Figure 18-3. Abduction at the hip joint, viewed from behind. A, Normally, when weight is borne on one (e.g., the right) limb (during the stance phase of walking), the pelvis tends to sag on the free, or swing (left), side (because of gravity). This is counteracted by abduction of the hip on the stance (right) side, chiefly by strong contraction of the (right) gluteus medius, which acts on the pelvis from a fixed femur. B, When abduction of the (right) hip is interfered with on the supported side (positive Trendelenburg's sign), e.g., by dislocation, fracture, or paralysis, the pelvis sags (arrow) on the unsupported side. (Based on von Lanz and Wachsmuth.) Click for high resolution image.