Painful Os Peroneum Syndrome: An Unusual Diagnosis.

The painful Os peroneum syndrome is subdivided into acute and chronic cases. The acute presentation is usually caused by trauma, most commonly a supination or inversion of the ankle, which consequently can lead to a fracture of the Os peroneum or even a rupture of the peroneus longus tendon. Furthermore, its chronic presentation comes as a result of recurrent foot injuries or even recovery from a fracture with calcification remodeling of this sesamoid bone. The problem of underdiagnosing this disease lies in the consequences attached to the remodeling of the peroneus longus tendon with its calcification, or even leading to a picture of tenosynovitis and subsequent tendon rupture. We report a 55-year-old female patient who complains of pain in the lateral region of her right foot for ten days. The right foot X-ray detected the presence of "Os peroneum." Magnetic resonance imaging (MRI) shows edematous ossification in the peroneus longus tendon compatible with Os peroneum and with swelling of the surrounding soft tissue and tendinopathy of the peroneus longus, precisely in the region indicated by the skin marker. The set of findings is compatible with painful Os peroneum syndrome. The patient was treated with a non-steroidal anti-inflammatory for five days with the resolution of symptoms.