Meng, Teo Yu
(2017)
Morphometric evaluation of C1 pedicle and lateral mass for screw fixation in Kelantan : feasibility study using CT scan.
Masters thesis, Universiti Sains Malaysia.
Abstract
Introduction
Posterior arch or pedicle screw is an alternative fixation method to lateral mass screw of the altas
(C1). Several studies had shown its advantages over conventional C1 lateral mass screw. The
most important factor to determine the feasibility of posterior arch screw insertion is the vertical
pedicle height of posterior arch, which several studied had proved its feasibility . However, it
must be used with caution in our population as the posterior arch size may not be able to
accommodate the conventional 3.5mm pedicle screw. Hence, we performed
a mophormetric study of C1 vertebrae using CT scan to determine the feasibility of screw
insertion.
Materials and methods
We performed a cross sectional study to analyse 113 C1 veterbrae using CT using 1.0mm slice
thickness. Those who had fracture of C1, infection of C1, tumorous condition of C1 and any
congenital deformities of C1 were excluded from this study. Desired axial and sagittal CT scan
slices was obtained for measurement after reconstruction of images and slice through the desired
anatomical landmark. Each parameter was defined anatomically using appropriate landmark. All
the parameters were measured up to 0.1mm twice and the mean was taken, and the statistical
analysis was done using SPSS version 20. Independent t-test was use to determine the
significant difference between sides and gender. Descriptive analysis for numerical variables
were described as mean.Results
The mean outer pedicle height were 3.5 mm for right and left sides. All lateral mass height in 82
male patients were more than 3.5mm. 19.5%(right) and 25.6%(left ) of lateral mass height in
male patients are smaller than 4.0mm. For outer pedicle height in 82 male patients, 43.9%(right)
and 40.2%(left) were smaller than 3.5mm,79.3%(right) and 78%(left) were smaller than 4.0mm.
For lateral mass height in 31 female patients, 12.9%(right) and 9.7%(left ) were smaller than
3.5mm, 48.4%(right) and 51.6%(left ) were smaller than 4.0mm, 83.9%(right) and 90.3%(left)
were smaller than 4.5mm. For outer pedicle height in female patients, 77.6%(right) and 74.2
%(left) were smaller than 3.5mm, 90.3%(right and left ) were smaller than 4.0mm. We also
found out that C1 posterior arch medullary cavity were absent in a significant number of patients
(male-28.0-31.7%, female-54.8-58.1%)
Conclusion
C1 posterior arch screw insertion in our population should be performed with caution and preoperative
CT scan is mandatory especially in female patients to determine the pedicle height and
present of posterior arch medullary cavity before any posterior arch screw insertion. Lateral mass
screw fixation is feasible and safer, therefore is the option of choice for C1 instrumentation
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