The trocar system includes a cannula insertable through a body wall using an obturator having a distal tip. A traction tread disposed interiorly of the obturator inverts at the distal tip and extends proximally along the outer surface of the obturator or cannula. At the distal tip the tread can facilitate parting rather than cutting the tissue. Along the outer surface, the tread can engage the tissue to pull it proximally along the advancing obturator. This produces counter forces which can result in a net proximal force facilitating distention of the abdominal wall and separation of the abdominal wall from internal organs. The traction tread can be axially and/or radially continuous. An associated method of operation includes the steps of contacting the body wall with the traction tread at the distal tip, and engaging the body wall with the traction tread along wall portions facing the outer surface.