U.S. patent application number 09/813441 was filed with the patent office on 2001-09-27 for artificial finger joint.
Invention is credited to Rauscher, Markus.
Application Number | 20010025199 09/813441 |
Document ID | / |
Family ID | 8174606 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010025199 |
Kind Code |
A1 |
Rauscher, Markus |
September 27, 2001 |
Artificial finger joint
Abstract
The invention shows an artificial finger joint comprising a
convex joint head (1) and comprising a concave joint shell (2)
which can be fastened independently of one another with a
respective shaft (3, 4) in a bone end (5, 6) and which can be moved
in an articulation plane from an extension position (7) with
parallel shaft axes (8, 9) into a hyperextension position (10) or
into an articulation end position (11). A guide pin (12) projects
out of the joint shell (2) in the direction of its shaft axis (9)
and protrudes into a pocket (13) of the joint head (1), with the
pocket (13) having a first abutment (16) for the guide pin (12) in
the hyperextension position (10). A second abutment (17) between
the joint shell (2) and the joint head prevents a tilting of the
guide pin (12) and shaft (4) of the joint shell (2) about the first
abutment (16) in the hyperextension position (10).
Inventors: |
Rauscher, Markus;
(Allenwinden, CH) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
8174606 |
Appl. No.: |
09/813441 |
Filed: |
March 20, 2001 |
Current U.S.
Class: |
623/21.13 ;
623/21.15 |
Current CPC
Class: |
A61F 2002/4251 20130101;
A61F 2002/3082 20130101; A61F 2002/30113 20130101; A61F 2310/00029
20130101; A61F 2002/30884 20130101; A61F 2230/0006 20130101; A61F
2002/30179 20130101; A61F 2230/0058 20130101; A61F 2002/30153
20130101; A61F 2/4241 20130101; A61F 2002/30662 20130101; A61F
2002/30878 20130101; A61F 2002/4243 20130101; A61F 2230/0019
20130101; A61F 2310/00023 20130101; A61F 2230/0023 20130101; A61F
2002/30156 20130101 |
Class at
Publication: |
623/21.13 ;
623/21.15 |
International
Class: |
A61F 002/42 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2000 |
EP |
00810236.0 |
Claims
1. Artificial finger joint comprising a convex joint head (1) and
comprising a concave joint shell which can be fastened
independently of one another with a respective shaft (3, 4) in a
bone end (5, 6) and which can be moved in an articulation plane
from an extension position (7) with parallel shaft axes (8, 9) into
a hyperextension position (10) or into an articulation end position
(11), characterized in that a guide pin (12) projects out of the
joint shell (2) in the direction of the shaft axis (9) of the
latter and protrudes into a pocket (13) of the joint head (1), with
the pocket (13) having a first abutment (16) for the guide pin (12)
in the hyperextension position (10); and in that a second abutment
(17) is present between the joint shell (2) and the joint head (1)
in the hyperextension position (10) and prevents a tilting of the
guide pin (12) and the shaft (4) of the joint shell (2) about the
first abutment (16).
2. Artificial finger joint in accordance with claim 1,
characterized in that the pocket (13) permits a pivotal angle
.alpha. between 80.degree. and 130.degree. between the
hyperextension position (10) and the articulation end position
(11).
3. Artificial finger joint in accordance with any one of the claims
1 or 2, characterized in that the concave joint shell (2) has in
the direction of the hyperextension position a formed on cap (18)
which when the hyperextension position (10) is reached encounters a
second abutment (17) at the joint head which is displaced by a
distance S from a point of rotation (19) in the joint head in the
direction towards the shaft (3) of the latter.
4. Artificial finger joint in accordance with any one of the claims
1 or 2, characterized in that beyond a point of rotation (19) the
pocket (13) has an undercut extension (20) with a second abutment
(17) which is arranged oppositely to the first abutment (16); and
in that the guide pin (12) protrudes outwardly beyond the point of
rotation (19) into the undercut extension (20).
5. Artificial finger joint in accordance with any one of the claims
1 to 4, characterized in that the guide pin (12) has a round
cross-section and a lateral total clearance (28) of more than 5% of
its diameter from guide cheeks (14, 15) of the pocket (13).
6. Artificial finger joint in accordance with any one of the claims
1 to 4, characterized in that the guide pin (12) has a rectangular
cross-section (25) and has a lateral total clearance (28) of more
than 5% of its width from guide cheeks (14, 15) of the pocket
(13).
7. Artificial finger joint in accordance with claim 6,
characterized in that the rectangular cross-section has a diagonal
which is longer than the spacing of the guide cheeks (14, 15) in
order to achieve a rotational securing.
8. Artificial finger joint in accordance with any one of the claims
1 to 7, characterized in that the convex bearing surface of the
joint head (1) and the concave bearing surface of the joint shell
(2) are congruent in the hyperextension position; and in that the
curvature of the convex bearing surface of the joint head (1)
increases in the direction of the articulation.
9. Artificial finger joint in accordance with any one of the claims
1 to 8, characterized in that a third abutment (21) in the pocket
(13) restricts the movement of the guide pin (12) in the
articulation end position (11); and in that a fourth abutment (22)
is present in the pocket (13) which prevents a tilting of the guide
pin (12) and its shaft (4) about the third abutment (21).
10. Artificial finger joint in accordance with any one of the
claims 1 to 9, characterized in that abutments (16, 17b, 21, 22)
are formed as bolts (23) which are subsequently fastened into the
pocket (13).
11. Artificial finger joint in accordance with any one of the
claims 1 to 10, characterized in that the joint head (1) and the
joint shell (2) with their shafts (3, 4) consist of metal.
12. Artificial finger joint in accordance with any one of the
claims 1 to 11, characterized in that the joint head (1) or the
joint shell (2) have articulation surfaces which consist of plastic
(29).
Description
[0001] The invention relates to an artificial finger joint
comprising a convex joint head and comprising a concave joint shell
which can be fastened independently of one another with a
respective shaft in a bone end and which can be moved in an
articulation plane from an extension position with parallel shaft
axes into a hyperextension position or into an articulation end
position.
[0002] Artificial finger joints occur between the metacarpal bone
and the finger bone or between individual finger bones. In order to
be able to operate at a finger joint of this kind, the surgeon must
expose the bone ends and push aside minute blood vessels, nerves
and tendons without overstretching them. It is therefore usual with
the lateral pushing aside, which would cause a stretching, to bring
the joint into articulation position, in which both bone ends are
exposed for a resection. Accordingly it is an advantage when the
joint head and the joint pan can be inserted independently of one
another and can be brought into engagement as in a natural joint
without the above mentioned overstretching arising.
[0003] Thus the patent specification U.S. Pat. No. 4,231,121 shows
a finger joint which consists of a joint head with a formed on
shaft and of a joint shell with a formed on shaft, which can be
pushed together in an articulation position. The freedom of
movement goes from an extension position into a hyperextension
position or into an articulation end position. An embodiment of
this kind has the disadvantage that in the end positions, for
example in the hyperextension, a sliding off of the joint shell
from the joint head can take place when a transverse force arises
since the equilibrium state depends substantially on the force with
which the two joint parts are held together by the ligaments which
surround them.
[0004] The object of the invention is to improve artificial finger
joints in this regard. This object is satisfied in that a guide pin
projects out of the joint shell in the direction of its shaft axis
and protrudes into a pocket of the joint head, with the pocket
having a first abutment for the guide pin in the hyperextension
position; and in that a second abutment is present between the
joint shell and the joint head in the hyperextension position and
prevents a tilting of the guide pin and the shaft of the joint
shell about the first abutment.
[0005] The invention has the advantage that, through the provision
of a second abutment in a position in which a first abutment is
reached for the hyperextension position and would provide a
momentary center for a continuation of the rotation, the movement
is stopped.
[0006] Further advantageous improvements result from the
subordinate claims 2 to 12.
[0007] Thus it is advantageous that through a corresponding design
of the pocket, pivotal angles .alpha. from 80.degree. to
130.degree. between the hyperextension position and the
articulation end position are possible which lie in the pivotal
range of a natural finger joint.
[0008] One embodiment provides a cap which is formed on at the
joint shell in the direction of the hyperextension position and
which when the hyperextension position is reached encounters a
second abutment at the joint head which is displaced by a distance
S beyond a point of rotation at the joint head in the direction
towards the shaft of the latter. An advantage of this cap is that
it holds specific ligaments at a distance and is at the same time
guided by these ligaments. The guide pin can project from the joint
shell as a round pin, which is simple in the manufacturing
technology. A further advantage of this cap consists in that the
palmar luxation is suppressed in a grasping movement.
[0009] A further embodiment provides for the pocket having beyond a
point of rotation an undercut extension with a second abutment
which is arranged oppositely to the first abutment in order to stop
the guide pin, which is extended beyond the point of rotation, when
it encounters the first abutment. This embodiment has the advantage
that the second abutment lies within the joint head and can not
disturb externally.
[0010] Between the guide pin and the pocket, a clearance from the
lateral guiding cheeks can be provided which amounts to more than
5% of the width of the guide pin in order to enable an articulation
in a laterally slightly angled off position of the shaft axes. This
has the advantage that fingers can articulate parallel to one
another in spite of the splay position of the metacarpal bone.
[0011] With a rectangular cross-section of the guide pin the
clearance from the guiding cheeks can be adjusted in such a manner
that a rotational securing is achieved through a rectangular
diagonal which is longer than the spacing of the guiding cheeks. A
guide pin which is reduced by the amount of the clearance from the
guiding cheeks has the advantage that the degrees of freedom as in
a natural finger joint are present for the joint movements.
[0012] A further advantage consists in that the bearing surfaces of
the joint head and the bearing shell are congruent in the
hyperextension position in order to be able to take up the greatest
bearing forces in this position, that the curvature of the joint
head may however increase in the articulation direction in order
not to tension the ligaments too strongly during the
articulation.
[0013] Analogously to the restriction of the movement in the
hyperextension, a third abutment can be provided in the
articulation end position and a tilting about this third abutment
can be prevented through a fourth abutment, which for example is
likewise provided in the pocket and acts on the guide pin.
[0014] In order to realize a pocket with undercut abutments in a
simple manufacturing technology, a pocket without undercuttings can
first be produced in which subsequently provided bolts form the
undercuttings and the abutments. The joint head and the joint shell
are advantageously manufactured of body compatible metals, for
example of titanium or titanium alloys or
cobalt-chromium-molybdenum alloys. The frictional relationships
between the articulation surfaces can be improved when one of the
surfaces consists of plastic, for example of polyethylene or PEAK
(polyaryl ether ketone).
[0015] In the following the invention will be illustrated with
reference to exemplary embodiments. Shown are:
[0016] FIG. 1 schematically, a highly enlarged longitudinal section
of an artificial finger joint in accordance with the invention in
the hyperextension position;
[0017] FIG. 2 schematically, a side view of the joint head of FIG.
1;
[0018] FIG. 3 schematically, a view of the end side of the joint
head of FIG. 2 with a rectangular guide pin which protrudes into
the pocket;
[0019] FIG. 4 schematically, a longitudinal section analogous to
FIG. 1 in which abutments for a guide pin are formed by
subsequently inserted bolts;
[0020] FIG. 5 schematically, a side view of the joint head of FIG.
4;
[0021] FIG. 6 schematically, a view of the end side of the joint
head of FIG. 5;
[0022] FIG. 7 schematically, a further solution analogous to FIG. 1
in which the joint head can be manufactured as an injection molded
part with a mold separation perpendicular to the
hyperextension;
[0023] FIG. 8 schematically, a view of the end side of the joint
head of FIG. 7;
[0024] FIG. 9 schematically, a side view of the joint shell and the
guide pin of FIG. 8;
[0025] FIG. 10 schematically, a longitudinal section through a
further embodiment of an artificial finger joint with a cap which
is formed on at the joint shell;
[0026] FIG. 11 schematically, a view of the joint head of FIG.
10;
[0027] FIG. 12 schematically, a bearing surface which is
manufactured as a plastic part and which can be pushed on at the
joint shell of FIG. 10;
[0028] FIG. 13 schematically, the joint shell of FIG. 10 with
reduced dimensions for the reception of the plastic part in FIG.
12; and
[0029] FIG. 14 schematically, a side view of the joint shell of
FIG. 10.
[0030] The figures of the exemplary embodiment show an artificial
finger joint comprising a convex joint head 1 and a concave joint
shell 2 which can be fastened independently of one another with a
respective shaft 3, 4 at a bone end 5, 6 and can be moved in an
articulation plane from an extension position 7 with parallel shaft
axes 8, 9 into a hyperextension position 10 or into an articulation
end position 11. A guide pin 12 projects from the joint shell 2 in
the direction of the shaft axis of the latter and protrudes into a
pocket 13 of the joint head 1, with the pocket 13 having a first
abutment 16 for the guide pin 12 in the hyperextension position 10.
A second abutment 17 between the joint shell 2 and the joint head
prevents in the hyperextension position 10 a tilting of the guide
pin 12 and the shaft 4 of the joint shell 2 about the first
abutment 16.
[0031] In the following, identical reference symbols are used for
identical functions.
[0032] In the exemplary embodiment of FIGS. 1, 2 and 3 the joint
head 1 is anchored with a shaft 3 in a bone end 5. The anchoring is
assisted through ribs 24 at the shaft 3. The joint head 1 is
provided with a spherical bearing surface 26, the center 19 of
which forms a point of rotation on the shaft axis 8. The side
surfaces of the joint head 1 have a flattening 27. A pocket 13 with
lateral guide cheeks 14, 15 is worked in into the joint head 1. In
the hyperextension position 10 of the joint shell 2 the pocket 13
forms a first abutment 16 for the guide pin 12, which projects from
the joint shell 2 in the direction of its shaft axis 9, and in the
articulation end position 11 a third abutment 21 for the guide pin
12. The pocket 13 is undercut and has an extension 20. Within this
extension 20 the guide pin 12, which is prolonged beyond the point
of rotation 19, can co-rotate and encounters in the hyperextension
position 10 a second abutment 17, which is rotated by 180.degree.
with respect to the first abutment 16 and prevents a tilting of the
guide pin 12 and its associated shaft 4 about the first abutment
16. The situation is similar in the articulation end position, in
which a fourth abutment 22 prevents a tilting about the third
abutment 21. The joint shell 2 rotates with its concave bearing
shell about the center 19. It is likewise anchored with a shaft 4
and with ribs 24 in a bone end 6. The joint shell can be moved out
of an extension position, in which both shaft axes align with one
another in their projection (FIG. 1) by a partial angle
.alpha..sub.1 into a hyperextension position 10 or by a partial
angle .alpha..sub.2 into an articulation end position 11, with the
movement in each case being limited by two cooperating abutments
16, 17; 21, 22. The pivotal angle .alpha. of the joint corresponds
to the sum of .alpha..sub.1 and .alpha..sub.2 and amounts to for
example 110.degree..
[0033] In FIG. 3 the cross-section 25 of a rectangular guide pin 12
is drawn in which has a total clearance 28 from the guide cheeks
14, 15 of the pocket 13 which corresponds to 40% of the shaft
thickness. Nevertheless the rectangular cross-section prevents with
a diagonal, which is longer than the spacing of the guide cheeks
14, 15, an extreme rotation of the guide pin 12 and of its
associated shaft 4 about the shaft axis 9.
[0034] The manufacture of the extension 20 of the pocket 13 can be
carried out in different ways. In a guide pin 12 with round
cross-section the extension 20 can be pre-bored and then machined
to a finish with a finger milling machine. Another possibility
consists in securing one guide cheek 14 to the joint head 1 only
after the production of the extension 20. A further possibility is
shown in FIGS. 4, 5 and 6.
[0035] In FIGS. 4, 5 and 6 the joint head 1 is conceived as an
injection molded part. The shaft 3, the ribs 24 and the joint head
1 are provided in a single piece. The pocket 13 and its extension
20 are dimensioned without undercutting for a mold removal in the
direction of the shaft axis 8. The first abutment 16 and the third
abutment 21 are formed by boundaries of the pocket 13. The second
abutment 17 for the hyperextension position 10 is formed by a
subsequently introduced bolt 23. Likewise the fourth abutment 22
for the articulation end position 11 is formed by a subsequently
introduced bolt 23. With two bolts 23 all abutments 16, 21, 17, 22
could in principle be realized with the bolts; but then however the
lever arm for a torque which is to be taken up becomes shorter. The
joint shell 2 with the guide pin 12 can be formed the same as in
FIG. 1.
[0036] In FIGS. 7, 8 and 9 an injection molded part without bolts
is proposed for the joint head 1, with a fourth abutment being
omitted. A slit-shaped extension 20 of the pocket 13 forms an
undercutting in the direction of the extension 7 with a second
abutment 17 for the hyperextension position 10, with a mold removal
being possible in the direction of the hyperextension. The guide
pin 12, which projects beyond the point of rotation 19, has been
reduced in width at its tip in order to be able to engage into the
slit-shaped extension 20 and to encounter the second abutment 17 in
the hyperextension position, whereas the first abutment 16 is
formed by the shoulders for the wider part of the guide pin 12
which remain adjacently to the slit. In the normally more weakly
stressed articulation end position 11 there is a third abutment 21,
which does not completely exclude a tilting about this abutment.
The securing elements, the shafts 3, 4 and the ribs 24 as well as
the outer dimensions are formed as in FIG. 1.
[0037] A further embodiment for an artificial finger joint is shown
in FIGS. 10 to 14. A joint head 1 with a shaft 3 having a shaft
axis 8 and with ribs 24 is provided. It forms a spherical bearing
surface 26 with a point of rotation 19. The side surfaces are
provided with flattenings 27. A pocket 13, which reaches from the
hyperextension position 10 up to the articulation end position 11,
forms lateral guide cheeks 15 and a first abutment 16 and a third
abutment 21 for a guide pin 12, which protrudes out of the joint
shell 2 into the pocket 13. FIG. 12 shows a plastic injection
molded part which can be pushed on onto a joint shell 2 in FIG. 13
as a plastic bearing surface 29. The thus pushed together joint
shell 2 (FIG. 14) can be anchored with a shaft 4 and ribs 24. The
guide pin 12 projects in the direction of the shaft axis 9 of the
joint shell 2. A cap 18 is formed on at the actual bearing shell in
the direction of the hyperextension. In the hyperextension position
10 (FIG. 10) of the bearing shell 2 and the joint head 1 this cap
18 projects by an amount S beyond the point of rotation 19 in its
projection onto the shaft axis 8 of the joint head and encounters
at the outer contour of the joint head a second abutment 17, which
prevents a tilting about the first abutment 16. The joint shell 2
can be pivoted out of an extension position 7, in which the
projected shaft ends 8, 9 coincide, by a partial angle
.alpha..sub.1 into the hyperextension position 10 or by a partial
angle .alpha..sub.2 into the articulation end position 11. The sum
of the two partial angles lies between 100.degree. and 110.degree..
The cap 18 is cut off laterally in analogy with the flattenings 27.
This has the advantage that the lateral ligaments can form a
rotational securing about the shaft axis 9.
* * * * *