The Bilateral Differences and the Normal Variability of the Anteversion Angle of the Femur Obtained by Computer Tomography

Abstract

Objective: The present study was to obtain a better insight into the clinical relevance of the rotational deformity after femoral shaft fracture treated with intramedullary osteosynthesis. The bilateral differences of the anteversion (AV) angles of the femora of fifteen healthy volunteers were determined by CT and compared with the bilateral differences of the AV angles of thirty-four patients treated with intramedullary nailing after femoral shaft fracture. Do differences exist between the groups? Suppose there are no differences between this control group and this patient group, except for some individual patients, what is the meaning of this for the interpretation of the rotational malformation? Also in this study the normal variability of the AV angle of the femur was evaluated by collecting data on the AV angles of sixty-four normal femora, measured by CT.
Setting and Design: In 1998 CT measurements were made of the bilateral differences of the AV angles of fifteen healthy volunteers at the Westeinde Hospital in The Hague. This control group consisted of eight males and seven females.
Results: The results of the measurements of the AV angles and bilateral differences are between -23.4° and 18.6°. The males tend to have a larger range of the bilateral difference than the females. The means of the absolute values of the bilateral differences for the whole group is 7.8°, for the males separately 10.6° and for the females 4.6°. For the patient group the range of the bilateral differences lies between -31.3° and 33.6°. The mean of the absolute values of the bilateral differences is 10.8°. The mean of the absolute values of the bilateral differences for the male is 11.2° and for the female 9.9°. Noteworthy are the five bilateral differences over 20°. Four of them are male. The physiological range of the AV angle was collected from sixty-six femora. There were thirty-eight male femora and twenty-eight female femora. The mean AV angle for the male femora was 22.1° (range 6.8° to 43.6°). The mean AV angle for the female femora was 28.1° (range 12.7° to 65.4°). In contrast with the difference between the sexes when the bilateral differences are compared (males tend to have a larger bilateral difference), the mean AV angle in female femora is 6.0° larger than the mean AV angle in male femora.
Conclusion: When the bilateral differences in a control group are measured by CT, a difference up to maybe 25° is normal. When this bilateral difference is measured in patients with femoral fractures treated with an intramedullary nail it can be within the normal physiological range.

Key words

Normal variability rotational deformity - Femoral fracture - Intramedullary nailing

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