Do Discs Open Anteriorly With Posterior-Only Correction of Scheuermann's Kyphosis?

Study Design. Retrospective radiographic analysis. Objective. To investigate where and to what degree the correction of Scheuermann's kyphosis occurred in two different procedures: posterior instrumentation/fusion with an anterior release and posterior-only instrumentation/fusion with Ponte procedure. Summary of Background Data. Controversy remains regarding the outcome for these two procedures. The postoperative segmental disc shape change that account for deformity correction has not been described for either procedure. Methods. Eleven patients undergoing a thoracoscopic anterior release followed by posterior instrumentation (A + P) and 11 patients having posterior-only (PO) instrumentation/fusion were retrospectively reviewed. In addition to conventional Cobb measurements, segmental measures of intradiscal angulation as well as anterior and posterior disc heights were made before and after surgery. Results. The thoracic hyperkyphosis was corrected to similar degrees in both groups (A + P vs. PO, P = 0.87). The PO group averaged 82.7 degrees +/- 6.4 degrees before surgery and corrected to 47.9 degrees +/- 5.4 degrees after surgery; while the A + P group averaged 84.9 degrees +/- 10.2 degrees before surgery and corrected to 48.6 degrees +/- 5.7 degrees after surgery. The segmental analysis demonstrated similar degrees of intradiscal angular changes between the two surgical procedures. The majority of the correction occurred at and below the apex and was independent of an anterior release. The changes in both anterior and posterior disc thicknesses were also similar between the two groups. Both groups' anterior disc spaces opened at T8 and below, whereas maximum anterior disc opening occurred at the thoracolumbar junction. To a lesser extent, the posterior disc heights were reduced, but also to similar degrees for both surgical approaches. Conclusion. For both surgical procedures, the majority of the kyphosis correction occurred in the lower thoracic levels and anterior disc heights increased up to twice as much as posterior disc heights shortened. The addition of the anterior release did not significantly alter the degree of correction or the disc shape changes.