What is the next best imaging test for an elderly patient with right hip pain after a fall, with osteopenia on x-ray, and who is taking phenytoin (antiepileptic) and losartan (angiotensin II receptor antagonist)?

MRI of the Right Hip

MRI of the right hip without IV contrast is the next imaging test that should be ordered for this elderly patient with hip pain after a fall and negative radiographs showing only osteopenia. 1

Clinical Context: Occult Hip Fracture Until Proven Otherwise

This presentation is a high-risk scenario for occult hip fracture that demands urgent clarification:

• Elderly patients with osteopenia who fall and have hip pain severe enough to prevent ambulation must be assumed to have an occult fracture until proven otherwise, even with negative initial radiographs 1, 2
• The ability to ambulate with a walker does not exclude fracture—many occult hip fractures, particularly stress or insufficiency fractures, allow limited weight-bearing initially 1
• Phenytoin use is a critical risk factor as it causes accelerated bone loss and significantly increases fracture risk in this population 1
• Pain with internal rotation is a classic finding for hip pathology, including occult fractures 2

Why MRI is the Definitive Next Step

The American College of Radiology gives MRI hip without IV contrast a rating of 9/9 (usually appropriate) for suspected hip stress/insufficiency fracture with negative radiographs 1:

• MRI is highly sensitive and specific for detecting occult fractures not visible on plain films 1, 2, 3
• It can identify bone marrow edema patterns that indicate impending or complete fractures requiring urgent intervention 1, 2
• Timing is critical: Delaying diagnosis of an occult femoral neck fracture can lead to displacement, requiring more extensive surgery and worse outcomes 2
• MRI simultaneously evaluates soft tissue structures (tendons, bursae, muscles) that could contribute to pain 1, 2, 3

Why Other Options Are Inappropriate

Bone scan receives only a rating of 6/9 (may be appropriate) and is inferior to MRI in this scenario 1:

• Less anatomic detail than MRI 1
• Timing after injury and patient age affect sensitivity 1
• Exposes patient to radiation 1
• Should only be considered if MRI cannot be performed 1

Ultrasound is rated 1/9 (usually not appropriate) for suspected fracture 1:

• Cannot detect occult bone fractures 1, 2
• Limited to superficial soft tissue evaluation only 1, 2

No further imaging is dangerous and inappropriate:

• Up to 10% of hip fractures are radiographically occult initially 2
• The combination of elderly age, osteopenia, fall mechanism, and inability to ambulate due to pain creates unacceptably high pretest probability 1, 2
• Missing an occult femoral neck fracture can lead to displacement and avascular necrosis 2

Repeat radiographs in 10-14 days receives only a rating of 5/9 and is explicitly discouraged in hip fractures 1:

• "Because of the high risk of complications, it is not advisable to wait 10-14 days in most cases" for suspected hip fractures 1
• This delay could allow a nondisplaced fracture to displace, dramatically worsening prognosis 1, 2

Critical Management Algorithm

1. Order MRI hip without IV contrast urgently (ideally within 24-48 hours) 1, 2
2. Keep patient non-weight-bearing or touch-down weight-bearing only until MRI results available 1
3. Optimize pain control to allow patient comfort while awaiting imaging 2
4. If MRI shows occult fracture, urgent orthopedic consultation is required 1, 2
5. If MRI is negative for fracture but shows soft tissue pathology (bursitis, tendinopathy), treat accordingly 1, 2

Common Pitfalls to Avoid

• Never assume negative radiographs exclude fracture in this high-risk population 1, 2
• Do not allow the patient's ability to ambulate with assistance to provide false reassurance—many occult fractures allow limited weight-bearing 1
• Do not delay imaging to "see if it gets better" in elderly patients with osteopenia and fall-related hip pain 1, 2
• Recognize phenytoin as a significant fracture risk factor that should lower your threshold for advanced imaging 1