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EP-4218683-B1 - IMPROVEMENTS IN OR RELATING TO CERAMIC FEMORAL RESURFACING HEAD PROSTHESIS

EP4218683B1EP 4218683 B1EP4218683 B1EP 4218683B1EP-4218683-B1

Inventors

  • COLLINS, SIMON NICHOLAS
  • TAYLOR, ANDREW CLIVE
  • TUKE, MICHAEL ANTONY
  • CARRASCO, Carolina Avila

Dates

Publication Date
20260506
Application Date
20181101

Claims (13)

  1. A ceramic femoral resurfacing head prosthesis (110) comprising: a ceramic convex part-spherical articulation surface (112) engagable with an acetabulum of a patient or an acetabular cup prosthesis; a concave inner fixation surface (114); and a ceramic stem (120) projecting from the inner fixation surface (114), the stem (120) adapted to be received by a stem bore; a rim (116) having an asymmetrical profile between the articulation surface (112) and the inner fixation surface (114) so that the inner fixation surface (114) extends axially further than the ceramic part-spherical articulation surface (112) to improve femoral engagement, characterised in that the asymmetrical profile of the rim (116) is curved to prevent or limit in use fracture, chipping or breakage.
  2. A ceramic femoral resurfacing head prosthesis (110) as claimed in claim 1, wherein the rim (116) comprises an outer edge (150) adjoining the ceramic part-spherical articulation surface (112), the outer edge (150) being defined by an outer arc having a first radius of curvature, and an inner edge (148) adjoining the inner fixation surface (114), the inner edge (148) being defined by an inner arc having a second radius of curvature.
  3. A ceramic femoral resurfacing head as claimed in claim 2, wherein the inner arc has an angular range of or substantially of 90°.
  4. A ceramic femoral resurfacing head as claimed in claim 2 or claim 3, wherein the outer arc has an angular range of less than 90°.
  5. A ceramic femoral resurfacing head as claimed in any one or claims 2 to 4, wherein the inner arc has a greater angular range than that of the outer arc.
  6. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of claims 2 to 5, wherein the first radius of curvature is greater than the second radius of curvature.
  7. A ceramic femoral resurfacing head prosthesis (110) as claimed in claim 6, wherein the first radius of curvature is in a range of 0.5mm and 2.0mm, and preferably is or substantially is 1.0mm.
  8. A ceramic femoral resurfacing head prosthesis (110) as claimed in claim 6 or claim 7, wherein the second radius of curvature is in a range of 0.2mm and 1.5mm, and preferably is or substantially is 0.5 mm.
  9. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of claims 2 to 8, wherein an axial extent of the inner edge (148) is less than an axial extent of the outer edge (150).
  10. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of claims 2 to 9, wherein the centre of radius for the first radius of curvature is axially offset with respect to the centre of radius for the second radius of curvature.
  11. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of claims 2 to 10, wherein the centre of radius for the first radius of curvature is or is substantially positioned at a radial centre between an axial end of the inner fixation surface (114) and an axial end of the ceramic part-spherical articulation surface (112).
  12. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of the preceding claims, wherein a plane defined by the rim (116) is non-perpendicular to a longitudinal axis of the ceramic stem (120).
  13. A ceramic femoral resurfacing head prosthesis (110) as claimed in any one of the preceding claims, wherein the rim (116) is non-planar.

Description

The present invention relates to a ceramic femoral resurfacing head prosthesis for use in hip resurfacing procedures. The invention may be used in a method of increasing a fixation-land area of a ceramic femoral resurfacing head and a femoral resurfacing head prosthesis system for selective engagement of a femoral resurfacing head prosthesis with a resected femur based on one or more characteristics of the resected femur. Femoral resurfacing has been developed as an alternative to conventional total hip replacement in a procedure for the treatment of arthritis of the hip, a condition which causes considerable pain and loss of movement. The hip is a ball and socket joint which allows the upper leg to move from side to side, back to front, and to rotate. The joint is made up of the head of the femur, the ball, which fits into the acetabulum, the socket. In a healthy hip, both the head of the femur and acetabulum are covered with cartilage which provides a smooth surface allowing the joint to move freely. In general, femoral resurfacing involves the process of capping the head of the femur with a femoral resurfacing head prosthesis, attaching the prosthesis via bone cement, and fitting an acetabular cup to the acetabulum, generally using cementless fixation via a Titanium and/or Hydroxyapatite plasma coating. The femoral resurfacing head prosthesis and acetabular cup are conventionally formed from metal. A femoral resurfacing head prosthesis 10 in accordance with the state of the art is shown in Figures 1 to 5 and typically comprises a substantially spherical convex outer contact surface 12, a concave inner fixation surface 14, a rim 16 between the two surfaces defining an opening 18 and a stem 20 projecting from the concave inner fixation surface 14 and through the opening 18. It has been found that a metal-on-metal resurfacing can result in the production of metal ions and subsequent diffusion or transport of the metal ions to the bloodstream or locality surrounding the hip replacement prosthesis. The presence of metal ions can result in allergic reaction or other adverse health effects for the patient. Additionally, there is a risk of partial or total detachment of the femoral resurfacing head prosthesis from the underlying bone cement, if the adhesion or bonding between them is insufficient. Therefore, an increase in the area of overlap between an inner surface of a femoral resurfacing head prosthesis to the femur is desired, in order to increase the adhesion and thus minimise said risk. Further, by maximising the bone volume within the head prosthesis, bone resorption that can occur from stress shielding may be minimised. FR 2686503A1 discloses a prosthesis for restoration of the femoral head having a thin spherical cap whose inner face is solidly attached to a truncated cone open towards a collar, this truncated cone leaving free, at its periphery, an annular skirt extending the cap. US 2010/0312353A1 discloses a cap-shaped implant for implanting on a prepared stump of a femoral head. The present invention seeks to provide a solution to these problems. According to the present invention, there is provided a ceramic femoral resurfacing head prosthesis as defined in claim 1. The use of ceramic is advantageous as the production of potentially hazardous metal ions is prevented or limited, given the reduction in the amount of metal used for the prosthesis. Additionally, ceramics are typically harder than most metals and therefore the wear of the prosthesis can be reduced compared to a typical arrangement, resulting in an increased longevity of the prosthesis. Hip resurfacing prostheses typically are not formed from ceramic as ceramics are generally brittle by nature and fracture can be unpredictable. The rim preferably comprises an outer edge adjoining the ceramic part-spherical articulation surface, the outer edge being defined by an outer arc having a first radius of curvature, and an inner edge adjoining the inner fixation surface, the inner edge being defined by an inner arc having a second radius of curvature. An asymmetric profile enables a radius of curvature of an external edge of the rim to be greater than the radius of curvature of the external edge of the rim of a conventional prosthesis. Furthermore, a radius of curvature of an internal edge of the rim, due to the asymmetry, may be the same or similar as the radius of curvature of a conventional prosthesis, for example. The similar internal edge curvature maximises the inner fixation surface by maintaining the abruptness or sharpness of the transition between the inner fixation surface and the rim, and the gradual, greater radius of curvature of the external edge reduces the risk of damage to the rim by reducing stress concentration adjacent to the external edge rim. 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 radial cross-section of a femora