What type of X‑ray should be ordered for a 68‑year‑old obese male with a two‑week history of right‑hip pain radiating to the posterior knee?

Standard Hip Radiography Series

For this 68-year-old obese male with two-week subacute hip pain radiating to the posterior knee, order standard hip radiographs consisting of an anteroposterior (AP) view of the pelvis and a frog-leg lateral view of the symptomatic right hip 1.

Rationale for This Imaging Approach

Radiography remains the initial imaging modality of choice for hip pain evaluation, even in non-traumatic presentations 1, 2. The 2025 ACR Appropriateness Criteria explicitly states that radiography is the first-line study, and this applies broadly to hip pain assessment 1.

Standard Views to Order

The recommended radiographic series includes:

• AP view of the pelvis with 15 degrees of internal hip rotation for bilateral comparison and assessment of hip symmetry
• Frog-leg lateral view of the affected right hip (preferred over cross-table lateral in non-traumatic settings)

1, 2

Note that while the ACR guideline emphasizes cross-table lateral views for acute trauma to avoid fracture displacement risk, the frog-leg lateral is appropriate for your patient's subacute, non-traumatic presentation 1.

Clinical Context Considerations

Why Radiography First

Plain radiographs are:

• Inexpensive and readily available
• Capable of detecting most relevant pathology including osteoarthritis, fractures, osteonecrosis, and bone lesions
• The validated first-line modality before considering advanced imaging 2, 3

What You're Looking For

In this demographic (elderly, obese male with posterior radiation), radiographs will evaluate for:

• Osteoarthritis: Joint space narrowing (<3mm), osteophytes, subchondral sclerosis 4, 3
• Occult fractures: Including stress fractures or insufficiency fractures
• Osteonecrosis: Early changes may be visible
• Other bone pathology: Tumors, infection, metabolic bone disease

When to Advance to MRI

If radiographs are negative or non-diagnostic but clinical suspicion remains high, proceed to MRI without IV contrast 2. MRI is superior for detecting:

• Occult fractures not visible on radiographs
• Early osteonecrosis of the femoral head
• Labral tears (though less likely given the posterior radiation pattern)
• Bone marrow edema and soft tissue pathology

2, 3

Common Pitfall to Avoid

Do not skip radiography and proceed directly to MRI. Despite MRI's superior sensitivity for soft tissue and early cartilage changes, radiography remains the appropriate and cost-effective initial study that will guide subsequent management in the vast majority of cases 1, 2, 5. The guideline evidence strongly supports this algorithmic approach, with MRI reserved for cases where radiographs are inconclusive 1.