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Although the most significant contributions to spinal
reconstruction, deformity correction, and stabilization have been
made during the last 30 years, surgical pre-planning remains an
important preparatory step in any spinal procedure. Reviewing the
patient's x-rays, CAT Scans, and/or MRI studies helps the surgeon to
visualize the surgical process in his mind's eye. Today, through
Image-Guided Surgery (IGS), the spine surgeon is able to see the
procedure as it is performed in real time! IGS illustrates how
advancements in instrumentation, computer technology, and imaging
have been developed to help surgeons perform complex spinal
reconstructions safer and faster.
Development of Image-Guided Surgery
The concepts
behind IGS are similar to those in a Global Positioning System
(GPS). Although GPS was developed for military use to guide
missiles, GPS has become a mainstream tool utilized by
archaeologists, search and rescue teams, and is even an option
available on some new cars today.
Image-Guided Surgery is actually part of a technology known as
Computer Assisted Surgery (CAS). IGS provides the surgeon image
visualization and analysis capabilities during live or 'real time'
surgery. This amazing technology was first used several years ago by
neurosurgeons to navigate the complexities of the brain during
difficult operations. Today spinal surgeons are adapting
image-guided surgical techniques to many laparoscopic and endoscopic
procedures to surgically reconstruct and stabilize the
spine.
Pre-Operative Planning
Prior to
the patient's surgery, CAT or MRI scans are taken. These
images are transferred to tape or optical disc to be read by
the system's computer during surgery. Pre-operative imaging
decreases or eliminates the need for intraoperative x-rays
thereby sparing the patient and surgeon radiation
exposure.
IGS in the Operating Room
An optical camera is
stationed in the operating room to receive signals from
special digitized instruments equipped with light emitting
diodes (LEDs). During surgery the camera receives and sends
the signals to a high-speed computer. The signals are received
from both the instrument (its position) and the patient
(anatomy).
The Optical Camera uses
triangulation, a form of geometry to establish the distance
between two points (instrument position and patient anatomy).
The computer integrates the 'triangulated signals' onto the
patient's CAT or MRI scan images. An image is then generated
projecting the instrument's exact location in relation to the
patient's anatomy. The surgeon views the image on a nearby
screen (e.g. computer monitor) to see the exact location of
his instrument.
Using Sub-Millimetric Accuracy, these
image guidance systems can pinpoint exactly where the tip of a
suregon's instrument is in relation to a patient's anatomy.
Although not generally necessary for routine spine procedures
such as microdiscectomies,this technology can provide
invaluable information to a surgeon who encounters distorted
or unusual anatomy during a complex spinal stabilization
procedure.
The Images generated through
use of IGS are not 'just' one-dimensional. The computer is capable
of preparing 3-D models that accurately reflects the position of the
instrument superimposed on the image. Three-dimensional views can
assist the surgeon in the precise placement of bone screws. Further,
IGS assists the surgeon by providing the means to reorient an
abnormal anatomy that can be misleading.
To take this technology a step ahead, helmets have been designed
that incorporate an internal screen to which real time images are
projected. These images guide the surgeon throughout the complex
spine procedure.
IGS: Not Quite Perfect
During some surgical procedures,
the patient is repositioned on the operating table. In patients
whose spinal anatomy is unstable (e.g. severe scoliosis), even minor
movement can alter physical spinal anatomy. This presents a problem
because the CAT and/or MRI scans obtained pre-operatively may no
longer be reliable following patient movement. However, all is not
lost!
Virtual Fluoroscopy
Virtual Fluoroscopy (VF) is another
type of image-guided companion for the spine surgeon. Using VF, the
surgeon obtains a fluoroscopic x-ray during surgery. Using the same
LED technology as in IGS, the computer re-triangulates the
coordinates again and again providing updated images for the
surgeon's use in multiple planes (e.g. 3-D). Virtual fluoroscopy
enables the surgeon to navigate his instruments in 'real time'.
Conclusion
Image-Guided Surgery and Virtual Fluoroscopy
offer many benefits, which includes enhancing the surgeon's ability
to navigate complex spinal anatomy in real time, place bone screws
more precisely, reduces operating time, and radiation exposure may
be minimized or eliminated. However, neither replaces or is a
substitute for surgical pre-planning. Most surgeons agree that
pre-planning is an important preparatory step for integrating the
procedural steps in their mind's eye.
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