CONSTRAINED PROSTHETIC KNEE WITH ROTATING BEARING
A constrained prosthetic knee having a modular hinge post and a rotating bearing. A cannulated hinge post is rotatably connected to the femoral component of the knee prosthesis so that a hinge post extension may be anteriorly positioned through the hinge post and into the tibial component of the knee prosthesis, after positioning of the femoral component in the femur and the tibial component in the tibia. The hinge post is preassembled to the femoral component so that such assembly is not required during the implantation procedure. A meniscal component forming the rotating bearing of the knee prosthesis is packaged together with the hinge post extension so that the appropriate hinge post extension is readily available. The meniscal component includes a mechanism for preventing lift off of the meniscal component from the tibial component, while allowing rotation of the meniscal component relative to the tibial component.
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This is a continuation of patent application Ser. No. 10/805,056 filed Mar. 19, 2004, which is a continuation of patent application Ser. No. 10/001,000 filed Nov. 2, 2001, now U.S. Pat. No. 6,719,800, which is a continuation-in-part of patent application Ser. No. 09/771,061 filed Jan. 29, 2001, now U.S. Pat. No. 6,485,519, the disclosures of which are expressly incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to prosthetic joints, and, more particularly to a constrained prosthetic knee having a modular hinge post and a rotating bearing.
2. Description of the Related Art
Generally, the knee is formed by the pair of condyles at the distal portion of the femur, the lower surfaces of which bear upon the correspondingly shaped proximal surface plateau of the tibia. The femur and tibia are connected by means of ligaments such as, the posterior cruciate ligament, the lateral collateral ligament, the medial collateral ligament, and the anterior cruciate ligament. These ligaments provide stability to the joint formed by the femur and tibia (i.e., the knee).
In a broad sense, prosthetic knee joints can be considered either constrained or unconstrained. For the purposes of this discussion, constrained prosthetic knees include femoral and tibial prosthetic components which are mechanically linked or constrained to each other by a hinge structure. An unconstrained prosthetic knee includes femoral and tibial components which are not mechanically linked. An unconstrained knee utilizes the patient's existing ligaments to provide joint stability. With this in mind, constrained prosthetic knees have particular applicability to cases in which a patient has experienced ligament loss and/or the existing ligaments do not provide adequate support and stability to the knee.
Tibial components of a prosthetic knee can be formed as a one-piece configuration in which the tibial tray forms the meniscal component of the prosthetic knee. Various other prosthetic knees utilize a modular meniscal component separate from the tibial component. Devices utilizing modular meniscal components include those in which the meniscal component (i.e., tibial bearing surface) is fixed to the tibial tray portion of the tibial component and is incapable of movement relative thereto. Alternative devices utilize a modular meniscal component capable of movement relative to the tibial tray. Devices in which relative rotational movement occurs between the meniscal component and the tibial component are typically referred to as rotating bearing knees. Rotating bearing knees thus allow movement between the bearing (i.e., meniscal component) and the tibial tray, as well as movement between the femoral component and the tibial bearing.
Constrained knees of the prior art include constructions in which a hinge post extension is first positioned within a tibial component (with an end protruding therefrom) and is thereafter connected to the femoral component by positioning the hinge post (rotatably attached to the femoral component) over the top of the protruding end of the hinge post extension and thereafter connecting the hinge post extension to the hinge post, e.g., by threading the hinge post extension into the hinge post. After making this connection, the meniscal component is thereafter slid into position between the femoral component and the tibial component. Meniscal components utilized with these prior art prosthetic knees are fixed to the tibial component.
The present invention is directed to a constrained knee prosthesis with a rotating bearing. The knee prosthesis of the present invention is structured to facilitate implantation thereof. The present invention is further directed to a prosthetic knee implant set having a plurality of matched modular hinge post and meniscal component pairs.
SUMMARY OF THE INVENTIONThe present invention provides an improved constrained knee prosthesis having a cannulated hinge post facilitating implantation of the knee prosthesis in a relatively minimally invasive procedure. The prosthetic knee implant set of the current invention includes a separately packaged femoral component, a separately packaged tibial component, and a third package containing a hinge post extension and the meniscal component. Packaging the individual components of a knee prosthesis in this fashion insures that the appropriate hinge post extension is readily available. A bearing box is interposed between the hinge post and the femoral component. The bearing box includes a hyperextension stop which cooperates with the hinge post to prevent hyperextension of the knee prosthesis. Various structures are utilized to prevent the disengagement of the constrained knee prosthesis of the present invention.
A prosthetic knee constructed in accordance with the present invention includes a femoral component having a pair of condyler surfaces and a hinge post rotatably connected to the femoral component between the condyler surfaces. The hinge post is cannulated and accommodates insertion of a hinge post extension shaft therein. The hinge post and hinge post extension include cooperating locking tapers for locking the hinge post extension to the hinge post. Additionally, the hinge post includes internal threads so that a set screw may be threaded therein to further hold the hinge post extension in place. In one exemplary embodiment, the proximal end of the hinge post extension is threaded to facilitate locking the hinge post extension to the hinge post. The tibial component includes a hinge post extension aperture into which the hinge post extension is seated. The meniscal component similarly includes an aperture to accommodate the hinge post and hinge post extension. The meniscal component of the current invention is free to rotate about the hinge post during flexion and extension of the knee joint.
Having a cannulated hinge post through which a hinge post extension may be anteriorly positioned and secured advantageously allows for a relatively minimally invasive knee replacement procedure.
The present invention advantageously provides a constrained prosthetic knee having a rotating bearing flush with the condyler surfaces of the femoral component.
Another advantage of the present invention is the packaging of the prosthesis components and specifically the packaging of the appropriate hinge post extension together with a meniscal component.
BRIEF DESCRIPTION OF THE DRAWINGSThe above-mentioned and other features and advantages of this invention, and the manner of attaining of them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the invention, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain the invention. The exemplifications set out herein illustrate embodiments of the invention, in alternative forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION Referring now to the drawings and particularly to
As illustrated in
Hinge post extension 42 is typically formed as a one-piece construction of an inert metal such, e.g., a cobalt-chromium alloy. Hinge post extension 42 may, however, be constructed of other bio-compatible metals or alloys, such as titanium. Throughout this document reference will be made to various components formed of a cobalt-chromium alloy. Any such component may also be constructed of other bio-compatible metals or alloys such as titanium, as is well-known. As illustrated in
As illustrated, e.g., in
Bearing box 70 is designed for placement between condyler bearing surfaces 28, 30 of femoral component 22 as illustrated, e.g., in
Hinge post 40 is rotatably connected to femoral component 22 via hinge pin 34. Hinge post 40 is placed between opposing walls of bearing box 70 and is positioned so that hinge pin aperture 52 is aligned with apertures 56, 58, and 62. The opposing walls of bearing box 70 thus act as a bearing surface between hinge post 40 and internal side walls 80 of femoral component 22. Prior to placement of hinge post 40 between opposing walls of bearing box 70, hinge pin sleeve 36 is operably positioned within hinge pin aperture 52 of hinge post 40. Hinge post 40 is formed from a cobalt-chromium alloy, while hinge pin sleeve 36 is formed from a suitable plastic, such as, e.g., UHMWPE. Hinge pin sleeve 36 acts as a bearing between hinge pin aperture 52 of hinge post 40 and hinge pin 34. Accordingly, hinge pin sleeve 36 includes hinge pin aperture 50 sized to accommodate hinge pin 34. After positioning hinge post 40 between the opposing walls of bearing box 70, hinge pin 34 is positioned through apertures 56, 62, 50, and 58. Hinge pin threads 60 are thereafter threadedly engaged in the threads of threaded hinge pin aperture 56 until the head of hinge pin 34 is flush with external side wall 82.
As illustrated in
Pre-assembly of hinge post 40 to femoral component 22 eliminates a number of meticulous assembly steps (many of which were performed during implantation) which were required with constrained knees of the prior art. Furthermore, the assembly of hinge post 40 and femoral component 22 as described above facilitates replacement of various portions of knee prosthesis 20. Specifically, the threaded connection of hinge pin 34 to femoral component 22 allows for removal and replacement of various components of knee prosthesis 20 including, e.g., bearing box 70, hinge pin sleeve 36, and hinge post 40.
In use, femoral bone stock may abut external side walls 82 of femoral component 22 and extend to the underside of condyler bearing surfaces 28, 30. To remove hinge pin 34, a hole saw is utilized to remove a relatively small portion of femoral bone stock to provide access to hinge pin 34. Advantageously, femoral component 22 does not require extensive removal of femoral bone stock for implantation thereof (since bone stock can extend to the underside of condylar bearing surfaces 28, 30), and, furthermore, does not require removal of femoral component 22 to effect replacement of, e.g., hinge post 40, bearing box 70, or hinge pin sleeve 36. Upon accessing hinge pin 34 (e.g., utilizing a hole saw as described above), hinge pin plug 120 is removed, e.g., with a scalpel and forceps to provide access to the hexagonal indentation of hinge pin 34 so that a hexagonal wrench may be inserted therein to unthread hinge pin 34 from femoral component 22.
Knee prosthesis 20 includes a pair of hyperextension stop mechanisms. The first hyperextension stop comprises a portion of condylar bearing surfaces 28, 30 of increased radius of curvature as compared to the remaining condylar bearing surface. At three degrees of hyperextension this portion of increased radius of curvature will contact meniscal component 26 and act to retard further hyperextension. If hyperextension continues, the area of increased radius of curvature will cause femoral component 22 to lift away from meniscal component 26. The second hyperextension stop mechanism functions at four degrees of hyperextension to prohibit further hyperextension of knee prosthesis 20. The second hyperextension stop mechanism comprises hyperextension stop surface 66 of hinge post 40 and hyperextension stop 68 of bearing box 70. Hyperextension stop surface 66 comprises the concave back wall of cannulated hinge post 40 as illustrated, e.g., in
Tibial component 24 is depicted in
Tibial component 24 further includes rotation protrusion 96. As illustrated, e.g., in
One embodiment of meniscal component 26 is illustrated in
Meniscal components of varying heights may be constructed in accordance with the present invention. In one advantageous aspect of the present invention, meniscal component 26 is packaged for sale and use together with hinge post extension 42 to facilitate component choice and, in one embodiment, to ensure proper extension of hinge post extension 42 into tibial component 24. The extension of hinge post extension 42 into tibial component 24 functions to prevent separation of knee prosthesis 20 after implantation thereof. As is known in the art, the femoral component of a knee prosthesis may, in some situations, move relative to and away from the tibial component in a direction parallel to the longitudinal axis of the hinge post extension. With this in mind, hinge post extension 42 is made to be of sufficient length to be retained within tibial component 24 even in situations in which femoral component 22 moves as described immediately supra. In one exemplary embodiment, hinge post extension 42 extends four centimeters into hinge post extension aperture 110 in tibial component 24.
Meniscal component 26 includes cutout 90 which cooperates with rotation protrusion 96 of tibial component 24 to guide rotation of meniscal component 26 and to resist lifting of meniscal component 26 from tibial tray 98 of tibial component 24. As illustrated, e.g., in
Meniscal component 26b illustrated in
As illustrated in
Positioning of meniscal component 26b as described above in conjunction with
As illustrated in
While this invention has been described as a prosthetic knee with a rotating bearing, it is contemplated that various aspects of the present invention, including, e.g., the cannulated hinge post will be utilized with a prosthetic knee having a fixed bearing.
While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.
Claims
1. A prosthetic femoral component, comprising:
- a femoral component body;
- a hinge post rotatably connected to said femoral component body, said hinge post rotatable relative to said femoral component body about an axis of rotation, said hinge post including an elongate aperture, said elongate aperture transverse to said axis of rotation.
2. The prosthetic femoral component of claim 1, further comprising:
- a hinge post extension, said elongate aperture of said hinge post sized for placement of said hinge post extension therein, whereby said hinge post extension traverses a first end of said elongate aperture of said hinge post and protrudes from a second end of said elongate aperture of said hinge post, said first and second ends of said elongate aperture of said hinge post comprising opposing ends of said elongate aperture of said hinge post.
3. The prosthetic femoral component of claim 2, further comprising:
- securing means for securing said hinge post extension to said hinge post.
4. The prosthetic femoral component of claim 3, wherein said securing means comprises:
- a male taper positioned on said hinge post extension; and
- a female taper positioned in said elongate aperture, said male taper engageable in said female taper to secure said hinge post extension to said hinge post.
5. The prosthetic femoral component of claim 1, further comprising:
- a bearing box connected to said femoral component body, said bearing box interposed between said hinge post and said femoral component body, said bearing box including a hyperextension stop, said hinge post including a hyperextension stop surface, said hyperextension stop contacting said hyperextension stop surface to prevent further hyperextension of the prosthetic femoral component body beyond a predetermined point of hyperextension.
6. The prosthetic femoral component of claim 5, wherein said predetermined point of hyperextension comprises four degrees of hyperextension of the prosthetic knee body.
7. The prosthetic femoral component of claim 5, wherein said hyperextension stop comprises a convex protrusion.
8. The prosthetic femoral component of claim 5, wherein said hinge post includes an internal wall, said hyperextension stop surface comprising said internal wall of said hinge post.
9. The prosthetic femoral component of claim 2, further comprising:
- a male taper positioned on said hinge post extension; and
- a female taper positioned in said elongate aperture, said male taper engageable in said female taper to secure said hinge post extension to said hinge post.
10. The prosthetic femoral component of claim 1, further comprising:
- a set screw, said first end of said elongate hinge post extension aperture being threaded, whereby said set screw will engage the threads of said elongate hinge post extension aperture, said hinge post extension including a locking taper, a hinge post extension aperture including a cooperating taper, whereby threading of said set screw into said elongate hinge post extension aperture forces said locking taper into locking engagement with said cooperating taper.
11. The prosthetic femoral component of claim 1, wherein said hinge post is rotatably connected to said femoral component body via a hinge pin, said hinge post rotatable about a longitudinal axis of said hinge pin, said hinge pin including an indentation on a first end thereof, and
- a hinge pin plug positioned within said indentation and being flush with said first end of said hinge pin.
12. The prosthetic knee of claim 11, wherein said hinge pin plug is formed from an ultra-high molecular polyethylene.
Type: Application
Filed: Dec 14, 2007
Publication Date: Apr 24, 2008
Applicant: ZIMMER TECHNOLOGY, INC. (Warsaw, IN)
Inventors: John Meyers (Columbia City, IN), G. Letson (Tampa, FL), Russell Windsor (Larchmont, NY), Vincent Webster (Warsaw, IN), Bill Sisk (Claypool, IN), Bill Haywood (Warsaw, IN), Adam Griner (Columbia City, IN), Michael Cook (Claypool, IN), Rodney Bays (Pierceton, IN), Jerry Aikins (Warsaw, IN), Marvin Figueroa (Warsaw, IN), Peter Walker (New York, NY)
Application Number: 11/956,998
International Classification: A61F 2/38 (20060101);