For a 58-year-old woman with bilateral knee osteoarthritis who fell two days ago and has negative plain‑film X‑rays, what imaging is indicated as the standard of care?

Standard of Care for Imaging After Fall in Patient with Known Knee Osteoarthritis

No additional imaging beyond the negative X-rays is indicated as standard of care for this patient. 1, 2

Clinical Reasoning

This 58-year-old woman has already received appropriate initial imaging with plain radiographs that were negative for fracture. The key question is whether MRI is now indicated.

Why MRI is NOT Standard of Care in This Scenario

The American College of Radiology explicitly states that MRI is not routinely used as the initial imaging study for evaluation of acute trauma to the knee. 1 More importantly, when radiographs are negative after acute trauma in a patient with pre-existing osteoarthritis, MRI is only indicated if there is clinical suspicion for specific internal derangement (meniscal tear, ligamentous injury) or occult fracture—not simply because the patient requests it. 1

When Would Further Imaging Be Appropriate?

MRI without contrast becomes the appropriate next study only if specific clinical findings persist after 5-7 days, including: 3

• Significant joint effusion with inability to fully bear weight 3
• Mechanical symptoms (locking, catching, giving way) suggesting meniscal injury 3
• Joint instability on examination suggesting ligamentous injury 3, 4
• Persistent inability to bear weight despite conservative management 3, 4

CT may be considered instead of MRI if there is high clinical suspicion for an occult fracture (such as tibial plateau fracture), as CT demonstrates 100% sensitivity versus 83% for plain radiographs. 1 However, CT has low sensitivity for soft-tissue injuries. 1

The Osteoarthritis Context

In patients with known osteoarthritis, imaging does not usually alter treatment for chronic knee pain, and most persons over age 45 with chronic knee pain have OA. 2 The research literature emphasizes that diagnostic imaging is usually not necessary in OA patients with characteristic history and physical findings, as treatment remains similar regardless of imaging findings. 2, 5

Importantly, meniscal tears are often incidental findings in older patients—the majority of people over 70 years have asymptomatic meniscal tears, and the likelihood of a meniscal tear being present in either a painful or asymptomatic knee is not significantly different. 1

Recommended Management Algorithm

1. Reassess clinical examination now (2 days post-fall): 1

   • Can she bear weight and take 4 steps?
   • Can she flex the knee to 90 degrees?
   • Is there focal bony tenderness (patella, fibular head)?
   • Is there a large effusion or signs of instability?

2. If examination is reassuring (able to bear weight, no mechanical symptoms, no instability): 3, 2

   • Conservative management with NSAIDs, ice, activity modification
   • Follow-up in 5-7 days
   • No MRI indicated at this time

3. If concerning findings persist at 5-7 day follow-up: 3

   • Then consider MRI without contrast for suspected internal derangement
   • Consider CT if occult fracture remains a concern

4. If examination reveals red flags now: 1

   • Gross deformity, palpable mass, or vascular compromise → immediate orthopedic referral
   • Unable to bear weight with large effusion → consider joint aspiration to rule out septic arthritis 1

Common Pitfalls to Avoid

Do not order MRI simply because the patient requests it or "to be thorough." 1, 2 Approximately 20% of patients with chronic knee pain inappropriately receive MRI without recent radiographs or clear clinical indication. 1

Do not assume that a fall in an OA patient automatically requires MRI. 2, 5 The negative X-rays have already excluded fracture requiring immediate intervention, and the pre-existing OA means that MRI findings (meniscal tears, cartilage loss, bone marrow edema) may be chronic and unrelated to the acute fall. 1, 2

Physician judgment should supersede clinical guidelines when appropriate, but in this case, the guidelines clearly support observation and reassessment rather than immediate advanced imaging. 1