Contributions to the design of circular surgical staplers for minimally invasive therapy

Circular staplers are used to join two hollow organs together from within, a procedure known as intraluminal anastomosis. A typical application would follow an excision from the food tract, where two ends need to be joined. A detailed study of what surgeons want from circular stapling technology was undertaken. Generally, it was found that surgeons want circular staplers which can allow greater access to awkward surgical sites, and which can facilitate the development of surgical techniques which are more minimally invasive than those permitted by current instruments. The specific conclusions from this study were refined to produce a product design specification (PIDS) for an ideal circular stapler for minimally invasive therapy (MIT). Circular staplers approximate tissue together before joining it ("firing" the stapler). An MIT version would have to approximate tissue and fire the stapling-cutting driver via a flexible extension. Knowledge of the extent to which tissue might be safely compressed was inadequate. The firing force, which limits the choice of remote actuation means, was also unknown. A test rig was designed to allow tests which, in conjunction with a materials testing machine, could emulate the approximation and firing functions and record the loads of both. A measure of the expulsion of intracellular potassium solution from the porcine intestines used was also measured with the tissue compression tests. The combined load and potassium output compression results indicate that porcine gut wall generally may experience some form of mechanical yielding from around 0.19 mm/ mm compressive strain. The various components of the firing load were identified and recorded. The biggest firing load recorded was approximately 1500 N The resulting analysis of the data has led to a clearer understanding of the constraints within which circular staplers should be designed (both generally and for MIT), as well as a theoretical account of how the design constraints imposed by the stapling function may be lessened. An example of a design which utilises this knowledge is given.