Gold standard is the dual-energy X-ray absorptiometry (DEXA) and the resulting T-score. Some studies have already shown that the reliability of DEXA is defeated to other methods of bone densitometry in terms of diagnosis and predictive power for subsequent fractures. The aim of this study is to compare the correlation between measured DEXA values compared to "Hounsfield units" (HU) in patients with severe manifest osteoporosis with osteoporotic vertebral fractures.
From 2021 to 2023 we examined 230 patients with osteoporotic fractures of the spine (mean age 77 ± 6,5 years). All patients received CT imaging to evaluate the "OF classification." 72 patients were evaluted by Dexa measurement. The HU were evaluated axially in each of three non-fractured vertebral bodies of the lumbar spine. A ROI was measured for each vertebral body below the cover plate, in the central plate and above the base plate in the spongy bone. The HU cut off value was determined for an osteoporotic fracture on the basis of previous postulations of <110 and compared with the T-score of the DEXA.
According to DEXA, only 46% of patients showed an osteoporosis (T- ≤-2,5). However, according to the HU, 97% of the examined patients presented an osteoporosis.While HU demonstrated a high sensitivity of 94% and specificity of 96% (positive predictive value (PPV): 95.6%, negative predictive value (NPV): 94.1%), comparatively DEXA showed a low sensitivity of 51% and specificity of 50% with a PPV of 46,5% and an NPV of 49,5%. In patients who did not show any osteoporotic fracture (>-1) in the T-score, the mean HU value showed: 73,53; in patients with a low suspicion (-1 to -2.5): 87,16 and with manifest osteoporosis (<-2.5): 78,53. After classification of the osteoporotic fracture via OF classification, a successive decrease in HU according to the severity of the osteoporotic fracture could be evaluated (OF2: 98,28; OF3: 91,83; OF4: 75,48; OF5: 68.297) with a significant correlation (p=0.03).
Although currently still the gold standard for bone densitometry and diagnosis of osteoporosis, DEXA does not seem to be suitable for reliably detecting manifest osteoporosis in the spine in contrast to HU. Based on our data, HU seem to be much more suitable to verify manifest osteoporosis.