Reply to Isayama et al.
25 July 2014 (online)
We read with great interest the Letter by Isayama et al. and would like to respond to their concerns on the first evaluation of the mechanical properties of esophageal stents .
We recognize that the experimental set-up for measuring the axial force of the available esophageal stents differed from the set-up used by Isayama et al. for measuring the axial force of biliary self-expandable metallic stents . Whereas the authors measured the axial force perpendicular to the bent stent axis, we applied the force perpendicular to the initial stent axis, this being the axis of the fixed stent part. Isayama et al. bent the biliary stents to an angle of 60° whereas we bent the esophageal stents to an angle of only 20° in order to measure the axial force. We agree that standard methods of axial and radial force measurements are required, but we should take into account that these standard methods can only apply to a specific lumen and a specific anatomical area. A 60° bending angle axial force is probably not as relevant for esophageal stents as it is for biliary stents. However, the axial force should not be considered irrelevant for esophageal stents. In certain clinical situations, such as severe distal or more proximal cervical strictures or extrinsic tumor compression on the esophagus, the esophagus may not behave as a simple straight tube. In addition, stents placed distally in the esophagus, especially those placed across the gastroesophageal junction, require low axial forces to avoid pressure necrosis to the lesser curve of the stomach.
The current study did not allow us to make a clear association between mechanical stent properties and clinical outcome. However, stents with a higher radial force may well have a lower tendency to migrate and improved sealing properties for leaks and fistulas in the esophageal wall. Conversely, stents with a higher axial force may be associated with pressure-related complications to the esophageal wall, such as perforation, fistula formation, and bleeding. We did not measure elasticity of esophageal stents in their long axis, which in our view may also be involved in stent-related problems to the esophageal wall. The goal of our paper was to give the physician more insight into the specific mechanical properties of most of the esophageal stent designs currently available. This information can also be used for validation purposes of studies using advanced computer simulations to further expand our knowledge on the mechanical design aspects of esophageal stents.
Based on our paper, esophageal stent performance can, at least partly, be linked to their mechanical properties, and this information can lead to the further development of well-performing esophageal stents that are less prone to cause complications.
- 1 Hirdes MM, Vleggaar FP, de Beule M et al. In vitro evaluation of the radial and axial force of self-expanding esophageal stents. Endoscopy 2013; 45: 997-1005
- 2 Isayama H, Nakai Y, Toyokawa Y et al. Measurement of radial and axial forces of biliary self-expandable metallic stents. Gastrointest Endosc 2009; 70: 37-44