A New Assessment Tool to Predict Stone Free Rates in Ureteroscopic Laser Lithotripsy


ABSTRACT:BACKGROUND:Holmium: YAG laser lithotripsy shows a high successful rate in fragmentation of ureteric stones , The S.T.O.N.E. Score is a novel assessment tool to predict stone free rate (SFR )in patients undergoing Ureteroscopic Lithotripsy( URS). OBJECTIVE: To develop a user friendly system (S.T.O.N.E. Score) to quantify and describe stone characteristics provided by computed axial tomography scan to predict ureteroscopic lithotripsy outcomes and to evaluate the characteristics that are thought to affect stone free rate.PATIENTS AND METHODS: The S.T.O.N.E. score consists of 5 stone characteristics: (S)ize, (T)opography (location of stone), (O)bstruction, (N)umber of stones present, and (E)valuation of Hounsfield Units. Each component is scored on a 1-3 point scale. The S.T.O.N.E. Score was applied to 50 ureteroscopic procedures performed , patients with anatomical abnormalities such as duplicated ureters, horseshoe kidney, ureteral strictures and renal failure were excluded from the study, postoperatively patient were evaluated by KUB,U/S and CT scan to assess stone free status. RESULTS: The mean patient age was( 37.3± 12.5 )year. 58% were male patients and 42% were female patients. mean stone size was13±3.9. Stones locations: 20(40%)stones were located in the lower ureter,13(26%) in the mid ureter ,17(34%) in the upper ureter. Mean operative time was 26.9±18.3 minutes. The overall SFR was 84%. Results of stone size on percent of stone destruction was very significant (p-value=0.001). Also the results of stone location on percent of stone destruction was very significant (p-value =0.002). whereas hydronephrosis, stone number, stone HU unite were not significant(p-value 0.8, 0.54, 0.61. respectively ). Results of stone score with SFR was significant (p-value 0.003).CONCLUSION:The S.T.O.N.E. Score is a new assessment tool to predict SFR in patients who require URS for the surgical therapy of ureteral disease. The features of S.T.O.N.E. are relevant in predicting SFR with URS. Stone size, location were statistically significant factors in multivariate analysis. The S.T.O.N.E. Score establishes the framework for future analysis of the treatment of urolithiasis .