PURPOSE: To explore the hypothesis that the subcutaneous fat wound depth in the involved lumbar surgical levels is a stronger risk factor for SSI than is BMI. STUDY DESIGN/SETTING: A retrospective review of patients treated at the University of Michigan hospital. PATIENT SAMPLE: 179 adult ($18 years) patients who underwent pos- terior lumbar surgeries involving midline incisions between 2003-2011 who had CT scans which included the spine and posterior skin. OUTCOME MEASURES: Surgical site infection. METHODS: Patients who developed SSIs were identified using hospital records. Additional demographic and perioperative data associated with SSIs (age, diabetes, tobacco use, BMI, revision procedure) were also col- lected. Using novel semi-automated analytic morphomic techniques with MATLAB (Natwick, MA) the distance from the spinous process to back skin was obtained at the T12 - L5 vertebral levels from CT scans. RESULTS: Data are presented as mean (6standard deviations).The over- all rate of SSIs was 10.1% (n518). Patients with an SSI had an average age of 50.3 years (617.6), BMI of 32.4 (67.8), wound depth of 53.4 mm (621.5), 27.8% had tobacco use (n55), 27.8% diabetes (n55) and 22% underwent revision operations (n54). Patients without an SSI (n5 161) had an average age of 53.7 years (615.4), BMI of 28.2 (66.9), wound depth of 38.2 mm (616.4), 27.3% had tobacco use (n544), 14.9% diabetes (n524) and 9.3% underwent revision operations (n515). Among factors previously identified to be associated with SSI, univariate analysis showed BMI (p !0.02) and wound depth (p ! 0.01) to be significant. In multivariate logistic regression analysis, BMI lost its significance and wound depth was determined to be the only significant risk factor (p ! 0.02) for wound infec- tion. For every millimeter thickness of subcutaneous fat there was a 4.9% (OR 5 1.049, 95% CI 1.010- 1.090) increase in the risk of developing an SSI. CONCLUSIONS: The thickness of subcutaneous fat is a risk factor for SSI in lumbar spine procedures in our model while BMI is not. Identifying patients with a critical threshold of subcutaneous fat tissue and targeting treatments such as incisional wound vacuum-assisted closures may be more economical to the health care system than identifying patients at risk using BMI. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2013.07.240 173. Selective Densitometry of the Lumbar Spine Jeremi M. Leasure, MS; The Taylor Laboratories, San Francisco, CA, US BACKGROUND CONTEXT: Bone mineral density (BMD) has been identified as a major factor in spine construct strength, with failures result- ing in pedicle screw loosening and pullout. Computed tomography (CT) scans have been shown to effectively measure BMD. Previous research has utilized this linear correlation of CT Hounsfield Units (HU) to BMD in order to determine BMD as a function of anatomic location within cer- vical vertebrae; however, the lumbar spine has not yet been reported on. The goal of this study was to describe BMD of anatomical regions within lumbar vertebrae using the correlation between HU and BMD. It was hy- pothesized that posterior elements of the spine would exhibit significantly different BMD than the vertebral body. This was tested through means comparison of BMD for each anatomical region. METHODS: Three-dimensional models of the lumbar spine (L1– 5) were generated by high-resolution helical CT scans of three fresh-frozen ca- daver subjects. The lumbar spine was digitally isolated from surrounding tissue with medical image processing software (Mimics; Materialise, Leuven, Belgium). Using this thresholding as well as manual segmenta- tion, the spine models were segmented into seven anatomic regions and de- termination of average HU. HU was then converted to BMD with calibration phantoms of known BMD RESULTS: Overall mean BMD in vertebral regions ranged from 172– 393 mg/cm3, with the highest and lowest BMD found in the lamina and verte- bral body, respectively. The vertebral body and transverse processes repre- sent one group, with significantly lower BMD (146 6 27, 172 6 62 mg/ cm3) than other regions. The spinous process, pedicles, and superior artic- ular processes represent a second group, with moderate BMD (281 6 74, 303 6 77, 304 6 79 mg/cm3). Finally, the inferior articular process and lamina represent a third group, with significantly higher BMD (390 6 98, 393 6 116 mg/cm3) than any other region. CONCLUSIONS: The lamina and inferior articular processes exhibited the greatest BMD, while the BMD of the pedicles was significantly lower. Pedicles are currently the most commonly used region for hardware fixa- tion. Results of this study, however, show that – based on BMD values – the lamina and inferior processes may be better candidates for anchoring to the lumbar spine, possibly mitigating spinal construct failures due to pedicle screw loosening or pull-out. These results contrast those found for cervical spine in which the pedicles exhibit highest BMD. The verte- bral body and transverse process had significantly lower BMD than all other anatomic regions. This finding was expected since the vertebral body is comprised mostly of cancellous bone and vascular cavities. However, this result also suggests that the standard procedure of determining spine BMD by DEXA scans of the vertebral body may be limited. Our observa- tions indicate a statistically significant difference between the region eval- uated for bone quality (vertebral body) and the region utilized for posterior fixation (pedicle). Poor vertebral body bone quality may correspond to de- creased pedicle bone quality; however, our results indicate a possible need to evaluate specific anatomical regions when bone quality is in question. Future research from our group will focus on understanding this relation- ship across demographic groups. Resulting data indicate that utilization of the posterior elements of the lumbar spine – especially the lamina and in- ferior articular processes – may be advantageous for hardware fixation. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2013.07.241 Friday, October 11, 2013 3:40 – 4:40 PM Concurrent Session: Osteoporosis 174. The Effects of Bone Growth Stimulator Treatments on Vertebral Bone Mass in an Osteoporosis Model Ronald J. Midura, PhD 1 , Caroline Androjna, PhD 2 , Maciej Zborowski, PhD 2 ; 1 Cleveland Clinic Foundation, Cleveland, OH, US; 2 The Cleveland Clinic, Cleveland, OH, US BACKGROUND CONTEXT: Osteoporotic patients face a heightened risk of non-union fractures and experience lower spine and cervical fusion success rates. Bone growth stimulation (BGS) devices are often adjunc- tively applied to promote bony fusion of adjacent vertebral bodies, as well as for noninvasive treatment of pseudoarthrosis and nonunion fractures. While these devices employ pulsed electromagnetic (or electrical) fields (PEMF) to promote bone formation activities, their osteogenic potential in an osteoporotic environment has not been elucidated. PURPOSE: The purpose of this study was to determine whether treat- ments with a BGS device would improve vertebral bone mass in a preclin- ical osteoporosis model when applied at an early disease stage. STUDY DESIGN/SETTING: An ovariectomy (OVX) rat model of oste- oporosis was used in this 12-week study (4 test groups; n 5 11 each). Group 1: underwent sham OVX surgery and represents normal bone re- modeling controls; Group 2: OVX rats received placebo treatments and 88S 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.