Osteology of the skull as it affects halo pin placement.

Twenty-seven cadaver skulls and 20 CT scans of skulls were measured above the orbital rim and ear but below the greatest diameter to determine optimal placement of halo pin sites. At the antero- and posterolateral portions of the calvaria, the outer table averaged 2 mm, the diploe 3 mm, and the inner table 2 mm. At the temporal fossa, the outer cortex averaged 1.7 mm, the diploe 2.0 mm, and the inner table 1.6 mm. Average distance between the anterior edge of the temporal fossa and the frontal sinus approximated 3 cm. These data confirm previously recommended halo pin insertion sites, anterolaterally and posterolaterally, where the bone is thickest and the thinner frontal sinus and temporal fossae are avoided.