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Orthopaedic device for implantation in the body of an animal and method for making the sameRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Implantable Prosthesis, Bone, PolymersOrthopaedic device for implantation in the body of an animal and method for making the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070093909, Orthopaedic device for implantation in the body of an animal and method for making the same. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This patent application is a continuation of U.S. patent application Ser. No. 10/310,394, filed Dec. 5, 2002, which claims priority to U.S. Provisional Patent Application Ser. No. 60/340,807, filed on Dec. 12, 2001, the disclosure of both of which is hereby incorporated herein by reference. FIELD OF THE DISCLOSURE [0002] The present disclosure generally relates a polymeric material for use in the construction of a device to be implanted in the body of an animal and associated methods for making the same. The present disclosure particularly relates to an implantable orthopaedic device constructed from a polymeric material and associated methods for making the same. BACKGROUND OF THE DISCLOSURE [0003] Various polymeric materials possess desirable characteristics which make them suitable for use in the construction of devices to be implanted in the body of an animal (e.g. a human). For example, many implantable orthopaedic prostheses include at least one component constructed from a polymeric material. In particular, a number of implantable prosthetic bearings include an articulating or bearing surface constructed from a polymeric material on which either a natural bone structure or a prosthetic component articulates. Specific examples of such polymeric bearing surfaces include acetabular bearings, glenoid bearings, tibial bearings, and the like, for use in hip, knee, shoulder, and elbow prostheses. In addition, typical prosthetic bearing designs include an engaging surface constructed from a polymeric material. The engaging surface may also include locking features constructed from a polymeric material. These locking features can be configured as pins, tabs, tapered posts, or the like for locking or otherwise securing the bearing to either another component associated with a prosthetic assembly (e.g., a metal shell or tray) or to the bone itself. Accordingly, in light of the above discussion, it should be appreciated that a number of devices for implantation in the body of an animal are constructed from, or include components constructed from, a polymeric material. Therefore, it is desirable to enhance or improve one or more characteristics of a polymeric material which is used in the construction of a device to be implanted in the body of an animal. SUMMARY OF THE DISCLOSURE [0004] A device for implanting into a body of an animal, and a method of preparing a polymeric material for implantation into a body of an animal, as for example, an orthopaedic implant, in accordance with the present disclosure comprises one or more of the following features or combinations thereof: [0005] A mass of polymeric material to be implanted into a body of an animal may be subjected to a treatment to remove low-molecular-weight compounds. The treatment to remove low-molecular-weight compounds from the polymeric compound may be performed after the polymeric material has been subjected to a free radical quenching process. For example, the polymeric material may be subjected to a free radical quenching process while positioned in a first chamber. Thereafter, the polymeric material may be removed from the first chamber and placed in a second chamber where low-molecular-weight compounds are removed from the polymeric material. The removal of low-molecular-weight compounds from the polymeric material may include heating the polymeric material while being subjected to a pressure less than 1 atmosphere. Alternatively, the removal of low-molecular-weight compounds from the polymeric material may include extracting the low-molecular-weight compounds with a fluid, such as a liquid or a supercritical fluid. Examples of low-molecular-weight compounds comprise those having a molecular weight less than about 5000, a molecular weight less than about 300, or a carbon number equal to, or less than, 20. The low-molecular-weight compounds may be, for example, hydrocarbons such as aliphatic hydrocarbons. An example of a polymeric material which can be utilized in the methods described herein is crosslinked UHMWPE. The polymeric material may be formed into a bearing configured for use in an orthopaedic implant and sterilized. Removing of the low-molecular-weight compounds may occur prior to, or subsequent to, forming the polymeric material into a bearing configured for use in an orthopaedic implant. The bearing formed from the polymeric material may have a concave bearing surface for engaging a convex articulating surface or a convex articulating surface for engaging a concave bearing surface. A polymeric orthopaedic bearing component containing 0.1% or less aliphatic hydrocarbons which have a molecular weight of 5000 or less may be obtained. For example, a polymeric orthopaedic bearing component which is substantially free of aliphatic hydrocarbons which have a molecular weight of 5000 or less may be obtained. [0006] Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the subject matter of the disclosure as presently perceived. BRIEF DESCRIPTION OF THE DRAWINGS [0007] FIG. 1 is a cross sectional view of an implantable prosthetic bearing that may be produced by processes described herein; [0008] FIG. 2 is a perspective view of an implantable glenoid bearing prosthesis that may be produced by processes described herein; [0009] FIG. 3 is a perspective view of an implantable acetabular bearing prosthesis that may be produced by processes described herein; [0010] FIG. 4 is a perspective view of an implantable tibial bearing prosthesis that may be produced by processes described herein; and [0011] FIG. 5 is a pressure-temperature phase diagram which illustrates the critical point and the associated supercritical fluid region. DETAILED DESCRIPTION OF THE DISCLOSURE [0012] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms described, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. [0013] The present disclosure generally relates to a polymeric material for use in the construction of a device to be implanted in the body of an animal (e.g. a human) and associated methods for making the same. The present disclosure particularly relates to implantable polymeric devices such as prosthetic orthopaedic bearings and methods for making the same. Such bearings may be utilized in a number of joint replacement or repair procedures such as surgical procedures associated with the hip, shoulders, knees, ankles, knuckles, or any other joint. For example, such implantable prosthetic bearings may be embodied as a glenoid bearing for implantation into a glenoid of a patient, an acetabular bearing for implantation into an acetabulum of a patient, or a tibial bearing for implantation into a tibia of a patient. A typical prosthetic bearing design includes an articulating or bearing surface on which either a natural bone structure or a prosthetic component articulates. In addition, a typical prosthetic bearing design also includes an engaging surface which may include locking features in the form of mechanisms such as pins, tabs, tapered posts, or the like for locking or otherwise securing the bearing to either another component associated with a prosthetic assembly (e.g., a metal shell or tray) or to the bone itself. [0014] Referring now to FIGS. 1-4, there is shown an implantable polymeric prosthetic bearing 10. The bearing 10 is shown schematically as a bearing 12 in FIG. 1, whereas specific exemplary embodiments of the prosthetic bearing 10, such as a glenoid bearing 14 for implantation into a glenoid of a patient (not shown), an acetabular bearing 16 for implantation into an acetabulum of a patient (not shown), and a tibial bearing 18 for implantation into a tibia of a patient (not shown) are shown in FIGS. 2-4, respectively. Each of the embodiments of the prosthetic bearing 10 includes an articulating or bearing surface 20 on which a natural or prosthetic component bears. For example, in the case of the glenoid bearing 14, a natural or prosthetic humeral head (not shown) bears on the articulating surface 20. Similarly, in the case of an acetabular bearing 16, a natural or prosthetic femoral head (not shown) bears on the articulating surface 20. Moreover, in the case of the tibial bearing 18, a pair of natural or prosthetic femoral condyles (not shown) bear on the articulating surface 20. [0015] Each of the prosthetic bearings 10 also includes an engaging surface 22 which may have a number of features defined therein for engaging either another prosthetic component or the bone into which the bearing 10 is to be implanted. For example, in the case of the glenoid bearing 14, a number of pins or pegs 24 may be defined in the engaging surface 22 thereof. The pegs 24 are received into a number of corresponding holes (not shown) formed in the glenoid surface of the patient. The pins 24 are typically held in place with the use of bone cement. Moreover, if the glenoid bearing 14 is utilized in conjunction with an implanted metal shell, the engaging surface 22 of the bearing 14 may be configured with a tapered post (not shown) or the like for securing the glenoid bearing 14 to the shell. [0016] In the case of the acetabular bearing 16, a number of keying tabs 26 are defined in the engaging surface 22 along the outer annular surface thereof. The keying tabs 26 are received into a number of corresponding keying slots (not shown) defined in an implanted metal acetabular shell (not shown) in order to prevent rotation of the acetabular bearing 16 relative to the implanted shell. In the case of fixation of the acetabular bearing 16 directly to the acetabulum of the patient (i.e., without the use of a metal shell), the engaging surface 22 of the bearing 16 may alternatively be configured with a number of posts or pegs (not shown) which are received into a number of corresponding holes formed in the patient's acetabulum. In such a case, the posts or pegs are typically held in place with the use of bone cement. Moreover, the acetabular bearing 16 may be cemented to the patient's acetabulum without the use of posts or pegs on the engaging surface 22 thereof. [0017] In the case of the tibial bearing 18, a tapered post 28 is defined in the engaging surface 22 thereof. The tapered post 28 is received into a corresponding tapered bore (not shown) defined in an implanted tibial tray (not shown) of a knee prosthesis (not shown). The engaging surface 22 of the tibial bearing 18 may also be configured with features to allow the tibial bearing 18 to be secured directly to the tibia without the use of an implanted tray (e.g., by use of bone cement). [0018] As indicated above, the bearing, or the preform from which it is constructed, may be formed from a polymer. As used herein, the term "polymer" is intended to mean any medical grade polymeric material which may be implanted into an animal (e.g. a human patient), including, but not limited to, polyesters, poly(methylmethacrylate), nylon, polycarbonates, and polyolefins. The term "polymer" is also intended to include both homopolymers and copolymers; thus, "polymer" includes a copolymer comprising ethylene and an acrylate derivative, such as methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, and butyl methacrylate. The term "polymer" also includes oriented materials, such as the materials disclosed in pending U.S. patent application Ser. No. 09/961,842 entitled "Oriented, Cross-Linked UHMWPE Molding for Orthopaedic Applications", which was filed on Sep. 24, 2001, by King et al., which is hereby incorporated by reference, and which is owned by the same assignee as the present application. A specific example of such a polymer is medical grade polyethylene. The term "polyethylene", as defined herein, includes polyethylene, such as a polyethylene homopolymer, high density polyethylene, high molecular weight polyethylene, high density high molecular weight polyethylene, ultrahigh molecular weight polyethylene, or any other type of polyethylene utilized in the construction of a prosthetic implant. A more specific example of such a polymer is medical grade ultrahigh molecular weight polyethylene (UHMWPE). [0019] The starting materials (e.g., polymers such as UHMWPE) for use in the methods described herein may be provided in a number of different forms. For example, the starting materials may be provided as a preform. What is meant herein by the term "preform" is an article that has been consolidated, such as by ram extrusion or compression molding of polymer resin particles, into rods, sheets, blocks, slabs, or the like. The term "preform" also includes a preform "puck" which may be prepared by intermediate machining of a commercially available preform. Polymer preforms such as polyethylene preforms may be provided in a number of different pre-treated or preconditioned variations. For example, as discussed in greater detail below, crosslinked or non-crosslinked (e.g., irradiated or non-irradiated) preforms may be utilized. Such preforms may be quenched or non-quenched. Continue reading about Orthopaedic device for implantation in the body of an animal and method for making the same... 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