Effect of rotation on radiographic dimensions of the humerus and femur

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Abstract
Ten humeri and 10 femora [human] were radiographed in 9 positions of longitudinal rotation. In each position total, medullary and cortical widths of the diaphyses (TW, MW, CW) were measured to assess the effect of rotation on these dimensions. The results were expressed as differences from the values in the neutral position (.DELTA.TW, .DELTA.MW, .DELTA.CW). In the humerus, medial rotation produced greater changes than lateral rotation. Though rotation in either direction increased CW, the systematic error due to medial rotation to only 5 degrees (about + 0.0058 cm /degree) was more than double that due to lateral rotation. In the femur, lateral rotation had the greater effect, producing a marked decrease in CW (about-0.0072 cm/degree). Medial rotation produced only a slight increase in CW. The ratios CW/TW (cortical index) and CA/TA (area ratio) were calculated and expressed as differences from the values in the neutral position (.DELTA.CW/TW, .DELTA.CA/TA). Rotation affected these variables much less than the linear dimensions. Though the variance of .DELTA.TW, .DELTA.MW and .DELTA.CW increased with increasing rotation, the variance of .DELTA.CW/TW and .DELTA.CA/TA increased only slightly or not at all. If radiographic morphometry is to be applied to the humerus and femur, these ratios rather than transverse dimensions should be used. Sequential changes in CW may be totally obscured by small rotational errors.

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