Heterotopic ossification around the lesser trochanter of the femur simulating a malignant lesion. A case report with long-term follow-up and revision of literature

We report the case of a 28-year-old female who complained of groin pain and restricted range of motion of the hip for the previous two months. A plain radiograph, CT scan and MRI of the pelvis showed a bone mass of uncertain origin around the lesser trochanter, simulating malignancy. An open biopsy was performed to obtain a correct diagnosis. The histological examination excluded a malignant lesion. Two months later, the mass was surgically excised and at follow-up, 9 years after surgery, the patient was completely asymptomatic, without any radiographic sign of recurrence. This is a rare case of heterotopic ossification of the proximal part of the femur, that appeared without any significant trauma or other predisposing risk factors; because the lesion led us to suspect a malignant disease, an open biopsy was needed to make the diagnosis. From an accurate review of the literature, heterotopic ossifications mimicking a malignant lesion that appeared without any predisposing factors are extremely rare.