Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-03-16
2002-06-25
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S064000, C623S021110
Reexamination Certificate
active
06409768
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to an improved joint prosthesis.
BACKGROUND OF THE INVENTION
In just over three decades since the inception of its widespread use, total hip replacement (THR) has changed the practice of orthopedic surgery. An entire new industry has been created to support THR and, more importantly, THR has improved quality of life of millions of patients to the extent unparalleled by any other single procedure in the history of surgery. All of this was originally made possible with the advent of cemented THR. Within the first decade following the pioneering work of Charnley, a broad base of trained surgeons, a highly motivated industry and compliant medical insurance policies have led to a world-wide acceptance of THR, evidenced by an exponential growth in the number of procedures being done, currently over 600,000 annually in the world.
This early period of unrestrained optimism was followed, however, by a wave of innovations after the longer-term results became available and the number of revisions (exchange or removal of one or both of the femoral and acetabular components of a THR) started to climb as well. Most of the blame for the increasing revision rate was placed on the bone cement, and efforts to eliminate it, by so-called cementless anchorage, dominated the next decade. But once again, the long term clinical outcomes forced a policy change—cementless THR designs did not match the standard set by the cemented, Charnley-type hip prosthesis design.
In spite of reasonably uniform medical training programs, and widely available and read professional literature, significant differences in attitudes controlling the practice of THR in different geographic regions persist until today and will probably continue to do so. There are countries where over 95% of THR procedures are cemented (e.g. Sweden), but also those where cementless have an edge (e.g. Germany, with about 2 out of 3 THR being cementless). Hybrid THR (i.e., in which one component is cemented and the other is not) has also gained a strong following, especially in the U.S., usually with the acetabular component being cementless and the femoral stem cemented, although the opposite approach has some supporters as well, and the latter is not without merit in view of some recently published clinical outcomes.
The Swedish Hip Registry (and the more recently implemented registries in Norway and in Finland) has been instrumental in weeding out approaches that perform poorly. However, only a limited number of the hip designs currently available worldwide are used in Sweden in numbers large enough to draw any conclusions. Many failures of innovation have also produced a very cautious surgical community, especially in Scandinavia. As the result of this practice of monitoring and control over selection of implants and surgical techniques, imposed by publishing the data from the Registry (including the performance of individual clinics), only one out of ten THR procedures currently done in Sweden is a revision. In comparison, less precise data suggests that one out of five THR procedures in the U.S. is a revision, and the number may be as much as one out of three or four in Germany.
Frequency of revision surgeries depends on many factors other than prosthesis design. However, it is indisputable that one of the primary factors is the still-superior performance of the cemented THR in comparison to cementless. In the Swedish Registry, the overall rate of revisions of cementless THRs is double that of cemented THRs using modem cementing techniques. The debate has come to be dominated by the use of a single outcome parameter of THR—one that the Swedish Registry is based on—the THR “survival rate.” The survival rate of a THR design is defined as the percentage of such THRs which remain in the patient (i.e., which are not revised). Since the survival rate is approximately 95% at ten years for a good prosthesis and a good cement, properly used, it seems that there should be much less pressure for innovation than suggested by the variation of THR models present on the market and by the continuing efforts to improve cementless designs and cementing techniques. One of the reasons spurring new innovation is that both the surgeons and implant manufacturers need something new to gain recognition and market share, which is difficult to do in the non-differentiated field of cemented Charnleys.
Despite the 95% ten-year survival of cemented THRs, it is recognized that there are real problems to solve in the long run. Accordingly, the Swedish Registry has recently undertaken a project to estimate the performance of a smaller number of cases which have not been revised (and thus, until now, were not entering the Registry with an outcome). It is anticipated that the results will show that some 15% of patients have a failed THR at 10 years, but have not been revised for various reasons, such as the advanced age (and limited remaining life expectancy) of the patient. In younger patients revision rates are higher, and cementless THRs currently available seem not to have made any positive impact.
Thus, the limitations of conventional approaches to THR which need to be solved in the long run can be summarized as follows:
in properly-designed cemented stems, most of the failures are due to limited fatigue endurance of the bone cement (leading to so called aseptic loosening);
in cementless stems most of the failures are due to bone loss induced by movement at the stem-bone interface;
in acetabular components, difficulty of matching the implant to highly compliant cancellous bone, with or without cement, leads to formation of soft tissue at the interface which may progress to gross instability;
biological response to wear debris, produced at all interfaces at which relative movement occurs, by intent or accident, including the artificial joint itself, can lead to activation of bone resorption, so called osteolysis, which may progress to gross loosening of prosthetic components, or even to bone fractures.
The invention described herein successfully addresses the challenges of interfacing prosthetic components to bone, allowing the patients unrestricted use of the replaced joint in the immediate post-operative period, yet providing a stable anchorage to the bone of unlimited duration. The invention is disclosed in full detail on an example of the femoral component of a total hip prosthesis, but it is clear that the same principles can be applied to many other prosthesis, e.g. shoulder (humeral component), elbow (both components), knee (both components), finger (both components). It is also applicable to dental and spinal implants. In this disclosure those other applications are only sketched—one skilled in the art of designing and using such components could certainly, following the example of the total hip prosthesis, produce all necessary implants, instruments and insertion procedures.
The present invention removes a drawback of the screw-fixed femoral components for total hip prosthesis known in the prior art, as exemplified by U.S. Pat. No. 5,458,654 (“the '654 patent”), namely the necessity to drill access holes in the lateral cortex of the proximal (or upper) femur, and the concomitant need to make incisions in the soft tissue and muscle overlying the lateral cortex. It will of course be appreciated by those of skill in the art that any unnecessary trauma to soft tissue or bone is preferably to be avoided, due to the trauma to the patient's body, weakening of the femur due to removal of healthy bone matrix, and the chance for infection.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide an orthopaedic implant system comprising an orthopaedic implant and at least one bone screw. The orthopaedic implant comprises an intraosseous portion, which intraosseous portion has a first side; a second side; and at least one screw hole. The screw hole has an entry opening at the first side and an internally-threaded portion. The bone screw has an externally-threaded, front end for engag
Hodge W. Andrew
Tepic Slobodan
Isabella David J.
Pennie & Edmonds LLP
LandOfFree
Screw anchored joint prosthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Screw anchored joint prosthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Screw anchored joint prosthesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2980909