Heterotopic Ossification of the Peroneus Brevis Tendon in a Pediatric Patient.

Heterotopic ossification (HO) is abnormal formation of mature lamellar bone in soft tissues. HO is most commonly diagnosed in the setting of localized trauma, which results in improper differentiation of progenitor cells, leading to aberrant tissue formation. In the pediatric population, nongenetic causes of HO have rarely been reported, especially HO involving the tendons of the ankle. We present a case of HO of the peroneus brevis tendon without systemic disease in a pediatric patient. The patient was a 7-year-old female with a normal birth and developmental history who first presented 6 weeks after a right ankle sprain with pain localized to the lateral calcaneus. Prominent swelling and tenderness to palpation were noted over the peroneal tubercle. Radiographic imaging showed dystrophic calcification within the peroneus brevis tendon. After failed conservative management, the heterotopic ossified mass (1.5 × 0.3 cm) was excised from the peroneus brevis tendon. The tendon was primarily repaired. The patient was followed up for 12 weeks postoperatively and achieved full resolution of her pain with a return to normal activity. HO has been theorized to be the result of an imbalance between bone mineralization and demineralization. In the setting of localized trauma, inductive agents have been implicated in pathologic bone formation. In the pediatric population, HO has rarely been diagnosed in the absence of genetic causes. In patients presenting with lateral foot and ankle pain, HO of the peroneal tendons should be considered in the differential diagnosis. In a patient with pain secondary to HO, surgical excision of the heterotopic mass can achieve symptom resolution.