The present invention relates to a novel non-irritating and shock-absorbing ureteral stent anchor. More particularly, the invention relates to the design of the anchor to enable it to minimize or eliminate irritation and discomfort associated with the bladder anchor of a ureteral stent.
The double-J or pigtail ureteral stent is widely used to maintain ureteral patency post-endoscopic procedures, as well as for relief of longer-term obstructive disease. The pigtail catheter provides a self-retaining capability due to a coil design at proximal and distal ends that work to securely anchor the stent in the urinary tract between the renal pelvis and the bladder. These anchors prevent stent migration proximally or distally despite urinary flow, patient movement, and ureteral peristalsis.
The stent anchor may irritate the bladder, causing patient discomfort and a need to pass urine frequently. Referred pain as well as pain upon urination is common, as is hematuria (blood in urine) in severe cases. It is believed that the relatively small bearing surface of the existing stent shaft contributes to the irritation.
These stent-related symptoms may impact large populations of patients. They include voiding symptoms including frequency, urgency, dysuria, incomplete emptying; flank and suprapubic pain; incontinence, and hematuria. To lessen these symptoms, a wide array of anchor designs and alternative stent tube materials has been proposed. Anchor designs other than the pigtail include the “Tailstent” with long floppy strands extending into the bladder (U.S. Pat. No. 6,656,146), stents utilizing a collapsible Mallecot type structure (U.S. Pat. No. 7,470,247), and stents with an expandable coil anchor (U.S. Pat. No. 4,531,933) or an expandable coil perpendicular to the stent axis (U.S. Pat. No. 6,620,202). Of significant interest are ureteral and urethral stents utilizing spherical, ellipsoidal and convex braided mesh anchors in the bladder and also in the GI tract (U.S. Pat. Nos. 6,395,021 and 6,558,350).
Several ureteral and other proposed stents are made entirely of a self-expanding mesh for the simultaneous purposes of self-anchoring and dilation of a duct or vessel. These are principally utilized in a blood vessel, and in the GI tract. The blood vessel devices are anchored in position by the wires of the mesh pressing into the wall of the vessel, causing extrusion of tissue into the openings of the mesh. This approach typically works much better in a blood vessel rather than in a GI lumen or a ureter where there is significant peristalsis. Some of the GI devices are anchored in this manner, more commonly others, used with one or more ends protruding into an expanded space, are anchored in a manner similar to a ureteral stent. Those devices depend on an enlarged section to prevent the stent from being pushed or pulled out of the lumen being treated. The typical expanded shape is a sphere or ellipse or an abrupt increase in diameter, one that is a natural result of a self-expanding device in an unconstrained space.
Use of a self-expanding mesh stent with spherical, elliptical, or abrupt or tapered convex anchor shapes, although simple to implement, create several difficulties. Most important, the bearing surface against the delicate tissue surrounding the ureteral entrance consists of small wires. Self-expanding braid, optimized for self-expansion and dilation of a constricted lumen are likely too stiff to be tissue friendly. When small diameter wires are pulled against the tissue by a change in patient position or by physiologic movement such as peristalsis, these small wires can cause local damage/abrasion via the “cheese-cutter” effect.
Secondly, the tissue in and immediately adjacent to the ureteral orifice in particular is known to be heavily enervated and sensitive to trauma. A spherical or elliptical mesh anchor, even if soft enough to provide some shock absorption, will not only irritate the tissue immediately adjacent to the ureteral entrance, but may be drawn into the duct itself, scraping the proximal intima with its wire mesh. If too soft, the anchor may not provide sufficient anchoring force. The difficulty in trading off avoidance of tissue damage, good shock absorption, and sufficient retention is the reason that these types of stents are not currently employed in the bladder and ureter, although they have some usage in the GI tract. The current invention addresses all three of these challenges in such a manner as to provide improvement in all three areas over current “double-J” products as well as prior self-expanding mesh anchors.
The present invention of a novel ureteral stent device is comprised of a polymer tube (of size 3 to 4 French for pediatric and 4 French and higher for adult) with a traditional pigtail shape tapered anchor for anchoring in the kidney, and a unique soft bladder anchor made out of a fine metal or polymeric braid. The braid is preferably made out of metallic alloy such as Nitinol (NiTI) material. NiTi can be a soft shape-memory alloy which may be shape-set into a desired form, such as an ovoid or sphere or cup with relatively high surface area as compared to stent tubing. NiTi is well known for its ability to return to its pre-set shape.
The braid alloy, wire size, and pick count are precisely selected in order to create a soft and non-irritating anchor in the bladder. The braid is heated to shape-set into a secondary shape such as a single or double spherical shape, oval, donut, cone, cup, etc. Sufficient flexibility is designed into the braided structure to allow it to deform to act as a retaining shock absorber, while still being a relatively soft, non-irritating bladder anchor.
The stent anchor of the present invention is formed of a cup or concave mesh anchor structure which forms a contact region spaced radially outwardly from the shaft or body of the ureteral stent. Thus, its annular ring bears on the tissue close to but not immediately adjacent to the bladder entrance of the ureter (commonly called the ureteral orifice or UO). This structure takes full advantage of the theoretical benefits of the prior spherical or elliptical mesh anchors which include relatively large diameter expansion, unrestricted flow of urine through the mesh, and large bearing surface against the bladder tissue as compared to the prevalent “Double J” design. However, the annular contact ring of the concave/cup configuration avoids contact of the anchor with tissue immediately adjacent to the ureteral orifice, with the orifice itself, as well as with the proximal ureter. To avoid trauma to the highly enervated bladder tissue adjacent to the ureteral orifice the diameter of non tissue contact should be a minimum of three times the diameter of the stent shaft, that shaft diameter typically defining the diameter of the ureteral orifice. The woven or braided mesh of the anchor can be formed from elements such as Nitinol and other metals or polymers such as polyester.
In one aspect of the invention, the characteristics of the braid itself may be adjusted to provide differing physical properties in various portions of the structure. Specifically, it would be desirable to have the “rim” of the cup structure that engages in tissue contact with the bladder, be woven with a construction that is more flexible and thus softer than the rest of the structure, the stiffer balance of the structure determining the retention force of the anchor. Thus, both lack of tissue irritation and appropriate retention force may be obtained simultaneously, unlike with a homogeneous structure.
In another aspect of the invention, the same effect may be accomplished by using wires of differing cross-section for different portions of the anchor. For example, the same wire may have a section that is flattened for maximum area in tissue contact and flexibility in one dimension, but retain its circular cross-section where stiffness is required.
In another aspect of the invention, the softer or more flexible braid section is extended further proximal to the tissue contact area. The additional flexibility of this section will add to the capability of the anchor to adapt to positional and other changes in length of the ureter, serving as a shock absorber and further limiting impact at the tissue surface. To the extent that the bladder anchor performs as a shock absorber, this will also limit tension on the kidney coil anchor at the other end of the stent, and possibly provide additional tissue sparing benefits in that location.
In another aspect of the invention, it may be that in certain applications that the ratio of tissue sparing, retention force, and shock-absorption cannot be satisfied by different physical braid configurations alone. In such a situation, a softer tissue-contact region of the braid may be attached to a stiffer retention section by an internal elastic member, thus providing linearly increasing resistance to deformation into the UO in addition to that provided by the braid itself.
In another aspect of this invention, two bladder anchors are arranged sequentially at the end of the stent tubing. The anchor typically in contact with the bladder wall is very soft and functions as a shock absorber and an anchor sufficient for retention of the stent in the bladder under normal circumstances. The second anchor is significantly stiffer and provides higher retention force only once the first anchor is fully collapsed against the bladder wall when unusually stressed such what may occur in an accident or a fall by the patient.
In a still further aspect of the invention, a means to slow or to prevent calcification of the mesh is described. Calcification of ureteral stents in general is a significant problem, particularly when a stent is needed for chronic problems rather than placed for several days after a procedure to ensure ureteral patency. This can result in increased discomfort, obstruction, and difficulty in removal, and has been shown to be a result secondary to formation of a bacterial biofilm on surfaces exposed to urine. Metallic silver has been shown to have broad spectrum antibacterial properties and has seen many applications in medicine from use as a silver foil covering for surgical lesions or bandages to ionic silver sources for transcutaneous external fixation and of course silver nitrate and silver sulfadiazine, both potent broad spectrum, topical antibiotics. Use of the appropriate silver alloy for the mesh wires can give additional protection from biofilm formation, as well as could silver coating or plating on other alloys such as Nitinol. Metallic silver can also be coated over polymeric materials via electroless plating or by sputtering.
Some embodiments of the present invention are illustrated as an example and embodiments are not limited by the figures of accompanying drawings:
Although a number of exemplary embodiments of the invention have been shown and described, many other changes, modifications, substitutions will now be apparent to those of ordinary skill in the art, without necessarily departing from the spirit and scope of this invention as set forth in the following claims.
Number | Date | Country | |
---|---|---|---|
62561577 | Sep 2017 | US |