Sawbones comparison of single-rod and double-rod derotation techniques for adolescent idiopathic scoliosis

Background:Although the single-rod derotation technique has been used traditionally to assist in the reduction of thoracolumbar spinal deformity, the double-rod technique may provide improved sagittal reduction. Our goal was to compare these two techniques for thoracolumbar spinal deformity correction. We hypothesized that the single-rod technique would lead to comparable or better correction in the coronal and sagittal planes.Methods:We used eight Sawboness (Pacific Research Laboratories, Inc., Vashon, WA) spine models with King type II deformities and obtained 36-inch anteroposterior and lateral conventional radiographs. The models were assigned, four each, to two technique groups. In each group, two models were instrumented with pedicle screw fixation from the T4 to L1 levels and two were instrumented from the T3 to L1 levels. Monoaxial screw heads were used at the apex level and at the two levels above and below the apex. Polyaxial screw heads were used in the remaining levels. Rods were contoured appropriately to each model, and the reductions were performed as described in the respective literature. Repeat radiographs were obtained, and measurements were recorded and compared.Results:The double-rod technique provided a 58% correction in the thoracic curve, a 55% correction in the lumbar curve, and a 1.1-cm increase in sagittal imbalance. The single-rod technique provided an 84% correction in the thoracic curve, a 75% correction in the lumbar curve, and a 1.5-cm reduction in sagittal imbalance.Conclusions: The single-rod technique achieved better coronal and sagittal correction. The double-rod technique had simultaneous rotation of both rods, leading to an incongruent final position and decreased correction.