PROSTHESIS FOR HIP REPLACEMENT WITH POLYETHYLENE HEAD AND ANTI-ROTATIONAL INTRA-PROSTHETIC ASSEMBLY

Abstract

This invention corresponds to a prosthesis for total or hip resurfacing replacement, which comprises a prosthetic femoral head made of highly cross-linked polyethylene, with a diameter ranging from 38 mm to 64 mm, to articulate with a cup or acetabular component made of metal. When the invention applies to total hip replacement, the polyethylene head includes a metal core, which contains inside the female counterpart (14) to mate with the male counterpart (13) of a Morse taper, located at the upper end of the femoral component. The use of this type of head for total hip replacement, articulated with an ultra-polished acetabular cup, reduces the risk of dislocation, transmits less angular and torque forces to the Morse taper than large metal heads, and avoids the problems related to the metal-metal bearing or with the use of large metal heads with thin polyethylene. When the invention relates to hip resurfacing replacement, the highly cross-linked polyethylene femoral head has a lower polyethylene extension or stem with or without internal metal reinforcement (151) or a metal stem integrated into a metal-back (152). Using these types of heads for hip resurfacing replacement heads eliminates the problems associated with metal-on-metal resurfacing replacements.

Claims

1. Hip replacement prosthesis characterized in that it comprises a highly cross-linked polyethylene (HCLPE) head (12A) from 38 mm to 64 mm in diameter with an anti-rotational intra-prosthetic assembly provided by an anti-rotational connecting core (17) which is fitted inside the head (12A), inside a cavity with the same geometric shape of the connecting core (17), and is fixed to said cavity by means of an axial locking mechanism (171) that is located in the third lower of the external surface of the connecting core (17), such anti-rotational connecting core (17) has the shape of a truncated polyhedral pyramid or is a truncated cone with longitudinal fins (172) located in its central or upper third.

2. The prosthesis according to claim 1, characterized in that it is a total hip replacement prosthesis in which the assembly of the polyethylene head (12A) to the femoral stem (11) is carried out by means of the anti-rotational connecting core (17), which contains the female counterpart (14) of the Morse cone to mate with the male counterpart (13) located at the upper end of the femoral component.

3. The prosthesis according to claim 1, characterized in that the rotational stability is given by the polyhedral pyramid shape of the anti-rotational connecting core (17) which is selected from the group consisting of a square, pentagonal, hexagonal, heptagonal shape or octagonal.

4. The prosthesis according to claim 3, characterized in that the polyhedral pyramid shape of the anti-rotational connecting core (17) is hexagonal.

5. The prosthesis according to claim 1, characterized in that the axial securing mechanism (171) of the anti-rotational connecting core is a perimeter beveled flange (1711), which projects into the lower third of the outer surface of the anti-rotational connecting core (17) and it is inserted in an also perimeter solo (121), located in the internal space of the head (12A).

6. The prosthesis according to claim 1, characterized in that the axial securing mechanism (171) of the anti-rotational connector core is a perimeter wire (1712) that fits into also perimeter grooves (122, 1713), located at the same level, one, in the internal space of the head (12A) and the other, in the external surface of the anti-rotational connector core (17).

7. The prosthesis according to claim 1, characterized in that the anti-rotational connecting core (17) is a truncated cone and comprises 1 to 6 longitudinal fins located in the central third or in the upper third of its external surface for rotational stability.

8. The prosthesis according to claim 1, characterized in that the walls of the anti-rotational connecting core (17) have a thickness between 4 mm and 8 mm.

9. The prosthesis according to claim 1, characterized in that the corners (173) of the anti-rotational connecting core (17) are rounded.

10. The prosthesis according to claim 1, characterized in that the anti-rotational connecting core (17) is made of a material selected from the group consisting of chromium-cobalt alloys, titanium alloys, stainless steel or ceramic.

11. The prosthesis according to claim 2, characterized in that the anti-rotational connector core (17) has an extension or skirt (174), which lengthens it and distally translates the position of the female component of the Morse taper.

12. The prosthesis according to claim 1, characterized in that it further comprises a cemented or uncemented metal cup (2), which internal surface which is ultra-polished.

13. The prosthesis according to claim 12 characterized in that the radius of curvature of the polyethylene head (12A) is between 50 and 150 microns less than the radius of curvature (21) of the interior of the metal cup (2) and the head contact (12A) in the acetabulum (2) is more polar (22) than equatorial (23).

14. Hip replacement prosthesis characterized in that it is a hip resurfacing replacement prosthesis and comprises a highly cross-linked polyethylene (HCLPE) femoral head (12B) with a diameter between 40 mm and 64 mm, mounted on an anti-rotational metal-back (152) with a metal stem (15), where such metal-back (152) is axially secured to the head (12B) on a circumferential rim (123), located inside said head (12B), which fits into the lower edge (153) of the metal-back (152), and is rotationally secured by tabs (124), which project from the inside of the head (12B), as an extension of the upper end of the circumferential rim (123), and they fit into the corresponding notches (154) of the lower edge (153) of the metal-back (152).

15. The prosthesis according to claim 14, characterized in that the metal-back (152) has a thickness of 2 mm to 3 mm.

16. The prosthesis according to claim 14, characterized in that it comprises between 2 to 4 anti-rotatory tabs (124) on the head (12B), opposite each other, and 2 to 4 notches (154) on the metal-back (152).

17. The prosthesis according to claim 16, characterized in that it comprises 2 opposed anti-rotatory tabs (124) and 2 notches (154).

18. The prosthesis according to claim 14, characterized in that it further comprises a metallic acetabular component (2) with ultra-polished internal and external surface for cementation or osteo-integration.

19.-22. (canceled)

Description

DESCRIPTION OF THE FIGURES

[0031] FIG. 1A. Prosthesis for total hip replacement with uncemented components.

[0032] FIG. 1B. Prosthesis for hip resurfacing replacement.

[0033] FIG. 2A. Cementless acetabular component with polyethylene insert and metal head.

[0034] FIG. 2B. Cementless acetabular component with polyethylene insert and ceramic head.

[0035] FIG. 2C. Cementless acetabular component with ceramic insert and ceramic head.

[0036] FIG. 3. Schematic of Morse taper in total hip replacement femoral head.

[0037] FIG. 4A. Arc of movement up to the impingement of the prosthetic femoral neck with the rim of the acetabular cup with a small head.

[0038] FIG. 4B. Arc of movement up to the impingement of the prosthetic femoral neck with the rim of the acetabular cup with a large head.

[0039] FIG. 5A. Metal-metal total hip prosthesis with large head.

[0040] FIG. 5B. Transmission scheme of the frictional torque to the Morse taper with large head.

[0041] FIG. 5C. Scheme of transmission of the frictional torque to the Morse taper with small head.

[0042] FIG. 6A. Scheme of the double mobility cup with the femoral component without flexion.

[0043] FIG. 6B. Scheme of the double mobility cup, showing the initial movement (A) between the metal head and the polyethylene core.

[0044] FIG. 6C. Scheme of the double mobility cup, showing the late movement (B) between the polyethylene core and the metal cup, after the contact of the neck of the femoral component hits the polyethylene rim.

[0045] FIG. 7A. Contact of the femoral neck with the rim of the polyethylene core.

[0046] FIG. 7B. Wear of the capture rim of the mobile polyethylene mobil polyethylene core by repetitive shock and friction.

[0047] FIG. 7C. Intra-prosthetic dislocation: the metallic head comes out of the mobile nucleus of polyethylene due to wear of the rim.

[0048] FIG. 8. Frontal longitudinal section of the hip with the prosthesis of the invention for total hip replacement.

[0049] FIG. 9A. Longitudinal section of the prosthesis of the invention for total hip replacement, with a truncated pyramid-shaped anti-rotational connector core

[0050] FIG. 9B. Cross section of the prosthesis of the invention, through A-A line of FIG. 9A, with an anti-rotational connecting core in the shape of a truncated pyramid with a hexagonal geometric shape.

[0051] FIG. 10A. Cross section of the prosthesis of the invention, where the head has a truncated pyramid-shaped anti-rotational connector core with a square geometric shape.

[0052] FIG. 10B. Cross section of the prosthesis of the invention, where the head has an anti-rotational connecting core in the form of a truncated pyramid with a geometric pentagonal shape.

[0053] FIG. 10C. Cross section of the prosthesis of the invention, where the head has an anti-rotational connecting nucleus in the shape of a truncated pyramid with a heptagonal geometric shape.

[0054] FIG. 10D. Cross section of the prosthesis of the invention, where the head has an anti-rotational connecting core in the shape of a truncated pyramid with an octagonal geometric shape.

[0055] FIG. 11A. Longitudinal section of the prosthesis of the invention with the truncated cone shaped anti-rotational connector core with anti-rotatory fins, and a flange as an axial securing mechanism.

[0056] FIG. 11B. Cross section of the prosthesis of the invention, through line A-A of FIG. 11A, showing the anti-rotatory mechanism.

[0057] FIG. 11C. Longitudinal section of the prosthesis of the invention with the truncated cone shaped anti-rotational connecting core with anti-rotatory mechanism and with a metal ring as axial locking mechanism.

[0058] FIG. 12A. Longitudinal section of the anti-rotational connector core without extension, to be assembled on the polyethylene head.

[0059] FIG. 12B. Longitudinal section of the anti-rotational connector core with skirted extension to be assembled to the polyethylene head.

[0060] FIG. 13A. Clearance between the cup and the head where its greatest contact is polar.

[0061] FIG. 13B. Clearance between the cup and the head where its greatest contact is equatorial.

[0062] FIG. 14A. Longitudinal section of the prosthesis of the invention for hip resurfacing replacement made of polyethylene.

[0063] FIG. 14B. Longitudinal section of the prosthesis of the invention for hip resurfacing replacement made of polyethylene with internal metallic reinforcement in the femoral neck.

[0064] FIG. 15. Perspective of the femoral component of the prosthesis for hip resurfacing replacement made of polyethylene with anti-rotational metal-back.

[0065] FIG. 16. Breakup view of the femoral component of FIG. 15. For the purposes of the representation, the stem has been separated from the metal-back.

[0066] FIG. 17A. Longitudinal section of the femoral component of the prosthesis of the invention of FIG. 15 coupled to an acetabular component.

[0067] FIG. 17B. Cross section of the prosthesis of the invention, through line A-A of FIG. 17A.

DETAILED DESCRIPTION OF THE INVENTION

[0068] The present invention relates to a hip replacement prosthesis comprising a highly cross-linked Polyethylene (HCLPE) polymeric femoral head, 38 mm to 64 mm in diameter (12A, 12B), which is characterized by containing a metallic or ceramic assembly (modular or not), with an axially and rotationally stable locking mechanism, to attach to the femoral component. This polymeric head is designed to articulate with a cemented or uncemented metal cup (2), whose internal face is ultra-polished, similar to the cups used in metal-metal implants or dual mobility implants, as shown in FIGS. 8, 9A, and 17A. That is, the invention consists of a polymeric head (12A, 12B) characterized by having an anti-rotational intra-prosthetic assembly to articulate with the femoral stem.

[0069] Highly Cross-Linked Polyethylene Head for Total Hip Replacement

[0070] In one embodiment of the invention, the polymeric head (12A) is part of a prosthesis to be used for total hip replacement, where the coupling mechanism to the femoral component is made using an anti-rotational connector core (17), stably assembled inside the polymeric head (12A), using a firm locking mechanism (171). This anti-rotational connector core (17) contains within it the female counterpart of the Morse cone (14) to couple with the male counterpart (13) of the upper end of the femoral component, as shown in FIGS. 8, 9A and 9B.

[0071] Said anti-rotational connecting core (17) is characterized in that it has the shape of a truncated polyhedral pyramid, selected from the group consisting of a square, pentagonal, hexagonal, heptagonal, octagonal, etc. shape, as illustrated in the Figures. 9A, 9B, 10A, 10B, 10C and 10D. The external shape of the anti-rotational connecting core (17) can also correspond to a truncated cone shape as shown in FIGS. 11A, 11B and 11C. Regardless of the shape of said pyramid or cone, the longitudinal section of the anti-rotational connector core (17) corresponds to a trapezoidal shape.

[0072] In a preferred embodiment of the invention, the anti-rotational connecting core (17) has the shape of a truncated hexagonal pyramid, where the longitudinal section of the anti-rotational connecting core (17) corresponds to a truncated cone and the core has a hexagonal shape in the transverse plane, as evidenced in FIG. 9B. Said core (17) is coupled to the polymeric femoral head (12A), within an internal cavity in said head, that has the same geometric shape, and is press-fitted.

[0073] In a preferred embodiment, said anti-rotational connecting core (17) is fixed inside the head (12A) by means of a locking mechanism, which consists of a flange (171) that projects perimetrically on the external surface of the anti-rotational connecting core (17) and fits in a slot (121), located in the internal space of the polymeric head (12A), as illustrated in FIGS. 8 and 9A. In this way, the axial stability of the anti-rotational connector core (17) is achieved and the rotational stability is provided by the geometric shape of the core, avoiding movement and the production of wear particles. The shape and size of the core allow complete contact of its walls and roof with the interior of the polymeric head, avoiding the presence of spaces that allow deformation of the polymer by loads. This core can be made of metal or ceramic alloys and can be assembled to the polymeric head either at the factory or produced separately and coupled during surgery. This last alternative has the advantage of reducing the inventory of polymeric heads necessary for each surgical procedure, since connector cores of different femoral neck lengths could be used for each head diameter and the same cores can be used for heads of different sizes.

[0074] In another alternative of the invention, the anti-rotational connecting core (17) has a truncated cone shape and the longitudinal section corresponds to a trapezoidal shape, but the core has a round shape in the transverse plane, as illustrated in FIGS. 11A and 11B. In this case, the implant includes an anti-rotatory mechanism (172), consisting of 1 to 6 longitudinal fins on the external surface of the anti-rotational connector core (17), and an axial securing mechanism that is selected from a beveled perimeter flange (1711) which fits into the perimeter groove (121) in the interior space of the head (12A), shown in FIG. 11A; or a metal ring (1712) that is located between a perimeter groove (1713) in the core (17) and a perimeter groove (122) in the interior space of the head (12A) represented in FIG. 11C.

[0075] In addition to the aforementioned characteristics, the anti-rotational connector core (17) of the prosthesis, in any of its modalities, has always rounded corners (173), to avoid stress concentration zones, as seen in FIGS. 8 to 12.

[0076] Likewise, the anti-rotational connector core may have an extension or skirt (174) of the Morse taper, as illustrated in FIG. 12B. Said extension or skirt (174) is intended to improve the versatility of the prosthesis by allowing the length of the prosthetic femoral neck to be increased a bit more, similar to what in conventional metallic femoral heads is called skirted heads.

[0077] Now, in order to provide adequate stiffness to the implant, the walls of the anti-rotational connector core (17) must have a thickness between 4 mm and 8 mm, to avoid deformations in their coupling to the femoral cone. This core is made of a material selected from the group consisting of chrome-cobalt alloys, titanium alloys or stainless steel, but it can also be made of ceramic.

[0078] The polymeric head is preferably made of Highly Cross-linked Polyethylene (HCLPE).

[0079] As for the radius of curvature (21) of the polymeric head (12A, 12B), it must have a tolerance in relation to the internal diameter of the cup, between 50 and 150 microns, which allows more polar contact (22) than equatorial (23) in the acetabular cup, as illustrated in FIG. 13A. The latter, in order to avoid friction zones in the equatorial area and achieve a better load transmission and lubrication.

[0080] Due to the properties of the invention, the total hip replacement prosthesis of the present invention has utility in the following situations:

[0081] 1. Total primary hip replacement procedures, especially in older patients or those at high risk of dislocation.

[0082] 2. The polymeric head can be articulated, either with a solid metal uncemented cup; with an uncemented metal cup with holes for screw fixation and modular metal insert; or with cemented metal cups. All of these cup options include ultra-polished metal articular surface, similar to cups used with metal-to-metal or dual mobility implants.

[0083] 3. Likewise, the prosthesis is ideal for total hip replacement revision surgeries, using either a metal cup without holes; or modular cups with metal inserts or cemented metal cups with or without a reinforcing ring.

[0084] 4. Likewise, the prosthesis can be used in large head metal-metal total hip replacement revision surgeries or in double mobility cup revision surgeries, preserving the original acetabular prosthetic component.

[0085] 5. It can also be used in revision hip replacement surgeries while retaining the original acetabular prosthetic component.

[0086] Highly Cross-Linked Polyethylene Head for Hip Resurfacing Replacement

[0087] In the other embodiment of the present invention, the prosthesis intended for hip resurfaing replacement is characterized in that the polymeric prosthetic femoral head (12B), with a diameter between 40 mm and 64 mm, has a lower extension or stem (15), which allows fixation to the femoral neck (16) with or without bone cement. Said femoral head (12B) articulates with an ultra-polished metallic acetabular component (2), as shown in FIG. 14A. In this embodiment of the invention, the fixation of the head (12B) to the femur is carried out with cement and the fixation of the acetabular component (2) can be cemented or uncemented.

[0088] In another alternative of this embodiment, the extension or lower stem (15) of the prosthetic femoral head (12B) can be made entirely of polyethylene or it can be made of polyethylene with an internal metal reinforcement (151), as illustrated in the FIGS. 14A and 14B, respectively.

[0089] In the preferred alternative of the prosthesis intended for hip resurfacing replacement, the implant of the invention comprises the polymeric head (12B) with a thin metal-back (152) attached to a metal stem (15), as shown in the FIGS. 15, 16, 17A and 17B. In order not to thin down the polyethylene, the metal-back (152) must have a thickness between 2 and 3 mm, preferably 2 mm.

[0090] In this embodiment of the invention, the polymeric head (12B) is secured to the metal-back (152) by means of an anti-rotational intra-prosthetic assembly, characterized by a circumferential flange (123) located inside the head which fits securely in the lower edge (153) of the metal-back (152), thus preventing the axial movement of the head (12B). Rotational stability is given by 2 to 4 anti-rotatory tabs (124), preferably 2 tabs, which project from the inner face of the polymeric head (12B) as an extension of the upper edge of the circumferential flange (123), one opposite to the other which fits into corresponding notches (154) located on the lower edge (153) of the metal-back (152).

[0091] The metallic stem and the metal-back can be made with external porous coating for uncemented use, or without porous cover for cemented fixation.

[0092] For better rotational stability, the stem (15) used in the cemented fixation of the femoral component, in any of its modalities, is conical or tapered in a rectangular geometric shape with rounded corners and tips (not sharp), to avoid stress areas in the cement mantle.

[0093] Likewise, the internal face of the polymeric head (12B) or the metal-back that will be in contact with the bone cement must have irregularities (grooves or grids not shown in the figures) for better interdigitation of the cement and rotational stability.

[0094] Due to the properties of the invention, the hip resurfacing replacement implant is useful in the following situations:

[0095] 1. Primary hip replacement in young patients.

[0096] 2. Primary hip replacement in cases of proximal femur deformity due to osteotomy or old fracture.

[0097] 3. Primary hip replacement in patients with a high risk of dislocation.

[0098] In order to clearly delimit the scope of the present invention, some terms which have been used in the description of the invention and which facilitate its understanding are specified below.

[0099] Press-fit. It refers to the stability or initial grip mechanism of the prosthesis, which provides the necessary stability to allow osteo-integration of the prosthesis. It is generally performed by preparing a bed slightly smaller in size than the final implant, so that the latter fits snugly, preventing axial, angular and rotational movements.

[0100] Hip joint. It is the site of union between the pelvis and the femur. The spherical head of the femur fits into the acetabular cavity of the pelvis and is the site of movement between the lower extremity and the pelvis. The term joint is also used to refer to the site of movement between the prosthetic head and acetabulum of total hip replacement.

[0101] Total hip replacement revision surgery. A surgical procedure that is performed to change partially or completely the components of a total hip replacement.

[0102] Femoral component. Refers to the prosthetic implant that is placed in the medullary canal of the superior end of the native femur in the hip replacement. Generally, the prosthetic head is modular and adapts to the prosthetic stem using a Morse taper mechanism.

[0103] Cemented femoral component (cemented femoral stem). Refers to femoral prostheses made to be implanted using bone cement (polymethylmethacrylate). These implants have a smooth or less rough surface and their fixation is always done with bone cement.

[0104] Uncemented femoral component (uncemented femoral stem). This refers to the porous-coated femoral prosthesis for osteointegration, which is implanted in the femur in total hip replacement.

[0105] Morse taper. It is the mechanism used to attach the prosthetic modular femoral head to the upper end or neck of the femoral stem. This ends in a segment in the form of a truncated cone (male), whose length is variable. The cone fits into the femoral head, which has a socket (female) with the same geometric shape and angulation. Its adjustment is made by impacting the head on the male component of the neck.

[0106] Acetabular cup. It is the component of a hip replacement prosthesis that is placed in the acetabular cavity of the pelvis. There are uncemented cups which are composed of a metallic cup with an external porous coating, generally hemispherical, and a modular component of polyethylene, ceramic or metal, which is assembled in the concavity of said cup. There are also cemented acetabular cups which are made entirely of polyethylene and are fixed to the bone with bone cement.

[0107] Linear wear. It refers to the magnitude of penetration of the prosthetic femoral head into the prosthetic articular acetabular surface as a consequence of material wear. It is generally expressed in millimeters.

[0108] Volumetric wear. It is the term used to quantify the volume of material removed from polyethylene or any other articular surface generated by movement and loads on the joint. The volume of polyethylene removed for an equal amount of penetration of the femoral head is greater in heads with a larger diameter.

[0109] Debris. Those are the wear particles that are released on the movement surfaces of the prostheses. There are polyethylene, metal or ceramic debris.

[0110] Intra-prosthetic dislocation. It is a term used to describe the unique situation of dual mobility hip replacements in which the femoral head is decoupled from the mobile polyethylene insert. This occurs because the polyethylene containment mechanism is lost due to wear.

[0111] Prosthetic dislocation. It is the situation in which the femoral head of the total hip replacement is decoupled from the acetabular component when taken to extreme movements, since there is normally no mechanism for containing the head within the acetabular cavity.

[0112] Modular. Refers to prosthetic components made up of separate parts that are assembled during surgical implantation. For example, the acetabular component has an internal insert of polyethylene or

[0113] ceramic that is assembled in the metal cup after placing it in the native acetabulum. This has two purposes, one is to allow the placement of the screws to fix the cup to the bone through holes in it and the other is to be able to use polyethylene with projections, eccentricity, lateralized as needed; or inserts made of ceramic or metal. Likewise, the prosthetic femoral head is modular with the body of the prosthesis, and its coupling is carried out by means of a Morse taper mechanism (male component-female component). This allows the length of the femoral neck to be modified according to the depth of the taper in the prosthetic head.

[0114] Osteo-integration. It refers to the process of bone growth on the porous covering of uncemented implants. When the bone growth on the cover is sufficient to provide stability to the implant, it is considered to be osteo-integrated.

[0115] Highly Cross-linked Polyethylene (HCLPE). Refers to a polymeric material made of high molecular weight polyethylene, which has been subjected to a process of irradiation with gamma rays or electron beams and heating, in order to produce crosslinking of the polymer chains. Both in hip simulators and in vivo wear measurements, a significant reduction in the amount of wear has been shown when used in the acetabular components of the total hip replacement.

[0116] Local corrosive processes. It refers to the processes of galvanic and crevice corrosion that occur in the metal-metal modularity sites, which end up releasing corrosion products, ions and metal particles to peri-prosthetic fluids and tissues, generating a local biological reaction and also, systemic repercussions (generalized or in distant organs).

[0117] Adverse tissue reactions. Refers to the biological reaction process of tissues around prosthetic components in response to metal ions or to the deposition of polyethylene or metal particles resulting from wear. This reaction can lead to bone resorption or the formation of pseudo tumors.

[0118] Porous coating. It refers to the coating that the uncemented implants have on the external surface that is in contact with the native bone. There are several types of porous coatings and their function is to allow bone growth within the pores or surface irregularities, to give implants long-term stability.

[0119] Peri-prosthetic tissues. It is used to refer to the bone and soft tissues adjacent to the implant, both in the femur and in the pelvis. The wear debris of the materials of the joint replacements are mainly deposited in these tissues.

[0120] Clearance. It refers to the difference in the radius of curvature of the acetabular cavity and the femoral head of the prosthesis. Low tolerance joints increase friction on the surface and make lubrication difficult.