DEXA Scan (Dual Energy Xray Absorptiometry)
- Definitions
Score type | Description |
T-Score | BMD relative to normal young matched controls (30-year-old women) |
Z-Score | BMD relative to similar-aged patients |
- usually performed in
- Lumbar spine:
- measures BMD from L2 to L4 and compiles scores
- Hip:
- measure BMD from femoral neck, trochanter, and intertrochanter region and compiles scores
- Sensitivity and specificity
- Most accurate with the least radiation exposure
- DEXA scans of the spine can be inaccurate due to
- Scoliosis
- Osteophytes spuriously elevating BMD,
- Presence of spinal fusion or instrumentation.
- Sardar 2022: Hip and Spine DEXA scans for diagnosing osteoporosis in patients aged 50 and above (using T-score) and between 20-50 (using Z-score).
Quantitative Computed Tomography (QCT):
- Most optimal method for measuring BMD in the spine due to its volumetric analysis of trabecular bone mineral density.
- A QCT BMD less than 90 mg/mL indicates an increased risk of pedicle screw loosening.
- Pros
- Precision
- Cons
- Limited availability
- Higher cost
- Increased radiation
Opportunistic CT Scan-Based Hounsfield Units (CTHU):
- Aiding in bone health assessment decisions.
- Measurements (typically at L1-4) correlate with DEXA-based BMD.
- An L1 CTHU of <100 is considered abnormal,
- Lower CTHU values are associated with vertebral fracture, adjacent segment fractures, and cage subsidence.
- while >150 is normal,
- Pros
- Commonly used: routinely performed before spinal instrumentation.
Biomechanical Computed Tomography analysis (BCT):
- Measures vertebral body strength using finite element analysis (FEA) and trabecular BMD.
- BCT has been reported to predict the risk of vertebral body fracture independently of BMD.
- Patients testing positive for osteoporosis using BCT had a
- 5 times higher risk of vertebral fractures
- 4 times the risk of reoperation after spinal fusion.
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