GB2508654A - Acetabular cup with polygonal engagement - Google Patents

Acetabular cup with polygonal engagement Download PDF

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Publication number
GB2508654A
GB2508654A GB1222089.3A GB201222089A GB2508654A GB 2508654 A GB2508654 A GB 2508654A GB 201222089 A GB201222089 A GB 201222089A GB 2508654 A GB2508654 A GB 2508654A
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GB
United Kingdom
Prior art keywords
outer shell
inner liner
acetabular cup
engagement element
polygonal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB1222089.3A
Other versions
GB2508654B (en
Inventor
Paul Mayon
Simon Nicholas Collins
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corin Ltd
Original Assignee
Corin Ltd
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Filing date
Publication date
Application filed by Corin Ltd filed Critical Corin Ltd
Priority to GB1222089.3A priority Critical patent/GB2508654B/en
Priority to PCT/GB2013/053238 priority patent/WO2014087177A1/en
Publication of GB2508654A publication Critical patent/GB2508654A/en
Application granted granted Critical
Publication of GB2508654B publication Critical patent/GB2508654B/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2/32Joints for the hip
    • A61F2/34Acetabular cups
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2002/30001Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30316The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
    • A61F2002/30329Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
    • A61F2002/30331Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit
    • A61F2002/30362Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit with possibility of relative movement between the protrusion and the recess
    • A61F2002/30364Rotation about the common longitudinal axis
    • A61F2002/30367Rotation about the common longitudinal axis with additional means for preventing said rotation
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2/00Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
    • A61F2/02Prostheses implantable into the body
    • A61F2/30Joints
    • A61F2002/30001Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
    • A61F2002/30316The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
    • A61F2002/30329Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
    • A61F2002/30476Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements locked by an additional locking mechanism
    • A61F2002/30495Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements locked by an additional locking mechanism using a locking ring
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2310/00Prostheses classified in A61F2/28 or A61F2/30 - A61F2/44 being constructed from or coated with a particular material
    • A61F2310/00005The prosthesis being constructed from a particular material
    • A61F2310/00179Ceramics or ceramic-like structures
    • A61F2310/00185Ceramics or ceramic-like structures based on metal oxides
    • A61F2310/00203Ceramics or ceramic-like structures based on metal oxides containing alumina or aluminium oxide
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61FFILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
    • A61F2310/00Prostheses classified in A61F2/28 or A61F2/30 - A61F2/44 being constructed from or coated with a particular material
    • A61F2310/00005The prosthesis being constructed from a particular material
    • A61F2310/00179Ceramics or ceramic-like structures
    • A61F2310/00185Ceramics or ceramic-like structures based on metal oxides
    • A61F2310/00239Ceramics or ceramic-like structures based on metal oxides containing zirconia or zirconium oxide ZrO2

Landscapes

  • Health & Medical Sciences (AREA)
  • Orthopedic Medicine & Surgery (AREA)
  • Cardiology (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Transplantation (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Vascular Medicine (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Prostheses (AREA)

Abstract

An acetabular cup 10 comprises an outer shell 12, an inner liner 14 receivable by the outer shell 12, and a two-part polygonal engagement element 16 at an interface between the outer shell 12 and the inner liner 14. The two-part polygonal engagement element 16 includes a Reuleaux polygon. The two-part engagement may be a protrusion 48 and recess 50 arrangement. An acetabular cup system utilising the said two-part acetabular cup 10, a second inner liner formed of a different material to the first inner liner 14, and a two-part taper engagement element at an interface between the outer shell 12 and the second inner liner. A method of inhibiting rotational disassociation of an inner liner 14 of an acetabular cup 10 when engaged with an outer shell 12 by means of a polygonal engagement 16.

Description

Acetabular Cup, System And Method The present invention relates to an acetabular cup, and more particularly for such a cup for a hip, to a system utilising such an acetabular cup along with a second inner liner, and to a method of inhibiting rotational and preferably also axial disassociation of an inner liner of such an acetabular cup when engaged with an outer shell.
Two-part acetabular cups are well known and are provided for use in total hip arthroplasty. Such acetabular cups provide a range of liners which are fittable in a common outer shell, and which utilise a variety of different materials and shapes. This enables a surgeon to intraoperatively choose a most appropriate combination for a particular patient, taking account of the patient's lifestyle and geometry of articulation.
It is common to provide a two-part acetabular cup, such as shown in international patent publication WO2Ol2lO86lOAi, having a metal outer shell and a plastics inner liner.
The outer shell and inner liner are interengaged via a circular locking ring on an outer surface of the inner liner which snap-fits into a complementary circular channel on an inner surface of the outer shell. This prevents or limits liner disengagement during clinical use, and for example by direct push-out or by being levered apart.
To inhibit rotational disassociation of the inner liner and outer shell, rounded toothed projections on the inner liner are received in complementarily shaped recesses within the outer shell. This rotational feature can also be used to allow liner forms that reduce subsequent dislocation of the hip by limiting a range of motion. These are commonly termed extended posterior wall (EPW) liners.
The requirement of two different locking arrangements increases the complexity of the acetabular cup and therefore the manufacturing cost.
It is also problematic using toothed projections for thin-walled' acctabular cups. A thin-walled acetabular cup typically has a total wall thickness in the range of 2 to 5 mm, and is used to minimise the bone removed from the acetabulum during the reaming process. Since the material that must be removed from the outer shell to accommodate suitably dimensioned teeth is reasonably significant, undue weakening of the thin wall of the outer shell occurs and as such, this engagement feature cannot be readily accommodated by a thin-walled cup.
The present invention seeks to provide a solution to these problems.
According to a first aspect of the invention, there is provided a acetabular cup comprising an outer shell, an inner liner receivable by the outer shell, and a two-part polygonal engagement element at an interface between the outer shell and the inner liner.
Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 13, inclusive.
According to a second aspect of the invention, there is provided an acetabular cup system comprising an acetabular cup in accordance with the first aspect of the invention.
a second inner liner formed of a different material to the first said inner liner, and a two-part taper engagement element at an interface between the outer shell and the second inner liner.
Preferable andlor optional features of the first aspect of the invention are set faith in claims 16 to 18, inclusive.
According to a third aspect of the invention, there is provided a method of preventing or inhibiting rotational disassociation of an inner liner of an acetabular cup according to the first aspect of the invention when engaged with an outer shell, the method comprising the step of urging a polar axis of the inner shell to move radially relative to a polar axis of the outer shell when a rotational force is imparted to at least one of the inner liner and the outer shell.
Preferable and/or optional features of the first aspect of the invention are set forth in claims 20 to 23, inclusive.
The invention will now be more particularly described, by way of example only. with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a first embodiment of a two-part acetabular cup, shown with the outer shell and inner liner separated, and in accordance with the first aspect of the invention; Figure 2 shows a partial cross-sectional view of the acetabular cup of Figure 1, shown with the outer shell and inner liner engaged; Figure 3 is a side elevational view of the inner liner of the acetabular cup, shown in Figures 1 and 2; Figure 4 is a perspective view of a second inner liner forming part of an acetabular cup system, in accordance with the second aspect of the invention; Figure 5 shows a perspective cross-sectional view of a second embodiment of a two-part acetabular cup, shown with the outer shell and inner liner engaged, and in accordance with the first aspect of the invention; and Figure 6 is an elevational view of the cross-section, shown in Figure 5, showing the two-part acetabular cup.
Referring firstly to Figures 1 to 3 of the drawings, there is shown a first embodiment of a two-part acetabular cup 10 which comprises an outer shell 12, an inner liner 14, and a two-part polygonal engagement element 16. An outer surface 18 of the outer shell 12 is at least in part part-spherical and is suitably dimensioned to fit a reamed acetabular opening of a patient.
Although the outer surface 18 is preferably at least in part part-spherical, it may be shaped such that the equatorial diameter of the outer surface 18 at a rim 20 is marginally greater than the poiar diameter of the outer surface 18 which extends perpendicularly to the equatorial diameter. This shape is beneficial to aid press-fit and uncemented fixation of the outer shefl 12 into a patientts acetabulum, which is generally reamed to the smaller polar diameter dimension.
The outer shell 12 also defines an inner cavity 22 dimensioned to receive as a close or tolerance fit the inner liner 14. The inner cavity 22 is preferably part-spherical at a region 25 which extends from a polar axis 24 of the outer shell 12 and to a point P partway towards the rim 20. A wall 26 of the inner cavity 22, from the part-spherical surface 28 to the rim 20, is preferably frusto-conical forming a first taper element 30 to enable a taper fit with the inner liner 14. However, in this embodiment, the frusto-conical surface 28 and taper fit engagement option are optional and not essential.
The outer shell 12 may, for example, be formed of, typically forged or cast, hi-compatible metal, and preferably cobalt chrome-alloy or titanium alloy and may be subjected to a heat treatment process to improve its mechanical properties. 1-lowever, the outer shell could be formed of a ceramic matenal, such as alumina, zirconia, or a combination thereof. The outer surface 18 of the outer shell 12 is also preferably coated with Titanium plasma, 1-lydroxyapatite and/or a porous metallic bone-like structure, to aid fixation and bone growth.
The inner liner 14 shown in the drawings is of plastics, typically Ultra 1-ugh Molecuuar Weight Polyethylene, compnsing an extenor surface 32 which is at least in part abuttable with the inner surface 34 of the outer shell 12. The inner liner 14 also includes IS a part-sphericaL typically hemispherical or substantially hemispherical, articulating surface 36 which extends from a polar region 38 of the inner liner 14. A diameter of the articulating surface 36 is appropriate for captively or non-captively receiving a natural or prosthetic femoral head.
The exterior surface 32 of the inner liner 14 is preferably complementarily shaped to match or substantially match the inner surface 34 of the outer shell 12. The exterior surface 32 includes a part-spherical portion 40 which extends from the polar region 38 of the inner liner 14, and a frusto-conical wall 42 having a diverging taper in a direction of a rim 44 of the inner liner 14 forming a second taper element 46. The taper of the second taper element 46 is substantially the same as that of the first taper element 30 of the outer shell 12.
As above, the frusto-conical wall 42 may be dispensed with, and in this case the part-spherical portion 40 of the exterior surface 32 may extend to or substantially to the rim 44, as required.
Although a frusto-conical wall may be preferred, the wall may be a plane section instead of being tapered, and in this case a circlip or other retaining means may be utilised to retain the liner within the outer shell.
The inner liner 14 may be one of a plurality of differently dimensioned inner liners available to a surgeon for intraoperative selection.
The two-part polygonal engagement element 16 comprises a projecting male engagement part 48 on the exterior surface 32 of the inner liner 14 and a recessed female engagement part 50 on the inner surface 34 of the outer shell 12. The projecting male engagement part 48 and the recessed female engagement part 50 include a plurality of sides 52, 54 defining complementary polygons 56. 58.
In this particular embodiment, the projecting male engagement part 48 and the recessed female engagement part 50 are considered endless, since there are no breaks in the rings that they define. However, it is feasiHe that one or both of the projecting male engagement part and the recessed female engagement part may be discontinuous, and therefore not considered to be endless.
In this embodiment, each said polygon 56, 58 is a Reuleaux polygon having an odd number of sides 52..4. each of which has a curving thngitudinal extent. A lateral extent of each side 52, 54 is preferably straight, but also may be curved or chamfered to aid introduction of the projecting male engagement part 48 with the recessed female engagement part 50.
The Reuleaux polygon 56, 58 has a constant diameter at any given point measured through a centre of a circle. Consequently, this provides a constant surface area of engagement between the projecting male engagement part 48 and the recessed female engagement part 50 at any point, thus improving push-out or lever-out resistance of the inner finer 14 from the outer shell 12.
Furthermore, a diameter of each Reuleaux polygon 56. 58 is not based on a fixed centre, and therefore rotation of the inner liner 14 about a fixed centre, such as the polar axis 24 of the outer shell 12 is prevented or limited. During the impartation of a relative rotational force between the inner liner 14 and the outer shell 12 about respective polar axes 24, 60, the curvilinear sides 52, 54 of the projecting male engagement part 48 and the recessed female engagement part 50 attempt to urge the polar axis 60 of the inner liner 14 laterally or radially relative to the polar axis 24 of the outer shell 12. Since the inner liner 14 is held captive by the outer shell 12, this lateral or radial movement of the polar axes 24, 60 is prevented or limited, and therefore relative rotation of the two parts is aho prcvcntcd or limited.
Consequently, the two-part p&ygonal engagement element 16 not only provides for resistance against push-out and lever-out of the inner liner 14 from the outer shell 12, but also provides for anti-rotation between the inner liner 14 and outer shell 12.
The two-part polygonal engagement element 16 is positioned to extend in a plane which is at or adjacent to an equatorial plane of the outer shell 12. It is also preferable that the two-part polygonal engagement element 16 extends perpendicularly or substantially perpendicularly to the polar axis 24 of the outer shell 12. The two-part polygonal engagement element 16 is preferably spaced slightly from the rim 20, thereby enabling IS the recessed female engagement part 50 to extend both over and under a received corner portion 62 of the projecting male engagement part 48. However, the polygonal engagement element may be at any position between a polar region of the outer shell and/or inner liner and the associated rim.
In this embodiment, the projecting male engagement part 48 and the recessed female engagement part 50 are integrally formed as one-piece with the inner liner 14 and the outer shell 12, respectively. The projecting male engagement part 48 essentially defines a polygonal ring 64 which extends continuously around the exterior surface 32 of the inner liner 14, in this case at the frusto-conical wall 42. The curvilinear sides 52 meet or substantially meet the frusto-conical wall 42 at or substantially at their midpoints, and the corners 66 defined between contiguous neighbouring sides 52 project.
A diameter of the polygonal sides 52 is constant, but the radius varies. Due therefore to the curvature and number of sides, a projecting extent can be defined. This latter feature aids a surgeon in controlling the push-out or lever-out resistance between the inner liner 14 and outer shell 12.
The recessed female engagement part 50 essentially defines a complementary polygonal channel 68 which extends continuously around the inner surface 34 of the outer shell 12, again in this case at the frusto-conica! wall 26. The curvilinear sides meet or substantially meet the frusto-conical wall 26 at or substantially at their midpoints, and the corners 70 defined between contiguous neighbouring sides 54 are recessed to rcccivc thc projccting corncrs 66 of thc niac cngagcmcnt part 48.
Although it is preferred that the two-part p&ygonal engagement element includes complementary Reuleaux polygons or polygons having arcuate sides of constant width, the polygona' sides may have straight or linear longitudinal extents. lii this case, rotational resistance is not as pronounced since there is a constant centre of rotation whereby the polar axes of the inner liner and outer shell remain at their fixed relative positions.
It may be feasible to provide the two-part polygonal engagement element having complementary engaging polygons with one or more arcuate sides and one or more IS linear sides. For example. the projecting male engagement part and the recessed female engagement part may each have one side with an arcuate longitudinal extent, as with a Reuleaux polygon, but the remaining sides may have straight or linear longitudinal extents. This would require a specific relative orientation between the inner liner and the outer shell. However, during attempted relative rotation, the arcuate sides would attempt to offset or move the polar axis of the inner liner relative to the polar axis of the outer shell, thus causing the required resistance and therefore the anti-rotation characteristic.
It is also feasible that the projecting male engagement part of the two-part polygonal engagement element could be provided on the inner surface of the outer shell, whereas the recessed female engagement pail could be provided on the exterior surface of the inner liner. However, a benefit of the first described arrangement is that the outer shell, by having no projecting elements on its inner surface, can be utilised with other kinds of inner liner. For example. a ceramic inner liner 72, as shown in Figure 4, only typically requires a taper-fit engagement. Consequently, by providing the inner surface 34 of the outer shell 12 with the required tapering frusto-conical wall 42, as described above, even though the recessed female engagement element i6 extends therearound, a ceramic or taper-only fit inner liner 72 being devoid of the projecting male engagement part 48 can still be utilised and engaged with the outer shell 12 via the first and second taper elements 30. 46 forming a self-locking two-part taper engagement element 74 at the interface between the inner liner 14 and the outer shell 12. As such, a greater range or variety of selectable inner liners, not only having different dimensions but also being formed of diffcrcnt bio-compatiblc rnatcrials, can be utiliscd with the outer shell 12 of the present invention.
Although a ceramic inner liner 72 is suggested above, other suitable bio-compatible materials may be considered.
As shown in Figures 5 and 6, to simplify manufacture of the outer shell i2 with the recessed female engagement part 50 of the polygonal engagement element 16, the polygonal part of the recessed female engagement part 50 may be formed separately as an independent member 50a. In this case, the inner surface 34 of the outer shell 12 is formed with a ring-like circular channel SOb, and at least one locating element SOc. such IS as a notch or tab, is provided therein. The female engagement part 50 can thus be considered to comprise two main separate independent elements 50a, 50b.
The separate female engagement pail is formed as a ring 50a, and this may be a split ring to aid insertion into the circular channel SOb of the outer shell 12. The ring-like female engagement part SQa preferably comprises a smooth or substantially smooth radially outer surface, and the polygonal radially inner surface. If the two-part polygonal engagement element 16 is utilising the Reuleaux polygons, then the sides of the polygonal radially inner surfaces are arcuate of constant radius to be complementary with those of the projecting male engagement part 48.
A further locating element or elements to complementarily match the first said locating element or elements in the circular channel of the outer shell 12 is/are formed on the separate female engagement part.
The separate female engagement part SOa can thus be received in the circular channel SOb of the outer shell 12, and held against relative angular displacement by the interlocking locating elements SOc. The inner liner 14 can then be inserted into the outer shell 12, whereby the projecting male engagement part 48 interengages with the independent recessed female engagement part.
As above, although the separate female engagement part may utilise an odd number of curvilinear polygonal sides, it is feasible that an even number of polygonal sides can be utilised and/or the polygonal sides or a proportion thereof may be linear. However, in these latter cases and as explained above, the push-out or lever-out resistance characteristics in combination with the anti-rotational characteristics may not be as great.
The acetabular cup having the inner liner and the outer shell may thus comprise a male polygonal engagement element and a female polygonal engagement element, wherein in this case the female polygonal engagement element includes two intercooperating members, one of which is independent of the outer shell and the inner liner.
It is also possible that the inner liner may be introduced into the outer shell prior to engagement of the polygonal engagement element. To this end, for example. the projecting male engagement part andlor the recessed female engagement part may be a separate independent part. This separate independent part may thus be inserted following insertion of the inner liner, for example, by dropping the separate independent part into the interface at or adjacent to the respective rims. A circlip or other retaining means may thus then be utilised to axially retain the separate independent part in place, thereby enabling the engagement of the polygonal engagement element.
It is thus possible to provide a two-part acetabular cup having an inner liner which can be hdd captive in an outer shell and which can be indexed relative thereto as required.
and which is also able to resist push-out and lever-out forces, in addition to rotational forces whilst in use through the use of a single two-part polygonal engagement element.
The use of separate features or mechanisms to prevent or limit axial separation as well as relative angular displacement is therefore dispensed with. It is also possible to utilise a two-part polygonal engagement element which utilises complementary Reuleaux polygons, whereby relative rotational disassociation is resisted due to the attempted lateral offset of a polar axis of the inner liner relative to the polar axis of the outer shell.
The invention can also be conveniently utilised by so-called thin walled' acetabular cups where a wall thickness of the outer shell is reduced to maximise an articulating surface dimension of the inner liner, since a receiving depth of the projecting male engagement part within the recessed female engagement element can be controlled by a number of polygonal sides utilised.
The embodiments described above are provided by way of examples only. and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined by the appended claims.

Claims (23)

  1. Claims 1. An acetabular cup comprising an outer shell, an inner liner receivable by the outer shell, and a two-part polygonal engagement dement at an interface between the outer shell and the inner liner.
  2. 2. An acetabular cup as claimed in claim 1, wherein the polygonal engagement element includes a Reuleaux polygon.
  3. 3. An acetabular cup as claimed in claim I or claim 2, wherein the polygonal engagement element extends in a plane which is at or adjacent to an equatorial plane of the outer shell.
  4. 4. An acetabular cup as claimed in any one of the preceding claims, wherein the polygonal engagement element extends in a plane which partway between a polar region of the outer shell and/or the inner liner and the associated rim.
  5. 5. An acetabular cup as claimed in any one of the preceding claims, wherein the polygonal engagement element extends in a plane which is parallel or substantially parallel with an equatorial plane of the outer shell and/or the inner liner.
  6. 6. An acetabular cup as claimed in any one of the preceding claims, wherein the polygonai engagement element extends in a plane which is parallel or substantially parallel with a rim of the outer shell and/or the inner liner.
  7. 7. An acetabular cup as claimed in any one of the preceding claims, wherein the polygonal engagement element comprises a projecting male engagement part on one of the inner liner and the outer shell and a recessed female engagement part for receiving the projecting male engagement part on the other of the inner liner and the outer shell, the projecting male engagement part and the recessed female engagement part including a plurality of sides defining complementary polygons.
  8. 8. An acetabular cup as claimed in any one of claims 1 to 6, wherein sides of the polygonal engagement element are straight.
  9. 9. An acetabuar cup as claimed in any one of daims I to 6, wherein sides of the polygona' engagement element are arcuate.
  10. 10. An acetabular cup as claimed in any one of the preceding daims, wherein a number of sides of the polygonal engagement element is odd.
  11. 11. An acetabular cup as claimed in any one of the preceding claims, wherein the two parts of the polygonal engagement element are integrally formed as one-piece with the outer shell and the inner liner, respectively.
  12. 12. An acetabular cup as claimed in any one of claims I to 10, wherein at least one said part of the polygonal engagement element is independent of the outer shell and inner liner, the said at least one part being engagable with the outer shell or inner liner.
  13. 13. An acetabular cup as claimed in any one of the preceding claims, wherein the outer shell is a biocompatible metal, and the inner liner is a biocompatible plastics.
  14. 14. An acetabular cup substantially as hereinbefore described with reference to the accompanying drawings.
  15. 15. An acetabular cup system compnsing an acetabular cup as claimed in any one of the preceding claims, a second inner liner formed of a different material to the first said inner liner, and a two-part taper engagement element at an interface between the outer shell and the second inner liner.
  16. 16. An acetabular cup system as claimed in claim 15, wherein the two-part taper engagement element includes a first taper element on an inner surface of the outer shell, and a second taper element on an outer surface of the second inner liner.
  17. 17. An acetabular cup system as claimed in claim 16, wherein the first and second taper elements extend from the rims of the outer shell and the second inner liner, respectively.
  18. 18. An acetabular cup system as claimed in any one of daims 15 to 17, wherein the second inner liner is ceramic.
  19. 19. A method of inhibiting rotational disassociation of an inner liner of an acetabular cup as claimed in any one of claims 1 to 14 when engaged with an outer shell, the method comprising the step of urging a poiar axis of the inner shell to move radially relative to a poiar axis of the outer shell when a rotational force is impared to at least one of the inner liner and the outer shell.
  20. 20. A method as claimed in claim 19, wherein the said relative movement of the polar axes on impartation of the said rotational force is caused by a plurality of contiguous curvilinear sides which abut each other at an interface between the outer shell and the inner liner.
  21. 21. A method as claimed in claim 19 or claim 20, wherein the said relative movement of the polar axes on impartation of the said rotational force is caused by a two-part polygonal engagement element at an interface between the outer shell and the inner liner.
  22. 22. A method as claimed in claims 19 to 21, wherein the said relative movement of the polar axes on impartation of the said rotational force is caused by complementary Reuleaux polygons at an interface between the outer shell and the inner liner.
  23. 23. An acetabular cup comprising an outer shell, an inner liner receivable by the outer shell, and a Reuleaux polygonal engagement element at an interface between the outer shefi and the inner liner.
GB1222089.3A 2012-12-07 2012-12-07 Acetabular cup, system and method Expired - Fee Related GB2508654B (en)

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GB1222089.3A GB2508654B (en) 2012-12-07 2012-12-07 Acetabular cup, system and method
PCT/GB2013/053238 WO2014087177A1 (en) 2012-12-07 2013-12-09 Acetabular cup, system and method

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WO2012045530A1 (en) * 2010-10-07 2012-04-12 Jossi Holding Ag Joint socket and method for producing a joint socket

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GB2551155A (en) * 2016-06-07 2017-12-13 Matortho Ltd Prosthesis
WO2017212243A1 (en) * 2016-06-07 2017-12-14 Matortho Limited Prosthesis

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GB2508654B (en) 2019-05-01

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