Vertebroplasty comparing injectable calcium phosphate cement compared with polymethylmethacrylate in a unique canine vertebral body large defect model Thomas M. Turner, DVM, Robert M. Urban, PhD, Kern Singh, MD, Deborah J. Hall, BS, Susan M. Renner, MS, Tae-Hong Lim, PhD, Michael J. Tomlinson, DVM, PhD, Howard S. An, MD* Department of Orthopedic Surgery, Rush University Medical Center, 1725 Chicago, IL 60612, USA Received 10 September 2006; accepted 13 December 2006 Abstract BACKGROUND CONTEXT: Vertebroplasty was developed to mechanically reinforce weakened vertebral bodies. Polymethylmethacrylate (PMMA) bone cement has been most commonly used but carries risks of thermal injury and respiratory and cardiovascular complications. Calcium phosphate (CaP) offers the potential for biological resorption and replacement with new bone, restoring vertebral body mass and height. PURPOSE: To compare compressive strength, elastic modulus of the adjacent motion segments, and histologic response of vertebral bodies injected with either CaP or PMMA in a canine verte- broplasty model. STUDY DESIGN: By using a canine vertebroplasty model, two level vertebroplasties were per- formed at L1 and L3 and studied for 1 month (n510) and 6 months (n510). In each canine, one vertebral defect was randomly injected with either CaP cement (BoneSource; Stryker, Freiberg, Germany) or PMMA. METHODS: Twenty dogs had an iatrogenically created cavitary lesion at two nonadjacent levels injected with either CaP or PMMA. Canines from each group were tested mechanically (n55) and histologically (n55). Histology consisted of axial sections of the L1 and L3 vertebral bodies and high-resolution contact radiographs. Sections from each specimen were embedded in plastic with- out decalcification to study the bone-cement interface. Bone-cement interfaces were compared for evidence of necrosis, fibrosis, foreign body response, cement resorption, and new bone formation between the PMMA and CaP treatments groups. Mechanical compression testing was performed on specimens from the 1-month (n55) and 6-month (n55) time periods. The T13 vertebral body was used as an intact control for the destructive compression testing of L1 and L3. Each vertebral body was compressed to 50% of its original height under displacement control at 15 mm/min to simulate a nontraumatic loading situation. Force and displacement data were recorded in real time. RESULTS: Vertebral sites containing PMMA were characterized by a thin fibrous membrane. PMMA was detected within the trabeculae, vascular channels, and the spinal canal. Unlike PMMA, CaP underwent resorption and remodeling with vascular invasion and bone ingrowth. Woven and lamellar bone was found on the CaP cement surface, within the remodeled material, and on the sur- rounding trabeculae. Vertebral body compression strength testing revealed no significant difference in vertebral body height and compressive strength between PMMA and CaP. There was a trend for CaP-treated vertebrae to increase in compressive strength from 1 month to 6 months, whereas PMMA decreased compressive strength when compared with adjacent nontreated vertebrae. Supported by Stryker Howmedica Osteonics, Inc. FDA device/drug status: approved for this indication. Nothing of value received from a commercial entity related to this manuscript. * Corresponding author. 1725 W Harrison St. #1063, Chicago, IL 60612. E-mail address: han@ortho4.pro.rpslmc.edu (H.S. An) 1529-9430/08/$ – see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.spinee.2006.12.007 The Spine Journal 8 (2008) 482–487