Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-04-02
2004-07-27
Ferko, Kathryn (Department: 3743)
Surgery
Instruments
Orthopedic instrumentation
C606S075000, C606S075000, C606S074000
Reexamination Certificate
active
06767350
ABSTRACT:
The invention concerns a fixing element for fixing a first bone fragment to a corresponding second bone fragment, as in an ankle joint fracture.
A problem which frequently arises in the case of fractures caused by over-stressing is that relatively small exposed bone regions are detached from the rest of the bone. Thus for example ankle fractures represent the most frequent break injury to the lower extremity. In that case, over-stressing in the region of the upper ankle joint means that the Inner ankle Is detached from the tibia and/or the outer ankle is detached from the fibula. In order to restore the function of the ankle joint, the ankle fragments must be fixed to the associated bone fragment until the break heals. Bone screws and the like are still frequently used for that purpose. As however generally particularly long and/or a plurality of bone screws are required for adequate stabilisation of the bone fragments by virtue of the slenderness of the bone screws, the fixing elements of the general kind set forth which are easier and quicker to implant are increasingly gaining in importance.
European patent application EP 0 409 364 A2 discloses a fixing element of the general kind set forth, in which at its proximal end, that is to say the end towards the surgeon, the fixing body has a step which permits the fixing body to be inserted into the receiving bores in the bone fragments, only as far as a given depth. The fixing body which in the initial condition has a conical main body with anchoring elements arranged thereon is spread open in particular at its distal end, by driving in the spreading body, to such an extent that the main body assumes a substantially cylindrical contour. The anchoring elements of the spread-open regions in that case penetrate into the surrounding bone and thus serve to provide for additional fixing.
That fixing element however suffers from the disadvantage that the presence of the step at the proximal end means that It Is only suitable for fixing bone fragments up to a given maximum dimension in the longitudinal direction of the fixing body. If that maximum dimension is exceeded, there is no longer any guarantee that the first bone fragment is adequately fixed to the second bone fragment. As the distal end of the fixing body is spread open In the spongiosa which is generally of low strength, it can tear out of the second bone fragment with a correspondingly short depth of penetration or in a situation involving locally reduced strength of the bone tissue. It is precisely a locally reduced level of strength in the bone tissue that can only be detected with difficulty during the operation, so that, with a depth of penetration which is possibly still sufficient in a normal situation, it can nonetheless tear out.
If the step at the proximal end of the fixing body is omitted, the fixing body can admittedly penetrate sufficiently far into the second bone fragment, irrespective of the dimension of the first bone fragment. As the spreading body at the proximal end is of a smaller diameter than the cavity, no expansion of the fixing body takes place immediately at the proximal end. Rather, expansion of the fixing body increases slowly in the direction towards the distal end so that the absence of the step means that there is precisely no guarantee of secure fixing of relatively thin first bone fragments.
The known fixing element in its respective configurations is therefore only limitedly suitable for fixing bone fragments of the most widely varying dimensions so that in practice an expensive set of fixing elements in a plurality of different dimensions is required for the respective situations of use.
U.S. Pat. No. 5,713,904 B1 to Errico, et al. (Feb. 3, 1998), discloses a fixing element of the general kind set forth, in which an integral tubular fixing body is provided at both ends with longitudinal slots so that, upon the insertion of a suitable spreading body into its internal cavity, it is spread open in a cup-shaped configuration at both ends while it remains undeformed in its central region. The fixing body in that case is provided with a male screwthread by which of which it can be screwed into the bore in the bone.
That fixing element has the disadvantage however that, in its middle region, the contact force between the fixing body and the surrounding bone is determined by the fit therebetween. In that respect, it is precisely in the comparatively soft spongiosa of a bone that a greater or lesser deviation of the bore diameter from its target diameter can occur, due to a minor deflection with the drill from the target axis for the bore. Depending on the over-size of the bore with respect to the fixing body, the situation can then involve a connection which is movable to a correspondingly greater or lesser degree transversely with respect to the longitudinal direction of the fixing body, if the central region of the fixing body is precisely in the region of the join between two bone fragments which are to be fixed to each other.
Therefore the object of the present invention is to provide a fixing element of the general kind set forth, which does not suffer from the above-stated disadvantages or which suffers therefrom at least to a lesser degree, and which in particular can be put to flexible use and ensures reliable fixing.
Based on a fixing element as set forth in the appending claims, that object is attained by the features recited therein.
The invention involves the technical teaching that a fixing element which can be put to flexible use is acquired if the fixing body is adapted to be introduced completely into the bores and by proximal insertion of the spreading body into the cavity can be spread open transversely with respect to its longitudinal direction by a wedge action substantially over its entire length for connection to the respective bone fragment. That ensures on the one hand that, irrespective of the thickness of the first bone fragment, the fixing body can be moved into a position in which the second portion of the fixing body is sufficiently deeply inserted into the second bone fragment in order to ensure fixing of the first bone fragment, which is adequate in any situation. In that respect, spreading the fixing body open in the region of its proximal end ensures that, even when dealing with particularly thin first bone fragments, reliable fixing is guaranteed with the fixing element according to the invention.
Reliable fixing is further achieved in that, in the spread condition, that is to say after substantially complete insertion of the spreading body into the cavity, the fixing body at the distal end of the second portion is of a larger dimension transversely with respect to its longitudinal direction than at the proximal end of the second portion. The fixing body is thus enlarged conically or bell-like at its distal end in the second bone fragment in which it is generally surrounded by spongiosa of lower strength, thereby achieving a positively locking engagement over a large area. That ensures secure anchoring even if the surrounding bone material is of a possibly reduced level of strength, insofar as it applies the anchoring loads uniformly to a larger volume of bone. That effectively prevents the fixing body from being torn out of the second bone fragment.
The operative surfaces in the region of the cavity and on the spreading element, which are responsible for spreading open the fixing body, can be designed in many known ways. Thus to provide that the second portion of the fixing body is expanded in a conical or bell-like manner, it is only necessary for the transverse dimension of the cavity to decrease towards the distal end. In that respect, the transverse dimension of the spreading element can remain constant or also decrease towards the distal end, in which case the decrease per unit of length must then be less than the decrease in the transverse dimension of the cavity towards the distal end.
The fixing body can consist of a single body which, for greater ease of being spread open in the regions which are to be s
Clark Robert J.
Ferko Kathryn
Hahn Loeser & Parks LLP
Odland Kathryn
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