station's screen. The entire registration process takes about 10 min-
utes. Now you're ready to begin the surgery.
The initial tibia bone cut is a basic flat cut, but it has to be done
accurately to properly align the tibial component of the implant.
That accuracy is aided by placing the robotic system's cutting block
at the top of the tibia. The computer senses where the block is
placed and, if it's properly positioned, gives you the green light to
make the flat cut to remove arthritic bone and cartilage.
Next, after placing a spacing device in the knee, the joint is put
through a full range of motion, allowing the computer to assess
instability based on ligament laxity or insufficiency. The computer
also captures points in time when the knee is straightened and
flexed. It uses these points to calculate the anatomical corrections
needed to establish a "zero" mechanical axis, which occurs when
alignment is in a straight line from the center of the hip, through the
knee and to the ankle.
Cuts on the femur have yet to be performed, but the computer has
already determined the gaps you'll create with cuts made for a select-
ed implant size for the femur bone. The computer calculates how
much to cut off the distal and posterior parts of the femur to create a
perfect balance of ligaments and center the mechanical axis.
Once you decide to move forward with the operative plan outlined
by the computer, you affix a robotic cutting jig onto the array pins
placed in the femur. The robotic arm then spins into position to set up
a cutting jig that's used to guide cuts displayed on the 3D bone model.
You then place joint prostheses at the end of femur and on the top
of the tibia to determine the accuracy of the cuts. You can use the
computer's tracking to confirm how perfectly the mechanical axis has
been restored and how stable the joint is through the entire range of
motion before cementing in the implant.
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