What is the Difference Between Heterotopic Ossification and Myositis Ossificans

The key difference between heterotopic ossification and myositis ossificans is that heterotopic ossification is the formation of extraskeletal bone in muscle and soft tissues after joint replacement surgery, while myositis ossificans is the formation of extraskeletal bone in muscle and soft tissues after trauma to the muscle or a broken bone. 

In both heterotopic ossification and myositis ossificans, the bone forms in and around soft tissue. There are three types of heterotopic ossification: traumatic heterotopic ossification, myositis ossificans progressive, and neurogenic heterotopic ossification. Therefore, myositis ossificans is a specific type of heterotopic ossification. However, men over the age of 65 are affected most often by heterotopic ossification, whereas children and young adults are affected most often by myositis ossificans.

CONTENTS

1. Overview and Key Difference
2. What is Heterotopic Ossification  
3. What is Myositis Ossificans
4. Similarities – Heterotopic Ossification and Myositis Ossificans
5. Heterotopic Ossification vs. Myositis Ossificans in Tabular Form
6. Summary – Heterotopic Ossification vs. Myositis Ossificans

What is Heterotopic Ossification?

Heterotopic ossification is a condition that occurs when extraskeletal bone develops in muscle or soft tissues. It most often happens after a joint replacement surgery. Occasionally, certain individuals may experience heterotopic ossification due to genetic conditions, with examples including fibrodysplasia ossificans progressiva (FOP) and progressive osseous heteroplasia (POH). Men over the age of 65 are affected most often by heterotopic ossification. The risk factors for getting heterotopic ossification include patients with ankylosing spondylitis or Paget’s disease and hip joint replacement without cement. The symptoms of non-genetic heterotopic ossification are pain, swelling, and tenderness, while symptoms of genetic heterotopic ossification are tenderness, misshapen big toe, spinal malformations, and structural problems in fingers.

Heterotopic ossification can be diagnosed through medical history, physical examination,  CT scan, MRI, positron emission tomography (PET) scan, ultrasound, and X-ray. Furthermore, heterotopic ossification can be treated with medications such as corticosteroids, physical therapy, and surgery (medical treatment and radiation therapy will be done after surgery to help prevent regrowth of the bone).

What is Myositis Ossificans?

Myositis ossificans is a specific type of heterotopic ossification that occurs after trauma to the muscle or a broken bone. In this condition, new bone cells form between the torn muscle fibers. Most commonly, this condition can be seen in areas like the elbow or thigh. Children and young adults are affected most often by myositis ossificans. The risk factors for this condition include young, active people, athletes of all levels, and people who are paralyzed from the waist down (paraplegia). Myositis ossificans can manifest through various symptoms, such as the development of a rapidly growing, painful, swollen, and tender bump in the arm or leg muscles. In individuals with paraplegia, these bumps might also emerge around the hips or knees. Additionally, these bumps can increase in size over time, limiting the range of motion and eliciting warmth upon touch.

Myositis ossificans can be diagnosed through medical history, physical examination, CT scan, MRI, positron emission tomography (PET) scan, ultrasound, X-ray, and biopsy. Furthermore, treatments for myositis ossificans may include icing the bump, limiting the activity to rest the area, stretching gently, taking nonsteroidal anti-inflammatory drugs (NSAIDs) such as acetaminophen and ibuprofen, using an elastic bandage to reduce swelling, physical therapy, and surgery to remove bony growth.

What are the Similarities Between Heterotopic Ossification and Myositis Ossificans?

• In both heterotopic ossification and myositis ossificans, bone forms in and around soft tissue.
• Both can be genetic as well as non-genetic.
• They can occur after a stiff joint is manipulated under anesthesia.
• Both can be diagnosed through medical history, physical examination, and imaging tests.
• They are treated through specific medications, therapies, and surgeries.

What is the Difference Between Heterotopic Ossification and Myositis Ossificans?

Heterotopic ossification is the formation of extraskeletal bone in muscle and soft tissues that normally occurs after joint replacement surgery, while myositis ossificans is the formation of extraskeletal bone in muscle and soft tissues that normally occurs after trauma to the muscle or a broken bone. Thus, this is the key difference between heterotopic ossification and myositis ossificans. Furthermore, the risk factors for getting heterotopic ossification include patients with ankylosing spondylitis or Paget’s disease and hip joint replacement without cement. On the other hand, the risk factors for this condition include young, active people and athletes of all levels, and people who are paralyzed from the waist down (paraplegia).

The infographic below presents the differences between heterotopic ossification and myositis ossificans in tabular form for side-by-side comparison.

Summary – Heterotopic Ossification vs Myositis Ossificans

Heterotopic ossification and myositis ossificans are two associated medical conditions. Both heterotopic ossification and myositis ossificans are characterized by extraskeletal bone formation in and around soft tissue. Myositis ossificans is the most common form of heterotopic ossification that normally occurs within large muscles. However, heterotopic ossification is the formation of extraskeletal bone in muscle and soft tissues that normally occurs after joint replacement surgery, while myositis ossificans is the formation of extraskeletal bone in muscle and soft tissues that normally occurs after trauma to the muscle or a broken bone. So, this summarizes the difference between heterotopic ossification and myositis ossificans.

Reference:

1. “Heterotopic Ossification.” National Center for Biotechnology Information.
2. “Myositis Ossificans: Diagnosis, Symptoms and Treatment.” Cleveland Clinic.

Image Courtesy:

1. “Heterotopic Ossification Hip1” By Tdvorak – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Feet of a patient affected with myositis ossificans Wellcome L0062623” By Welcome (CC-BY-4.0) via Commons Wikimedia