Assessment of bone quality at the lumbar and sacral spine using CT scans: a retrospective feasibility study in 50 comparing CT and DXA data

PURPOSE: Computed tomography (CT) is a standard diagnostic tool for preoperative screening for many indications in spinal and pelvic surgery. The gold standard for diagnosing osteoporosis is standard dual-energy X-ray absorptiometry (DXA). The aim of the present study was to compare the accuracy of Hounsfield unit (HU) measurements not only at the lower lumbar, but also at the sacral spine using standard CT scans.

PATIENTS AND METHODS: Main inclusion criterion for this retrospective analysis in 50 patients was the availability of both a CT scan of the lumbar and sacral spines and a DXA scan. HUs were measured in intact vertebral bodies L4, L5 and S1. Results of the HU in CT scan were compared to the T-score and bone mineral density in DXA. A group with normal bone density (T-score higher - 1, n = 26) was compared with a group with impaired bone density (T-score lower - 1, n = 24).

RESULTS: A multivariant binary logistic regression analysis showed significant results for HU measurement in L4 (p = 0.009), L5 (p = 0.005) and S1 (p = 0.046) with respect to differentiation between normal and impaired bone quality. Cutoffs between normal and impaired bone density values for trabecular region of interest attenuation for L4, L5 and S1 are presented. In L4 100% sensitivity to detect normal bone was reached when HU was higher than 161, HU higher than 157 in L5 and HU higher than 207 in S1.

CONCLUSIONS: HU measurements in CT scans have proven to be a feasible tool to additionally assess bone quality at the lumbar and sacral spine with good sensitivity, when compared with the gold standard DXA.

LEVEL OF EVIDENCE: III. These slides can be retrieved under Electronic Supplementary Material.