The mechanisms underlying the variety of preoperative directionalities of shoulder tilting in adolescent idiopathic scoliosis patients with double thoracic curve

Preoperative directionality of shoulder tilting seems to be independent of the radiographic features of proximal thoracic (PT) curve in adolescent idiopathic scoliosis (AIS) patients. To date, no study had investigated the mechanisms underlying the variety of preoperative directionalities of shoulder tilting in AIS patients. The purpose of this study was to evaluate the differences of radiographic features between Lenke type 2 (double thoracic curve) AIS patients with different preoperative directionalities of shoulder tilting. A total of 130 Lenke type 2 AIS patients were included in this study and were divided into two groups according to the value of radiographic shoulder height (RSH). There were 78 cases (71 females and 7 males) with RSH less than 0 cm in Group A and 52 cases (44 females and 8 males) with RSH equal to or more than 0 cm in Group B. Preoperative standing anteroposterior X-ray films of the spine were obtained in all these subjects and were analyzed with respect to the following parameters: T1 tilt, PT Cobb angle, main thoracic (MT) Cobb angle, the apical level of PT curve, the apical level of MT curve, and RSH. These parameters were compared between these two groups and the correlations between RSH and the other parameters were analyzed in all of these subjects. No significant difference was found between these two groups with respect to PT Cobb angle or the apical level of PT curve (P > 0.05). The apical level of MT curve was significantly more proximal in Group A compared with Group B (P < 0.05). The MT Cobb angle was significantly larger in Group A compared with Group B (P < 0.05). Both the T1 tilt and the PT Cobb angle/MT Cobb angle ratio in Group A were significantly smaller than those in Group B (P < 0.05). The RSH was positively associated with T1 tilt, the apical level of MT curve, and the PT Cobb angle/MT Cobb angle ratio, but was negatively associated with MT Cobb angle (P < 0.05). The directionality of shoulder tilting is diverse in Lenke type 2 AIS patients. The preoperative directionality of shoulder mainly depends on the profile of MT curve rather than that of PT curve. The RSH should be carefully evaluated before making a surgical plan in these patients.