In the average, normal spine there are 7 cervical, 12 thoracic, and 5 lumbar vertebra, a sacrum and coccyx.
From the skull to the sacrum, each vertebra is separated by
a mobile disc, which is a highly complex structure which provides stability and
motion at the same time.
In spinal deformity, such as scoliosis, the spine twists and
bends, first through the discs and then the actual vertebra start to become
misshapen, more trapezoidal instead of being more rectangular.
When we do surgery to correct spinal deformity (scoliosis)
the first step is to get fixation into the vertebra so we can move those
vertebra to a better, more desired position and then hold this new position
firmly. In 2022 the most secure and most
commonly utilized spine fixation are metal pedicle screws (usually made of
titanium +/- cobalt chrome), which are placed from the back of the spine, into
the bone, through the pedicle and into the vertebra.
Alternatively, hooks, wires and bands can also be used but these
are not as good a fixation option when compared to screws.
The next step is to connect these screws (or hooks, wires,
and bands) together with rods. These
rods can then move the screws (or hooks, wires, and bands) to the desired position
and then held rigidly in the new position.
These rods, in my practice, are 98% of the time are cobalt chrome, the
stiffest metal currently available and can obtain the optimal 3-d alignment of
the spine in my hands.
These metal screws and rods are VERY strong and
durable. However, we know the day we
place them in surgery is when they are their strongest and have the strongest
grip/fixation on the spine, and each day that goes by after surgery the metal
gradually and almost imperceptibly gets weaker and the screws/hooks/wires/bands
can get looser in/on the bone.
So 1 of 3 outcomes happen after we do spine surgery, at EACH
VERTEBRAL LEVEL:
1. 1. The screws, hooks, wires, bands get loose from
the bone.
2. 2. The rods, screws, hooks, wires and bands break.
3. 3. The spine fuses.
To achieve a spine fusion, we roughen the area to be fused
with a drill, and then place bone graft.
The body then breaks down/dissolves the bone graft which is then used by
bone cells to create a solid bony connection over the area we want to fuse.
The aim of bone graft is to develop a spine fusion before
the spine implants get loose from the bone or break.
Next blog post will discuss the different type of bone
grafts.