Pedicle Screws and Rods
When an extensive decompression of the lumbar spine is
performed, the lumbar nerves are relieved of compression, and lower
extremity pain will be hopefully improved. Back pain, however, is
unlikely to be helped. If some of the pain is coming from degenerated
segments, then a fusion may help.
Pedicle screws are placed from the posterior approach.
They act to stabilize the spine while the bone
graft undergoes fusion.
Procedure to implant pedicle screws
Typically, after the decompression of bone has been
performed, the surgeon will place the pedicle screws under fluoroscopic
control. This is accomplished through the use of a "C arm," which
provides real time x-ray imaging of the spine as the screw is being placed.
Alternatively, a computer guidance system may be used. Typically, the
screws are approximately 6.5 mm in diameter, and roughly 50 mm in length.
The diameter of the screws is not much smaller than the diameter of the
pedicles, and if the cortex (boy surface) of the pedicle is breached during
placement, then nerve root injury may result. Electrical monitoring of
the nerves help to warn the surgeon if there is any contact between the
screws and nerve roots.
Once the screws are placed, rods are attached to each
screw on that side of the spine, thus providing a latticework of stability
from pedicle to pedicle.
The majority of screws and rods implanted today are
composed of a titanium alloy, which yields less artifact during MRI and CT
scans, than its stainless steel counterpart.
The screws and rods are generally left in place,
although they can be removed after the fusion has healed, if they are
pushing through the skin or causing other problems.
Although uncommon, breakage or screws and rods does
occasionally occur. Screws can also pull out of the bone. It is
important to stress that smoking does interfere with the likelihood of a
successful fusion.
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