OBJECTIVE: To ascertain the incidence of asymmetry of the occipital condyles. The a priori hypothesis of symmetry (which is pervasive both in the determination of "subluxation" and in the means chosen for correction) was tested.

DESIGN: Data set design was used with a convenience sample. The condyles were chosen for convenience of visualization from plain film radiographs. The study was retrospectively designed, albeit with prospective implications for analytic investigation.

SETTING: The research department of Cleveland Chiropractic College, Kansas City, MO.

PATIENTS OR OTHER PARTICIPANTS: One hundred fifty-one submentovertex radiographs were examined using a computer-assisted digitizer. The radiographs were randomly obtained from the patient files of two doctors of chiropractic who routinely use this type of radiograph in their patient analysis.

INTERVENTIONS: The study was a side-to-side comparison of the condyles, which were subject to neither intervention nor change.

MAIN OUTCOME MEASURES: Surface area of left and right condyles for 151 examined pairs.

RESULTS: Analysis with Pearson's correlation coefficient implied a lack of symmetry between condyles (r = .37; p < .0001). The scatterplot revealed values widely dispersed about the regression line, and the standard error of the estimate was 36.7.

CONCLUSION: The data suggest that the underlying premise of symmetry in chiropractic analysis needs to be reexamined.

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