Background:
Laparoscopic surgery involves instrumented grasping of the colon with the risk of iatrogenic injury. We aimed to analyses the mechanical and histological response of the wall of the large bowel to indentation stresses.

Material and Methods:
Indentation stresses of 50kPa, 160kPa and 255kPa were applied to fresh, ex vivo porcine colon using a modular universal surface tester and held for 5, 30 or 60s on the serosal surface. Indentations were repeated 20 times. The percentage decrease in thickness of each histological layer was compared to a control region and muscle disruption was identified.

Result:
For 50kPa indentation the percentage reduction of the submucosal depth increased with increasing time (15% for 5s, 28% for 30s and 45% for 60s). In the 160kPa indentation the submucosal depth also reduced by 45% over a 60s indentation even despite a sample with a thick submucosal layer. In 255kPa samples the longitudinal muscle and serosal depth were affected but not as markedly (20% reduction over 5 seconds and 27% reduction over 60 seconds). The 255kPa samples were unique as in the 30s and 60s group there were slides with completely obliterated longitudinal muscle, indicating that at this level the submucosal layer may be unable to withhold the applied stress.

Conclusion:
Mechanical stresses, equivalent to those in laparoscopic grasping, result in changes to the depth of the colon wall, particularly in the submucosa and at longer durations of stress application. Further analysis will determine safe tissue handling thresholds.