Slight head extension: does it change the sagittal cervical curve?Deed E. Harrison1, Donald D. Harrison2, Tadeusz J. Janik3, , Burt Holland4 and Leonard A. Siskin5 (1) Elko, Nevada, USA (2) CBP Nonprofit, Inc, Harvest, Alabama, USA (3) Time Domain Corporation, Cummings Research Park, 7057 Old Madison Pike, Huntsville, Alabama 35806, USA (4) Department of Statistics, Temple University, Philadelphia, Pennsylvania, USA (5) Green Brook, New Jersey, USA Abstract. It is commonly believed that slight flexion/extension of the head will reverse the cervical lordosis. The goal of thepresent study was to determine whether slight head extension could result in a cervical kyphosis changing into a lordosis.Forty consecutive volunteer subjects with a cervical kyphosis and with flexion in their resting head position had a neutrallateral cervical radiograph followed immediately by a lateral cervical view taken in an extended head position to level the biteline. Subjects were patients at a spine clinic in Elko, Nevada. All radiographs were digitized. Global and segmental angles ofthe cervical curve were compared for any change in angle due to slight extension of the head. The average extension of thehead required to level the bite line was 13.9? This head extension was not substantially correlated with any segmental orglobal angle of lordosis. Subjects were categorized into those requiring slight head extension (0?13.9? and those requiring asignificant head extension (>13.9?. In the slight head extension group, the average change in global angle between posteriortangents on C2 and C7 was 6.9? and 80% of this change occurred in C1-C4. In the significant head extension group, theaverage change in global angle between posterior tangents on C2 and C7 was 11.0? and the major portion of this changeoccurred in C1-C4. Out of 40 subjects, only one subject, who was in the significant head extension group and had only aminor segmental kyphosis, changed from kyphosis to lordosis. The results show that slight extension of the head does notchange a reversed cervical curve into a cervical lordosis as measured on lateral cervical radiographs. Only small extensionangle changes (mean sum=4.8? in the upper cervical segments (C2-C4) occur in head extension of 14?or less.