Updated: 10/27/2021

Myositis Ossificans

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  • summary
    • Myositis Ossificans is a reactive soft tissue bone-forming process that commonly occurs following a traumatic event to soft tissues.
    • The condition typically presents in patients between ages 15 and 35 who develop pain, tenderness, swelling, and decreased range of motion following localized trauma.
    • Diagnosis is made with radiographs showing peripheral bone formation with central lucent area within soft tissues. 
    • Treatment is usually observation as lesions typically resolve over time. Surgical excision is indicated for lesions that remain persistently symptomatic.  
  • Epidemiology
    • Demographics
      • most common in young active males (15 to 35 years old)
    • Anatomic locations
      • quadriceps, brachialis and gluteal muscles
  • Etiology
    • A form of heterotopic ossification that is the result of
      • direct trauma
      • intramuscular hematoma
        • most common location is the diaphysis of long bones
    • Associated conditions
      • 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)
    • Genetics
      • almost always a posttraumatic condition
  • 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
  • Prognosis
    • Usually self limiting
      • mass usually begins to decrease in size after 1 year

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Flashcards (2)
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Questions (10)

(SBQ20BS.17) A 23-year-old male football player presents to your office with complaints of a painful mass in his anterior thigh. The patient reports the mass is tender to the touch and is associated with local swelling. He has also noticed decreased range of motion to the ipsilateral knee since the mass appeared. Representative XR and MRI are shown in Figures A and B. Which of the following is most closely linked to this patient's condition?

QID: 215803
FIGURES:

Cartilage oligomeric matrix protein gene mutation

4%

(25/648)

Abnormal type X collagen

1%

(8/648)

Reciprocal translocation involving chromosomes 9 and 22

4%

(28/648)

History of thigh trauma

75%

(487/648)

p53 tumor suppressor gene mutation

15%

(96/648)

L 3 E

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(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?

QID: 4714
FIGURES:

Extraskeletal chondrosarcoma

7%

(340/4735)

Myositis ossificans

80%

(3802/4735)

Sessile osteochondroma

4%

(177/4735)

Ossifying soft tissue metastasis

2%

(102/4735)

Parosteal osteosarcoma

6%

(292/4735)

L 2 B

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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:

QID: 4687
FIGURES:

Elevated serum phosphate and serum creatinine

3%

(186/5422)

Mutation in ACVR1 gene

29%

(1546/5422)

HLA B27 antigen

17%

(939/5422)

Mutation in EXT gene

50%

(2709/5422)

Diabetes

0%

(16/5422)

L 5 B

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(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?

QID: 3599
FIGURES:

Ossifying lipoma

3%

(107/3363)

Synovial sarcoma

1%

(35/3363)

Myositis ossificans

94%

(3159/3363)

Periosteal chondrosarcoma

1%

(44/3363)

Inguinal hernia

0%

(6/3363)

L 1 C

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Evidence (10)
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