Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-01-24
2004-06-29
Robert, Eduardo C. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S08600R
Reexamination Certificate
active
06755835
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a bone screw having a screw body which is provided with an external thread and which comprises flow-through means for bone cement that is used for the production of a cement jacket around the bone screw.
Bone screws of this type are, for example, employed as anchoring screws in a stabilisation system when several bone elements have to be connected together. The formation of a cement jacket around the bone screw following the implantation process increases the stability of the anchorage. This is of particular importance when the bone is of reduced quality, such as is the case for osteoporosis of the bony tissue for example.
A bone screw comprising a longitudinal channel along which there is provided a plurality of radially extending transverse channels that are in contact with this longitudinal channel is known from EP 0 305 417 B1.
Based upon this prior art, the object of the invention is to provide a bone screw which, in comparison with the bone screws known from the prior art, will be anchored in a highly stable manner after being implanted in a bone, and especially after it has been implanted in bones of reduced quality.
SUMMARY OF THE INVENTION
In accordance with the invention, this object is achieved in the case of a bone screw of the type mentioned hereinabove, in that the flow-through means comprises at least one longitudinal recess which is formed in the screw body such that it extends transversely relative to the radial direction and transversely relative to the peripheral direction.
By virtue of a recess which is constructed and arranged in this manner and by means of which bone cement can be introduced into the intermediary space between an implanted bone screw and the bone bed, a uniform cement jacket can be formed around the screw. As a result of this feature, the bone screw in accordance with the invention will be anchored in a highly stable manner. Each of the areas between the turns of the external thread can be supplied with bone cement and a highly effective flow of bone cement can be achieved by means of such a longitudinal recess which is formed substantially along the length of the screw body. By contrast, in the case of the bone screw of EP 0 305 417 B1, an individual radial channel basically has to be provided for each of the intermediary spaces. Moreover, in order to also enable a cement jacket to be built-up in the region around the frontal end of the screw, the longitudinal channel used there must extend through the whole of the screw body. Construction of the screw in the form of a self-tapping screw is thereby adversely affected. By contrast, in the case of the bone screw in accordance with the invention, a longitudinal recess basically suffices, and a cement jacket can also be formed about the frontal end of the bone screw by means of appropriate recesses in the turns of the external thread.
It is expedient if the at least one longitudinal recess is arranged such that it is perpendicular to the radial direction and especially so, if it is arranged to be perpendicular to the peripheral direction.
It is particularly advantageous if the flow-through means comprise a hollow channel formed in the screw body and if a longitudinal recess is connected to the hollow channel. Consequently, bone cement introduced into the hollow channel can flow out directly from the body of the screw via such a longitudinal recess without encountering substantial barriers to the flow of material so as to form a uniform cement jacket around the bone screw. It is thereby ensured that the bone screw in accordance with the invention will be anchored in a highly stable manner after the implantation process. It is expedient if a longitudinal recess is connected to the hollow channel in the longitudinal direction of said recess so as to minimise the resistance encountered by the flow of bone cement.
It is particularly advantageous if the dimensions of a longitudinal recess in the longitudinal direction thereof are such that it extends over a plurality of turns of the external thread. Due to this feature, the bone cement can be supplied to the whole of the screw body using essentially just one longitudinal recess.
In a particularly advantageous embodiment, a longitudinal recess has corresponding recesses associated therewith in the turns of the external thread. This enables the bone cement to flow between different intermediate regions i.e. the regions between adjacent turns of the thread so as to enable the bone cement to be distributed uniformly and thus produce a uniform build-up of the cement around an implanted bone screw. It is expedient if a turn of the external thread is broken-through in the vicinity of a longitudinal recess so as to enable the bone cement to flow therethrough.
For manufacturing purposes, it is particularly expedient if a longitudinal recess is in the form of a slot. This feature enables the recess to be produced in a simple manner by a machining process, for example, a milling process. It is advantageous if a plane of the slot is substantially perpendicular to the peripheral direction of the screw body. In particular hereby, the slot is formed by an upper slot plane and a lower slot plane which are in parallel with one another. Due to the construction perpendicular to the peripheral direction, the slot plane can be oriented in the radial direction. This enables an efficient flow of bone cement when the screw body is rotationally symmetrical. Furthermore, it is also expedient if a plane of the slot is disposed substantially radially relative to the screw body.
It is particularly advantageous if a plane of the slot is located substantially longitudinally relative to the screw body. On the one hand, this ensures that such a longitudinal recess is easy to produce, and it also ensures an efficient flow of bone cement on the other.
For the purposes of forming a cement jacket which will ensure a high degree of stability for the anchorage, it is particularly advantageous if a plurality of longitudinal recesses are arranged over the periphery of the screw body. This feature ensures that the regions between the turns of the external thread taken with reference to the periphery of the screw body will be uniformly supplied with bone cement.
In one advantageous variant of this embodiment, three longitudinal recesses are arranged along the periphery of the screw body. On the one hand, this enables the number of break-throughs in the turns of the external thread and in the body of the screw to be kept low, and it also enables uniform application of the bone cement on the other.
Hereby, it is of especially great advantage if the plurality of longitudinal recesses are substantially symmetrical relative to a longitudinal axis of the screw body. In this manner, the bone cement, which is introduced into the body of the screw, flows uniformly via the longitudinal recesses into the regions between the turns of the external thread and forms a uniform cement jacket.
In a particularly advantageous embodiment, the bone screw in accordance with the invention comprises successive sections in the longitudinal direction of the screw body which differ in regard to the construction of the outer surfaces thereof. Due to these outer surfaces being constructed such as to have differing geometrical shapes, a particularly highly stable anchorage is attainable by, on the one hand, forming one or more sections which will ensure that the thread is held firmly in the bone and, on the other hand, forming sections which will exhibit a sealing effect in regard to the outward flow of the bone cement. In this manner, a cement jacket can be built-up which will increase the anchoring forces in every direction by virtue of it interlocking with the bone in the manner of meshing gears. The volume of bone cement that needs to be supplied can be precisely metered by appropriate selection of the dimensions of the sections. Consequently, problems associated with the heating effects produced by reactions in the cement are, to a great extent, avoided.
It is e
Claes Lutz
Kinzl Lothar
Schultheiss Markus
Aesculap AG & Co. KG
Lipsitz Barry R.
McAllister Douglas M.
Ramana Anuradha
Robert Eduardo C.
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