The Effect of Ponte Osteotomies on the Sagittal Shape of Rods and Spine Derotation in Adolescent Idiopathic Scoliosis: A Single-Center, Retrospective Cohort Study

BACKGROUND: Adding a Ponte osteotomy (PO) to other surgical techniques for correcting adolescent idiopathic scoliosis (AIS) profoundly affects the entire sagittal shape of the rod. POs are an effective procedure for correcting thoracic hypokyphosis in patients with AIS. METHODS: A retrospective review of 40 patients with AIS was conducted. The sample was divided into 2 groups: PO and non-PO. On a lateral radiograph, the rod end angle (A) was calculated using the intersections of the tangents with the rod end points. The maximal deflection (D) was obtained for each rod. In addition, the rod apex angle (B) was calculated using the intersection of the tangents at 2 points, each 1 cm to 1 side of the rod apex; the distance between the rods at the apex was then measured. RESULTS: Concave rods tended to be straight or even lordotic at the apex in the non-PO group (−0.9° vs. +5.9° in the PO group; P = 0.000). The rod end angle and deflection were significantly lower in the non-PO group (15.2° and 7.1 mm vs. 26.3° and 17.8 mm in the PO group; P = 0.000 and P = 0.000). The convex rods were less kyphotic in the non-PO group; for the non-PO group, the end angle and deflection were 27.6° and 16 mm versus 33.4° and 23.8 mm in the PO group (P = 0.03 and P = 0.000). No significant difference between the groups was observed for the convex rod apex angle (P = 0.8). The rod apices were more superimposed in the PO group (2.9 mm vs. 9.3 mm in the non-PO group; P = 0.000). CONCLUSIONS: POs increase the overall sagittal kyphosis and improve the three-dimensional derotation of the apex in patients with AIS.