Study design: This study analyzed intraoperatively the three-dimensional displacement of vertebrae during rotation of the Cotrel-Dubousset rod for scoliosis correction, using an optoelectronic method.
Objective: To evaluate three-dimensional transitions and rotations of instrumented and uninstrumented vertebrae, produced by the Cotrel-Dubousset instrumentation "derotation" maneuver.
Summary of background data: Published reports indicate that Cotrel-Dubousset instrumentation has been more effective in producing spinal derotation than vertebral axial derotation, but no study analyzed intraoperatively the effects on the vertebrae produced solely by rotation of the rod.
Methods: Eight patients with idiopathic scoliosis treated with Cotrel-Dubousset instrumentation underwent intraoperative optoelectronic monitoring using infrared cameras (Vicon). Markers were implanted in the spinous processes of the lower and upper instrumented vertebrae (LIV, UIV), the adjacent uninstrumented vertebrae below and above (-LIV, +UIV), and the apical vertebra. During rod rotation, acquisition and processing of cameras data were performed to obtain three-dimensional displacements of vertebrae.
Results: Translations and rotations of LIV and UIV were in identical directions to those of -LIV and +UIV, respectively. Orientation of the LIV hook influenced the displacement of LIV and -LIV. Posterior translation of the apical vertebra was commonly observed in thoracic King II, III, or V curvatures (apical vertebra = T9), and anterior translation in King I and IV and thoracolumbar curvatures (apical vertebra = T11-T12). Axial rotation of the apical vertebra was increased in thoracic curvatures and decreased in thoracolumbar and lumbar curvatures. Lateral translation was the major displacement observed.
Conclusions: Rotation of the rod produces rotational and translational changes along each axis. These results are preliminary, but substantial. Technical improvement would allow more accurate results in the near future.