Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-04-18
2001-04-17
Millin, Vincent (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020140, C623S022110, C623S023600, C623S023500, C427S523000
Reexamination Certificate
active
06217615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to arthroplasty, i.e., an operation to restore motion between the bones of a skeletal joint, and concomitant function to muscles, ligaments and other tissue which control that joint. The present invention more particularly relates to cementing prostheses to bone.
2. The Prior Art
A prosthesis for a freely movable (synovial) skeletal joint comprises at least one member that has a configuration which presents an articulating surface and an anchor surface. The anchor surface is anchored to bone. The articulating surface bears against the corresponding articulating surface of another member.
In conventional hip, knee and like arthroplasties, for example, a member of a plastic or metal prosthesis is positioned with an anchor surface that is directly in contact with and mechanically anchored to bone either with or without cement. In the absence of cement, the integrity of the anchor typically relies upon the configuration of the anchor surface of the prosthesis member and intergrowth of bone and/or tissue with that surface. In the presence of cement, the integrity of the anchor typically relies, not only on adhesion, but also upon mechanical interlocking between (1) the cured cement, and (2) the adjoining or conjunctive anchor surfaces of the prosthesis member and the bone. Various problems have been encountered in implementing the above techniques.
Metal prostheses conventionally have been composed of either a titanium alloy or a cobalt-chromium alloy. Although these materials have advantages. in strength and surface integrity, they may suffer from problems that include less than desired in vivo performance. Plastic prostheses conventionally have been composed of ultra high molecular weight polyethylene (UHMWPE), and the cement therefor conventionally has been composed of polymethyl methacrylate (PMMA). These materials have excellent biocompatibility, but have suffered from poor adhesion to each other, as a result of which loosening occurs and debris is produced.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the adhesion between a high molecular weight polyene and an alkyl polyacrylate cement is radically improved if the surface of the polyene, prior to cementing, is predeterminedly modified by ion implantation, ion beam assisted deposition (IBAD), and/or sputter deposition.
The primary object of the present invention is to provide a prosthesis for a synovial joint, characterized by at least one polymeric member that has, (1) for anchoring to bone, an anchor surface that has been modified by ion implantation, ion beam assisted deposition, and/or sputter deposition, and (2) an articulating surface that is adapted to bear against the corresponding articulating surface of another member of the prosthesis member. The object of the present invention more specifically is to provide, in vivo, an assemblage comprising, in combination, such a prosthesis and a polymeric cement mantle interconnecting the anchor surface of the prosthesis and contiguous bone. The polymeric member contains a polyethylene with a molecular weight of greater than 200,000 as one of its characteristic ingredients, preferably an ultrahigh molecular weight polyethylene with a molecular weight ranging from 3×10
6
to 6×10
6
. The cement contains an acrylic resin bonding agent/cement as one of its characteristic ingredients, preferably polymethyl methacrylate.
Preferably, in the case of ion implantation, an infusion of biocompatible ions is concentrated primarily in the outer 25 &mgr;m of the anchor surface. Preferably in the case of ion beam assisted deposition and sputter deposition, a coating of deposited material ranges in thickness from 2 to 5,000 nm. It is believed that the mechanism for enhanced adhesion in the case of ion implantation is an increased concentration of carbonyl groups, hydroxyl groups and/or three dimensional cross links, by which the surface becomes more hydrophilic. It is believed that the mechanism for enhanced adhesion in the case of IBAD and sputter deposition is the presence of inorganic atoms or molecules at the anchoring interface and the superior adhesion of the cement to those inorganic atoms or molecules.
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Bricault, Jr. Raymond J.
Sioshansi Piran
Engellenner Thomas J.
Koh Choon P.
Millin Vincent
Nutter & McClennen & Fish LLP
Spire Corporation
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