What is the best course of action for an adult or adolescent patient with a history of left ankle pain or trauma, considering an MRI (Magnetic Resonance Imaging) of the left ankle?

MRI of the Left Ankle: Evidence-Based Imaging Pathway

MRI of the left ankle should NOT be the initial imaging study for acute ankle trauma or chronic ankle pain—start with standard three-view radiographs (anteroposterior, lateral, and mortise views) and reserve MRI for specific clinical scenarios where radiographs are negative but clinical suspicion remains high, or when soft tissue injury assessment is critical for treatment planning. 1, 2

Initial Imaging Approach

For Acute Ankle Trauma

• Apply the Ottawa Ankle Rules first to determine if any imaging is needed 1, 3:

  • Order radiographs only if the patient has point tenderness over the posterior edge or tip of either malleolus, over the talus, or over the calcaneus 1
  • Order radiographs only if the patient cannot bear weight immediately after injury and cannot walk four steps in the clinical setting 3
  • If Ottawa Ankle Rules are negative, NO imaging is routinely indicated—neither radiographs nor MRI 1

• Standard radiographs are the first-line study when Ottawa Ankle Rules are positive, with three mandatory views: anteroposterior, lateral, and mortise (obtained by internally rotating the foot 15-20 degrees) 1, 2

For Chronic Ankle Pain

• Radiographs should be the initial study even in chronic presentations, as they can reveal osteoarthritis, osteochondral abnormalities, stress fractures, calcified intra-articular bodies, or evidence of prior trauma 1
• MRI is not routinely the first study for chronic ankle pain evaluation 1

When MRI Is Indicated

After Negative Radiographs with Persistent Clinical Concern

Order MRI without IV contrast when: 1, 2

• Initial radiographs are negative but clinical suspicion for fracture remains high (persistent point tenderness, inability to bear weight) 2
• Patient has persistent ankle pain for more than 1 week after injury despite negative radiographs 2, 3
• Clinical examination suggests ligamentous injury with instability (positive anterior drawer test, excessive joint laxity) 1

MRI detects occult injuries missed on radiographs in critical scenarios: 1, 2

• Hairline fractures may be radiographically occult in up to 50% of cases, particularly lateral talar process fractures ("snowboarder's fracture") 2
• Bone marrow edema patterns indicating stress reactions or occult fractures are visible only on MRI 2, 3
• 15% of syndesmotic ligament injuries show no fracture on radiographs but are clearly visible on MRI 1

After Positive Radiographs Requiring Soft Tissue Assessment

MRI without IV contrast is the next study when radiographs show: 1, 3

• Fracture with suspected associated ligamentous injury requiring surgical planning 1
• Potential osteochondral injury needing cartilage integrity assessment 1, 3
• Complex fracture patterns where soft tissue evaluation will change management 1

MRI provides critical information for treatment planning: 1, 4

• Grading of syndesmotic ligament, anterior talofibular ligament, and deltoid ligament injuries (grades 1,2, or 3) is essential for return-to-sport decisions 1
• Distinction between tendinopathy, sprain, and partial versus complete tears guides surgical versus conservative management 1
• Detection of bone bruises and adjacent soft-tissue edema has higher association with acute ligamentous injuries 1

For Chronic Instability Despite Conservative Treatment

Consider MRI even with prior negative imaging if: 5

• Patient continues to have symptoms of ankle instability (pain, locking, giving way) after 6-12 weeks of conservative therapy 5
• Clinical examination demonstrates chronic instability with positive stress tests 5
• Critical caveat: A negative ankle MRI does NOT rule out chronic ankle instability—clinical examination trumps imaging, and surgical reconstruction may still be warranted based on clinical findings alone 5

MRI Protocol Specifications

Order "MRI ankle without IV contrast" as the standard protocol 2, 3:

• This provides superior visualization of bone marrow edema, subtle cortical disruptions, ligamentous injuries, and tendon pathology 2, 3
• IV contrast is NOT routinely needed for traumatic or degenerative conditions 2
• Higher magnetic field strength (3T) improves signal-to-noise ratio but increases metal artifact if hardware is present 6

Common Pitfalls to Avoid

• Do not order MRI as the first study when Ottawa Ankle Rules are negative—no imaging is needed 1
• Do not order MRI as the first study when Ottawa Ankle Rules are positive—start with radiographs 1, 2, 3
• Do not rely solely on radiographs when clinical suspicion for fracture or ligamentous injury is high but initial radiographs are negative—MRI is more sensitive 2, 3
• Do not order CT instead of MRI when suspecting hairline fractures or ligamentous injuries—MRI is more sensitive for bone marrow abnormalities and soft tissue pathology 2, 3
• Do not assume a negative MRI rules out chronic instability—clinical examination and functional testing are paramount, and surgical intervention may be appropriate despite normal imaging 5

Special Populations Requiring Modified Approach

Patients with neurologic disorders or peripheral neuropathy: 3

• Ottawa Ankle Rules cannot be reliably applied due to poor pain proprioception 3
• Start with radiographs regardless of clinical examination findings, as these patients may have fractures without typical pain or point tenderness 3
• Consider MRI earlier in the diagnostic pathway if radiographs are negative but mechanism of injury suggests significant trauma 3