MAGNETIC PROSTHETIC SYSTEM
BACKGROUND OF THE INVENTION
A first embodiment of the present invention relates to a magnetic weight-bearing prosthetic socket system for coupling a prosthesis to an artificial limb. In this first embodiment, the system has two opposing magnetic fixtures repelling each other: one implanted at the point of amputation of a bone, and a second incorporated into the prosthesis. In a second embodiment of the present invention opposing magnetic fixtures are implanted into adjacent bone surfaces on either side of an articulating joint. The magnetic fixtures are oriented to repel each other and thus hold the bones apart. In a third embodiment, the magnetic fixtures are positioned in pairs on either side of an articulating joint to reduce lateral movement of the joint.
Artificial joints using magnetism to connect two opposing parts are known. For examples see U.S. Pat. No. 4,332,037 to Esformes et al., Italian patent 514,679 to Rosa, or German patent 320,756 to Heegewaldt. These patents all illustrate the use of the attractive force of magnets to hold a joint in place so that the artificial joint can move in a somewhat normal manner.
It is also true that artificial joints using the repulsive properties of magnets are known. For example, see U.S. Pat. No. 4,024,588 to Janssen et al. However, the illustrated device requires repelling magnets to operate within a cooperatively shaped magnetic socket for the device to work. Soft tissue covering a remnant bone can not be accommodated. The implantation requires that the end of each bone entering the joint be destroyed in order to effect the implantation. The magnets are positioned in a ball and socket relationship.
A need exists for a socket system which can be used to couple a prosthesis to an amputated limb. The socket system should be capable of transferring weight directly between the bone structure and the associated prosthesis without causing pain or discomfort to the person wearing the prosthesis. A first embodiment of this invention has as an object a requirement to transfer weight directly to a remnant bone so that any soft tissue covering the remnant bone will not be rubbed and irritated as the device is being used.
A need also exists for a magnetic system which can be used with an existing but damaged articulating joint to comfortably hold the bones of the joint apart. As the bones rotate in the articulating joint, a repelling force is needed which will keep the bones separated and reduce the friction associated with the rotation of the bones relative to one another. The structure should be capable of being inserted into ends of the bones forming the joint, but at the same time conserve and preserve the preexisting contour of the recipient bones.
A need also exists for a magnetic system which can be used with an existing but damaged articulating joint to comfortably hold the bones of the joint apart and at the same time reduce lateral movement of the joint.
SUMMARY OF INVENTION
A first embodiment of the present invention relates to a magnetic weight bearing prosthetic socket system for coupling a prosthesis to an amputated limb. A pair of magnetic fixtures are used to hold the prosthesis in spaced apart relation with the amputated limb. One of the magnetic fixtures is implanted in the remnant bone and the other magnetic fixture is embedded in the prosthetic socket. The
magnetic fixtures are magnetically oriented to oppose one another. The magnetic fixtures for implanting in the remnant bone include a magnetic material vacuously encased inside a material suitable for implantation without having rejection by a body. Suggested materials are, but not limited to, stainless steel, titanium, or medical plastics. The magnetic material, being hermetically sealed inside the implantable material, produces a mechanism for transferring weight from the magnetized implant fixture in the amputated bone to the other magnetized fixture positioned in the prosthesis. The magnetic force of repulsion between these magnets is used to transfer loads associated with typical weight-bearing surfaces through the soft tissue covering the remnant bone without having the magnetic structures physically touch. These repelling magnetic fields also act to dampen shock whenever the prosthesis is forced in a direction against the amputated limb.
Conventionally, the soft tissue covering amputated limbs suffers from the pressure of a prosthetic device transferring body weight to a counteracting bone structure. By using repelling magnetic fixtures wherein magnetic lines of force easily pass through soft tissue, a socket system can be made which transfers weight and shock without pressing a remnant bone against the soft tissue capping the bone.
In a second embodiment of the present invention, repelling magnetic fixtures are implanted within opposing bones in an articulating joint to hold the bones apart. The implanted magnetic fixtures have a cap on the exposed surface that is formed to match a preexisting contour of the bone. By implanting a plurality of magnetic fixtures in one of the joint bones along a direction of rotation, the joint bones are held apart even when the joint is rotated. Optionally, the magnetized fixtures are designed to be orthoscopically adjusted in depth after implantation. This allows the separation between magnets to be adjusted so as to increase or decrease the weight bearing capacity by increasing or decreasing the effects of the magnetic field between the two opposing magnetic fixtures.
A third embodiment of the present invention includes dividing the magnetic fixtures of the second embodiment into pairs with each fixture of each pair being spaced apart from the other fixture of each pair. The spacing distance between the magnetic fixture on one side of the joint is different than the spacing distance on the other side of the 45 joint to help prevent relative lateral movement of the bones comprising the joint.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be clearly understood and readily carried into effect, preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein:
FIG. 1 is a top plan view of a prosthetic socket system of the present invention;
FIG. 2 is a cross-sectional view of the prosthetic socket system and a illustrative prosthesis taken along the line 2—2 in FIG. 1 with an amputated leg inserted in the socket;
FIG. 3 is an enlarged view of the socket portion of the prosthesis shown in FIG. 2 with parts broken away;
FIG. 4 is an enlarged view of the amputated limb shown in FIG. 2 with parts broken away;
FIG. 5 is an elevational view of a pair of leg bones comprising a knee joint with an embodiment of the present invention installed;
FIG. 6 is a cross sectional view of the knee joint shown in FIG. 5 along the medial line 6—6 in FIG. 5 looking into the paper;