Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1986-06-27
1989-09-19
Schoefer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524408, 524430, 524437, C08K 310
Patent
active
048682373
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a bone cement based on physiologically tolerated polymers, in particular on polyacrylates and/or polymethacrylates prepared from prepolymers and monomers, and to a process for mechanically disrupting fully polymerized plastics, in particular these bone cements.
A central problem in the implantation of joint endoprostheses is the anchorage of the prosthesis in the bone substrate. For this purpose, it is known to use bone cements which are based on acrylate and which are prepared by mixing and fully polymerizing pulverulent prepolymers with liquid monomers containing initiators and accelerators for the polymerization. These are used in orthopaedic surgery for the reliable and rapid primary fixing of the joint implant to the bone, thus enabling the patient to put a load on the joint at an early stage. The bone cement, which initially is still pasty in the mixing phase and cures slowly, fills the space between the bone and the joint implant almost without any gaps, but very rapidly gains its full strength as a result of the continuing polymerization process.
This type of fixing joint endoprostheses to the bone by means of fully polymerized bone cement is nowadays a surgical technique which is used and recognized throughout the world in orthopaedic surgery. Problems such as excessive liberation of energy and hence an unduly high temperature during the polymerization, whch leads to necrotization of the tissue, have been solved in principle, as have the questions of adequate biocampatibility of the bone cement.
In the long term, however, loosening of the metal implant or of the plastic implant in the bone cement substrate can occur, so that prosthesis replacements with removal of the bone cement become necessary. The removal of the bone cement from tubular bones is technically very difficult and involves a long operating time in the case of re-operations of joint endoprostheses, so that the predominantly old patients are put at considerable risk by long operating times, long bleeding times of the exposed soft tissues and an increased danger of infection due to long times with an open wound. The importance of this problem can be gauged by the fact that up to 20% of all joint prosthesis operations carried out nowadays are re-operations.
SUMMARY OF THE INVENTION
It was therefore the object to provide a bone cement which meets all the requirements with respect to stability and processability, but which can easily and quickly by removed from the bone in the case that a re-operation becomes necessary.
This object has been achieved by the present invention. In fact, it has been found that perturbation elements which have been incorporated into the polymer matrix and the acoustic resistance of which differs from that of the polymer matrix can be excited by means of acoustic waves in such a way that tensile and compressive stresses, which lead to disintegration of the polymer matrix, are generated at the acoustic interfaces.
The invention therefore relates to a bone cement based on physiologically tolerated polymers, in particular on polyacrylates and/or polymethacrylates prepared from prepolymers and monomers, wherein acoustic perturbation elements having an acoustic resistance differing from that of the polymer are incorporated into the polymer.
The invention also relates to a process for mechanically disrupting fully polymerized plastics, in particular bone cements based on physiologically tolerated polymers, in particular on polyacrylates and/or polymethacrylates prepared from prepolymers and monomers, which comprises incorporating acoustic perturbation elements having an acoustic resistance differing from that of the polymer, before the polymer is fully cured, and destroying the polymer matrix by selective excitation of the perturbation elements by means of acoustic waves.
The advantage of the present invention is that the bone cement according to the invention can be used by the surgeon in the same way as the hitherto known bone cements. With respect to short-
REFERENCES:
patent: 4341691 (1982-07-01), Anuta
patent: 4456711 (1984-06-01), Pietsch et al.
patent: 4490497 (1984-12-01), Evrard et al.
Hoff Gunter
Ohnsorge Jochen
Merck Patent Gesellschaft mit beschrankter Haftung
Reddick J. M.
Schoefer Joseph L.
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