P114. Tip of the iceberg, normal lumbar bone density does not predict normal cervical bone density

BACKGROUND CONTEXT The Hounsfield unit (HU) is a measurement of X-ray beam attenuation in computer tomography (CT) scans and have shown strong correlation to Dual-energy X-ray absorptiometry (DEXA), the current standard for measurement of bone density. Unlike DEXA, Hounsfield units may be opportunistically assessed on preoperative CT scans for osteoporosis screening. While the lumbar spine has been well studied using this technique, difference in the biomechanics of loading between the cervical spine and lumbar spine poses the question of whether lumbar HU can be correlated to cervical HU. PURPOSE To investigate associations between lumbar and cervical Hounsfield unit measurements. STUDY DESIGN/SETTING Retrospective single center study. PATIENT SAMPLE A total of 182 patients. OUTCOME MEASURES Hounsfield units. METHODS In addition to basic demographics and clinical information, HU measurements were collected by three independent reviewers at C2, C4, C7, T1, L1, L2, L3, L4 and S1 within a sagittal region of interest (ROI) in the vertebral body. These were compared and correlated to BMD as measured by DEXA scans. RESULTS There were 182 patients included. Interrater reliability was excellent between the three reviewers for all measurements. Linear regression analysis showed a significant association between lumbar and cervical HU (r-square: 0.436; std error: 37.3). Hounsfield units of the spine were strongly associated with DEXA of the spine, however not to the radius or hip. Interestingly 92% of patients with an osteoporotic cervical spine have a non-osteoporotic lumbar spine while only 1.3% of patients that have a non-osteoporotic cervical spine have an osteoporotic lumbar spine. CONCLUSIONS A region of the spine can be a good predictor of overall bone quality; however, it is not specific enough to predict the bone quality in another spinal region. The lumbar spine cannot be used as a predictor of bone quality in the cervical spine. However, if the cervical spine is normal, it is likely that the lumbar spine is normal as well. Planned fusion surgeries on the cervical spine should not use lumbar DXA or HU as a surrogate for cervical bone quality. Finally, future studies should evaluate if the cervical spine can be used as an early indicator for osteoporosis screening. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.