Na. Ebraheim et al., AN ANATOMIC STUDY OF THE THICKNESS OF THE OCCIPITAL BONE - IMPLICATIONS FOR OCCIPITOCERVICAL INSTRUMENTATION, Spine (Philadelphia, Pa. 1976), 21(15), 1996, pp. 1725-1729
Study Design. The authors measured the thickness and quality of occipi
tal bone regions to determine screw placement during occipitocervical
fusion and described the projection of the posterior dural venous sinu
ses. Objective. This study provides anatomic data relevant to areas of
screw placement into the occiput during occipitocervical fixation. Su
mmary of Background Data. Few reports exist regarding the morphometric
s of the occipital bone and intracranial structures relevant to occipi
tocervical fusion. Method. The thickness of the posterior inferior occ
ipital bone was measured relative to a 10 x 5 cm grid. Sections were e
valuated grossly and histologically. The projections of the posterior
dural venous sinuses were determined by direct measurements. Results.
The maximum thickness of the occipital bone, which ranged from 11.5 to
15.1 mm in males and from 9.7 to 12.0 mm in females, was at the level
of the external Occipital protuberance. The occipital bone was thicke
r than 8 mm in an area extending laterally from the external occipital
protuberance for 23 mm and consisted of dense cortical bone with litt
le or no diploic bone. The projection of most of the torcula on the ex
ternal surface of the occipital bone was located superior to the cente
r of the external occipital protuberance (mean, 12.6 mm superior and 4
.7 mm inferior to external occipital protuberance), whereas that of th
e transverse sinus was distributed more evenly above and below the ext
ernal occipital protuberance (mean, 7.3 mm superior and 6.5 mm inferio
r). Conclusions. Screws that are 8-mm long may be inserted in the regi
on of the superior nuchal line (Level 0) extending 2 cm laterally from
the center of the external occipital protuberance, 1 cm from the midl
ine at a level 1 cm inferior to the external occipital protuberance (L
evel 1), and 0.5 cm from the midline at a level 2 inferior to the exte
rnal occipital protuberance (Level 2). The major dural venous sinuses
are situated immediately beneath the thickest regions of the occiput a
nd are at screw placement.