DEVELOPMENT
OF URETERAL STONE BASKET
RONALD R. PFISTER, ROB SCHWARTZ,
M.D.
M.S.
From the Division of Urology and Department University of Colorado, Denver, Colorado
of Electrical Engineering,
ABSTRACT -A new ureteral stone basket is presented which has several advantages over any available: it can be autoclaved, is less than 4 French, and has six wires. Clinical evaluation is included.
In view of this, we devised a stone basket which is 3.6 F in size and can be autoclaved. Rather than high carbon steel with plating for anticorrosion protection, we used a cobalt-nickelchromium alloy (Elgiloy). This alloy is: (1) essentially corrosion free, it outperforms 17 per cent chrome stainless steel by over 700 per cent in ferric chloride; (2) it has 20 per cent more strength than spring steel without any increase in size; (3) it can experience over 100 per cent more cycles than carbon steel without breakage; and (4) it retains its strength over 275 per cent longer than carbon steel. It might be of interest that Elgiloy was used in the construction of the springs of the lunar module. The advantages of this alloy over spring steel are evident. The catheter material (Teflon) was chosen for its heat resistant capability, its low coefficient of static and kinetic friction for ease in operating the basket in and out, and its relative physiologic unreactivity. Lastly, the new basket has six wires instead of four as in the Dormia and Johnson baskets (Fig. 1). Having six wires, a small distortion of one or two wires in all likelihood would not so impair the over-all configuration as to render the basket ineffective. Also, a different shape is formed by the basket wires whereby the proximal and distal wire terminators are not collinear as in the Dormia helix. The fact that the wires are 0.008 inches means they are less stiff, and in in vitro experiments the wires part easily to allow the calculus entry into the cage. Strength tests done on the new basket show that the basket itself will withstand 58 pounds longitudinal stress compared to 60 pounds on the
For the past fifteen years, the Dormia stone basket (a refinement of the original 1926 Countill* design) has been a widely used instrument for retrieving ureteral stones. Many urologists consider it the state of the art in wire cage stone extractors. The Dormia device has four wires (each 0.010 inches in diameter) which fit into a 5 F catheter. Each wire is a helix with the entire assembly extending to 1 inch. In our own experience, it has been the most satisfactory device available until recently, although many other devices are in use. About two years ago we began work on an ultrasonic stone drill for use in the ureter. One of the problems we encountered was a need to fix the stone in a secure position for the ultrasonic probe. It was believed that a wire cage was the best choice, with provision for accepting the ultrasonic probe within a central cable. This would allow the probe to exit and impinge on the stone captured in the cage. Certain regularly recurrent problems with the Dormia device prompted us to improve on it. If the Dormia basket is not perfect in configuration, the chances of stone retrieval are reduced. Further, although the instrument is generally regarded as being 5 F, the distal end is larger, closer to 6 F. Because of its size, occasionally it is difficult to pass beyond stones wedged in the ureter when a smaller catheter might pass easily. Further, it is not possible to autoclave the device. *Councill, W.
dilator, J.A. M.A.
UROLOGY
/
A new ureteral stone extractor and A.: 86: 1907 (1926).
SEPTEMBER
1975
/
VOLUME
VI, NUMBER
3
337
FIGURE 1.
Pfster-Schwartz
basket compared with Dormia and Johnson
Dormia, using an Instron stress tester. Resolution of the testing machine was + 1 pound. Our initial experience with the new basket was purposefully limited to inexperienced operators
baskets.
and first year residents in order to measure basket performance rather than skill. So far, 17of 21 ureteral stones were removed without difficulty. Of the remaining 4 stones, 2 were engaged but could not be brought through the ureteral meatus because of the size of the stone. The other two stones were not engaged; of the 21, 19 (90 per cent) were engaged. Characteristically, the stone basket was passed as easily as a 4 F ureteral catheter, and it seemed possible to feel the stone through the catheter (Fig. 2). In conclusion, the new basket* appears to have significant advantages over other instruments available. The size and flexibility should lend itself to use in the biliary tract as well. 4200 East Ninth Avenue
Denver, Colorado 80220 (DR. PFISTER) To Mr. David Jones, DepartACKNOWLEDGMENT. ment of Civil and Environmental Engineering, University of Colorado, Boulder, Colorado.
FIGURE 2.
338
Over-all view of new basket.
*V. Mueller, Division American Corporation, Chicago, Illinois.
UROLOGY /
Hospital
Supply
SEPTEMBER 1975 / VOLUME VI, NUMBER 3
OF URETERAL STONE BASKET
RONALD R. PFISTER, ROB SCHWARTZ,
M.D.
M.S.
From the Division of Urology and Department University of Colorado, Denver, Colorado
of Electrical Engineering,
ABSTRACT -A new ureteral stone basket is presented which has several advantages over any available: it can be autoclaved, is less than 4 French, and has six wires. Clinical evaluation is included.
In view of this, we devised a stone basket which is 3.6 F in size and can be autoclaved. Rather than high carbon steel with plating for anticorrosion protection, we used a cobalt-nickelchromium alloy (Elgiloy). This alloy is: (1) essentially corrosion free, it outperforms 17 per cent chrome stainless steel by over 700 per cent in ferric chloride; (2) it has 20 per cent more strength than spring steel without any increase in size; (3) it can experience over 100 per cent more cycles than carbon steel without breakage; and (4) it retains its strength over 275 per cent longer than carbon steel. It might be of interest that Elgiloy was used in the construction of the springs of the lunar module. The advantages of this alloy over spring steel are evident. The catheter material (Teflon) was chosen for its heat resistant capability, its low coefficient of static and kinetic friction for ease in operating the basket in and out, and its relative physiologic unreactivity. Lastly, the new basket has six wires instead of four as in the Dormia and Johnson baskets (Fig. 1). Having six wires, a small distortion of one or two wires in all likelihood would not so impair the over-all configuration as to render the basket ineffective. Also, a different shape is formed by the basket wires whereby the proximal and distal wire terminators are not collinear as in the Dormia helix. The fact that the wires are 0.008 inches means they are less stiff, and in in vitro experiments the wires part easily to allow the calculus entry into the cage. Strength tests done on the new basket show that the basket itself will withstand 58 pounds longitudinal stress compared to 60 pounds on the
For the past fifteen years, the Dormia stone basket (a refinement of the original 1926 Countill* design) has been a widely used instrument for retrieving ureteral stones. Many urologists consider it the state of the art in wire cage stone extractors. The Dormia device has four wires (each 0.010 inches in diameter) which fit into a 5 F catheter. Each wire is a helix with the entire assembly extending to 1 inch. In our own experience, it has been the most satisfactory device available until recently, although many other devices are in use. About two years ago we began work on an ultrasonic stone drill for use in the ureter. One of the problems we encountered was a need to fix the stone in a secure position for the ultrasonic probe. It was believed that a wire cage was the best choice, with provision for accepting the ultrasonic probe within a central cable. This would allow the probe to exit and impinge on the stone captured in the cage. Certain regularly recurrent problems with the Dormia device prompted us to improve on it. If the Dormia basket is not perfect in configuration, the chances of stone retrieval are reduced. Further, although the instrument is generally regarded as being 5 F, the distal end is larger, closer to 6 F. Because of its size, occasionally it is difficult to pass beyond stones wedged in the ureter when a smaller catheter might pass easily. Further, it is not possible to autoclave the device. *Councill, W.
dilator, J.A. M.A.
UROLOGY
/
A new ureteral stone extractor and A.: 86: 1907 (1926).
SEPTEMBER
1975
/
VOLUME
VI, NUMBER
3
337
FIGURE 1.
Pfster-Schwartz
basket compared with Dormia and Johnson
Dormia, using an Instron stress tester. Resolution of the testing machine was + 1 pound. Our initial experience with the new basket was purposefully limited to inexperienced operators
baskets.
and first year residents in order to measure basket performance rather than skill. So far, 17of 21 ureteral stones were removed without difficulty. Of the remaining 4 stones, 2 were engaged but could not be brought through the ureteral meatus because of the size of the stone. The other two stones were not engaged; of the 21, 19 (90 per cent) were engaged. Characteristically, the stone basket was passed as easily as a 4 F ureteral catheter, and it seemed possible to feel the stone through the catheter (Fig. 2). In conclusion, the new basket* appears to have significant advantages over other instruments available. The size and flexibility should lend itself to use in the biliary tract as well. 4200 East Ninth Avenue
Denver, Colorado 80220 (DR. PFISTER) To Mr. David Jones, DepartACKNOWLEDGMENT. ment of Civil and Environmental Engineering, University of Colorado, Boulder, Colorado.
FIGURE 2.
338
Over-all view of new basket.
*V. Mueller, Division American Corporation, Chicago, Illinois.
UROLOGY /
Hospital
Supply
SEPTEMBER 1975 / VOLUME VI, NUMBER 3
