Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-09-02
2001-02-27
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S080000
Reexamination Certificate
active
06193722
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hollow milling tool in accordance with the preamble of the independent patent claim.
Hollow milling tools of this kind are used for example in the transplantation of tissue pillars. For example cartilage defects are in certain cases nowadays “repaired” at stressed locations, such as e.g. joints, in such a manner that a blind bore is produced at the defect. location which reaches into the subchondral bone. At a less stressed harvest location then a tissue pillar is taken out which consists of bone which is covered with healthy cartilage. This tissue pillar is transported to the defect location and implanted there into the blind bore.
Various instruments have been proposed for the production of the tissue pillar at the harvest location such as e.g. punches or hollow milling tools (in some cases also designated as “crown borers”). A hollow borer of this kind has teeth which are arranged at the front side and which ablate the tissue in the production of the tissue pillar. The ablated tissue can be transported away through the inner space of the hollow milling tool or via the space which surrounds the hollow milling tool.
Bone tissue is ablated in the production of the tissue pillar. In this the tissue heats up in the immediate vicinity of the distal end of the milling tool (chip forming method). On the other hand, the bone tissue contains materials such as e.g. proteins which can stand only a very limited temperature increase because they could otherwise denature. In this, both tissue which is arranged directly outside round about the milling tool can be affected by a temperature increase of this kind as well as tissue which is directly surrounded by the milling tool, thus the tissue pillar or at least parts thereof.
SUMMARY OF THE INVENTION
An object of the invention is thus to propose a hollow milling tool in which it is ensured that neither the tissue directly surrounding the milling tool at the harvest location nor that of the tissue pillar can be damaged in the production and the removal of the tissue pillar.
This object is satisfied with the help of a hollow milling tool such as is characterised by the features of the independent patent claim. Advantageous embodiments of the hollow milling tool in accordance with the invention result from the features of the subordinate claims.
This object is satisfied in accordance with the invention by providing the hollow milling tool with means for the cooling of the region of the milling tool lying near the distal end during the ablation of tissue. Through this it is avoided that the milling tool can reach a temperature which can damage the tissue in that region with which it comes into contact with the tissue.
In one exemplary embodiment the means for the cooling can comprise discrete passage bores which are formed in the wall of the milling tool near the distal end. This is a particularly simple constructional measure.
In this a plurality of passage bores can be arranged in the wall of the milling tool at a uniform mutual spacing when viewed in the peripheral direction. Viewed in the axial direction a plurality of layers of passage bores of this kind, which are uniformly mutually spaced when viewed in the peripheral direction, can be provided in the wall of the milling tool.
In another exemplary embodiment the means for the cooling can comprise at least one groove which extends in spiral shape in the outer wall of the milling tool, and the orientation of which can be opposite to the direction of rotation during the ablation of tissue so that during the ablation a coolant, e.g. a physiological salt solution, can arrive through the groove at the distal end of the milling tool. Thus in this exemplary embodiment a (body compatible) coolant is actively supplied. Through the fact that the orientation of the spiral-shaped groove is opposite to the direction of rotation during the ablation of tissue, the supplied coolant can also arrive at the location where the cooling is to take place, namely at the region near the distal end of the milling tool, where the milling tool comes into contact with the tissue. The supplied coolant can be transported off through the inner space of the hollow milling tool together with the ablated tissue.
In a further exemplary embodiment of the hollow milling tool in accordance with the invention the cutting teeth which are arranged at the front side are conically outwardly sharpened to a point in the direction towards the distal end of the hollow milling tool starting at the inner wall or vice versa (i.e. they are sharpened to a point from the outside inwardly). Through this it is achieved that the milling tool can not slide off even when it is not applied exactly orthogonally to the cut surface.
The tips of the cutting teeth, which are arranged at the front side, can be rounded off (preferably with a very small radius), through which the lifetime of the cutting teeth is increased.
In the region of the distal end of the milling tool the inner diameter can at first be constant and then enlarge when viewed in the proximal direction. The outer diameter can in the region of the distal end of the milling tool also first remain constant and then decrease when viewed in the proximal direction. After the tissue pillar has been produced the hollow milling tool must be taken out again while the tissue pillar is still anchored at its base at the harvest location. It is then separated at its base with a suitable extractor and can then be taken out and transported to the defect location. The two described measures now serve to facilitate this removal of the hollow milling tool, but they can also be present in combination. If the inner diameter in the region of the distal end is first constant and then enlarges when viewed in the proximal direction, this means that the tissue pillar is still in contact with the inner wall of the hollow milling tool only at its distal end. Through this the hollow milling tool can be taken out more easily than if the tissue pillar were in contact with the inner wall of the hollow milling tool over its entire length. The same holds for the contact with the surrounding tissue. The hollow milling tool is now only in contact with the surrounding tissue at the distal end because the outer diameter of the hollow milling tool then decreases when viewed in the proximal direction. This likewise facilitates the removal of the hollow milling tool. In this it should be observed that it is a matter of only a slight change of the diameter here because the wall thickness of the hollow milling tool, which is not arbitrarily large anyway, cannot be arbitrarily reduced; quite considerable forces must be nonetheless transmitted to the cut surface during the milling of the subchondral bone.
Markings can be provided on the outer wall in the region of the distal end of the hollow milling tool which indicate to the surgeon or orthopedist the respective current penetration depth of the hollow milling tool and make it easier for him to produce a tissue pillar of a precisely determined length.
Furthermore, markings can be provided on the outer wall of the milling tool which contain other information on the milling tool (e.g. milling tool inner diameter, milling tool outer diameter, etc.). These are however preferably placed in a region different from that of those markings which indicate the current penetration depth of the hollow milling tool.
Further advantageous embodiments result from the description of the following exemplary embodiments of the hollow milling tool in accordance with the invention with reference to the drawings.
REFERENCES:
patent: 4649918 (1987-03-01), Pegg et al.
patent: 5205685 (1993-04-01), Herbert
patent: 5556399 (1996-09-01), Huebner
patent: 5873684 (1999-02-01), Flolo
patent: 5921987 (1999-07-01), Stone
patent: 6012881 (2000-01-01), Scheer
patent: 611624 (1994-08-01), None
patent: 824893 (1998-02-01), None
Favre Alain
Zech Manfred
Philogene Pedro
Sulzer Orthopaedic AG
Townsend and Townsend / and Crew LLP
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