Working Diagnosis:
Myositis Ossificans

Treatment:
Patient placed in a walker boot at the initial visit and the MRI of the tibia and fibula was obtained the following day. Radiology sent him directly to the Emergency Department from MRI. Orthopedics and Hematology/Oncology were consulted. His work-up was more worrisome for sarcoma than infection so patient scheduled for close outpatient follow-up. Surgical biopsy obtained 1 week later unexpectedly confirming myositis ossificans.

Outcome:
Patient was seen 1 week after his biopsy with no surgical complications. Then 1 month later repeat radiographs obtained demonstrating a healing proximal fibular fracture with an adjacent soft tissue calcific mass. Case Photo #7 Case Photo #8 At that visit he reported significantly improved symptoms but persistent palpable mass. Surgical removal was discussed but declined. Gradual resumption of normal daily activities started.

Author's Comments:
Myositis ossificans (MO) is a benign, ossifying soft tissue mass typically seen in the active sporting population. These typically occur within large skeletal muscle, such as the quadriceps, after a traumatic history. This case demonstrates an atypical presentation of myositis ossificans in a non-athlete without trauma. Early in the work-up more ominous etiologies, such as osteosarcoma, were expected based on his clinical history and initial imaging. Fortunately, with surgical biopsy it was confirmed that MO was the uncommon cause of this young patient's lower leg pain. Like with most myositis ossificans, this patient had an excellent outcome with conservative treatment with no need for surgical excision.

Editor's Comments:
This case demonstrated several key factors in working up musculoskeletal complaints in adolescents. This patient had pain that would awaken him at night with no known injury. An initial x-ray showed concerning periosteal reaction in the proximal fibula which prompted the additional workup. Fortunately, after a thorough workup he was ultimately diagnosed with myositis ossificans. This is an uncommon presentation for myositis ossificans whereas most patients recall a specific injury or repetitive stress leading to the diagnosis. Treatment is often multidisciplinary but this is typically a self-limiting and self-resolving process so conservative measures to help reduce pain and improve strength and function are often sufficient.

References:
1. Walczak BE, Johnson CN, Howe BM. Myositis Ossificans. J Am Acad Orthop Surg. 2015 Oct; 23(10):612-22
2. Morris SJ, Trieu J, Chin R, Allman K, Van Der Wall H. Fibula stress fracture and confounding myositis ossificans. Clin Nucl Med. 2004 Dec;29(12):813-4

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