Rotation

ROTATION (Lat. rotatio — rotation) in anatomy denotes the rotation of a body segment as a whole around its longitudinal axis. Thus, this term is applied to designate: a) rotation of the head around the vertical axis due to the mobility of the atlanto-axial joint, b) rotation of the arm around its longitudinal axis passing through the centers of the shoulder and radiocapitular joints, and c) rotation of the thigh around its longitudinal (biomechanical) axis connecting the center of the hip joint with the center of the cruciate ligament of the knee joint. The limits of mobility of these movements, according to some authors (Weber, Volkmann, Langer, Hughes, Mollier, and Brans): head — 30–40°, head together with neck — 90°, arm in the average position — 90°, thigh in the average position — up to 90°. Near the extreme positions of flexion-extension and abduction-adduction, when the articular bags of the proximal joints are taut, the arm and thigh exhibit less rotational mobility, passing for extreme deviations into a state of forced rotation. The greatest abduction of the arm (backward, behind the back) corresponds to forced external rotation, the greatest adduction (forward, forward-inward) — to internal rotation. In an upright stance, the limits of rotation of the thigh are approximately 13° outward and 37° inward.