PROSTHESIS

Abstract

The invention relates to a femoral component (2) of a knee prosthesis. The component comprises a curved outer surface (4) for bearing against a tibial component. Said curved outer surface includes a posterior end and an anterior end. The curved outer surface includes an area (A) which extends from a first position closer to the posterior end to a second position closer to the anterior end, wherein said area (A) includes no parting line.

Claims

1. A femoral component of a knee prosthesis, the component comprising a curved outer surface for bearing against a tibial component, the curved outer surface including a posterior end and an anterior end, the curved outer surface includes an area (A) which extends from a first position closer to the posterior end to a second position closer to the anterior end, wherein the area (A) includes no parting line.

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. The femoral component as claimed in claim 1, wherein the component includes an undercut region.

9. The femoral component as claimed in claim 8, wherein the undercut region is defined in a surface of the femoral component which faces in a direction which is opposite to the direction in which the outer surface faces.

10. The femoral component as claimed in claim 9, wherein the undercut region is arranged to define a cement pocket in the femoral component for retaining cement which may be used to facilitate securement of the femoral component to a femur during implantation.

11. The femoral component as claimed in claim 10, wherein the cement pocket has a depth of at least 0.5 mm.

12. The femoral component as claimed in claim 11, wherein the femoral component includes multiple undercut regions.

13. The femoral component as claimed in claim 12, wherein a series of ribs are provided in the surface of the femoral component which faces in a direction which is opposite to the direction in which the outer surface faces.

14. The femoral component as claimed in claim 13, wherein the ribs are equi-distantly spaced, preferably running parallel to one another.

15. The femoral component as claimed in claim 14, wherein the ribs run parallel to the flexion extension axis.

16. (canceled)

17. (canceled)

18. (canceled)

19. (canceled)

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

Description

[0065] Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0066] FIG. 1 is a schematic side elevation of a femoral component;

[0067] FIG. 2 is a schematic vertical cross-section through a femoral component of FIG. 1.

[0068] FIG. 3 is a schematic perspective view of the femoral component in the general direction of arrow III of FIG. 1 to show an inside surface of the component;

[0069] FIG. 4 is a schematic perspective view of the femoral components of FIG. 1 focussing on an outside surface of the component;

[0070] FIG. 5 is a schematic showing a femoral component (in vertical cross-section taken through its axis of rotation) contacting a planar surface and illustrating extreme positions of the femoral component as it is on the planar surface.

[0071] FIG. 6 is a schematic representation of a typical prosthetic knee assembly including a femoral component in its fully flexed condition;

[0072] FIG. 7 is a schematic representation of a prosthetic knee secured to a femur and tibia and showing a patella;

[0073] FIG. 8 is a schematic front view from an anterior end of part of the curved outer surface of the femoral component;

[0074] FIG. 9 is a schematic vertical cross-section through an injection moulding tool;

[0075] FIG. 10 is a schematic cross-section through the tool during disassembly of part of the shell of the tool;

[0076] FIG. 11 is a schematic cross-section through the tool after removal of part of the outer shell; and

[0077] FIG. 12 is a view similar to FIG. 3 except that a femoral component of a posterior stabilised knee is shown.

[0078] In the Figures, the same or similar parts are annotated with the same reference numerals.

[0079] A femoral component 2 (shown in FIG. 1 to 4) of a prosthetic knee assembly comprises a one-piece, monolithic injection moulding. The component 2 includes a curved outer surface 4 which comprises a first condyle 6 and a second condyle 8. The first and second condyles 6, 8 define an articulation surface of the femoral component and are arranged to contact an articulation surface of a tibial component 9 shown in FIGS. 6 and 7. A bearing surface representing an articulation surface of a tibial component is represented in FIG. 5 (although in use the surface would be non-planar) to illustrate how the femoral component is able to rotate and roll over the articulation surface of the tibial component, between extreme positions, during flexion and extension of a prosthetic knee assembly, in use. The curved outer surface 4 includes parting lines 10, 12, 14 formed on the outer surface at junctions defined between elements of an injection moulding tool used to mould the component 4, as described hereinafter with reference to FIGS. 9 to 13. Thus, the femoral component includes a first posterior parting line 10 formed on the first condyle 6, a second posterior parting line 12 formed on the second condyle 8, and a third anterior parting line 14 extending transversely across an anterior part of surface 4. In the figures, the height and width of the parting lines are exaggerated in the interests of clarity.

[0080] The parting lines 10, 12, 14 are positioned so the femoral component 2 can move between its extreme positions during flexion and extension (i.e. move through approximately 160°) without parting lines 10, 12, 14 (or for the avoidance of doubt any parting line associated with any part of the femoral component) contacting the articulation surface of the tibial component. Consequently, the only regions of the femoral component which contact the tibial component are “as-moulded” surfaces of the femoral component. Such surfaces can be moulded to have a low Ra. As-moulded articulation surfaces are preferred compared to surfaces which may be polished or otherwise treated to adjust their Ra (or remove parting lines or other undesirable features) since there is a risk, with any post-treatment, of articulation surfaces being contaminated, for example with metal from a tool used to effect a treatment or otherwise damaged during the process. In addition, avoiding post-treatment as described simplifies the manufacturing process for the femoral component which may make it quicker, easier and cheaper. Further details are provided below.

[0081] An internal face 16 of femoral component 2 includes respective undercut regions 18, 20 (FIGS. 2 and 9) associated with posterior and anterior edges of the femoral components. The undercut regions are adapted to facilitate retention of cement to aid securement of the femoral component into a femur of a patient being provided with a prosthetic knee. In addition, the internal face 16 includes a series of transverse ribs 19 which are also adapted to facilitate retention of cement as aforesaid.

[0082] Spaced apart projecting conical stems 22 extend inwardly away from the internal face 16, the stems being arranged to engage corresponding sockets formed in a patient's femur. In some embodiments, such stems may be omitted or may be a shape other than conical.

[0083] Referring to FIGS. 1 and 3, the first posterior parting line 10 has a height (above the adjacent outer surface 4) of 0.025 mm and has a substantially constant cross-section along its extent. The parting line 10 extends the entire distance from one transverse side wall 33 to an opposite side wall 35 of the first condyle 6. The parting line 10 curves between its opposite ends to define an arc shape on the outer surface 4 which includes a concave edge 30 which faces a posterior end 32 of the first condyle 6. The concave edge 30 is situated at or close to posterior end 32. The maximum distance between the posterior end 32 and the concave edge 30 (distance 29 in FIG. 1) may be less than 5 mm. At the inner edge of concave edge 30 which faces the second condyle 8, the concave edge may be contiguous with the posterior end. It is suitably substantially a mirror image of concave edge 40 of the second condyle 8 which is shown, at position 42, to be contiguous with posterior end 44.

[0084] The second posterior parting line 12 on the second condyle is substantially a mirror image of the first posterior parting line 10 and the above description of the first posterior parting line applies to the second posterior parting line mutatis mutandis.

[0085] An opening 50 between the first and second condyles 6, 8 defines an intercondylar notch arranged to receive a stem 52 (FIG. 6) provided on the tibial component 9. The intercondylar notch and stem are suitably arranged to restrict transverse movement of the femoral component 2 relative to the tibial component 9.

[0086] As shown in FIG. 4, the third anterior parting line 14 extends the entire distance from transverse side 56 to transverse side 58, across a region of the outer surface 4 spaced from the first and second condyles in the direction of anterior end 60 of outer surface 4. The parting line 14 has a height (above outer surface 4) of 0.025 mm and a substantially constant cross-section along its extent.

[0087] FIG. 7 illustrates a patella 62. The patella 62 is in sliding engagement with the femur 64 via a projection (not shown) which extends between the first and second condyles 6, 8 within the intercondylar notch defined in opening 50. It is preferred that the parting line 14 does not contact the underside (or any part) of the patella during articulation of the prosthetic knee. To this end, a central curved region 66 (FIGS. 4 and 8) of parting line 14 retreats towards the intercondylar notch. Thus, as illustrated in FIG. 8, parting line 14 includes a first region 68 (leftwards of dashed line 69) which has a substantially convex surface 75 facing towards the anterior end 60 of surface 4 and a substantially concave surface 77 facing towards first condyle 6; and a second region 79 (rightwards of dashed line 71) which has a substantially convex surface 8 facing towards the anterior end 60 and a substantially concave surface 81 facing towards second condyle 8. The central curved region 66 extending between dashed lines 69 and 71 incudes a substantially concave surface 82 facing towards the anterior end 60 of surface 4 and a substantially convex surface 83 adjacent the intercondylar notch. Thus, with the arrangement described, first and second regions 68, 79 are curved so as to optimise the length of the surface of the condyles 6, 8 which can contact the articulation surface of the tibial component without any of parting line 14 contacting the articulation surface. Furthermore the space available to receive the patella 62 such that its underside is not contacted by parting line 14 during articulation of the femoral component is optimised. It is preferred for curved region 66 to be as close to the perimeter of the intercondylar notch, defined by opening 50, as possible so to minimise the risk of it contacting the tibial component in use, as shown in FIG. 4. In some embodiments, the shape 14 may be different than described, depending upon the shape of the femoral and/or tibial components.

[0088] As described, the femoral component is able to roll and/or rotate through a significant angle (e.g. 160° or more) over a surface of a tibial component without any parting line (e.g. parting lines 10, 12, 14) contacting the tibial component. Thus, potential wear on the tibial component by such parting lines is avoided.

[0089] Assessment (A) below provides a general method with reference to FIG. 5, for assessing the extent to which a femoral component can move over a planar surface without any parting line contacting the planar surface.

Assessment (A)—Assessing Extent of Movement of Femoral Component Over a Planar Surface without a Parting Line on the Femoral Component Contacting the Planar Surface

[0090] Referring to FIG. 5, a femoral component 2 to be assessed is placed on a planar surface 86 of a table top 88 (or the like) with the component 2 initially in the position illustrated by arrow A. In this case, the component is arranged with first and second condyles 6, 8 contacting the surface and in a rotational position so parting line 12 just avoids contact with the surface. Similarly, although not shown in FIG. 5, parting line 10 also avoids contact. Thus, position A represents one extreme position of the femoral component, wherein parting lines are very close to but do not contact the surface 86.

[0091] Next, the femoral component is pivoted and/or rolled linearly across the surface to the position illustrated by arrow B. It may suitably be moved from position A to position B about axis of rotation 90 of the femoral component which may be determined in accordance with ISO14243-1:2009(E). In position (B), component 2 is arranged so parting line 14 just avoids contact with the surface 86. Thus, position (B) represents another extreme position of the femoral component 2, wherein parting lines are very close to but do not contact the surface 86.

[0092] The angle through which femoral component moves between positions (A) and (B) can be assessed. In FIG. 5, the angle is approximately 160°. This is referred to herein as the “normalized femoral rotation angle” (since it involves rotation across a planar surface). The normalized femoral rotation angle is also comparable to the angle through which the femoral component can move when engaged with a tibial component as illustrated in FIGS. 6 and 7. Thus, the femoral component 2 is arranged such that the positions A and B approximately correspond to the extreme positions of the femoral component when it moves over a corresponding tibial component between its positions of maximum flexion and extension. Movement of a femoral component over an actual tibial component may be assessed as described in Assessment B.

Assessment (B)—Assessing Extent of Movement of Femoral Component Over a Tibial Component in an Assembly Comprising the Femoral Component and Tibial Component

[0093] A femoral component and tibial component of a knee assembly for implantation are selected. The extent of movement can be assessed by assembling the components in vitro as shown in FIG. 6 with the femoral component held at a first position (illustrated generally in FIG. 6) which represents the extreme of flexion of the femoral compound on the tibial component, provided no parting line associated with the femoral component contacts the tibial component (although a parting line may be positioned very close to the tibial component). The femoral component may be rotated and/or rolled across the tibial component (as it would be when implanted) to a second position which represents the extreme of extension of the femoral component on the tibial component, provided no parting line associated with the femoral component contacts the tibial component at the first position, second position or any position between the first and second positions (although a parting line may be positioned very close to the tibial component, for example when in the second position). The angle through which the femoral component moves between the first and second positions (without any parting line on the femoral component contacting the tibial component) is referred to herein as the “practical femoral rotation angle” (since it is based on the angle achieved in an assembly which is suitable for and intended for implantation in a human body). The practical femoral rotation angle is typically in the range 140°-170° and may be patient dependent.

[0094] Thus, it should be appreciated that, advantageously, the femoral component can move through approximately up to 170° without any parting line on the femoral component contacting and potentially increasing the wear upon the tibial component. Thus, an assembly as described may have improved wear compared to assemblies which include parting lines at other positions on the femoral component.

[0095] It will be appreciated from the embodiments described that at angles greater than the normalized femoral rotation angle or the practical femoral rotation angle (e.g. when the femoral component is rotated beyond the first and second positions described) a parting line on the femoral component would contact the surface 86 (in Assessment A) or the surface of the tibial component (in Assessment B). However, this is not detrimental since the femoral component is not intended to be rotated beyond the first and second positions described. Nonetheless, by retaining a parting line produced in the manufacture of the femoral component as described, the femoral component may be more efficiently manufactured (since no additional parting line removal step is required) and the femoral component can be used substantially “as moulded”, without the bearing surface of the femoral component being polished or otherwise treated to adjust its surface roughness, thereby obviating the risk of contaminating or damaging the articulation surface of the tibial component.

[0096] The femoral component 2 is injection moulded using virgin polyetheretherketone (PEEK) which may be PEEK-OPTIMA (Trade Mark), a long-term grade polyetheretherketone with a melt-viscosity of approximately 0.45 KNsm.sup.−2, obtainable from Invibio Limited, UK.

[0097] The tibial component 9 is made from ultra-high molecular weight polyethylene (UHMWPE) which is softer than the PEEK. Consequently, steps are taken as described herein to minimise wear on the UHMWPE tibial component by the harder PEEK femoral component.

[0098] The position of parting lines (and areas which have no parting line) on the femoral component 2 has been described above. Such a femoral component 2 may be manufactured by injection moulding as hereinafter described with reference to FIGS. 9 to 13.

[0099] Referring to FIG. 9, a mould 90 for injection moulding the femoral component 2 comprises: a shell having a first element 92, a second element 94, and a third element 96; and a first inner up and way element 98, and a second inner up and away element 100.

[0100] The shell of the mould is arranged to define the outer surface 4 of the femoral component and the parting regions 10, 12, 14.

[0101] The second element 94 of the mould is arranged to define the entirety of the outer surface 4 of the femoral component which is arranged between parting lines 10, 12, 14. To this end, element 94 includes shaped surface 102 and first and second end faces 104, 106 which extend substantially parallel to one another. The shaped surface of the mould curves through an angle of about 180° to define the outer surface of the femoral component arranged between parting lines 10, 12, 14.

[0102] First element 92 cooperates with the second element 94 to define a first split line 108. To this end, first element 92 includes a shaped surface 110 and first and second end faces 112, 114. The first end face 112 abuts the end face 104 and defines part of the split line 108. The shaped surface 110 of element 92 curves through an angle of about 80° between its first and second end faces 112, 114,

[0103] The element 92 cooperates with first up and away element 98 to define a second split line 116 adjacent the proximal anterior flange of the femoral component.

[0104] Third element 96 comprises a central portion 97 located between said elements 98 and 100, and an arm portion 99. The arm portion 99 is joined to the central portion 97 such that movement of element 96 causes simultaneous movement of said portions 97 and 99. The arm portion 99 cooperates and makes face to face contact with second end face 106 of outer element 94 to define respective split lines 118, 120 adjacent superior posterior condyles of the femoral component 4.

[0105] The first, second and third up and away elements 96, 98, 100 cooperate to define the internal face 16 of the femoral component including undercut regions 18, 20.

[0106] The mould of FIG. 9 is injected with molten PEEK to fill the mould. After allowing the PEEK to cool, the moulded femoral component can be removed from the mould. Referring to FIG. 9, initially, element 96 moves up as indicated by arrow 101. The outer shell of the mould is then removed by moving elements 92 in the direction of arrow 122, and the second element 94 in the direction of arrows 124. This is shown most clearly in FIG. 10.

[0107] The removal of elements 92, 94, 96 causes the second and third up and away elements 98, 100 to move inwardly towards one another as represented by arrow 132, 134 in FIG. 11 and disengage from the femoral component 2.

[0108] Consequently, the parting lines are thus formed at locations on the surface of the component which do not obstruct use, or cause damage to a corresponding mating surface. Most advantageously, the moulding tool assembly results in a component having parting lines in favourable locations.

[0109] As an alternative to the FIG. 3 arrangement which is a design wherein a patient's cruciate ligament is retained and an opening 50 defines an intercondylar notch in which the cruciate ligament is positioned, the femoral component may include a bridge 150 which extends between first and second condyles 6, 8, as shown in FIG. 12 which illustrates a posterior stabilised arrangement.

[0110] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.