Fixed obliquity of the pelvis, as contrasted with obliquity due to actual shortening of a leg, is caused by a contracture either of the structures connecting pelvis and thigh, or pelvis and spine. It is characterized by the fact that, when both legs are held parallel to the mid-line of the body, it is impossible to square the pelvis, even when the patient is in the recumbent position. Its practical significance is due to the apparent difference in the length of the legs which it causes. Five types may be distinguished:
(1) Due to contracture of the abductors.
(2) Due to contracture of the adductors.
(3) Due to contracture of both abductors and adductors.
(4) Due to contracture of spinal and abdominal muscles, and of the quadratus lumborum.
(5) Combinations of Groups 1, 2, or 3, with Group 4.
The deformity can be corrected in the early cases by a push-and-pull apparatus; in the more advanced cases by suitable division of the contracted structures, coupled with stabilizing procedures to prevent recurrence of the deformity.