Key result
Fifteen-degree femoral rotation changes proximal femoral dimensions on AP roentgenograms by ~3 mm.
Why the study?
Does femoral rotation change proximal femoral dimensions on supine AP hip roentgenograms?
Does femoral rotation change proximal femoral dimensions on supine AP hip roentgenograms?
Small amounts of femoral rotation (15 degrees) can cause significant changes (up to 3 mm) in proximal femoral dimensions on AP hip roentgenograms, necessitating precise rotational matching for accurate longitudinal measurements.
May confound serial radiographic femoral assessments; leaves open whether rotational standardization is required for accurate clinical measurements.
Three human adult femurs were examined using anteroposterior (AP) roentgenograms in anatomical position and in 15 degrees, 30 degrees, and 45 degrees of internal and external rotation. Relatively small (15 degrees or less) amounts of femoral rotation can cause significant changes in proximal femoral dimensions on supine AP hip roentgenograms, and the magnitude of these changes increases with rotation. Fifteen degrees of rotation can change it by almost 3 mm. These changes are comparable to the medullary canal expansion of a normal adult femur over a five- to ten-year period. These changes in measured proximal femoral dimensions with rotation necessitate either an improved roentgenographic technique or precise rotational matching of standard supine roentgenograms to obtain accurate measurements of their changes over time.
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Bell et al. (1989) studied this question. Femoral rotation vs. Anatomical position was evaluated on Changes in proximal femoral dimensions. Femoral rotation of 15 degrees can change proximal femoral dimensions on supine AP hip roentgenograms by almost 3 mm, comparable to normal medullary canal expansion over a 5- to 10-year period.
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