Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-10-23
2001-06-26
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C606S095000
Reexamination Certificate
active
06251141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to articles and methods for blocking a flow of material within a bone canal, and, more particularly, to canal plugs and associated methods.
2. Description of Related Art
In procedures in which an implant is placed within a bone canal it is typical to anchor a distal portion of the implant with a cement material that flows in a liquid state and hardens upon drying. Once sufficient cement has been added under pressure to the canal and permitted to partially dry, the implant distal end is inserted, with a complete drying of the cement achieving a permanent fixation within the canal. In such procedures it is undesirable for the flowing cement to continue beyond the desired implant site, under pressure from the insertion of the implant, since such a displacement would lessen the amount of cement available to achieve optimal fixation.
Such procedures include hip replacement, which involves cutting off the head of the femur, opening the top of the femur, and cleaning out the canal to a length commensurate with the length of the implant stem. The canal is then plugged at the bottom of the cleaned-out space, the implant stem is inserted, and cement is forced around the pin to keep it in place.
The femoral canal plugs used at present are typically provided in a set of incrementally sized high-molecular-weight polyethylene truncated cones that are force-fit into the canal. However, femoral canals are not circular in cross section, but are oval or elliptical. Using a plug having a circular cross section thus leaves gaps surrounding the plugs through which cement may leak and extrude down the canal potentially as far as the knee region.
A further problem can occur with a plug that does not conform sufficiently well to the canal: With modern cement techniques, under the high pressures with which the cement is forced into the canal, plug “blowout” can occur, forcing the plug below the desired location. If these cases go on to require revision surgery at a later time, which occurs with a frequency of 5-10%, a very extensive and potentially destructive (relative to bone stock) operation must be undertaken to remove the cement.
Several intramedullary bone plugs are known in the art, including those that have elements adapted to change shape or expand after insertion into the canal. Among these are those disclosed by Seidel et al. (Eur. Pat. Appl. No. 0 006 408), Haynes (U.S. Pat. No. 4,697,584), Hardinge (U.S. Pat. No. 4,276,659), Swanson (U.S. Pat. No. 4,302,855), Weber (U.S. Pat. No. 4,447,915), Murray (U.S. Pat. No. 4,625,722), Frisch (U.S. Pat. No. 4,686,973), Kummer et al. (U.S. Pat. No. 5,092,891), Wilson (U.S. Pat. No. 5,383,932, and Huene (U.S. Pat. No. 5,531,792).
None of the plugs thus far disclosed, however, adequately conforms to the cross-sectional shape of a bone canal without leaving gaps through which cement may extrude and also is unlikely to experience “blowout.”
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a plug for insertion into a bone canal that is adapted to prevent cement passage therepast.
It is an additional object to provide such a plug that resists being displaced distal ward under pressure from cement insertion.
It is a further object to provide a plug that is insertable at a predefined force level.
It is another object to provide a plug having elements that are adapted to closely conform to the wall of a bone canal.
It is yet an additional object to provide a method of making such a bone canal plug.
It is yet a further object to provide a method of inserting such a bone canal plug.
These objects and others are attained by the devices, systems, and methods of the present invention. A first aspect of the invention comprises a plug adapted for insertion into a bone canal. The plug has a plurality of interleaving arms that are disposed about an insertion axis that extends from a first end of the plug. The arms are affixed at a second end and are flarable at the first end. In an insertion position the arms are relatively close packed; in a flared position the arms are radially flared, each arm having a portion remaining in overlapping relation to an adjacent arm.
In a particular embodiment each arm has interleaving arms, each having a generally paisley-like shape in axial cross section, oriented so that the head section faces generally toward the insertion axis and the tail section faces generally radially outward.
Also in a preferred embodiment the plug has an axial cross-sectional shape commensurate with that of its intended site; for example, for use in a femur, a generally oval cross section is preferred. This shape is not intended as a limitation, however, as other shapes will be known by one of skill in the art to be preferable for different intended sites.
The bore is adapted to receive an expansion member for separating the arms upon a progressive insertion thereof along the insertion axis. In a preferred embodiment the expansion member comprises a member tapering outward from a second end, such as a tapered plug, a screw, or a ratchet-type member.
The invention further comprises a method for preventing flowing material from extruding beyond a predetermined location in a bone tunnel. The method comprises the steps of inserting a bone plug such as described above into a bone canal to a desired location. Next the arms are opened to a position wherein the arms are flared. The paisley-like shape permits each arm tail section to remain in overlapping relation to an adjacent arm, thus preventing flowing material from escaping into the tunnel beyond the plug. The arms are continued to be flared until the plug is securely pressed against a wall of the bone tunnel. The plug can be inserted either second or first end first, with the expansion member, respectively, either inserted or pulled into the plug's bore.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.
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The DePuy Cement Restrictor Product Brochure,Inhibits Distal Migration of Bone Cement, 1991 DePuy Inc.
Justin Daniel F.
Pierson, III Raymond H.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Snow Bruce
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