CEREBRAL ANEURYSM CLIP

Abstract: A cerebral aneurysm clip (1) composed of blade parts (2a, 2b) capable of clipping the root of a lump of cerebral aneurysm and a spring part (3) of imparting a clipping force to the said blade parts, which is characterized in that the said blade parts are made of a synthetic resin or ceramic.

Description: The present invention relates to a cerebral aneyrysm clip and, in particular, to that which may apply to a patient with no trouble in X-ray CT (computed tomography) or NMR (nuclear magnetic resonance) -CT examination. Cerebral aneurysm is caused by expansion of the artery of a brain in the form of a lump, and when it is broken, it would cause subarachnoid hemorrhage or the like serious condition to endanger life. Prior to the surgical operation on the cerebral aneurysm, the existence thereof is first ascertained by X-ray CT or NMR-CT as cerebral angiography, and thereafter the root part of the lump is clipped with a particular metal clip which is called a cerebral aneurysm clip whereby the surgical operation is finished. After the operation, the clip used is kept in the brain as it is. Hitherto, various proposals have been made on the shape and the material of the cerebral aneurysm clip, but the clips which have heretofore been proposed and actually used for the purpose are metallic e.g. are made of a stainless steel or a Co-Cr alloy (Japanese Patent Application Laid-Open Nos. 54-4488 and 59-8948, and Japanese Utility Model Application Laid-Open No. 61-205517). However, where the body to be examined by X-ray CT has a metal or the like substance therein during the examination, X-ray would be reflected and scattered on the surface of the substance to give an artifact on the image photographed and, as a result, the result of the examination could not be accurately read out from the image. As NMR-CT uses a strong magnetic field (recently about 2 tesla or so) and a high frequency, existence of a magnetic substance in the body to be examined would cause a noticeable strain in the image obtained or the clip (magnetic substance) would be moved or heated in the body (brain) during examination by NMR-CT. In addition, existence of an electroconductive metal in the body would also be dangerous, since the metal would generate an induced current in a magnetic field or high frequency field and the current would damage the body. Furthermore, other many problems on the metal clip for clinical NMR-CT examination have variously been reported and investigated in the field. For instance, it is reported in NMR Medical Technology, Vol. 4, No. 2 (1984), pages 20 to 23 with title of "Influence of Static Magnetic Field to Metal in Body", that NMR-CT should not be effected on the patent having a metal clip in the body. Under the situation, there is an extremely serious problem that the patient who had an operation on its cerebral aneurysm and therefore have a metal clip in its brain could no more undergo an X-ray CT or NMR-CT examination, which has an important role in the cerabral surgical operation such as operation on cerebral aneurysm, after the operation. US-A-4671281 discloses a hemostatic clip for use in occluding vessels. The specification discloses a clip comprising a means which is made of a synthetic resin and which has the capability of clipping the root part of a lump of cerebral ameurysm and a spring means which imparts a force to said clipping means. The present invention provides a clip for a cerebral aneurysm comprising a clipping means which has a function of clipping a root part of a lump of cerebral aneurysm and a non-metallic spring means which has a function of imparting a force for clipping said root part to said clipping means characterised in that the clipping means is made of a ceramic. Preferably, the clipping means is made of a ceramic having an HN value in X-ray CT of 2500 or less. Preferably, the spring means is made of a rubber or synthetic resin. Preferably, the ceramic is selected from alumina, AlN, sialon, silicon nitride and silicon carbide. More preferably, the ceramic is alumina, AlN or silicon nitride. More preferably, the clipping means is made of a ceramic having an HN value in X-ray CT of 2000 or less. Preferably, the synthetic resin is selected from polyethylenes, polypropylenes, polystyrenes, methacrylic resins, epoxy resins, silicone resins, unsaturated polyester resins and fluorine resins. More preferably, the synthetic resin is polymethyl methacrylate, polytetrafluoroethylene or polyether sulfone. Preferably, the spring means is made of a fibre reinforced synthetic resin. Preferably, the fibre is selected from carbon fibre, alumina fibre, SiC fibre, glass fibre or high polymer fibre. Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Fig. 1 to Fig. 5 are front views, each of which shows a different embodiment of the present invention, Fig. 6 is a front view to show the blades used in the clips of Fig. 1 and Fig. 2; and Fig. 7 is a side view to show the same, Fig. 8 is a front view to show the blades used in the clips of Fig. 3 to Fig. 5; and Fig. 9 is a side view to show the same. In this invention, the blades are made of a ceramic, which is preferably one having an HN value in X-ray CT of 2500 or less. The HN value in X-ray CT indicates the value or an attenuation constant of each material. Specifically, it indicates a factor to represent the transmittance of X-ray, where water is defined to have the value of 0, air to have the value of -1000 and bone to have the value of 1000. (In this connection, an image is formed in CT because of the excellent resolving power (density resolving power or attenuation constant resolving power) to the attenuation constant.) Precisely, CT value is generally represented by the following formula: where µ t means the attenuation constant of the material; µ w means the absorption constant of water; and K means a constant. Where K = 1000, the value is an HN value in X-ray CT. Preferably, ceramics having an HN value in X-ray CT of 2000 or less, which are insulating materials at room temperature and have a high strength and which are free from the problem of artifact in a high magnetic field or high frequency field, are used in the present invention. Various ceramics are shown in Table 1 below, together with the HN value in X-ray CT and the degree of artifact. As is obvious from Table 1 above, alumina, bone china AlN, sialon , silicon nitride and silicon carbide are preferred for use in the present invention in view of the HN value in X-ray CT and of the artifact, but bone china is unsuitable to the present invention as it has a poor strength. From the viewpoint of the electric insulating property, alumina, AlN and silicon nitride are preferred for use in the present invention. A cerebral aneurysm clip is required to have a high clipping force capable of strongly clipping the cerebral aneurysm, but it is extremely difficult to expect ceramics to have such spring function. In accordance with the present invention, therefore, a material which is harmless to living bodies and is hardly deteriorated and which does not have any bad influence on X-ray CT or NMR-CT but has a high spring fuction is used for forming the spring pact of the clip of the invention. The synthetic resin for forming the spring is one which satisfies the requirements that it does not decompose or, for example, does not hydrolyze with a body juice (physiological salt solution), it does not release a substance having a harmful influence on a body, and it does not absorb water. For instance a rubber such as silicone rubber, fluorine resins, methacrylic resins and other thermoplastic resins such as polyethylene, polypropylene or polystyrene can be used. In addition, the spring may also be made of thermosetting resins such as epoxy resins, silicon resins or unsaturated polyester resins. Preferred examples of the resins include, for example polymethyl methacrylate, polytetrafluoroethylene, silicon resins and polyether sulfone. Further, the spring may also be made of a material comprising the above-mentioned resin and a reinforcing agent, for example, a fiber-reinforced synthetic resin. As the reinforcing fibers for constituting the fiber-reinforced synthetic resin, there are preferably mentioned carbon fibers such as graphite whiskers, alumina fibers such as alumina whiskers, SiC fibers such as SiC whiskers, glass fibers (especially preferably those having a low content of heavy metal oxides or phosphates) and high polymer fibers. Fibre reinforced plastics are particularly effective from the viewpoint of strength, corrosion resistance and durability. In particular, the formation of the spring is easy, and the spring may have the spring function because of the elasticity of the synthetic resin whereby a strong clipping force can be imparted to the blades. As one preferred embodiment of this invention, the spring may be made of a fiber-reinforced synthetic resin, whereby the spring force may be reinforced. Accordingly, the cerebral aneurysm clip of the present invention may easily be manufactured by first forming the blades from a sintered substance of a determined ceramic or a CVD-coated substance thereof and then joining them to a spring part as separately formed from, for example, FRP. In accordance with the invention, the blades are made of a ceramic and the spring is made of a synthetic resin such as a fiber-reinforced synthetic resin, whereby a clip which can safely be used in a living body because of the excellent chemical stability, corrosion-resistance, durability as well as mechanical characteristics such as high strength of the ceramic can be obtained. In addition, the clip may have a satisfactory clipping force in the blades because of the elasticity of the synthetic resin. Further, the synthetic resin does not have any bad influence on a living body and additionally the ceramic and synthetic resin are non-magnetic materials and therefore do not have any bad influence on X-ray CT or NMR-CT examination. Accordingly, after the clip of the kind of the invention is used in an operation for cerebral aneurysm, the patient thus operated may generally undergo the successive X-ray CT or NMR-CT examination. In particular, where a ceramic having a relatively high X-ray transmittance, for example, an HN value in X-ray CT of 2500 or less, is used for forming the clip of the invention, the clip does not interfere with the image in X-ray CT so that the image in X-ray CT may noticeably be improved. Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings. Use of the clips of the present invention can appropriately be effected by one skilled in the art in accordance with the shape and size of the lump of cerebral aneurysm to be treated. Fig. 1 to Fig. 5 show embodiments of the cerebral aneurysm clip of this invention. In the clip (13) shown in Fig. 1, a pair of blade parts (14a,) and (14b) as positioned to face to each other are made of a ceramic. The pair of blade parts (14a) and (14b) have a function of clipping a lump of cerebral aneurysm between the clipping parts (16a) and (16b) on the basis of the joint part (15) as the fulcrum, as shown in Fig. 6 and Fig. 7. In this embodiment, a hopping type spring part (17), for example a spring rod made of a synthetic resin, is inserted into the gap formed between the blade parts (14a) and (14b) composed of the joint part (15) and the clipping parts (16a) and (16b), whereby the clipping power is imparted to the blade parts by the action of the spring part. In such constitution, the spring part (17) is compressed when the clipping parts (16a) and (16b) of the blade parts (14a) and (14b) are to be opened, while a strong clipping force may be obtained by the function of the spring part (17) when the clipping parts (16a) and (16b) clip a lump of cerebral aneurysm. The clip (18) shown in Fig. 2 is composed of blade parts (14a) and (14b) of Fig. 6 and Fig. 7 and a ring-shaped scissor type synthetic resin spring part (19) as integrated therewith. In the constitution, the ring-shaped spring part (19) has a function of imparting a clipping force to the clipping parts (16a) and (16b) which are in the top of the blade parts (14a) and (14b), respectively. The clips (20), (21) and (22) shown in Fig. 3 to Fig.5 respectively, are composed of blade parts (25a) and (25b) of Fig. 8 and Fig. 9 where the clipping parts (24a) and (24b) are constituted to clip a lump of cerebral aneurysm therebetween on the basis of the joint part (23) as the fulcrum, and a different spring part. Specifically, the clip (20) of Fig. 3 has a squared ring-shaped spring part (26) made of a synthetic resin; and the clip (21) of Fig.4 has a sheath-type spring (27) made of a synthetic resin, with which the blade parts are sheathed. In the constitution of the clips (20) and (21), when the blade parts (25a) and (25b) are opened, a clipping force is imparted to the clipping parts (24a) and (24b) because of the elastic force of the spring parts (26) and (27). In the clip (22) of Fig.5 a plastic spring part (28) is sandwiched between the opened ends of the blade parts (25a) and (25b) in the side of the fulcrum (23). Also in the constitution of the clip (22), when the clipping parts (24a) and (24b) of the blade parts (25a) and (26b) are opened, the spring part (28) is compressed whereby a clipping force is imparted to the clipping parts (24a) and (24b) of the blade parts (25a) and (25b). As mentioned in detail in the above, the cerebral aneurysm clip of the present invention does not have any bad influence on an X-ray CT or NMR-CT examination. Accordingly, where the clip of the present invention is used in an operation for a cerebral aneurysm, the patient thus operated can undergo the following X-ray CT or NMR-CT examination. It is therefore admitted that the present invention noticeably contributes to the progress of clinical medicine. In addition, the clip of the present invention is chemically stable and is harmless to living bodies and additionally it has excellent corrosion-resistance, durability and mechanical characteristics. Accordingly, the operated part may favorably be kept good when the clip of the invention is used in the operation. Preferred embodiments of the present invention can overcome the above-mentioned problems in the prior art and provide a cerebral aneurysm clip which does not give a troule to CT-examination after the operation with the clip. Preferred embodiments of the present invention can also provide a cerebral aneurysm clip which is chemically stable and harmless to a living body and which has excellent corrosion-resistance, durability and mechanical characteristics.

Claims: A clip (13) for a cerebral aneurysm comprising a clipping means (14a,14b) which has a function of clipping a root part of a lump of cerebral aneurysm and a non-metallic spring means (17) which has a function of imparting a force for clipping said root part to said clipping means (14a,14b) characterised in that the clipping means (14a,14b) is made of a ceramic. A clip (13) for a cerebral aneurysm as claimed in claim 1, in which the clipping means (14a,14b) is made of a ceramic having an HN value in X-ray CT of 2500 or less. A clip (13) for a cerebral aneurysm as claimed in claim 1 or claim 2, in which the ceramic is selected from alumina, AlN, sialon, silicon nitride and silicon carbide. A clip (13) for a cerebral aneurysm as claimed in claim 3, in which the ceramic is alumina, AlN or silicon nitride. A clip (13) for a cerebral aneurysm as claimed in any foregoing claim, in which the clipping means (14a,14b) is made of a ceramic having an HN value in X-ray CT of 2000 or less. A clip (13) for a cerebral aneurysm as claimed in any foregoing claim, in which the spring means (17) is made of a rubber or synthetic resin. A clip (13) for a cerebral aneurysm as claimed in claim 6, in which the synthetic resin is selected from polyethylenes, polypropylenes, polystyrenes, methacrylic resins, epoxy resins, silicone resins, unsaturated polyester resins and fluorine resins. A clip (13) for a cerebral aneurysm as claimed in claim 7, in which the synthetic resin is polymethyl methacrylate, polytetrafluoroethylene or polyether sulfone. A clip (13) for a cerebral aneurysm as claimed in any foregoing claim in which the spring means (17) is made of a fibre reinforced synthetic resin. A clip (13) for a cerebral aneurysm as claimed in claim 9 in which the fibre is selected from carbon fibre, alumina fibre, SiC fibre, glass fibre or high polymer fibre.

Inventors: FUJITA, SHIGEKIYO, HIROMITSU, HIRAIWA, KUNO, HIROAKI, KURUSHIMA, TOYOKAZU
Applicants: FUJITA, SHIGEKIYO, INAX CORPORATION
Application year: 1989
Main classification: A61B17
IPC codes: A61B17, A61L31