Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-07-18
2003-12-30
Lucchesi, Nicholas D. (Department: 3764)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S095000
Reexamination Certificate
active
06669733
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a bone plug, for blocking of a canal in a bone, comprising a radially expandable blocking element which comprises an at least nearly solid body, which body under axial compression expands into radial direction and is provided with a continuous axial opening, which body has a height and an average wall thickness along said height, which bone plug comprises means to keep the body in expanded condition locked in the axial direction, which means comprise two locking elements which can be fixed on various distances to each other, in between which the body with its axial boundaries is positioned, of which a first locking element comprises a stem which is provided with a number of radial protrusions which are positioned next to each other in axial direction on the stem, which stem protrudes through the axial opening of the body, whereby the second locking element is positioned around the stem and can hook behind the protrusions. With the height of the body is meant the size of the body in the longitudinal direction of the stem. The term—“average wall thickness along the height”—is used, to be able to bename the wall thickness in case of non cylindrical shapes of the body like for example a cambered shape.
Bone plugs are used in the medical field for permanent or temporarily blocking of a canal in a long bone. For fixating of an endoprosthesis or artificial joint, for example an artificial hip prosthesis, in a bone, a stem of the prosthesis is inserted in the intramedullary canal of a long bone which is filled with bone cement. In order to prevent the bone cement to protrude in the canal any further than necessary for fixating of the stem and to assure that the bone cement is only present between the stem and the endosteal wall of the bone and to prevent leaking of the bone cement any further into the intramedullary canal, the canal beneath the stem is blocked with a bone plug.
BACKGROUND OF THE INVENTION
A bone plug of the abovementioned type is known from the French patent publication FR-A-2708193. The body of the known bone plug is made out of a flexible, resorbable, biocompatible material which under axial compression expands into radial direction. The body of the blocking element of the known bone plug is slim and has in relation to the height a minor wall thickness. In practice it has shown that such ratio of the sizes of the body are unsuitable in order to obtain a sufficient large radial expansion of the body. At such large axial compression the body will fold and crumple instead of expanding in radial direction, which is adversable for obtaining a good blocking of the canal in a bone. Hence the use of the known bone plug for blocking of canals is of limited value.
SUMMARY OF THE INVENTION
Part of the invention is to provide a bone plug of the kind described in the introduction, which is better than the known bone plug. Therefor the bone plug according to the invention is characterized in that the height of the body is at most 8 times the average wall thickness of the body. With this ratio between the height and the wall thickness, the body will also evenly expand in radial direction in case of large axial compression and will not crumple up in an irregular manner. Hereby the range of application is considerably larger than of the known bone plug. Preferred embodiments of the bone plug according to the invention are characterized in that the height of the body is at most 7, 6 or 5 times the average wall thickness, and in practice a suitable value has shown to be nearby 5.
A bone plug of the abovementioned type is known from the French patent publication FR-A-2708192. The body of the known bone plug is made out of a flexible, resorbable, biocompatible material which under axial compression expands into radial direction. The body of the blocking element of the known bone plug is slim and has in relation to the height a minor wall thickness. In practice it has shown that such ratio of the sizes of the body are unsuitable in order to obtain a sufficient large radial expansion of the body. At such large axial compression the body will fold and crumple instead of expanding in radial direction, which is endosteal wall.
An embodiment of the bone plug according to the invention is characterized in that the radial protrusions are located at least nearly to each other in the longitudinal direction of the stem. This makes compression of the body possible in smaller steps than with the known bone plug, where the protrusions are positioned on a relatively large distance to each other. By this possibility of accurate control of the amount of compression of the body, the bone plug can better be installed in a canal and a canal can better be blocked than with the known bone plug. Preferably the radial protrusions have an at least nearly saw-tooth shape in a longitudinal section of the stem.
It is noted that a bone plug with a stem with protrusions, which are positioned near to each other in the axial direction of the stem, is known from patent publication DE-A-92 13120.4. However a fully different shape of the body has been applied here. Experience showed that in particular by a combination of a solid body with a stem provided with protrusions which are positioned near to each other, a well functioning bone plug is obtained.
It is noted that the beneficial effect of the fact that the protrusions are positioned near to each other also occurs when the ratio between the height of the body and the average wall thickness does not fulfil the abovementioned condition, by which explicitly the possibility is preserved to claim this feature separately from the feature that the height of the body is at most 6 times the average wall thickness of the body.
A further embodiment of the bone plug according to the invention is characterized in that the material of the body of the blocking element has at least nearly elastomeric properties. A body of an elastomeric material is nearly incompressible, whereby the axial compression is nearly fully converted in a radial expansion without loss of volume. In case of the known bone plug an axial compression will in contrary not only result in a radial expansion, but the body itself is also compressed, which means that the volume decreases. Hereby, the bone plug according to the invention will, at equal axial compression, achieve a larger radial expansion than the known bone plug and the bone plug according to the invention will better be fixed in the canal than the known bone plug.
It is noted that the beneficial effect of a body of an elastomeric material also occurs when the ratio between the height and the average wall thickness does not fulfil the aforementioned condition by which explicitly the possibility is preserved to claim this feature separately from the feature that the height of the body is at most 6 times the average wall thickness of the body.
A preferred embodiment of the bone plug according to the invention is characterized in that the material of the body of the blocking element is composed mainly from a mixture of gelatine, glycerine and water. It is noted that a material composed from a mixture of gelatine, glycerine and water is known on itself and that it is known to use such a material for the production of bone plugs. This known application for bone plugs however is only used in order to obtain a flexible material which is biologically degradable. Hereby no advantage is made of the specifically for the type of bone plug according to the invention, beneficial incompressible properties of the material.
It is also noted that the beneficial effect of the fact that the material of the body of the blocking element is composed mainly of a mixture of gelatine, glycerine and water also occurs when the ratio between the height and the average wall thickness of the body does not fulfil the aforementioned condition, by which explicitly the possibility is preserved to claim this feature separately from the feature that the height of the body is at most 6 times the average wall thickness of the body.
A further
Lucchesi Nicholas D.
Mathew Fenn C
Milde & Hoffberg LLP
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