Slight head extension: does it change the sagittal cervical curve?

It is commonly believed that slight flexion/extension of the head will reve rse the cervical lordosis. The goal of the present study was to determine w hether slight head extension could result in a cervical kyphosis changing i nto a lordosis. Forty consecutive volunteer subjects with a cervical kyphos is and with flexion in their resting head position had a neutral lateral ce rvical radiograph followed immediately by a lateral cervical view taken in an extended head position to level the bite line. Subjects were patients at a spine clinic in Elko, Nevada. All radiographs were digitized. Global and segmental angles of the cervical curve were compared for any change in ang le due to slight extension of the head. The average extension of the head r equired to level the bite line was 13.9 degrees. This head extension was no t substantially correlated with any segmental or global angle of lordosis. Subjects were categorized into those requiring slight head extension (0 deg rees -13.9 degrees) and those requiring a significant head extension (>13.9 degrees). In the slight head extension group, the average change in global angle between posterior tangents on C2 and C7 was 6.9 degrees, and 80% of this change occurred in C1-C4. In the significant head extension group, the average change in global angle between posterior tangents on C2 and C7 was 11.0 degrees, and the major portion of this change occurred in C1-C4. Out of 40 subjects, only one subject, who was in the significant head extension group and had only a minor segmental kyphosis, changed from kyphosis to lo rdosis. The results show that slight extension of the head does not change a reversed cervical curve into a cervical lordosis as measured on lateral c ervical radiographs. Only small extension angle changes (mean sum=4.8 degre es) in the upper cervical segments (C2-C4) occur in head extension of 14 de grees or less.