Robot-Assisted Prostate Surgery
FIGURE 11. A typical trocar 'tube' to
allow instruments to easily enter
the body. The inner pointed part is
removed after insertion.
FIGURE 10. Endo Wrist head showing cable reels.
(not because they get worn out since most Endo Wrists can
last much longer) to insure a very safe limit for a device
that is used within a human body. At this point, the tiny
memory chip on the green circuit board inside the head of
the Endo Wrist (shown in Figure 10) has recorded each
surgical use and it informs the da Vinci system that it can
no longer be used (or it can be given to an overly-curious
patient like me). The blue plastic port and attached clear
tubing above the circuit board allows a saline solution to be
circulated at the Endo Wrist’s working site.
Before I was given the Endo Wrist instruments, I
assumed that the actual end-effector received its
mechanical movement via a series of rotating carbon fiber
tubes; the smallest fitting within a slightly larger diameter
tube, and so on. I discovered that the Endo Wrist uses four
small reels that move four stainless steel cables in or out
that run up the carbon fiber tube to the end-effector. The
largest diameter reel (# 1 in Figure 10) moves a short cable
that runs to another smaller reel about 5 mm below, whose
axis is 90° to the larger and faces down the outer tube; this
causes the whole tube and end-effector to rotate almost
520°. The cables from two smaller reels at the far end of
the blue attachment box (#2 and #3 in Figure 10) are each
fastened to one of the two sides of forceps or scissors.
Rather than have one reel open and close both halves of a
pair of forceps or scissor tips, one reel/cable controls each
half of the ‘jaws’ and allows the forceps or scissors to
swivel and cut/pinch in a 200°+ arc. The fourth small reel’s
(#4 in Figure 10) set of cables moves the tip in a 180º arc
at a 90° angle to the jaw motion.
So, the surgeon has four degrees of freedom with the
four cable reels, and a fifth axis which gives the robot the
ability to move the instrument in and out along the axis of
the tube. There are actually two more axes of motion —
78 SERVO 04.2012
though limited — with the ability to
tilt the instrument back and forth
in an x-y motion. With a choice of
three instruments to manipulate,
hold, cut, pinch, and perform other
functions, plus a high definition,
magnified, and stereoscopic view
of the operating site through the
EndoScope camera system, many surgeons say that “this is
the only way to perform delicate surgeries such as a
prostatectomy or hysterectomy.” Another plus over
handheld instruments using arthroscopic or laparoscopic
procedures is that the surgeon does not have to hold his or
her various instruments in a certain position for long
periods of time — the robot does it. Doctors can rest a
moment and determine the next step in the operation.
Positioning of the Robotic
Endo Wrist End-ef fectors
You may be wondering how the instruments are
positioned into the surgery area. Obviously, a surgeon
cannot have the robot blindly insert an instrument into a
patient. The instruments must be positioned at the
operation site without damaging nearby tissue or organs.
Trocars are the guiding tubes that the surgeon inserts
through the abdominal wall into the operating area. Figure
11 shows a typical trocar with the pointed insert. Figure 12
shows my personal trocar sites; these are the small entry
sites for the surgical instruments. Six small incisions were
made in my skin. The photo looks a bit scary but the scars
have all but disappeared. This is a delicate manual
procedure because the surgeon must not puncture any
arteries, veins, or organs. The pointed end of the trocar
moves slowly through tissue to the operation site; the point
is then collapsed and removed so the surgeon can later
insert, manipulate, and remove the Endo Wrist instrument.
My surgeon used trocars of several different sizes to
create entry sites ranging from 5, 8, and 12 mm in diameter.
The largest incision ( 12 mm which was later extended to 4-
5 cm) that was made on my body was just above my navel;
this was first used for the camera, and then was extended
to remove my prostate and seminal vesicles.