A robotic medical system comprising: a cannula having a first defined remote center of motion and a second defined remote center of motion spaced apart axially from the first defined remote center, wherein an outer surface of the cannula comprises stability ridges configured to engage a tissue wall of a patient; an elongate medical instrument configured to be inserted into the patient through the cannula; a robotic arm (76, 82) configured to manipulate the elongate medical instrument to perform a medical procedure; and a controller configured to control movement of the robotic arm while maintaining movement about the first defined remote center and to switch from maintaining movement about the first defined remote center to maintaining movement about the second defined remote center, wherein a first segment of the stability ridges is disposed on a first side of the first defined remote center and a second segment of the stability ridges is disposed on a second side of the first defined remote center axially spaced apart from the first side of the first defined remote center, wherein the first segment of the stability ridges is separated from the second segment of the stability ridges by a non-ridged segment of the cannula, wherein the first defined remote center is positioned at the non-ridged segment, and wherein a third segment of the stability ridges is disposed on a first side of the second defined remote center and a fourth segment of the stability ridges is disposed on a second side of the second defined remote center axially spaced apart from the first side of the second defined remote center. a cannula having a first defined remote center of motion and a second defined remote center of motion spaced apart axially from the first defined remote center, wherein an outer surface of the cannula comprises stability ridges configured to engage a tissue wall of a patient; an elongate medical instrument configured to be inserted into the patient through the cannula; a robotic arm (76, 82) configured to manipulate the elongate medical instrument to perform a medical procedure; and a controller configured to control movement of the robotic arm while maintaining movement about the first defined remote center and to switch from maintaining movement about the first defined remote center to maintaining movement about the second defined remote center, wherein a first segment of the stability ridges is disposed on a first side of the first defined remote center and a second segment of the stability ridges is disposed on a second side of the first defined remote center axially spaced apart from the first side of the first defined remote center, wherein the first segment of the stability ridges is separated from the second segment of the stability ridges by a non-ridged segment of the cannula, wherein the first defined remote center is positioned at the non-ridged segment, and wherein a third segment of the stability ridges is disposed on a first side of the second defined remote center and a fourth segment of the stability ridges is disposed on a second side of the second defined remote center axially spaced apart from the first side of the second defined remote center.