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. The ureter has mechanical properties that vary along the anatomical length and change with age. In this Review, the authors provide an overview of ureter properties and discuss how understanding the mechanical forces that the ureter is exposed to during clinical interventions can be leveraged to improve surgical outcomes. The ureter shows variation in passive mechanical properties along the anatomical length. The proximal and distal ureter have the highest and lowest compliance, respectively.The uniaxial tensile strength of the ureter is anisotropic between axial and circumferential directions; however, results vary between studies, and further experiments are needed in human tissues.The passive mechanical properties of the ureter change with age, probably owing to the remodelling of the ureter wall.Various factors affect the forces required to insert ureteroscopes and ureteral access sheaths into the ureter, including sheath diameter, medications and the use of safety wires.Excessive insertion and withdrawal forces are associated with substantial ureteral trauma, and further testing of insertion forces in humans with a focus on defining a safe upper limit are required.