LAUSR

Extraskeletal bone formations within the soft tissues can be the presentation of benign self-limited ossifying processes such as heterotopic ossification (HO) or malignant neoplasms such as extraskeletal osteosarcomas. Depending on the involved tissue, a number of synonymous terms have been established to describe these lesions. Myositis ossificans (MO) is the most common and refers to benign bone formation within skeletal muscles, whereas fasciitis and panniculitis ossificans refer to lesions in the fascia or the adipose tissue, respectively. The terms heterotopic ossification and myositis ossificans are often used interchangeably in the literature. The etiology of MO is variable and classified as hereditary or acquired, with the latter being the most common type. Hereditary MO includes fibrodysplasia ossificans progressiva and progressive osseous heteroplasia; both very rare, autosomal dominant inherited conditions associated with debilitating progressive heterotopic ossification. The acquired MO is further subclassified into traumatic and nontraumatic depending on the presence of history of trauma. Although its underlying pathophysiology has not yet been clearly defined, traumatic MO has been largely associated with various types of musculoskeletal injury, including fractures and soft tissue trauma, as well as orthopaedic procedures (hip, knee, and shoulder arthroplasties). The most commonly affected site of traumatic HO is the quadriceps femoris. Other causes of traumatic MO include central nervous system injury and severe burns. However, there are rare cases of MO that occur in the absence of a discrete traumatic etiology. Despite being a benign condition, nontraumatic MO poses a significant diagnostic challenge, as its clinical presentation mimics that of sinister conditions such as osteosarcoma. Here, we present a unique case of HO in the right anterior brachialis muscle of a young healthy man with no previous history of trauma or injury, who had recently started working out at the gym. To the best of our knowledge, this is the first report of HO secondary to recreational exercise. Informed consent was obtained from the patient.