WO2006092613A2

WO2006092613A2 - Hip replacement device and method

Info

Publication number: WO2006092613A2
Application number: PCT/GB2006/000762
Authority: WO
Inventors: Peter James Raffan; Martin Elloy
Original assignee: Veterinary Innovations Limited
Priority date: 2005-03-03
Filing date: 2006-03-03
Publication date: 2006-09-08
Also published as: WO2006092613A3

Abstract

A hip prosthesis comprises an acetabular cup having a concave side (9) and a convex side (7) and a femoral implant comprising a head (1) and neck portion (2) in alignment with a stem (3) . The head is adapted to index the acetabular cup. The neck portion includes a flange (4) adapted to engage the calcar-f emorale and a blade (5) projecting from the neck so as, in use, to cut into the femur. Also described is an alignment device for ensuring correct alignment of the hip prosthesis, and methods for inserting the hip prosthesis.

Description

HIP REPLACEMENT DEVICE AND METHOD

Field of Invention

The present invention relates to a hip replacement device and method. In particular, although not exclusively, the present invention relates to femur-neck engaging prosthetic devices for hip replacement.

Background of the Invention

Hip replacement, or arthroplasty, is a surgical procedure in which the diseased parts of the hip joint are removed and replaced with new, artificial parts. The goals of hip replacement surgery are to improve mobility by relieving pain and improving function of the hip joint. Basically the procedure installs a new cup in the hip and a new ball at the head of the femur which act in much the same way as a regular hip joint.

Traditional designs of hip replacement implants have a femoral head and neck component attached to the femur by means of a stem passing down the medullary canal, articulating with a socket component fixed to the prepared acetabulum. The femoral stem is usually shaped to conform to the Anterior/Posterior (AJF) profile and may be straight and less conforming to the natural curve in the medial/lateral (M/L) profile of the femoral medullary cavity. Some have curvature in the M/L profile to be more conforming to the natural medullary curvature. There is considerable variance in the natural geometry of the femur and a large range of shapes and sizes of femoral stems are required to achieve a universal quality of fit.

Additionally the extra-osseous (head and neck) part of the prosthesis is required in a variety of sizes and with various alignments to the femoral stem. To deal with this a further extension in range of geometries and various degrees of modularity had been introduced. One way of overcoming these difficulties is by fixing the femoral implant by means of a stem restricted to the neck region of the femur. Many of these designs do not adequately transfer joint loads from the head to the shaft of the femur. Another problem associated with this sort of design is a lack of torsional stability about the neck axis.

It is an object of the invention to overcome the disadvantages associated with the art or to at least provide the public with a useful alternative.

Summary of the Invention

Accordingly, in a first aspect the present invention provides a hip prosthesis comprising an acetabular cup having a convex side and a concave side and a femoral implant comprising a head and neck portion in axial alignment with a stem wherein the head has a substantially spherical shape which indexes the acetabular cup and the neck portion includes a flange which, in use, engages the calcar-femorale and a blade projecting from the neck which, in use, cuts into the femur and resists rotation of the stem relative to the femur.

The prosthesis may be made of any suitable material. Preferred embodiments are of metal or metal alloy, for example cobalt-chromium alloy.

The acetabular cup suitably is sized to receive the head portion of the particular femoral implant to be used and has a high polish on the concave (femoral implant engaging) side. In preferred embodiments the acetabular cup includes an apical spigot which can engage a centrally disposed hole in the floor of the acetabulum. In embodiments for particular veterinary applications, such as for use in dogs, the apical spigot preferably has a diameter of between 4 and 6mm, more preferably around 5mm and has a length of between 6 and 8mm, more preferably around 7mm. Preferably, the spigot comprises radially extending ribs. The acetabular cup may additionally include a coating on the concave side such as graphite-like carbon (GLC) or diamond-like carbon (DLC) or it may have any other low friction, low wearing surface. In embodiments for particular veterinary applications, such as for use in dogs, the cup is preferably adapted to receive a head having a diameter of from 17 to 20mm, more preferably around 19mm.

Preferably, the outside lip of the acetabular cup is chamfered to increase the range of movement of the prosthesis. In preferred embodiments the concave side and the convex side of the acetabular cup meet to form a face, and a portion of the face is chamfered towards the convex, outer side of the acetabular cup. Alternatively, or additionally, a portion of the face is chamfered towards the concave, inner side of the acetabular cup. Alternatively, the entire face is chamfered towards either the concave inner side or the convex outer side of the acetabular cup. Preferably the chamfer is between 10° and 30°, more preferably around 17.5°.

The head suitably is sized to index the acetabular cup of the implant to be used and may have a high polish or be coated with a low friction, low wearing coating as for the acetabular cup.

The head forms a lobe on the end of the neck and in preferred embodiments the neck is profiled to give 134° or more range of movement in all planes. In embodiments for particular veterinary applications, such as for use in dogs, the neck has a section with a maximum diameter of from 6 to 10mm, more preferably around 7mm.

The stem may be of any cross-sectional shape but is preferably straight and of circular cross section. In embodiments for particular veterinary applications, such as for use in dogs, when of circular cross-section, the stem is preferably from 4 to 6mm, more preferably around 5mm in diameter.

To enhance fixation, the stem region may be coated with any material that encourages bone apposition or ingrowth, such as hydroxyapatite or a porous coating. Generally the stem is of a length not greater than the distance from the resection plane to the lateral cortex. In those embodiments for use in veterinary treatment the stem may be as small as 30-60mm in length. For larger animals and humans, however, the stem will be significantly longer. It is preferred that the stem in situ is substantially flush with the edge of the lateral cortex, though in practice it may protrude slightly beyond, rather than fall short of, the lateral cortex.

The flange preferably extends radially from the stem axis suitably by 12mm or less, preferably 10mm or less, more preferably around 5-6mm.

The flange and the blade may be incorporated into the neck in any suitable orientation to one another. They can be on opposite sides. In particularly preferred embodiments the flange and the blade are substantially diametrically opposed to one another, and the device can be used for both left and right hips. In this arrangement the flange can engage the strong bone of the calcar-femorale in the inferior neck of the femur while the blade engages the superior regions of the proximal neck of the femur. In use the particular arrangement transfers the load to the femur via the calcar femorale in a near-physiologically normal manner.

The blade is preferably shaped such that it transfers substantially no load to the femur, substantially all the load being transferred via the flange and the calcar femorale. The blade can be sharpened on its leading edge, the edge distal to the head, so that it may cut into the bone of the femoral neck when implanted. In preferred embodiments the blade is sharpened to a knife edge.

Preferably the blade extends from the neck a distance the same or greater than a minor dimension of the stem. In preferred veterinary embodiments the blade extends a distance greater than or equal to 5mm from the neck.

In preferred embodiments, the blade extends from the stem with an included angle, formed between a cutting edge of the blade and the stem, of between 30° and 75°.

Preferably, the included angle is around 60°. It has been found that the use of a blade with such an included angle is particularly effective for engagement with the superior region of the proximal neck of the femur.

The blade presents sufficient area to the bone to resist torsion about the stem. Preferably the blade is adapted so that in use it does not extend a distance into the neck of the femur significantly greater than the distance that it extends out from the neck of the prosthesis. Thus, in preferred veterinary embodiments the blade presents an area to the bone of the femur of around 5mm x 5mm.

In use, the blade engages the cancellous bone in the superior neck region of the femur to provide torsional restraint. In some embodiments of the device there may be more than one blade and the device may comprise two or more blades spaced apart and projecting from the neck. Having several blades may increase the stability of the device. A single blade substantially opposite the flange has the advantage it can be used on either hip.

In some embodiments the stem fits inside an additional telescopic component which is adapted for attachment to the lateral cortex of the femur to accommodate various stem lengths. The telescopic component is adapted to receive the stem of the femoral component and so has a complementary shape, for example if the stem is circular in cross section then the telescopic portion is tubular. The stem and corresponding telescopic component can be non-circular in cross section, which can assist in providing torsional restraint, without axial constraint. Preferably, the stem has a reduced diameter for insertion into the telescopic component. Thus, the overall diameter of the stem plus telescopic component does not exceed the original diameter of the stem. Preferably, the telescopic component comprises a self cutting thread for facilitating fixation into the lateral cortex of the femur.

In further embodiments of the invention the acetabular cup further comprises at least one rib on the convex outer side. Preferably, the acetabular cup comprises at least 2 ribs forming at least one pair of ribs diametrically opposite each other. Further preferably, the rib or ribs are positioned and adapted for limiting movement of the acetabular cup when sited in an acetabulum. The rib or ribs may also comprise at least one cutting edge for engagement with the acetabulum. These ribs, therefore, lock the acetabular cup in place, preventing rotation of the cup within the acetabulum.

In preferred embodiments, the rib or ribs do not extend beyond a meeting point of the concave and convex surfaces of the cup. Preferably, the rib or ribs do not extend beyond a plane defined by the angle of the face. Accordingly, the ribs do not interfere with the range of movement of the femoral head with the acetabular cup.

According to another embodiment, the cup comprises a hole for engagement with a fitting instrument. The provision of the hole aids a surgeon when fitting the acetabular cup in the acetabulum.

According to a further aspect of the invention, there is provided an alignment device for facilitating alignment of a telescopic component of the prosthesis. Preferably, the alignment device is adapted for engagement with the stem of the prosthesis. In this respect, the alignment device preferably comprises a recess formed in its axial end for engagement with a spigot formed at the distal end of the stem of the prosthesis.

In particular preferred embodiments, the alignment device is configured for allowing the telescopic component of the prosthesis to pass over the alignment device when the alignment device is in engagement with the stem of the prosthesis. Preferably, the alignment device is of a substantially rod shape.

In a further aspect the invention also provides a method of performing a hip replacement comprising surgically implanting the device according to the invention.

The methods of the invention may be performed on a wide range of animals. Preferred examples include humans, canine, feline, rodent, bovine or equine animals. In typical use of the invention, bone preparation consists of preparing a hole passing along the femoral neck and into the floor of the acetabulum. In the femoral neck, the hole provides support for the stem of the femoral component and, in the acetabulum it provides support for the apical spigot (if present). It also sets the angle of inclination of the device and its components for each individual patient. This technique also allows the angle of anteversion to be set accurately for each individual patient.

The invention further provides a method of performing a hip replacement, comprising placing the femur and pelvis of a patient into a desired orientation, and drilling through the femur from the lateral cortex thereof. This enables the surgeon to set the desired position so that the location of the prosthesis and its angle of inclination and anteversion are correct.

The desired orientation is generally a neutral position or the neutral position, and the method hence allows the surgeon to set the prosthesis at the correct angles for each patient.

In order to ensure that the correct joint tension is produced, a femoral reamer is preferably inserted into a hole formed in the femur. A back reamer head is then fitted on to the end of the reamer and the femoral neck is back reamed to give a neck surface on which the flange fits substantially flat. In order to ensure the correct joint tension is produced, the neck is preferably back reamed by a small amount and then the tension is checked, preferably using a template. This process of back reaming by a small amount and then checking the tension is preferably repeated until the desired joint tension has been achieved.

This method, therefore, permits a surgeon to implant the prosthesis with the correct angles and joint tension, thus maximising patient compliance and the long term stability of the prosthesis.

Preferably, the method comprises drilling through the femur into the pelvis, forming a recess in the pelvis, further preferably drilling through from a point on the lateral cortex level with the distal margin of the lesser trochanter. It is also preferred that the method comprises drilling through the mid point of the resected neck of the femur, proximal to the calcar femorale.

The method suitably comprises fitting an acetabular cup having an apical spigot, the spigot locating in the recess. In especially preferred embodiments, the method comprises fitting a hip prosthesis according to other aspects of the invention as described herein. In a further embodiment, the method comprises using an alignment device as described herein to ensure correct alignment of the prosthesis.

The invention is applicable generally to humans and animals, especially domestic animals. Preferably the method of the invention is carried out on a non-human animal, more preferably a dog.

The invention also provides a kit for a prosthetic hip comprising an acetabular cup and a femoral implant according to the invention.

The invention provides a prosthesis which goes down the neck of the femur into the lateral cortex - prior art devices do not so extend and are generally thicker and longer with a bent stem, going down the medulla of the bone and requiring cement. The device of the invention can be a press fit, with no cement needed, resting on hard bone at each end.

Description of Drawings

The present invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 : shows a perspective view of a femoral implant according to a preferred embodiment;

Figure 2: shows a perspective view of an acetabular implant according to a preferred embodiment;

Figure 3 : shows a cross-section through a femoral implant according to a preferred embodiment of the invention;

Figure 4: shows (a) a perspective view of a femoral implant and attachment of a telescopic component, (b) a perspective view of a femoral implant and an alignment device, and (c) a perspective view of a femoral implant, an alignment device and a telescopic component, according to preferred embodiments of the invention;

Figure 5 : shows (a) a front view of an acetabular cup, (b) a side view of an acetabular cup, (c) a perspective view of an acetabular cup, (d) an enlarged view of an apical spigot of an acetabular cup, and (e) an enlarged view of a rib of an acetabular cup, according to preferred embodiments of the invention; and

Figure 6: shows (a) a side view of a femoral implant, (b) a top view of a femoral implant, (c) a perspective view of a femoral implant, (d) an enlarged perspective view of the blade of a femoral implant, and (e) an enlarged side view of the blade of a femoral implant, according to preferred embodiments of the invention.

Detailed Description

The femoral implant shown in Figure 1 is of cobalt chrome alloy and has a head (1) of a spherical shape adapted to index the acetabular cup. The head is connected to the stem via the neck portion (2) which is in axial alignment with the stem (3).

The neck portion includes a flange (4) adapted to engage the calcar-femorale and a blade (5) projecting from the neck. When installed the stem passes into the neck of the femur, the flange (4) transfers weight to the calcar-femorale, the blade (5) engages the superior region of the proximal femur neck, and the head and neck protrude from the femur. The blade hence locks the implant in place, preventing rotation of the stem inside the neck of the femur. The blade is sharpened, to facilitate insertion but also so as not to impede axial movement so that the flange bears all axial load. This avoids stress shielding and consequent osteolysis.

The acetabular cup shown in figure 2 is of cobalt chrome alloy and has an apical spigot (6) protruding therefrom and a hemispherical outer portion (7) that fits into the floor of the acetabulum. The cup has a chamfered edge (8) adjacent the femoral implant engaging (concave) side (9) and a high polish on the femoral implant engaging side.

In use the apical spigot engages a hole which the surgeon has previously made in the, floor of the acetabulum and the concave femoral implant engaging face (9) is positioned so as to receive the femoral implant. Both the apical spigot (6) and the hemispherical outer portion (7) of the acetabular cup are coated with hydroxyapatite. Alternatively, the apical spigot (6) and the hemispherical outer portion (7) of the , acetabular cup may be coated with a porous coating.

The femoral implant shown in figure 3 has a telescopic portion (10) which surrounds the stem (3) at the end distal to the head. The inclusion of the telescopic portion allows different effective stem lengths to be utilised without the need to actually supply femoral implants with different stem lengths.

As shown in figures 4A, 4B and 4C, in order to facilitate addition of the telescopic portion without increasing the overall diameter of the stem, a section of the stem (11) at the distal end to the head is provided with a reduced diameter, permitting the telescopic portion to be formed of the same diameter as the stem adjacent the neck portion and to surround the distal section of the stem. The telescopic portion is provided with a self cutting thread (12) formed at its distal end to facilitate fixation into the lateral cortex of the femur. The thread may be tapered and provided with cutting edges (13).

In order to facilitate alignment of the telescopic portion when the stem is hidden within the femoral neck, an alignment device (14) with an external diameter matching that of the distal section of the stem (11) is provided. A recess (15) is formed in the axial end of the alignment device for engagement with a spigot (16) formed at the distal end of the stem.

The distal end (17) of the alignment device may be reduced in diameter for convenience of use. Once the telescopic portion has been secured in position, the alignment device can be discarded.

A further example of an acetabular cup according to the invention is shown in figures 5 A to 5E. As can be seen, the face of the acetabular cup is chamfered at its outer edge (18), leaving a planar area (19) adjacent to the femoral implant engaging side (9).

The cup has four ribs (20) on its outer surface which extend towards the apical spigot (6) of the cup. The ribs lie flush with the chamfered edge (18) and do not extend beyond the conical surface of the chamfer.

The ribs each have a cutting edge (21) to facilitate cutting into the acetabulum. The ribs, therefore, lock the acetabular cup in place, preventing rotation of the cup within the acetabulum.

The spigot (6) is provided with ratchet shaped ribs (22) to allow easy insertion into the hole made in the floor of the acetabulum with restricted removal therefrom. The ratchet shaped ribs extend radially from the spigot such that the diameter of the spigot plus ribs is wider than the diameter of the hole. In order to aid insertion of the acetabular cup into engagement with the acetabulum, the cup is provided with a hole (24) to accept insertion of an instrument.

As shown in figures 6 A to 6E, the blade (5) which projects from the stem of the femoral implant is shaped to form a cutting edge (23) having an included angle θ of around 60°.

Although the invention has been described with reference to particular embodiments one of skill in the art will appreciate that variation may be made to the device and/or method without departing from the scope of the invention as claimed herein. In particular where known equivalents exist, these may be substituted whilst remaining within the scope of the claims.

Claims

1 A hip prosthesis comprising an acetabular cup having a concave side and a convex side and a femoral implant comprising a head and neck portion in alignment with a stem wherein the head is adapted to index the acetabular cup and the neck portion includes a flange adapted to engage the calcar-femorale and a blade projecting from the neck so as, in use, to cut into the femur.

2 A hip prosthesis according to claim 1 wherein the acetabular cup includes an apical spigot.

3 A hip prosthesis according to claim 2 wherein the apical spigot has a diameter of around 5mm and a length of around 7mm.

4 A hip prosthesis according to any previous claim wherein the concave side and the convex side of the acetabular cup meet to form a face, and wherein a portion of the face is chamfered towards the convex, outer side of the acetabular cup.

5 A hip prosthesis according to any previous claim wherein the concave side and the convex side of the acetabular cup meet to form a face, and wherein a portion of the face is chamfered towards the concave, inner side of the acetabular cup.

6. A hip prosthesis according to any of claims 1 to 3 wherein the concave side and the convex side of the acetabular cup meet to form a face, and wherein the entire face is chamfered towards either the concave inner side or the convex outer side of the acetabular cup.

7 A hip prosthesis according to any of claims 4 to 6 wherein the chamfer is between 10° and 30°.

8 A hip prosthesis according to claim 7 wherein the chamfer is around 17.5°.

9 A hip prosthesis according to any previous claim wherein the concave side of the acetabular cup has a low friction, low wearing surface selected from graphite-like carbon (GLC) and diamond-like carbon (DLC).

10 A hip prosthesis according to any previous claim wherein the head has a low friction, low wearing surface selected from graphite-like carbon (GLC) and diamond- like carbon (DLC).

11 A hip prosthesis according to any previous claim wherein the acetabular cup is adapted to receive a head having a diameter of around 17-20mm.

12 A hip prosthesis according to any previous claim wherein the head has a diameter of around 17-20mm.

13 A hip prosthesis according to any previous claim giving around a 134° range of movement in all planes.

14 A hip prosthesis according to any previous claim wherein the neck has a section with a maximum diameter of around 10mm.

15 A hip prosthesis according to any previous claim wherein the stem has a circular cross-section.

16 A hip prosthesis according to any previous claim wherein the convex side of the acetabular cup and the stem are coated with a material that encourages bone apposition or ingrowth.

17 A hip prosthesis according to any previous claim wherein the convex side of the acetabular cup and the stem are coated with hydroxyapatite or a porous coating.

18 A hip prosthesis according to any previous claim wherein the stem is around 30-60mm in length.

19 A hip prosthesis according to any previous claim wherein the stem has a circular cross-section having a diameter of around 5-6mm.

20 A hip prosthesis according to any previous claim wherein the blade extends from the neck a distance of 12mm or less.

21 A hip prosthesis according to any previous claim wherein the blade extends from the stem with an included angle, formed between a cutting edge of the blade and the stem, of between 30° and 75°.

22 A hip prosthesis according to claim 21 wherein the included angle is around 60°.

23 A hip prosthesis according to any previous claim wherein the blade is adapted so that in use it extends a distance into the femur of around 5-6mm or less.

24 A hip prosthesis according to any previous claim wherein the flange extends radially from the stem axis by a distance of 10- 12mm or less.

25. A hip prosthesis according to claim 24 wherein the flange extends radially from the stem axis by a distance of around 5-6mm.

26 A hip prosthesis according to any previous claim wherein the flange and the blade are diametrically opposed to one another about the axis of the stem.

27 A hip prosthesis according to any previous claim wherein the blade is chamfered to a knife edge.

28 A hip prosthesis according to any previous claim additionally including an additional telescopic component adapted for attachment to the lateral cortex of the femur. 29 A hip prosthesis according to claim 28 wherein the stem has a reduced diameter for insertion into the telescopic component.

30 A hip prosthesis according to claim 28 or 29 wherein the telescopic component comprises a self cutting thread for facilitating fixation into the lateral cortex of the femur.

31 A hip prosthesis according to any previous claim wherein the acetabular cup further comprises at least one rib on the convex outer side.

32 A hip prosthesis according to claim 31 wherein the acetabular cup comprises at least 2 ribs forming at least one pair of ribs diametrically opposite each other.

33 A hip prosthesis according to claim 31 or 32 wherein the rib or ribs are positioned and adapted for limiting movement of the acetabular cup when sited in an acetabulum.

34 A hip prosthesis according to claim 33 wherein the rib or ribs comprise at least one cutting edge for engagement with the acetabulum.

35 A hip prosthesis according to any of claims 31 to 34 wherein the rib or ribs do not extend beyond a meeting point of the concave and convex surfaces of the cup.

36 A hip prosthesis according to any of claims 31 to 34, when depending upon any of claims 4 to 30, wherein the rib or ribs do not extend beyond a plane defined by the angle of the face.

37 A hip prosthesis according to any previous claim where in the cup comprises a hole for engagement with an instrument.

38 A hip prosthesis according to any previous claim wherein the spigot comprises radially extending ribs. 39 An alignment device for facilitating alignment of a telescopic component of a prosthesis according to any of claims 28 to 38.

40 An alignment device according to claim 39 adapted for engagement with the stem of a prosthesis according to any of claims 28 to 38.

41 An alignment device according to claim 40 comprising a recess formed in its axial end for engagement with a spigot formed at the distal end of the stem of a prosthesis according to any of claims 28 to 38.

42 An alignment device according to any of claims 39 to 41 configured for allowing a telescopic component of a prosthesis according to any of claims 28 to 38 to pass over the alignment device when the alignment device is in engagement with the stem of the prosthesis.

43 An alignment device according to any of claims 39 to 42 formed of a substantially rod shape.

44 A method of performing a hip replacement comprising surgically implanting the prosthesis according to any of claims 1 to 38.

45 A method according to claim 44 wherein the method is performed on an animal.

46 A method according to claim 45 wherein the animal is a human, canine, feline, rodent, bovine or equine.

47 A kit for a prosthetic hip comprising a hip prosthesis according to any of claims 1 to 38. 48 A kit according to claim 47 further comprising an alignment device according to any of claims 39 to 43.

49 A method of performing a hip replacement, comprising :- placing the femur and pelvis of a patient into a desired orientation; and drilling through the femur from the lateral cortex thereof.

50 A method according to claim 49, wherein the desired orientation is the neutral position.

51 A method according to claim 49 or 50, comprising:- inserting a reamer into a hole formed in the femur; and reaming the femoral neck and forming a surface on which the flange of a prosthesis according to any of claims 1 to 38 fits substantially flat.

52 A method according to claim 51, further comprising:- repeatedly reaming the femoral neck and checking the joint tension until a desired joint tension is achieved.

53 A method according to any of claims 49 to 52, comprising drilling through the femur into the pelvis, forming a recess in the pelvis.

54 A method according to claim 53, comprising drilling through from a point on the lateral cortex substantially level with the distal margin of the lesser trochanter.

55 A method according to claim 53 or 54, comprising drilling through the mid point of the resected neck of the femur, proximal to the calcar femorale.

56 A method according to any of claims 53 to 55, comprising fitting an acetabular cup having an apical spigot, the spigot locating in the recess. 57 A method according to any of claims 49 to 56, comprising fitting a hip prosthesis according to any of claims 1 to 38.

58 A method according to claim 57, when dependent upon a hip prosthesis according to any of claims 28 to 38, comprising aligning the telescopic component with an alignment device according to any of claims 39 to 43.

59 A hip prosthesis substantially as herein described and claimed.

60 An alignment device substantially as herein described and claimed.

61 A method substantially as herein described and claimed.

62 A kit substantially as herein described and claimed.