The novel concept of removing stone fragments with a magnetic tool was first described by Tracy et al. in 2010 [1]. In order for stone fragments to be extracted with a magnet, the calcium based stones had to first be coated with solution that had a polymer that allowed binding to the stone attached to 1 μm microparticles with an iron oxide core (Invitrogen, Carlsberg USA). Tracy et al. then placed the coated stone fragments in a bladder model and found a 53 % reduction time in the extraction of the stone fragments compared to a 2.4Fr tipless nitinol basket [1].

Evaluation of the performance envelope for stone capture found that target capture was effective in the low, single digit millimeter distance range favoring smaller stones up to 3 mm in diameter [2]. An in vitro comparison of the magnetic tool with a conventional nitinol basket for ureteroscopic stone retrieval in a bench top simulator found that the magnetic tool improved the efficiency of retrieving stone particles rendered paramagnetic that were less than 2 mm but showed no advantage for larger fragments [3]. The toxicity of the iron oxide microparticles was evaluated in a murine model [4]. The microparticles were not found to cross intact urothelial membranes and when introduced systemically, they led to minimal inflammatory changes in the lung and liver, thus additional longer term studies will be required to further assess toxicity.

Though the ferromagnetic extraction of stone fragment model was mainly devised in the case of fragment extraction during ureteroscopy and laser lithotripsy for renal stones or via PCNL it may also be applicable for ureteral stones [5]. The use of a magnetic tool versus a nitinol basket would: (1) allow easier extraction of smaller stone fragments, which can be difficult to basket extract (2) result in less passes in the ureter compared to the use of the basket for stone extraction thus leading to less ureteral trauma and perhaps even negating the risks of ureteral avulsion (3) aid in the extraction of stone fragments when there is poor visualization from bleeding. After this promising technique is further developed, human clinical trials will be required to evaluate its efficacy and applicability compared to stone basket extraction.

The flexible Sensai® robotic catheter system (Hansen Medical System, Mountain View, CA) has been applied for robotic flexible ureteroscopy [6]. The system is based on a remote master-slave system that consists of: (1) a surgeon console, including the master input device (MID) (2) remote catheter manipulator (3) the flexible catheter system (4) an electronics rack which contains all the video and computer hardware. The MID has a 3-dimensional joystick that the surgeon uses to manipulate the catheter tip. The display monitor shows endoscopic visualization, real-time fluoroscopic views and a catheter animation on the LCD display that gives the surgeon the location and orientation of the ureteroscope tip in the collecting system. The remote element consists of the remote catheter manipulator which is an arm that attaches to the operating table on which the steerable catheter sheath and guide catheter are attached [6]. The robotic system is built to treat renal stones as the flexible ureteroscope is fixed to and guided by the inner catheter (10–12Fr) which is placed through an outer catheter sheath (12–14Fr) which stabilizes the inner catheter at the level of the ureteropelvic junction. The maximum deflection of the flexible catheter system is 270°.

Desai et al. performed the preliminary animal studies of the flexible ureteroscope robotic system in the swine model and demonstrated ureteroscopy with holmium laser lithotripsy of 4 mm human stones that had been placed in the kidneys [7]. Balloon dilation of the ureter was required in 2/10 ureters to accommodate the robotic catheter system. The early animal studies allowed for further changes to the robotic system including decreasing the diameter of the robotic ureteroscope to improve drainage of the irrigant fluid.

The first clinical study using the flexible ureteroscopy robotic system was performed in 2011 when 18 patients with renal calculi were treated [8]. All patients did have pre-existing ureteral stents in place 2 weeks prior to the procedure. Flexible robotic ureteroscopy with laser lithotripsy was performed successfully in all 18 patients. The mean operative time was 91 min, the mean stone size was 11.8 mm, mean robotic docking time was 7.3 min and total robot time including docking time was 41.4 min. No intraoperative complications were observed and there was no evidence of renal perforation as confirmed by contrast injection at the end of each case. Complete stone free status was achieved in ten patients (56 %) at 2 months based on CT-imaging and 15 patients (89 %) at 3 months based on intravenous pyelogram. One patient required an auxiliary procedure for clearance of symptomatic residual stone debris. There was no evidence of ureteral stricture on follow-up at 3 months.