Biomedical Engineering Reference
In-Depth Information
Figure 1.7
Commonly used needle driver for minimally invasive surgery
requirements to familiarize surgeons as to the full potential of this technique. Therefore,
MIS is limited to a number of relatively simple procedures, such as cholecystectomy
[64] (gall bladder removal) for which there is actually a consensus within the medical
fraternity that such practice is, in fact, beneficial. Perhaps the most common form of MIS
is laparoscopy [65 - 67] during which the patient's abdomen is insufflated with CO
2
,and
cannulas (essentially metal tubes) in which pneumatic check valves are passed through
small (approximately 1 - 2 cm) incisions to provide entry ports for laparoscopic surgical
instruments. The instruments include an endoscope for viewing the surgical site (a CCD
camera/lens combination with a slender shaft), and tools, such as needle drivers, graspers,
scissors, clamps, staplers, and electrocauteries. The instruments differ from conventional
instruments in that the working end is separated from its handle by an approximately 30
cm long, 4 - 13 mm diameter shaft (Figure 1.7) [68].
The surgeon passes these instruments through the cannula and manipulates them inside
the abdomen by sliding them in and out, rotating them about their long axis and pivoting
them about centers of rotation defined roughly by their incision site in the abdominal wall.
Typically, a one-degree-of-freedom device (gripper, scissors, etc.) can be actuated with a
handle via a tension rod running the length of the instrument. As shown in Figure 1.8,
the surgeon monitors the procedure by means of a television monitor which displays the
abdominal work-site image provided by the laparoscopic camera.
1.12.1 Advantages/Disadvantages of MIS
[61, 62, 70 - 72]:
1. Visualization of the surgical site is reduced. The operating site is viewed on an upright,
two-dimensional video monitor placed somewhere in the operating room. The surgeon
is deprived of three-dimensional depth cues and must learn the appropriate geometric
transformations to properly correlate hand motions to the tool tip motions.
2. The surgeon's ability to orient the instrument tip is reduced. The incision point/cannula
restricts the motions of the instrument from six DOF to four. As a result, the surgeon
can no longer approach tissue from an arbitrary angle and is often forced to use
secondary instruments to manipulate the tissue in order to access it properly or to use
additional incision sites. Suturing becomes particularly difficult.
3. The surgeon's ability to feel the instrument/tissue interaction is virtually eliminated.
The instruments are somewhat constrained from rotating and sliding within the cannula
due to sliding friction with the air seal, and the body wall constrains pivoting motions
of the instrument shaft. The mechanical advantage designed into MIS instruments
reduces the ability to feel grasping/cutting forces at the handle [72 - 76].
