Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2002-01-22
2003-11-11
Robert, Eduardo C. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020290, C623S018110
Reexamination Certificate
active
06645251
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices, structures and processes for reducing friction and wear of orthopaedic implant components, particularly bearing components, and more particularly ultra-high molecular weight polyethylene (UHMWPE) components, by providing certain novel textured or patterned surfaces on such components.
2. Description of Related Art
Orthopaedic implants are becoming increasingly prevalent as millions of patients have been relieved of suffering from joint degenerative diseases and other conditions that affect proper hip, knee, shoulder and other joint function. Total or partial joint replacement procedures involve removal of damaged parts of the relevant joint and replacing them with prosthetic components. During surgery, implant components especially selected to match the patient's needs are located and implanted in the bones forming the joint. In a total joint replacement, it is often the case that a bearing component is interposed between two other components that articulate, or move in a manner that corresponds to relative motion of the bones forming the joint, particularly when the articulating components are formed of metal. For purposes of this document, implant component surfaces disposed against or adjacent to each other in normal operation of the implant are referred to as bearing surfaces. Bearing surfaces may be articulating bearing surfaces, when the two components engage in articulating motion relative to each other, or non-articulating bearing surfaces when they do not engage in articulating motion relative to each other.
A common problem involved with joint replacements is the high wear rates that occur once the components have been implanted. Particularly, mobile bearing components, such as those formed of ultra-high molecular weight polyethylene (“UHMWPE”), present wear rates that are substantially higher than those for corresponding fixed bearing components. This increased wear causes the need for increased replacements and revisions, which are commonly more labor intensive, more expensive, and more traumatic to the surrounding tissue and bone.
Accordingly, there is a great need to reduce the wear that accompanies artificial joints. Such wear occurs in all types of artificial joints, including knee, hip, shoulder, elbow, finger, toe, or spinal systems.
More specifically, the prosthetic components contact one another during all types of forward, backward, and side to-side movements. Some replacement joints, such as knee joints, have a mobile bearing insert located between the components implanted in the tibia (such as a tibial tray attached to a tibial stem) and the components implanted in the femur (such as a condylar component attached to a femoral stem). The insert acts, among other things, to ease and facilitate movement of the components and to retain the knee components in place. Particularly if the knee is reconstructed as a mobile bearing knee, the insert is allowed to rotate and translate with the actual motion of the knee. The insert is not constrained, so that it can move in the anterior-posterior direction and/or the medial-lateral direction, which often creates considerable wear. (Other joints also experience wear due to sliding movement.)
For example, many presentations and articles that address mobile bearing knees note that the wear behavior expected of these joint replacements is similar to that obtained with total hip arthroplasty. Specifically, the wear mechanisms include adhesive and abrasive wear, generating a large number of relatively small (micrometer and submicrometer) polyethylene wear particles. The reduction of wear debris generated by orthopaedic devices is one of the leading issues regarding long term performance of orthopaedic joint prostheses.
Wear debris has been associated with adverse biological responses which can lead to local cell death (osteolysis for bone cells), premature loosening and failure of orthopaedic devices, and subsequent need for revision surgery. The majority of wear debris originates from articulating surface of orthopaedic devices, typically a UHMWPE insert or cup surface that is disposed against a metal or ceramic plate or ball surface in a manner such that the surfaces engage in articulating motion relative to each other. (Wear can also occur on non-articulating surfaces, such as a non-mobile bearing component surface against a tibial tray, or the convex, nonarticulating surface of a liner against the inner diameter of an acetabular cup; the present invention is also applicable to any and all such nonarticulating surfaces.) Additionally, abrasive third body debris, such as bone cement (for example, polymethylmethacrylate (“PMMA”) bone cement) and bone debris may migrate to the interface between bearing or articulating surfaces, further accelerating abrasive wear due to so-called three body motion.
Another factor that can influence implant stability and wear is the frictional force generated at the interface between the bearing surfaces. For example, many cases of premature loosening of hip components have been attributed to excessive frictional torque between the femoral head and the acetabular component. Increased friction is also a direct indication of adhesive interaction, or solid—solid contact between bearing surfaces and typically results in increased wear of one, or both bearing surfaces. It is known that increasing the lubricity of the bearing surfaces reduces friction within the artificial joint.
In spite of the increased wear rates, however, mobile bearing joints, such as mobile bearing knee joints, provide a number of advantages over fixed bearing joints. For example, mobile bearing joints provide more natural kinematics and lower stresses at the implant-bone interface. Accordingly, because of the benefits provided, it is important to provide solutions to the increased wear that is generated by mobile bearing joints, even though the present invention is useful for any bearing structure, whether mobile or fixed, articulating or nonarticulating.
Consider the knee. In general, proper knee function such as in walking depends upon the complex interaction and interoperation of a number of bones, ligaments, tendons and cartilage components found in the knee. In particular, condyles forming the distal end of the femur articulate in a hinge-like fashion against the plateau that forms the proximal end of the tibia. A number of ligaments and tendons retain the condyles and tibial plateau in position relative to each other throughout the range of motion, from flexion to extension of the knee. Cartilage components, including meniscal components, are interposed between the condyles and the tibial plateau and thus provide natural bearing surfaces that, among other things, reduce friction and bone wear in the knee. The patella is held in place with tendons and ligaments as it rides in a groove on the anterior surface of the condylar head throughout the range of motion.
In knee joint replacement surgery, a surgeon typically affixes prosthetic components to the patient's bone structure; a first to the patient's femur and a second to the patient's tibia. These components are typically known as the femoral component and the tibial component, respectively. Each component may be formed of a range of subcomponents, such as in a modular fashion. For instance, a tibial tray that corresponds in some ways to the tibial plateau is supported in some prosthetic designs by a cemented or non-cemented tibial stem that is inserted into the canal of the tibia. Similarly, the condylar component can be supported by a stem or other structure that attaches to or inserted into the femur.
The femoral component is placed on a patient's distal femur after appropriate resection. The femoral component is usually metallic, having a highly polished outer condylar articulating surface.
A common type of tibial component uses a tray or plate that generally conforms to the patient's resected proximal tibia. The tibial component also usua
Carson Christopher Patrick
Harbaugh Mark
Salehi Abraham
Sauer Willard L.
Ewing, IV James L.
Kilpatrick & Stockton LLP
Mallatt Kristin D.
Ramana Anuradha
Robert Eduardo C.
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