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Myositis ossificans
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Myositis ossificans (MO) is a benign process characterized by heterotopic ossification usually within large muscles. Its importance stems in large part from its ability to mimic more aggressive pathological processes. Myositis ossificans is one of the skeletal “don’t touch” lesions.
There are some conditions that are related to, or share a similar name to, myositis ossificans 1:
myositis ossificans circumscripta: refers to new bone that usually appears after trauma
myositis ossificans progressiva: a rare, inherited disorder characterized by fibrosing and ossification of muscle, tendon and ligaments of multiple sites that are disabling and ultimately fatal
panniculitis ossificans: similar to MO but occurring in subcutaneous tissues
fibro-osseous pseudotumor of the digits: variant of MO occurring in the fingers and toes
The remainder of this article focuses on the former. Myositis ossificans progressiva, panniculitis ossificans and fibro-osseous pseudotumor of the digits are discussed separately.
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Myositis ossificans
Dr Henry Knipe◉◈ and Dr Saqba Farooq et al.
Myositis ossificans (MO) is a benign process characterized by heterotopic ossification usually within large muscles. Its importance stems in large part from its ability to mimic more aggressive pathological processes. Myositis ossificans is one of the skeletal “don’t touch” lesions.
There are some conditions that are related to, or share a similar name to, myositis ossificans 1:
myositis ossificans circumscripta: refers to new bone that usually appears after trauma
myositis ossificans progressiva: a rare, inherited disorder characterized by fibrosing and ossification of muscle, tendon and ligaments of multiple sites that are disabling and ultimately fatal
panniculitis ossificans: similar to MO but occurring in subcutaneous tissues
fibro-osseous pseudotumor of the digits: variant of MO occurring in the fingers and toes
The remainder of this article focuses on the former. Myositis ossificans progressiva, panniculitis ossificans and fibro-osseous pseudotumor of the digits are discussed separately.
On this page:
Article:
Epidemiology
Clinical presentation
Pathology
Radiographic features
Treatment and prognosis
Differential diagnosis
See also
References
Images:
Cases and figures
Imaging differential diagnosis
Epidemiology
Most cases of myositis ossificans occur as a result of trauma, and thus, the primary demographic is young adults 1. Another group which is especially prone to myositis ossificans are paraplegics, usually without evidence of trauma 2.
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Clinical presentation
Typically presents as a painful, tender, enlarging mass, which in 80% of cases is located in large muscles of the extremities, often following recognized local trauma, although a definite traumatic event is not always recalled 1,3. In the case of paraplegics, recognized episodes of trauma are often absent, and the disease occurs particularly around the knees and hips 2.
Pathology
Myositis ossificans is essentially metaplasia of the intramuscular connective tissue resulting in extraosseous bone formation (without inflammation).
It has a zonal organization 1:
peripheral, well-organized mature lamellar bone
intermediate osteoid region
central immature non-ossified cellular (fibroblasts) focus
Unfortunately, the histologically of myositis ossificans can appear similar to osteosarcoma, and thus, can lead to inappropriate management.
Radiographic features
The typical radiographic appearance of myositis ossificans is circumferential calcification with a lucent center and a radiolucent cleft (string sign) that separates the lesion from the cortex of the adjacent bone.
Plain radiograph
Calcification usually begins to become apparent on plain radiographs within 2-6 weeks, and the lesion reaches the classic well-circumscribed peripherally calcified appearance by two months. Over the following 4 or so months, they typically become smaller and denser 1,3.
The cleft between it and the subjacent bone may be difficult to see on plain radiographs.
There are some conditions that are related to, or share a similar name to, myositis ossificans 1:
myositis ossificans circumscripta: refers to new bone that usually appears after trauma
myositis ossificans progressiva: a rare, inherited disorder characterized by fibrosing and ossification of muscle, tendon and ligaments of multiple sites that are disabling and ultimately fatal
panniculitis ossificans: similar to MO but occurring in subcutaneous tissues
fibro-osseous pseudotumor of the digits: variant of MO occurring in the fingers and toes
The remainder of this article focuses on the former. Myositis ossificans progressiva, panniculitis ossificans and fibro-osseous pseudotumor of the digits are discussed separately.
MENU

SEARCH
ARTICLES
CASES
COURSES
LOG IN
Become a Radiopaedia Supporter and go Ad-Free
Myositis ossificans
Dr Henry Knipe◉◈ and Dr Saqba Farooq et al.
Myositis ossificans (MO) is a benign process characterized by heterotopic ossification usually within large muscles. Its importance stems in large part from its ability to mimic more aggressive pathological processes. Myositis ossificans is one of the skeletal “don’t touch” lesions.
There are some conditions that are related to, or share a similar name to, myositis ossificans 1:
myositis ossificans circumscripta: refers to new bone that usually appears after trauma
myositis ossificans progressiva: a rare, inherited disorder characterized by fibrosing and ossification of muscle, tendon and ligaments of multiple sites that are disabling and ultimately fatal
panniculitis ossificans: similar to MO but occurring in subcutaneous tissues
fibro-osseous pseudotumor of the digits: variant of MO occurring in the fingers and toes
The remainder of this article focuses on the former. Myositis ossificans progressiva, panniculitis ossificans and fibro-osseous pseudotumor of the digits are discussed separately.
On this page:
Article:
Epidemiology
Clinical presentation
Pathology
Radiographic features
Treatment and prognosis
Differential diagnosis
See also
References
Images:
Cases and figures
Imaging differential diagnosis
Epidemiology
Most cases of myositis ossificans occur as a result of trauma, and thus, the primary demographic is young adults 1. Another group which is especially prone to myositis ossificans are paraplegics, usually without evidence of trauma 2.
Become a Radiopaedia Supporter and go Ad-Free
Clinical presentation
Typically presents as a painful, tender, enlarging mass, which in 80% of cases is located in large muscles of the extremities, often following recognized local trauma, although a definite traumatic event is not always recalled 1,3. In the case of paraplegics, recognized episodes of trauma are often absent, and the disease occurs particularly around the knees and hips 2.
Pathology
Myositis ossificans is essentially metaplasia of the intramuscular connective tissue resulting in extraosseous bone formation (without inflammation).
It has a zonal organization 1:
peripheral, well-organized mature lamellar bone
intermediate osteoid region
central immature non-ossified cellular (fibroblasts) focus
Unfortunately, the histologically of myositis ossificans can appear similar to osteosarcoma, and thus, can lead to inappropriate management.
Radiographic features
The typical radiographic appearance of myositis ossificans is circumferential calcification with a lucent center and a radiolucent cleft (string sign) that separates the lesion from the cortex of the adjacent bone.
Plain radiograph
Calcification usually begins to become apparent on plain radiographs within 2-6 weeks, and the lesion reaches the classic well-circumscribed peripherally calcified appearance by two months. Over the following 4 or so months, they typically become smaller and denser 1,3.
The cleft between it and the subjacent bone may be difficult to see on plain radiographs.
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