Why can't stones be passed after lithotripsy for ureteral calculi?

The main reasons why stones may not be expelled after lithotripsy for ureteral calculi are as follows: 1. When the stone is large, even after fragmentation, its size may still exceed the diameter of the ureter, causing the stone to become lodged in the ureteral wall and preventing smooth expulsion. 2. Hard stones tend to become impacted at narrow segments of the ureter during passage, making it difficult for them to pass through and leading to pain and obstruction. 3. Irregularly shaped stones are prone to getting stuck at narrowed portions of the ureter, resulting in difficulty in stone expulsion. 4. Conditions such as urethral stricture and benign prostatic hyperplasia increase the difficulty of stone passage. Urethral stricture can obstruct urine flow, while prostatic hyperplasia may increase urethral resistance, further exacerbating difficulties in stone expulsion.