Derotation of the Spine Suken A. Shah, MD a,b, * a Department of Orthopedic Surgery, Alfred I. duPont Hospital for Children, Nemours Children’s Clinic, 1600 Rockland Road, PO Box 269, Wilmington, DE 19899, USA b Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA, USA With the application of modern techniques of instrumentation for idiopathic scoliosis, it is now possible to address correction of the deformity in three dimensions. Historically, Harrington instru- mentation addressed the coronal plane with distraction forces applied along the concavity of the curve but was observed to create iatrogenic flatback by decreasing thoracic kyphosis or lum- bar lordosis. Segmental instrumentation with hooks, wires, or hybrid instrumentation addressed these sagittal plane concerns to some extent but was insufficient to correct the axial plane rota- tional deformity present in idiopathic scoliosis. Proponents of the Cotrel-Dubousset procedure [1] believed that rotational correction of the scoliosis would occur with the rod derotation maneuver, but this was later disproved with pre- and postop- erative CT scans of instrumented patients. Labelle and colleagues [2] used three-dimensional digi- tizers during surgery; they showed that the Co- trel-Dubousset rod derotation maneuver did exert coronal and sagittal plane correction and re- located the instrumented portion of the spine but that little axial plane rotation had occurred. Hook and wire fixation lacks the ability to derotate the spine, because force is applied posterior to the instantaneous axis of rotation (IAR) and the moment arm is inadequate to apply sufficient tor- que. True correction of axial plane vertebral rota- tion, and consequent elimination of the convex thoracic or thoracolumbar prominence, is difficult to achieve without anterior diskectomy and chest wall violation with thoracoplasty. Pedicle screws and derotation of the spine The challenges of three-dimensional correction of scoliosis with posterior-only surgery are well addressed with the use of segmental pedicle screw fixation and, specifically, the application of direct vertebral rotation, as first described by Lee and colleagues [3]. Pedicle screws extend into the verte- bral body anterior to the IAR and can be manip- ulated with the use of long derotator instruments attached to the screw heads to achieve true three- dimensional correction of the scoliotic deformity. Segmental fixation with pedicle screws addresses the most rigid rotated portion of the spine, spreads the corrective force over multiple im- plants, can pull the concavity out of the chest, and results in little loss of correction over time. Assessment of axial rotation The clinical examination of a typical patient with thoracic scoliosis can reveal the nature of the coronal plane deviation along the curve(s), the hypokyphosis or apical lordosis in the sagittal plane, and the axial plane rotation present along the apex of the curve, as seen by an elevation of the ribs along the convexity and a relative de- pression of the ribs along the concavity (Fig. 1). The Adams forward bend test gives a more appar- ent picture of rotation and posterior topography; when combined with an inclinometer, it can attempt to quantify the rib prominence in degrees of axial trunk rotation. CT is the ‘‘gold standard’’ for accurate assess- ment of vertebral rotation but is limited in its * Department of Orthopaedic Surgery, Alfred I. du- Pont Hospital for Children, Nemours Children’s Clinic, 1600 Rockland Road, PO Box 269, Wilmington, DE 19899. E-mail address: sshah@nemours.org 1042-3680/07/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.nec.2007.02.003 neurosurgery.theclinics.com Neurosurg Clin N Am 18 (2007) 339–345