Coronal balance in idiopathic scoliosis: a radiological study after posterior fusion of thoracolumbar/lumbar curves (Lenke 5 or 6).

PURPOSE: To explore the compensation mechanisms of immediate postoperative coronal imbalance (CIB) and identify the correlation between preoperative lumbosacral obliquity and postoperative CIB in patients with Lenke 5/6 adolescent idiopathic scoliosis (AIS) during a 2-year follow-up period.

METHODS: Medical records of patients with Lenke 5/6 AIS who were admitted in our hospital between Jan. 2008 and Jan. 2013 were reviewed retrospectively. General information of the patients including gender, age, and Risser classification was collected. Patients were divided into coronal balance (CB) and CIB groups according to the postoperative CB. Radiographic assessment included preoperative, postoperative and full-length anteroposterior and lateral radiographs and passive lateral bending radiographs of the spine at the last follow-up.

RESULTS: Altogether 80 patients (37 in CIB group and 43 in CB group) were included in this study, of whom 27 patients in CIB group achieved balance at the last follow-up. Binary logistic regression showed that preoperative bending L5 tilt (OR = 1.498) was a potential risk factor of postoperative CIB (p < 0.05). Pearson correlation analysis showed that the distal wedge angle was significantly associated with immediate postoperative CB.

CONCLUSIONS: Preoperative L5 tilt on bending radiographs was an important risk factor of postoperative CIB in Lenke 5/6 AIS, which might be compensated by the way similar to that seen in the Lenke 1 distal adding-on phenomenon. Appropriate shortening of the fusion segments may help reduce the occurrence of postoperative CIB in patients with a relatively large L5 tilt on the postoperative bending radiograph.