OBJECTIVETo analyze the influence of thoracic kyphosis on the sagittal compensatory mode of the spine in idiopathic thoracic scoliosis after the selective thoracic fusion.

METHODSNinety AIS patients (mean age 14.5 years old) who received selective thoracic fusion from February 1999 to December 2005 in one institution with at least 24-month follow-up were evaluated. Forty-one patients underwent anterior spinal fusion and forty-nine patients underwent posterior spinal fusion. And then the patients were divided into two subgroups according to the magnitude of preoperative thoracic kyphosis (TK): Group A, TK less than 10 degrees ; and Group B, TK more than 10 degrees . The radiological parameters were measured including: thoracic and lumbar curve magnitude, TK, lumbar lordosis (LL), thoracolumbar junction kyphosis (T(10)-L(2), TJK), distal junctional kyphosis (DJK), sagittal vertical axis (SVA).

RESULTSAt final follow-up, TK, TJK and DJK increased significantly compared with preoperative Cobb angle in subgroup A patients who underwent anterior spinal fusion (P < 0.05). Generally, there was a lordosis loss of TJK and DJK during follow-up. While in subgroup B, TJK at final follow-up increased apparently compared with preoperative Cobb angle (P < 0.05). And there was a increased trend of DJK in spite of no significant difference, however, there was no obvious change of TK in subgroup B. At the final follow-up, TK and TJK increased significantly in subgroup A patients who underwent posterior spinal fusion (P < 0.05). And there was a increased tendency of DJK during follow-up, although there was no significant difference. And there was no obvious change of TK, TJK and DJK in subgroup B. There was a increased trend of LL in spite of no significant difference in group A patients who underwent anterior or posterior spinal fusion. The sagittal balance maintained well during follow-up in both groups.

CONCLUSIONSFor AIS patients with thoracic hypokyphosis, normal TK and LL could be achieved during follow-up with selective thoracic instrumentation. However, the increase of DJK and TJK may occur during the follow-up, and the risk factors may be the anterior short segmental fusion and the reconstruction of the sagittal profile in the hypokyphosis patients.