Purpose: Stone fragility is a key factor for the success of shock wave lithotripsy (SWL). Dual x-ray absorptiometry is the gold standard for measuring bone mineral content and density, which helps in determining bone mass and the fracture risk. The same principle was applied to determine the relationship of stone mineral content (SMC) and density (SMD) to predict the fragility of stone before SWL.
Materials and methods: A total of 102 patients with a solitary renal and upper ureteral stone of less than 3 cm treated at a single center with a lithotriptor were included. Prior to SWL all patients underwent dual x-ray absorptiometry evaluation for SMC and SMD. Plain x-ray documented disintegration after SWL. Stone size and site, the number of shock waves and energy levels were recorded. Failure was defined as no fragmentation to a size of less than 4 mm, which would pass unaided, up to a maximum of 3,000 shock waves.
Results: Overall 94 patients with renal stones were included. Mean stone size was 16.68 +/- 7 mm (range 5 to 30). Mean and median SMC was 0.63 +/- 0.83 and 0.34 gm (range 0.01 to 5.54), and mean and median SMD was 0.48 +/- 0.19 and 0.46 gm/cm2 (range 0.05 to 1.12), respectively. Overall 67 patients (71%) had successful fragmentation and clearance at a mean of 1,623.58 +/- 658.77 shock waves (range 355 to 3,000). On logistic regression analysis only SMC was the significant factor affecting the outcome in terms of fragmentation. At a SMC of more than 1.27 gm 95% of the stones would not fragment or needed more than 3,000 shock waves.
Conclusions: Patients with high stone mineral content (SMC greater than 1.27 gm) could be directly offered percutaneous nephrolithotomy, thus, avoiding the unnecessary cost of prior SWL.