• Nathan C Ho, Scott J Hollister, Virat Agrawal, Colleen L Flanagan, Chloe Lee, Matthew B Wheeler, Huan Wang, Edward Ebramzadeh, and Sophia N Sangiorgio.
• The J. Vernon Luck, Sr., M.D. Orthopaedic Research Center, Orthopaedic Institute for Children and UCLA Department of Orthopaedic Surgery, Los Angeles, CA.
• Spine. 2023 Feb 15; 48 (4): E46E53E46-E53.

Study DesignPreclinical biomechanical study of topology optimization versus standard ring design for bioresorbable poly-ε-caprolactone (PCL) cervical spine fusion cages delivering bone morphogenetic protein-2 (BMP-2) using a porcine model.ObjectiveThe aim was to evaluate range of motion (ROM) and bone fusion, as a function of topology optimization and BMP-2 delivery method.Summary Of Background Data3D printing technology enables fabrication of topology-optimized cages using bioresorbable materials, offering several advantages including customization, and lower stiffness. Delivery of BMP-2 using topology optimization may enhance the quality of fusion.MethodsTwenty-two 6-month-old pigs underwent anterior cervical discectomy fusion at one level using 3D printed PCL cages. Experimental groups (N=6 each) included: Group 1: ring design with surface adsorbed BMP-2, Group 2: topology-optimized rectangular design with surface adsorbed BMP-2, and Group 3: ring design with BMP-2 delivery via collagen sponge. Additional specimens, two of each design, were implanted without BMP-2, as controls. Complete cervical segments were harvested six months postoperatively. Nanocomputed tomography was performed to assess complete bony bridging. Pure moment biomechanical testing was conducted in all three planes, separately. Continuous 3D motions were recorded and analyzed.ResultsThree subjects suffered early surgical complications and were not evaluated. Overall, ROM for experimental specimens, regardless of design or BMP-2 delivery method, was comparable, with no clinically significant differences among groups. Among experimental specimens at the level of the fusion, ROM was <1.0° in flexion and extension, indicative of fusion, based on clinically applied criteria for fusion of <2 to 4°. Despite the measured biomechanical stability, using computed tomography evaluation, complete bony bridging was observed in 40% of the specimens in Group 1, 50% of Group 2, 100% of Group 3, and none of the control specimens.ConclusionA topology-optimized PCL cage with BMP-2 is capable of resulting in an intervertebral fusion, similar to a conventional ring-based design of the same bioresorbable material.Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc.

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