Adjacent Level Changes in the Entire Thoracolumbar Spine Following Surgical Intervention as Measured Using a Novel In Vivo/In Vitro Active/Passive Robotic Simulator

For patients with low back pain who fail conservative therapy, surgery is an option. Every surgical procedure alters the native environment in the spine due to the inherent tissue disruption. Procedures with less tissue disruption such as microdiscectomy are less likely to alter the biomechanics and kinematics of the spine following surgery, whereas fusions, which eliminate (or alter) intersegmental motion, are more likely to alter spine kinematics and biomechanics. Long term clinical follow up of fusion patients has led to the identification of adjacent level disease (ALD). However, the relationship between adjacent level disease and surgical intervention remains controversial. Procedures with less tissue disruption, and motion preserving and dynamic stabilization therapies purport to eliminate deleterious effects on adjacent levels, but these assertions have not been confirmed with long term clinical trials. Current analyses are limited short term outcomes and predictive models. In vitro testing affords repeatability and the opportunity for relative comparison between treatments, but the clinical relevance of in vitro testing that is not based on in vivo loads or motions remains questionable. We have established a novel in vivo/in vitro method for quantifying motion of the entire thoracolumbar spine using a robotic simulator, based on active motion. The purpose of this study was to measure the three-dimensional redistribution of motion of the entire thoracolumbar spine following surgical intervention as a means of predicting adjacent level disease.