Spontaneous knotting of urinary catheters: clinical and experimental observations.

Urinary catheters are known to spontaneously knot inside the bladder. Approximately 40 cases of this complication have been recorded in the world literature. Clinical observation in 4 children and simulation experiments done using a balloon model are described herein. Risk factors identified in this study includes catheter size less than 10 Fr, overdistended bladder and insertion of more than 10 cm length of catheter inside the bladder. Water-current generated by the flow of urine appears to play an important role in the pathogenesis of catheter knotting.