What is the preferred imaging modality, X-ray or ultrasound, for a patient presenting with a foot injury from stepping on an object 5 days ago, characterized by bleeding, tenderness, a hard central erythematous (red) area, and swelling?

From the Guidelines

For a foot injury from stepping on an object 5 days ago with bleeding, tenderness, a hard central red area, and swelling, an X-ray would be the recommended first-line imaging study. This recommendation is based on the American College of Radiology's (ACR) appropriateness criteria for acute trauma to the foot, which suggests that radiographs are the mainstay of initial imaging in this setting 1. The ACR criteria, which have a sensitivity of 99% for detecting foot fractures, indicate that radiographs are necessary if there is pain in the midfoot and any one of the following: point bone tenderness of the navicular, point bone tenderness of the base of the fifth metatarsal, or inability to bear weight or to walk 4 steps 1.

Given the clinical presentation of bleeding, tenderness, a hard central red area, and swelling, it is essential to rule out bone involvement or fractures that might have occurred during the injury. X-rays can quickly identify retained foreign bodies, especially if they are radiopaque like metal, glass, or some types of wood. If the X-ray is negative but clinical suspicion remains high for a retained foreign body, an ultrasound would be the appropriate next step. Ultrasound is excellent for detecting non-radiopaque foreign bodies like wood splinters, plastic, or thorns that X-rays might miss, and can also visualize soft tissue inflammation, abscesses, or fluid collections 1.

The hard central red area could indicate either a foreign body reaction or early abscess formation, which ultrasound can help identify. Given that it's been 5 days, infection is a concern, so prompt evaluation is important. While waiting for imaging, it is crucial to keep the wound clean, elevate the foot to reduce swelling, and monitor for increasing pain, redness, or drainage, which could indicate worsening infection requiring antibiotics.

Some key points to consider in the management of this patient include:

• The Ottawa rules for the foot have a sensitivity of 99% and a median specificity of 26% for combined evaluation of the ankle and midfoot 1.
• Radiographs are indicated by positive Ottawa rules with 99% sensitivity in determining the presence of a foot fracture 1.
• Ultrasound may be useful but is not typically considered the first line of imaging for the evaluation of acute trauma to the ankle with positive Ottawa rules 1.
• CT of the foot without IV contrast or MRI of the foot without IV contrast is usually appropriate for the next imaging study when radiographs are normal or equivocal of an adult or child older than 5 years of age with acute trauma to the foot and suspected Lisfranc injury, tendon injury, or occult fracture or dislocation 1.

From the Research

Diagnosis of Foot Injury

The symptoms presented, including bleeding, tenderness, a hard central red area, and swelling, 5 days after stepping on an object, could be indicative of an abscess or other soft tissue injury.

• The use of ultrasound is valuable in diagnosing abscesses that are not clinically evident and in guiding incision and drainage (I&D) procedures 2.
• Ultrasound can be used as an adjunct to clinical examination in diagnosing certain types of abscesses, such as dental abscesses 2.
• There is no direct evidence provided to suggest that an X-ray would be more appropriate than an ultrasound in this case.
• However, in cases where there is a need to evaluate the underlying bone structure, an X-ray may be necessary.

Imaging Modalities

The choice of imaging modality depends on the suspected underlying cause of the symptoms.

• Ultrasound is a useful tool in diagnosing soft tissue injuries, such as abscesses 2, 3.
• X-ray may be more appropriate for evaluating bone fractures or other bony abnormalities.
• In some cases, advanced imaging modalities such as MRI may be necessary to differentiate between abscesses and other intracranial or soft tissue lesions 4.

Management of Abscesses

The management of abscesses typically involves incision and drainage (I&D), with or without the use of antibiotics.

• Ultrasound-guided I&D can be an effective treatment for abscesses 2.
• The use of antibiotics may be necessary in certain cases, such as when there is evidence of surrounding cellulitis or other signs of infection 2, 5.