Myositis Ossificans: Symptoms, Types, Causes and Treatment

Myositis ossificans is a fascinating yet potentially debilitating condition marked by the abnormal formation of bone tissue within muscles or other soft tissues. While it is most often discussed in sports medicine, it can affect people of all ages and backgrounds, sometimes with no clear cause. In this article, we'll explore the symptoms, various types, underlying causes, and modern treatment approaches to offer a comprehensive understanding of this unique disorder.

Symptoms of Myositis Ossificans

When myositis ossificans develops, the initial signs are often subtle but can rapidly progress to more pronounced and bothersome symptoms. Recognizing these early can be crucial for proper diagnosis and management, especially since symptoms may mimic those of more serious conditions. Below, we break down the key symptoms and what they mean for patients.

Symptom	Description	Frequency/Association	Source(s)
Pain	Localized, often at injury site	Common in early and late stages	2 3 5 9
Swelling	Soft tissue swelling over muscle	Common initial presentation	2 3 9
Stiffness	Restricted joint/muscle motion	Especially in major muscle groups	2 3 4 12
Trismus	Limited jaw opening	Especially with jaw involvement	1 7 9
Tenderness	Localized sensitivity	Early/acute phase	3 5
Palpable Mass	Hard lump in muscle	Develops as lesion matures	2 5 9

Table 1: Key Symptoms

Pain and Swelling

One of the earliest and most common symptoms is pain, particularly at the site of muscle injury or involvement. This pain is usually accompanied by swelling, which may be mistaken for a simple muscle bruise or hematoma, especially following trauma 2 3 9. Over time, as bone forms within the muscle, the pain may persist or intensify, especially with movement.

Loss of Motion and Stiffness

As the ossified mass grows, it can restrict the movement of the affected muscle or nearby joint. This stiffness is especially noticeable in large muscle groups like the quadriceps (thigh) or brachialis (upper arm), but can also occur in smaller muscle groups, such as those controlling the jaw (resulting in trismus) 1 2 4 7 12.

Palpable Mass and Tenderness

In many cases, a hard, palpable lump develops within the muscle. This is the actual bone forming in soft tissue, which distinguishes myositis ossificans from other soft-tissue injuries. Tenderness over the affected area is common, particularly in the acute and subacute stages 2 3 5.

Special Symptoms: Trismus and Jaw Involvement

When myositis ossificans affects the muscles of mastication (those involved in chewing), a unique symptom called trismus (limited jaw opening) occurs. This can severely impact eating and speaking and is a key clue to diagnosis in facial cases 1 7 9.

Types of Myositis Ossificans

Not all cases of myositis ossificans are alike. Understanding the different types helps inform both diagnosis and treatment, as each has distinct features and implications.

Type	Key Features	Typical Onset/Population	Source(s)
Traumatic (Circumscribed)	Follows injury; solitary lesion	Athletes, trauma patients	2 4 5 6 9
Non-Traumatic (Idiopathic)	No clear cause; single/multiple	Any age; rare	5 6 9
Progressive (Hereditary)	Genetic, ongoing ossification	Children, familial cases	1 5 6 10
Neurogenic	Linked to nervous system injury	After CNS trauma, e.g., SCI	6

Table 2: Main Types of Myositis Ossificans

Traumatic Myositis Ossificans (Circumscripta)

This is the most common type and typically develops after a significant muscle injury, such as those experienced in sports or accidents. It usually presents as a solitary lesion in large muscles, like the quadriceps or brachialis 2 4 5 6 9. The condition is often referred to as "traumatic" or "circumscribed" myositis ossificans.

Non-Traumatic (Idiopathic/Pseudomalignant)

Not all cases are linked to trauma. Sometimes, bone forms in muscle without any obvious trigger. These idiopathic cases may mimic more aggressive conditions, which is why careful diagnosis is essential 5 6 9.

Progressive (Fibrodysplasia Ossificans Progressiva, FOP)

This rare, severe, genetic form is marked by ongoing, widespread ossification in muscles and connective tissue. It often begins in childhood and can be identified by characteristic malformations, such as shortened great toes 1 5 6 10. Unlike other forms, FOP is irreversible and disabling.

Neurogenic Myositis Ossificans

This rare subtype is associated with nervous system damage, such as spinal cord or brain injury. Ossification occurs near joints, most commonly the hips, and can further limit mobility in affected patients 6.

Causes of Myositis Ossificans

Understanding what triggers this unusual condition helps both with prevention and early intervention. While the exact mechanisms remain a topic of research, several key factors have been identified.

Cause	Description	Associated Type(s)	Source(s)
Trauma	Direct injury, contusion, repetitive strain	Traumatic/Circumscribed	2 4 5 9 12
Genetic Mutation	Mutation (e.g., ACVR1 in FOP)	Progressive (FOP)	1 5 6 10
Surgery/Procedures	Postoperative or dental interventions	Traumatic	1 4 7
Neurological Injury	CNS trauma (spinal/brain)	Neurogenic	6
Unknown	No clear cause, may involve local factors	Idiopathic	5 6 9

Table 3: Established and Suspected Causes

Trauma and Repetitive Injury

Most commonly, myositis ossificans arises after a significant muscle injury (e.g., a contusion or blunt trauma). The risk is increased by repeated injuries or inadequate care after the initial trauma. Sports such as football, diving, and contact athletics are common settings 2 4 5 9 12.

How Trauma Leads to Ossification

• Damage to muscle allows bone or cartilage fragments to become embedded in soft tissue.
• Bone morphogenic proteins (BMPs), especially BMP-4, are released or produced in excess.
• These factors stimulate local cells (mesenchymal stem cells) to become bone-forming osteoblasts, leading to heterotopic bone formation 9.

Genetic Causes: Progressive Myositis Ossificans

In fibrodysplasia ossificans progressiva (FOP), a mutation in the ACVR1 gene leads to uncontrolled bone formation throughout life, often triggered by minor injuries. Early signs include malformed great toes 1 5 6 10.

Surgical or Medical Procedures

Dental procedures (e.g., extractions, local anesthesia) and other surgical interventions can, in rare cases, trigger localized myositis ossificans, especially in the jaw's muscle groups 1 4 7.

Neurological Injury

Severe injuries to the central nervous system, such as spinal cord or brain trauma, can cause neurogenic myositis ossificans, typically near immobilized joints 6.

Idiopathic/Unknown Causes

In up to 25% of cases, no clear cause can be identified. These idiopathic cases may involve subtle or forgotten injuries, local inflammation, or genetic predisposition 5 6 9.

Treatment of Myositis Ossificans

Managing myositis ossificans requires a tailored approach, considering the type, stage, and location of the lesion, as well as the patient's symptoms and needs. Treatment aims to control symptoms, restore function, and prevent recurrence.

Treatment	Indication/Use	Outcome/Prognosis	Source(s)
Conservative	Early, mild cases; most traumatic MO	Usually excellent, self-limited	2 5 12
Physical Therapy	Regain motion, prevent stiffness	Improves function, mobility	1 2 12
Surgery	Large, mature, symptomatic lesions	Good if lesion is mature	1 3 5 12
Medications	Diphosphonates (FOP), anti-inflammatory	Variable; may slow progression	10
Acetic Acid Iontophoresis	Dissolve early calcification	Promising in selected cases	11

Table 4: Main Treatment Strategies

Conservative Management

Most cases respond well to conservative care:

• Rest and Immobilization: Especially important in the early phase after trauma, to avoid further injury and inflammation 2 12.
• Ice and Elevation: Reduce swelling and pain.
• Gradual Return to Activity: Early physical therapy focusing on active and passive range-of-motion exercises is key once acute symptoms subside 2 12.
• Monitoring: Regular imaging may be required to assess lesion progression.

Surgical Intervention

Surgery is reserved for:

• Mature, well-circumscribed ossified masses causing pain, weakness, or loss of function.
• Cases unresponsive to conservative measures after 6–12 months 1 3 5 12.

Timing is critical: Surgery before the lesion matures can increase recurrence risk. Complete excision generally results in excellent outcomes 1 3 12.

Emerging and Adjunct Therapies

• Physical Therapy: Essential both after surgery and in conservative care to regain function 1 2 12.
• Acetic Acid Iontophoresis: A non-invasive method that may help dissolve early ossifications, especially in athletes 11.
• Medications: In progressive forms (FOP), medications like diphosphonates have been trialed to slow new bone formation, with variable success 10.

Special Considerations for FOP and Neurogenic Cases

• Avoid Trauma: In FOP, even minor procedures or injections can exacerbate ossification 6 10.
• Multidisciplinary Care: Collaboration between orthopedists, geneticists, and rehabilitation specialists is essential for complex or hereditary cases 5 6.

Conclusion

Myositis ossificans, while rare, is a significant condition that can impact quality of life if not recognized and managed promptly. Its presentation varies widely, from localized post-traumatic lesions to severe, progressive genetic disorders. With advances in diagnosis and treatment, outcomes are increasingly positive, especially when care is individualized.

Key Points:

• Myositis ossificans involves abnormal bone formation in muscle or soft tissue.
• Key symptoms include pain, swelling, stiffness, and, in some cases, a palpable mass.
• Types include traumatic, idiopathic, progressive (hereditary), and neurogenic forms.
• Causes range from direct trauma to genetic mutations and neurological injuries.
• Treatment is typically conservative but may require surgery or emerging therapies.
• Early recognition and tailored management are vital for optimal outcomes.

Awareness of this condition among patients, athletes, and healthcare providers is critical for early intervention and minimizing long-term disability.