OBJECTIVE: To determine the intra- and interexaminer reliability of a specific method of mensuration commonly used to evaluate the positional configuration of the lumbopelvic spine viewed on lateral lumbar radiographs.

DESIGN: A blind, repeated-measures design was used. Lateral lumbopelvic radiographs were presented to each of three examiners in random  order. Each film was marked and measurements were recorded. The films were cleaned of all markings and randomized again for a second run by each examiner. Each examiner's measurements were unavailable to the other examiners.

SETTING: Private, primary-care chiropractic clinic.

MAIN OUTCOME MEASURES: Anterior/posterior thoracic translation in millimeters, Ferguson's sacral-plane angle to horizontal, arcuate line angle to horizontal, L1 to L5 absolute rotation angle and four relative rotation angles for L1-L2, L2-L3, L3-L4 and L4-L5. Intra- and interrelibility of the three radiographic examiners were analyzed.

RESULTS: Intraexaminer reliability for (a) L1-L5 absolute rotation angle was .98, with confidence intervals included in the range of 0.95-0.99, (b) anterior/posterior thorax translation [+/- Sz] was .97-.99, with confidence intervals included in the range of 0.94-1.00, (c) arcuate angle (AA) .40-.81, with confidence intervals included in the range of 0.07-0.90, (d) Ferguson's angle (FA) was .91-.97, with confidence intervals included in the range of 0.82-0.98, (e) relative rotation angle reliability ranges were L1-L2, .84-.94; L2-L3, .80-.85; L3-L4, .78-.89; L4-L5, .87-.92. Interexaminer reliabilities for the three examiners ranged from .66-.98.

CONCLUSION: With the exception of the arcuate angle measurement, the reliabilities for all other measurements were at least .78. Those measurements with reliabilities approaching .80 or better would be considered accurate enough for use in future clinical studies. The arcuate angle measurement may have been least reliable because of the subjective nature of the method of affixing a best-fit line to a radiographic landmark that often takes on the appearance of a mild curvature. Establishing reliability is an important first step toward evaluating these and other similar radiographic measurements that have yet to be examined for their validity.

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