Patent Application
20060190089
This invention relates generally to orthopedics and, in particular, to a versatile reconstruction system associated with an acetabular prosthetic implant.
The replacement of members of a natural hip joint (femoral and acetabular) with prosthetic implants has become widespread and is being accomplished with ever-increasing frequency. The variety of conditions encountered when effecting such implants has led to the use of various bearing materials and attachment methods placed at an optimum position and orientation, as determined by conditions encountered at the site of the implant. The choice of a particular material for the bearing, as well as the size, positioning and orientation of the bearing member, is determined by the surgeon performing the procedure. Usually such choices are made on the basis of a pre-operative assessment of the needs of a particular patient; however, at times the choices are not completed until the implant site actually is being prepared and conditions encountered at the site can be evaluated during the implant procedure itself. Accordingly, it would be advantageous to have available a greater range of interoperative choices, as well as pre-operative choices, so as to enable a surgeon to accommodate the needs of a particular patient as determined by either or both a pre-operative assessment and an evaluation of conditions encountered at a particular implant site, and to do so in a practical manner.
Especially in the case of revision surgical procedures wherein the pelvis has been severely compromised or deteriorated, it is known to use support structures to receive an acetabular prosthetic device. More particularly, this invention relates to outer shells or cages which include wings, straps or flanges to enhance the support of the acetabular prosthesis on the pelvis. The cages include tapered inner surfaces to receive adaptors having tapered outer surfaces. The adaptor has a cavity for receiving a bearing element. Such a system is disclosed in co-pending U.S. application Ser. No. 10/878,787, entitled “INTERNAL FIXATION ELEMENT FOR HIP ACETABULAR SHELL” assigned to the assignee of the present application. The disclosure of that application is incorporated herein by reference.
Another such structure is disclosed in U.S. Pat. No. 5,314,490 to Wagner et al., entitled OUTER CUP FOR AN ARTIFICIAL HIP JOINT SOCKET. According to this patent, an artificial hip joint socket for fastening to a pelvic bone includes a metallic outer cup forming a concavity for receiving a hip, which terminates in an equatorial edge to which supporting flaps are fastened. The flaps include holes to receive bone screws and have preset lines or grooves to enabling preferential bending to provide conformance with the pelvic region surrounding the procedure.
U.S. Pat. No. 5,425,778 relates to an acetabular socket supporting ring having at least one attaching strap for attachment to a corresponding bone portion. This construction has a disadvantage that the support ring must be used in all applications since it receives the outer shell of the acetabular prosthesis.
U.S. Pat. Nos. 5,871,548 and 6,340,370 disclose modular outer shells having wings, straps or flanges which selectively attach to the shell if required.
U.S. Pat. Nos. 6,475,243 and 6,610,097 and European Patent No. 0 773 007 relate to modular acetabular cup systems with inserts which can position bearing liners at various angles to the open face of the outer cup shell. The disclosure of U.S. Pat. No. 6,475,243 is incorporated herein by reference. The prosthetic modular acetabular system of the present invention allows the user to create an outer shell or base (dome and plates or straps) construct for the reconstruction of an acetabulum joint member in revision surgery. This design allows the user to independently set the position of an acetabular liner (polyethylene, metal or ceramic) through the insertion of a metal adaptor or sleeve.
The metal adaptor or sleeve will preferably be available in (0°, 10°, 20°, etc.) inclinations and will connect to the base outer cage construct through a taper junction. The presence of a symmetrical taper, on the outside of the metal sleeve, allows anteversion and placement of the metal sleeve around a circular or 360° range prior to taper locking. A bolt between the sleeve or adaptor and the cage base will ensure locking of the tapers. The main purpose of the design is to obtain independent placement, inclination and fixation of an acetabular bearing liner from the already established base construct by means of the metal sleeve described above.
The present invention allows the base construct and the orientation/inclination of the liner to be independently assessed, set and fixed through a metal adaptor component. The metal adaptor or sleeve component can be easily removed from the base construct and reoriented if necessary according to the user's needs. The procedure for implanting the modular cage is as follows: the shell is placed into the acetabulum and secured with screws through the dome and external plates. This allows a solid foundation to be established. Next, a trial adaptor sleeve is inserted into the shell to establish the correct inclination and orientation of the sleeve. At this point, the bearing liner is also trialed. The correct adaptor or sleeve implant is impacted into the shell to engage the taper junction between the shell and sleeve. A bolt or screw is then inserted into the construct. The bearing liner is trialed for a second time. The proper bearing liner implant is impacted into the cage/sleeve construct.
The present invention provides the surgeon with the ability to choose, either pre-operatively or intra-operatively, an optimum, position and orientation for an acetabular cup assembly to be implanted at a particular implant site, with increased ease and at lowered expense. As such, the present invention attains several objects and advantages, some of which are that it allows the choice of the size, position and orientation of the bearing surface of a bearing member selected for assembly with a particular acetabular shell; increases the range of the bearing size, positioning and orientation, and renders the choices available in a practical manner for either pre-operative or inter-operative selection; allows a surgeon greater latitude in accommodating the needs of different patients while meeting the requirements imposed by various conditions encountered at a particular implant site, and enables appropriate choices to be made intra-operatively, as well as pre-operatively; promotes greater accuracy in the replacement of a natural hip joint, with increased economy; provides a surgeon with the ability to make both pre-operative choices and inter-operative choices from a wider range of options; facilitates the insertion and securement of a selected bearing member within an acetabular shell in appropriate alignment and orientation of the bearing member within the acetabular base, cage, or shell; provides an acetabular cup assembly having accurate sizing, positioning and orientation, with economy of manufacture and use, and long-term reliability.
As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.
The above aspects and advantages, as well as further aspects and advantages, are attained by the present invention which may be described briefly as an acetabular cup assembly for receiving a proximal end of a femoral component of a prosthetic hip implant, the femoral component including a head member and a neck member depending from the head member, the acetabular cup assembly having an external cage or shell member with an internal cavity, including a coupling element, an adaptor with an internal cavity and an internal bearing member of a ceramic, metal or polymer for securement within the adaptor cavity to receive the head member of the femoral component for rotational movement within the bearing member. The internal bearing member has an external coupling element and may be selected from a plurality of bearing members which may have different characteristics. The cup assembly may include a metallic outer shell or cage having wings, flanges or straps extending radially outwardly therefrom which cage is provided for reception within the cavity of the acetabulum. The adaptor extends between an upper end and a lower end of the cage and preferably includes a tapered external securing element and an internal coupling element for engaging the external coupling element on the bearing member. The wings, flanges or straps may be modular or integral with the shell or cage. Preferably, the wings, flanges or straps are ductile enough to be bent or deformed by the surgeon to closely conform to adjacent bones. Alternatively, the wings, flanges or straps may have grooves or thinner areas to aid in bending. The outer cage preferably has an internal locking surface for receiving the adaptor. The preferred internal locking surface on the outer shell and the corresponding outer locking surface on the adaptor are preferably mating locking tapered surfaces. In the preferred embodiment, there are multiple adaptors, the tapered surfaces on the adaptors with respect to its open face vary from one adaptor to another with respect to the angle of the tapered surface with the outer cage polar axis. Thus, since the adaptor tapered surface axis is inclined with respect to the cage polar axis, rotation of the adaptor, prior to it being locked within the shell results in multiple orientation of the bearing surface with respect to the cage.
Further, the present invention provides a cage or shell member and adaptor for use in an acetabular cup assembly having an internal polymeric or ceramic bearing member for securement within the adaptor. The internal polymeric or ceramic bearing member is selected from a plurality of bearing members having different characteristics such as bearing surface size for different heads or inclinations. The adaptor member includes an internal wall of its cavity with a coupling element matching on the external wall of the bearing member. A tapered coupling element may be on the adaptor inner surface and would be compatible with the external tapered securing characteristics of the plurality of bearing members such as ceramic bearings. Optionally, a second additional bearing coupling element may be provided within the cavity of the adaptor, the second securing element being compatible with the securing characteristics of other internal bearing members so that a, for example, polymeric bearing element may be introduced directly into the adaptor. The first coupling element and the second optional coupling element being juxtaposed with one another and placed at relative locations such that the effectiveness of each of the first and second securing elements is maintained in the presence of the other of the first and second securing elements, whereby the one and the another of the internal bearing members each is selectable for effective securement within the adaptor member which in turn is selectable for implantation into the outer cage or shell to complete the acetabular cup assembly.
The coupling element or elements formed on the inner surface of the adaptor may also be present on the inner surface of the outer cage. This allows a bearing element to be mounted on the tapered conical inner surface of the outer cage. The outer cage or shell includes outwardly extending wings, flanges or straps for engaging the bone adjacent the acetabulum. The wings or flanges include holes to accommodate bone screws which engage the pelvic bone. The straps or wings may be modular and have mounting features, such as screws which engage corresponding mounting features on the securing elements for their assembly to the hemispherical adaptor body. Such features are well known in the prior art. As discussed above, in addition, the flanges or wings may be bendable to allow the surgeon to conform the shape of the wings or straps to the pelvic bone. This may be done, for example, by making the straps or wings of a deformable material such as a ductile metal or making the material cross-section relatively thin throughout its length or at least at selected areas along the length of the wing or strap.
In addition, the present invention includes a kit of component parts for assembling an acetabular cup assembly having an adaptor secured within an outer shell or cage and an internal bearing member secured within the adaptor member, the kit comprising: a plurality of bearing members having different characteristics such that the acetabular cup assembly selectively is provided with characteristics corresponding to the characteristics of a selected one of the internal bearing members (preferably made of ceramic or polyethylene); a plurality of cage or shell members comprising: an internal cavity having at least one coupling element in the form of a tapered inner surface with a first coupling element within the cavity of the cage member being compatible with the tapered outer surface of a plurality of adaptors; and optionally, a second coupling element within the cavity of the shell member, the second coupling element being compatible with the securing characteristics of at least one of the plurality of internal bearing members; the first and second coupling elements may be juxtaposed with one another and placed at relative locations such that the effectiveness of each of the first and second coupling elements is maintained in the presence of the other of the first and second coupling elements, whereby the one and the another of the internal bearing members each is selectable for effective securement within the outer shell member as the selected one bearing member to complete the acetabular cup assembly. The tapered inner surface of the shell lockingly engages the adaptor which in turn lockingly receives the bearing element. The plurality of adaptors have inner surfaces oriented at different angles or inclinations such as 0°, 10°, 20°, etc. with respect to the polar axis of the outer part spherical cage. Preferably these surfaces are also inwardly tapered i.e., tapered inwardly from the open end towards the polar area of the adaptor to engage complimentary tapered surfaces on the outside of the bearing component.
These and other objects of the invention are set forth in an acetabular cup assembly used in a prosthetic hip joint replacement which has an outer shell for attachment to the acetabulum, a bearing insert portion and an adaptor. The outer shell or cage has a part spherical inner surface and a preferably tapered coupling mechanism adapted to receive the adaptor. The bearing has an external coupling element for engagement with a complementary coupling element on the internal surface of the adaptor. The adaptor has a tapered outer surface for engaging the inner tapered surface of the outer shell or cage with its inner surface adapted for receiving the bearing element. The adaptor tapered surface may be inclined with respect to the tapered shell surface. The shell may have at least one radially extending strap, flange or wing which either conforms with or can be deformed in a manner to conform with the bone surrounding the acetabulum.
The deformable wing, flange or strap is deformable at least in a direction perpendicular to the radial direction and may be oriented at various angles around and extend various lengths with respect to the body of the adaptor. Obviously, the longer the length, the greater the engagement with various areas of the pelvis are possible. The wing, strap or flange may include a reduced cross-section to facilitate deformation or may be made of a ductile material. Alternately, the flange can have a groove or series of grooves to facilitate bending.
The engagement or coupling mechanism between the cage and the outer surface of the adaptor is preferably a complementary conically tapered surface. The surface has a tapered angle so that a locking coupling can be formed between the shell or cage and the adaptor. Preferably, additionally the cage and adaptor includes a threaded coupling which extends in the polar region of either the cage and can threadably couple the cage and adaptor together. Preferably, tightening of the threaded coupling forces locking engagement between the complementary preferably conically tapered surfaces.
The above structure can be supplied in kit form with a variety of shells, adaptors, bearing inserts, which bearings are preferably made of polyethylene and/or ceramic. If ceramic, the bearing may be surrounded by a press-fit metal adaptor. The cages or shells may have one or more wings located in fixed positions around the circumference of the shell or, in fact, may be modular and therefore attachable such as by threaded connectors, such as screws, at any desired angular orientation around the circumference of the shell. Thus, the parts may be selected intraoperatively. This is especially helpful when the pelvis is deformed or otherwise missing natural bone so that shells or cages having straps oriented in various angular locations and of various lengths can be selected from the kit and placed in position usually utilizing screws.
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The preferred method of use of the acetabular cup system 10 is for the surgeon to initially implant outer cage 12 in a desired location utilizing a plurality of bone screws. Bone screws may be used in both the holes 62 in the part-spherical shell 12 and also in holes 32 of straps 30. The screw may be inserted in a mono-axial fashion into holes 32, 62 or holes 32, 62 may include part-spherical walls having a part-spherical ring 102 allowing for polyaxial orientation of the screw. Such a design is shown in U.S. Patent application filed this date listing Gregory Plaskon as inventor and assigned to the assignee of the present invention. The outer shell 12 may be chosen from a series of different size shells depending on the size of the acetabulum or location of the straps 30. Once implanted, an adaptor 14 can be chosen from a plurality of adaptors and mated with outer shell 12 via the interlocking of tapered surfaces 40 and 42. The plurality of adaptors 14 have polar axis 46 located at different angles to the polar axis of 44 of shell 12 as discussed above and, on insertion, can be oriented in a manner which best corresponds to the anatomy of the patient. Once properly oriented the surgeon inserts screw 18 through hole 49 and into hole 22 and locks the shell/adaptor assembly together. Alternatively the adaptor and bearing may be impacted into place.
The surgeon may then insert the desired ceramic or polyethylene bearing liner 16, 16a. Alternatively, if screw 18 is not used, the bearing liner 16 can be assembled into the adaptor 14 prior to insertion of the adaptor 14 into outer cage 12.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
