Stability of long multiple-rod constructs and dual-rod constructs in the thoracic spine: a biomechanical cadaveric study
Abstract
Spinal fusion to correct spinal deformity is typically performed with a 2-rod construct spanning the targeted area of fusion. More evidence is starting to emerge around the utility of multiple-rod constructs (typically 3 or more rods) to increase the stiffness and stability of a spinal fusion construct. Much of this work has focused on the lumbar spine, and little has been published around how these constructs behave in a long construct spanning the thoracic spine. The purpose of this thesis is to compare the stability of a two-rod (dual-rod) construct (DRC) to a four-rod (multiple-rod) construct (MRC) in cadaveric thoracic spines. Nine intact human cadaveric thoracic spines (T1-T12) were instrumented with either a DRC or MRC, and biomechanical testing was then carried out to compare range of motion (ROM) and stiffness between these two constructs. Results demonstrated comparable absolute total ROM and stiffness between DRCs and MRCs, and this was consistent across all measured vertebral levels. However, after undergoing a 1-hour bodyweight simulation fatigue test, DRCs exhibited an increase in flexion/extension ROM and decrease in stiffness while MRCs did not. Overall, these findings support previous clinical and biomechanical results in the lumbar spine and adult spinal deformity literature that MRCs can potentially be used to increase the stability of thoracic spine constructs.