The changes of the interspace angle after anterior correction and instrumentation in adolescent idiopathic scoliosis patients

BACKGROUND In idiopathic scoliosis patients, after anterior spinal fusion and instrumentation, the discs (interspace angle) between the lowest instrumented vertebra (LIV) and the next caudal vertebra became more wedged. We reviewed these patients and analyzed the changes of the angle. METHODS By reviewing the medical records and roentgenograms of adolescent idiopathic scoliosis patients underwent anterior spinal fusion and instrumentation, Cobb angle of the curve, correction rate, coronal balance, LIV rotation, interspace angle were measured and analyzed. RESULTS There were total 30 patients included. The mean coronal Cobb angle of the main curve (thoracolumbar/lumbar curve) before and after surgery were 48.9 degrees and 11.7 degrees , respectively, with an average correction rate of 76.1%. The average rotation of LIV before surgery was 2.1 degree, and was improved to 1.2 degree after surgery. The interspace angle before surgery, on convex side-bending films, after surgery, at final follow up were 3.2 degrees , -2.3 degrees , 1.8 degrees and 4.9 degrees , respectively. The difference between the interspace angle after surgery and that preoperatively was not significant (P = 0.261), while the interspace angle at final follow-up became larger than that after surgery, and the difference was significant(P = 0.012). The interspace angle after surgery was correlated with that on convex side-bending films (r = 0.418, P = 0.022), and the interspace angle at final follow-up was correlated with that after surgery (r = 0.625, P = 0.000). There was significant correlation between the loss of the interspace angle and the loss of coronal Cobb angle of the main curve during follow-up(r = 0.483, P = 0.007). CONCLUSION The interspace angle could be improved after anterior correction and instrumentation surgery, but it became larger during follow-up. The loss of the interspace angle was correlated with the loss of coronal Cobb angle of the main curve during follow-up.