A three-dimensional anatomic study on placement of occipital condyle screws

Objective To evaluate the safety and feasibility of implanting occipital condyle screws in cadavers.Methods Screws of 3.5 mm in diameter and 20.0 mm in length were implanted into the ambilateral occipital condyles in 10 cadaveric specimens.CT scanning was performed after the procedure on the occipitocervical region for three-dimensional reconstruction of the region.In the three-dimensional occipitocervical models,relationships between the occipital condyle screw and its important surrounding tissues,like vertebral artery,spinal cord and hypoglossal canal,were measured.The length,upper and inside tilting angles of the screw,and distances between the screw and the hypoglossal canal and between the condylar entry point and the medial wall of the occipital condyle were also measured.Results Three-dimensional reconstruction models showed that all the occipital condyle screws were successfully implanted into the 20 occipital condyles in 10 cadaveric specimens.There was no injury to the spinal cord,nerve root,hypoglossal nerve or vertebral artery.At the left occipital bone,the average length,upper tilting angle and inside tilting angle of the condylar screws were respectively 20.96 ± 0.87 mm,31.00° ± 1.59° and 11.24° ± 0.71 °; the distances averaged 4.84 ±.0.52 mm between the condylar screw and the hypoglossal canal and 5.13 ±.0.79 mm between the condylar entry point and the medial wall of the occipital condyle.At the right occipital bone,the average length,upper tilting angle and inside tilting angle of the condylar screws were respectively 20.59±0.54 mm,30.85° ± 0.97° and 11.11 °±0.61°; the distances averaged 4.70±0.27 mm between the condylar screw and the hypoglossal canal and 5.04 ± 0.68 mm between the condylar entry point and the medial wall of the occipital condyle.Conclusions A surgeon who is familiar with the anatomy and skillful in operation can use occipital condyle screws in occipitocervical fusion without any injury to the important surrounding tissues.The screws,with definite parameters regarding entry point,course and length,can be used safely as an alternative or a modification of the conventional occipitocervical fusion in clinic. Key words: Imaging, three-dimensional; Spinal fusion; Anatomy