The modified prone position : a new approach for treating pre-vesical stones with extracorporeal shock wave lithotripsy

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1 Original Article The modified prone position : a new approach for treating pre-vesical stones with extracorporeal shock wave lithotripsy * Urotip ESWL Centre, Bursa, and *Department of Urology, Kocatepe University School of Medicine, Afyon, Turkey Accepted for publication 20 September 2003 OBJECTIVE To investigate the utility of a new modifiedprone position for treating pre-vesical stones with extracorporeal shock wave lithotripsy (ESWL), usually considered an acceptable and effective treatment for such stones, but for which many different body positions have been used in an attempt to increase its efficacy. PATIENTS AND METHODS The study included 268 consecutive patients with a solitary pre-vesical stone who underwent ESWL either prone (69) or in the modified-prone position (199) between May 1999 and August Only those with one stone between the ureteric orifice and 1 cm proximal to the vesico-ureteric junction were included. In each case the stone diameter, days to stone clearance, number of shock waves applied per treatment, and number of sessions required to become stone-free were recorded. If the treatment failed this was also noted. Success rates in the prone and modified-prone groups were compared and analysed to assess which of the variables influenced success with ESWL. RESULTS After ESWL, 95.5% of the 268 patients were stone-free; the rates in the prone and modified-prone groups were 89.9% and 97.5%, respectively (P = 0.015). The probability of success with ESWL therapy for pre-vesical calculi in modified-prone position was about five times (odds ratio 4.56, 95% confidence interval ) greater than that expected with when prone. The modifiedprone position was an independent factor most significantly influencing success with ESWL in these patients. CONCLUSION The modified-prone position for ESWL is a new and very effective way to treat patients with pre-vesical stones. KEYWORDS ESWL, pre-vesical stone, modified-prone position, outcome INTRODUCTION The optimal treatment for pre-vesical calculi is still a matter of debate. In most situations in modern urological practice, these stones are managed either by ESWL or ureteroscopy. Until recently, pre-vesical calculi were treated by endoscopic ureteric orifice meatotomy, blind or fluoroscopyguided basketing, or open ureterolithotomy. All these methods are associated with relatively high complication rates [1]. The introduction of ESWL revolutionized the management of pre-vesical calculi. However, blockage of shock waves by the bony pelvis reduces the efficacy of this method, and a variety of different patient positions have been tested to address this problem. It has been reported that ESWL with the patient prone is a safe and effective form of treatment for calculi in the distal ureter [2]. In the present study we compared the outcomes when patients with pre-vesical stones were treated with ESWL either prone or in a novel modified-prone position. The aim of this new approach was to increase the success of ESWL in these patients by maximizing the contact between the water cushion of the lithotripter and the patient s body, and by focusing the beam as directly as possible on the stone. PATIENTS AND METHODS The study included 268 patients with solitary pre-vesical ureteric stones treated with ESWL while prone (in 69) or modifiedprone (in 199) between May 1999 and August The location of the stone was confirmed by excretory urography or plain abdominal X-ray, with renal and bladder ultrasonography. Pre-vesical stones were defined as stones located between the ureteric orifice and 1 cm proximal to the vesico-ureteric junction. Patients with other stones in the distal ureter, those with persistent fragments of renal and ureteric stones that had previously been treated with ESWL, and any with steinstrasse were excluded from the study. In 186 (69%) of the patients there was mild to moderate hydronephrosis; 82 (31%) patients had normal upper urinary tracts. The two groups were established as follows: initially one patient was systematically assigned to be treated prone and the next in the modified-prone position, and this was repeated until 138 patients (69 in each group) had undergone ESWL. At this stage it was apparent that the modified-prone position yielded better results so for ethical reasons all remaining patients (130) were treated in the modified-prone position. Each ESWL procedure was conducted with the patient under sedoanalgesia using recommended doses of pethidine and diclofenac. The lithotripter was a 9200 Spark Gap unit (Multimed Corp), with a C- arm fluoroscopy unit used to locate each 2004 BJU INTERNATIONAL 93, doi: /j x x 369

2 stone and for shock-wave generation. The shock-wave generator was fixed to the main unit and the treatment table was movable. The amount of shock-wave energy delivered was recorded as mean power (kv) and as the number of shocks per treatment. FIG. 1. A computer-generated image of the ESWL system with a patient prone. The treatment table is horizontal and the body contact with the water cushion is not as close as in the modified-prone position. When the patient was prone the stonebearing side was positioned closest to the shock-wave generator with the treatment table horizontal (Fig. 1). In the modified-prone position for ESWL the side of the body opposite the ureter containing the stone was positioned on the water cushion of the lithotripter and the treatment table rotated externally (Fig. 2a,b). Figure 3 shows the path of shock-wave transmission in the modifiedprone position. One day after ESWL a plain abdominal X-ray was taken to assess stone fragmentation, and another taken 2 weeks after ESWL. If no stone or fragments were detected at this stage the patient was considered to be stone-free and was asked to return 3 months later for control radiography. If the second film revealed any stone material, ESWL was repeated and the patient radiographed 2 weeks later. This system was repeated until the patient became stone-free. In each case the stone size, stone clearance time, number of shock waves applied per treatment and number of sessions required to achieve stone-free status were recorded. Failed cases were also detailed. Stone size was registered as the maximum diameter measured on a plain abdominal film. The number of days to stone clearance was calculated from the date of the first ESWL session to the date that radiological evaluation confirmed the stone-free status. The number of shock waves per treatment was established by dividing the total number of shock waves received by the patient by the number of sessions required to become stone-free. Treatment failure was defined as radiologically confirmed persistence of the stone with no fragmentation after three ESWL sessions. All failed cases were treated with ureteroscopy. The results were analyses statistically using Student s t-test, Fisher s exact test, the chisquare test, and odds ratio analysis, with P < 0.05 considered to indicate significance. Logistic regression was used for multivariate analysis. TABLE 1 The outcomes of ESWL in the two groups Result Modified-prone Prone Total or P Outcome, n (%)* Stone-free 194 (97.5) 62 (89.9) 256 (95.5) Failure 5 (2.5) 7 (10.1) 12 (4.5) Total Mean (SD) Stone clearance, days 19.2 (1.2) 32.6 (3.0) <0.001 No. of shock waves applied (160.5) (306.9) per treatment No. of sessions to stone-free 1.44 (0.01) 2.04 (0.1) *Fisher s exact test, P = 0.015, with odds ratio 4.38 (95% CI ); Student s t-test. RESULTS The 268 patients included 188 men (70.1%) with a median (range) age of 42 (17 68) years, and 80 women (29.9%) aged 39 (19 63) years. Overall, 256 (95.5%) of the patients became stone-free after ESWL; in the remaining 12 (4.5%) ESWL failed to clear the stones. The rate of stone-free status in the prone group was 89.9% and the corresponding rate in the modified-prone group was 97.5% (P = 0.015; Table 1). The mean (SD, range) power used for the ESWL sessions was 16.2 (1.8, 12 18) kv and the mean fluoroscopic imaging time 4.3 ( ) min. Patients in both groups had minor complications, e.g. self-limiting haematuria, dysuria and pain that responded to oral analgesics. None of the patients required hospitalization or placement of a ureteric catheter or a JJ stent. Obesity and cardiorespiratory problems caused no problems in either position. Of the stones, 128 (47.8%) were in the right ureter and 140 (52.2%) in the left. The stone was 3 5 mm in nine (3.4%) patients, 6 10 mm in 168 (62.7%), mm in 79 (29.5%) and >15 mm in 12 (4.5%). The BJU INTERNATIONAL

3 FIG. 2. A closer view of the modified-prone position (a) from the rear shows the convexity of the cushion forming a smooth fit with the concavity of the body and (b) an aerial view of the modified-prone position depicts the rotated position of the treatment table and shows the water cushion in contact with the side of the body opposite the ureter containing the stone. a b mean stone size in the prone was similar to that in the modified-prone group, at 1.03 and 0.99 mm, respectively (P = 0.524). In all, eight (2.9%) patients had impacted stones with moderate hydronephrosis, four of whom were treated in the prone and the other four in the modified-prone position. The mean values for stone clearance time and number of sessions to stone-free status were both significantly lower in the modified-prone group (both P < 0.001). The mean number of shock waves applied per treatment in the prone group was significantly higher than that in the modifiedprone group (Table 1). Comparisons of the group results for the different variables are also shown in Table 1. Logistic regression analysis was used to identify which variables independently affected the success of ESWL, assessing position, number of sessions to stone-free status (<3 and >3), days to stone clearance, and number of shock waves per treatment. Stone size was excluded because there was no significant difference between the groups. Regression analysis showed that the position had the greatest influence on treatment success, and that the probability of success with the modified-prone position was 4.56 times greater than when prone (Table 2). DISCUSSION TABLE 2 Logistic regression analysis Variable B SEM Wald d.f. P R Exp(B) (95% CI) Position ( ) No. of shock waves < < < ( ) <3 sessions (< ) Constant <0.001 According to the guidelines of the AUA and the European Association of Urology, ESWL and ureteroscopic stone removal are both acceptable and effective methods for treating adults with distal ureteric stones of 10 mm diameter [3,4]. There is still no agreement on which of these is the optimum method for this patient group. Although advances in ureteroscopic equipment and greater experience with ureteroscopy have improved success rates, the associated morbidity caused by invasive treatment remains a problem [5]. The main disadvantages of ureteroscopic stone removal are the need for anaesthesia, the possibility of an inpatient stay, and the frequent need for stent placement. In addition, stone-related swelling at the ureteric orifice can make ureteroscopic removal of intramural stones difficult. A recent randomized study [6] showed similar results for ESWL and ureteroscopic stone removal, but the outcomes with ESWL were slightly better because of the shorter operative time, fewer complications and more rapid convalescence [7] BJU INTERNATIONAL 371

4 As noted, many different body positions for ESWL have been attempted to improve efficacy. Jenkins and Gillenwater [2] found ESWL with the patient prone to be a safe and effective method for treating pre-vesical stones. Ackaert et al. [8] reported that the straddle (horse-riding) position was successful in 89% of 110 patients with distal ureteric stones. Becht et al. [9] treated 39 cases of distal ureteric stones using ESWL with the patient supine and the pelvis nearly horizontal, which allowed X-rays and shock waves to enter through the foramen obturatum or the greater sciatic notch; the authors reported a 95% success rate. FIG. 3. An image of the body in cross-section with the patient in modified-prone position; the angle of the patient s body allows for more direct transmission of shock waves to the stone. Using the novel modified-prone approach the treatment table is rotated externally and shock waves transmitted to pre-vesical stones in the ureter on the side opposite the lithotripter. Success with ESWL was 4.56 times more likely if the patient was in the modifiedprone position than prone. One of the factors that affects ESWL outcome is the quality of contact between the water cushion and the patient s body, which must be firm and uniform, as any wrinkling of the cushion results in energy loss. When patients with pre-vesical stones undergo ESWL while prone the concavity of the body and the convexity of the water cushion do not always form a close fit (Fig. 1). In the modified-prone position the water cushion is in very close contact with the body and this close fit allows the shock waves to be focused directly on the stone with minimal energy loss (Fig. 2, 3). The mean time to stone clearance in the modified-prone group was significantly less than in the prone group (Table 1). A longer delay to stone clearance means more frequent flank pain, many visits to the emergency room, potential loss of work and pay, and increased risk of serious complications, e.g. obstruction, infection and silent loss of renal function. The more rapid clearance time with the modified-prone position reduces these problems. In line with this advantage, the number of shock waves used per treatment and the number of sessions to be stone-free were also significantly lower in the modifiedprone group (Table 1); these factors are very important for the financial costs. Overall, the results show that when treating pre-vesical stones with ESWL the modified-prone position is more economical and better for patient comfort and satisfaction than the prone position. A limitation of the study was that stone composition was not considered. Nine stones of 3 5 mm were treated with ESWL and all these patients were symptomatic when they presented. In all cases the radiological evaluation showed mild or severe hydronephrosis on the ipsilateral side, and urine analysis and urine culture showed no infection. Initially, these patients were treated conservatively with analgesics and hydration. ESWL was used if the stone persisted for >15 days in the same location and there was evidence of increasing pelvicalyceal dilatation despite treatment. Only 2.5% of the present patients who had ESWL in the modified-prone position required ancillary procedures to become stone-free; an impacted stone was the most frequent reason for failure in these cases. Mugiya et al. [10] reported that endoscopic lithotripsy is an effective first-line therapy for impacted stones and avoids the futile repetition of ESWL, but in contrast Deliveliotis et al. [11] suggested that the initial approach for treating impacted stones should be by ESWL, as if this fails alternative solutions, e.g. endoscopy, can be used to remove the stone. In the present study, four patients in each group had impacted stones and we were unable to render them stone-free. Another important factor is poor visualization of the calculus; we were unable to clearly visualize the stones of another four patients in whom ESWL was unsuccessful. There was mild to moderate hydronephrosis in 186 (69%) of the present patients and we were unsuccessful in eight (4%) of these patients, who also had impacted stones. Kirkali et al. [12] concluded that urinary obstruction does not affect stone disintegration or passage, and Singh et al. [13] found that the degree of hydroureteronephrosis does not significantly affect the clearance rates for upper ureteric stones in ESWL. We consider that unsuccessful treatment was mainly a result of impacted stones rather than hydroureteronephrosis in these patients. Obesity had no effect on the successful fragmentation of stones, but noted that patient compliance was closely linked to outcome. Interestingly, compared with more proximal stones, stones closer to the bladder appeared to fragment more easily with ESWL in the modified-prone group. In conclusion, these results suggest that the modified-prone position is very effective for ESWL in patients with pre-vesical stones BJU INTERNATIONAL

5 ESWL in this position should be considered the first-line treatment for pre-vesical stones and that ureteroscopy should only be used if this method fails. REFERENCES 1 Ather MH, Memon A. Therapeutic efficacy of Dornier MPL 9000 for prevesical calculi as judged by Efficiency Quotient. J Endourol 2000; 14: Jenkins AD, Gillenwater JY. Extracorporeal shock wave lithotripsy in the prone position. Treatment of stones in the distal ureter or anomalous kidney. J Urol 1988; 139: Segura JW, Preminger GM, Assimos DG et al. Ureteral Stones Clinical Guidelines Panel summary report on the management of ureteral calculi. J Urol 1997; 158: Tiselius HG, Ackermann D, Alken P, Buck C, Conort P, Gallucci M. Guidelines on urolithiasis. Eur Urol 2001; 40: Morse R, Resnick M. Ureteral calculi. Natural history and treatment in an era of advanced technology. J Urol 1991; 145: Pearle MS, Nadler R, Bercowsky E et al. Prospective randomized trial comparing shock wave lithotripsy and ureteroscopy for management of distal ureteral calculi. J Urol 2001; 166: Jermini FR, Danuser H, Mattei A, Burkhard FC, Studer UE. Noninvasive anesthesia, analgesia and radiation-free extracorporeal shock wave lithotripsy for stones in the most distal ureter: experience with 165 patients. J Urol 2002; 168: Ackaert KS, Dik P, Lock MT, Kurth KH, Schroder FH. Treatment of distal ureteral stones in the horse riding position. J Urol 1989; 142: Becht E, Moll V, Neisius D, Ziegler M. Treatment of prevesical ureteral calculi by extracorporeal shock wave lithotripsy. J Urol 1988; 139: Mugiya S, Nagata M, Un-No T, Takayama T, Suzuki K, Fujita K. Endoscopic management of impacted ureteral stones using small caliber ureteroscope and a laser lithotriptor. J Urol 2000; 164: Deliveliotis C, Chrisofos M, Albanis S, Serafetinides E, Varkarakis J, Protgerou V. Management and follow-up of impacted ureteral stones. Urol Int 2003; 70: Kirkali Z, Esen AA, Celebi I, Guler C. Are obstructing ureteral stones more difficult to treat with extracorporeal electromagnetic shock wave lithotripsy? J Endourol 1993; 7: Singh I, Gupta NP, Hemal AK et al. Impact of power index, hydroureteronephrosis, stone size and composition on the efficacy of in situ boosted ESWL for proximal ureteral calculi. Urology 2001; 58: Correspondence: M. Demirbas, Dumlupinar Mah. Ordu Bulvari Bereket Apt. No: 17/16, Afyon, Turkey. muratdemirbas@doctor.com 2004 BJU INTERNATIONAL 373