Several chiropractic techniques depend on x-ray analysis to determine the presence and degree of vertebral misalignment. The upper cervical techniques in particular claim that angular displacements as small as 0.5 degrees from an orthogonal normal position are capable of producing nerve inteiference.
However, some doubt exists regarding the ability of x-ray analysis methods to reliably detect such small positional changes. In various studies, intra-examiner error has been found to range from as little as 1 percent  to as great as 71 percent [ 12], while the error between examiners has ranged from 7p ercent  to 57 percent [ 12]. From these error calculations the accuracy of the upper cervical xray analysis is estimated to range from .41 degrees  to 40 degrees . Clearly, this dispute warrants yet another look. In order to help objectify the process of x-ray analysis and investigate the sources of error, a computer-aided analysis has been developed for this study.
The analysis system makes use of a sonic digitizer to locate structures visible on the cervical radiographs and an Apple II+ computer to calculate structural relationships. In all, the operator is instructed by the program to locate 144 points in a predetermined sequence on the cervical series consisting of Lateral, Nasium and Vertex views. Listings, such as Atlas laterality and rotation, head tilt and cervical curve are calculated from the coordinates of the skeletal landmarks.
A preliminary test of the reliability of upper cervical x-ray analysis using this system has shown that intra-examiner accuracy in point location on radiographs averaged .52 cm. in the horizontal direction and .28 cm. in the vertical at the 95% confidence level. The Inter-examiner accuracy for four doctors, at that level of confidence, was .42 cm. horizontal, and .96 cm. vertical.
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