Os trigonum syndrome with clinical and radiological findings

Os trigonum

Abstract

Os trigonum is a rare accessory bone located posterior to the os talus. This bone develops as a secondary ossification center in the posterior of the talus between the ages of 7-13 years and fuses with the talus via synchondrosis within the following year. If this union does not occur, an accessory bone called the os trigonum is formed, which is usually asymptomatic. Os trigonum syndrome (OTS) refers to a clinical condition characterized by posterior foot pain during forced plantar flexion of the ankle due to compression between the posterior malleolus of the tibia and the tuber calcaneus. Diagnosis is based on the patient's clinical history, examination, and radiological findings. We present the case of an 18-year-old male with a history of an ankle sprain sustained during strenuous sports activity. Clinical evaluation revealed pain, swelling, and ecchymosis on the posterior foot. Magnetic resonance imaging (MRI) demonstrated an accessory os trigonum with medullary edema in the posterior talus, fluid accumulation, and flexor hallucis longus tenosynovitis. Conservative treatment involving a three-week break from sports and medical management was prescribed. This case highlights the importance of considering OTS in the differential diagnosis of posterior foot pain aggravated by plantar flexion.