Alternatives to DEXA for the Assessment of Bone Density: a Systematic Review of the Literature and Future Recommendations

Objective: Osteoporosis has significant implications in spine fusion surgery, for which reduced spinal bone mineral density (BMD) can result in complications and poorer outcomes. Currently, dual-energy x-ray absorptiometry (DEXA) is the gold standard for radiographic diagnosis of osteoporosis, although DEXA accuracy may be limited by the presence of degenerative spinal pathology. In recent years, there has been an evolving interest in using alternative imaging, including CT and MRI, to assess BMD. In this systematic review of the literature, the authors assessed the use and effectiveness of MRI, opportunistic CT (oCT), and quantitative CT (qCT) to measure BMD.

Methods: In accordance with the PRISMA guidelines, the authors conducted a systematic search for articles posted on PubMed between the years 2000 and 2022 by using the keywords "opportunistic CT, quantitative CT, MRI" AND "bone density" AND "spine." Inclusion criteria consisted of articles written in English that reported studies pertaining to human or cadaveric subjects, and studies including a measure of spinal BMD. Articles not related to spinal BMD, osteoporosis, or spinal surgery or reports of studies that did not include the use of spinal MRI or CT were excluded. Key study outcomes were extracted from included articles, and qualitative analysis was subsequently performed.

Results: The literature search yielded 302 articles. Forty-two articles reported studies that met the final inclusion criteria. Eighteen studies utilized MRI protocols to correlate spinal BMD with vertebral bone quality scores, M-scores, and quantitative perfusion markers. Eight studies correlated oCT with spinal BMD, and 16 studies correlated qCT with spinal BMD. With oCT and qCT imaging, there was consensus that Hounsfield unit (HU) values > 160 demonstrated significant reduction in risk of osteoporosis, whereas HU values < 110 were significantly correlated with osteoporosis.

Conclusions: Osteoporosis is increasingly recognized as a significant risk factor for complications after spinal fusion surgery. Consequently, preoperative assessment of BMD is a critical factor to consider in planning surgical treatment. Although DEXA has been the gold standard for BMD measurement, other imaging modalities, including MRI, oCT, and qCT, appear to be viable alternatives and may offer cost and time savings.