One
reason is that known prostheses do not stabilize the proximal
metacarpal, which means that the prosthesis dislocates.
[0014] There has therefore long been a need for a solution to the
abovementioned problems which would allow satisfactory
reconstruction of damaged joints in humans and animals.
[0015] The present invention makes available an implant which is of
the type set out in the introduction and which completely
eliminates the abovementioned problems.
[0016] The implant according to the invention is characterized in
that least one spacer member is intended to be placed between the
ends of the bones which are to be connected, one end of the spacer
member being designed to form a joint surface against one of said
bone ends, a joint-stabilizing connection is arranged to connect
said bones, the spacer member is made of at least one
tissue-compatible material, and the joint-stabilizing connection is
intended, upon use of the implant, to extend in the longitudinal
direction across the joint and in over at least one side of the two
bones which are connected by the joint.
[0017] Since the implant comprises a spacer member, direct contact
between adjacent bones is avoided, and thus also the occurrence of
pain caused by bone rubbing against bone.
[0018] By means of the arrangement of said spacer member and a
joint-stabilizing connection it is possible to ensure that during
the period of growth of new tissue the implant has the correct form
and also appropriate strength and mobility.
[0019] According to one embodiment of the invention the material is
porous, entirely or partly. This, in combination with a pore size
permitting ingrowth of new biological tissue means that the implant
according to the invention substantially recreates a functioning
joint.
[0020] According to one preferred embodiment, the spacer member and
the joint stabilizing connection are made of degradable
material.
[0021] According to a further embodiment the joint-stabilizing
connection is made in one piece with the spacer member.
[0022] According to one embodiment the degradable material consists
of polyurethane urea.
[0023] According to another embodiment the degradable material
consists of poly-L-lactide.
[0024] According to a further embodiment the degradable material
consists of polydiaxone (PDS).
[0025] According to another embodiment the degradable material
consists of poly-.beta.-hydroxybutyrate (PHB).
[0026] According to another embodiment the degradable material
consists of chitin or chitosan or polysaccharide.
[0027] According to a further embodiment the degradable material
consists of collagen or protein.
[0028] According to a further embodiment the material consists of
polyuretan.
[0029] According to a further embodiment the material consists of
silicone.
[0030] According to a further embodiment the material consists of
polyethylene terephtalate (PET).
[0031] According to another embodiment the inventiontion is
characterized in that the implant in its entirety in cross-section
mainly has the form of a T, where the stem is said spacer
member.
[0032] According to one embodiment the invention is characterized
in that the spacer member includes a film-like element which is
intended to serve as said joint surface.
[0033] One embodiment of the invention is characterized in that the
spacer member comprises a degradable and tissue-compatible material
in the form of foam, fibre or thread, which material is cast,
knitted or woven or in some other way formed to give the desired
three-dimensional structure.
[0034] According to one embodiment, said connection consists of
flexible thread-like elements.
[0035] According to one embodiment, the invention is characterized
in that the joint-stabilizing connection consists of flexible
thread-like elements, that said thread-like elements have at least
one portion on both sides of the centre line of the two bones, that
opposite ends of each of said portions are anchored in the
respective bone, and that said portions span the joint and are
designed to prevent mutual pivoting of the bones in the lateral
direction.
[0036] According to a further embodiment, the invention is
characterized in that said thread-like elements comprise two
portions which each connect the two bones, and that said portions
are designed to intersect each other across the joint, as a result
of which movements in more than one plane are permitted. When an
implant according to this embodiment is arranged for reconstruction
of a joint at the base of the thumb, the thumb can be moved in a
more natural way during the healing process, which in turn means
that growth of new tissue is stimulated, permitting an improved
joint function for the thumb.
[0037] Further preferred embodiments are set out in the attached
patent claims.
[0038] The invention will be described in more detail below with
reference to illustrative embodiments which are shown in the
attached drawing, where:
[0039] FIG. 1 shows a perspective diagrammatic view of a first
illustrative embodiment of an implant according to the
invention.
[0040] FIG. 2 shows a cross section through an implant according to
FIG. 1 arranged in a joint between two bones.
[0041] FIG. 3 shows a section along the line III-III in FIG. 2.
[0042] FIG. 4 shows a cross section of an implant according to FIG.
1 arranged in a joint between two bones, in a modified way compared
to FIG. 2.
[0043] FIG. 5 shows a perspective view of the bones in a hand and
wrist.
[0044] FIG. 6 shows a portion of the hand shown in FIG. 5, with an
implant according to FIG. 1 arranged in a joint at the base of the
thumb.
[0045] FIG. 7 shows a second illustrative embodiment of an implant
according to the invention arranged in a joint between two
bones.
[0046] FIG. 8 shows a side view of the implant and bones according
to FIG. 7.
[0047] FIG. 9 shows a view similar to FIG. 7 with an implant
according to a third illustrative embodiment, slightly modified in
relation to the embodiment according to FIG. 7.
[0048] FIG. 10 shows a side view of the implant and bones according
to FIG. 9.
[0049] FIG. 11 shows a fourth illustrative embodiment of an implant
according to the invention arranged in a joint between two
bones.
[0050] FIG. 12 shows a side view of the illustrative embodiment
according to FIG. 11.
[0051] FIGS. 13 and 14 show two sizes of spacer bodies which are
included in the implant according to the illustrative embodiments
in FIGS. 7-12 and which are intended to form articular heads in a
joint.
[0052] FIGS. 15 and 16 show two sizes of spacer bodies which are
included in the implant according to the illustrative embodiments
in FIGS. 9 and 10 and which are intended to form articular sockets
in a joint.
[0053] FIGS. 17 and 18 show the structure of a spacer member in an
implant according to a fifth embodiment.
[0054] FIGS. 19 and 20 show, in longitudinal section, the structure
of a spacer member in an implant according to a sixth
embodiment.
[0055] FIGS. 21 and 22 show the structure of a spacer member in an
implant according to a seventh embodiment.
[0056] The implant in the illustrative embodiment according to FIG.
1 has a T-shaped cross section with a spacer member 1 and two
connection branches 2, 3 which, during use of the implant, are
intended to form a joint-stabilizing connection. In the
illustrative embodiment shown, the implant is cast in one piece.
Suitable materials for the implant are polymers comprising urethane
groups with hydrolyzable ester groups or polymers comprising urea
and urethane groups with ester links which are hydrolyzable. A
suitable starting material for the implant is linear block polymers
comprising urea and urethane groups with hydrolyzable ester groups.
Material of this type is described in Swedish Patent 505,703. The
material according to this publication can be cast into forms of
the type shown in FIG. 1 or spun into fibres which are then knitted
or woven and shaped to give the desired finished product. Another
suitable material is a network polymer which essentially lacks urea
groups. Material of this type is described in Swedish Patent
510,868. Implants made of said materials can also be formed by a
combination of casting and knitting or weaving. For example, a
spacer member can be formed by casting the polymer in question on a
reinforcement of the same material, which reinforcement can be
designed as a hose or the like and intended to be engaged on a bone
end. By choosing their structure and the molecular chains involved,
and by adding various substances, the materials of said types
described in said Swedish Patents 505,073 and 510,868 can be
controlled with respect to their mechanical properties and also
with respect to their degradation time.
[0057] The implant according to the invention is intended to be
used in the reconstruction of damaged joints in humans and animals.
The geometric design and the mechanical properties are chosen in
accordance with the intended purpose. The implant will temporarily
replace the damaged joint and the time of degradation of the
implant must exceed the time for formation of cartilage-like tissue
in the spacer member and joint-stabilizing connective tissue for
forming a joint-stabilizing connection. The implant is designed so
that, during the rehabilitation period, it fulfils the intended
joint functions with sufficient strength and mobility. This, in
combination with the fact that the spacer member is porous and has
a pore size permitting ingrowth of new biological tissue, means, as
has been mentioned above, that the implant according to the
invention stimulates recreation of a functioning joint, at the same
time as the implant is degraded. Material according to SE 505,703
and SE 510,868 is broken down by hydrolysis and thereafter
eliminated from the body.
[0058] In FIG. 2, the implant according to FIG. 1 has been arranged
in a damaged joint, for example a finger joint, between two bones
4, 5. The spacer member 1 is arranged between the bone ends 6, 7 of
the respective bones, by which means direct contact between
adjacent bone ends is prevented and pain caused by bone rubbing
against bone is avoided. Before the implant has been fitted,
recesses 8 have been formed in the bones 4, 5 and are intended to
accommodate the joint-stabilizing connection formed by the branches
2, 3. The bone end 7 serves as an articular socket and the bone 5,
in the position shown in FIG. 2, is pivotable in the direction of
the arrow A about the temporary joint surface which is formed by
the spacer member 1. The implant is flexible but substantially
non-stretchable during normal use, i.e. under the forces which
occur when a finger joint is bent in a natural manner. The bone 5
can thus be bent from the position shown in FIG. 2 by the order of
magnitude of 90.degree. and back, but not clockwise from the
position shown in FIG. 2. The opposite surface of the spacer member
is in contact with a bone end 6 serving as an articular head on the
bone 4, and the bone 4 can pivot correspondingly in relation to the
bone 5 in the direction of the arrow B. The spacer member, like the
rest of the implant, is porous with a pore size which permits
ingrowth of new cartilage tissue for continuous re-formation of a
permanent joint. The pore size also permits ingrowth of
joint-stabilizing connective tissue in the branches 2, 3 of the
implant, for continuous replacement of the temporary
joint-stabilizing connection. Re-formation of new cartilage tissue
for the spacer body takes something in the region of 11/2 to 2
years and the total degradation time for the temporary spacer body
must therefore exceed this period of time. The connective tissue
which replaces the temporary connection is re-formed in a shorter
time than cartilage tissue, and it takes something in the region of
six months to 11/2 years for connective tissue to completely
re-form.
[0059] In the illustrative embodiment shown in FIGS. 2 and 3, the
implant has been secured in the bones 4, 5 by means of suture
threads 9 which, as is shown in FIG. 3, connect the branches 2, 3
of the implant to the respective bones.
[0060] In the illustrative embodiment shown in FIG. 4, details
corresponding to similar ones in the illustrative embodiment
according to FIGS. 2 and 3 have been provided with the same
reference numbers. Compared to FIGS. 2 and 3, FIG. 4 shows an
alternative means of securing the implant according to FIG. 1.
Instead of the recess 8, grooves 10 for the branches 2, 3 have been
formed in the bones 4 and 5, as can be seen from FIG. 4. These
branches, which form a joint-stabilizing connection, have been
secured in the bones 4 and 5, respectively, by means of continuous
screws 9'. In the method according to FIG. 4, an uninterrupted hard
outer bone surface is obtained on both the bones 4 and 5.
[0061] As was stated in the introduction, primary wear, for example
in the carpometacarpal joints of the thumb, is a common type of
condition which causes degradation and attrition of joint
cartilage. FIG. 5 shows the bones of the hand from above, i.e. the
back of the hand. In the drawing, the 1st metacarpal has been
indicated by 12 and the trapezoid bone by 13. Said joint condition,
namely arthrosis of the base of the thumb, occurs in the joint
between the 1st metacarpal 12 and the trapezoid bone 13.
[0062] FIG. 6 shows how an implant according to FIG. 1 can be
arranged between said bones 12 and 13. In the example shown, a worn
portion of the trapezoid bone 13 has been removed and the spacer
member 1 has been arranged between this sectioned bone and the 1st
metacarpal 12. The spacer member 1 bears tightly on the surface of
the sectioned bone. The branches 2, 3 have been connected by means
of suture threads 9 to the respective bones 12 and 13 in order to
form a joint-stabilizing connection at the base of the thumb.
[0063] FIGS. 7 and 8 show a second illustrative embodiment of an
implant according to the invention arranged in a joint between two
bones 4 and 5, for example in a finger or a toe. A spacer member 14
is arranged in the joint between the two bones. This spacer member
14 is preferably made of the same material as the implant according
to the first embodiment. The spacer member 14 of the type included
in the implant according to FIGS. 7 and 8 is shown separately in
FIGS. 13 and 14. A spacer member of this type can be produced in
different sizes and thicknesses. FIG. 13 shows a very thin spacer
member 14, and FIG. 14 shows a very thick spacer member 14. For
joints in the hands and feet, the necessary thickness of the spacer
member varies in the range of 0.5 to 7 mm. For joints in animals,
the thickness of spacer bodies of the type shown in FIGS. 13 and 14
can preferably vary within wider limits. The spacer bodies 14 are
provided with securing portions 15 which are expediently made of
the same material as the rest of the spacer body. The securing
portions 15 according to FIG. 13 are made for example as woven or
knitted ligaments. Alternatively, the securing portions can consist
of suture threads or some other degradable, preferably bio-erodable
material. The securing portions 15 are used for anchoring the
spacer member 14 on one of the bones. FIG. 7 shows diagrammatically
how the securing portions 15 have been connected to the bone 4 by
means of suture threads 9. The implant according to FIGS. 7 and 8
includes a flexible thread-like element 16 which is intended to
serve as a temporary joint-stabilizing connection. As can be seen
from FIGS. 7 and 8, the thread-like element has a portion 17, 18 on
both sides of the centre line of the two bones, which portions
extend in the longitudinal direction of the bone and over the
joint. In this illustrative embodiment, the thread-like element is
made in one piece and extends with portions 19 and 20 through holes
in the bones 4, 5, respectively.
[0064] As in the embodiment according to FIGS. 2 and 3, the bones 5
and 4 can be bent from the position shown in FIG. 8 in the
direction of the arrows A and B, respectively. The thread-like
element is made of a degradable, preferably bio-erodable material,
preferably of a linear block polymer of the type which has been
described above, and has further been designed with mechanical
properties similar to a natural ligament within its natural range
of movement. This means that the thread-like element has, at least
within a normal ligament's range of functioning, similar mechanical
properties but that beyond this range of functioning it may be
overdimensioned compared to a normal ligament. The thread-like
element 16 is flexible but substantially non-stretchable, which
means that the bones 4, 5 in the position shown in FIG. 8 cannot be
bent about the joint in the direction counter to the arrows A and
B, respectively.
[0065] A third illustrative embodiment according to FIGS. 9 and 10
corresponds to a large extent to the embodiment according to FIGS.
7 and 8. Corresponding details in said embodiments have been
provided with the same reference numbers. What distinguishes the
implant according to FIGS. 9 and 10 from the embodiment described
in connection with FIGS. 7 and 8 is that a further spacer member 21
has been arranged against the bone end 7 of the bone 5. Spacer
members of this type and designed as an articular socket are shown
separately in FIGS. 15 and 16. In the same way as has been
described in connection with FIG. 13 and 14, the thickness of the
spacer member can be varied within the same limits. Moreover, the
spacer members designed as articular sockets are provided with
securing members 15 which are intended to anchor the spacer body 21
on the bone 5 by means of suture threads 9, as shown in FIGS. 7 and
8.
[0066] FIGS. 11 and 12 show a fourth illustrative embodiment of an
implant according to the invention. This fourth embodiment differs
from the illustrative embodiment shown in FIGS. 7 and 8 only with
respect to the thread-like element. This has been arranged with
thread portions 22, 23 intersecting across the joint between two
bones 4, 5, as can be seen from FIGS. 11 and 12. The thread-like
element is made in one piece 16 and has portions 24, 25 which
extend through holes in the bones 4 and 5. Since the thread
portions 22 and 23 run more freely on one side of the bone compared
to the embodiments described in connection with FIGS. 7 to 10,
where respective thread portions 17 and 18 run on both sides of the
longitudinal centre line of the bones and prevent mutual pivoting
of the bones in the lateral direction, the bones 4 and 5 can, in
addition to the possibility of pivoting in the direction of the
arrows A and B in FIG. 12, also be pivoted in another plane, such
as is indicated by the arrows C in FIG. 11.
[0067] FIG. 17 shows a knitted or otherwise formed network
structure 26 made of a degradable material, preferably from said
linear block polymers according to SE 505,703. Said structure has
the shape of a hood and is intended to serve as reinforcement in an
implant. The latter is formed by means of a degradable material,
preferably in the form of polyurethane with hydrolyzable ester
groups, being cast from outside onto the top of the hood. Said
material is described in SE 510,868.
[0068] FIG. 18 shows the finished spacer member after casting,
intended to serve as an articular head in a joint, for example a
finger joint. The cast-on material has been indicated by 27 in FIG.
18. The network structure 26 forms a hose which strengthens the
spacer body from the inside, and the network portion 28 protruding
from the cast body 27 forms a hose portion which is intended to be
engaged on a bone which is to be connected to an adjacent bone via
the joint. A further purpose of the network structure, besides that
of serving as a strengthening means, is to create a high degree of
friction against the bone and facilitate growth therein. The
network structure 26 is also stable for sewing in upon fixation to
the bone.
[0069] FIG. 19 shows, in a similar way to FIG. 17, a knitted or
otherwise formed network structure 29 which is intended to form an
outer reinforcement for a spacer member, which is intended to serve
as an articular socket, i.e. as a complement to a spacer member of
the type which has been described in connection with FIGS. 17 and
18.
[0070] The network structure 29 is provided with one or more
securing portions 30 which are intended to be secured on the
outside of a bone by means of suture thread or the like. The
securing portion 30 can go all the way round or be made up of one
or more securing portions.
[0071] An illustrative embodiment with two securing portions 30 is
shown in the drawing.
[0072] A degradable material, preferably in the form of
polyurethanes with hydrolyzable ester groups, is cast onto the
inside of the network structure, as can be seen from FIG. 20, for
forming an articular socket. The cast-on material has been
indicated by 31 in FIG. 20. The purpose of the network structure
according to FIG. 20 is the same as has been described in
connection with FIG. 18, i.e. to serve as reinforcement in the
spacer member, create friction against the bone and facilitate
growth in the bone.
[0073] FIGS. 17 to 21 show relatively thin spacer members
corresponding to the spacer members shown in FIGS. 13 and 15.
[0074] FIGS. 21a and 21b show a knitted or otherwise formed network
structure 32 of the type which has been described in connection
with FIG. 17 above.
[0075] The network structure 32 differs from that shown in FIG. 17
in that the top 33 of the structure is condensed and in that the
reinforcement in the top 33 has a depth which will substantially
correspond to the thickness of the degradable material 34, see FIG.
22, which is cast from the outside and in across the depth of the
network structure in the top 33. The cast material 34 like the
network structure is expediently made of polyurethanes with
hydrolyzable ester groups.
[0076] The actual spacer member in the embodiment according to FIG.
22 has a thickness which substantially exceeds the thickness of the
spacer member according to FIG. 18. In principle, the difference
arises in the same way as the difference in size which has been
described in connection with FIGS. 13 and 14 above. The network
structure 32 fulfils the same purposes as have been described above
in connection with FIGS. 17 to 20.
[0077] However, the network structure 32 has a substantial depth at
the top 34 and in this area it will serve also as internal
reinforcement in the cast-on material. It is important that the
spacer member in a joint does not collapse under the pressures
which arise during natural use of the joint, and instead the
temporary spacer member must hold adjacent bone ends at a distance
from each other. It is of course also important that the temporary
spacer members are resistant to wear.
[0078] The different embodiments of the spacer members shown in
FIGS. 17 to 22 are combined with a joint-stabilizing connection,
for example in the form of flexible thread-like elements which have
been described in connection with FIGS. 7 to 12.
[0079] The invention is not limited to the illustrative embodiments
described above, and instead it can be modified in a number of ways
within the scope of the attached patent claims.
[0080] The spacer member, which can consist of a cast or spun and
thereafter knitted or woven structure or an otherwise formed
structure, can be provided, as has been described above, with
strengthening threads of the same material as the rest of the
structure or of another degradable and tissue-compatible
material.
[0081] Said strengthening threads can be arranged to form a
reinforcement skeleton which is intended to give the structure
stability without locking it. The strengthening threads can for
example be arranged in a defined direction in order to afford
increased strength in this direction.
[0082] The reinforcement skeleton can consist of a shell which
surrounds the rest of the structure. In addition to said shell, the
reinforcement structure can also comprise strengthening threads in
one or more defined directions.
[0083] In the above described embodiment have been mentioned
suitable examples of materials for a degradable implant. Further
examples of degradable materials for the implant in accordance with
the invention are defined in the following patent claims.
[0084] The invention is not restricted to implants of degradable
materials. Examples of non-degradable materials are silicone and
polyethylene terephtalate.
[0085] The implant according to the invention can have different
forms than have been described above. All corners of the in the
figures schematically shown T-shaped implant are preferably
rounded.
[0086] The implant can be shaped as a plate with integrated
fastening members or joint-stabilizing connections. The implant can
have a sponge-like shape with integrated stabilizing
connections.
[0087] Within the scope of protection is an implant arranged such
that the shape of the implant is adapted to the anatomic shape when
exposed to load.
[0088] The joint-stabilizing connection can be designed in a
different way than has been described above.
[0089] The material of the spacer member can consists of
polytetrafluoro ethylene (PTFE). Also the joint-stabilizing
connection can be made in the same material. This material is
generally known under the trade name TEFLON.RTM..
* * * * *