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representative voids in the segmentation which correspond to the precise screw
locations. The virtual spine model with the templated screw holes in place is tiled
into a surface using an adaptive deformation algorithm [
21
23
] and exported as a
-
stereo-lithography (STL)
file. To improve the stability of the delicate spinal
structure, a narrow ribbon is added to the anterior spine model before printing. The
resultant STL
file is printed using a ZCorp Spectrum Z510 printer. This printer can
generate large-volume, full color models.
The pre-surgical plan report is used in advance to prepare the instrumentation
inventory for the operation. The 3D patient-speci
c model, along with the report, is
used in the procedure room to provide real-time visualization and guidance for
accurate pedicle screw placement.
3.2.5 Proposed Surgical Planning Work
fl
ow
To better illustrate the functionality and capabilities of the spine surgery planning
platform, we follow a hypothetical patient through the work
ow associated with the
proposed interventional planning protocol. Following diagnosis based on a routine
CT scan, the patient is typically recommended for surgery, in which case additional
imaging exams may be ordered, to better examine a speci
fl
c region of interest in the
spine anatomy. Based on the pre-operative spine image dataset, the surgeon or
physician assistant will conduct the surgical plan using the proposed virtual plat-
form. Each vertebral segment that needs to be instrumented will be realigned
according to the true vertebral axis in order to enable true size measurements of the
pedicles and vertebral body. These preliminary measurements of the pedicle width
and length will serve as initial estimated of the virtual pedicle screws that are to be
selected from the available database that compiles a wide variety of screws
according to the speci
cations of several different manufacturers, so they closely
match the vertebral anatomy. Each vertebral segment is then instrumented by
“
a virtual
representation of the physical screw) in the image dataset through the pedicle body
mimicking the actual intra-operative implantation procedure. The position and
orientation of each screw is then evaluated by panning through the image data
containing the virtual pedicle screw to ensure the screw is fully contained within the
pedicle (i.e., ne pedicle rupture) and does not interfere with the surrounding anat-
omy. In the event that more than one screw type (i.e., of close diameter and length)
or several trajectories are permissible, the Fastening Strength is evaluated for each
screw and each trajectory and based on the results, the screw and trajectory yielding
the largest Fastening Strength will be selected, again, under the constraints that no
interference exists between the screw and surrounding anatomy.
These steps are repeated for each vertebral segment that needs to be instrumented.
Following completion of the plan, the platform provides a report that lists each
instrumented vertebral segment specifying the implant gauge (i.e., screw diameter
and length), implant trajectory (measured with respect to the axial and sagittal
angles), and, if needed, the Fastening Strength computed for each implant. Note that
inserting
”
the selected virtual screw (in the form of an object map
—
