Heterotropic Bone Formation

Question 1

Bone formation in soft tissues or where bone doesn’t normally exist is…

Answer 1

Heterotopic ossification (HO)

Question 2

Where is the acquired form of HO most frequently seen?

Answer 2

Musculoskeletal trauma (M/C)
[also, spinal cord injury/paralysis]

Question 3

The severity of heterotopic bone formation depends on the size ____ -cm and number of mineralized bone fragments

Answer 3

> 1cm

Question 4

Post-traumatic Mysoitis Ossificans (MO) is a _____ process characterized by heterotopic ossification usually within ____ muscles.

Answer 4

• Benign

- Large

Question 5

The radiographic-clinical importance of MO stems from its ability to mimic more ___________ (eg. __)

Answer 5

aggressive pathological processes (eg. osteosarcoma)

Question 6

What is the clinical presentation of MO most commonly viewed by?

Answer 6

Radiography and CT scanning

Question 7

What is the physical clinical presentation of the site of soft tissue ossification?

Answer 7

• Fever
• ST swelling
• Poor mobility

Question 8

______ is essentially metaplasia of the intramuscular connective tissue resulting in extraosseous bone formation…

Answer 8

Myositis ossificans

Question 9

What is the most important feature of MO?

Answer 9

Zonal organization phenomenon

Question 10

In looking at zonal phenomenon, what are the three characteristics of this development?

Answer 10

1. Peripheral well organized mature lamellar bone
2. intermediate osseous region
3. central immature non-ossified focus

Question 11

What may exacerbate the existing benign lesion?

Answer 11

Tissue biopsy

Question 12

MO is known as “_________”

Answer 12

“Don’t touch.” or “Leave it alone lesions”

Question 13

______ can occur within ____ days after the causative insult.

Answer 13

• Mineralization

- 10-14 days

Question 14

Calcification from MO usually starts _____ and remains a very important diagnostic feature of _______

Answer 14

• Peripherally

- Zonal phenomenon

Question 15

Circumferential calcification with a ___ centre, and a ______ that separates the lesion from the cortex of the adjacent bone.

Answer 15

• lucent centre

- radiolucent cleft STRING sign

Question 16

Calcification of this lesion begins to become apparent on radiographs at what time interval?

Answer 16

2-6 weeks

Question 17

The lesion of MO reaches its classic well circumscribed peripherally calcified appearance by ____ months.

Answer 17

2 months

Question 18

The lesion in MO will end up doing what?

Answer 18

Become smaller and denser

Question 19

What is the most likely cause of post-traumatic MO?

Answer 19

Blunt trauma [this is due to the bleeding/hematoma deep within the muscle]

Question 20

Myositis Ossificans - what sign separates the lesion from the cortex?

Answer 20

Cleft-string sign

Question 21

MO helped to differentiate from aggressive lesions by formation of what?

Answer 21

Zonal phenomenon

Question 22

Marked osteopenia and Heterotopic bone formation in what type of patient, and usually occurs where in this type of patient?

Answer 22

• Paraplegic patient

- Pelvis/Hip

Question 23

Post-traumatic MO should be differentiated from a form of sever and progressively fatal congenital disorder known as _______

Answer 23

Fibrodysplasia ossificans progressive (FOP)

[LOOK AT SLIDE 16-18 for pictures of this]

Question 24

What is the difference between extra-osseous or extra-skeletal osteosarcoma vs. Zonal phenomenon?

Answer 24

osteosarcoma has more of a sclerotic center due to aggressive bone formation - Zonal proliferation has a sclerotic periphery [almost rim like with a radiolucent center]