Posterior Correction and Fusion Using a 4D Anatomical Spinal Reconstruction Technique Improves Postural Stability Under the Eye-Closed Condition in Patients with Adolescent Idiopathic Scoliosis

Abstract

Background: Patients with adolescent idiopathic scoliosis (AIS) has been reported to exhibit impaired postural stability. Posterior correction and fusion using four-dimensional (4D) anatomical spinal reconstruction techniques may improve postural stability to correct the spine for optimal anatomical alignment. This prospective study aimed to determine the effect of posterior correction and fusion using a 4D anatomical spinal reconstruction technique on postural stability in the eye-open and eye-closed standing position in patients with thoracic AIS. Methods: Thirty-three patients with AIS, excluding those with Lenke type 5C AIS, participated in the study. The mean and standard deviation of the minimum values of the time-to-boundary (TTB) were determined. All patients were asked to perform the quiet standing position under the eye-open and eye-closed condition on a force plate preoperatively and at 1 week and 2 years postoperatively. The TTB value was calculated from the velocity and distance to the foot boundary of the acquired center-of-pressure data. Results: Under the eye-closed condition, the mean and standard deviation of the minimum TTB were significantly higher at 2 years postoperatively than preoperatively and at 1 week postoperatively. The mean and standard deviation of the minimum TTB values were significantly lower at 1 week postoperatively than preoperatively. Conclusions: The results of this study suggest that surgery using the 4D anatomical spinal reconstruction technique reduces postural stability immediately after surgery; however, it improves postural stability at 2 years compared to the preoperative values.

Keywords: adolescent idiopathic scoliosis; anatomical spinal reconstruction; center of pressure; force plate; prospective study; time-to-boundary.

Figure 1

(A) Preoperative anteroposterior and lateral views of a 17-year-old woman with Lenke type 1A scoliosis, and (B) anteroposterior and lateral radiographs at 2 years postoperatively.

Figure 2

(A) The time-to-boundary (TTB) in each direction is calculated by dividing the distance between the center of pressure (open circle) and the imminent boundary of the foot by the corresponding center-of-pressure velocity. Assume that the center of pressure (COP) was shifting toward the forward and leftward directions. Under such circumstances, the TTB is determined by dividing the distance to the forward and leftward limits of the foot by the velocity. (B) A typical dataset illustrating the displacement of the center of pressure during testing of eye-closed bilateral standing. The minimum distances to the boundaries in the left region (shown by crosses) are identified at the valleys.

Figure 3

Mean and standard deviation values of the mean minimum of the log-transformed time-to-boundary in leftward, rightward, forward, and backward directions during the quiet standing (A) eye-open and (B) eye-closed conditions. Because repeated-measures two-way analysis of variance in all comparisons showed significant interactions, a post hoc test with Bonferroni correction was performed.

Figure 4

Mean and standard deviation values of the minimum of the log-transformed time-to-boundary in leftward, rightward, forward, and backward directions during the quiet standing (A) eye-open and (B) eye-closed conditions. Because repeated-measures two-way analysis of variance in all comparisons showed significant interactions, a post hoc test with Bonferroni correction was performed.