Yonsei Medical Journal Vol. 46, No. 3, pp. 372 - 378, 2005 Cortical Margining Capabilities of Fins Associated with Ventral Cervical Spine Instrumentation Byung-Ho Jin, Heum-Dai Kwon, and Yong-Eun Cho Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Korea. Fins incorporated into the design of a dynamic cervical spine implant have been employed to enhance axial load- bearing ability, yet their true biomechanical advantages, if any, have not been defined. Therefore, the goal of this study was to assess the biomechanical and axial load-bearing contribu- tions of the fin components of the DOC ventral cervical stabili- zation system. Eighteen fresh cadaveric thoracic vertebrae (T1-T3) were obtained. Three test conditions were devised and studied: Condition A (DOC implants with fins were placed against the superior endplate and bone screws were not inserted); Condition B (DOC implant without fins was placed and bone screws were inserted); and Condition C (DOC implant with fins were placed against the superior endplate and bone screws were inserted). Specimens were tested by ap- plying a pure axial compressive load to the superior platform of the DOC construct, and load-displacement data were col- lected. Condition C specimens had the greatest stiffness (459 ± 80 N/mm) and yield load (526±168 N). Condition A speci- mens were the least stiff (266±53 N/mm), and had the smal- lest yield loads (180±54 N). The yield load of condition A plus condition B was approximately equal to that of condition C, with condition A contributing about one-third and condition B contributing two-thirds of the overall load-bearing capacity. Although the screws alone contributed to a substantial portion of axial load-bearing ability, the addition of the fins further increased load-bearing capabilities. Key Words: Biomechanics, cervical plate, fins INTRODUCTION Cervical corpectomy with vertical strut grafting Received December 23, 2004 Accepted February 4, 2005 Reprint address: requests to Dr. Byung-Ho Jin, Department of Neurosurgery, Yongdong Severance Hospital, Yonsei University College of Medicine, 146-92 Dogok-dong, Kangnam-gu, Seoul 135- 720, Korea. Tel: 82-2-3497-3395, 3497-3390, Fax: 82-2-3461-9229, E-mail: bhjin61@yumc.yonsei.ac.kr Yonsei Med J Vol. 46, No. 3, 2005 and plating is a common surgical technique for treating degenerative and traumatic conditions of the cervical spine. The graft acts as an axial load-bearing strut, while providing a substructure for bony ingrowth and biological bonding and integration during the fusion process.1,2 An ideal ventral plating system not only minimizes the chance of strut graft extrusion, but also provides immobility and helps to maintain alignment.3-9 However, complications such as graft collapse, graft extrusion, graft subsidence with endplate fracture, pseudoarthrosis, and failure of fusion may occur after surgery.4,10,11 There are many factors that may contribute to the development of these complications, such as implant failure, im- plant-bone interface failure, and bone-bone inter- face failure. The majority of the applied axial loads stress the point of contact between the vertebral body and the bone graft. Therefore, the interface between the bone graft and the vertebral body is associated with a greater risk of failure. The ventral approach to the cervical spine is often complicated by the subsidence of interbody grafts into the vertebral bodies. This process in- volves a combination of the pistoning of the strut into the vertebral bodies, the collapse of the graft itself, and angular deformation of the cervical lordosis. A sub-optimal "fit" between the bone graft and the vertebra, which is a common techni- cal error, also contributes to the problem. Subsi- dence is usually exaggerated by an inadequate weight bearing capacity of the bone graft, verte- bral body, and implanted device. Overall, it is the axial load resisting ability of the graft, both endplates, and the vertebral implant that affects the fusion process in the postoperative period. Theoretically, a stronger construct can be achieved