Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a joint prosthesis and,
more particularly, to anchoring means for anchoring a
joint prosthesis, and a method of fitting an anchoring
means, in a bone.
It is a well known medical technique to replace
worn out, damaged or diseased joints in human and animal
bodies with artificial joint prostheses. Such
prostheses may, for example, comprise a replacement
joint articulation, such as a metal ball and socket or
other pivotable means. Alternatively, the joint
prosthesis may replace only part of the joint. For
example, the ball of a ball and socket joint may be
replaced with a joint prosthesis comprising an
artificial replacement ball designed to sit in the
original socket of a natural joint. Specifically, it is
intended for the purposes of this application that the
term 'prosthesis' or 'joint prosthesis' is not limited
to a component which takes the form of a natural joint,
but is intended to include any component for replacing
part or all of the function of a natural joint.
Regardless of whether a joint prosthesis replaces
all or part of a joint, the joint prosthesis, or parts
of the joint prosthesis, needs to be anchored in or
located on bone adjacent or near to the joint. Joint
prostheses therefore generally further comprise means
for anchoring the replacement articulation, joint
surface or joint part in a bone. For example, a joint
prosthesis for replacing a ball and socket joint, such
as the human shoulder or hip, often has a replacement
articulation comprising a ball and socket. The
replacement ball may be located on, or formed integrally
with, anchoring means comprising a pin arranged to be
inserted in the medullary canal of a bone, such as the
femur or humerus, after the natural ball has been
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removed. Similarly, a replacement socket may be carried
in, or formed integrally with, anchoring means
comprising a cup which is arranged or shaped to be
cemented into the.bone surrounding the socket, such as
5 the acetabulum (hip bone) or scapula (shoulder blade).
Alternatively, the replacement socket may be carried on
anchoring means comprising a pin which is inserted into
an artificial bore in the acetabulum (hip bone) or
scapula (shoulder blade).
10 Many problems arise concerning such fixation of
joint prostheses in or to bones. For example, micro-
movement of the anchoring means in the~bone prevents
bone from re-growing around the anchoring means and
securing the anchoring means in place. This micro
15 movement may even cause the joint prosthesis to work
loose. Also, redistribution of load bearing in the
bone, particularly near joints that carry heavy loads,
such as the human hip or knee, causes localised
deterioration or resorption of bone around the anchoring
20 means and can lead to loosening of the joint prosthesis.
In other words, movement of the anchoring means once it
is in place, or in vivo erosion or destruction of bone
around the anchoring means, results in the joint
prosthesis working loose or never achieving stability.
25 It is these problems that often result in large numbers
of patients having their implanted joint prostheses
replaced or operated on after they are first fitted.
The Applicant has identified that the above
mentioned problems arise, at least in part, due to
30 anchoring means being located in Spongiform bone, which
is found inside, or in the central core, of human and
animal bones. In particular, anchoring means that
comprise pins are often inserted deep in a bone, for
example in the medullary canal of bones such as the
35 human femur or humerus. Spongiform bone is softer and
less resilient than Cortical bone which is found in the
outer layer or surface of human or animal bone. Thus,
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bone erosion, resorption or destruction around a joint
prosthesis is more likely when a joint prostheses is
fitted or anchored by anchoring means located in
Spongiform bone.
5 ' Another problem is that conventional procedures for
fitting joint prosthesis are generally very invasive.
Joints are buried deep in the human or animal body, so
to replace natural joints with joint prostheses and to
insert anchoring means into bone around a joint requires
10 a large amount of tissue, including muscle, ligaments
and cartilage which support the joint to be cut or
destroyed. This leads to a long recovery time for
joint replacement operations and a large failure rate.
More recently, however, less or "minimally" invasive
15 surgical techniques have been developed for joint
replacements. Such a technique is disclosed in the
Applicant's International Patent Application No.
W098/34567, where it is disclosed to carry out a joint
replacement by inserting the replacement parts through a
20 bore in a bone. Such a bore is made through an incision
distal from the joint being replaced and this reduces
trauma to the tissue surrounding the joint.
According to a first aspect of the present
invention there therefore provided a hip prosthesis
25 comprising a first fastening assembly intended for being
mounted in the hip bone and an anchoring means for being
mounted in the top end of the femur, wherein the first
fastening assembly and the anchoring means are
interconnected by means of a pivotable connection,
30 wherein all parts of the hip prosthesis are so small
and/or slender that they can each be arranged in the
intended end position thereof via a bore in the femur,
said bore extending from an inlet opening in the
cortical bone on the lateral outer side of the femur
35 through the femoral neck substantially in the direction
of the imaginary longitudinal centre line of the femoral
neck to the femoral head, wherein the anchoring means
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comprises, adjacent a lateral end thereof, locking means
movable from a first position into a locked position,
wherein said locking means can pass the inlet opening of
the femoral bore in the first position, wherein said
5 locking means cannot pass the inlet opening of the
femoral bore in the locked position, wherein in a
mounted condition of the anchoring means the locking
means is in the locked position and engage a side,
facing a femoral inner space, of the lateral cortical
bone wall of the femur bounding the inlet opening.
Thus, the anchoring means, and indeed the whole hip
prosthesis, may be fitted using a minimally invasive
technique, in which all access to the joint is gained
through the bore in the bone. This vastly reduces
15 trauma to area of the joint, and therefore shortens
recovery time and reduces failure rate. Furthermore,
the anchoring means is smaller than those of the
conventional type as it extends across rather than along
the bone. Thus, less bone is destroyed with the result
20 that the procedure is less traumatic and may be
recovered from more quickly.
An anchoring means or joint prosthesis that is
supported by the inside surface of cortical bone wall
is, however, more widely applicable. The bore may, for
25 example, extend in a different direction through a bone
and the anchoring may be used to support various other
joint prostheses for replacing joints in the human and
animal body, such as the human shoulder joint for
example.
30 According to a second aspect of the present
invention there is therefore provided a joint prosthesis
having an anchoring means arranged to be placed in a
bore in a bone via an inlet opening of the bore distal
to the intended position of the prosthesis, the
35 anchoring means having locking means movable from a
first position, in which it may be inserted through the
inlet opening, into a locked position when mounted in
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the bore, the locking means in the locked position
preventing the anchoring means from passing back out
through the inlet opening and supporting the anchoring
means by resting against the inside surface of the
cortical bone wall adjacent the inlet opening.
Also, according to a third aspect of the present
invention there is provided a method of anchoring a
joint prosthesis in a bore in a bone, comprising
inserting the anchoring means through an inlet opening
10 of the bore distal to the intended position of the
prosthesis, and moving a locking means into a locked
position when the anchoring means is mounted in the
bore, which position prevents the anchoring means from
passing back out through the inlet opening and supports
15 the anchoring means by resting against the inside
surface of the cortical bone wall adjacent the inlet
opening.
A minimally invasive surgical technique may
therefore still be used as the anchoring means is
20 inserted from a position distal from the joint.
However, the invention may be applied to a variety of
different joint replacements and the whole joint may not
even be replaced. For example, the anchoring means may
support a replacement ball for a humerus, the ball being
25 adapted to fit with the socket of the scapula (shoulder
blade).
The locking means of the above aspects of the
invention rests against and is supported by an inside
surface of the cortical bone wall. As cortical bone is
30 stronger, more rigid and more resilient than Spongiform
bone, the anchoring means is supported with more
stability and there is less chance of micro-movement
causing erosion of bone around the anchoring means in
position. Furthermore, as cortical bone generally
35 carries the largest load in a bone, there is a more
natural load distribution in the bone, which decreases
the chance of resorption of bone due to load
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redistribution.
Considering the application of this type of
anchoring or fixation in bones more widely, it will also
be appreciated that an anchoring means that rests
5 against the inside surface of the cortical bone wall can
be used to fix not only joint prostheses in position but
other components for fitting in or to bones, such as
plates that are fitted to the outside of broken or
fractured bones for support. In other words, an
10 anchoring means of this type can be used in place of
conventional screws and the like which are used to
attach artificial components to bones.
According to a fourth aspect of the present
invention there is therefore provided an anchoring means
15 arranged to be mounted in a bore in a bone through an
inlet opening, the anchoring means having locking means
movable from a first position, in which it may be
inserted through the inlet opening, into a locked
position when mounted in the bore, the locked position
20 preventing the anchoring means from passing back out
through the inlet opening by resting against the inside
surface of the cortical bone wall adjacent the inlet
opening.
The anchoring means can therefore be used to secure
25 prostheses or components to the surface of bones, for
example adjacent to the inlet opening, such that the
prosthesis or component cannot be pulled away from the
bone. Advantageously, the locking means may distribute
the load exerted on the cortical bone wall by the _
30 anchoring means over a wider area than a conventional
screw type fitting and this increases strength and
durability.
The form of the locking means may vary. For
example, the locking means may comprise one or more
35 deformable bridges which are displaced outwardly in the
locked position to rest against the inside surface of
the cortical bone. Thus, the locking means can be
CA 02340158 2001-02-09
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inserted through the inlet opening and the bridges
subsequently displaced to a locking condition. This
provides a convenient locking means for resting against
the cortical bone wall.
5 The bridges may extend between two sleeves formed
around the anchoring means, and the locked position may
be achieved by moving the sleeves toward one another,
such that the bridges flex or extend outwardly. This
provides a simple way to extend and retract the bridges.
10 The outward flexation may be made more reliable by
providing a weak point or hinge along the length of the
bridges. This ensures the bridges have the desired
shape in use as the bridges will always bend at their
weak point.
15 Preferably two or more bridges are provided, at
least one bridge longer than the other. More
specifically, the longer bridges may have weak points or
hinges provided at a position that causes them to extend
in use, further toward the cortical bone wall than the
20 shorter bridges. Thus where the anchoring means in use
is not perpendicular to the cortical bone wall, the
longer and shorter bridges may still be arranged to
contact the cortical bone wall evenly. This provides
more stable support as the force exerted on the cortical
25 bone wall may be evenly spread.
Long and short bridges may also be used to
accommodate the particular shape of the cortical bone
wall of a femur or other bone in which the anchoring
means is to be fitted. In particular, where the
30 anchoring means does not extend perpendicularly from the
cortical bone wall, the longer bridges) may be provided
on a side of the anchoring means that extends obtusely
from the cortical bone wall, and the shorter bridges)
may be provided on a side of the bridge that extends
35 acutely from the cortical bone wall.
Alternatively, the locking means may comprise a peg
that is rotatably connected to the anchoring means such
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that it can be rotated out of a first position
substantially within the radial dimensions of the
anchoring means to a locked position extending beyond
the radial dimensions of the anchoring means.
5 Another alternative is for the locking means to
comprise a peg that can be moved from a first position
outside the anchoring means to a locked position in
which it extends between and through two radially
opposing holes in a cylindrical wall of a tubular
10 anchoring means. In this embodiment it is preferable
that the peg is entirely separate from the anchoring
means in the first position.
The locking means may not, however, be movable in
the bore, but some other provision may be made for
15 engaging the cortical bone wall.
Thus, according to a further aspect of the present
invention there is provided a joint prosthesis having an
anchoring means arranged to be mounted in a bore
extending through a bone via an inlet opening on the
20 side of the bone distal from the intended position of
the prosthesis, the anchoring means being provided with
locking means effective when mounted in the bore, to
prevent the anchoring means from passing back out
through the inlet opening by resting against the inside
25 surface of the cortical bone adjacent the inlet opening.
The locking means may comprise a bulb of cement
which is located e.g. in a recess on an outer wall of
the anchoring means and which, when set, cooperates
between the cortical bone wall and the anchoring means.
30 This has the advantage that the cement may take the
exact form of the cavity and therefore can abut the
cortical bone wall in a very stable manner.
Considering the advantages of the anchoring means
more generally, it will be understood that an anchoring
35 means that rests against the inside surface of the
cortical bone wall opposite a joint that is being
replaced may be inserted using conventional surgical
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_ g _
techniques. In this case, a movable or separate locking
means may not be required but the anchoring means may
simply have a shape suitable for resting against the
cortical bone wall, either side of the anchoring means.
5 Thus, according to a further aspect of the present
invention there is provided a joint prosthesis having an
anchoring means arranged to be placed in an extra
medullary bore in a bone, the anchoring means arranged
to rest against and be supported by an inside surface of
10 the cortical bone wall remote from the intended position
of the prosthesis.
Also, according to a further aspect of the present
invention there is provided a method of anchoring a
joint prostheses in a bone comprising placing an
15 anchoring means in an extra medullary bore in a bone
such that it rests against and is supported by an inside
surface of the cortical bone wall remote from the
intended position of the prosthesis.
By extra medullary, it is intended that the bore
20 may extend in any direction in a bone other than along
the medullary canal. For example, the bore may extend
across the bone or, more specifically along the
imaginary centre line of a femoral neck for example.
Unlike prior art arrangements, therefore, the
25 anchoring means is firmly supporting the inside surface
of the cortical bone wall.
In this aspect of the invention the cortical bone
wall may be unapertured and hence intact, with the
anchoring means being inserted from the opening of the
30 bore facing the joint, as in conventional prosthesis.
The anchoring means may having at least two
generally opposed elements extending radially therefrom,
each of which elements is arranged to rest against and
be supported by the inside surface of to cortical bone
35 wall. Thus, the anchoring means is supported in at
least two locations, either side of a central axis of
the bore. These elements may be spaced apart around the
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axis of the bore, or may be part of a continuous element
extending around the anchoring means and engaging the
bone wall in at least two locations to provide firm
support.
5 As mentioned above, it is desirable to distribute
load bearing of loads exerted by a joint through an
anchoring means in a way that mirrors the way in which
load is born by the bone when a natural joint is still
in place. In the human hip joint, for example, a large
10 load is born by the bone wall adjacent the femoral neck.
Preferably, the anchoring means therefore further
comprises a radially extending lip for resting against a
resected bone surface proximal to the joint. The bone
surface may be the resection plane of the bone, for
15 example at a femoral neck of a femur. Thus the load
distribution of the load exerted, in use, through the
anchoring means is close to the natural load
distribution in the bone. This decreases the chance of
bone resorption and subsequent loosening of the
20 anchoring pin in the bone.
Preferred embodiments of the present invention are
now described, by way of example only, with reference to
the accompanying drawings, in which:
Fig. 1 is a front view of a sleeve forming part of
25 an anchoring means according to the invention;
Fig. 2 is a sectional view taken on the line II-II
of Fig . 1;
Fig. 3 is a rear view of the sleeve shown in Fig.
1;
30 Fig. 4 is a sectional view of the sleeve taken on
the line IV-IV of Fig. 3;
Fig. 5 is a sectional view of a coupling sleeve
forming part of the anchoring means taken on the line V-
V of Fig. 6;
35 Fig. 6 is a view of the lateral end face of the
coupling sleeve shown in Fig. 5;
Fig. 7 shows a longitudinal section of the
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anchoring means, with a locking means being in a second
position;
Fig. 8 shows the sleeve in a femur in a first
position;
5 Fig. 9 shows the sleeve with an associated clamping
tool, the locking means being in a position between the
first and the second position;
Fig. 10 shows the anchoring means mounted in the
femur;
l0 Fig. 11 is a sectional view of a femur containing a
second exemplary embodiment of an anchoring means
according to the invention;
Fig. 12 is a sectional view of a femur containing a
third exemplary embodiment of an anchoring means
15 according to the invention in an unlocked condition; and
Joint prostheses may be used to replace virtually
all joints in the human and animal body. Likewise, this
invention may be used in the replacement of any joint in
the human and animal body. However, it is particularly
20 applicable to the replacement of hip and shoulder joints
and, for convenience, preferred embodiments will be
described with reference to the replacement of the human
hip joint. The preferred embodiments relate in
particular to a hip prosthesis in accordance with that
25 described in International Patent Application No.
W098/34567.
As is described in detail in W098/34567, the parts
of such a hip prosthesis are designed such that they can
all be placed into their end positions through a bore in
30 the femur Fo, which bore extends from the lateral outer
side Fo of the femur F through the femoral neck Fn
substantially in the direction of the imaginary
longitudinal centre line of the femoral neck to the
femoral head (see Figure 8). During the positioning of
35 the hip prosthesis, a relatively small incision is made
in the leg, providing access to the lateral outer side
of the femur F. Next, a bore is made in the femur F for
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example as described in W098/34567. Via this bore, the
femoral head is removed with a special tool, for example
also as described in the above-cited International
patent application. Next, a first fastening assembly
5 can be mounted in the hip bone via the bore in the femur
F. After the positioning of the first fastening
assembly and any other components of the joint
prosthesis, an anchoring means in accordance with the
present invention, can be mounted.
10 Referring to Figures 1 to 11, the anchoring means
1, 51 comprises, adjacent a lateral end thereof, locking
means 2, 2', 3, 3', 52, movable from a first position
into a second position. In the first position, these
locking means 2, 2', 3, 3', 52 can pass the inlet
15 opening Fi of the femoral bore. In the second position,
these locking means 2, 2', 3, 3', 52 cannot pass the
inlet opening Fi of the femoral bore. In a mounted
position of the anchoring means 1, 51, the locking means
2, 2', 3, 3', 52 are in the second position and engage a
20 side C, facing a femoral inner space I, of the lateral
cortical bone wall C of the femur F bounding the inlet
opening Fi. The axially directed forces exerted on the
anchoring means 1,51, for instance when the carrier of
the hip prosthesis is walking or standing, are
25 transmitted, by means of the locking means, to the firm
lateral cortical bone wall C of the femur F, which bone
wall C bounds the inlet opening. The locking means 2,
2', 3, 3', 52 press against the inside C of the cortical
bone wall and can be of such design that a relatively _
30 large pressure area is created.
Such locking of the anchoring means 1, 51 is much
stronger than anchoring means of the prior art which
were, for example, screwed down with an end plate on the
lateral outer side of the cortical bone wall of the
35 femur at the location of the inlet opening. In that
case, all axial forces exerted on the anchoring means
were taken up by means of the screws screwed into the
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cortical bone wall.
Such screwed connection is not stable for a long
period, in particular in the case of changing loads.
Indeed, the contact area between the bone screws and the
5 cortical bone wall is considerably smaller than the
contact area that can be created by means of locking
means 2, 2', 3, 3', 52 engaging a side C of the lateral
cortical bone wall of the femur F, which side C faces
the femoral inner space I.
10 The anchoring means 1 of the first exemplary
embodiment is shown in assembled condition in Figs. 7
and 10. The anchoring means 1 comprises a sleeve 4 and a
coupling sleeve 8. The anchoring means 1 further
comprises a pin 15 whose medial end comprises at least a
15 number of pivot parts for forming a pivotable connection
between the first fastening assembly and the anchoring
means 1. In Figs. 1-10, these pivot parts are not
shown. However, the pivot parts may for instance be
formed by a ball of a ball joint, as shown in Fig. 11.
20 Other possible pivotal connections are described in the
above-cited International Patent Application W098/34567.
The pin 15 is mounted in the sleeve 4 within a
cylindrical lining 24. Adjacent a lateral end, the
sleeve 4 comprises a deformation zone 2, 2', 3, 3' or
25 plurality of bridges constituting the locking means. For
clarity's sake, some elevations of the sleeve 4 are
shown in Figs. 1-4. In these elevations, the locking
means 2, 2', 3, 3' are in the first, not yet deformed
position. The first position of the locking means
30 corresponds to a not yet deformed condition of the
deformation zone 2, 2', 3, 3'. The position of the
locking means corresponds to a deformed condition of the
deformation zone 2, 2', 3, 3'.
In the not yet deformed condition of the
35 deformation zone 2, 2', 3, 3', the transverse dimensions
of the sleeve 4 at the location of the deformation zone
2, 2', 3, 3' substantially correspond to the sleeve
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diameter Do on the other parts of the sleeve 4. In the
deformed condition of the deformation zone 2, 2', 3, 3'
(Figs. 7 and 10), the deformation zone has obtained
transverse dimensions D1 which are enlarged in at least
5 one direction relative to the other parts of the sleeve.
As is clearly demonstrated in the Figures, the
sleeve 4 comprises a medial sleeve part 5 and a lateral
sleeve part 6. The deformation zone 2, 2', 3, 3'
interconnects the medial and lateral sleeve parts 5, 6.
10 In the present exemplary embodiment, the deformation
zone comprises some ribs 2, 2', 3, 3', each having three
local weakenings 7. The weakenings 7 are provided such
that when a pressure force is exerted on the end faces
of the medial sleeve part 5 on the one hand and the
15 lateral sleeve part 6 on the other, the ribs 2, 2', 3,
3' fold together outwards, as shown in Fig. 7. Viewed
over the circumference of the sleeve, the deformation
zone 2, 2', 3, 3' is asymmetrical, such that the parts
of the deformation zone 2, 2', 3, 3' which, in deformed
20 condition, extend radially outwards, substantially abut
against the cortical bone wall C bounding the inlet
opening Fi. This abutment must be realized in a
condition in which the sleeve 4 has the desired angular
position relative to the femur F, i.e. a condition in
25 which the centre line of the sleeve substantially
coincides with the centre line of the femoral bore in
the femur F.
To provide that the deformation zone 2, 2', 3, 3'
retains its shape, in particular when the anchoring
30 means 1 is subjected to a load, the anchoring means 1
also comprises a coupling sleeve 8 having medial
engagement means 9 intended for cooperation with the
medial sleeve part 5. The coupling sleeve 8 further
comprises lateral engagement means l0a intended for
35 cooperation with the lateral sleeve part 6. In the
present exemplary embodiment, the medial engagement
means 9 are designed as external screw thread mating
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- 15 -
with internal screw thread 11 provided in the medial
sleeve part 5. At its lateral end, the coupling sleeve 8
comprises means 12 for engaging a tightening tool
therewith. In the_present exemplary embodiment, these
5 means are formed by a hexagonal socket which can be
engaged by a socket wrench.
In the present exemplary embodiment, the lateral
engagement means 10 are designed as a locking bore l0a
directed perpendicularly to the longitudinal axis of the
10 coupling sleeve 8, and two locking pins (not shown)
insertable into this locking bore. The lateral sleeve
part 6 is provided with a transverse bore 13 which, in a
deformed condition of the deformation zone 2, 2', 3, 3',
registers with the locking bore l0a of the coupling
15 sleeve 8. The two locking pins extend through both the
locking bore l0a and the transverse bore 13. Hence, the
locking pins provide the connection of the lateral
sleeve part 6 to the lateral end of the coupling sleeve
8.
20 As is already described herein above, the
anchoring means 1 is provided with a pin 15 connected to
pivot parts of the pivotable connection between the
first fastening means and the anchoring means 1, and
with a lining 24. The pin 15 with the lining 24 are
25 accommodated in a bore 14 in the coupling sleeve 8,
which bore 14 extends from the medial end 8M in
longitudinal direction of the coupling sleeve 8.
Provided in the coupling sleeve 8 is a set screw bore
(not shown) accommodating a set screw (not shown) which
30 abuts against a free end of the pin 15 remote from the
pivotable connection. By means of the set screw, the
axial position of the pin 15 relative to the coupling
sleeve 8 and, accordingly, relative to the sleeve 4 and
the cortical bone wall C can be set.
35 For positioning the anchoring means 1, the sleeve 4
is inserted into the femoral bore until the stops 26 of
the sleeve 4 abut against the outwardly facing side of
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the lateral cortical bone wall. The medial end of the
sleeve 4 extends into or beyond the opening at the
femoral neck Fn created due to the fact that the femoral
head has been removed from the femur F. This situation
5 is shown in Fig. 8. Next, the deformation zone 2, 2', 3,
3' is brought into the deformed condition by means of a
clamping tool 17. To that end, the clamping tool 17
comprises a cylindrical clamping pin or bush 22. The
clamping pin 22 has its medial end provided with
10 engagement means 18 arranged for engagement with the
medial sleeve part 5. In the present exemplary
embodiment, the engagement means 18 are designed as
external screw thread 18 suitable for mating with the
internal screw thread 11 in the medial sleeve part 5 of
15 the sleeve 4. The clamping pin 22 has a lateral end
thereof provided with external screw thread 21 suitable
for mating with internal screw thread 20 of a pressure
element 19. The pressure element 19 comprises lever
means 23 for exerting a considerable tightening moment.
20 For deforming the deformation zone 2, 2', 3, 3', the
clamping pin 22 is screwed into the medial sleeve part 5
by means of the engagement means 18. Next, the pressure
element 19 is screwed onto the lateral end of the
clamping pin 22 by means of the screw thread 20 until
25 the pressure element 19 abuts against the lateral end
face of the lateral sleeve part 6. By screwing the
pressure element 19 further onto the clamping pin 22
with increased force, the ribs 2, 2', 3, 3' of the
deformation zone will be compressed in the manner shown,
30 due to the fact that the clamping tool draws the medial
sleeve part 5 towards the lateral sleeve part 6. The
degree of deformation can for instance be observed by
means of X-ray images. It is also possible that the
clamping tool is provided with markings or like means,
35 by means of which the degree of deformation can be
determined. When the desired deformation of the
deformation zone 2, 2', 3, 3' has been effected, the
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- 17 -
locking means have assumed the position and the
clamping tool can be unscrewed. Fig. 9 shows the sleeve
4 in a partially deformed condition which occurs during
the deformation of the deformation zone by means of the
5 clamping tool 17.
After the deformation as shown in Fig. 7 has been
accomplished, the clamping tool 17 can be removed. To
ensure that the sleeve 4 retains its deformed condition,
the coupling sleeve 8 is subsequently secured in the
10 screw thread 11 of the medial sleeve part 5 by means of
the screw thread 9. The coupling sleeve 8 is rotated
into the medial sleeve part 5 so far that the locking
bore 10 in the sleeve 8 registers with the transverse
bore 13 in the medial sleeve part 6. Next, the two
15 locking pins can be arranged, to establish a connection
between the lateral sleeve part 6 and the coupling
sleeve 8. This connection does not merely prevent an
axial displacement of the lateral sleeve part 6 relative
to the coupling sleeve 8, but also a rotation of the
20 coupling sleeve 8 relative to the medial sleeve part 5.
It is readily understood that before the coupling sleeve
8 is positioned, the pin 15 and the lining 24 must first
be provided in the sleeve 4. Then, by means of the set
screw, the axial position of the pin 15 relative to the
25 coupling sleeve 8 and the sleeve 4 can be set. The
further fixation of the anchoring means 1 will be
created through the growth of bone material around the
sleeve 4. If necessary, the sleeve 4 may for this
purpose be provided with a coating or the sleeve 4 may-
30 be manufactured from porous material enabling bone
ingrowth. Fig. 10 shows the fastening assembly 1 in a
condition in which it is completely mounted in the
femur F.
A further exemplary embodiment of the invention is
35 shown in Fig. 11. In this exemplary embodiment, an
anchoring means 51 comprises a pin 53 which is
receivable in the femoral bore.. A locking means
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comprises an anchor 52 pivotally connected to a lateral
end 53L of the pin 53. In longitudinal direction, the
anchor 52 has a dimension L greater than the diameter Dp
of the pin 53. When the anchor is in the first position,
5 the anchor has its longitudinal axis extending parallel
to the longitudinal axis of the pin 53. In a position,
the anchor 52 is swivelled relative to the pin 53 such
that the free ends of the anchor 52 extend beyond the
circumferential contour of the pin 53. In Fig. 11, the
10 first position of the anchor 52 is shown in dotted
lines. The position of the anchor 52 is shown in full
lines. To enable the swivel movement of the anchor 52,
the anchor is pivotable about a pivotal axis 54
extending perpendicularly to the pin 53, and provided in
15 the pin 53 is a slot 55 in which the anchor 52 in the
first position is at least partially accommodated. When
the anchoring means 51 is being positioned, the anchor
52 is brought into the dotted position and the pin 53 is
temporarily inserted slightly too far into the femoral
20 bore. Next, the anchor 52 can be swivelled into the
position indicated in full lines, after which the pin 53
can be withdrawn slightly in lateral direction, causing
the anchor 52 to abut against the side C of the cortical
bone wall which side faces the femoral inner space I.
25 Referring to Figure 12, a third exemplary
embodiment of the present invention has an anchoring
means 100 comprising a hollow body 101, such as a
cylindrical metal tube, in which an elongate cylindrical
supporting pin 102 carrying a joint articulation (not
30 shown) is housed. The cylindrical body of the
supporting pin 102 can be fitted in the hollow body 101,
for example, by a frictional fit or by a screw thread,
or the two components may be formed integrally.
The supporting pin 102 only extends part way along
35 the hollow body such that an empty space 103 is provided
at the end of the hollow body distal from the joint
articulation. The hollow body 101 has two radially
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opposing holes 104,105 in its circumferential wall, also
at the end of the body distal from the joint
articulation such that the holes 104,105 are adjacent
the empty space 103.
5 A locking pin 106 is provided which can be inserted
through the distal end of the hollow body 101, into the
empty space 103 and into a position in which it extends
between the holes 104,105 and protrudes through each of
the holes 104,105 beyond the outer surface of the hollow
10 body 101. The locking pin 106 must therefore be narrow
and short enough to fit in the hollow space 103 and be
manipulated into a position extending through the holes
104,105, yet be long enough to extend through each of
the holes and outside of the hollow body when in place.
15 The anchoring means 100 is inserted into a bore in
a bone, such as the femur F, such that the holes 104,105
are located adjacent to the inside surface of the
cortical bone wall distal from the joint articulation.
The pin is then inserted into the hollow body and into a
20 locked position in which it extends through both of the
holes 104,105. The pin therefore rests against the
inside surface of the cortical bone wall distal from the
joint articulation and the anchoring pin is supported in
the direction of its main axis away from the joint
25 articulation by the holes abutting the locking pin 106.
Still referring to Figure 12, in this embodiment
the anchoring means 100 has a proximal support section
107 which comprises a lip 108 which is arranged to abut
the surface of the cortical bone wall, in this case
30 proximal to the femoral neck below the joint
articulation. This enables the anchoring means 100 to
be supported at its proximal end by resting on a surface
of the femur or femoral neck left after the femoral head
has been resected, which may be referred to as the
35 'resection plane'. This may comprise substantially
cortical bone or part cortical bone, part spongiform
bone dependant on the positioning of the bore. In the
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femur in particular, this is an area of high natural
loading and supporting the anchoring means 100 in this
way reduces unnatural redistribution of the load in the
bone which in turn reduces resorption.
5 In all of the above exemplary embodiments the
anchoring pin or fastening means is inserted in a bore
in a bone. The locking means is then positioned in the
inner space of the bone, such as the femoral inner space
I, such that it abuts or rests against the inside
10 surface of the cortical bone wall. The procedure for
fitting such an the anchoring means is as follows.
Firstly, an incision is made in the flesh such that
access to the bone may be achieved. A bore is then made
through the bone from an inlet opening in the intended
15 position of the anchoring means. In the case of a hip
joint being replaced in accordance with the method
described in W098/34567, the bore may be from the outer
surface of the femur, the lateral outer side Fo, through
the femoral neck Fn. Regardless of how the bore is
20 made, after the bore has been made, a portion of the
inner space of the bone adjacent the inside surface of
the cortical bone wall distal from the joint
articulation or adjacent the inlet opening is resected
to provide a cavity in which the locking means can be
25 located when locked. In the case of an anchoring pin
for a femur F in accordance with the devices described
in W098/34567, the cavity Ca is generally a space above
and below the Femoral inlet opening Fi.
In a fourth exemplary embodiment of the present
30 invention (not shown in the drawings) the locking means
comprises a bulb of cement filling a cavity next to the
inside surface of the cortical bone wall distal from the
joint articulation. When set the cement therefore rests
against the inside surface of the cortical bone wall
35 distal from the joint articulation and the cortical bone
wall supports the anchoring pin.
It is understood that the invention is not limited
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to the exemplary embodiments described, but that various
modifications are possible within the framework of the
invention.
