433 Orientation of the Lumbar Spine During Dynamic Compression Influences Fracture Characteristics

Abstract

INTRODUCTION: Characteristics of lumbar spine fractures dictate patient outcomes and clinical treatment decisions. Understanding injury biomechanics associated with different fracture types can assist injury prediction and development of safety enhancements. METHODS: Twenty human lumbar spines (T12-L5) were isolated and attached to novel whole-column experimental dynamic compressive loading apparatus. Specimens were attached to the lower platform on a drop tower and a decoupled upper platform held a mass to simulate the torso inertially loading the lumbar spine as the lower platform was decelerated at the drop tower base. Each specimen was tested at increasing deceleration magnitudes until failure. Pre-test x-rays were used for the measurements to quantify spinal orientation. Fractures were classified using post-test x-rays and CT scans. RESULTS: Fractures were classified into six categories [Wedge (AO Spine A1): n = 8, Burst (AO Spine A3/A4): n = 7, Hyperextension (AO Spine B2): n = 5]. Spines that sustained hyperextension fractures had significantly larger Cobb angles compared to spines that sustained burst fracture (p = 0.03). Spines that sustained wedge fracture had significantly larger lumbar spine angles (i.e., closer to vertical orientation) compared to spines that sustained burst (p = 0.03) and hyperextension (p = 0.02) fracture. Spines that sustained wedge fracture also had a nearly significant longer horizontal distance between the T12 centroid and the load location compared to spines that sustained burst fracture (p = 0.07). CONCLUSIONS: This study demonstrated that orientation of the lumbar spine at the time of dynamic load application affected fracture characteristics and, therefore, post-injury spinal stability and patient outcomes. The clinical importance of these findings includes a better understanding of injury mechanisms and a recognition that a wide variety of injury outcomes (stable versus unstable; anterior versus middle versus posterior column) can result from identical loading situations with different spinal orientations.