Postoperative shoulder balance in Lenke type 1 adolescent idiopathic scoliosis patients with large thoracic curve (Cobb angle ≥ 70 degrees): a radiographic study

BACKGROUND: Large amounts of thoracic curve correction had been considered as a risk factor for postoperative shoulder imbalance (PSI) in adolescent idiopathic scoliosis (AIS) patients. This study aims to evaluate postoperative shoulder balance in Lenke type 1 AIS patients with large thoracic curve (Cobb angle ≥ 70 degrees) and compared it with those with moderate thoracic curve (Cobb angle < 70 degrees). METHODS: A total of 47 Lenke type 1 AIS patients underwent posterior correction surgery between Sept. 2016 to Nov. 2018 in our institution were included. All these patient were divided into 2 groups based on the severity of main thoracic (MT) curve. Group A consisted of 25 cases with MT curve equal to or more than 70 degree while Group B consisted of 22 cases with MT curve less than 70 degree. Proximal thoracic (PT) Cobb angle, MT Cobb angle, MT apical vertebral translation (AVT), T2-T5 kyphosis, T5-T12 kyphosis, and radiographic shoulder height (RSH) were compared between these 2 groups preoperatively, immediately after surgery, and at a minimum of two-year follow-up. RESULTS: Although all the correction of PT Cobb angle (15.8° ± 6.0° vs 12.5° ± 3.6°, P = 0.028), that of MT Cobb angle 47.3° ± 9.1° vs 30.9° ± 6.7°, P < 0.001) and that of MT AVT (35.1 mm ± 16.0 mm vs 24.1 mm ± 8.9 mm, P = 0.007) were significantly larger in Group A when compared with Group B, RSH was comparable between these 2 groups at last follow up (7.5 mm ± 7.4 mm vs 9.2 mm ± 4.2 mm P = 0.363). Most of the patients gained satisfactory shoulder balance with only 7 cases with minimal PSI in group A (28%) and only 6 cases with minimal PSI in group B (27.3%) at last follow-up (P > 0.05). CONCLUSIONS: Although Lenke type 1 AIS patients with large thoracic curve had more amounts of MT curve correction when compared with those with moderate thoracic curve, it did not lead to higher incidence of PSI if the correction rate is proper.