Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. Fixed-Angle, Posteriorly Connected Anterior Cage Reconstruction Improves Stiffness and Decreases Cancellous Subsidence in a Spondylectomy Model Matthew W. Colman, MD, z Andrew Guss, y Kent N. Bachus, PhD, , y W. Ryan Spiker, MD,  Brandon D. Lawrence, MD,  and Darrel S. Brodke, MD , y Study Design. An idealized biomechanical model. Objective. The aim of this study was to evaluate the biomecha- nical properties of a construct designed to minimize interverteb- ral cage subsidence and maximize stiffness. Summary of Background Data. Reconstruction after vertebral resection typically involves posterior segmental fixation and anterior interbody support. However, poor bone density, adjuvant radiation, or the oncologic need for endplate resection make interbody device subsidence and resultant instrumentation failure a significant concern. Methods. An idealized thoracolumbar spondylectomy recon- struction model was constructed using titanium segmental instrumentation and Delrin plastic. In vivo mechanical stress was simulated on a custom multi-axis spine simulator. Rigid body position in space was measured using an optical motion- capture system. Cancellous subsidence was modeled using a 1 cm thick wafer of number 3 closed-cell Sawbones foam at one endplate. Ten foam specimens were tested in a control state consisting of posterior segmental fixation with a free interbody cage. Ten additional foam specimens were tested in the test state, with the Delrin interbody cage ‘‘connected’’ to the posterior rods using two additional pedicle screws placed into the cage. Foam indentation was quantified using a precision digital surface-mapping device, and subsidence volume calcu- lated using geometric integration. Results. The control group exhibited significantly greater foam indentation after cycling, with a mean subsidence volume of 1906 mm 3 [95% confidence interval (95% CI) 1810–2001] than the connected cage group subsidence volume of 977 mm 3 (95% CI 928–1026 mm 3 ; P < 0.001]. Construct stiffness was greater in the connected cage group (3.1 Nm/degree, 95% CI 3.1–3.2) than in the control group (2.3 Nm/degree, 95% CI 2.2–2.4; P < 0.001). Conclusion. In an idealized spondylectomy model, connecting the anterior column cage to the posterior instrumentation using additional pedicle screws results in a construct that is nearly 40% stiffer and exhibits 50% less cancellous subsidence compared with a traditional unconnected cage. Key words: biomechanics, connected, instrumentation, interbody, reconstruction, spine, spondylectomy, stiffness, subsidence, tumor. Level of Evidence: N/A Spine 2016;41:E519–E523 I n the setting of vertebral body bone loss in the mobile spine, anterior column reconstruction may be employed to correct coronal or sagittal alignment, improve fusion rates, limit posterior fusion extent, and to provide biome- chanical support for the posterior tension band. Modern options include structural allograft, autograft, or static, modular, or expandable synthetic cages, with or without anterior plate or rod systems. 1–6 In most circumstances, fusion will occur even in the face of limited cage subsidence, and the reconstruction hardware will become secondary to biologic bony support. However, there are certain clinical scenarios wherein the biomechanical or biologic attributes of the local anatomy are so disrupted that biologic reconstitution will not occur or will significantly lag the fatigue point of the synthetic reconstruction hardware. Examples include any scenario From the  Department of Orthopaedics, University of Utah School of Medicine; y Orthopaedic Research Laboratory, University of Utah Ortho- paedic Center, Salt Lake City; and z Department of Orthopedic Surgery, Rush University Medical College, Chicago, IL. Acknowledgment date: May 6, 2015. First revision date: October 13, 2015. Acceptance date: October 13, 2015. The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication. No funds were received in support of this work. Relevant financial activities outside the submitted work: consultancy, royalties, stocks, grants, payment for lectures. Address correspondence and reprint requests to Darrel S. Brodke, MD, University of Utah Department of Orthopaedics, 590 Wakara Way, Salt Lake City, UT 84108; Tel: +801 587 5450; E-mail: Darrel.brodke@hsc.utah.edu DOI: 10.1097/BRS.0000000000001312 Spine www.spinejournal.com E519 SPINE Volume 41, Number 9, pp E519–E523 ß 2016 Wolters Kluwer Health, Inc. All rights reserved BIOMECHANICS