Densitometric vertebral fracture assessment (VFA) is an image of the lumbar and thoracic spine acquired on dual energy x-ray absorptiometry (DXA) scanners, for the purpose of diagnosing osteoporotic vertebral fractures.
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Terminology
The technique is available on DXA scanners under a variety of proprietary names including:
- instant vertebral assessment (IVA)
- lateral vertebral assessment (LVA)
- dual energy vertebral assessment (DVA)
- morphometric x-ray analysis (MXA)
To reduce confusion and variation in academic publications, the generic term vertebral fracture assessment (VFA) has been recommended to describe spinal images acquired on DXA scanners to diagnose vertebral fractures 1.
Indications
Indications for VFA vary by country and performing site, however in general VFA should be considered in patients with a T-score less than -1.0 on DXA, and 1:
- women >70 years or men >80 years
- greater than 4 cm historical height loss
- previous vertebral fracture (including self-reported vertebral fractures)
- history of long-term (>3 months) systemic corticosteroid use
Advantages and limitations
The advantages of VFA include:
- reduced parallax effect due to the beam path always being parallel to the vertebral endplates
- low radiation dose
- can be performed at the same time as DXA measurements on bone mineral density
Limitations include:
- reduced image resolution compared to spinal radiographs
- reduced accuracy to diagnose mild fractures (see interpretation section)
Acquisition
Dependent on the scanner capabilities, scans may be acquired either in a lateral decubitus position or supine with the tube/detector in a lateral position (c-arm style scanners).
Scans typically include from L5/S1 and scan upward to include T4, or as high as possible while individual vertebrae remain identifiable.
Positioning aids (pads, straps, backboards) will be used to reduce patient rotation and ensure the spine is parallel to the table as much as possible.
On some scanners, the scan may be acquired in single-energy or dual-energy mode. Dual-energy mode has the advantage of improved image detail, with the drawback of increased radiation dose.
Interpretation
VFA images can be interpreted using the same radiological techniques as used for spinal radiographs, for the diagnosis of vertebral fracture (see: osteoporotic spinal compression fracture). The technique is not validated for the diagnosis of other spinal pathology, however, it is important to be able to differentiate vertebral fractures from other pathology which may mimic fracture (e.g. Scheuermann disease, Schmorl nodes).
Some sites automatically perform quantitative vertebral morphometry on all vertebrae. When interpreting vertebral morphometry, visual inspection is important to confirm fracture and reduce the risk of false positives.
VFA has good sensitivity and excellent specificity compared to spinal radiographs for moderate and severe vertebral fractures (>25% vertebral height loss) 2.
Where mild fractures (<25% height loss) are suspected, confirmation with spinal radiography should be considered 1.
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