Mechanical characteristics of the ureter and clinical implications.

The ureteric wall is a complex multi-layered structure. The ureter shows variation in passive mechanical properties, histological morphology and insertion forces along the anatomical length. Ureter mechanical properties also vary depending on the direction of tensile testing and the anatomical region tested. Compliance is greatest in the proximal ureter and lower in the distal ureter, which contributes to the role of the ureter as a high-resistance sphincter. Similar to other human tissues, the ureteric wall remodels with age, resulting in changes to the mechanical properties. The passive mechanical properties of the ureter vary between species, and variation in tissue storage and testing methods limits comparison across some studies. Knowledge of the morphological and mechanical properties of the ureteric wall can aid in understanding urine transport and safety thresholds in surgical techniques. Indeed, various factors alter the forces required to insert access sheaths or scopes into the ureter, including sheath diameter, safety wires and medications. Future studies on human ureteric tissue both in vivo and ex vivo are required to understand the mechanical properties of the ureter and how forces influence these properties. Testing of instrument insertion forces in humans with a focus on defining safe upper limits and techniques to reduce trauma are also needed. Last, evaluation of dilatation limits in the mid and proximal ureter and clarification of tensile strength anisotropy in human specimens are necessary.