From the Guidelines
An MRI of the foot is not necessary as the initial imaging study for chronic foot pain of unknown etiology, and radiography foot is usually appropriate for the initial imaging. According to the American College of Radiology Appropriateness Criteria 1, radiography can be useful to distinguish among different causes of chronic foot pain and is usually the first imaging study in evaluating patients with chronic foot pain. The value of radiographs in the diagnosis of tarsal coalitions has been extensively demonstrated, with overall sensitivities ranging from 80% to 100% and specificities ranging from 97% to 98% 1.
Initial Evaluation
Before considering an MRI, a thorough clinical examination and plain radiographs (X-rays) should be performed, as they are often sufficient for many common foot conditions. Radiographs are useful to assess several causes of forefoot pain, including sesamoid dislocation and osteoarthritis, and can help diagnose sesamoid dislocation and osteoarthritis, or distinguish between bipartite versus fractured sesamoid 1.
Indications for MRI
An MRI may be indicated if there is persistent pain, suspected stress fracture, soft tissue injury, or unclear diagnosis after initial evaluation and X-rays 1. MRIs are particularly useful for evaluating ligament or tendon injuries, osteochondral lesions, tarsal coalition, infection, or tumors. For example, MRI foot without IV contrast is usually appropriate as the next imaging study after negative or equivocal radiographs in patients with chronic foot pain, especially when clinical concern includes entrapment syndromes like Baxter’s neuropathy 1.
Clinical Decision-Making
The decision to order an MRI should be based on how the results might change the management plan, as MRIs are costly and may not always provide additional useful information for straightforward conditions that respond to conservative care. If symptoms persist despite conservative treatment for 4-6 weeks, or if there are concerning features like night pain, weight loss, or rapidly progressing symptoms, an MRI would be appropriate 1.
From the Research
Necessity of MRI for Foot Conditions
- The necessity of Magnetic Resonance Imaging (MRI) for foot conditions is a topic of debate, with some studies suggesting that it may be overused 2.
- A study published in 2007 found that 87% of pre-referral MRI scans were thought to be unnecessary, and 48.4% had radiographic interpretations that were considered either immaterial to the patient's pertinent clinical diagnosis or inconsistent with the specialist's interpretations 2.
- However, another study published in 2020 found that MRI can be useful in diagnosing and managing complex regional pain syndrome (CRPS) in the foot, although it may not be able to distinguish between CRPS and non-CRPS patients 3.
Specific Conditions Where MRI May Be Necessary
- For diabetic Charcot foot, MRI can be useful in monitoring the progression of bone marrow edema and assessing the response to treatment 4.
- In cases of chronic foot pain, whole-body fluorodeoxyglucose (18F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) may be useful in identifying pain generators and guiding treatment 5.
Considerations and Risks
- The use of MRI contrast agents, such as gadolinium-based agents, carries risks, including nephrogenic systemic fibrosis (NSF) in patients with end-stage kidney disease or acute kidney injury 6.
- Patients with moderate-to-severe chronic kidney disease are considered to be at high risk for contrast-induced nephropathy (CIN) when undergoing CT scans with iodinated contrast media 6.