STUDY DESIGN/SETTING: Prospective clinical cohort. PATIENT SAMPLE: 16 subjects with operative AIS. OUTCOME MEASURES: COM and COP interaction and COM sway. METHODS: Prospective clinical, radiographic, and formal 3D motion- capture gait analysis were collected pre- and post spinal fusion for AIS (n, 5, 16). COM-sway was calculated based on side-to-side displacement from a straight line fitted to the patient’s path. In sagittal and coronal planes, the left- and right-sided peak COM-COP inclination angles were also mea- sured during gait. Pre- and Postoperative COM sway, and sagittal/coronal plane left- and right-sided peak inclination angles were evaluated with paired t-test. Multivariate analysis was used to identify radiographic param- eters with the greatest influence on motion. RESULTS: Sixteen patients (12 females, age 14.4 þ/- 3.8 at surgery, with predominantly 1AN and 5CN curves) were included in the analysis. Sixteen patients were included in the analysis. The preoperative COM peak lateral displacement decreased from a mean of 7.2 cm (SD58.0) to 2.6 cm (SD52.5) (p50.012). In the sagittal plane left pre- and postopera- tive means of peak inclination angles were 25.6  and 21.6  (p50.029), and right pre- and postoperative means were 26.4 and 22.8 (p50.026), while left and right coronal peak inclination did not reach significance (p50.349 and 0.055, respectively). A multivariate linear regression identi- fied changes in sagittal alignment parameters thoracic kyphosis (TK) and sagittal vertical alignment (SVA) (R250.717) as predictors of the change in COM lateral displacement after spinal fusion surgery for AIS patients. An increase in TK was associated with reduced COM lateral displacement, while reducing SVA was associated with reduced displacement. CONCLUSIONS: Results show reduction in lateral sway after fusion as measured by lateral displacement of the COM during gait. Previous reports demonstrate the average lateral displacement is about 5 cm for normal gait. These data suggest that spine fusion surgery can improve gait efficiency as indicated by reducing COM sway. The sagittal plane is shown to be espe- cially important and radiographic parameters in this plane may be more important for motion performance in the AIS population than previously thought. It is unclear if changes represent reduced motion from fusion or an energy-efficient adaptation to curve correction. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2013.07.333 P60. The Unknown Primary Tumour Presenting as Metastatic Spinal Cord Compression Nasir A. Quraishi, MD 1 , Sakthivel Rajan Rajaram Manoharan, MS 1 , Georgios Arealis, MD, PhD 1 , Hossein Mehdian, FRCS 2 , Bronek M. Boszczyk, MD 3 ; 1 Queen’s Medical Centre, Nottingham, UK; 2 Nottingham, England, UK; 3 The Centre for Spinal Studies and Surgery, Nottingham, UK BACKGROUND CONTEXT: Patients presenting with MSCC due to an unknown primary (UKP) present an interesting problem with limited liter- ature available to provide guidance on management. PURPOSE: Our aim was to analyse all patients with MSCC due to an UKP, review their outcome and treatment (with comparisons to those with a known primary). STUDY DESIGN/SETTING: We hypothesized that patients with MSCC due to an unknown primary have worse neurological outcome and poorer survival and we investigated whether this hypothesis is true. PATIENT SAMPLE: Of the 243 patients with MSCC 14 had compression due to an UKP (5.7 %; mean age 61 years, 3 M, 11 F). OUTCOME MEASURES: Neurological outcome (Frankel grade). METHODS: All data were collected retrospectively from October 2004- October 2009, then prospectively from October 2009-Oct 2011 (7 years). We reviewed all patient records held on the database, including patient de- mographics, primary tumour, neurological outcome (Frankel grade), com- plications and survival. RESULTS: During the 7 year study period, out of the 302 patients who underwent emergency surgery for MSCC, 243 patients were included in whom complete information was available. Of these, 14 patients presented with MSCC due to an UKP (5.7 %; mean age 61 years, 3 M, 11 F). Most UKP had a histological diagnosis of adenocarcinoma (9/14; 64%), largely from the lung (3/14; 21.4%). When compared to those with a known pri- mary, the UKP group had a significantly longer duration of symptoms prior to surgery (124 days versus 38 days, p !0.05), a trend towards worse neu- rological outcome (p50.17), a similar complication rate (29% vs 35%, p O 0.05), similar revised Tokuhashi score (8 vs 9, p O 0.05) and an incli- nation to poorer survival (268 days vs 385 days, p O0.05). CONCLUSIONS: In our series, patients with MSCC due to an UKP (5.7 %) appeared to have longer duration of symptoms prior to surgery, but a trend towards worse neurological outcome and poorer survival. Our ex- perience would suggest that we need to treat these patients expeditiously. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2013.07.334 P61. Hospital Outcomes of Multiple-Level Anterior and Posterior Cervical Fusions from 2002-2009 Steven J. Fineberg, MD 1 , Sreeharsha V. Nandyala, BA 2 , Alejandro Marquez-Lara, MD 3 , Matthew W. Oglesby, BA 2 , Miguel A. Pelton, BS 2 , Alpesh A. Patel, MD, FACS 4 , Kern Singh, MD 3 ; 1 Chicago, IL, US; 2 Midwest Orthopaedics at Rush University Medical Center, Chicago, IL, US; 3 Rush University Medical Center, Chicago, IL, US; 4 Northwestern Department of Orthopaedics, Chicago, IL, US BACKGROUND CONTEXT: Anterior and posterior cervical fusions (ACF and PCF) are commonly performed for both single level and mul- ti-level degenerative pathologies. The epidemiology, complication rates, and cost differences based upon the number of fusion levels is not well characterized. PURPOSE: To characterize differences in cervical fusions based on the number of levels fused, a population-based database was analyzed with re- gards to patient demographics, complications, mortality, and costs. STUDY DESIGN/SETTING: Retrospective national database analysis. PATIENT SAMPLE: Patients undergoing ACF or PF recorded in the Na- tionwide Inpatient Sample (NIS) database from 2002-2009. OUTCOME MEASURES: Length of stay, in-hospital costs, mortality, and rates of in-hospital pulmonary embolism (PE), deep vein thrombosis (DVT), wound infections, cardiac events, hematomas, cerebrospinal fluid (CSF) leaks, shock, and neurologic complications. METHODS: Data from the NIS of the Health care Cost and Utilization was obtained for each year from 2002-2009. Patients undergoing ACF and PCF were identified and separated into cohorts by number of levels fused (1-2 levels or 3 or greater levels). Patient demographics, co-morbid- ities, hospitalization days, costs, and major complications were assessed. SPSS v.20 was used to assess statistical significance using the c2 test for categorical data and ANOVA for continuous data. Due to the large sam- ple size, a p-value ! 0.0005 was used to denote statistical significance. RESULTS: There were 111,240 patients undergoing 1-2 level ACFs ver- sus 44,201 patients undergoing a greater than 3 level ACF. PCFs numbered 7,581 for single or two level fusions versus 9074 multilevel ( O 3) posterior procedures. Patients in ACF and PCF cohorts undergoing 3 or more fusion levels were older with more co-morbidities than 1-2 level fusions (p ! 0.0005). ACF and PCF patients undergoing 3þ levels of fusion had in- creased hospitalizations and costs and experienced a statistically signifi- cant increase in mortality, overall complications, infections, hematomas, and neurologic complications. PCF-treated patients with 3þ level fusions also had statistically significant greater cardiac complications, PEs, and DVTs when compared to PCFs of 1-2 levels. CONCLUSIONS: Our study demonstrates a higher rate of mortalities and complications in patients undergoing 3þ level fusions compared to fusion 129S Proceedings of the NASS 28th Annual Meeting / The Spine Journal 13 (2013) 1S–168S Refer to onsite Annual Meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosures and FDA device/drug status at time of abstract submission.