Myositis ossificans (MO) is a benign condition where bone forms within muscles due to increased activity of the periarticular tissues. Trauma is the most common cause. Nontraumatic MO is exceedingly rare. We present a rare instance of nontraumatic MO affecting the hip in a 32-year-old patient. The patient had a known case of seizure disorder and also had a history of a cerebrovascular accident (CVA). Despite the absence of trauma or known predisposing factors, the patient developed a sizable mass in the left hip, causing pain and restricted range of motion (ROM). Surgical excision of the mass was successful, resulting in complete removal and subsequent improvement in hip function and pain relief during postoperative recovery. Histopathological examination confirmed the diagnosis of MO. The patient\'s ROM normalized, and there were no signs of recurrence at the one-year follow-up. This case highlights the importance of recognizing MO in hip pain cases without trauma. Timely surgery through the approach described effectively removes the mass, preventing recurrence without compromising vital structures. It showcases a successful multidisciplinary approach for rare musculoskeletal conditions, offering valuable insights into similar cases.

BACKGROUND: Nontraumatic myositis ossificans is a rare disease whose specific pathogenesis is unclear. Early diagnosis of this disease is very difficult in children because of difficulties in determining medical history and nonspecific early clinical manifestations, which may lead to the failure of timely and effective diagnosis and treatment in some patients. We report the diagnosis and treatment of a child with nontraumatic myositis ossificans and summarize the clinical characteristics and diagnosis and treatment of the disease.
METHODS: An 8-year-old girl first came to our hospital for more than a week with pain in the right lower limb. There was no history of trauma or strenuous activities. On physical examination, no mass on the right thigh was found, and the movement of the right lower extremity was limited. Ultrasonography showed synovitis of the hip, and bed rest was recommended. Three days later, the child\'s pain persisted and worsened, accompanied by fever and other discomforts. She came to our hospital again and a mass was found on the right thigh with redness and swelling on the surface. The images showed a soft tissue tumor on the right thigh with calcification. Routine blood tests revealed that the inflammation index was significantly increased. In case of infection, the patient was given antibiotics, and the pain was relieved soon after, without fever. However, the right thigh mass persisted and hardened. The patient underwent incision biopsy more than 1 mo later, and the postoperative pathology showed nontraumatic myositis ossificans. After approximately 9 mo of observation, the tumor still persisted, which affected the life of the child, and then resection was performed. Since follow-up, there has been no recurrence.
CONCLUSIONS: Due to the difficulty in discerning a child\'s medical history and the diverse early manifestations, it is difficult to diagnose nonossifying muscle disease in children in its early stage. Measures such as timely follow-up and periodic image monitoring are conducive to early diagnosis of the disease. The disease has a certain degree of self-limitation, and it can be observed and treated first. If the tumor persists in the later stage or affects functioning, then surgery is considered.

Myositis ossificans is a benign disorder characterized by the formation of heterotopic bone in skeletal muscle or soft tissues. It is extremely rare in children, <1% of cases occur in children under 10 years. We present a 17-day-old boy that, after 10 days of Intermediate Care Unit stay, was referred to our hospital for a developmental dysplasia of the hip. On clinical examination, he had swelling on the left thigh and increase in size compared to the contralateral one, therefore was admitted for studying. Imaging findings including plain radiographs, CT, MRI and bone scintigraphy, as well as treatment performed, are described. To the best of our knowledge, is the youngest case reported in the literature.

BACKGROUND: Myositis Ossificans Cicumscripta is a rare condition characterized by aberrant bone formation in paramuscular soft tissue of the extremities usually associated with trauma or a genetic mutation. Very few cases involve the head or neck and it is rarely found in the pediatric population.
OBJECTIVE: We present a case of a 5-month old with a rapidly growing posterior neck mass suspicious for neoplasia, which was treated with surgical resection and found to be a non-traumatic, non-genetic form of Myositis Ossificans. The workup, treatment, and findings of the patient are outlined and a review of the literature on this disease is discussed.
CONCLUSIONS: Myositis Ossificans is characterized by aberrant bone formation typically occurring after trauma but may be secondary to an underlying genetic abnormality. The case presented in the absence of trauma or an underlying genetic abnormality and is therefore an exceedingly rare instance of the sporadic form that presented spontaneously in the head and neck of a pediatric patient.