vertebrae were divided into Black line or non-Black line. On lateral view at 6 months X-p, pseudarthrosis and kyphosis were evaluated. Dynamic mo- tion or cleft sign in fractured vertebra was defined as pseudarthrosis. Ky- phosis rate was obtained by subtracting the anterior vertebral height in the injured vertebra from the average anterior vertebral height of the normal vertebrae above and below the injured vertebra in the lateral images and dividing the value by the average vertebral height of the normal vertebrae. Kyphosis progression rate was obtained by subtracting the kyphosis rate on initial examination from that at 6 months and dividing the value by the ini- tial examination. All measurements were performed with the investigator blinded concerning the patient’s name, clinical findings, and other imaging data. Visual analogue scale for back pain (VAS) was evaluated at 6 months examination. The chi-square test was used for pseudarthrosis rate, and the Student’s t-test was used for kyphosis progression rate and VAS. p ! .05 was taken as a statistically significant difference. RESULTS: Fourteen of 63 vertebrae (22%) resulted in pseudarthrosis. Powder sign (n516) included 0 (0%) pseudarthrosis, and non-Powder sign (n547) included 14 (30%), and Powder sign included pseudarthrosis sig- nificantly less than non-Powder sign (p5.01). Sensitivity of bone union by Powder sign was 33%, and specificity of that was 100%. Black line (n524) included 11 (46%) pseudarthrosis, non-Black line (n539) included 4 (10%), and Black line included pseudarthrosis significantly more than non-Black line (p5.004). Sensitivity of pseudarthrosis by Black line was 71%, and specificity of that was 71%. Kyphosis progression rate of Powder sign was 11% (621%) and that of non-Powder sign was 23% (625%), and there was no significant difference (p5.08). Kyphosis progression rate of Black line was 32% (622%) and that of non-Black line was 13% (622%), and there was a significant difference (p5.003). The average value of VAS of powder sign was 26mm (618 mm) and that of non- Powder sign was 28 mm (623 mm), and there was no significant differ- ence. The average value of VAS of Black line was 35mm (626 mm) and that of non-Black line was 23 mm (617 mm), and there was a signif- icant difference (p5.04). CONCLUSIONS: On MRI STIR, Powder sign can predict bone union, and Black line was the risk factor of pseudarthrosis, kyphosis progression and back pain on osteoporotic vertebral fractures. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2011.08.237 Friday, November 4, 2011 4:45–5:45 PM Focused Paper Presentations: Biomechanics 183. In Vivo Evaluation of a Novel Expanding Pedicle Screw: A Six-Month Study in a Sheep Model Mark Levy, MD, ScD 1 , Ory Keynan, MD 2 , Orna Popper 3 , Elad Sapir 3 , Yair Spanier 3 , Michal Ruchelsman 3 , Jaffar Hleihil 3 ; 1 Technion Israel Institute of Technology, Haifa, Isreal; 2 Kokhav Yair, Isreal; 3 Expanding Orthopedics, Caesarea, Isreal BACKGROUND CONTEXT: Solid fixation of pedicle screws is the cor- nerstone of successful spinal fusion. It’s particularly important in compro- mised bone quality such as elderly population, various bone pathologies and revision surgery. Early fixation of pedicle screws as well as long term implant osteointegration, minimize the rate of failure optimizing the chan- ces of fusion. PURPOSE: The objective of the study was to evaluate in-vivo a novel ti- tanium expanding pedicle screw, comprising a screw section in the pedicle and a 4-wing expandable portion in the vertebral body. The study assessed the mechanical performance and biological fixation with time, including implantation and deployment, characterization of bone ingrowth on the exterior and interior surface of the expandable portion and the ability to remove the screw after bone ingrowth. STUDY DESIGN/SETTING: A GLP-compliant animal study using stan- dard and expanding pedicle screws for lumbar spine fusion. PATIENT SAMPLE: Eleven skeletally-mature Suffolk sheep, 80-120 kg at implantation day. OUTCOME MEASURES: Clinical and radiographic data, histology of specimens, deployment and un-deployment, removal of the expanding ped- icle screw. METHODS: Lumbar spines of 11 sheep were implanted with a total of 44 expanding pedicle screws Ø5.8 mm and 22 standard pedicle screws Ø5.5 mm (control), using standard spinal fusion techniques and instrumen- tation. In each spine 6 screws were inserted, one per vertebra, through a standard posterior trans-pedicle approach, in 3 one-level unilateral fusion pairs: one pair of controls and 2 pairs of expanding pedicle screws. Each pair was connected using Ø5 mm rods. No discs were removed and no bone graft was added. Pre and post-operative x-ray films were obtained. The animals were kept up to 180-day follow-up period with no activity restriction. Intermediate time points were at 35, 77 and 90 days post- operation. At the end of each time point, the animals were sacrificed and the spines were harvested for removal of the screws or histological evaluation. RESULTS: Successful deployment of the expanding pedicle screws was achieved in all implanted screws using an active mechanism. The histologi- cal analysis demonstrated osteointegration of the expanding pedicle screw in exterior and interior surface of the expandable portion from the 35-day time point and onward. The average amount of bone ingrowth inside the expand- able area was elevated with each consecutive time point showing maturation of the bone matrix from woven bone to lamellar osteonal bone over time. Removal of the expanding pedicle screws was achieved for all screws despite the bone ingrowth, due to an active undeployment mechanism allowing col- lapse of the expandable area and removal through the pedicle. CONCLUSIONS: Implantation and deployment of a novel expanding pedicle screw was demonstrated in the lumbar spine of mature sheep. The increased surface area of the metal-bone interface allowed immediate fixation. The increased osteointegration with time, as well as bone in- growth inside the expandable area, provided a progressively robust fixation of the screw within the vertebral body. The immediate mechanical fixation followed by the long-term biological fixation was designed to enhance construct stability and subsequent fusion. The ability to undeploy and re- move the screws demonstrated the mechanical properties of this novel screw and its instrumentation. FDA DEVICE/DRUG STATUS: Expanding Pedicle Screw: Not approved for this indication. doi: 10.1016/j.spinee.2011.08.239 184. Biomechanical Aspects of Pedicle Screw Loosening in the Lumbar Spine Joel Boerckel, PhD 1 , Liz Peters 2 , Lalissie Merga 3 , Tamkeenat Syed 4 , Mona Arabshahi 3 , Rick Chappuis, PA-C 3 , James Chappuis, MD, FACS 5 ; 1 Georgia Tech, Atlanta, GA, USA; 2 Ball Ground, GA, USA; 3 Atlanta, GA, USA; 4 Crystal Lake, IL, USA; 5 Orthopaedic & Spine Surgery of Atlanta, Atlanta, GA, USA BACKGROUND CONTEXT: Previously at NASS, we reported that removal of pedicle screws following fusion resulted in significant reduc- tion in pain and medication use and increased activity and quality of life. As posterior pedicle screw systems increase in strength and rigidity, more loads are present at the bone screw interface and loosening can occur. PURPOSE: The purpose of this study was to quantify pedicle screw loos- ening using insertion and removal torque and evoked EMG measurement and identify factors which may predict loosening. STUDY DESIGN/SETTING: Patients received either pedicle screw in- sertion or removal at Emory University Hospital, Midtown, Atlanta, GA. 96S Proceedings of the NASS 26th Annual Meeting / The Spine Journal 11 (2011) 1S–173S All referenced figures and tables will be available at the Annual Meeting and will be included with the post-meeting online content.