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CAS - Knee Replacement
Computer Assisted Knee Replacement
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Total knee replacement surgery isn't
new. It has been practiced worldwide for 40 years, and as might
be imagined, the procedure has been refined to the point where
hundreds of thousands of people every year are returning to a
life of pain-free mobility. However, standard knee replacement
surgery has its limitations - the laws of physics being chief
among them. A surgeon must implant the orthopedic device in such
a manner that its components, a metal and plastic platform atop
the tibia and a metal surface on the bottom of the femur-rub
together, or "articulate," at precise angles in order to prevent
premature or excessive wear of the implant.
As is commonly practiced today, a
surgeon achieves proper alignment through "feel." That is, the
surgeon uses specialized cutting blocks combined with his years
of operating room experience to determine where best to remove
bone for the implant. Once the cut is made, the natural bone
cannot be replaced. Thus, a carpenter's advice to "measure
twice, cut once" is especially vital in knee replacement
surgery. |
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The
New Solution
Computer-assisted surgery (CAS) addresses this issue of alignment with
an advanced convergence of multiple medical technologies. Using infrared
cameras, images and advanced tracking devices, computer-assisted knee
replacement procedure achieves precise alignment.
How
it works
The logic is simple: By combining digital images of the femur and tibia
with an implant-specific software package, the computer hardware can
track the precise position of the patient's knee and the surgeon's
instruments at all times during the procedure. It is as if the patient's
leg has a satellite tracking system the computer uses to follow it
during surgery.
Do not fear! Dr. Bowers
performs the surgery. The computer simply puts together all of the
information coming in from the patient and the instruments and tells him
where the precise cut should be made. Given that every patient's knee
geometry is different, this level of patient-specific, computer-guided
accuracy is unprecedented in the history of knee replacement surgery.
Patient Benefits
As you might imagine, a surgeon armed with these tools has the potential
to achieve better outcomes for the patient. As the computer-assisted
procedure evolves, it will become less and less invasive. It has already
eliminated the use of an intramedullary (IM) rod; a device inserted up
the length of the femur used for determining proper knee implant
alignment in relation to the hip joint. Since the data generated by the
computer replaces this device, patients undergoing computer-assisted
knee surgery may have a reduced risk of fat embolism, caused when the IM
rod forces body fat into the patient's blood stream. If fat travels
through the blood stream, it could become lodged in the heart or brain
and cause heart failure, dementia or stroke.
Further, the quality and
accuracy of the virtual image provided to the surgeon by the computer
enables smaller incisions while achieving the same successful outcomes.
Smaller incisions lead to faster surgeries, shorter hospital stays and
shorter rehabilitation.
The benefits to the patient
include:
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The elimination
of the IM rod reduces the risk of fat embolism. The
increased "vision" the procedure provides facilitates
minimally invasive surgery. This means a shorter scar, less
physical therapy and a faster return to your normal life.
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The accurate
alignment and placement of the implant may extend its
lifespan and prevent future corrective surgeries.
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Since the computer
accurately assesses "joint laxity," or soft tissue balance, the surgeon
may not need to disrupt as much soft tissue-such as muscle, ligaments
and tendons-when determining how tightly the new implant fits in place.
This also reduces rehabilitation time and returns you to your active
lifestyle more quickly.
The Arrays
"Arrays" are metal prongs with small reflective spheres at their
extremities. These devices attach to the surgical instruments
and to the patient's tibia and femur. Once they are fixed in
place, their positions in space are tracked throughout the
procedure. That way, the computer will know exactly where the
instruments are in relation to the patient's bones, based on
where the spheres are at any given second.
The
Camera
The camera emits infrared light that reflects off the spheres
connected to the arrays. It collects this reflected infrared
light, and sends the information about the location of the
source of the reflection (the spheres on the arrays) to the
computer. |
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The Computer
The computer receives information about where the spheres are in
space, and combines that data with three-dimensional virtual
images of the orthopaedic implants and surgical instruments.
The
Software
The software displays on the screen the virtual images of the
instruments, implants and bones and guides the surgeon through
each step of the procedure. The software alerts the surgeon when
the instrument is in the most accurate position to make the
ideal cut. Also, it helps determine where to best place the knee
implant against the bones.
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3/24/2007
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