A historic example of improper case selection for endoscopic manipulation (blind basketing) with a Johnson extractor. Open ureterotomy needed to release extractor and recover stone. (From Butt )
The advent of rigid and semirigid ureteroscopes allowed the direct visualisation of the stone to allow more accurate assessment of the stone size in relation to the ureter and more precise engagement of retrieval instruments. Furthermore, ureteroscopy afforded the opportunity to apply stone fragmentation energies such as electrohydraulic lithotripsy, pneumatic lithotripsy and, latterly and most successfully, laser energy.
Miniaturisation and improvement in optics revolutionised the success and safety of ureteral stone retrieval, and blind basketing and open ureterolithotomy are no longer performed, having been replaced by ureteroscopy, shockwave lithotripsy and medical expulsive therapies. The advent of flexible ureteroscopes allowed retrograde fragmentation of stones within the renal pelvis or calyces, and its improvement with miniaturisation and exaggerated-deflection scopes in the years immediately following the millennium led to a dramatic growth in retrograde intrarenal surgery [9, 10].
Techniques of endoscopic stone management are discussed in Chapter 8. Small stones can sometimes be removed without fragmentation with a basket or forceps, but such stones have often passed spontaneously and not required ureteroscopy. The majority of ureteral or kidney stone treated will require at least some fragmentation. The holmium:YAG laser offers the possibility of disrupting the stone with a high-frequency energy so that it is partially vaporised and the residue becomes fine dust which can then be allowed to wash out (dusting). An alternative approach is to use the laser at a lower frequency but higher energy per pulse to cause the stone to fragment into a small number of intermediate-sized pieces that can be retrieved with a basket or forceps (fragmenting). The use of the fragmenting techniques in the kidney normally requires the surgeon to place a ureteral access sheath, as normally a number of passes of the scope and basket are required. The surgeon should be aware that the number of scope passes is proportionate to the stone volume and that the stone volume is proportionate to the third power of the stone’s maximum diameter (assuming a spherical stone shape). Stone volume is the best predictor of operative time .
The surgeon will need to judge how small a fragment needs to be before it is appropriate to attempt to retrieve it. When treating a ureteral stone, it is not uncommon to push the stone back a little from its initial resting position which might be associated with mucosal oedema. It is not uncommon to attempt to remove too large a fragment which might not pass the tighter lower ureter or vesico-ureteral junction, so the surgeon should withdraw with care and under full vision. The use of a ureteral forceps allows easier release of stone fragments, but the surgeon might be more likely to inadvertently drop smaller fragments compared to using a basket. The surgeon needs to be particularly careful when using a basket in the upper ureter given the greater distance of ureter needed to be traversed.
When treating kidney stones, careful consideration also must be given to the fragment size and access sheath choice. Larger access sheaths have improved flow and allow the surgeon to remove larger fragments, but their deployment in tight and unstented ureters can be associated with risk to the ureter (see chapters 9 and 12). Fragmenting a kidney stone too much will increase the number of scope passes required for retrieval, or it may force you to change from a fragmenting strategy to a dusting strategy . It is probable that most cases of fragmenting involve at least some element of dusting.
Baskets or forceps may also be used to reposition stones before laser treatment. The placing of a device through a flexible ureteroscope inevitably causes some loss of deflection. The first generation of flexible ureteroscopes could deflect to about 100–150° with an empty instrument channel. When a laser fibre was placed through the working channel, the scopes could barely deflect 90°, so that it was not possible to treat lower-pole stones. Importantly, about half of kidney stones sit in the lower pole. The disposable baskets tend to be less rigid than even a 200 μm laser fibre, and it was often possible to reposition the lower-pole stone into an upper-pole calyx to allow the laser to be used there [12, 13].
With currently available exaggerated-deflection flexible ureteroscopes, it is normally possible to target lower-pole stones in situ, but there are other reasons why the surgeon might still choose to reposition the stone. Firstly, it might simply be easier to treat the stone in an upper-pole calyx, and you might choose a calyx where the stone resulting fragments might be less likely to shoot off but be encouraged to bounce back and forth in front of your firing laser fibre improving fragmentation efficiency (popcorning). Secondly, if you have chosen a dusting approach to a stone, the small residue might be more likely to complete wash out if it is sitting in an upper-pole calyx. This consideration might be important if the lower-pole calyx has a long, narrow infundibulum and a tight pelvi-calyceal angle. Finally, using a laser at high energy setting with a high degree of deflection risks melting the laser fibre at the point of maximum deflection which is likely to destroy your flexible ureteroscope. There is quite a lot of variability in laser energy ratings of the differently available fine laser fibres, and the surgeon should consider this when choosing the most appropriate stone treatment strategy.
Types of Retrieval Devices
An ideal stone retrieval device needs to be strong and durable enough to last a long procedure but narrow enough to not obstruct the flow of irrigation through the working channel and flexible enough to not reduce the deflection of the flexible ureteroscope. The retrieval device should be able to efficiently pick up a range of stone fragment sizes but must also be able to release them easily.
Nitinol helical baskets have also been produced, e.g. NForce® (Fig. 7.6, Cook Medical LLC, IN USA) and Dormia® N.Stone® (Coloplast A/S, Denmark), and tend to be lighter in weight and more flexible than the stainless steel helical baskets.
Some manufacturers have produced baskets with a finer mesh designed to sweep smaller fragments from a calyx or ureter, e.g. the NCompass® (Fig. 7.6, Cook Medical LLC, IN USA) or the Leslie Parachute™ (Boston Scientific Corp, MA, USA). These might be kept as part of the armamentarium of an endourologist for use in situations where it might be particularly important to clear all very small fragments .
Retrieval Device Comparisons
Undoubtedly, personal preference plays a role in selecting a stone retrieval device, but several investigators have conducted comparative trials to help guide what device might be safest and most efficient in a range of circumstances. Hudson et al.  showed that the failure rate to pass a ureteroscope increased dramatically once the scope size reaches 9FG, and larger scopes will also have reduced irrigation outflow between the scope and inner ureteral wall. However, smaller scopes will inevitably have a small working channel also limiting irrigation flow. To optimise irrigation flow there will be a trade-off between external scope size and internal working channel size. Placing wires or baskets through the working channel has a dramatic effect on flow, and the relationship between basket diameter and flow is marked. Bedke et al.  demonstrated that using a 1.2FG basket resulted in a 13.6x increase in irrigation flow compared to a 2.2FG basket in the flexible ureteroscope they tested, albeit the 1.2FG was very much weaker on their breaking strength tests. There is a further trade-off between basket size and strength.
An in vitro model comparing five different basket types showed that the double-helical and parachute basket types performed best in retrieving different-sized beads from a simulated ureter. The flat-wire basket performed poorly. In a simulated calyx, the only basket to successfully remove beads was a tipless basket . Monga et al.  evaluated the characteristics of 17 commercially available baskets in 2004. He found that tipless baskets opened more quickly to their target basket width than flat-wire or helical baskets and that the NCircle® basket exhibited linear opening allowing more precise control. A more recent comparison by Monga’s group  found that the 1.5FG Halo™ basket performed better than the larger compared tipless baskets in the penetration force (safety metric), radial dilation force (functional metric for ureteral calculi), and limitation of deflection tests (functional metric).
Ptashnyk et al.  tested the efficiency and safety of a variety of stone retrieval devices in four ex vivo models including a single ureteral stone model, an impacted ureteral stone model, a steinstrasse model and a lower-pole kidney model. For the single ureteral stone and impacted ureteral stone models, the two-pronged grasper did best, and the helical basket also fared well. The three-pronged grasper and parachute type basket caused most damage to the mucosa. For the steinstrasse model, the helical basket was more efficient than the two-pronged grasper, and the parachute basket was found to risk significant ureteral damage. For the lower-pole stone model, no difference was found between the nitinol basket and graspers tested. Lukaswycz et al.  compared the efficiency of six tipless and four helical baskets in removing ureteral stones in a simulated model of the human ureter. Overall no significant difference was seen in the mean time of stone removal between the groups, and all devices removed the stone with a mean time of less than 16 s.
Complications Related to Retrieval Devices
A complete discussion of complications of ureteroscopy is in Chapter 12. Complications specifically related to retrieval devices may range from minor mucosal abrasions to ureteral avulsion. Ureteral avulsion was reported in 0.5% of cases in a review from 1987 . Thirty years later the Clinical Research Office of the Endourological Society (CROES) reported a rate of 0.1% ureteral avulsion in 8543 patients . The risk was 0.3% in patients with impacted stones but 0.02% in unimpacted stones (p < 0.001). Avulsion often occurs while using a basket but can also occur by pushing a ureteroscope with excessive force into a tight ureter. Problems related to flexible ureteroscope deflection mechanism locking or bunching of the distal bending rubber in a flexible ureteroscope  have also been reported to cause ureteral avulsion. This serious complication may be recognised immediately as the invaginated ureter is withdrawn into the bladder or out the urethra as the scope is withdrawn. It is likely that the risk is higher when using a basket in the upper ureter, and it is thought that the upper ureter has less muscular support than the lower ureter . In benchtop and ex vivo porcine ureteroscopy models, Najafi et al.  found that only about 10 N of force was required to avulse a ureter. Ureteroscopists must be very aware of the risk of this complication and be ready to place a stent and return rather that exerting excessive force attempting to access a tight ureter. Care must be taken to not engage too large a stone in the basket, and impacted stones should be fragmented and disimpacted before extraction is attempted. Ureteral avulsion may be managed with early repair or nephrostomy and delayed repair, but complications following such reconstructions are high . Lower ureteral avulsion injuries might be best managed with ureteral reimplantation with or without a Boari flap.
Perforation of the ureter may be caused by basket or forceps tips or from tearing due to applying excessive force on a large stone fragment. They may be more likely with the more robust stainless steel retrieval devices and can normal be managed by ending the procedure promptly and placing a ureteral stent for a period of time .
Basket entrapment occurs when a surgeon engages a stone in the basket which is subsequently found to be too large to withdraw, but then the surgeon is unable to release the stone from the basket. Using excessive force in this situation risks serious injury including intussusception, tearing or avulsion of the ureter. Most baskets have a handle mechanism that can be disassembled. Doing so will allow the surgeon to withdraw the ureteroscope leaving the remaining basket and stone in situ. The surgeon can then reinsert the ureteroscope alongside the basket and fragment the stone sitting in the basket ultimately allowing retrieval of both . Depending on the relative sizes of the basket and working channel, it may also be possible to place a laser fibre directly alongside the basket wire to fragment the stone without disassembling the basket handle. Entrapment is not a risk associated with the use of forceps for stone retrieval.
Repeated use during a long procedure can cause baskets to break, but laser energy, when applied directly, may also break a nitinol or stainless steel basket. Certain basket configurations, particularly tipped baskets, can spring open if broken, so care may be needed in withdrawing the basket to avoid lacerating the ureteral mucosa .
Semirigid ureteroscopes require saline irrigation to allow the surgeon to view the stone and safely perform stone fragmentation without damaging the ureteral mucosa. Ureteral stones often come to rest at a narrow point in the ureter, and gentle dislodging of the stone from the narrowed segment is into the more dilated proximal portion of ureter and allows the surgeon to get a clearer approach to the stone with the fragmentation device. Both the flow of irrigation and the actions of the fragmentation device (laser and, especially, the pneumatic lithotripter ) can cause further proximal migration of the stone into the kidney. This was a particular problem for upper ureteral stones in the earlier days of ureteroscopy when flexible ureteroscope and laser availability was poor. In such a situation, a ureteral stent was placed, and the patient needed to return for shockwave lithotripsy. Distal ureteral stones can also migrate into the proximal ureter during treatment, and this location can sometimes be more challenging to reach with a semirigid ureteroscope rendering the procedure more difficult . A number of antiretropulsion devices have been developed to help avoid these problems. In modern practice some units will always have a flexible ureteroscope available so that if fragments of stone do wash back into the kidney, they can be dealt with at the same sitting. Other surgeons prefer to use antiretropulsion devices so that the stones can be completely extracted from the ureter to their satisfaction. A recent report from CROES database showed that 14.5% of 9877 ureteroscopies for ureteral stones were performed with an antiretropulsion device . Moreover, the cases which employed such a device had marginally higher stone-free rates (+2.8%; p < 0.001) and marginally shorter lengths of stay (−4.7%; p = 0.001).
Physical Techniques and Gels to Reduce Retropulsion of Stone Fragments
Control of irrigation pressure is likely to be the most important factor in reducing stone fragment retropulsion. Irrigation flow can determine the ureteroscopic view and may be increased by raising the height of the irrigation bottle or bag or by using pressure bags or pumps. A balance needs to be found between the perfection of the view and washing stones backwards. Placing the patient into a reverse Trendelenburg position might help but may compromise the surgeon’s operating position.
Several authors have recommended injecting 1–2 ml of lidocaine jelly proximal to the stone through a 5 or 6FG ureteral catheter at the start of the procedure [33, 34]. The viscous jelly remains in the ureter long enough to slow down the fragment retropulsion before washing out, and Zehri et al.  found that retrograde stone migration was only 4% with this technique in a small randomised trial compared to the control procedure group where it was 28%. Stone clearance at 2 weeks was superior with the lidocaine jelly method (96% compared to 72%).
BackStop™ (Pluromed Inc., Woburn, MA, USA) is a reverse thermosensitive water-soluble polymer designed to be injected into the ureter proximal to the stone and used in the same way as lidocaine jelly. It later dissolves and washes out. Rane et al.  found that retropulsion occurred in 9% of cases using BackStop™ compared to 53% in a control group of ureteroscopic procedures, and it dissolved successfully in all cases.