Ultrasound or x-ray for foreign bodies?

One of our surgical trainees called me because they had developed a severe pain in the sole of the foot with a granuloma over an area of previously suspected plantar fibroma on the sole of the foot. This had happened spontaneously the previous day with no aggravating factors.

The area was evaluated under ultrasound (Figure 1) which suggested an inclusion cyst with a foreign body. On further questioning, he had trodden on a nail 25 years previously but had no further problems. The foreign body was the shape of the head of a nail and he was sent for x-ray to confirm the diagnosis. However, the x-ray (Figure 2) did not show any foreign body.

Figure 1. US of inclusion cyst with foreign body

Figure 2. X-ray which does not show any foreign body

Given the sudden onset and level of pain, it was decided to explore the area and the granuloma was excised via a transverse double ellipse to follow the skin tension lines to minimise problems with a scar on the sole of the foot. This revealed a 5mm irregular piece of metal which appeared oxidised (Figure 3).

This is a clear example of the sensitivity of ultrasound over x-ray even for a metallic object which one would expect to see on x-ray.

Figure 3. Piece of metal removed from sole of foot