A patient came to the ED with complaints of pain on the bottom of his foot after stepping on glass. He reported that it felt like glass was still in his foot.
On physical exam, no abnormality was appreciated other than tenderness on the sole of the foot. An XR was obtained to evaluate for presence of a foreign body.
Here is a zoomed in image of the area where the patient had tenderness.
No foreign body was appreciated on the XR by the providers taking care of the patient or by the radiologist. The patient was adamant that a foreign body was present, and a bedside ultrasound was performed to evaluate for a foreign body.
What do you see?
There is a foreign body in the subcutaneous tissue of the foot that the providers taking care of the patient appreciated easily with ultrasound. If you are not sure what is going on in the clips, here is a still pointing out the structures seen:
With the assistance of ultrasound the foreign body was retrieved easily.
Steps to Ultrasound Guided Foreign Body Removal:
- Have the patient point to the area of maximal pain.
- Place the linear ultrasound transducer directly over that area (if planning on removing FB and not just detecting it, we should mention that sterile technique should be used so either put a tegaderm over the end of the ultrasound or a sterile probe cover).
- Once the FB is detected, take your lidocaine (bupivicaine, etc…) in a syringe with needle attached, and under ultrasound guidance with the FB “in plane,” inject the numbing agent along the track of the FB.
- Make a small skin incision with a scalpel where you plan to enter.
- Under ultrasound guidance, enter the skin incision you made with forceps, a hemostat, etc, and retrieve the FB.
As with everything related to ultrasound, detection and ability to remove are operator dependent. Studies have shown that detection of FB with ultrasound has a sensitivity of about 85-95% and a specificity of 54-100%. (1-3) Ultrasound also has the advantage of being able to detect radiolucent FBs (wood); whereas, XR only has a 40% sensitivity of radiolucent and semiradiopaque FBs. (4)
Bottom Line:
- Believe your patients. They are often right about what is going on.
- Ultrasound is better at detecting foreign bodies than XR and can make retrieval much easier.
References
1. Allen GM, Drakonaki EE, Tan ML, Dhillon M, Rajaratnam V. High-resolution ultrasound in the diagnosis of upper limb disorders: a tertiary referral centre experience. Ann Plast Surg. 2008;61(3):259-264.
2. Saul T, Siadecki SD, Rose G, et al. Ultrasound accurately identifies soft tissue foreign bodies in a live anesthetized porcine model. Acad Emerg Med. 2015;22(8):950-954.
3. Saboo SS, Saboo SH, Soni SS, Adhane V. High-resolution sonography is effective in detection of soft tissue foreign bodies: experience from a rural Indian center. J Ultrasound Med. 2009;28(9):1245-1249.
4. Cohen DM, Garcia CT, Dietrich AM, Hickey RW, Jr. Miniature C-arm imaging: an in vitro study of detecting foreign bodies in the emergency department. Pediatr Emerg Care. 1997;13(4):247-249.
