Kinematic Analysis of Lumbar Spine Undergoing Extension and Dynamic Neural Foramina Cross Section Measurement Yongjie Zhang1, Boyle C. Cheng2, Changho Oh1, Jessica L. Spehar2 James Burgess3 Summary The spinal column plays a vital biomechanical role in the human body by providing structural support and facilitating motion. As degenerative changes occur in the spine, however, chronic pain can result which frequently forces patient to seek surgical treatment. Such treatments seek to address that pain, frequently by addressing both spinal motion and structural integrity. Spinal implant devices are designed to either restrict motion, e.g., fusion constructs, or preserve motion in a functional spinal unit such as spinal arthroplasty devices. Recent motion restriction designs have allowed new surgical intervention strategies such as interspinous process spacers. The efficacy of these devices has been established clinically and appears to rest on their ability to restrict or minimize motion while unfolding ligamentous structures that, if unchecked, leads to neural compression and disability. In this study, we used novel image processing techniques to characterize the performance of interspinous spacers in addition to standard biomechanical methods of comparison such as range of motion (ROM). Controlled bending protocols for flexibility testing were applied and the three dimensional kinematic response was measured. A sequence of fluoroscopy imaging data were recorded during the flexibility protocol with an interspinous process spacer device placed at L2-L3. A fast marching method and the principal component analysis were developed and utilized for kinematics analysis of lumbar spine undergoing flexion extension bending and dynamic measurement of neural foramina cross section that ideally would be applicable to patient datasets. The implanted level exhibited a major reduction in ROM (approximately 10.4% compared to the intact state in flexion extension bending) but minor change in cross sectional foramina area (about 5.6%). Effectiveness of such devices in extension bending is important from a translational medicine point of view and requires information beyond ROM measures alone.