GB2434749A

GB2434749A - Hip prosthesis

Info

Publication number: GB2434749A
Application number: GB0602285A
Authority: GB
Inventors: Kamal Deep
Original assignee: HIP DYNAMICS Ltd
Current assignee: HIP DYNAMICS Ltd
Priority date: 2006-02-06
Filing date: 2006-02-06
Publication date: 2007-08-08
Also published as: GB0602285D0

Abstract

The prosthesis comprises a head component having a substantially hollow, part spherical cap 11, and a head mounting element 13, 14 disposed on the interior surface of the cap; wherein the head mounting element forms a tapered surface around the inner periphery of the cap, to promote stability of the head component when placed on a suitably prepared resected femur. Also disclosed is a socket component 30 having a complementary cup for receiving the cap of the head component and permitting articulated movement of the head component when it is received therein, and a socket mounting element 33 disposed on the exterior surface of the cup. A kit comprising a plurality of different sized head and socket components is also provided.

Description

HIP RESURFACING

Technical Field

This invention relates to hip resurfacing arthroplasty and thus concerns the restoration of the integrity and functionality of hip joints. In particular, the invention relates to the components for use in hip resurfacing arthroplasty procedures. * *

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Background of the Invention:*.... *.*

The concept of hip resurfacing arthroplasty has been around for a long time.

However, some major drawbacks of the conventional procedures include the surgical approach, the materials employed and the reliability of the design: features of the components used to replace the hip joint. a... * I S S. *

In the hip joint replacement field, two main arts may be delineated: on one hand is conventional hip replacement arthroplasty, where most of the femoral neck and the whole of the femoral head is cut and thrown away and is replaced with a prosthetic implant, with most of the stem part of the femoral implant being positioned in the upper shaft of the femur; on the other hand is bone preserving hip replacement, one particular type of bone preserving hip replacement being resurfacing hip replacement, in which event only the outer articulating portion of the femoral head is replaced with a resurfacing head implant. In the latter procedure, the whole of the neck and most of the head part of the upper femur is saved and the upper shaft of the femur is not violated. Hence, hip resurfacing arthroplasty would be considered the more favourable approach if its drawbacks and complications can be avoided.

In this regard, there are several drawbacks of the prevailing hip resurfacing designs in the market and in surgical practice. These include concerns about early and late stability of the components, the complication of femoral neck fracture and osteonecrosis of the femoral head.

A particular drawback of the acetabular component is that conventional peripheral press fit designs do not allow exact seating of the components on the relevant bone surfaces, without considerable forcible hammering. This * *

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type of hammering may damage the bone stock of the patient and/or damage the implant itself. :* The present designs are restricted by a size mismatch since the acetabular * size is dictated, in the available designs, by the femoral neck and head size. : If the anatomy of the hip being operated upon for replacement is not standard, as can happen often in the case of arthritic hips, the acetabulum being too shallow or too big for the neck and head size, then the surgeon has to abandon the resurfacing procedure in favour of conventional total hip replacement. This size mismatching may also affect the lubrication mechanism of the artificial hip joint, thus resulting in increased wear of the components and impaired function of the joint.

Further, there is no facility in the existing designs for altering the offset, which relates to the horizontal disposition of the femur, or the leg length.

This may be important for certain patients, like those with dysplastic hips.

In the current state of the art, the femoral components include a central post that is sited in the femoral neck and acts as a stress riser around its tip, thus predisposing the patient to neck fracture.

The currently available designs all use cemented femoral head components and cement can cause thermo necrosis of the head of the femur, thus contributing to the osteonecrosis and femoral neck fracture. * *

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Presently available femoral head and acetabular hip resurfacing components:.

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are machined from metallic materials, mostly cobalt-chrome. Metal on metal articulation has an incidence of wear as well and the major drawback of the release of metal ions into the body. The long-term consequence of this is, as: yet, unknown and could be dangerous in that metal bearings can have a systemic, end-organ and mitotic effect. * In addition, the instrumentations commonly used for the procedure are difficult and not all the surgeons find them comfortable to work with. The surgical approach to the hip joint also poses questions. The approach itself is usually bigger and more difficult than for conventional total hip replacement, and can contribute to the already jeopardised vascularity of the head, leading to osteonecrosis.

It is therefore an aim of the present invention to provide improved components for use in hip resurfacing arthroplasty procedures.

It is also an aim of the present invention to provide hip joint resurfacing components that can increase surgical versatility and proficiency in bone-conserving hip resurfacing procedures.

It is another aim of the present invention to provide improved postoperative results following hip resurfacing and to decrease the complications by employing better designed components. * .

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It is yet another aim of the invention to utilise an improved bearing surface * material in hip resurfacing arthroplasty components. *

Further aims hereof are extant. : .. *0S5 * S

* ** S *

Statements of the Invention S:

In accordance with a first aspect of the present invention there is provided a head component for use in hip resurfacing arthroplasty, the head component comprising: a substantially hollow, part spherical cap, and a head mounting element disposed on the interior surface of the cap; wherein the head mounting element forms a tapered surface around the inner periphery of the cap, to promote stability of the head when placed on a suitably prepared resected femur.

The advantage of this head component is that it provides both immediate and on-going stability of the joint, in use. It also allows for easier and more accurate positioning of the head component on the resected femur, without requiring forceful hammering which may damage the component and/or the bone.

Preferably, the head component also comprises a support post depending from the interior surface of the cap or head mounting element.

Preferably, the head mounting element further comprises a substantially planar surface, for seating the head component on the suitably prepared resected femur. * 3

*****.

Preferably, the head mounting element further comprises a substantially ** curved surface, to provide a generally smooth transition between the tapered surface and the planar surface. This feature also helps to prevent stress risers. **. a * * ****

* S 53 Preferably, the head mounting element is porous and/or coated with a bone.. : inducing substance to promote bony in-growth and fix the head component to the resected femur, in use.

This has the advantage that cement does not need to be employed, and its attendant drawbacks, like thermo necrosis of the head of the femur, are overcome.

Preferably, the bone inducing substance is hydroxyapatite.

Alternatively, the head mounting element may be grooved for use with cement.

Preferably, the cap is made from a ceramic material. More preferably, the cap is made from corundum ceramic.

Use of ceramic as a bearing surface is advantageous in that it suffers from less wear than a metal bearing surface, and does not result in the release of potentially harmful metal ions into the body.

Alternatively, the cap is made from a metal or other materials including but not restricted to tantalum, alloys, biologically active substances or artificially grown cartilage, bone cartilage composites, prepared from cell cultures.

Optionally, the head component further comprises a neck rod, attached to support post.

S S S...

The neck rod may be employed to stabilise the neck and prevent future neck.. : fracture due to augmentation of bone in the neck region, by bony in-growth into the neck rod. Also it will act as a stabilising fixing device in case the fracture happens. The outer surface of the rod is porous coated and/or coated with hydroxyl apatite or other bone inducing substance.

In accordance with a second aspect of the present invention there is provided an implant for use in hip resurfacing arthroplasty, the implant comprising: a head component having a substantially hollow, part spherical cap, and a head mounting element disposed on the interior surface of the cap; and a socket component having a complementary cup for receiving the cap of the head component and permitting articulated movement of the head component when it is received therein, and a socket mounting element disposed on the exterior surface of the cup; wherein the head mounting element forms a tapered surface around the inner periphery of the cap, to promote stability of the head when placed on a suitably prepared resected femur.

Preferably, the socket mounting element includes projections, to promote stability in the interface between the socket component and bone, when in use. *

S.....

Preferably, the projections are in the form of spikes, wedges, steps, ridges or pegs. *. * * S S

Preferably, the projections are disposed on only a portion of the socket S...

mounting element, to help with accurate positioning in the acetabulum. S... * S S * S

Alternatively, the projections are disposed across substantially on the whole of the socket mounting element.

Preferably, the socket mounting element is porous and/or coated with a bone inducing substance to promote bony in-growth and fix the acetabular component to the prepared bone surface of the acetabulum.

Preferably, the bone inducing substance is hydroxyapatite.

Alternatively, the socket mounting element may be grooved for use with cement.

Preferably, the socket mounting element includes holding means. More preferably, the holding means comprises opposed notches or slots on the outer aspect of the socket mounting element.

Preferably, the cup is made from a ceramic material. More preferably, the cup is made from corundum ceramic.

Alternatively, the cup is made from a metal or other materials including but i....

not restricted to tantalum, alloys, biologically active substances or artificially *:::* grown cartilage, bone cartilage composits, prepared from cell cultures. * . S

In accordance with a third aspect of the present invention there is provided a S...

modular kit for use in hip resurfacing arthroplasty, the kit comprising: a S...

plurality of head components and a plurality of socket components, wherein.. : each head component comprises a substantially hollow, part spherical cap, of a certain diameter, and a head mounting element, of a particular thickness, or set of thicknesses, disposed on the interior surface of the cap; each socket component comprises a cup of a corresponding diameter, for receiving the cap of one of the head components and permitting articulated movement of the head component when it is received therein, and a socket mounting element, of a particular thickness, or set of thicknesses, disposed on the exterior surface of the cup; and wherein, the kit comprises a plurality of head components, with a range of caps of different certain diameters, and for each cap of a certain diameter, there is a plurality of head components with a range of head mounting elements, of a different particular thickness, or set of thicknesses; and plurality of socket components, with a range of cups for receiving different certain diameter caps, and for each cup corresponding to a certain diameter of cap, there is a plurality of socket components with a range of socket mounting elements, of a different particular thickness, or set of thicknesses.

The advantage of the modular kit is that corresponding cup and head sizes can be selected so that there is a constant clearance margin between the two bearing surfaces, regardless of the size of the head or acetabulum into which the components are to be implanted. In other words, the availability of:....

mating head and cups, with respective different sized mounting elements, *".

ensures good size matching. The resulting constant clearance margin also ensures proper lubrication in the joint at all times with resultant decrease in * , wear and improved hip function. S...

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Also, the availability of different mounting element thicknesses, facilitates.. : altering the offset, or the horizontal disposition of the femur, as well as allowing leg lengthening, without impacting upon the functionality of the joint. Implants of this type may therefore be of particular importance for patients with dysplastic hips.

Preferably, the head components in the kit also comprise support posts depending from the interior surface of the cap or head mounting elements.

Optionally, the kit according to the third aspect of the invention, further comprises a plurality of different sized neck rods, for attachment to a support post of a head component.

Brief Description of the Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation showing a cross section of a particular head component according to the present invention.

Figure 2 is a schematic representation of the side view of an optional neck rod according to the present invention. :...:. S...

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Figure 3 is a schematic representation showing a cross section or coronal section of a particular socket component, according to the present invention. S...

Figure 4 is a superior view from above, of the socket component shown in * S...

Figure 3, showing a possible arrangement or combination of projecting.. : spikes.

Figure 5 is an underside view of the socket component of Figures 3 and 4, showing a possible arrangement of holding means in the form of opposed notches/slots.

Detailed Description of the Invention

The present invention is based on the development of components for use in treating arthritis of the hip joint, among other things. It provides a bone conserving or bone preserving arthroplasty solution.

Accordingly, the components of the present invention can be used to treat arthritis of the hip in a patient. In practice, this may be performed by -11 -approaching the diseased hip joint, with the surgeons preferred approach, removing the diseased surface of the bone and replacing this with the components described herein.

The term "patient" refers to patients of human or other mammal and includes any individual it is desired to examine or treat using the components of the present invention. However, it is understood that "patient" does not imply that symptoms are present. Suitable mammals that may benefit from use of a..

the present invention include but are not restricted to, primates, livestock animals, laboratory test animals, companion animals (eg. cats and dogs) and captive wild animals. a..

Aspects of the present invention include: . S

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1. A head component 10, with a ball cap 11, spherical in outer section, with an open bottom end 12, to allow placement on a prepared femoral head stump (not shown). As can be seen from Figure 1, a taper 13 is built into the design of the inner surface to provide immediate stability upon mounting.

2. A head wall or head mounting element 14, extends with a minimal thickness in all or parts of the head component 10.

3. The inner design of the head component 10 is configured to seat on the top flat surface of a prepared femoral head. The head mounting element 14 then curves down on the side wall of the cap 11 to the inner built in taper 13 distally. The taper 13 gives initial and late stability and the curve prevents any stress risers.

4. An optional central neck rod 20 is shown in Figure 2, the length of which can be varied. This can be attached to the central head post 15, which can pass distally into the neck of a femur, passing from medial to lateral from the -12 -femoral head to the neck up to or piercing the lateral femoral wall. The rod can be screwed or attached onto a central bore or post 15 of the said head component 10, if it is required by the surgeon. Thus this is an optional item.

5. The inner surface of the head 10 can be porous and/or can be coated/applied with bone inducing substance such as hydroxyapateite or ceramic, for an uncemented version. It can be grooved and smooth and/or rough for a cemented version.

6. A head-receiving articular cup or socket component 30, having an * articular surface or cup 31 and a mountable back surface or socket mounting * element 32, the articular surface 31 of which, when the head-receiving cup (or acetabular component) 30 is suitably mounted in the bone of the acetabulum, mates in articulating, leading to fluid film lubrication with the S...

smooth external surface 11 of the head component 10, when it is suitably.. S..,

mounted in the receiving stock of the femur. The clearance margins between.. : the bearing surfaces of the components 10, 30 are constant irrespective of the sizing of the components 10, 30 involved. The thickness of the wall or socket mounting element 32, of the socket component 30 may vary.

7. Both components 10, 30 will have modifications for cemented and/or uncemented fixation to suitable bone stock.

8. The bone cup interface stability may be achieved by mechanical means which may include press fit, wedges 33, spikes, steps, groves, porous surface, variously shaped spikes of different dimensions, pegs etc arranged in various configurations an various heights on variable or all of the socket mounting surface 32 of the socket component 30. It can also get stability by chemical means like adhesive substances and/or biological means like coating or application by various methods of different substances,tissues and/or cell -13 -cultures/moulds which may induce, conduce or provide a scaffold for bone growth on to the socket component 30.

9. The materials used in the socket 30 and head 10 components may vary.

10. It may be that the ceramic material used in the resurfacing arthroplasty described herein is corundum ceramic, which has the properties of biological compatibility, chemical immunity to biological fluids, high adhesion to osseous tissue, high compressive strength and easy sterilisability. In addition, due to the nature of the material, there is a possibility of varying the:...:.

pore structure across the dimensions of the material such that one end can be SI.

porous or soft to enable bone in-growth and the other hard to enable smooth articulation. Thus the components 10, 30 may be formed from ceramicised..

metal or ceramic coated metal, with ceramic bearing surfaces 11, 31. S..

Alternatively, fully ceramic components 10, 30 may be produced which have.... S...

smooth bearing surfaces 11, 31 and porous mounting elements 14, 32, to.. : promote bony in-growth.

11. In the present invention other materials including but not restricted to various metals, polyurethanes, gels, polyethylene in various forms, ceramics alone or in combination, and other substances may be used. These may vary in thickness on the components.

Significantly, by the present invention, problems in the art are ameliorated if not overcome, with one, more or all of the aforementioned aims being satisfied. Among its advantages, the present invention allows for noticeably increased versatility and efficiency in surgical procedures, as the proper components 10, 20, 30 can be mixed and matched with the physical needs of the patients in mind. The invention, as well, with the surgeon able to so mix and match components 10, 20, 30, provides for a more economical system -14 -with respect to manufacture and materials utilization. Of great significance, corundum ceramic material is now beneficially adapted for employment in the fabrication of femoral resurfacing implants for resurfacing arthroplasty.

In relation to metal, the corundum ceramic has a much lower coefficient of friction with particular respect to an articulating surface, and as a consequence, arthroplasties may be made to be more successful and longer lasting. Numerous further advantages attend the invention. * *...

Referring to the drawings, a head component 10, according to the present *.

invention, is shown in Figure 1. This particular head component 10 may be implanted with or without the use of cement.

In Figure 1, NXPYO is a part of a sphere of centre C, which forms the cap....

11 bearing surface. NO denotes the neck diameter 12. AB is less than NO.. : making it a taper 13 design. EFGH is the central head post 15. The wall or head mounting element 14 thickness may or may not be uniform.

The neck diameter 12 determines the head 10 size. In a particularly preferred embodiment, the head 10 and articulating acetabular component 30 have a constant clearance margin, thus ensuring desired lubrication at all times.

In another preferred form, the wall 14 thickness especially at the proximal end or other part of the head 10 can be varied thus enabling the present invention to cope well with size mismatch and also ensuring a constant clearance margin thereby obviating the need to resort to total hip replacement as is the case in the current state of the art, when size mismatch is present.

-15 -In a particularly preferred form, the undersurface of the head 10 contains a post EFGH, 13 of variable length and dimension, which has within it a suitable mating mechanism, either a screw type, female slot or spring loaded clip or any combination or type of mating mechanism within which can be received or placed the opposite matching part of the mechanism which in turn is part of the optional central neck rod 20 (shown in Figure 2) which extends from the undersurface of the head component 10 to the lateral wall of the i...:.

femur in varying lengths and dimensions. The central neck rod 20 may or may not be coated with a bone inducing substance or growth factor in order to encourage bone in-growth and thus augment femoral neck bone stock and * prevent or decrease the risk of neck fracture thus obviating the need for further surgery or revision. It will also stabilize the fracture automatically if it were to happen. .. : Features of the femoral head 10 design include the following: 1. The taper 13 of the inner walls 14 of the head 10, which allow for seating on an adequately prepared femoral bone stock. The taper 13 design allows for immediate stability of the femoral head component 10 as well as long term stability.

2. Uncemented femoral head 10 design, wherein the undersurface 14 of the femoral head 10 can be impacted or placed onto suitable femoral bone stock without the use of cement. Initial stability may also be provided for by porous coating and/or coating/application by any method, the inner surface 14 with hydroxyl apatite and/or any other bone inducing substance. In another preferred form the undersurface 14 may be patterned or grooved in -16 - any combination and with variable porosity to allow for optimum bone in-growth.

3. In a particularly preferred embodiment the femoral head 10 design allows for increase of offset by varying the thickness of the (metal) cross section 14 thus allowing for increasing the neck length and leg length and offset if required. This feature may be useful when dealing with patients with certain disease conditions for example DDH or Developmental Dysplasia of the Hip, where the neck may be shortened.

4. In a cemented embodiment, the inner surface 14 is grooved for cement * extrusion. The grooves may follow any combination to ensure adequate and efficient cement extrusion. *. :* 5. The curved sections MI and KL of the head mounting element 14 are used to avoid any stress risers in the transition of wall 14 thickness to taper S...

13 from the top flat surface. This is new as the presently available designs in ** : the market use a bevel with sharp edges which can act as stress risers.

6. The presence of a constant clearance margin at all times between the acetabular socket component 30 and femoral head components 10, due to the ability of the socket and head mounting element 14 wall thickness to be varied. This will ensure desired lubrication and or fluid film lubrication.

7. An optional central neck rod 20, which passes distally into the neck of the femur, passing from medial to lateral from the femoral head to the lateral wall of the femur which it may or may not pierce.

8. A ceramicised or metal backed ceramic articulating surface 11, which will allow low friction, fluid film lubrication and decreased wear thus bypassing the complications of metal ions present in the current state of the art.

-17 - 9. In the composition of the wall 14, it may be made of single or double or triple layers, the thickness of which may vary. The constituent substance used for these layers may be the same or different in the same head 10. These substances can be bonded/stuck/ingrained/joined/sprayed/glued to each other by various manufacturing techniques.

10. These substances may be metallic, non metallic or ceramics or others including but not restricted to physical elements, alloys, chemical elements or biological forms.

11. The substances used may be Magnetic Resonance Scan friendly, thus * allowing to evaluate the vascularity of the head 10, which is not possible in the currently available designs.

A socket component 30, according to the present invention, is shown in **

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Figures 3, 4 and 5. In Figure 3, XYZ is a part of a sphere of centre C. In.. : the particular example shown in Figure 5, there are four equally spaced slots or notches 34 on the outer rim of the socket mounting element 32. These are provided to aid handling and placement of the socket component 30, in use.

The acetabular cup 31 may be cemented in place or seated uncemented in suitable prepared bone stock of the acetabulum. If uncemented, the outer bone interface surface, or socket mounting element 32, may or may not have a porous coating and/or a coating/application, by any method, of a hydroxy apatite or any other bone inducing substance. In a preferred form the outer surface 32 may be patterned or grooved in any combination and/or with variable porosity to allow for optimum bone contact and in-growth.

-18 -For the cemented version, the outer socket mounting element 32 surface may be smooth or covered with grooves or steps or ridges of various shapes sizes, configurations and distribution to optimize the cement bonding.

For the uncemented version as well, for initial stability, wedges 33, steps, grooves or ridges or jump spikes of various shapes, sizes, configurations, and distributions may be employed to optimize the stability. * *

* I.. **

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In another preferred form the outer bone interface surface 32 may be covered with a quadrant of spikes 33, as shown in Figure 4, which preferably are to be inserted in the postero superior quadrant, which is the thickest part of * * acetabular bone stock in most cases. * S *5SS S...

In yet other preferred forms the spikes or protuberances 33, which may be: shaped variably including but not restricted to conical, pyramidal, wedge, tubular, tapered etc, may cover the outer surface of the socketcomponent 30 in any variety of shapes, permutations or divisions of the whole. Various combinations and subcombinations of features may be practiced, in accordance with the present invention.

The spacing between the spikes or protuberances 33 may be in any combination or subcombination.

The height of the spikes or protuberances 33 may also vary in any combination or subcombination and may increase or decrease with or without reference to other permutations and combinations of the present invention.

-19 -The spikes 33, preferably allow the acetabular cup 31 to be accurately positioned wherein the socket component 30 is tilted in spikes 33 first and when an adequate position or hold is established may or may not be hammered in order to ensure adequate seating within the acetabular cavity.

Features of the acetabular cup 30 design include the following: 1. Size mismatch between the femoral 10 and acetabular 30 components can be resolved with the present invention by varying the thickness of the...:. S...

acetabular wall 32 or the femoral head component wall 14. S 2. There is a range of matching sizes to allow for a constant clearance margin between the acetabular cup 31 and the femoral head cap 11 to ensure.: desired lubrication.

3. The presence of spikes 33 or other features may improve the initial a a.

biomechanical stability and allow proper and accurate seating of the..

acetabular implant 30 in the receiving bone stock.

4. A ceramicised or metal backed ceramic articulating surface 31, which will allow low friction, fluid film lubrication and decreased wear thus bypassing the complications of metal ions present in the current state of the art.

5. In the composition of the wall 32, it may be made of single or double or triple layers, the thickness of which may vary. The constituent substance used for these layers may be the same or different in the same cup. These substances can be bonded/stuck/ingrained/joined/sprayed/glued to each other by various manufacturing techniques.

6. These substances may be metallic, non metallic or ceramics or others including but not restricted to physical elements, alloys, chemical elements or biological forms.

-20 - 7. The substances used may be Magnetic Resonance Scan friendly, thus allowing to evaluate the vascularity of the head, which is not possible in the currently available designs

EXAMPLE

I-lip Resurfacing Arthroplasty -Ceramic on Ceramic Bearing Surfaces.

Uncemented Use. :...:. S... * S *

A patient is positioned in a lateral position and secured safely; however, an alternative position may be used. A pelvic holder may be employed. Parts are cleaned and draped. S.. * *.S. S..

A posterior approach or any other approach to the hip joint may be used by: conventional or minimally invasive methods. The hip joint is reached and dislocated.

The next step is to size the femoral head. A special guide pin centralising neck sizer is used for this step. The head diameter to be used is determined from maximum neck diameter and an approximate idea of the acetabular cup diameter is taken here from.

At this point, attention is switched to the acetabulum and osteophytes removed according to surgeon preference in order that the entire acetabular rim is visualised. At this stage, the true floor of the acetabulum is revealed by adequate clearance of soft tissue and reaming any remaining cartilage by -21 -successively sized reamers to the ideal acetabular size, taking care not to breach the walls.

Following reaming, an assessment of cup size is made using trial cups provided in the kit. Reaming is to a similar size as the intended acetabular component 30 or 1 mm less, as a line to line fit or press fit is aimed for. A specially designed cup holder is used-to mount the trial cup and place it in the desired position. The trial cup should be firm in the acetabulum. S...

S S *..

Remove the trial cup and wash out the acetabulum and dry thoroughly.

Prepare the quadrant of spikes if using them, using a specially designed spike: preparation handle. Ensure that the quadrant of spikes is positioned in the thickest aspect of the acetabular wall -usually in the postero superior quadrant. If using the cement or other type of cup it should be placed accordingly.

Mount the cup 30 onto the cup holder and ensure the cup is held securely at its notches 34. With the pelvis orientated in the true lateral position the cup is placed/impacted in the correct orientation. Confirm this by observing full cup to bone contact and previous mark made during use of the trial cup.

Remove the cup holder. Test the firmness of the cup 30 fit and assess cup 30 orientation.

Attention is now turned to the femur. A central neck pin is placed with help of at least two centralising pin sizers, used perpendicular to each other. Three or four of these can be used to ensure exact central pin placement. Thus the central guide wire is drilled in place. If the guide pin position, depth and -22 -version is satisfactory, a cannulated drill is used to over drill the guide wire to the depth indicated for the chosen head. At this point the decision is made whether or not to incorporate the neck rod system 20. A different depth is indicated if the neck rod system 20 is being used. The cannulated guide rod is then inserted up to the required depth. If the position of the central pin is not up to satisfaction and margins are not clear as checked by a margin assessor, then with a special instrument the guide wire position can be changed very easily.

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The desired head 11 size is dialled into a guarded taper cut femoral head reamer which is slowly advanced over the guide rod as far as the head neck: junction. The femoral neck will not be notched due to a built in guard. Use 5..

swabs to prevent any debris from entering the soft tissue. The all in one reamer is used to prepare the head and neck. Now remove the guide rod.

Use the correct sized head template to check the correct fit and shape. Mark the head edge position on the neck with a sterile pen or diathermy. This will act as a depth mark for the resurfacing head and confirm when fully seated.

The selected femoral head 10 is now placed/impacted or cemented depending on the type being used.

The joint is washed thoroughly. The hip is reduced taking great care to reduce the components 10, 30 cleanly without scraping the head 11 on the cup 31 rim. Perform a full check to ensure that there is no entrapment of soft tissues and that the range of movement and stability is satisfactory.

-23 -Follow the preferred method to re-attach capsule, tendons and muscular structures and suture the fascia and fat and skin layers, inserting a drain if desired.

Postoperative rehabilitation involves following the standard protocols.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood, and persons skilled in the art will appreciate, that only the preferred embodiments have been presented and that all changes, modifications and further applications:..

that come within the spirit of the invention, are desired to be protected.

Various combinations and subcombinations and features may be practiced with or without reference to other combinations, subcombinations and/or features, alone or in combination, in the practice of the invention, and, moreover, numerous further adaptations and modifications can be effected within its spirit, the scope of which has been described herein.

Claims

CLAIMS: I. A head component for use in hip resurfacing arthroplasty,

the head component comprising: a substantially hollow, part spherical cap, and a head mounting element disposed on the interior surface of the cap; wherein the head mounting element forms a tapered surface around the inner periphery of the cap, to promote stability of the head component when placed on a suitably prepared resected femur.

2. A head component according to claim 1 further comprising a support post depending from the interior surface of the cap or head mounting element.

3. A head component according to either preceding claim wherein the head mounting element further comprises a substantially planar surface, for seating the head component on the suitably prepared resected femur.

4. A head component according to claim 2 wherein the head mounting element further comprises a substantially curved surface, to provide a generally smooth transition between the tapered surface and the planar surface.

5. A head component according to any preceding claim wherein the head mounting element is porous and/or coated with a bone inducing substance to promote bony in-growth and fix the head component to the resected femur, in use.

6. A head component according to claim 5 wherein the bone inducing substance is hydroxyapatite.

7. A head component according to any of claims 1 to 4 wherein the head -2S mounting element is grooved for use with cement.

8. A head component according to any preceding claim wherein the cap is made from a ceramic material.

9. A head component according to claim 8 wherein the cap is made from corundum ceramic.

1 ft A head component according to any of claims 1 to 7 wherein the cap is made from a metal.

11. A head component according to any of claims 1 to 7 wherein the cap is made from a material comprising tantalum, an alloy, a biologically active substance or artificially grown cartilage or bone cartilage composite prepared from cell culture.

12. A head component according to claim 2 further comprising a neck rod attached to the support post.

13. A head component according to claim 12 wherein the outer surface of the rod is porous coated and/or coated with hydroxyapatite or other bone inducing substance.

14. An implant for use in hip resurfacing arthroplasty, the implant comprising: a head component having a substantially hollow, part spherical cap, and a head mounting element disposed on the interior surface of the cap; and a socket component having a complementary cup for receiving the cap of the head component and permitting articulated movement of the head component when it is received therein, and a socket mounting element disposed on the exterior surface of the cup; i wherein the head mounting element forms a tapered surface around the iimer periphery of the cap, to promote stability of the head component when placed on a suitably prepared resected femur.

15. An implant according to claim 14 wherein the socket mounting element includes projections, to promote stability in the interface between the socket component and bone, when in use.

16. An implant according to claim 15 wherein the projections are in the form of spikes, wedges, steps, ridges or pegs.

17. An implant according to claim 15 or 16 wherein the projections are disposed on only a portion of the socket mounting element, to help with accurate positioning in the acetabulum.

18. An implant according to claim 15 or 16 wherein the projections are disposed across substantially on the whole of the socket mounting element.

19. An implant according to any of claims 14 to 18 wherein the socket mounting element is porous and/or coated with a bone inducing substance to promote bony in-growth and fix the acetabular component to the prepared bone surface of the acetabulum.

20. An implant according to claim 19 wherein the bone inducing substance is hydroxyapatite.

21. An implant according to any of claims 14 to 18 wherein the socket mounting element is grooved for use with cement. *11

22. An implant according to any of claims 14 to 21 wherein the socket mounting element includes holding means.

23. An implant according to claim 22 wherein the holding means comprises opposed notches or slots on the outer aspect of the socket mounting element.

24. An implant according to any of claims 14 to 23 wherein the cup is made from a ceramic material.

25. An implant according to claim 24 wherein the cup is made from corundum ceramic.

26. An implant according to any of claims 14 to 23 wherein the cup is made fromametal.

27. An implant according to any of claims 14 to 23 wherein the cup is made from a material comprising tantalum, an alloy, a biologically active substance or artificially grown cartilage or bone cartilage composite prepared from cell culture.

28. A kit for use in hip resurfacing arthroplasty, the kit comprising: a plurality of head components and a plurality of socket components, wherein each head component comprises a substantially hollow, part spherical cap, of a certain diameter, and a head mounting element, of a particular thickness, or set of thicknesses, disposed on the interior surface of the cap; each socket component comprises a cup of a corresponding diameter, for receiving the cap of one of the head components and permitting articulated movement of the head component when it is received therein, and a socket mounting element, of a -..

particular thickness, or set of thicknesses, disposed on the exterior surface of the cup; and wherein, the kit comprises a plurality of head components, with a range of caps of different certain diameters, and for each cap of a certain diameter, there is a plurality of head components with a range of head mounting elements, of a different particular thickness, or set of thicknesses; and plurality of socket components, with a range of cups for receiving different certain diameter caps, and for each cup corresponding to a certain diameter of cap, there is a plurality of socket components with a range of socket mounting elements, of a different particular thickness, or set of thicknesses.

29. A kit according to claim 28 wherein the head components further comprise support posts depending from the interior surface of the cap or head mounting element.

30. A kit according to claim 29 further comprising a plurality of different sized neck rods, each configured for attachment to a support post of a head component.

31. A head component substantially as hereinbefore described with reference to Figure 1.

32. An implant substantially as hereinbefore described with reference to Figures 1 and 3 to 5.

33. A kit substantially as hereinbefore described with reference to Figures 1 and 3 to 5.