Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1997-10-02
2001-04-24
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
Reexamination Certificate
active
06221100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an endoprosthesis percutaneously implantable by means of a catheter in the body of a patient, particularly in tubular vessels or organs, said endoprosthesis being designed in the form of an oblong, hollow body and, upon placement in the correct position during implantation, being changeable from a small lumen during insertion into a larger lumen conforming to its functional position.
2. The Prior Art
Prostheses capable of being inserted percutaneously and changeable in their lumen are known. They serve the purpose of opening or widening vascular lumina either by mechanical expansion by means of known balloon catheters from a small to a larger lumen, or such a prosthesis expands by itself after prior compression by spring force prior to the implantation, due to the initial stress produced in the spring during the compression.
EP-A-0,292,587 describes an endoprosthesis that is received on a balloon catheter and expandable by dilation, as well as detachable from the catheter and placed in a vessel. This prosthesis is a “stent” manufactured by knitting or crocheting from metal or plastic thread material into the form of a hose-like hollow body, in connection with which the individual stitches consist of loosely meshing loops. During expansion, widening, due to dilation of the balloon of the catheter, the meshing loops undergo plastic deformation, and the expanded prosthesis thus remains in its expanded position.
Self-expanding stents have been described in the prior art, for example in EP-A-0,183,372, U.S. Pat. No. 4,732,152 and DE-OS 4,137,857. Prior to their implantation, these prostheses are compresses against inherent spring return forces to a reduced cross section, inserted into the body in the compressed state, and, upon placement in the correct position, expand again in the respective vessel or hollow body of the patient's body due to cancellation of the force of retention, and are fixed thereby.
The endoprosthesis described in EP-A-0,183,372 is one which, for the purpose of implantation, is compressed to a reduced cross section and then pushed in the compressed state by means of a pusher through a catheter previously inserted in the vessel, until it is positioned in the right position in the vessel. Such advancing of the prosthesis through the catheter requires a considerable expenditure of force because the displacement is counteracted by high frictional forces.
A woven and elastically designed endoprosthesis has been described earlier in U.S. Pat. No. 4,732,152, which, in the compressed state, is kept together by a double cover, which is closed at the distal end. This cover is pulled back from the folded prosthesis in the same way as a stocking is pulled from the foot of a wearer. For the purpose of avoiding the friction occurring in this process, liquid may be filled in between the two leaves of the cover. However, this system, which seems to be initially suitable due to the reduction of the frictional resistances, is very complicated with respect to handling.
DE-OS 4,137,857 describes a hollow body. This prosthesis is compressed against the action of resetting spring forces to a cross section that is reduced versus the widened functional position, and kept in this position by means of a mountable covering. After the covering has been mounted, the prosthesis automatically widens to a cross section conforming to the functional position. The covering, which may be a meshwork approximately in the form of a round crocheting, extends over the entire length of the prothesis and consists of at least one through-extending filament and one pull-up line. The prosthesis, which is kept in a radially compressed position by the covering, can be advanced, for example on a guide wire, or also rigidly received axially on the end of a probe or catheter.
Finally an endoprosthesis is known, for which no documentation is available in the form of a published reference made from a memory alloy. This endoprosthesis is an oblong hollow body with a jacket that is broken many times and embodied in the way of a stretched metal.
This endoprosthesis automatically widens from a smaller insertion lumen to a larger lumen. However, this endoprosthesis has little flexibility and in any case potentially has the hazard of fatigue fractures when implanted via a joint. Not all of the struts forming the jacket are connected with each other in the corner points, and, in the implanted state, such struts may thus detach themselves from the vascular wall and protrude into such a wall.
SUMMARY OF THE INVENTION
Contrary to the above mentioned prior art, it is an object of the present invention to provide an endoprosthesis which, as compared to the stents known according to the state of the prior art, is more flexible and has superior strength and stability in the expanded state.
This object is achieved in accordance with the present invention in that the endoprosthesis is a hose-like netting produced from at least one elastic filament, such netting having the structure of a wire screen fence with mesh forming polygons, in which the filaments each grip around each other in their corner points in the direction of the meshes following one another in the direction of the longitudinal axis of the prosthesis.
An endoprosthesis of the invention, which may be self-expanding by means of a balloon catheter, is adaptable to the requirements in any given application in a simple way, and represents a flexible structure that is implantable without problems also in joint regions and then capable of following the movements of the joint of the patient without impediment. In particular, it has been found that as compared to the prior art, such an endoprosthesis has an enhanced ratio between a small and a large radius in the widened position. This means that the insertion catheter to be inserted during implantation can be kept smaller than possible in connection with known prostheses.
It has been found that it is especially preferable if the hose-like netting forming the endoprosthesis comprises at least one through-extending filament, which is braided into a round shape, forming meshes. Alternatively, the endoprosthesis can be produced from an initially flat netting that is then rolled into a hose shape, whereby two longitudinal edges of the netting are then joined with each other by means of a longitudinal seam.
According to a particularly preferred embodiment of the invention, provision is made that the filaments loosely grip around each other, in each of the meshes adjacent to each other in the longitudinal direction of the prosthesis. In this manner, the prosthesis can be shortened from its maximum length so that the filaments will be abutting each other in the corner points of the meshes, by pushing the meshes together.
With such an embodiment, the endoprosthesis is one that can be changed in its length within predetermined limits, whereby in the case of maximum axial expanse, the filaments gripping around each other abut one another in the corner points of the meshes. On the other hand, in the case of a shortening, these filaments grip around each other with more or less axial play. The special advantage of such an embodiment of the prosthesis is that whenever the length is adjusted to a length smaller than the maximum length, no shortening occurs during widening because the material required for widening in the radial direction has not be made available by shortening the length, but is available through the filaments of the individual meshes which do not abut one another axially.
Furthermore, it has been found that it is desirable if the filaments are provided in the corner points of the meshes with interlocks engaging one another in a form-locked way. Such interlocks provide the prosthesis with a particularly pronounced strength in its widened condition.
The aforementioned interlocks may be depressions formed by compressing the filaments intersecting each other in the stretched condition of the prosthesis in the corner points to appr
Hamilton Brook Smith & Reynolds P.C.
Jackson Suzette J.
Willse David H.
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