In a human body, urine flows from the kidney through the ureter to the urinary bladder, and then exits a person's body via the urethra. This system can be intermittently or permanently blocked by a hard stone-like material which is known as calculus. Such blockage can be painful and dangerous, since it restricts the flow of urine through the ureter. An obstructed ureter in the presence of infection may result in sepsis and death. Urinary calculi may pass spontaneously, but not always. Especially in those cases when the stone is large, jagged, or has an unfavorable location, surgical intervention may be required for successful extraction.
In general, the number of hospital admissions for removal of urinary calculi or stones averages about 0.1% of the population. Among the above-mentioned patients, a considerable percentage (2.9 admissions per 1000 hospital admissions) belongs to patients with ureteral stones.
Different types of intervention are now used in urology to facilitate successful passage or extraction of urinary calculi, including extracorporeal shockwave lithotripsy, ultrasonic, laser and electrohydraulic lithotripsy, and stone basketing techniques. Basket extraction remains simple and reliable, especially with stones in the distal ureter.
The most common stone extractor is made from a cable having a wire basket at one end of the cable with a relatively short, somewhat flexible rod-like end element, known as a filiform. The filiform is located on the distal end of the cable. The basket is usually made of several, e.g., four, equally spaced wires, which are sufficiently rigid to hold a large, V-shaped configuration (see U.S. Pat. No. 4,625,726 to Everette J. Duthoy, 1986). The wires and basket are located in a tubular catheter, so that only the filiform protrudes through the distal end of the catheter, while the basket portion is held inside the catheter in a contracted form.
In operation, the catheter containing the rod and the basket is inserted into the bladder through an endoscope placed in the urethra. In this case, the catheter is passed into the bladder under visual observation through the ureteral orifice. The catheter is then retracted so that the wires which form the basket are released, expanding the basket under the springing action of the rods. The basket is then maneuvered so that the stone is caught inside the basket through spaces between the wires, and then the rod is pulled toward the catheter; as this happens the and spaces or windows between the wires are reduced to dimensions smaller than the size of the stone. In this position the stone cannot fall out from the basket and is removed from the urinary tract by pulling the catheter and the basket from the patient's body.
However, the stone may be impacted in some place of the ureter due to edema, inflammation, or spasm, thus complicating the passage of the extractor, as well as the subsequent removal of the stone. Because an irregular configuration and sharp edges of the stone, or entrapment of the ureteral mucosa with the basket may injure or cut the endothelium during extraction, it is necessary to exercise great care in conducting this procedure.