Multilevel Spinal Growth Modulation With an Anterolateral Flexible Tether in an Immature Bovine Model

Study Design. A bovine model was used to evaluate the effects of a multilevel anterolateral flexible tether in a growing spine. Objective. To evaluate the radiographic changes in a growing spine with a multilevel anterolateral tether. Summary of Background Data. Spinal growth modulation has long been considered as a conceptually attractive and elegant possible alternative to arthrodesis in the treatment of idiopathic scoliosis. Although some experimental studies have described spinal growth modulation, few have described a purely mechanical tether. Clinical studies of spinal epiphysiodesis have described inconsistent curve stabilization and/or correction. Methods. A total of 33 one-month-old male calves underwent a single thoracotomy and placement of vertebral screws at T6–T9. In 11 animals, one screw per level was connected by a 3/16 in. stainless steel cable (single tether). In 11 animals, two screws per level were connected by two cables (double tether). In the remaining 11 animals, single screws in each level were left unconnected (control). After 6 months, the spines were harvested and underwent radiographic analysis. Results. In the control group, there was little change in the coronal and sagittal measurements during the survival period. In the single tether group, there was variable instrumentation fixation and inconsistent creation of coronal deformity, which ranged from 0° to 31°. The double-tether group had more consistent creation of deformity, ranging from 23° to 57°. Conclusions. Given adequate bony fixation, a flexible lateral spinal tether can affect growth modulation. This technique of growth modulation may serve as a future fusionless method of correction in a growing patient with scoliosis.