3-DIMENSIONAL SIMULATIONS OF THE SCOLIOSIS DEROTATION MANEUVER WITH COTREL-DUBOUSSET INSTRUMENTATION

The derotation maneuver using Cotrel-Dubousset instrumentation (CDI) i s intended to correct the counterdirectional transverse plane rotation s of the spine and of the vertebrae in thoracic scoliosis. This was si mulated in a finite element model of an idealized thoracic scoliosis w ith an initial 65 degrees scoliosis angle and 0 degrees kyphosis angle . After 90 degrees of rod rotation the apical vertebra derotated 50 de grees towards the sagittal plane but the apical vertebra axial rotatio n worsened by 8 degrees. The scoliosis angle corrected to 29 degrees a nd a 54 degrees kyphosis was created. If the initial rod curvature was reduced by 9 degrees, the model predicted only small changes in spina l curvature resulting from the forces required to connect the vertebra e to the hooks. Decreased kyphosis and scoliosis curvatures but increa sed vertebra axial rotation were produced by the derotation maneuver. The increase in apical vertebra axial rotation was reversed by modifyi ng the representation of the motion segments by repositioning their ef fective axes 30 mm posteriorly.