Post-Pregnancy Stress Fracture and DEXA Scanning
Yes, a DEXA scan should be obtained when a stress fracture is diagnosed on MRI in a postpartum woman, as pregnancy-related stress fractures may indicate underlying pregnancy-associated osteoporosis or transient osteoporosis of pregnancy, which requires assessment of bone mineral density to guide treatment and prevent future fractures.
Rationale for DEXA Assessment
Understanding Pregnancy-Related Bone Fragility
Pregnancy-related osteoporosis is rare but represents a distinct pathophysiologic entity where patients develop abnormally low bone density during or immediately after pregnancy 1.
The pathogenesis involves decreased serum calcium levels during pregnancy due to decreased 1,25-dihydroxyvitamin D3, decreased calcitonin levels, and cytokine effects on bone remodeling 1.
Women with pregnancy-related osteoporosis are predisposed to insufficiency fractures in the spine, pelvis, femoral neck, and sacrum 1.
Distinguishing Stress Fractures from Insufficiency Fractures
The literature documents uncertainty in pregnancy-related fractures about whether they represent true stress (fatigue) fractures from mechanical overload or insufficiency fractures occurring in weakened bone 1.
This distinction is clinically critical because insufficiency fractures indicate underlying bone pathology requiring treatment, while pure stress fractures may resolve with activity modification alone 1.
Risk factors for pregnancy-related sacral fractures include vaginal delivery of high-birth-weight infants, increased lumbar lordosis, excessive weight gain, and rapid vaginal delivery 1.
Clinical Decision-Making Algorithm
When DEXA is Indicated
Any postpartum woman with a stress fracture diagnosed on MRI should undergo DEXA scanning to determine if underlying osteoporosis or osteopenia is present 2, 3.
DEXA allows accurate diagnosis of osteoporosis, estimation of future fracture risk, and provides baseline values for monitoring treatment response 2.
The diagnosis of osteoporosis is confirmed when BMD T-score values at the lumbar spine, femoral neck, or total hip are at or below -2.5 2, 3.
Timing of DEXA Assessment
DEXA should be performed after the acute fracture is diagnosed on MRI but does not need to delay initiation of conservative fracture management 1.
The scan provides essential information for determining whether pharmacologic bone-protective therapy is needed beyond fracture healing 3.
Treatment Implications Based on DEXA Results
If DEXA confirms osteoporosis (T-score ≤ -2.5), oral bisphosphonates are first-line treatment after the postpartum period, with parenteral therapy if oral agents are contraindicated or not tolerated 3.
If DEXA shows osteopenia (T-score between -1.0 and -2.5), calcium and vitamin D supplementation with lifestyle modifications may be sufficient, with repeat DEXA monitoring 3.
Normal BMD (T-score > -1.0) suggests a true mechanical stress fracture rather than insufficiency fracture, and treatment focuses on activity modification and fracture healing 4.
Important Clinical Considerations
High-Risk Fracture Locations
Femoral neck stress fractures, particularly lateral tension-type fractures, are inherently unstable and prone to displacement, often requiring percutaneous screw fixation 1.
Femoral head stress fractures have increased rates of delayed union, nonunion, displacement, and avascular necrosis if not recognized promptly 1.
These high-risk fractures make early DEXA assessment even more critical to guide aggressive management 1.
Avoiding Common Pitfalls
Do not assume that all pregnancy-related fractures are purely mechanical stress fractures without assessing bone density 1.
Do not delay DEXA scanning indefinitely—the information is needed to determine if long-term bone-protective therapy is required 2, 3.
Do not rely solely on clinical risk factors to predict bone density, as they are poorly predictive of actual BMD measurements 5.
Remember that vertebral fractures are generally diagnostic of osteoporosis even if spine BMD values are not in the osteoporotic range 3.
Additional Diagnostic Considerations
DEXA should be performed at both the lumbar spine and hip, as there is only moderate agreement between these sites (kappa 0.33), and either may be preferentially affected 5.
The 10-year risk of major osteoporotic fracture should be calculated using tools that incorporate BMD results to guide treatment intensity 3.
For women under age 65, DEXA is particularly useful in determining whether bone-protective treatment is needed immediately or can be delayed 3.