MRI is Superior to CT for Ruling Out Hip Fracture
When radiographs are negative but clinical suspicion for hip fracture remains high, MRI without IV contrast is the definitive imaging modality of choice, demonstrating near 100% sensitivity compared to CT's significantly lower accuracy. 1
Algorithmic Approach to Hip Fracture Imaging
Step 1: Initial Imaging
- Obtain standard radiographs first: anteroposterior (AP) pelvis view with 15 degrees internal rotation and cross-table lateral view of the affected hip 1, 2
- Radiographs identify approximately 90% of proximal femoral fractures 1
- Critical limitation: 10% of hip fractures are radiographically occult 2, 3
Step 2: When Radiographs Are Negative But Suspicion Remains High
Why MRI Over CT: The Evidence
MRI Diagnostic Performance
- Sensitivity approaches 99-100% for proximal femoral fractures 1
- Coronal STIR sequence alone demonstrates 100% sensitivity 1
- Adding coronal T1 sequence increases confidence and specificity 1
- Detects concomitant pelvic fractures (present in 38% of cases) and soft tissue injuries 1
- Accurately characterizes fracture morphology, including intertrochanteric extension of seemingly isolated greater trochanter fractures 1
CT Diagnostic Limitations
- CT is explicitly "not as sensitive as MRI" per ACR guidelines 1
- Research demonstrates CT's significant diagnostic failures: in one study of 6 patients undergoing both modalities, 4 CT scans resulted in misdiagnosis 4
- A 2016 study of 44 patients found MRI changed the primary CT diagnosis in 27 cases (61%), with reviewers concluding "a negative CT finding cannot completely rule out a hip fracture" 5
- High inter-observer variability even among experienced radiologists 5
- Experience level is highly influential in CT interpretation, whereas MRI diagnoses show no disagreement regardless of radiological experience 5
Clinical Impact on Morbidity and Mortality
Why Accurate Diagnosis Matters
- Surgical delays >12 hours significantly increase 30-day mortality risk 1
- Delays in diagnosis increase costs, complication rates, and hospital length-of-stay 1, 2, 6
- MRI enables confident emergency department discharge when negative, reducing unnecessary admissions 1
- Rapid diagnosis of surgical fractures allows timely treatment with improved outcomes 1
Treatment Planning Benefits
- MRI accurately depicts fracture extent, guiding conservative versus surgical management 1
- Incomplete intertrochanteric fractures may be treated conservatively when properly characterized 1
When CT May Be Considered
CT has limited advantages over MRI:
However, these practical advantages do not overcome CT's fundamental diagnostic inferiority 1. The ACR explicitly reserves CT only as a "problem-solving modality following radiography" for better depicting fracture morphology in already-identified fractures, not for ruling out occult fractures 1.
Common Pitfalls to Avoid
- Never rely on CT alone to exclude hip fracture when clinical suspicion persists after negative radiographs 5
- Do not assume CT's speed justifies its use over MRI's superior diagnostic accuracy 4, 5
- Avoid missing the 39% rate of radiographically occult surgical hip fractures in elderly patients with negative initial radiographs 7
- In patients with isolated greater trochanter fractures on radiographs, 92% have additional surgical hip fractures requiring MRI evaluation 7
- Failing to image comprehensively misses concomitant pelvic fractures in 30% of cases 8
High-Risk Populations Requiring Advanced Imaging
Advanced imaging (preferably MRI) is particularly critical in:
- Patients aged ≥80 years (44% occult fracture rate) 7
- Those with equivocal radiographic reports (58% occult fracture rate) 7
- Patients with trauma history (41% occult fracture rate) 7
The evidence unequivocally supports MRI as the superior modality for ruling out hip fracture, with CT reserved only for situations where MRI is contraindicated or unavailable. 1, 4, 5