Importance of fixation angle in posterior instrumented occipitocervical fusion.

Occipitocervical fusion with the head in a functionally neutral position is critically important. Various methods have been proposed for measuring the angle of the craniovertebral junction based on lateral radiography. We describe a simple and reliable measurement of fixation angle during occipitocervical fusion using the line parallel to the bony palate and the posterior longitudinal line of the C2 vertebra. The normal range of the angle of the craniovertebral junction was measured in 30 normal healthy volunteers, 15 males and 15 females aged from 17 to 77 years (mean 45.1 years), without symptoms of neck pain or limitations of neck movement. The angle ranged from 85 to 118 degrees. The mean angle was 97.1 degrees in males and 102.6 degrees in females, with overall mean +/- standard deviation of 99.9 +/- 8.1 degrees. Careful adjustment of the angle of the craniovertebral junction can help to avoid postoperative complications such as dysphagia, dyspnea, and subaxial subluxation.