Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-12-04
2001-04-17
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020140
Reexamination Certificate
active
06217619
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application Serial No. 197 54 079.1, filed Dec. 5, 1997, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention generally relates to an endoprosthesis for replacing at least part of the tibia.
After carrying out, for example, a complicated tumor resection or after encountering a failure in the anchoring of a replacement knee prosthesis, substantial problems may arise in the area of the tibia when forces are transmitted from the knee joint to the ankle joint. In particular, it is conceivable that portions of the tibia must be resected, without any possibility to connect the bone components between which the resected portions are removed. In these situations, amputations are frequently the only option.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved endoprosthetic implant, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved endoprosthesis for situations requiring removal of parts of the tibia or the entire tibia or in which existent tibia parts do not exhibit a sufficient strength for realizing a force transmission, with resorting to amputation.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing an elongate shaft which extends longitudinally in direction of a lower leg and has an upper end facing a knee joint and a lower end facing a natural ankle joint, an endoprosthetic knee joint having a tibial plateau secured to the upper end of the shaft, and a coupling portion supported by the ankle joint and linked to the lower end of the shaft.
Such an endoprosthesis can be successfully implanted in situations where a portion of the tibia is either completely missing or so weakened as to be insufficient to transmit forces. In these cases, the shaft is utilized as a replacement for the tibia. This shaft may extend along the entire length or only partially through the tibia, if portions thereof are still existent. In this case, soft parts such as ligaments, tendons and muscles required to carry out motions have grown onto bony material that covers the shaft.
According to a preferred embodiment of the present invention, the shaft is formed as round rod, with a recess being provided on the upper end of the shaft for engagement by a pin which is fastened to the tibial plateau and secured in the recess. This type of embodiment allows the use of conventional endoprosthetic knee joints; however, in which accordance with the present invention, the pin on the tibial component is, unlike in conventional embodiments, not anchored directly in the tibial bone but in the shaft that completely or partially replaces the tibial bone. By anchoring the pin, which is made of steel, in a mating recess of the shaft which is also made of steel, relatively high forces can be transmitted while still enabling to provide the endoprosthesis with mutually guiding parts that exhibit comparably small dimensions.
According to another feature of the present invention, the coupling portion includes an arched or curved plate which is secured to the lower talus-proximal end of the shaft. This arched plate has a comparably large area for transmission of forces into the talus so that comparably small contact pressure is experienced in the area of force transmission. Preferably, the coupling portion includes an adapter having a lower end which terminates in the arched plate and is detachably secured to the shaft. With such an adapter the entire endoprosthesis can be precisely suited to the required length between the knee joint, on the one hand, and the ankle joint, on the other hand.
According to still another feature of the present invention, the adapter has a talus-distal upper end which engages a guide sleeve fixed to the shaft. This type of attachment ensures an accurate guidance of the adapter when transmitting relatively substantial bending moments.
Preferably, a template is secured to the sleeve for guiding the adapter in longitudinal direction, with the template extending in parallel relationship to the adapter. In this manner, the adapter is supported along its entire length by the template, thereby further promoting a precise guidance of the adapter while preventing a loosening thereof even when subject to substantial impact forces. Suitably, the template and the adapter have coextensive mating surfaces, thereby further enhancing the guidance of the adapter and preventing detachment from the template. The mating between the coextensive surfaces of the template and the adapter may be effected by way of a positive engagement or interference fit.
According to still another feature of the present invention, the adapter and the template define a common cross section which substantially corresponds to a cross section of the shaft. This ensures that the force-transmitting cross section of the endoprosthesis is the same over its entire length to avoid areas prone to fracture or flexure.
Suitably, the guide sleeve is attached to the shaft at a region in which the shaft is not covered by bony components of the tibia so that the template as well as the adapter can be placed through the lower end of the tibia. Thus, muscles, tendons and ligaments can remain articulated unaltered to the bony components of the tibia.
According to yet another feature of the present invention, a guiding system is positioned between the arched plate and the talus, which supports the arched plate, for guiding the arched plate. For example, the guide system may include a projection for engagement in a complementary recess of the talus. This prevents the arched plate from sliding off the talus when subject to impacts. Thus, the endoprosthesis is accurately guided with respect to the talus.
REFERENCES:
patent: 4268920 (1981-05-01), Engelbrecht et al.
patent: 4865606 (1989-09-01), Rehder
patent: 5268000 (1993-12-01), Ottieri et al.
Feiereisen Henry M.
GMT Gesellschaft fur Medizinische Technik mbH
Isabella David J.
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