Early Stress-Related Changes in the Femoral Head
Imaging Characteristics of Early Changes
- Bone marrow edema is the earliest detectable change, appearing as T1 hypointense and T2 hyperintense signal in the femoral head before any fracture line develops 2
- Linear T1 and T2 hypointense signal represents actual fracture lines when stress progresses beyond the edema-only stage 2
- MRI demonstrates stress abnormalities as early as bone scintigraphy but with significantly greater specificity 1, 2
- Initial radiographs are typically negative in early stress changes, with sensitivity of only 15-35% 1
- Follow-up radiographs at 10-14 days show increased sensitivity (30-70%) as overt bone reaction develops 1, 2
Anatomic Distribution Patterns
- Femoral head stress fractures are classified as high-risk due to increased rates of delayed union, nonunion, displacement, and avascular necrosis if not recognized promptly 1, 2
- Lateral "tension-type" femoral neck stress fractures are inherently unstable and prone to displacement 1
- Medial "compression-type" femoral neck stress fractures are considered low-risk 1, 2
Clinical Implications and Diagnostic Approach
- Pain may manifest in the back, buttock, or thigh rather than isolated groin pain 3, 4
- History of repetitive mechanical loading or increased activity level 4
- Initial radiographs are appropriate first-line imaging despite low sensitivity 1, 2
- MRI without contrast is the preferred second-line study after negative radiographs to prevent delayed diagnosis—it does not use ionizing radiation and has excellent sensitivity 2
- Immediate MRI is indicated in "need-to-know" situations or high-risk patients where delayed diagnosis could lead to fracture completion 2
- Do not rely on clinical examination alone—hip examination tests have good sensitivity but poor specificity and cannot reliably distinguish hip-related pain from other causes 3, 4
- Do not delay MRI in high-risk scenarios—femoral head stress fractures have devastating consequences if diagnosis is delayed 1, 2