Three-Dimensional Distribution of Intersegmental Motion on the Entire Intact Thoracolumbar Spine As Measured by a Novel In Vivo/In Vitro Active/Passive Testing Protocol

Advanced image analysis techniques have become available for use in quantifying motion of the spine using plain radiographs (for example, Medical Metrics, Houston, TX). This has allowed quantitative analysis of range of motion and center of rotation of individual motion segments before and after treatment. However, this valuable technology is limited to analysis of static images and also is limited to analyzing the number of levels that are captured on a plain film. In vitro mechanical testing has historically been used to quantify three dimensional motion of the spine in response to loads. In vitro testing affords repeatability and the opportunity for measuring dynamic three dimensional motion, but the clinical relevance of in vitro testing is limited by the fidelity by which in vitro testing mimics the in vivo environment. Commonly, in vitro testing is conducted by application of arbitrary loads on specimens consisting of three motion segments or fewer. In these cases, the loads may not reflect in vivo conditions and additional motion artifact is introduced because motion is constrained to three (or fewer) levels. We have established a novel in vivo/in vitro active/passive 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 dynamic three dimensional motion of individual motion segments of the entire intact thoracolumbar spine during active voluntary motion