Pre-operative angle of trunk rotation in prone position estimates postoperative correction results

This study investigated whether postoperative rotational deformity in adolescent idiopathic scoliosis patients could be predicted by prone-position pre-operative angle of trunk rotation (ATR). Surgical rib hump correction is performed with the patient in a prone position. However, the association between pre-operative ATR in the prone position and postoperative ATR results is unknown. Thirty-four consecutive patients who underwent skip pedicle screw fixation for Lenke type 1 or 2 adolescent idiopathic scoliosis were retrospectively reviewed. All subjects were followed for a minimum of 1 year. ATR measurements were taken for the standing-flexion position with a scoliometer before surgery and at 1 year afterward. Pre-operative measurements were also taken for the prone position. Correlations between pre- and postoperative ATR were calculated by means of Pearson correlation coefficient. Associations between the correction angle from the standing-flexion position to prone position and postoperative standing-flexion correction angle were determined by linear regression analysis. Pre- and postoperative ATR for the standing-flexion position showed a moderate association (r = 0.64, P < .01). A similar correlation was seen for pre-operative prone-position ATR and postoperative standing-flexion ATR (r = 0.56, P < .01). In linear regression analysis, there was significant proportional error between the correction angle from the standing-flexion position to prone position and postoperative standing-flexion correction angle (β = 0.40, P < .01). In conclusion, pre-operative ATR in either standing-flexion or prone position and postoperative standing-flexion ATR displayed moderate associations. Linear regression analysis revealed that ATR correction angle could be estimated by calculating the correction gains of 0.4° per 1° of correction angle in the prone position.