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Year : 2011  |  Volume : 27  |  Issue : 3  |  Page : 429-430

Magnets in stone extraction: Fact or fiction?

Department of Urology, C.S.M. Medical University (Upgraded King George's Medical College), Lucknow, Uttar Pradesh, India

Date of Web Publication26-Sep-2011

Correspondence Address:
Apul Goel
Department of Urology, C.S.M. Medical University (Upgraded King George's Medical College), Lucknow, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

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How to cite this article:
Nagathan DS, Dwivedi A, Goel A. Magnets in stone extraction: Fact or fiction?. Indian J Urol 2011;27:429-30

How to cite this URL:
Nagathan DS, Dwivedi A, Goel A. Magnets in stone extraction: Fact or fiction?. Indian J Urol [serial online] 2011 [cited 2021 Sep 28];27:429-30. Available from:

Tracy CR, McLeroy SL, Best SL, Gnade BE, Pearle MS, Cadeddu JA. Rendering stone fragments paramagnetic with iron-oxide microparticles improves the efficiency and effectiveness of endoscopic stone fragment retrieval. Urology 2010;76:1266.e10-4.

   Summary Top

The ultimate goal of surgical intervention for stone disease is complete clearance. Studies have shown that complete removal of upper tract stones at the time of primary treatment is achieved in only 50%-80% of patients during ureteroscopy (URS) or percutaneous nephrolithotomy (PCNL). [1] These residual or "insignificant" fragments, when observed, cause symptoms in 21-59% of patients over 5 years and 69% subsequently require a surgical procedure. [2] Even advancement in technology like flexible ureteroscopy, miniaturization of instruments, holmium laser, and advanced optical imaging has failed to provide complete clearance after a single procedure. The various reasons being endoscope imposed constraints on access to all calyces, cost, and availability of diverse baskets or graspers needed for removal of removal of stones in different locations.

In this experimental study the authors have devised a new technology to overcome the above limitations. The authors have shown that the surface of calcium oxalate stones have positively charged particles. They, therefore, used negatively charged amino acids mixed with a matrix containing iron oxide core to coat the surface of these stones thereby making the stones paramagnetic.

This experimental study was conducted in two phases. In phase 1, seven trials were conducted and each trial had 10 stone fragments of size 1-3 mm placed in 200 ml saline in in vitro bladder models with and without refluxing ureteral orifices. Physicians were required to extract the fragments by either a 2.4-Fr nitinol basket or using 8-Fr prototype magnetic extraction devices. The magnetic extraction device could reduce the total time for extraction by 53%. For removal of all fragments, the magnetic device required an average of 3.7 extractions (mean 2.7 stones per extraction), while the basket required an average of 9.4 extractions (mean 1.1 stones per extraction). In no case, the basket was able to extract more than two fragments at a time, while the magnet removed up to 10 fragments in a single extraction.

Second phase of the study was conducted to know the minimum time required and the least microparticle solution concentration required rendering the stones paramagnetic. Studies were performed using two stone fragment sizes (1-2 mm [small] 2-3 mm [large] at three different incubation times (2, 5, and 10 minutes) at three separate concentration of magnetic particle. Hundred percent successful extractions of small stone fragments were possible at 0.5 and 1 mg/ml after 2 minute incubation time. 70% and 100% larger stone fragments extraction was possible at 0.5 and 1 mg/ml after 10 minute incubation.

   Comments Top

Magnetization of stone fragments and removal with a magnetic extraction device decreases operative time by increasing the efficiency of extraction through removal of multiple fragments with each extraction. This technology has the potential to obviate the need for complex maneuvers and second-look procedures to remove every fragment, leading to improved efficiency of fragment removal. Magnetic system may facilitate attraction of not only larger "graspable" fragments but also may attract tiny fragments that are too small to engage in available retrieving devices. Magnetic strength could be modulated such that forces required to inflict ureteral damage would cause uncoupling of the stone as a "built-in" safety release.

The limitations of the study were that larger fragments required higher concentrations and exposure times to be rendered paramagnetic. Stone fragments need to be fragmented into smaller size so as to extract them and the largest size of stone fragment which can be extracted effectively need to be documented. Current instrument requires placement within 1 mm of the fragments, the maximum distance from which stone particles can be attracted remains unknown and is a function of magnet size, strength, shape, and volume of particles attached. This technology is designed only for calcium oxalate stones, but further peptide modification and stone surface analysis should allow us to develop a solution that works with other common forms of urinary calculi. Reversible magnetic instruments that optimize the attraction and retention of particles but readily release them if they are too large to remove need to be developed in the future. The safety and biocompatibility of the microparticles needs evaluation even though each compound is nontoxic individually. In this study, the irrigation fluid was static, compared with an in vivo model where stones would be continuously "washed" due to the production of urine.

This study provides proof of the new concept of using magnets in stone management effectively during PCNL and URS, thus achieving the goal of 100% extraction.

   References Top

1.Macejko A, Okotie OT, Zhao LC, Liu J, Perry K, Nadler RB. Computed tomography determined stone-free rates for ureteroscopy of upper-tract stones. J Endourol 2009;23:379-82.  Back to cited text no. 1
2.Raman JD, Bagrodia A, Gupta A, Bensalah K, Cadeddu JA, Lotan Y, et al. Natural history of residual fragments following percutaneous nephrostolithotomy. J Urol 2009;181:1163-8.  Back to cited text no. 2


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