Surgical trocar and method for placing a trocar sleeve in a body wall

An incising assembly for an incising end of a trocar-type instrument, comprising:

• an incising assembly comprising first and second elements mating along helical interfaces and defining a helically-protruding edge for threadably engaging an anatomic structure and movable relative to one another along said interfaces, thereby transforming said assembly between an incising position and a non-incising position, said incising position providing at least a distal portion of said edge in a sharp configuration capable of incising tissue, said non-incising position providing said at least distal portion of said edge in a dull configuration not capable of incising tissue;
• a spring structure urging said assembly toward said non-incising position from said incising position;
• a probe element with a distal tip and mating along said helical interfaces of said first and second elements and moveable between a projected position and a retracted position, in said projected position said distal tip being distal of distal ends of said first and second elements, in said retracted position said distal tip being proximal of said distal ends of said first and second elements;
• and
• a probe spring coupled to said probe element, thereby urging said probe element toward said projected position from said retracted position.