Objective: To analyze the influence of thoracic kyphosis on the sagittal compensatory mode of the spine in idiopathic thoracic scoliosis after the selective thoracic fusion.
Methods: Ninety 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).
Results: At 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.
Conclusions: For 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.