Femoral anteversion

MRI for the

preoperative evaluation of femoroacetabular impingement. Calculation of femoral version corrected for distal femoral rotation. On the straight axial image(s) of the hip/pelvis covering the femoral head and neck, a line is drawn between the center of the femoral head and center of the femoral neck at its narrowest point to calculate the uncorrected femoral anteversion angle (A; A is a negative value when the femur is retroverted). To correct for distal femoral rotation, another line is drawn along the posterior border of the femoral condyles to calculate the angle (B; B is a negative value when the knee is internally rotated). Femoral version = A − B. A positive value indicates femoral anteversion. A negative value indicates femoral retroversion. Normal femoral anteversion is approximately 12–13°

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Femoral anteversion refers to the orientation of the femoral neck in relation to the femoral condyles at the level of the knee. In most cases, the femoral neck is oriented anteriorly as compared to the femoral condyles. In the case of posterior orientation, the term femoral retroversion is also applied.

Actually describing the intrinsic rotation of the femur over its length from the hip to the knee, femoral anteversion may also be more aptly termed femoral antetorsion.

Femoral anteversion averages between 30-40° at birth, and between 8-14° in adults , with males having a slightly less femoral anteversion than females .

Some authors will distinguish femoral neck version as the angle of the femoral neck relative to the pelvic horizontal (interischial line), with a normal range of 5-25 degrees of anteversion and femoral neck torsion as the angle between the femoral neck and posterior condylar axis of the distal femur, with a normal range of 10-20 degrees of antetorsion .

Pathology

An increased femoral anteversion is often seen in patients with developmental dysplasia of the hip . Moreover, it has been shown that abnormal femoral anteversion can contribute to the development of femoroacetabular impingement (FAI); reduced femoral anteversion is associated with cam-type FAI .

Radiographic features

Femoral anteversion can be determined by measuring the angle formed between the long axis of the femoral neck and a line parallel to the dorsal aspect of the femoral condyles (posterior condylar axis, or PCA) on axial slices at MRI or CT.

Depending on the measuring tools available this can be done either directly by measuring the anteversion angle over two different axial slices at once (one at hip level and one at knee level) or by taking two separate angle measurements using a horizontal line as a static reference on either slice and subsequently adding or subtracting the resulting angles, depending on their orientation in the same direction (e.g. both measurements clockwise > subtract) or in different directions (e.g. femoral neck measurement counterclockwise and condyle measurement clockwise > add).

It is often easiest to generate a relatively thick MIP at both levels if using CT.

Treatment and prognosis

In many patients, there is no need for individual correction of an abnormal femoral anteversion. In patients with severe femoral anteversion or retroversion, a subtrochanteric rotational osteotomy of the femur may be performed .

History and etymology

The concept of femoral anteversion was first described in 1868 by the anatomist Julius Wolff .