The present invention relates to surgical implants. More particularly, the invention relates to wear-resistant surgical implants.
The use of surgical implants to compensate for diseased, damaged, or missing anatomical elements is well known. In a common application, implants are used to replace skeletal elements, such as articulating bone joints and related bone structures. For example, total knee arthroplasty involves the replacement of portions of the patellar, femur and tibia with implants.
Some implants can last a few decades. However, a significant number fail within 10 to 15 years. While this may be acceptable for some older patients, longer service lives are needed as implants are used in increasing numbers of younger patients and more active older patients.
The service life of a surgical implant is largely dependent on the amount of wear and tear to which the implant's load bearing surface and fixation surface are exposed. Localized stress from interaction between each of these surfaces and respective opposing surfaces generates small particulate debris that breaks off and contaminates the tissues and fluid surrounding the implant. In response, the body's immune system will secrete enzymes in an attempt to degrade these particles. However, the enzymes often kill adjacent bone cells or cause osteolysis resulting in mechanical loosening and failure of the implant. Further, protuberances in the bearing surface can scratch an opposing surface, which leads to microcrack formation and ultimately to failure of the implant. Therefore, it is important to minimize the wear-rate of an implant's load bearing and fixation surfaces.
Accordingly, there is a need in the art for implants with improved surfaces. It would be particularly advantageous if such implants exhibited increased resistance to the release of wear debris, the formation of microcracks, and the expansion of microcracks. In this manner, the effective service of life of implants can be prolonged.
In the interest of providing implants of improved durability, the present invention was conceived. The invention provides an implant and a method for forming an implant. The implant includes a fixation surface having at least a portion made up of an oxidized material.
The following detailed description, given by way of example, but not intended to limit the invention solely to the specific embodiments described, may best be understood in conjunction with the accompanying drawings wherein like reference numerals denote like elements and parts, in which:
For purposes of brevity of description, the preferred embodiments will be described in the context of implants used in total knee arthroplasty. However, it should be noted that the embodiments are not limited to implants used in total knee arthroplasty. Upon review of this disclosure, one skilled in the art will readily appreciate how the described embodiments are applicable to a wide range of implants.
Further, for purposes of clarity of description, the following terminology is used. When referring to bones or other body parts, the term “proximal” means closest to the heart and the term “distal” means more distant from the heart.
Referring now to
The femoral and tibial implants shown in
It should be noted that tibial implant bearing surface 105′ is often referred to as the “tibial implant mating surface.” However, for purposes of facilitating the description and claims of this specification surface 105′ will be referred to as the tibial implant “bearing surface.”
Typically, the femoral implant and tibial implant are respectively attached to the distal femur and the proximal tibia through the use of acrylic bone cement. That is, the femoral implant is attached to the distal femur by using cement to adhere the femoral implant fixation surface to the resected surface of the distal femur, and the tibial implant is attached to the proximal tibia by using cement to adhere the tibial implant fixation surface to the resected surface of the proximal tibia. The cement is not shown in
It has been recognized by the inventors that wear and corrosion limits the service life of implants like the one shown in
Attempts have been made to overcome the wear problem in knee implants. In particular, manufacturers have provided implants made of Ti-6Al-7Nb with a bearing surface hardened by oxygen diffusion and a fixation surface that is rough-peened or sandblasted (collectively “roughened”) for fixation without cement. However, there are several drawbacks associated with these types of implants. One drawback is that the oxygen diffused layer that makes up the bearing surface is a thin layer (approximately 20-50 um) of titanium oxide (TiO2), which has insufficient hardness (approximately 700-900 Vickers at 25 g load) to overcome the articulation wear problem, especially when the presence of bone chips precipitates the wear. Another drawback is that the roughened fixation surface does not allow for sufficiently durable fixation without the use of cement.
Further, manufactures have provided titanium-based implants having a fixation surface that is roughened for fixation with cement. However, such implants do not overcome the fretting wear and corrosion problems. The inventors have recognized that the fretting wear and corrosion problems may be related to the titanium's characteristics as a soft metal, and are therefore not overcome through roughening, either without cement or with cement.
In view of the drawbacks associated with prior implants, the inventors conceived and developed implants that make cement fixation workable.
It should be noted that each of the terms “coated” and “coating” as used in this disclosure include both cases in which the entire object of the term is coated and cases in which less than the entire object of the term is coated. Thus, when a bearing surface coated with chromium oxide is discussed in this disclosure, such surface may be entirely coated with chromium oxide or only partially coated with chromium oxide. Further, in cases of partial coating, such coating may be applied to a single unitary portion of the surface or to a multiple of unitary portions of the surface.
Similarly, it should be noted that each of the terms “oxidized” and “oxidizing” as used in this disclosure include both cases in which the entire object of the term is oxidized and cases in which less than the entire object of the term is oxidized. Thus, when an oxidized fixation surface is discussed in this disclosure, such surface may be entirely oxidized or only partially oxidized. Further, a partially oxidized fixation surface refers to either a surface in which only a single unitary portion of the surface is oxidized or a surface in which a multiple unitary portions of the surface are oxidized.
In any event, the femoral implant bearing surface of
The fixation surfaces of the
It should be noted that the femoral implant fixation surface and the tibial implant fixation surface of
As these and other variations and combinations of the features discussed above can be utilized without departing from the present invention as defined by the claims, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the invention as defined by the claims.
This application is related to commonly owned concurrently filed U.S. patent application Ser. No. ______ (Attorney Docket No.: OSTEON 3.0-643) and commonly owned concurrently filed U.S. patent application Ser. No. ______ (Attorney Docket No.: OSTEON 3.0-685), the disclosures of which are hereby incorporated by reference herein.