Background and Objective: Occipitocervical fusion (OCF) has been used to treat instability and deformity of the craniocervical junction. This specific area requires detail of morphologic knowledge to prevent surgical complications, the most important factor is thickness of occipital bone which is poorly documented in Thai population. The aim of this study was to determine the area of screw placement for optimal fixation in Thai population.

Methods: Thai patients without head and neck disease who underwent CT brain at our hospital in 2016 were included. The thickness of occipital bone was measured based on CT by using external occipital protuberance (EOP) for the reference point. Measurements were taken according to matrix of 153 points following a grid with 5 mm spacing.

Results: 97 patients, composed of 50 males and 47 females were the subjects of this study. Male tended to have a thicker occipital bone than female but no significant differences. The EOP had the greatest thickness, with average values of 17.4 ±2.5 mm (12.9-23.7mm). Areas with thicknesses > 8 mm were more frequent at the EOP and up to 25 mm laterally both sides, as well as up to 20 mm laterally both sides at a level of 5 mm inferior to EOP, up to 10 mm laterally both sides at a level of 10 mm inferior to EOP and up to 35 mm inferior to EOP in the midline.

Conclusions: The results of this first study in Thai population suggest that it is possible to effectively and safety insert screws over wider area than the previous reference range, thus reducing the risk of fixation failure and other complications.