1993-10-28
1995-02-28
Manuel, George
Surgery
Truss
Pad
A61B 800
Patent
active
053927796
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for testing an implant attached to a bone of a human or animal subject. The use of implants involves the insertion of a metal fixture into a prepared hole in the bone. During the healing process, the surrounding bone develops an intimate contact with the implant surface and after a suitable time a prosthesis may be attached to the fixture. Such implants are frequently used in dentistry and in cosmetic surgery.
There is a need for a means of clinically observing the quality of the union between the bone and the implant surface. Implant failures can be caused by errors in placement, and premature or inappropriate loading. A nondestructive test which could be used before loading the implant would help to reduce failures of this type, and would also enable periodic tests to be carried out on implants which are in use to ensure that they are still satisfactory. The test could also provide a quantitative comparison between different implant systems.
X-rays are sometimes used to test the condition of an implant, but they can only show the presence of gross bone loss around the implant. It is also very difficult to monitor the progress of integration over time with x-rays, since it is difficult to reproduce the viewing position and angle with sufficient accuracy. A different sort of test, albeit a crude one, is to tap the structure attached to the implant with a surgical instrument. This test can only distinguish between satisfactory implants and the most grossly defective systems.
It is therefore an object of the present invention to provide a non-destructive test which is capable of giving a reliable indication of the quality and/or extent of the union between an implant and the bone to which it is attached.
Accordingly there is provided a method of testing an implant attached to a bone of a human or animal subject, the method comprising the steps of bringing a member into contact with the implant; detecting at least one resonance frequency of the member when it is in contact with the implant; and interpreting the detected resonance frequency in terms of the degree of the attachment of the implant with respect to the bone.
The stiffness of the joint or interface between the implant and the bone, and also the exposed length of the implant, will affect the resonance frequency of the member. Hence, monitoring this resonance frequency provides a means of assessing the integrity of the joint.
Preferably, the member is releasably attached to the implant.
According to one preferred arrangement, the member comprises a cantilever beam. The implant often includes a threaded bore by means of which the prosthesis, or a pillar or post (called an abutment) intended to carry the prosthesis, is screwed to or into the implant. The abutment or an associated fixing screw also usually has a threaded bore by means of which the prosthesis is screwed to or into the abutment. The cantilever beam, conveniently, can be screwed to or into the implant, or abutment, using the associated threaded bore in the latter.
The detected resonance frequency is conveniently compared with one or more values for the resonance frequencies of the same or similar members in contact with other implants. By comparing the detected resonance frequency with values obtained on other satisfactory or less satisfactory implants, an indication of the degree of integration of the implant can be obtained. Furthermore, the same implant could be tested when it is initially inserted, and periodically thereafter, both during the healing process, when it is intended to attach the prosthesis, and thereafter, and the various resonance frequency values compared, to obtain an indication of the progress of the integration process, whether and when a prosthesis or abutment should be attached, and, subsequently, whether the condition of the implant is still satisfactory.
The resonance frequency is conveniently detected by exciting the member with an AC signal, detecting the response of the member to the AC signal, and varyin
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Cawley Peter
Meredith Neil
Imperial College of Science Technology & Medicine
Manuel George
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