X-ray of the Femur: Definition and Description
An x-ray of the femur is a radiographic imaging study that uses ionizing radiation to create two-dimensional images of the femur (thighbone), visualizing its bony structure, cortical thickness, trabecular architecture, and any pathological changes such as fractures, lesions, or bone density abnormalities. 1
Technical Characteristics
Standard femur radiography typically includes anteroposterior (AP) and lateral views, though recent evidence suggests the lateral view may not be necessary for all proximal femoral fractures, particularly extracapsular fractures where the AP view alone provides adequate diagnostic information. 2 The lateral view does add value for detecting displacement in intracapsular fractures that appear undisplaced on AP imaging. 2
Clinical Applications and Diagnostic Capabilities
Fracture Evaluation
- Radiography demonstrates high reliability for evaluating femoral fractures, with sensitivity and specificity ranging from 90% to 95% and 68% to 100% respectively. 1
- The American College of Radiology (ACR) establishes radiography as the gold standard for detecting atypical femoral fractures, superior to DXA scanning in symptomatic patients. 1
- For proximal femoral fractures, the AP view alone is adequate for surgical planning in most cases, avoiding unnecessary radiation exposure and patient discomfort. 2
Detection of Atypical Femoral Fractures
Plain radiographs can detect incomplete atypical femoral fractures (iAFFs) as active lesions with a lucent line ("beaking") in the middle of cortical thickening at the lateral femoral cortex. 1 These fractures:
- Typically occur below the lesser trochanter to the distal supracondylar flare 1
- Show focal periosteal or endosteal thickening of the lateral cortex 1
- May require bilateral imaging, as up to 30% demonstrate bilateral involvement 1
Metastatic Disease Assessment
The combination of radiographic imaging findings and lesion-related pain is predictive of pathologic femur fracture risk in patients with metastatic carcinoma or myeloma, though specific parameters that accurately predict fracture risk remain poorly defined in the literature. 1 The American Academy of Orthopaedic Surgeons (AAOS) notes that femoral fractures from metastatic disease almost always require surgery and dramatically alter quality of life and survival. 1
Extended Imaging Techniques
Extended-length femur radiography from the lesser trochanter to the supracondylar flare allows visualization of the entire femoral shaft, which is particularly important for detecting atypical fractures that may occur at various locations along the diaphysis. 1 This approach does not substantially alter bone mineral density measurements when performed via DXA. 3
Radiation Considerations
The ACR emphasizes that radiation exposure is an important factor when selecting imaging procedures, with relative radiation levels varying widely between different diagnostic modalities. 1 Pediatric patients face inherently higher risk from radiation exposure. 1
Limitations and Complementary Imaging
When radiographs are insufficient or equivocal, advanced imaging may be necessary:
- CT is useful for discerning lucency in incomplete fractures and excluding neoplastic pathologic fractures 1
- MRI determines radio-occult stress-related changes and defines cortical involvement extent, which guides conservative versus surgical treatment decisions 1
- Bone scintigraphy serves as a second-line diagnostic test 1
Clinical Pitfalls to Avoid
- Do not routinely obtain lateral views for all proximal femoral fractures; reserve them for cases where displacement assessment is critical on intracapsular fractures appearing undisplaced on AP view 2
- Do not rely solely on radiography for early detection of atypical fractures in asymptomatic patients on long-term bisphosphonate therapy; extended-field DXA may have a screening role 1
- Always consider bilateral imaging when atypical femoral fractures are suspected, given the 30% bilateral involvement rate 1