PLUG FOR THE CRANIAL BONE

Abstract: A plug for the cranial bone is conical and comprises a conical body (3), whose large end face is formed with one or more depressions (4) for engagement of the plug by means of a plug turning tool and whose circumferential surface is formed with irregularly distributed projections.

Description: PLUG FOR THE CRANIAL BONE The present invention relates to a plug for the cranial bone. An operation in the head or skull, which is required, for instance, in case of brain tumour or cerebral haemorrhage, is in most cases begun with the removal of a piece of the cranial bone. To this end, a number of spaced-apart holes are drilled in the cranial bone along a contour line corresponding to the periphery of the piece of cranial bone to be removed, whereupon the cranial bone is sawn through between the drill holes such that the piece of cranial bone is released and can be removed. After performing the operation, the piece of cranial bone is restored, and straight-circular-cylindrical plugs are inserted in the drill holes. At present the plugs consist in most cases of hydroxyapatite and have a head like a fungus. Under the scalp, the head of the plug rests against the outside of the skull and prevents the plug from falling into the skull. The projecting head of the plug causes a cosmetic problem. The circular-cylindrical shape of the plug results in a poor fit in the hole and consequently a long healing period. This is caused by the fact that it is not possible to drill in a consequently circular-cylindrical manner. The drill holes will often be elliptic or have a shape deviating from a circular cross-section. Hydroxy¬ apatite breaks easily, for instance when subjected to a blow. The object of the invention is to remedy the above¬ mentioned drawbacks. The object is achieved by means of a plug according to the characterising clause of claim 1, according to which the plug consists of a conical body, in whose large end face a depression or depressions is/are formed for engagement of the plug by means of a plug-turning tool and whose circumferential surface is provided with ir¬ regularly distributed projections. The inventive plug thus has no head, and its irregu¬ larly distributed projections accomplish, as the plug is turned into the skull, rasping-off of necrosis in the wall of the drill hole and levelling-out of wrong dril¬ lings and, consequently, a close engagement of at least portions of the outside of the plug with and in the wall of the hole. The plug is turned in until its large end face is aligned with the cranial bone. It should be noted that, for instance, in tooth im¬ plantations, corrections for wrong drillings have already been made by using progressively increasing drill diame¬ ters, but such time-consuming measures cannot be taken when operating in the skull, for example after a cerebral haemorrhage. The turning of plugs without heads in cavities in the human body is per se known, but only, as far as the applicant is aware, in connection with plugs whose body is threaded, see e.g. EP-A-469,441 and DE-A-3, 505, 567, and which are intended to serve as fixing screws for im¬ plants or which are straight-circular-cylindrical. Such screws do not yield the rasping effect aimed at by the invention. The inventive plug may consist of any osseointegrat- ing or biocompatible material whatever, of which the cur¬ rently most preferred is titanium. The manufacture of the plug according to the inven¬ tion can take place, for instance, by diecasting of tita- nium. It is understood that the transverse dimension of the plug should be adapted to the transverse dimension of the drilled hole so as to bring about the above-described rasping effect, the surgeon being supplied with plugs having different basic dimensions. The projections have a length starting from the body and radially outwards, and a width transversely of said direction, of 1.5 mm at most, since greater lengths and widths may create problems of bone growing into the body of the plug and with the turning-in of the plug. For optimum tissue ingrowth against the body of the plug, the projections should be undercut, i.e. have a relatively narrow base adjacent to the body. They may be, for example, grain- or ball-shaped. An embodiment of the invention is illustrated in the accompanying drawing in longitudinal section. A straight-conical, symmetrical plug 1 of titanium, without head, for insertion into the skull after an opera¬ tion has the following dimensions: large diameter 7 mm, small diameter 6 mm and height 4 mm, the diameter figures including 0.6 mm ø ball-shaped projections 2 formed on a body 3, said projections being irregularly distributed on the circumferential surface of the body. The large end face of the plug is formed with a square depression 4 for engagement of the plug for rotation by means of a square spanner.

Claims: CLAIMS 1. A plug for the cranial bone, c h a r a c t e r - i s e d in that it is conical and comprises a conical body (3) , in whose large end face one or more depressions (4) are formed for engagement of the plug by means of a plug-turning tool and whose circumferential surface is formed with irregularly distributed projections. 2. The plug as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the projections (2) are undercut. 3. The plug as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the projections are grain- or ball-shaped. 4. The plug as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the dimensions of the projections are 1.5 mm at most. 5. The plug as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that it is made of titanium.

Inventors: BRUCE INGRID, BRUCE LARS, BRUCE, INGRID, BRUCE, LARS
Applicants: BRUCE INGRID, BRUCE LARS, IDEA AB, AB IDEA, BRUCE, INGRID, BRUCE, LARS
Application year: 1996
Main classification: A61F2
IPC codes: A61B17, A61F2