Influence of Axial Rotation on Chiropractic Pelvic Radiographic Analysis

Exploratory evaluation of the effect of axial rotation, focal film distance and measurement methods on the magnitude of projected lumbar retrolisthesis on plain film radiographs

OBJECTIVE

The purpose of this exploratory study was to evaluate the amount of error in retrolisthesis measurement due to measurement methods or projection factors inherent in spinal radiography. In addition, this study compared how accurately these methods determine positions of the lumbar vertebrae being studied and the expected projected size of the retrolisthesis.

METHODS

Vertebral models were situated in a retrolisthesis position. Radiographs of the models were obtained in positive and negative y-axis rotations at 40- and 84-in focal film distances. The projected retrolisthesis was measured using the Gohl, Iguchi, and Lopes methods.

RESULTS

At the 40-in focal film distance, the Iguchi method and Lopes methods were significantly more accurate than the Gohl method. At the 84-in focal film distance, the Lopes method was significantly more accurate than the Gohl method. Almost all measurements overestimated both the actual amount of retrolisthesis as well as the amount of trigonometrically calculated retrolisthesis that should have been present on the radiographs. Findings suggest that measurements were less accurate with vertebrae rotated more than 10°.

CONCLUSIONS

This study demonstrated that lumbar vertebral rotation, focal film distance, and measurement methods are potential sources of error in retrolisthesis measurement.

Computer modeling of selected projectional factors of the 84-in focal film distance anteroposterior full spine radiograph compared with 40-in focal film distance sectional views

OBJECTIVE

The purpose of this study was to compare the 84-in focal film distance anteroposterior (A-P) full spine view to selected sectional views taken at a 40-in focal film distance for angles of divergence and changes produced by lateral translation and variation in source object distance.

METHODS

Computer models were used to determine angles of divergence and study the effects of lateral translation and changes in source object distance.

RESULTS

Lateral translation produced less projected axial (y-axis) vertebral rotation on the 84-in A-P full spine view than the film at 40 in. Angles of divergence are equal on the 14 × 17-in film at 40 in compared with the 84-in A-P full spine, and 70% of the 84-in full spine view is within the angles of divergence of the 40-in 10 × 12. The 84-in A-P full spine produced lowering and lengthening of the projected ilium when source object distance was reduced.

CONCLUSION

In this study, the 84-in A-P full spine produced less projected vertebral rotation on lateral translation. Its angles of divergence were greater than the 40-in 10 × 12 and equal to the 40-in 14 × 17-in film. Except for a 5.4-in section at both the upper and lower margins, the 84-in full spine view was within the angles of divergence of a 40-in 10 × 12. The full spine film produced projected ilium lengthening and lowering.

Geometry of coplanar stereoscopic radiographic pairs for analysis of the lateral cervical radiograph: a study using mathematical models

OBJECTIVE

This study evaluated 3-dimensional (3D) assessments of points of interest on a phantom replica of the human skull and cervical vertebrae to better understand how structures are represented in space using mathematical methods.

METHODS

Three basic geometric equations derived from the "Law of Similar Triangles" are introduced, and measurements are taken after 4 trials to demonstrate how 3D data extracted from 2-dimensional (2D) digitized radiographic pairs can be used to produce coordinate points associated with 3 areas on the atlas.

RESULTS

An analysis of variance test for multiple group comparison shows no significant statistical difference between 4 trials (P = 0.995). In addition, 6 strong positive correlations are evident using Pearson product-moment coefficient test (r = 0.9008 through 0.9977, P = 0.002).

CONCLUSION

This study suggests that it is possible to use coplanar stereoscopic radiographic pairs to define an object's location in 3D space by taking retrospective measurements directly from 2D digitized radiographs.