1. The authors have found twenty-two cases of alternating scoliosis mentioned in the literature. The apparent rarity of this condition is due to the fact that only the more spectacular cases have been reported.
2. The authors have found sixty-eight cases of alternating scoliosis in their records of 506 examinations for low-back disability. Six cases showed the spectacular type of active alternation.
3. The pain of alternating scoliosis is the typical sacrarthrogenetic telalgia that is caused by pathological tension in the extra-articular ligaments of the upper sacral joints.
4. The scoliosis is caused by one or more fixed pathological positions of one or more of the upper sacral joints.
5. Alternation is due to a change in the fixed pathological position of one or more of the upper sacral joints.
6. Either sacro-iliac joint may become fixed in one of four pathological positions (sacro-iliac slips) which the authors have classified as follows: a. Sacral slips:
a. Sacral slips:
(1) Flexion slips;
(2) Extension slips.
b. Iliac slips:
(1) Increased-angle slips;
(2) Decreased-angle slips.