Updated: 10/23/2017

Myositis Ossificans

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Introduction
  • A reactive process that is characterized by a well-circumscribed proliferation of fibroblasts, cartilage, and bone within muscle
  • A form of heterotopic ossification that is the result of
    • direct trauma
    • intramuscular hematoma
      • most common location is the diaphysis of long bones
  • Must differentiate from tumors 
  • Fibrodysplasia ossificans progressiva (FOP) is a rare subtype of heterotopic ossification 
    • involves mutation of the ACVR1 gene (activin A type I receptor gene, a BMP type-1 receptor) 
  • Epidemiology
    • demographics
      • most common in young active males (15 to 35 years old)
    • body locations
      • quadriceps, brachialis and gluteal muscles
  • Genetics
    • almost always a posttraumatic condition
  • Prognosis
    • usually self limiting
      • mass usually begins to decrease in size after 1 year
Presentation
  • Symptoms
    • pain, tenderness, swelling and decreased range of motion that usually presents within days of the injury
      • pain and size of the mass decrease with time
    • mass increases in size over several months (usually 3 to 6 cm)
      • after the mass stops growing, it becomes firm
  • Physical exam
    • palpable soft tissue mass
    • restricted range of motion
Imaging
  • Radiographs 
    • peripheral bone formation with central lucent area
    • may appear as "dotted veil" pattern
  • MRI with gadolinium 
    • rim enhancement is seen within the first 3 weeks
  • CT scan
    • lesion has an eggshell appearance
Histology
  • Characteristic histology shows zonal pattern
    • periphery of lesion
      • mature trabeculae of lamellar and woven bone
      • calcification seen on xray
    • center of the lesion
      • irregular mass of immature fibroblasts
      • cartilage component may be present
      • (no calcification seen on xray) 
      • no cellular atypia seen
Treatment
  • Nonoperative
    • rest, range of motion exercises, and activity modification
      • passive stretching is contraindicated (makes it worse)
      • physical therapy
        • utilized to maintain range of motion
    • radiographic monitoring
      • obtained to confirm maturation of the lesion
  • Operative
    • surgical excision
      • indicated only if it remains a problem after it matures
      • do not operate in acute phase, wait at least six months
        • excision of the lesion within 6 to 12 months predisposes to local recurrence

References

 

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Questions (7)
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(OBQ13.52) A 26-year-old man presents with generalized back and joint stiffness and difficulty opening his mouth. His elder sister has similar complaints. Since childhood, he has had 3 surgeries for excision of recurrent bony prominences around his knees. He walks with a stooped over posture seen in Figure A. Radiographs of his feet, knee, hip and spine are seen in Figures B-E respectively. This patient will likely have: Review Topic

QID: 4687
FIGURES:
1

Elevated serum phosphate and serum creatinine

4%

(149/3763)

2

Mutation in ACVR1 gene

27%

(1011/3763)

3

HLA B27 antigen

19%

(729/3763)

4

Mutation in EXT gene

49%

(1847/3763)

5

Diabetes

0%

(4/3763)

ML 5

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ13.79) Three years after total knee arthroplasty, a 66-year-old male patient with a history of previously treated prostate cancer presents with right knee stiffness and swelling for 6 months after being struck in the anterior thigh by a baseball. Range of active motion is 10 to 40 degrees. Imaging and gross and microscopic appearance of the lesion are seen in Figures A-F. What is the diagnosis? Review Topic

QID: 4714
FIGURES:
1

Extraskeletal chondrosarcoma

7%

(272/3636)

2

Myositis ossificans

81%

(2931/3636)

3

Sessile osteochondroma

3%

(124/3636)

4

Ossifying soft tissue metastasis

2%

(73/3636)

5

Parosteal osteosarcoma

6%

(219/3636)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

(OBQ11.176) A 25-year-old male presents complaining of a groin mass which he noticed after a football injury that occurred 1 year ago. He states he was struck in the groin with an opposing player's helmet during a tackle and had a large amount of bruising and pain. While his pain and bruising subsided, he states he noticed this groin mass soon there after and that it hasn't grown and is non-tender. He is otherwise healthy. Inlet pelvis radiograph and T2 MRI with gadolinium scan are shown in Figures A and B. What is the most likely diagnosis? Review Topic

QID: 3599
FIGURES:
1

Ossifying lipoma

3%

(63/2448)

2

Synovial sarcoma

1%

(23/2448)

3

Myositis ossificans

95%

(2322/2448)

4

Periosteal chondrosarcoma

1%

(26/2448)

5

Inguinal hernia

0%

(5/2448)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
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