A cannula is provided that includes a head portion that defines a proximal opening sized to receive one or more surgical instruments； an elongated inner tube rigidly fastened to the head portion defines an elongated conduit； a surgical instrument can be inserted within the conduit； an elongated overtube rigidly fastened to the head portion is coaxially aligned with the inner tube and extends about a portion of the inner tube； an inner wall of the overtube is spaced apart from an outer wall of the inner tube； sensors are disposed on the overtube to provide an indication of forces applied to the outer wall of the overtube in a direction generally transverse to the longitudinal dimension of the overtube.
