Abstract
Summary Statement
It is now possible to diagnose osteoporosis using incidental abdominal CT scans; applying this approach to fractures of the cervical spine demonstrates levels of osteoporosis in patients over 65.
Introduction
Recently published data now makes it possible to screen for osteoporosis in patients who, in the course of their hospital stay, have had Computed Tomography (CT) scans of their abdomen for reasons other than direct imaging. This is as a result of CT derived bone mineral density (BMD) in the first lumbar vertebra (L1) being correlated BMD derived from Dual-energy X-ray absorptiometry (DEXA) scans. The advantage of this is the reduction in both cost and radiation exposure. Although age has a detrimental effect on BMD, relatively few patients have formal DEXA studies. The aims of this study were to evaluate the utility of this new technique in a cohort of patients with acute fractures of the cervical spine and to compare relative values for BMD in patients aged over 65 with those aged under 65, and thus define the role of osteoporosis in these injuries.
Methods & Patients
Following Institutional review board approval, we performed a retrospective study of patients who presented to a level I trauma center with acute fractures of the cervical spine between 2010 and 2013; patients also had to have had a CT scan of their L1 vertebra either during the admission or within 6 months of their admission (for any other clinical reason). Using a picture archiving and communication (PACS) system, we generated regions of interest (ROI) of similar size in the body of L1 (excluding the cortex), in line with the publication by Pickhardt et al., and computed the mean values for Hounsfield units (HU). These values were compared against established threshold values which differentiate between osteoporosis and osteopenia; for a balanced sensitivity and specificity, <135 HU is the threshold and for 90% sensitivity a HU threshold of <160 HU is set. Comparisons were also performed between age stratified groups.
Results
A total of 187 patients were reviewed for eligibility, 91 patients met the criteria with 53 patients aged 64 years or younger (range 23–64) and 38 patients aged above 65 years (range 65–98). In the younger cohort, 6/53 (11% were osteoporotic, using the lower threshold, while the higher threshold indicated 5/53 (17%) of patients under 65 years were osteoporotic; mean HU for the group was 195.8 (SD 43.3). In the older cohort, 24/38 (63%) were osteoporotic using the lower threshold, whereas 34/38 (89%) were osteoporotic using the higher threshold. Mean HU for the cohort aged over 65 years was 118.7 (SD 38.4). Age based comparison of the mean values, regardless of threshold, was statistically significant (p<0.001) in both cases.
Discussion and Conclusions
This study demonstrates, for the first time in the cervical spine (including C2), the role of age related osteoporosis in acute fractures of the cervical spine. This new technique harnessing the presence of opportunistic CT scans of the abdomen saves on the extra cost and radiation exposure that may be associated with DEXA scanning. In younger patients, the higher threshold indicated 17% were osteoporotic – in the setting of an opportunistic scan, this may afford them the opportunity to commence prophylactic treatment to prevent future fractures. We believe these result have the potential to significantly impact future clinical practice.
