Study Design, This study examines the C2 vertebrae using both direct anatom
ic and computed tomographic measurements,
Objective. To define the relation of the C2 vertebrae bony elements to the
vertebral artery and the spinal canal, to determine individuals at risk for
vertebral artery injury during C1-C2 transarticular screw placement
Summary of Background Data. Recent literature assessing the safety of upper
cervical spine transarticular screws has concentrated on technique, includ
ing the optimal point of entry and path projection of the screw. The actual
dimensions of the C2 isthmus of the pars interarticularis has not been exa
mined in a large number of specimens.
Methods. C2 isthmus width and height measurements were made on 205 human ca
daveric C2 vertebrae. Vertebrae predicted to be at risk for vertebral arter
ial injury were imaged by computed tomography,
Results. There were 102 female and 103 male specimens with mean isthmus wid
ths of 8.2 +/- 1.5 mm and 7.2 +/- 1.3 mm, respectively. Five specimens (2.4
%) had an isthmus width less than 5 mm. The mean isthmus heights were 8.6 /- 2.0 mm and 6.9 +/- 1.5 mm for male and female specimens, respectively. I
n twenty-four specimens (11.7%), one or both isthmi had a height of less th
an 5 mm. Six of these specimens were male and 18 were female. The right C2
isthmus was generally smaller than the left. Computed tomographic measureme
nts closely approximated those of the actual dimensions of the isthmi.
Conclusions. Placing a 3.5 mm screw in a patient with narrow C2 isthmus dim
ensions (smaller than 5 mm in either the height or width) is technically di
fficult. Because of narrow C2 isthmus width and/or height, approximately 10
% of patients may be at risk for a vertebral artery injury with placement o
f C1-C2 transarticular screws.