The following discussion about the rotator action of the adductors is not an attempt to solve the controversy that appears to exist but, rather, to present some of the reasons why this controversy exists.
For the accompanying illustration, it is important to note that in the anatomical position, from the anterior view, the femur extends obliquely, with the distal end being more medial than the proximal end. From the lateral view, the shaft of the femur is convexly curved, in an anterior direction. The anatomical axis of the femur extends longitudinally along the shaft. If rotation of the hip took place about this axis, there would be no doubt that the adductors, attached as they are posteriorly along the linea aspera, would be lateral rotators.
Rotation of the hip joint, however, does not occur about the anatomical axis of the femur but, rather, about the mechanical axis, which passes from the center of the hip joint to the center of the knee joint and is at the intersection of the two planes represented by the solid black lines in the accompanying figure.
The muscles or major portions of muscles that insert on the part of the femur that is anterior to the mechanical axis will act as medial rotators of the femur. (See lateral view.) On the other hand, the muscles or major portions of muscles that insert on the part of the femur posterior to the mechanical axis will act as lateral rotators.
When the position of the extremity in relation to the pelvis changes from that illustrated as the anatomical position, the actions of the muscles also change. Thus, if the femur is medially rotated, a larger portion of the shaft comes to lie anterior to the mechanical axis, with the result that more of the adductor insertions will be anterior to the axis and, therefore, will act as medial rotators. With increased lateral rotation, more of the adductors will act as lateral rotators.
Besides the change that occurs with movement, normal variations also occur in the bone structure of the femur that tend to make the rotator action of the adductors variable.
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