Artificial hip joint

Abstract

An artificial hip joint consists of a femoral implant, a socket member and a bearing support for the socket member. The femoral implant is intended for implantation in a prepared cavity in the femur of a patient and has a stem for insertion in the cavity, a femoral neck attached to the stem and a condyl on the femoral neck. The socket member is intended for location in the patient's hip socket which has previously been surgically enlarged and receives the femoral condyle. The bearing support is intended to be embedded in the hip socket in the patient's pelvis and has an exterior flange, which is arranged to bear against the bone surrounding the hip socket, and a recess to accommodate the socket member. The bearing support can be formed separately from or integrally with the socket member.

Description

FIELD OF THE INVENTION

This invention relates to an artificial hip joint.

BACKGROUND OF THE INVENTION

In the treatment of degenerative diseases of the hip joint accompanied by substantial destruction of the joint (coxarthrosis) it has been a common practice since 1946 to replace the femoral condyle by a prosthetic implant of metal comprising a femoral condyle, a femoral neck and a metal stem.

A "total" artificial hip joint was developed in 1961. In this a hemispherical socket of plastics is inserted into the previously enlarged bone socket, which is provided with some grooves to provide better keying of the bone cement, to cooperate with the metallic femoral neck. The plastics socket is secured by means of bone cement. This total artificial hip joint has since been modified.

Some patients suffering from degenerative hip joint deformations exhibit primary or secondary protrusio acetabuli. In this special form of coxarthrosis the bone socket base gradually curves forward into the minor pelvis in the course of years and is also gradually reduced, i.e. at the end of the pathological process the base of the bone socket is replaced exclusively by soft tissue which is unable to perform any load-supporting function. The descent of the femoral condyle into the minor pelvis also reduces the distance between the minor and major rolling surface on the one hand and the pelvic inlet plane on the other hand so that this feature is additionally accompanied by a reduced or limited movability of the hip joint.

The cause of primary protrusio acetabuli, which is usually double-sided, is unknown. In recent times one-sided secondary cases occurred frequently as the result of so-called "socket looseness" after the insertion of an artificial hip joint. Bone resorption occurs after the insertion of an artificial hip joint through causes which are not accurately known but are generally the result of slow infections. These pathological processes again result in forward curving of the residual bone socket into the minor pelvis.

Known artificial hip joints which are used for the operative treatment of protrusio acetabuli and have hemispherical sockets may lead to a central dislocation of the artificial joint into the minor pelvis and result in reduced mobility because the inlet plane of the plastics sockets is located deeply in the natural socket and the resection face of the femoral neck on movement strikes against the natural bony pelvic inlet.

DESCRIPTION OF THE PRIOR ART

It has been proposed to use a fine gauge wire mesh in the operative treatment of protrusio acetabuli.

The main purpose of such a mesh was to prevent the bone cement penetrating into the soft parts of the minor pelvis. Prior to securing the artificial socket and prior to the introduction of bone cement the procedure was to chase three grooves by means of a chisel into the bony pelvis behind the socket inlet. The mesh was intended mainly to prevent the ingress of bone cement via the grooves into the minor pelvis. However, the biomechanics of the hip socket are not likely to be improved by the presence of this mesh.

An improved mesh of this kind constructed of physiologically compatible metal in the form of a grid and in accordance with another proposal also prevents the ingress of bone cement into the minor pelvis and in addition improves anchoring of the socket but without exerting any substantial effect on the biomechanics of the artificial hip joint.

BRIEF DESCRIPTION OF THE INVENTION

I have now discovered, through observations made during operations and by subsequent X-ray investigations as well as by pathological-anatomical investigations, that protrusio acetabuli is accompanied by increased bone stability at the hip socket inlet due to an annular selerotic condition of the pelvis in this region. The invention accordingly makes use of this knowledge and utilizes this stability and mechanical strength of the existing bone tissue of the pelvic bone at the inlet to the hip joint socket and surrounding such inlet in order to support the plastics socket and therefore the entire artificial hip joint.

It is accordingly a principal object of the invention to provide an artificial hip joint which avoids the disadvantages of the above mentioned prior art operation methods and implants.

It is also an object of the invention to provide an artificial hip joint in which the distance between the hip inlet plane and the resection face of the femoral neck is increased.

It is a further object of the invention to provide an artificial hip joint in which the hip socket is mounted in a plane different from that in which the plastics socket was hitherto secured to the pelvis.

A still further object of the invention is to provide a support bearing for the hip socket of an artificial hip joint in which the bearing forces are taken up by the surface of the bony part of the pelvis surrounding the previously enlarged hip socket in the pelvis.

According to the invention an artificial hip joint, comprising the femoral condyle, femoral neck and the stem which is to be inserted into the femur on the one hand and the hemispherical socket which is to be inserted into the hip joint socket on the pelvis on the other hand is characterized by a support bearing for the hemispherical socket in the form of a spherical section with a surrounding flange. The internal diameter of the spherical section is slightly larger, preferably about 1 to about 2 mm larger than the external diameter of the hemispherical socket. The spherical section is preferably approximately or equal to a hemisphere. The flange is broad, preferably having a width of 8 - 12 mm. The spherical section and/or the flange is provided with apertures. The apertures of the spherical section may be constructed so that, when seen in plain view, arrow-shaped claws or fingers extend from the flange in the surface of the spherical section while leaving free a central opening. The spherical section surface between the claws can also be constructed in the form of narrow webs which converge in the centre. The spherical section surface may also exclusively comprise a plurality of narrow webs which converge in the centre. The edges of the narrow webs may be provided with corrugations or hooks.

The surface of the spherical section and/or the claws and/or the narrow webs are preferably provided with beads that extend radially. In one embodiment of the invention the flange is provided with eight claws or fingers whose ends advantageously terminate at a position about 20 to about 25 mm from the flange. In another embodiment the flange is provided with three webs disposed at identical distances in a star pattern, two claws being formed between every two such webs.

An annular web can also be formed between the flange and the centre in the surface of the spherical section to bridge the spaces between the radial webs or the ends of the claws.

The support bearing according to the invention can be constructed of a chemically stable and physiologically compatible strong metal plate, preferably of the same material as that of which the femoral condyle is constructed. The support bearing may however also be constructed from a physiologically compatible plastics material and can be joined to the hip joint socket, which is also constructed of plastics, or it may be integrally constructed with the hip joint socket.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a front view of the hip region of a human skeleton, the right hip joint of which has been replaced by an artificial hip joint according to the invention;

FIG. 2 is a perpsective view of the individual parts of the artificial hip joint of FIG. 1;

FIG. 3 is a perpsective view of the hemispherical socket of the artificial hip joint of FIG. 2 which is inserted into one form of a support bearing according to the invention;

FIG. 4 is a side view, partially in section, of another form of support bearing according to the invention;

FIG. 5 is a plan view of the support bearing of FIG. 4;

FIG. 6 is a side view of yet another form of support bearing according to the invention;

FIG. 7 is a plan view of the support bearing of FIG. 6;

FIG. 8 is a side view of a further form of support bearing according to the invention;

FIG. 9 is a plan view of the support bearing of FIG. 8; and

FIG. 10 is a plan view of part of a still further form of support bearing according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 is a front view of a pelvis of a patient whose right hip joint has been replaced by an artificial hip joint according to the invention (in the drawing the artificial hip joint is disposed on the left hand side). The artificial hip joint comprises a femoral part 1 which is inserted by means of a pin into the femur 4 after removal of the upper part of this bone. A support bearing 3 according to the invention is fixedly mounted in the joint socket of the pelvis 5 and retains a hemispherical socket 2 which forms the seat for the ball head (condyle) of the femoral part 1.

The prosthetic implant or femoral part 1 which is inserted after removal of the top part of the femur 4 comprises a metal stem 6, a femoral neck 7 and a femoral condyle 8. This contiguous part is generally constructed integrally from a physiologically compatible metal. The femoral condyle 8 is shaped in the form of a sphere and is inserted into a hemispherical socket 2 which is generally constructed of a physiologically compatible plastics material and whose external surface is provided with different indentations so that it can be inserted with bone cement into a prepared bone socket in the pelvis 5. As shown in FIGS. 1 and 2 a support bearing 3 is however previously inserted into the bone socket of the pelvis 5 and is secured with bone cement and the hemispherical socket 2 is inserted thereafter into the support bearing 3.

The support bearing 3 according to the invention substantially comprises a spherical section 10 of special shape which is surrounded by a flange 11.

The spherical section 10, generally in the shape of a hemisphere or approximately in the shape of a hemisphere is provided with apertures and one embodiment is constructed as may be seen by reference to FIGS. 2 and 3 so that arrow-shaped claws 13 extend inwardly from the annular flange 11 in the surface of the spherical section. The opening of the spherical section surface is complete above the ends of the claws 13 and the individual aperture members that extend between the claws 13 are broadened directly above the flange 11. The length of the claws 13 from their base on the flange 11 to their end is 20 - 25mm in a preferred embodiment, given an internal diameter of the spherical section of approximately 50 cm and a flange width of 8 - 12 mm.

After preparing the bone socket in the pelvis 5 the support bearing 3 is inserted with bone cement into the socket so that the annular flange 11 bears all round firmly against the bone tissue which surrounds the socket inlet on the pelvis, where appropriate by the interposition of bone cement. At least some parts of the spherical section of the support bearing 3 bear against load bearing bone fabric in the socket of the pelvis through the interposition of bone cement. After the insertion of the aforementioned support bearing the plastics shell i.e. socket 2 of the artificial hip joint is inserted into the support bearing and can be adjusted within the support bearing taking into account the angle of inclination and the so-called antetorsion, i.e. the axis setting in the saggital and frontal plane so that the femoral condyle 8 which is inserted into the smooth uninterrupted internal surface of the hemispherical socket 2 assumes approximately the same pivoting centre as the natural femoral condyle. The hemispherical socket 2 is also secured in the support bearing by means of bone cement in the upright position imparted to it.

As may be seen more particularly by reference to FIG. 1 a support bearing 3 according to the invention prevents the femoral condyle and hemispherical cup-shaped socket from gradually penetrating either immediately or in the course of time into the pelvic bone. Such penetration would result in a displacement of the pivoting point of the hip joint. Furthermore the pressure conditions of artificial hip joints are improved and at the same time the artificial hip joint socket is firmly secured. The support bearing 3 additionally improves the movability of artificial hip joints. The distance between the major and minor rolling surface on the one hand and the pelvic inlet plane on the other hand is also prevented from diminishing; no further reduction or limitation of the hip joint movability therefore occurs. The support bearing according to the invention necessarily increases the distance between the inlet plane of the artificial hip socket and the resection face on the femoral neck.

FIGS. 4 and 5 show a further and particularly advantageous form of support bearing according to the invention. The flange 11 is provided with apertures 14 in the form of drilled or punched holes. The spherical section surface with apertures which surrounds the flange 11 comprises claws 13 of the shape already described in connection with the embodiment of FIGS. 1 to 3 and also includes three webs 15 which extend radially and converge in the centre. Two claws 13 are disposed between every two webs 15. The webs 15 are provided with radially extending beads 16. The purpose of these beads on the one hand is to stiffen the webs 15 and on the other hand to provide additional retention for the hemispherical socket 9. They also provide additional and advantageous anchoring in the surrounding bone cement.

In general it should be noted that the internal diameter of the spherical section 10 of the support bearing 3 is advantageously larger by 1 to 2 millimeters than the external diameter of the hemispherical socket 9 so that sufficient space for the introduction of bone cement remains between the spherical section surface parts in the form of claws 13 or webs 15.

Another form of support bearing is illustrated in FIGS. 6 and 7 and is provided with webs 15 which are radially disposed and converge in a star pattern at the center to form a skeletal structure. These webs can also be provided with radial beads 16. In the support bearing of FIGS. 8 and 9 the webs 15 are provided at half their height with an annular web 17 which has the same centre as the centre of the support bearing. The annular web 17 can also be provided with a bead. If desired, the internal parts of the radial webs 15 which are disposed between the ring 17 and the centre of the support bearing of FIGS. 8 and 9 can be omitted. As shown in FIG. 10 the edges of the webs 15 can be provided with corrugations or hooks 18 which additionally improve anchoring in the bone cement.

Also, if desired, the support bearing 3 can be constructed of a physiologically compatible plastics material and can be joined to the hemispherical socket 2 or integrally constructed therewith so that the view of FIG. 3 represents a single, contiguous part which is constructed all of the same material.

Claims

What I claim as my invention and desire to secure by Letters Patent is:

1. A support bearing for embodiment in a prepared socket in a pelvis comprising a generally cup-shaped element defining a substantially part-spherical internal cavity for reception of a socket for a femoral condyle and having an external flange adjacent the mouth of said cavity, said cup-shaped element comprising a plurality of fingers connected to the flange and formed integrally therewith, the fingers defining at least in part the cavity and having barbed tips, which, when viewed in a direction perpendicular to the plane of the flange axially of the opening to the cavity, resemble arrow heads.

2. A support bearing according to claim 1, in which the cup-shaped element further comprises a plurality of webs connected at one end to the flange and formed integrally therewith and mutually connected at their other ends on the axis of the opening to the cavity.

3. A support bearing according to claim 2, in which the free edges of the webs are provided with corrugations.

4. A support bearing according to claim 2, in which the free edges of the webs are provided with hooks.

5. A support bearing according to claim 1, in which there are eight fingers whose tips lie a distance of from about 20 to about 25mm from the flange.

6. A support bearing according to claim 2, in which there are three webs and in which there are two fingers between each web, the fingers and webs being symmetrically disposed with respect to the axis of the opening to the cavity.

7. A support bearing according to claim 2, in which the cup-shaped element further comprises a secondary web extending in an annular fashion with respect to the axis of the opening to the cavity between the flange and the meeting point of the first-mentioned webs.

8. In or for an artificial hip joint comprising a femoral implant for implantation in a femur, the femoral implant comprising a stem for embedding in a prepared cavity in a femur of a patient, a femoral neck attached to the stem and a femoral condyle on the femoral neck, and a hemispherical socket member for reception of the femoral condyle, said socket having uninterrupted internal and external surfaces for adjustment of said socket, the improvement comprising bearing support means for the socket member adapted for embedding in a prepared cavity in the pelvis of the patient, the bearing support means comprising a substantially part-spherical element having a recess for reception of the socket member, an external flange for bearing against the bone surrounding the prepared cavity in the pelvis and at least one aperture affording communication between the external surface of the bearing support and the recess for the socket.

9. An artificial hip joint comprising a femoral implant for implantation in a prepared cavity of a femur of a patient and a socket device for insertion in a previously enlarged socket in the pelvis of the patient, said socket device including a bearing support having an external flange adapted to bear against the bone surrounding the socket in the pelvis and a recess having at least one aperture affording communication between the external surface of the bearing support and said recess, said socket device further including a hemispherical socket having a continuous external surface for adjustment within said recess of said bearing support and a smooth uninterrupted internal surface for receiving femoral implant.

10. An artificial hip joint according to claim 9 wherein socket socket device is made of a plastics material.

11. A support bearing for embedment in a prepared socket in a pelvis comprising a generally cup-shaped element defining a substantially part-spherical internal cavity for reception of a socket for a femoral condyle and having an external flange adjacent the mouth of said cavity and having a plurality of fingers extending in cantilever fashion inwardly from said flange into said cavity to define at least one aperture affording communication between the external surface of the bearing support and the socket.

12. A support bearing according to claim 11 in which the flange is provided with a plurality of apertures.

13. A support bearing according to claim 11, in which at least one external surface of the cup-shaped element is provided with a bead.

14. A support bearing according to claim 13, in which the bead extends in a generally radial direction with respect to the axis of the opening to the cavity.

15. In combination, a femoral implant having a femoral condyle; a socket member for receiving said femoral condyle; and a support bearing having a part-spherical internal cavity for reception of said socket, an external flange, and a plurality of fingers extending from said flange and defining at least one aperture within said cavity to permit passage of a bone cement for anchoring of said socket in a pelvis cavity.

16. A support bearing for embedment in a prepared socket in a pelvis comprising a generally cup-shaped element defining a substantially part-spherical internal cavity for reception of a socket for a femoral condyle and having an external flange adjacent the mouth of said cavity, and having a plurality of spaced webs defining a plurality of apertures therebetween and a skeletal structure, each said aperture affording communication between the external surface of the bearing support and the socket.

17. In combination, a femoral implant having a femoral condyle; a socket member for receiving said femoral condyle; and a support bearing having a part-spherical internal cavity for reception of said socket, an external flange, and a plurality of webs defining at least one aperture within said cavity to permit passage of a bone cement for anchoring of said socket in a pelvic cavity.