#193 Biomechanical Modeling of Vertebral Compression Fractures

General Session: What's New in Biologics and Biomechanics

Presented by: A. Mehta

Author(s):

A.K. Mehta (1)
S. Marcinek (1)
S. Lee (1)
T. Slater (1)

(1) Medtronic Spine & Biologics, Research and Development Department, Sunnyvale, CA, USA

Abstract

Introduction: Biomechanical testing of human cadaver spines is a useful tool for the design and development of spinal medical devices. A cadaveric model of vertebral compression fracture (VCF) allows assessment of performance of VCF treatment options in a realistic environment. The objective of this study was to develop a cadaveric model of an anterior wedge VCF (the most clinically relevant fracture type) that can allow biomechanical evaluation of fracture reduction systems.

Methods: Each two functional spinal unit (2FSU) specimen (e.g., T12-L2, L3-L5) was excised from a thoracolumbar cadaver spine and stripped of soft tissues while preserving bone, disc and ligaments. Cortical bone in the anterior wall of the middle vertebra (vertebral level of interest) in the 2FSU was scored in order to induce an anterior wedge fracture. The scored specimen was installed on a multi-axis spine tester (Instron BioPuls). The specimen was then anteriorly flexed within the range of 10°-17° (depending on the specimen and the vertebral levels tested) while simultaneously maintaining zero shear loads. The flexed specimen was then axially loaded in displacement control at 1mm/sec until anterior height loss of the middle vertebra was at least 30%. C-Arm allowed visualization of VCF creation and determination of percentage anterior height loss. An Inflatable Bone Tamp (IBT) was inserted into the fractured vertebra and inflated while the specimen was still on the machine. Operating the spine tester in displacement control, so that the top and bottom fixtures are fixed relative to each other, the performance of the IBT inflation can be measured via data such as lift force, anterior-posterior torque, and medial-lateral torque. Conversely, operating in load control, so that the top fixture can move relative to the bottom fixture, maintaining a constant load, the ability of the IBT to restore height and kyphotic angle in the fractured vertebra can be determined. This test method simulates the clinical use of IBT while collecting data.

Results and Conclusion: A test method has been developed to replicate a VCF and the clinical use of an IBT to treat it. To date, the VCF model has consistently produced an anterior wedge fracture in nine 2FSU specimens, with anterior height loss ranging from 30-40%. Lift force and torque can be plotted against inflation volume to objectively evaluate fracture reduction systems. Height and kyphotic angular restoration is measured from the radiographs of the intact and the fractured vertebra using image processing applications, and is plotted against inflation volume for further analysis. Further research studies are essential to explore the capabilities of the cadaveric VCF model.

VCF Test Set-Up

IBT in Fractured Vertebra