Keywords

1 Introduction

Ureteral stents entered the urologists armamentarium after Finney described the first Double-J in the late 1970s [1]. Despite the problems they create, yearly 1.5–2 million ureteral stents are inserted world-wide, either in their original JJ shape or in their various modifications for short and long indwelling periods. About 15% of these stents are used in chronically obstructed ureters.

With their worldwide use came also reports on the problems they create which are very common and can affect nearly 60–80% of the patients [2]. Without taking into consideration the medical problems of infection, encrustation, migration, stent breakage etc. the patients complain of urinary frequency (up to 60%), urgency/urge incontinence (up to 60%) and flank pain (up to 35%). Most of these symptoms are caused by their inherent design flaws common in all JJ and pigtail stents being in close contact with certain areas of the bladder. Urinary frequency, urgency and urge incontinence are caused by mechanical irritation of the bladder trigone induced by the bladder-end coil of the stent, which is in almost constant contact with the trigone. Additionally, during respiration, the up and down movement of the kidney, moves the bladder-end of the stent back and forth in the bladder, creating continuous friction with the trigone. The bladder trigone is an anatomical entity formed by the two ureteral orifices and the bladder neck very rich in innervation. Maximal vertical motion of the kidney from the end-expiratory to its end-inspiratory position is 39 mm [3]. Thinking that this friction may be reduced by using a softer material at the bladder end of the stent, in my Closing Remarks of the Second International Symposium on Urological Stents (ISUS-2) held in Belgrade in March 18–20, 1999, I asked theoretically if using a softer material at the bladder-end of a JJ stent could reduce the irritative symptoms. Although the more rigid stents caused more dysuria, flank and suprapubic pain, Lenon’s study could find no significant differences in the incidence of urgency, frequency, nocturia and hematuria [4]. A few years later the Polaris Ureteral Stent made of dual durometer material come to the market. The bladder-end of this stent was made of softer polymer with the hope that it will be better tolerated by the patients. To check if material softness can make a difference in the irritative symptoms Joshi’s group, about a decade later run a blinded, randomized controlled trial comparing the firmer (Percuflex) and the softer (Contour) stents. This study also could not find a statistical difference in the patient’s comfort and overall ureteral stent experience [5]. Dual durometer stents with a smooth transition from a firm polymer for the kidney end to a softer polymer at the bladder end (Polaris]) were also compared with a firm polymer made stent [Inlay Stent], but no difference between these stents could be found in any of the measured parameters [6]. Even coating the softer bladder-end with a hydrophilic material to reduce the friction between the stents and the trigone could not prevent the irritative symptoms [7, 8].

Another culprit for stent related symptoms is the use of an inappropriate stent length. Studies showed that inappropriate stent length induces the most disturbing symptoms. Al-Kandari’s study found that “Symptoms were worst when the bladder end crossed the midline” [9]. This was confirmed by a study done by Dellis group that also showed that stent symptoms are worsened if the bladder end of the stent crosses the midline of the bladder [10]. Another study done by Ho’s group indicated that longer than needed stents are associated with significantly higher incidence and severity of frequency and urgency, but they found no difference in the incidence of hematuria, bladder and flank pain, nocturia and urge incontinence [11].

Even if seemingly an appropriate length is inserted, there is an additional cause for the irritative symptoms: Respiration. During respiration, the up and down movement of the kidney, moves the bladder-end of the stent back and forth in the bladder, creating continuous friction with the trigone inducing the irritation. The maximal vertical motion of the kidney from the end-expiratory to its end-inspiratory position was found to be 39 mm [3]. These “up and down movements of the kidneys” make measurement of the ureteral length a challenge.

Flank pain is usually caused by urine refluxing from the bladder to the renal pelvis through the stent when the bladder is full or during urination when the intravesical pressure increases, increasing also the intra-renal pressure. This is the period the patients experience most of the pain.

Drug eluting ureteric stents were also tried for reducing stent related symptoms. Ketorolac-loaded stents showed only limited benefit in younger male patients who required less pain medication on days 3 and 4 compared with controls. “Drug-coated stents have had only very limited success in reducing stent symptoms” [12].

The current, JJ or pig-tail ureteral stents have a 2-dimensional design, in which their renal- and bladder-ends are on the same plane but their curl in opposite directions (Fig. 1).

Fig. 1
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Common ureteral double-J stent

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2 Are There Any Solutions?

By analyzing the JJ related symptoms in detail we concluded that by making certain changes in the design, the irritative and painful ureteral stent related symptoms can be prevented or significantly reduced by re-engineering the bladder-end of the JJ. A change of shape and/or in the material of the bladder segment or its coating probably can reduce/prevent its thrusting to the trigone caused during its “in- and out-of-the-ureter movement” during respiration. Comparison between loop-tail and regular pigtail ureteral stents on urination-related QoL showed that patients with loop tail stents emptied their bladder better than those with regular pigtails [13].

Accordingly, by accurately measuring the length of the ureter at inspiration and expiration we can chose the appropriate stent length. In addition, by modifying the position of the bladder-end of the stent we can prevent the constant contact between the bladder-end of the stent with the trigone. Also by adding a simple mechanism to the bladder end of the stent, we can create an anti-reflux mechanism. To these changes we can add a structural modification to allow its easy un-curling and re-curling of the bladder end of the stent during respiration, and by this, further preventing the friction of the in and out movement of the stent.

For reaching these goals we took the following steps.

2.1 Accurate Measurement of the Ureter

JJ stents are usually available in lengths between 20 and 28 cm to fit the length of the individual ureter of each patient. Urologists know that accurate measurement of the ureteral length is important for choosing the appropriate stent length to ensure patient comfort and reduce irritative symptoms. The reason for using the inappropriate stent length is mainly the empirical practice of deciding the length of the stent to be used, or the use of whatever length is available at the OR. Longer than needed stents will have a redundant part in the bladder, and shorter than needed ones may retract into the ureter, making their removal more difficult. Taking into consideration the patient’s height as a predictor for choosing the appropriate stent length may work “in the majority of ureters (grade 0 = 61%), with no stent being too short. In comparison, direct ureteric measurement oversized the stent in 83%, correctly predicting stent length in only 17%” [14] where others chose different measuring means [15,16,17].

Easy and accurate ureteric length measurement for selecting the appropriate stent length is important. During respiration, the “up and down movements of the kidneys” makes accurate measurement of the ureteral length a challenge. At inspiration the distance between the kidney and the bladder is the shortest. The solution for this problem is to find a way for accurate measurement of the ureter. Even if we take the average length measured at inspiration (the kidney in its low position) + length at expiration [the kidney in its high position] the stent still will have a 2 cm of it moving up and down in the bladder (Fig. 2). The “in- and out-of-the-ureter movement” of the bladder-end of the stent during respiration causes continuous thrusting with the trigone 12–16 times every minute, meaning 17.280–23.040 in and out movements during 24 h.

Fig. 2
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X-ray view of the bladder end stent at inspiration (a) and expiration (b)

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That is the reason for accurate measurement of the ureteral length for choosing the appropriate stent length that can reduce this irritative cause. Flexible length ureteral stents with their distal parts made of softer material to allow easier furling and unfurling of its bladder-end were developed for this reason. Although these modifications somehow reduced the length related problems but still could not prevent the friction caused irritative symptoms.

A Fogarty Balloon Catheter with centimetric markings we designed can be used to measure the length of the ureter during the respiratory movements and decide the optimal double-J stent length. For further simplifying the making of an accurate measurement, we designed a simple Ureteral Length Measuring Ruler with a 2-flanged Malecot-type distal end activated by a slider handle (Fig. 3). This ureteral ruler allows measuring the ureteral length at inspiration, when the kidney is in its lowest position. The logic behind using this short distance will become clear when #4 will be presented.

Fig. 3
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Malecot-type ureteral length measuring ruler with a slider to open the Malecot wings

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2.2 Making Positioning Adjustment of the Bladder-End of the Stent

By rotating the axis of the bladder-end segment from flat to forward by 90°, the intravesical segment was positioned perpendicular to the trigone for minimizing its contact with the trigonal mucosa (Figs. 4a, b and 5a, b) This positioning adjustment requires separate stents for insertion to the right or the left ureter.

Fig. 4
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90° forward direction of the bladder-end curl new double-J for the right (a) and left (b) ureter

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Fig. 5
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(a) Continuous contact of the bladder-end curl of a common double-J stent with the trigone. (b) The 90° forward direction of the bladder-end curl of the new double-J stent, separating the curl from the trigone

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2.3 Creating a Simple Anti-Reflux Mechanism

The place of the bladder-end opening of the stent was relocated to the side, creating a groove. This grove at the distal end of the bladder-end curl was covered with a pre-shaped soft silicone made sleeve-like tube to create an antireflux mechanism. The shape of the sleeve allows the guide-wire to pass along the lumen and the groove and then to pass between the stent tip and the sleeve by elevating the edge of the silicone sleeve. The soft silicone sleeve allows also the urine to drain into the bladder easily (Fig. 6a, b).

Fig. 6
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Bladder-end of the new double-J stent with a soft silicone sleeve covering it for preventing reflux (a), and the way the guide-wire elevates the sleeve (b) similar to how urine will be drained into the bladder under the sleeve

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2.4 Making Changes at the Bladder-End to Allow Its Easy Un-Curling and Re-Curling for Keeping the Stent Body in the Ureter

Additionally, we made a manufacturing change in the distal segment of the stent in order to reduce further its thrusting to the trigone during respiration, caused by its “in- and out-of-the-ureter movement”. The manufacturing change was using multiple-durometer extrusion technology for producing a very soft bladder-end to allow its un-curling at expiration and re-curling at inspiration with the help of an embedded metal coil along the softer segment (Fig. 7a, b).

Fig. 7
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At inspiration the bladder-end of the new double-J stent curve as a pig-tail but in a 90° forward direction distancing itself from the trigone (a), at expiration the bladder-end of the new double-J stent un-curls and allow its partial retraction into the ureter (b), again preventing contact with the trigone

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3 The Way the New JJ Will Work

Since a double-J stent is a commodity used almost by all urologists it is important that the learning curve for the insertion and retrieval of the new stent design should be as easy and as near as possible to the insertion and retrieval of a common JJ.

With the new stent, the accurate ureteral measurement will be taken at the end of inspiration when the kidney is in its lowest position using the Ureteral Length Measuring Ruler.

The appropriate stent length for the appropriate side [right or left side] will be chosen for insertion.

The pre-inserted guide-wire’s proximal end will be threaded from the renal end opening of the stent until it comes out between the side groove opening and the silicone sleeve at the bladder end as seen in Fig. 6.

Then the guide-wire will be threaded through the pusher’s side opening to allow engaging the stent tip.

The stent will be pushed upward, until the bladder-end marker reaches the orifice and then it will be released by pulling out the guide wire and the pusher to allow curling of the bladder end.

After its release the un-curling and re-curling of the bladder-end of the stent will be observed during the respiratory movements.

3.1 Expected Advantages of the New Ureter JJ Stent

The general shape of the new stent is almost similar to current stents.

The learning curve for the physician will be quite short, because the insertion and retrieval of the new stent will be very similar to the current JJ stents, with the difference that the selected stent should be either for the right or left ureter.

The re-engineered features of bladder-end of the stent will minimize the contact between the new stent and the trigone and also prevent vesico-ureteral reflux.

With these changes in the design, the proprietary new JJ [*] is expected to prevent or significantly reduce most of the ureteral stent related symptoms.

[*] Patents Granted: USA: 11,007,046 B2 [2021]; EP: 3,297,573 [2020]; CN: 107847312 B.[2021]—Pending in other counties.