Patent Application
20090222007
1. Field of the Invention
The present invention relates to orthopedic implants and, particularly, to modular orthopedic components.
2. Description of the Related Art
To repair diseased and/or damaged bone, orthopedic implants may be utilized. Orthopedic implants are designed to replace the diseased and/or damaged bone and to replicate the anatomy of the same. Thus, when a bone becomes diseased and/or damaged, such as a femur, the diseased and/or damaged portion of the bone may be osteotomized. An implant, replicating the function of the osteotomized bone, may then be implanted. For example, when the head of a femur becomes diseased and/or damaged, the same may be resected and a stem implanted within the intramedullary canal of the femur. The stem may include an integral head configured to replicate the function of the osteotomized natural femoral head or, alternatively, the stem may be one component of a modular prosthesis system. To help retain the stem in its proper position, the head of the stem may be formed to include porous surfaces that facilitate tissue ingrowth. These porous surfaces may be located at a position on the head of the stem that is separated from the surface of the osteotomized bone.
The present invention relates to orthopedic implants and, particularly, to modular orthopedic components. In one exemplary embodiment, a modular stem component is provided and may include a shaft portion, a head, and a discrete sleeve. The shaft portion of the stem is configured for receipt within the intramedullary canal of a bone and the head of the stem is configured to extend above the osteotomized bone. The head of the stem may also receive another component of a modular prosthetic system, such as a femoral neck, thereon. In one exemplary embodiment, the sleeve, which is formed as an independent component and is made at least partially of a highly porous biomaterial, is dimensioned to be received on the exterior of the head of the stem. With the sleeve received on the head of the stem, implantation of the shaft portion within the intramedullary canal of a bone results in the sleeve directly contacting the osteotomized bone to facilitate boney ingrowth and further secure the stem component within the intramedullary canal of the bone. For example, in one embodiment, the sleeve is captured between the resected bone and a flange extending from the head of the stem. In another exemplary embodiment, the sleeve is retained on the head of the stem by a taper lock or adhesive, for example.
Advantageously, by forming the sleeve as an independent part of the modular stem component, the shaft portion and head of the stem may be formed and prepared without the need to protect the highly porous biomaterial forming the sleeve. Thus, the number of masks and the amount of special fixturing used during production are substantially decreased. As a result, the cost of manufacturing the modular stem component is correspondingly reduced. Additionally, due to the sleeve being at least partially formed from a highly porous biomaterial, the sleeve facilitates bony ingrowth and otseointegration of the bone with the modular stem component. This boney ingrowth may help to seal the intramedullary canal of the bone in which the shaft portion is implanted and provide additional stability to the head of the stem. Further, the interaction between the sleeve and the bone helps to prevent pistoning of the stem within the intramedullary canal of the bone and eliminates the need to drill stability holes in the bone to prevent rotation of the stem.
In one form thereof, the present invention provides a modular prosthetic component configured for implantation within a bone, the modular prosthetic component including: a stem having an elongate shaft portion defining a longitudinal axis; a head extending from said stem, said head having a stop; and a sleeve dimensioned for receipt on said head, said sleeve formed at least partially from a highly porous biomaterial, said highly porous biomaterial allowing tissue ingrowth therein, said sleeve having an exterior surface, an interior surface defining an internal bore, and opposing ends connecting said exterior surface and said interior surface, said sleeve dimensioned for sliding receipt on said head in a first direction, wherein said stop limits movement of said sleeve in the first direction, whereby said sleeve is captured by said stop and the bone when said stem is implanted in the bone.
In another form thereof, the present invention provides a modular prosthetic component configured for implantation within a bone, the modular prosthetic component including: a stem having a shaft portion defining a longitudinal axis; a head having a throughbore formed therein, said throughbore dimensioned to receive at least a portion of said stem therein; and a plurality of sleeves having different dimensions, each of said plurality of sleeve formed at least partially from a highly porous biomaterial and configured for interchangeable receipt on said head.
In yet another form thereof, the present invention provides a method of implanting a modular prosthetic component having a head and a stem, including the steps of: positioning a sleeve formed at least partially from a highly porous biomaterial on the head interoperatively; implanting at least a portion of the stem in the intramedullary canal of a bone; and seating the stem to provide direct contact between an end of the sleeve and the bone.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring to
Referring to
Nut 18 of modular stem component 10 is configured for receipt on post 28 of stem 12. Specifically, the internal surface of nut 18 defines bore 56 having threads 58 extending therefrom. Threads 58 are dimensioned to threadingly engage threads 32 extending from post 28 of stem 12. Additionally, impaction slots (not shown) may be formed in end 30 of stem 12 and may align be aligned with slots 60 formed in nut 18. Impaction slots (not shown) may be dimensioned to matingly engage an impaction tool (not show) and facilitate the impaction of stem 12 into the intramedullary canal of a bone, as described in detail below.
As stated above, modular prosthesis 10 also includes head 14. Extending through head 14 is internal bore 36. Referring to
The exterior of head 14 includes tapered surface 48 separated from tapered surface 20 by flange 50. Referring to
In another exemplary embodiment of modular stem component 10, shown in
Sleeve 16 of modular stem component 10 is configured for receipt on exterior tapered surface 48 of head 14. Specifically, internal surface 54 of sleeve 16 defines internal bore 53 dimensioned for receipt on tapered surface 48. In one exemplary embodiment, internal bore 53 is dimensioned such that inner surface 54 matingly engages tapered surface 48 of head 14. For example, inner surface 54 of sleeve 16 may be correspondingly tapered to lock sleeve 16 on tapered surface 48. In another exemplary embodiment, sleeve 16 may be retained on tapered surface 48 of head 14 by an adhesive (not show). By utilizing an adhesive, such as bone cement, a resin, or another biocompatible slip resistant material, the need to heat treat head 14 to secure sleeve 16 thereto is eliminated. Additionally, in another exemplary embodiment, surface 48 may be design to increase friction between surface 48 and sleeve 16 to facilitate the retention of sleeve 16 thereon. For example, surface 48 may be knurled, have at least one dimple formed thereon, or have a polymethylmethacrylate coating.
In another exemplary embodiment, a plurality of sleeves 16 may be provided with the modular prosthesis system, each having different dimensions, which may correspond to sleeves 71 (
Referring
In one exemplary embodiment, internal bore 53 of sleeve 16 may be dimensioned such that, when sleeve 16 is positioned over head 14, a gap is formed between inner surface 54 of sleeve 16 and exterior tapered surface 48 of head 14. In this embodiment, sleeve 16 may be canted relative to head 14 when modular stem component 10 is finally implanted. For example, as shown in
Sleeve 16 is made at least in part of, and may be made entirely of, a highly porous biomaterial useful as a bone substitute and/or cell and tissue receptive material. A highly porous biomaterial may have a porosity as low as 55, 65, or 75 percent and as high as 80, 85, or 90 percent. An example of such a material is produced using Trabecular Metal™ technology generally available from Zimmer, Inc., of Warsaw, Ind. Trabecular Metal™ is a trademark of Zimmer Technology, Inc. Such a material may be formed from a reticulated vitreous carbon foam substrate which is infiltrated and coated with a biocompatible metal, such as tantalum, etc., by a chemical vapor deposition (“CVD”) process in the manner disclosed in detail in U.S. Pat. No. 5,282,861, the disclosure of which is expressly incorporated herein by reference. In addition to tantalum, other metals such as niobium, or alloys of tantalum and niobium with one another or with other metals may also be used.
Generally, the porous tantalum structure includes a large plurality of ligaments defining open spaces therebetween, with each ligament generally including a carbon core covered by a thin film of metal such as tantalum, for example. The open spaces between the ligaments form a matrix of continuous channels having no dead ends, such that growth of tissue, such as cancellous bone, through the porous tantalum structure is uninhibited. The porous tantalum may include up to 75%-85% or more void space therein. Thus, porous tantalum is a lightweight, strong porous structure which is substantially uniform and consistent in composition, and closely resembles the structure of natural cancellous bone, thereby providing a matrix into which tissue, such as cancellous bone, may grow to provide fixation of sleeve 16 to the surrounding bone, as described below.
The porous tantalum structure may be made in a variety of densities in order to selectively tailor the structure for particular applications. In particular, as discussed in the above-incorporated U.S. Pat. No. 5,282,861, the porous tantalum may be fabricated to virtually any desired porosity and pore size, and can thus be matched with the surrounding natural bone in order to provide an improved matrix for bone ingrowth and mineralization.
With sleeve 16 received on head 14, as described in detail above, stem 12 may be inserted within internal bore 36 of head 14. Specifically, threaded end 30 of stem 12 may be inserted within internal bore 36 and advanced in the direction of counterbored portion 38, allowing head 14 to extend radially around at least a portion of stem 12. With stem 12 advanced toward counterbored portion 38, head engagement portion 24 of stem 12 may contact stem engagement portion 40 of head 14. In one exemplary embodiment, head engagement portion 24 and stem engagement portion 40 form corresponding male and female tapers, respectively. Thus, as stem 12 is advanced within internal bore 36, the engagement of the corresponding tapers of head engagement portion 24 and stem engagement portion 40 substantially prevent additional advancement of stem 12 therethrough.
Once stem 12 is positioned within internal bore 36 of head 14, nut 18 is received within counterbored portion 38 of internal bore 36 and threadingly engaged with post 28. Specifically, threads 58 of nut 18 threadingly engage threads 32 of post 28. As nut 18 is threadingly advanced via a tool (not shown), which may also engage slots 60, nut 18 seats against flange 44 and provides a securement mechanism to prevent migration of stem 12 from internal bore 36. With stem 12 properly seated within bore 36, clearance C, shown in
Once stem 12, head 14, sleeve 16, and nut 18 are secured to one another to form modular stem component 10, the bone is resected to remove the diseased or damaged portion and modular stem component 10 is inserted within the intramedullary canal of the bone and impacted. Alternatively, the bone may be resected prior to the assembly of stem 12, head 14, sleeve 16, and nut 18 to form modular stem component 10. Specifically, to implant modular component 10, nose 23 (
Advantageously, due to sleeve 16 being at least partially constructed from a highly porous biomaterial, sleeve 16 facilitates bony ingrowth and osteointegration of the bone with modular stem component 10. This boney ingrowth and osteointegration may help to seal the intramedullary canal of the bone in which stem 12 is inserted and provide additional stability to head 14. Further, the interaction between sleeve 16 and the resected end of the bone helps to prevent pistoning of stem 12 within the intramedullary canal of the bone and eliminates the need to drill stability holes in the bone to prevent rotation of stem 12.
Referring to
While this invention has been described as having a preferred design, the present invention can 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 and which fall within the limits of the appended claims.
