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Chiropractic Research Review

Vertebral Displacement and Projection/Distortion Errors

Many clinicians and technique systems regard images viewed on two-dimensional (2D) radiographs as representing exact vertebral position or subluxation in three dimensions (3D). However, 2D measurements may sometimes be complicated by poorly aligned x-ray equipment, patient-positioning errors, or rotations/translations of the skull, vertebrae and pelvis that are present in upright human postures.

This experiment was conducted to evaluate the projection/distortion errors on anteroposterior (AP) radiographs caused by lateral translation of vertebrae, and to investigate the effect of vertebral shape on projection errors. Lateral vertebral translation of the x-axis resulted in apparent vertebral rotation, and increasing magnitudes of x-axis vertebral translation resulted in increasing magnitudes of projected vertebral rotation. Vertebral shape also seemed to influence the projected rotation.

Three-dimensional lateral translation (x-axis) projects as axial rotation on the two-dimensional AP radiograph. Distortions may be influenced by several factors, including the shape of the object and the increasing angle of the x-ray beams. These findings suggest that there is no simple method to predict the exact 3D position of a vertebra from the projected image seen on an AP radiograph. Chiropractors who are aware of this projection/distortion potential and consider the contributing factors will minimize their likelihood of error.

Coleman RR, Bernard BB, Harrison DE. The effects of x-axis vertebral translation on projected y-axis vertebral rotation. Journal of Manipulative and Physiological Therapeutics, June 1998;21(5), pp333-40. Reprints: Tel: (800) 638-6423; Fax: (410) 528-8596

Chiropractic Research Review

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