Concepts of Surgical Correction-Segmental Derotation and Translation Techniques John H. Chi, MD, MPH * , Ryan Lee, BS, Praveen V. Mummaneni, MD Division of Neurospinal Disorders, Department of Neurosurgery, University of California, 505 Parnassus Avenue, M779, PO Box 0112, San Francisco, CA 94143, USA Spinal deformity surgery once aimed only at stopping progressive disfigurement. With modern techniques, spinal deformity surgery now attempts not only to stop the structural imbalance but to reduce it back to as normal an alignment as possible. New surgical tools, advanced instrumen- tation, and innovative operative techniques allow the spine surgeon to reduce and reconstruct pre- viously inoperable or uncorrectable deformities. In idiopathic scoliosis, the spine can be imbal- anced in all three of its planes: sagittal, coronal, and axial. Sagittal deformity in scoliosis can be seen as hypokyphosis, hyperkyphosis, or lordosis of the thoracic spine. Coronal deformity appears as lateral deviations resulting in major and minor curves in the thoracic and lumbar spine. These cause trunk imbalance over the pelvis and shoul- der imbalance over the trunk. Axial deformity attributable to rotation, typically at the apical vertebrae, can induce the disfiguring rib hump of scoliosis. Consequently, deformity in any one plane does not develop in isolation and seems to be coupled to curvature, rotation, and translation in the other planes [1,2]. Thus, complete correc- tion of spinal deformities requires attention to all three planes, which is the basis of the recent Lenke classification system. Segmental correction Early techniques of deformity correction com- prised nonsegmental anchoring instrumentation at the adjacent normal structural level, with no fixation at the levels between. Nonsegmental correction with Harrington distraction or com- pression rods, which are anchored by hooks at the upper and lower stable vertebrae, relied on single- vector forces for reduction of deformity and achieved acceptable coronal correction. These methods resulted in significant sagittal plane complications, namely, iatrogenic flatback syn- drome, however [3]. Segmental correction is simply defined as the application of corrective forces at each required segment of the deformed spine. The earliest versions of segmental correction used sublaminar wiring to Luque rods at individual segments of the spine to achieve reduction and stabilization [4]. Sublaminar wiring would typically begin on the concave side, reducing the scoliotic spine by trans- lating it toward the rod as the wires were sequen- tially shortened. Newer wiring techniques using specialized rod frames have reported excellent re- sults with greater than 50% correction of the ma- jor curve, 31% apical derotation, and greater than 95% shoulder and trunk imbalance [2,5]. The development of hook instrumentation (Cotrel-Dubousset instrumentation) allowed rigid polysegmental fixation for the first time [6]. Hook pullout and rostral-caudal end failure were con- stant problems, however [7,8]. Wiring and hook constructs allowed for correction of scoliosis and translational deformity [9] but were reported to be inadequate for rotational correction because of the lack of torque necessary for triplanar cor- rection [8,10–12]. Modern pedicle screw instru- mentation now provides rigid segmental fixation far surpassing that of previous techniques and * Corresponding author. E-mail address: chijo@neurosurg.ucsf.edu (J.H. Chi). 1042-3680/07/$ - see front matter Ó 2007 Published by Elsevier Inc. doi:10.1016/j.nec.2007.02.004 neurosurgery.theclinics.com Neurosurg Clin N Am 18 (2007) 325–328