Hip Prosthesis

Abstract

In a hip prosthesis, a socket is supported on a nail protruding from the back of the socket and adapted to enter the acetabulum. The socket axis is disposed off center with respect to the axis of the nail towards the outside of the body approximately 20.degree.. In line with the nail, the socket has a threaded bore which cooperates with a threaded extension on the end of a driver and the driver in the preferred embodiment has a plastic ball which engages the socket. The ball which engages the socket for operation of the hip joint is of plastic, preferably high density polyethylene, and rotates on a pin which is supported in the femur by a nail. The axis of the pivot pin is preferably 145.degree. from the axis of the femur nail.

Parent Case Text

This application is a continuation-in-part of my co-pending application Ser. No. 67,475 filed Aug. 27, 1970 for Hip Prosthesis, now abandoned.

Description

The present invention relates to a hip prosthesis, particularly to a total hip joint. The invention applies to a hip joint for use by man and also to a hip joint used in veterinary medicine, on any of the higher vertebrates.

A purpose of the invention is to support a hip socket prosthesis on a nail driven into the acetabulum.

A further purpose is to dispose the hip socket axis off center with respect to the axis of the nail toward the outside of the body, preferably 20.degree..

A further purpose is to mount a threaded bore in the socket in prolongation of the nail to engage a threaded extension on the end of a driver in the threaded bore.

A further purpose is to mount a plastic ball on the driver which engages the hip socket in driving.

A further purpose is to mount a hip ball on a nail which is supported in the femur, making the ball of plastic and preferably of high density polyethylene.

A further purpose is to rotatably mount the ball on a trunnion supported by the nail and to dispose the trunnion axis approximately 145.degree. from the nail axis.

A further purpose is to interpose a plastic layer between the socket and the ball and secure the layer either to the socket or to the ball.

A further purpose is to lock the ball against rotation and as the ball is supported on the pin to provide interlocking between the ball and the pin.

Further purposes appear in the specifications and the claims.

In the drawings I have preferred to illustrate a few only of the embodiments in which the invention may appear, choosing the forms shown from the standpoints of convenience in operation, satisfactory illustration and effective showing of the embodiments desired.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the prosthetic hip socket of the invention inserted in the acetabulum.

FIG. 2 is a side view of the prosthetic hip socket.

FIG. 3 is a front view of the prosthetic hip socket.

FIG. 4 is a rear view of the prosthetic hip socket.

FIG. 5 is a longitudinal section of the prosthetic hip socket.

FIG. 6 shows the prosthetic hip socket of the invention connected to the driver, the whole being in longitudinal section.

FIG. 7 is a fragmentary view on section showing the prosthetic hip ball in place in the femur.

FIG. 8 is a side view of the prosthetic hip ball of the invention.

FIG. 9 is a front view of the prosthetic hip ball of the invention.

FIG. 10 is a fragmentary rear view of the prosthetic hip ball of the invention.

FIG. 11 is a fragmentary section of the prosthetic hip ball of the invention, the section begin through the ball trunnion.

FIG. 12 is a fragmentary side elevation showing the prosthetic hip socket and the prosthetic hip ball assembly in the position that they will be held by the muscles of the hip.

FIG. 13 is a fragmentary sectional view of an established hip joint with a plastic layer interposed between the ball and the socket and secured to the socket, the socket being mounted on a hip nail.

FIG. 14 is a variation of FIG. 13 shown in longitudinal section in which the socket is adapted to be cemented to the acetabulum.

FIG. 15 is a fragmentary longitudinal section of a ball and a portion of its support, having a coating of plastic over the ball and secured thereto.

FIG. 16 is a fragmentary longitudinal section of a plastic ball mounted on a pin anchored to the leg bone, and prevented from turning by a spline between the pin and the ball.

FIG. 17 is a fragmentary section of FIG. 16.

FIG. 18 is a view corresponding to FIG. 17 and showing a different form of interlocking between the pin and the ball.

FIG. 19 is a view corresponding to FIG. 17 and showing a further variation of the interlocking between the pin and the ball.

In the present treatment of hip joints, particularly for human beings, but also for higher animals, the tendency in recent years has been to make a total hip joint of prosthetic components, not using either the ball or the socket provided by nature. Both the McKee and the Ring variation of this joint have been widely used. In McKee the components are secured to the boney structure of the body by a cement, suitably methyl methacrylate. In Ring the socket is mounted on a screw secured to the acetabulum. While this does not involve medical complications which are present from the cementing procedure, it does require extensive twisting of the body which I find to be undesirable.

In the present invention the socket, suitably of stainless steel, is mounted on a nail protruding from the back and resembling Tronzo U.S. Pat. No. 3,076,453, dated Feb. 5, 1963 for Hip Nail. Unlike the Tronzo patent nail, it is applied to the acetabulum and not to the femur.

I find that the socket axis should not be in straight alignment with the securing means as in the prior art, but should be offset or inclined toward the outside of the body in the sidewise direction, preferably about 20.degree.. This is more consonant with the pull of the muscular structure in holding the ball in place.

I likewise locate a driver attachment off center and in line with the axis of the nail, the driver having a threaded projection which screws into a blind bore in the socket. I also provide the driver with a ball of resilient material, for example high density polyethylene, which engages the inside of the socket during driving.

In the prior art there are stainless steel balls pivotally mounted on pins and suspended by nails driven into the femur. Unlike the prior practice, however, I find that much wear is prevented by making the ball, still rotatable, of a plastic such as high density polyethylene.

Unlike the prior art which disposes the axis of the stainless steel pivot at approximately 130.degree. to the nail, I find that much better muscular function is obtained if the pivot axis is about 145.degree. with respect to the axis of the nail.

In the form of FIGS. 1 to 12 inclusive the socket 20 consists of a hemispherical hollow body which is adapted to be mounted in the acetabulum in line with the former hip socket. From the back of the socket and suitably integral, protrudes a dominant nail 21, which has extended over its full length three flutes 22 which are equally circumferentially placed. The flutes are smooth and tapering at 24, but they have on the end shark's teeth 25 as shown in the Tronzo patent above referred to.

At the back of the socket are three evenly circumferentially spaced protruding spikes 26. The spikes engage the acetabulum and prevent rotation of the socket.

The nail is offset at 28 with respect to the axis of the socket by about 20.degree., so that the socket will be inclined outward toward the side of the body.

In line with the nail in the socket is a threaded bore 29, which is adapted to receive a threaded projection 30 on the end of the driver 31, having a driving end 32 adapted to receive taps of a hammer. The driver has a hemispherical ball 33 on its end near the forward projection, adapted to sit in the socket. The ball provides a cushioning effect in driving, due to play in the thread, and is made of high density polyethylene plastic.

The natural ball on the end of the femur is removed in operative procedure, and the prostetic ball 34 is mounted on a nail 35 driven in the femur. The nail 35 has a pivot pin 36 offset from it preferably at an angle of 145.degree. and the prosthetic ball 34 has a central round opening 40 which engages it and allows it to turn around the pin, and has a face 41 which cooperates with end face 42 on the pin. The ball is made of a plastic, preferably high density polyethylene which will give good wear with the socket.

The nail 35 has a series of teeth 44 on the rear end on a curved side 45 and a longitudinal flute 46 on its straight side 47. The nail is pointed at 48 at the forward end and has a threaded driver bore at 50 at the rear end.

In operation, of FIGS. 1 to 12 inclusive, the hip joint is opened and the natural hip ball is removed. The nail 21 using the driver, is inserted in the acetabulum to position the hip socket as shown, slightly disposed outwardly with respect to the straight line because the socket axis is off center about 20.degree. from the axis of the nail. A guide hole may be drilled before inserting the socket nail. The driver is then removed from the socket nail ball. The nail 35 is inserted in the femur suitably first drilling a guide hole if required. The ball trunnion is disposed outwardly to engage in the socket, and the ball is placed on the trunnion. As soon as the muscles come into play, they hold the ball in the socket and normal operative procedure is used to close the joint.

FIG. 13 shows a variation in the total hip joint of the invention in which a plastic layer is provided between the ball and the socket secured to the socket. A socket 20', which may be the socket of FIGS. 1 to 12 inclusive, has an inside spherical layer 60 of plastic, preferably high density polyethylene which is secured to the socket as by a layer of cement 61. The high density polyethylene is preferably treated on its surface to be cemented as by moderate exposure to a flame or an electric discharge as commonly used in printing polyethylene. The cement may be epoxy cement of commercial grade. Equally well the inside surface of the socket may be sand blasted and the layer 60 applied by spraying as are known in the art.

The ball 34' may be a plastic ball as used in FIGS. 1 to 12 supported on anchorage or nail 35 in which the pin 36' is adapted to prevent rotation, as by a locking pin 62 which passes through the ball and the pin 36'. Prevention of rotation is optional but is preferred in some cases by patients who think the rotation of the ball reduces stability.

In FIG. 13 the nail or other anchorage to the leg bone has the window openings omitted.

It will be evident that the construction in FIG. 13 as using a metal ball, can provide a ball integral with the anchorage for the ball.

In FIG. 14 a metallic socket 20.sup.2 has slots 63 partially through its surface from the back and is anchored to the acetabulum as by cement such as methyl methacrylate cement or other suitable cement which is compatible with the human system. It has on the inside a layer of plastic 60 which is secured as by cement 61 as described in connection with FIG. 13, or the plastic sprayed on a roughened surface.

FIG. 15 shows a ball 34.sup.2 of suitable metal rigidly affixed to a nail or other support 35. The ball is coated on the outside with a layer of plastic 60', suitably of high density polyethylene, united by a suitable cement 61' or sprayed on preferably over a roughened surface.

FIGS. 16 and 17 show a plastic ball 34.sup.3 suitably of high density polyethylene which fits on a pin 36.sup.2 of a suitable nail or other support. The surface of the pin and the cooperating surface of the opening in the ball have suitable spines 64 that restrict the ball against rotating imparting greater stability to the patient.

In FIG. 18, instead of the spline 64, there are winged projections 64' on the pin which fit in recesses on the opening in the ball.

In FIG. 19, the ball and the spline have longitudinal interlocks 64.sup.2 which prevent the ball from rotating.

In operation any of the forms of the FIGS. 13 to 15 provide the strength of a metallic ball but the lubricity of a plastic surface between the ball and the socket. They may operate with or without rotation of the ball.

In the form of FIGS. 16 to 19 the ball mounts on the pin of the support in the leg bone, but is prevented from rotation.

In the preferred embodiment all the metal parts are preferably made of stainless steel corrosion-resistant or a corrosion-resistant alloy such as one of the cobalt-chromium-molybdenum alloys used for prothesis, and all the plastic parts are preferably made of high density polyethylene.

In view of the my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I therefore claim all such insofar as they fall within the reasonable spirit and scope of my claims.

Claims

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A hip prosthesis comprising a metallic socket, a dominant nail on the socket adapted to be inserted in the acetabulum and comprising three equally circumferentially disposed flutes and teeth on the end, spikes mounted on the back of the socket around the nail, the socket axis being off center toward the outside of the body with respect to the nail axis approximately 20.degree., the socket having a blind threaded bore for a driver in line with the nail, a plastic ball in the socket, a trunnion rotatably mounting the plastic ball and a femur nail connected to the trunnion for supporting the trunnion in the femur and having an angle with respect to the trunnion axis of approximately 145.degree. .

2. A hip prosthesis comprising a metallic socket, a dominant nail protruding from the back of the socket adapted to be inserted in the acetabulum in line with the axis of the socket, spikes mounted on the back of the socket around the nail, the socket axis being off center toward the outside of the body with respect to the nail axis approximately 20.degree., a plastic ball in the socket, a trunnion rotatably mounting the plastic ball and a femur nail connected to the trunnion for supporting the trunnion in the femur.

3. A hip prosthesis comprising a metallic socket, a dominant nail on the socket adapted to be inserted in the acetabulum in line with the axis of the socket and comprising three equally circumferentially disposed flutes and teeth on the end, the socket axis being off center toward the outside of the body with respect to the nail axis approximately 20.degree., the socket having a blind threaded bore for a driver in line with the nail, a plastic ball in the socket, a trunnion rotatably mounting the plastic ball and a femur nail connected to the trunnion for supporting the trunnion in the femur.

4. In a hip prosthesis, a hemispherical socket, a dominant nail protruding from the back of the socket and adapted to be embedded in the acetabulum, the socket having an axis which is off center with respect to the nail axis approximately 20.degree. toward the outside of the body.