GB2551155A

GB2551155A - Prosthesis

Info

Publication number: GB2551155A
Application number: GB1609942.6A
Authority: GB
Inventors: Alan Bird Timothy; Clive Taylor Andrew; Nicholas Collins Simon; Anthony Tuke Michael
Original assignee: MatOrtho Ltd
Current assignee: MatOrtho Ltd
Priority date: 2016-06-07
Filing date: 2016-06-07
Publication date: 2017-12-13
Also published as: GB201609942D0; WO2017212243A1

Abstract

An acetabular cup comprising inner 14 and outer 12 surfaces, defining a rim 16 including a non-sacrificial protruding formation 34, presenting a female engagement formation 18, which is preferably radially inwardly facing. The formation 18 may engage with a liner, preferably a polymeric or EPW (extended posterior wall) liner, or an impaction cap or introducer tool, which may be part of a kit. Surface 14 may transition to rim 16 by a rounded, angled or bevelled shoulder region 44, preferably at an angle of 25°- 60° (for example 50°). The formation 34 may be an extension of surface 12, extending around the circumference of the cup, and have a first surface 40, defining the engagement formation 18, and as second surface 42 terminating in a rounded, bevelled or angled region 46, preferably with an angle of 25°- 60° (for example 50°). The width of the female engagement opening 36 may be 0.2mm-2mm, preferably 0.8mm. The thickness of portion 34 may be 0.2mm-2mm, preferably 0.9mm. There may be a bulge 38, in the order of 0.5mm. There may be formations to prevent liner rotation. The cup may be non-metallic, preferably ceramic, and have a mono-block, homogenous structure.

Description

Prosthesis

The present invention relates to a prosthesis. More particularly, it relates to an acetabular hip prosthesis.

The efficient functioning of the hip joint is important to the well-being and mobility of the human body. Each hip joint is comprised of the upper portion of the femur which terminates in an offset bony neck surmounted by a ball-shaped portion, known as the femoral head, which rotates within the acetabulum of the pelvis. Diseases such as rheumatoid- and osteoarthritis can cause deterioration and erosion of the cartilage lining of the acetabulum so that the femoral head and the hip bone rub together causing pain and further erosion. Bone erosion may cause the bones themselves to attempt to compensate for the erosion which may result in the bone becoming misshapen.

Operations to replace the hip joint with an artificial implant are weli-known and widely practiced. Generally, the hip prosthesis wiil be formed of two components, namely: an acetabular component which lines the acetabulum; and a femoral component which replaces the femoral head. The femoral component may be total femoral head replacement in which the component includes a head, and a stem and a neck connecting the head to the stem. In use the stem is inserted into the medullary canal of a prepared femur. Alternatively, where appropriate, the femoral head component may be a resurfacing prosthesis which is attached to a suitably machined femoral head. This resurfacing arrangement does not invade the medullary canal and is generally more bone conserving.

In an operation to insert a prosthetic acetabulum into a patient's pelvis the surgeon first uses a reamer to cut a cavity in the patient's pelvis. An acetabular cup is then inserted into the cavity. Normally, it is desirable to retain as much of the original healthy bone surface as possible.

Once the acetabulum has been prepared, the acetabular cup prosthesis can be inserted, in one arrangement, the acetabular cup prosthesis may be fabricated from polyethylene. These cups are general cemented into the acetabulum and require only light pressure to seat them in the bone cement which is used to fix the prosthesis in position. Generally, polymethylmethacrylate bone cement is used.

One alternative type of acetabular cup prosthesis has a polyethylene finer for articulation with the femur and a metai shell in which the liner sits which is inserted into the pelvic cavity. The shell is first located in the acetabulum and the liner is then placed in the shell. The metai shell may be implanted without cement such that it relies on a jamb fit between the metal shell and the patient’s acetabulum to provide primary fixation. However, in some arrangements, screws may be used to secure the cup shell in position in the pelvis before the liner is placed in position. The insertion of the metal shell into the pelvis requires considerable force. As the surgeon applies this force, there is a risk that the metal shell can become damaged or deformed. There is also a possibility that during the application of the force, the shell may move so that it is not in the optimum alignment in the acetabulum. Often the metal shells have outer surfaces or coatings which encourage bone to grow into them over time; this biological fixation is often referred to as secondary fixation.

With this type of prosthesis, the polyethylene liner unit is generally snapped or screwed into the metal shell after the metal shell has been seated in the acetabulum. Thus the inner surface of the liner forms the socket part of the joint.

More recently, ceramics have been used as an alternative to the plastics liner as historically the use of plastic liners has created wear debris during use leading to some bone death such as osteolysis. In this arrangement, the metal shell is inserted into the pelvis and the ceramic liner is then inserted into the shell. However, as discussed in EP2174621 there are problems associated with the insertion of this ceramic liner and in achieving an accurate fit between the liner and the cup. There have therefore been suggestions of using preassembled acetabular cups with ceramic liners whereby it is the combination of the cup and liner which is inserted into the acetabulum.

There has also been a suggestion that the cups should be made substantially completely from ceramic, that is to say that the cups do not require a metal shell or they have a metal shell which is sufficiently thin that it cannot support being introduced separately into the pelvis. However, the use of a ceramic acetabular hip prosthesis may suffer from various disadvantages. In particular, the ceramic, which is either unsupported by a shell or only has a thin shell, may not have sufficient strength to withstand the rigours of insertion and the ceramic may fail from brittle fracture.

One proposal for addressing this by strengthening the rim of the ceramic acetabular cup is described in EP2174621 in which the prosthesis comprises an acetabular cup which is preferably formed from a ceramic and a metal band is applied around the outer circumference of the acetabular cup prosthesis and adjacent to the rim. The presence of the metal band provides additional strength to the ceramic prosthesis and holds it in hoop compression enabling it to be inserted in the acetabulum.

Whatever the composition and configuration of the acetabular cup prosthesis, an insertion tool is generally required to facilitate the insertion and correct positioning of the prosthesis in the pelvis. Cups which rely solely on a jamb fit with the bone require a greater force to be applied via the insertion tool than is the case with cemented polyethylene cups. This force is primarily to direct impact into the acetabulum but force may also be applied to adjust the angular position of the cup or to remove it if it has been position incorrectly.

In order to ensure that the required forces are accurately and safely applied to the cup, it is generally necessary that the insertion tool positively grips the cup. However, it is also important that the means by which the tool grips the cup does not impinge upon the outside of the cup in order that the tool does not become trapped between the shell and the pelvic bone. Further, as the wall thickness of the shell is generally kept to a minimum to minimise bone loss, the tool cannot generally grip the wall. Insertion tools are therefore usually designed so that their interaction with the acetabular cup does not negatively impact on the subsequent function of the acetabular hip prosthesis and its interaction with the pelvis. Further, it is general good practise to avoid gripping the internal surface of the cup as doing so could damage the bearing surface and also affect the wear performance of the prosthesis.

One means for connecting the acetabular cup prosthesis to an insertion tool is described in GB2323036. In the described arrangement, a cable is attached to the prosthesis and this is then used to connect the prosthesis to the tool. Once the prosthesis is located in the desired position, it may be necessary to cut the cable so that the tool and the prosthesis can be separated.

In an alternative arrangement, such as that described in EP1634552, an impaction cap is connected to the prosthesis by cables and the insertion tool then connects to the impaction cap. An alternative impaction cap system is described in EP1721586.

Other suggestions for enabling insertion tools to be connected to acetabular cup prostheses are described in, for example, US4677972, US590488, US5904688, US2004/0186586, and WO2014/108540.

Accordingly, while it is important when preparing/inserting an acetabular cup prosthesis to achieve a reliable and mechanically strong/sound connection between the cup and an introducer tool, or any acetabular liner, it is also an important requirement of any such engagement formation provided for such purpose in the cup does not in any way interfere with the functional requirements of the cup once in place.

Known arrangements for providing such engagement formations and in a manner not to impact on the subsequent deployment of the acetabular cup prosthesis are disadvantageously limited.

It is desirable to provide an arrangement which allows for the practical use of acetabular cup prosthesis which have thin wails and/or which are made of materials such as ceramic which can be damaged during the forces required for impaction. It is also desirable to provide a prosthesis which can readily co-operate with an insertion tool. In is further desirable to provide an acetabular cup prosthesis which provides two or all of these requirements.

It is now proposed that some or all of these problems may be addressed by the use of an acetabular cup prosthesis having a rim from-which protrudes a non-sacrificial formation configured to present an inwardly, or outwardly, facing female engagement formation.

The engagement formation in particular may be utilised to enable interaction with an introducer tool or an impaction cap, or indeed any required form of liner.

Thus according to one aspect of the present invention there is provided an acetabular cup prosthesis comprising an inner cup surface, an outer cup surface, and a rim between the said inner cup surface and the said outer cup surface, the said rim including a non-sacrificial protruding formation configured to present a radially inwardly, or radially outwardly, facing female engagement formation of the cup.

The invention is advantageous insofar as reliable and mechanically strong/sound engagement between an acetabular cup prosthesis and a secondary element such as a liner or introducer tool can be provided and which can offer the required strength and reliability of connection between such a wide variety of elements irrespective of the material from which the cup is formed. A particular advantage therefore is that the acetabular cup prosthesis of the present invention can be formed from ceramic and, if required, can comprise a ceramic acetabular cup prosthesis arranged for engagement with a polymeric rescue liner. in one configuration, the inner cup surface of the acetabular cup prosthesis is arranged to transition to a surface of the rim by way of a shoulder transition region. So as to prevent any potential interference of surfaces of the acetabular cup prosthesis during use, the said transition region can advantageously be shaped so as to prevent such interference but without compromising the strength of the engagement formation.

In one example, the transition region can be formed as a rounded region although alternative arrangements can comprise an angled, or bevelled, region.

Should the transition region be angled, or bevelled, so as to prevent a substantially flat surface, said surface can be arranged to extend at a typical angle in the range of 25° to 60°, and for example 50°, relative to an equatorial line of the cup.

In one particular example, the protruding formation includes a radially inwardly extending portion so as to define the female engagement formation as a radially inwardly female engagement formation.

In this manner, a surface of the protruding formation can be arranged to provide part of the surface of the opening of the female engagement formation.

Yet further, such a radially inwardly extending portion can be arranged to have first and second surfaces on opposite sides thereof and wherein the said first surface forms part of the surface of the opening of the female engagement formation.

The said second surface of the radially inwardly extending portion can be arranged to terminate, in the radially inwardly direction by way of a rounded, angled or bevelled region.

Again, and as with the shoulder transition region between the inner cup surface and the rim surface, the rounded, angled or bevelled region can be configured so as to prevent interference of the acetabular cup prosthesis with a full potential range of hip movement while in use, in a manner not compromising the potential mechanical strength of the engagement formation.

Preferably, the rounded, angled, bevelled region can include a substantially fiat surface at a typical angle in the range of 25° to 60°, and for example 50°, relative to an equatorial line of the cup. This can assist in the use of an artificial iabrum as discussed further below.

As a particular preferred feature, emphasizing the advantageous characteristics of the present invention, the engagement formation can be provided at a location above the equator of the outer diameter of the cup. In particular, the surface of the rim forming part of the opening of the female engagement formation is advantageously provided above the equator of the outer diameter of the cup to avoid interruption of the cup bearing surface and permit a full arc of bearing coverage.

Yet further, the acetabular cup prosthesis can also be arranged such that the engagement formation is located below the equator of the inner surface of the cup.

Likewise therefore, the surface of the rim defining part of the opening of the female engagement formation can be provided below the equator of the inner surface of a cup.

In order to enhance the structure of the acetabular cup prosthesis in the region of the rim, the inner and/or outer cup surface can be provided with a bulge arranged to provide for increased thickness. In one particular example, this portion of the inner and/or outer wall can bulge in the order of 0.5mm.

As can be appreciated, the present invention can advantageously provide for a ceramic acetabular cup prosthesis which, as a further advantage, can be arranged for receipt of, for example, a polymeric, liner. Such rescue liners are often used in what is known as a salvage procedure where a liner can extend the life of a well-fixed outer shell as revision of the shell is generally much more traumatic for the patient.

The engagement formation of the present invention can provide a further advantage insofar as the engagement formation can be adapted with anti-rotation engagement formations serving to prevent rotation of any such liner relative to the cup. The liner can then advantageously be provided with cooperating formations arranged to engage with the antirotation formations of the cup.

One particular example, the anti-rotation formations can comprise shallow recesses in the protruding formation configured to present the female engagement formation, and corresponding outwardly extending tangs provided in the outer circumferential region of the liner.

As will be appreciated, the present invention can be provided either as a mono-block, or uniform, cup structure and the female engagement formation can be arranged for the receipt of an impaction cap, introducer tooi and/or for engagement with any form of liner, whether rescue iiner, polymeric liner or Extended Posterior Wall (EPW) liner to prevent persistent dislocation. it will be understood that in use, the inner cup surface will provide the articulation surface for the femoral head and the outer cup surface will be implanted into the pelvis.

In one arrangement, the engagement formation extends around the entire circumference. Where the engagement formation does not extend around the entire circumference, there may be two or more separate engagement formations. Where are a plurality of separate engagement formations are present, they may be equally spaced.

The acetabular cup prosthesis may be formed from any suitable material, in one arrangement it may be formed from ceramic. Examples of suitable ceramic materials include alumina, zirconia, zirconia toughened alumina and silicon nitrides. For the purposes of this application, the term 'ceramic’ should be construed as meaning not oniy true ceramic materials but also other materials which display ceramic-like properties. Ceramic-like properties for the purposes of the present invention are those where strength, stiffness, and rigidity, are similar to those of ceramics. Examples of suitable ceramic-iike materials include glasses. In one arrangement, a metal and/or hydroxyapatite coating may be provided on the ceramic.

The cup itself may be of any suitable configuration. Generally it will be substantially hemispherical. However, in one arrangement, the top edge may have a wave configuration. In this arrangement, the cup may be handed such that a different wave configuration is required for each side of the body.

In another embodiment of the present invention there is provided a kit comprising the acetabular cup prosthesis of the above first aspect and an impaction cap or an introducer tool, said impaction cap or introducer tool comprising an engagement formation configured to cooperate with the engagement formation of the cup or the lip member such that when the engagement formation on the respective parts are in engagement, the impaction cap or introducer tool is attached to the cup either directly or via the lip.

Thus an introducer tool may, in use, be connected directly to the acetabular cup prosthesis or an impaction cap may, in use, be connected to the acetabalur cup prostheses. In this latter arrangement an introducer tool will then generally be connection to an introducer tool.

In one arrangement the impaction cap or introducer tool may sit on the upper surface of the cup. In another arrangement, it may be configured to extend into the bowl of the cup formed by the inner surface. In one arrangement in which the cap does extend into the bowl, the impaction cap or introducer tool may include a protuberance which in use interlocks with a recess or aperture in the bowl of the cup.

The impaction cap or introducer tool can be held in position during impaction by the interaction of the engagement formations. However, as the forces which are applied are substantial, it may be desirable to include additional fixation means to ensure that the impaction cap or introducer tool stays in position. Thus in one arrangement a wire arrangement such as circlip may be used although alternative means may be used. For example, the impaction cap or introducer tool may only engage with some of the engagement formations of the cup and the remainder could be used to enable a fixing means to be applied over the impaction cap to hold it in position.

Once the cup has been inserted, the impaction cap or introducer tool is removed. The cup may be left or the lip member and/or the plug component as described above may be applied. A further advantage of the present invention is that the engagement formation in the inner wall of the cup can be used to enable a liner to be attached to the cup. The liner can be made of any suitable material but will generally be polymeric. In one arrangement where there is an engagement formation on the inner cup surface, the liner will be provided with a cooperating engagement formation on the outer surface such that in use it engages with the inner surface.

The ability to introduce a polymeric liner may be advantageous in the event that the acetabular cup prosthesis were to fail. This is because inserting a liner may be preferable to removal of the cup which would otherwise be required in a revision operation. It may also be desirable to use a liner where it is desirable to use a smaller size replacement head on the femur.

In this arrangement where there is a sacrificial portion, one or more additional engagement formations may be located at a point below the engagement formation which forms the point at which the sacrificial portion is removed. These one or more engagement formations will enable a lip member to be applied to the cup if desired once the sacrificial part has been removed.

According to a further aspect of the present invention, there is provided a method of incorporating an acetabular cup prosthesis in which a cup according to the first aspect of the present invention has an impaction cap connected thereto via the respective engagement formations and the acetabular cup prosthesis is impacted into the pelvis.

Once the cup has been impacted, the impaction cap or tool wiii be removed.

According to a further aspect there is provided, an acetabular cup prosthesis comprising: an inner cup surface and an outer cup surface, said inner cup surface meeting said outer cup surface at a rim of said cup, wherein said inner cup surface, said outer cup surface or both said inner cup surface and said outer cup surface comprises an engagement formation located proximal to said rim, said engagement formation extending around at least a portion of the circumference of the cup; said engagement formation being configured to allow, in use, interaction with an impaction cap or introducer tool, and/or any form of liner whether rescue liner, polymeric liner or Extended Posterior Wall (EPW) liner to prevent persistent dislocation.

The present invention will now be described, by way of example, with reference to the following drawings in which:

Fig. 1 is a perspective view of an acetabular cup prosthesis according to one embodiment of the present invention;

Fig. 2 is a vertical cross sectional view through the acetabular cup prosthesis of Fig. 1.

Fig. 3 is a plan view of the acetabular cup prosthesis of Fig. 1;

Fig. 4 is a sectional view similar to that of Fig. 2 but also illustrating a revision liner received by the cup;

Fig. 5 is a perspective view of the arrangement of Fig. 4 comprising a combined cup and revision liner;

Fig. 6 is another vertical cross sectional view of the acetabular cup prosthesis of Fig. 1 and in engagement with an instrument for cup implantation;

Fig. 7 is a further vertical cross sectional view of the acetabular cup prosthesis of Fig. 1 and with reference to a first equatorial line defined with reference to the outer surface of the cup;

Fig. 8 is an expanded part view of the right hand rim region of the cup as illustrated with reference to Fig. 7;

Fig. 9 is a vertical cross sectional view of an acetabular cup prosthesis embodying the invention and illustrated in receipt of a replacement resurfacing femoral head: and

Fig. 10 is an enlarged part view of the cross section of Fig. 9

Turning first to Fig. 1, there is provided a perspective view of an acetabular cup prosthesis comprising cup 10 having an outer cup surface 12 and an inner cup surface 14.

Between the outer 12 and the inner 14 cup surfaces there is provided a rim 16 from which extends, and upon which is formed, a female engagement formation 18.

As discussed in further detail below, the female engagement formation 18 is formed by way of a protruding formation extending both upwardly (as seen in Fig. 1) from the rim 16 and then also radially inwardly so as to define a female engagement formation 18 offering a radially inwardly facing opening.

Also formed within the engagement formation 18 are recesses 20, which, as described below, are arranged to function as anti-rotation formations when cooperating with a cup liner (not shown in Fig 1.).

Turning now to Fig. 2, there is provided a vertical section through the cup 10 of Fig. 1 and so as to clearly further illustrate the configuration of the outer 12 and the inner 14 surfaces of the cup, and also the rim 16 and female engagement formation 18. A plan view of the cup 10 illustrated with reference to Figs. 1 and 2 is shown in Fig. 3 and so as to more clearly show the circumferential separation of the anti-rotation formations 20 within the female engagement formation 18 extending from the rim 16 of the cup 10.

Fig. 3 also clearly illustrates, within the particular embodiment, the extent to which the female engagement formation 18 extends radially inwardly above the rim 16.

While it will be appreciated that an acetabular cup prosthesis embodying the present invention can be formed as a unitary ceramic member arranged for operation without a liner or other secondary element, the illustrated embodiment of Figs. 1-3 includes the anti-rotation formations 20 specifically for engagement with a liner so as to prevent relative rotation between the liner and the cup.

Reference is now made to Fig. 4 which comprises a vertical cross section through the cup 10 of Figs. 1-3 but with a revision polymeric liner 22 in place.

The revision liner 22 is effectively clipped in place though engagement of an outwardly extending circumferential rib 24 of the liner 22 with the female engagement formation 18 of the cup 10 so as to provide for secure connection there between. Of course, relative rotation between the cup 10 and liner 22 is prevented through the engagement between mutually cooperating engagement formations of the circumferential region of the liner 22 and the female engagement formation 18.

Further details of these anti-rotation features are illustrated with reference to Fig. 5 which comprises a perspective view of the combined cup 10 and revision liner 22.

As illustrated, the outer circumferential region of the liner 22 is provided with four outwardly radially extending tangs 26 arranged to cooperate with, and be received in, the corresponding recesses 20 formed in the female engagement formation 18.

As will be appreciated from the present application, a particular feature of the engagement formation of the present invention is that it can be readily adopted by an acetabular cup prosthesis formed of any appropriate material, and can provide for required secure, and strong, mechanical engagement of the cup not only with associated element such as the revision liner 22 illustrated with reference to Figs. 4 and 5, but also in relation to tools adapted to be used with the cup for example, during implantation, removal and/or replacement.

Reference is now made to Fig. 6 which illustrates by way of a further vertical sectional view of a cup 10 of the present invention engagement between an introducer tool 28 including an impaction cap 30 and the cup 10.

As wiil be appreciated, outer circumferentiaS regions of the impaction cap 30 is provided with a circumferentially extending rib 32 which is arranged to cooperate with, and be received in, the female engagement formation 18 of the cup 10.

Turning now to Fig. 7, and with reference to a further vertical cross sectional view of the cup 10 of the previous figures, a further advantageous feature of the present invention is illustrated.

Including in Fig. 7 is an equatorial line A-A of the cup 10 and defined with reference to the curvature of the outer surface 12 of the cup 10. That is, the outer substantially hemispherical outer surface 12 of the cup 10 presents an equator at the position A-A illustrated in Fig. 7 and wherein, importantly, the engagement formation 18 is provided above that equator line A-A.

Also, the curvature of the inner surface 14 of the cup 10 defines a near complete hemisphere which, if envisaged as complete, will possess an equator line located above the female engagement formation 18.

Further detail of the rim 16 and female engagement formation 18 of a cup 10 according to the illustrated embodiment of the present invention is illustrated with reference to Fig. 8 and which comprises an enlarged view of the upper right hand portion of the cross sectional view of Fig. 7.

In addition to the outer surface 12, inner surface 14 and female engagement formation 18 of the cup, there is more clearly illustrated in Fig. 8 the rim 16 and configuration of the protruding formation extending initially upwardly from the rim 16 and then presenting a radially inwardly extending portion 34 serving to define, in combination with the surface of the rim 16 and opening 36 of the female engagement formation 18.

The equatorial line A-A discussed in relation to Fig. 7 is also illustrated in Fig. 8 along with a line B-B representing the level of the surface of the rim 18.

As will be appreciated with reference to the particular embodiment of Fig. 8, while the engagement formation comprising the radially inwardly extending portion 34 is located above the equator line A-A defined with reference to the outer surface 12 of the cup 10, the surface of the rim 16 is provided at a level B-B approximately 0.25mm beneath the equator A-A.

As will be appreciated from the configuration of the inner wail 14 illustrated in Fig. 8, an ongoing extension of that wall following the line of curvature would define a further equator line (not shown in Figure 8) with reference to the inner wall 14 which is located above the female engagement formation 18. The outer surface 12 of the cup 10 as illustrated in Fig. 8 includes a bulge 38 by which the thickness of the cup increases by, in the order of, 0.5mm

In addition to the relative location of the engagement formation with respect of at least one of the equator lines defined in relation to the outer and/or inner surfaces 12, 14 of the cup 10, there are further advantageous features present within the specific illustrated embodiment and relating to the configuration of the rim and the radially inwardly extending portion 34 of the female engagement formation 18.

Reference in this regard is now made to Fig. 9 which is a vertical sectional view through an acetabular cup 10 embodying an aspect of the present invention, and a replacement resurfacing femoral head 39 received therein. As discussed further below, the rim region of the cup 10 is configured having regard to the arc of motion of the replacement resurfacing femoral head 30 and the femoral bone it sits on to prevent the rim region serving to limit, or at least interfere with, that arc of movement

Fig. 10 is an enlarged part view of a vertical section through the upper left circumferential region (as viewed in Fig. 10) of a cup 10 embodying the present invention.

As with the enlarged view of Fig. 8, Fig. 10 clearly illustrates the outer wall 12, inner wall 14 and female engagement formation 18 of a cup 10 embodying the present invention and part of the replacement femoral head 39. In addition, further details of the radially inwardly extending portion 34 and the opening 36 of the female engagement formation are also illustrated.

As will be appreciated, the radially inwardly extending portion 34 includes a first (upper) surface 40 and a second (lower) surface 42 separated by the width of the radially inwardly extending portion 34 which, as one particular example, can be 0.2mm to 2mm and typically in the order of 0.9mm.

Also, the lower surface 42 of the radially inwardly extending portion 34 combines with a surface of the rim 16 to define the radially inwardly opening 36 presented by the female engagement formation 34.

Again, the width (i.e. height as illustrated in Fig. 9) of this opening 36 can be 0.2mm to 2mm and typically is in the order of 0.8mm.

As with the illustration provided by Fig. 8, the outer surface 12 of the cup illustrated in Fig. 10 includes a bulge 38 by which the thickness of the cup increases by, in the order of, 0.5mm. Such increase in thickness due the presence of the bulge 38 serves to enhance the mechanical strength of the circumferentially outer regions of the cup 10 at which the rim 16, radially inwardly opening 36 and female engagement formation 34 are formed.

As a further advantageous feature of the present invention, the inner surface 14 of the cup 10 transitions to the rim surface 16 by way of a shoulder transition region presenting a flat angled surface 44. As illustrated this flat surface can extend an angle X in the range of 25° to 60e, and for example 50°, with respect to an equatorial line Y, or a iine parallel to such an equatorial line.

Yet further, the radially inward extent of the upper surface 40 of the inwardly extending portion 34 of the female engagement formation 18 terminates at an angled or bevelled region which again advantageously presents an angled flat surface 46. As with the flat surface 44, the flat surface 46 can extend an angle that is the same as the angle X of the surface 44, and so, in the illustrated example, also at an angle in the range of 25° to 60°, and for example 50°, with respect to an equatorial line Y, or a line parallel to such an equatorial line.

In accordance with a particular advantageous configuration of a cup according to the present invention, the angles of the flat surfaces 44, 46 can sit on a common line, or as illustrated in the example of Fig. 10, on lines falling on parallel but separated planes. The distance of separation can be typically in the order of 0.25mm to 2mm. In particular, the distance of separation can be such as to allow for a further member, such as an artificial labrum to abut the surface 46 without interfering with the arc of movement of the replacement femoral head.

The configuration of the inner wall 14, rim 16 and female engagement formation 34 as illustrated in Fig. 9 proves particularly advantageous in enhancing the reliability and mechanical strength of the coupling provided by the female engagement formation, while avoiding any interference between the acetabular cup prosthesis 10 of the present invention and the replacement resurfacing femora! head permitting the potential for maximum range of motion of the reconstructed hip.

Claims

1. An acetabular cup prosthesis comprising: an inner cup surface, an outer cup surface, and a rim between the said inner cup surface and the said outer cup surface, the said rim including a non-sacrificial protruding formation configured to present a radially inwardly, or radially outwardly, facing female engagement formation of the cup,

2. An acetabular cup prosthesis according to Claim 1, and formed from a non-metallic material.

3. An acetabular cup prosthesis according to Claim 2, and formed from ceramic,

4. An acetabular cup prosthesis according to Claim 1, 2 or 3 wherein the protruding formation extends around the circumference of the cup.

5. An acetabular cup prosthesis according to any one of Claims 1 to 4 wherein the inner cup surface transitions to a rim surface via a shoulder transition region.

6. An acetabular cup prosthesis according to Claim 5, wherein the shoulder transition region is rounded.

7. An acetabular cup prosthesis according to Claim 5, wherein the shoulder transition region is bevelled.

8. An acetabular cup prosthesis according to Claim 5 or 7, wherein the shoulder transition region is angied.

9. An acetabular cup prosthesis according to Claim 5, 7 or 8, wherein the shoulder transition region presents an angle in the range of 25° to 60°, and for example 50°, relative to an equatorial line of the cup.

10. An acetabular cup prosthesis according to any one of Claims 1 to 9, and wherein the said protruding formation includes a radially inwardly extending portion defining at least in part a radially inwardly facing female engagement formation of the cup.

11. An acetabular cup prosthesis according to Claim 10, wherein the radially inwardly extending portion has first and second surfaces on opposite sides thereof, the first surface forming part of the surface of the female engagement formation.

12. An acetabular cup prosthesis according to Claim 11, wherein the said second surface of the said radially inwardly extending portion terminates in the radially inward direction by way of a rounded, or bevelled or angled region.

13. An acetabular cup prosthesis according to Claim 11, wherein the said rounded, angled or bevelled region presents a surface at an angle in the range of 25° to 60°, and for example 50°, relative to an equatorial line of the cup.

14. An acetabular cup prosthesis according to any one of Claims 10 to 13, wherein part of the protruding formation configured to present the female engagement formation is defined by an extension region of the outer cup surface.

15. An acetabular cup prosthesis according to any one of Claims 10 to 14, wherein the width of the female opening of the female engagement formation is in the range 0.2mm to 2mm and typically 0.8mm.

16. An acetabular cup prosthesis according to any one of Claims 10 to 15, wherein the thickness of the radially inwardly extending portion is in the range 0.2mm to 2mm and typically 0.9mm.

17. An acetabular cup prosthesis according to any one of the preceding claims, wherein the female engagement formation is provided above the equator of the outer diameter of the cup.

18. An acetabular cup prosthesis according to any one of the preceding claims, wherein at least part of the female engagement formation is provided below the equator of the inner diameter of the cup.

19. An acetabular cup prosthesis according to any one of the preceding claims, wherein a surface of the rim defining part of the female engagement formation is provided above the equator of the outer diameter of the cup.

20. An acetabular cup prosthesis according to any one of the preceding claims, wherein a surface of the rim defining part of the female engagement formation is provided below the equator of the inner diameter of the cup.

21. An acetabular cup prosthesis according to any one of the preceding claims, wherein the wail of the cup on a side opposite the female engagement formation exhibits a bulge to provide for increased thickness.

22. An acetabular cup prosthesis according to Claim 21, wherein the said bulge is in the order of 0.5mm.

23. An acetabular cup prosthesis according to any one of the preceding claims, wherein the inner cup surface incudes anti-rotation formations for engaging with a liner to prevent relative rotation between the cup and liner.

24. An acetabular cup prosthesis according to any one of the preceding claims, and comprising a mono-block structure.

25. An acetabular cup prosthesis according to any one of Claims 1 to 24, and comprising a substantially homogenous cup structure.

26. An acetabular cup prosthesis according to any one of the preceding claims, wherein the female engagement formation is arranged for the cooperation of an impaction cap and/or introducer tool with the cup.

27. An acetabular cup prosthesis according to any one of the preceding claims, wherein the female engagement formation is arranged for the cooperation of a liner with the cup.

28. An acetabular cup prosthesis according to Claim 27, wherein the female engagement formation is arranged for the cooperation of a polymer liner with the cup.

29. An acetabular cup prosthesis according to Claim 27 or 28, wherein the female engagement formation is arranged for the cooperation of an EPW liner with the cup.

30. An acetabular cup prosthesis according to any one of the preceding claims, and comprising a ceramic cup with a female engagement formation arranged for the cooperation of a polymeric liner with the cup.

31. An acetabular cup prosthesis according to any one of the preceding claims, and comprising, in combination, a ceramic cup and a polymeric liner.

32. A kit comprising the acetabular cup prosthesis of any one of Claims 1 to 31 and an impaction cap or introducer tool, said impaction cap or introducer tool comprising an engagement formation configured to cooperate with the engagement formation of the cup.

33. A kit according to Claim 32, and arranged such that the impaction cap or introducer tool can extend into the bowl of the cup.