Myositis Ossificans

Other Names

• Myositis Ossificans Traumatica
• Myositis Ossificans (MO)
• Myositis (fibrous) ossificans progressive
• Traumatic circumscripta
• MO circumscripta
• Fibrodyspolasia ossificans progressive
• Rider’s bone
• Shooter’s bone

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Background

• This page refers to Myositis Ossificans (MO)
  • This can be defined as a benign, solitary, frequently self-limiting, ossifying soft-tissue mass found in skeletal muscle often encountered in the active sporting population
  • Although there are multiple types, this review will primarily focus the traumatic form seen in Athletes

Definition

• WHO subtypes
  • Traumatic
  • Atraumatic, sometimes termed pseudomalignant
  • MO associated with paraplegia
  • Progressive MO

History

• In 1905, Jones and Morgan questioned whether MO is a pure inflammatory condition
• In 1913, Coley described the challenges in distinguishing it from malignancy

Epidemiology

• Incidence is somewhat challenging because it may occur with or without trauma
• Traumatic MO represents 60-75% of all cases
• Simon et al estimated that muscle trauma represents 10% - 55% of athletic lesions, but not all muscle trauma leads to MO
• Up to 40% of cases can be insidious without clear history of trauma
• Demographics
  • More common in males than females
  • Most often in 20s, 30s
• Location
  • 9% - 20% of Quadriceps Femoris injuries result in MO

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Pathophysiology

• General
  • Internal lesions: Strains, pulls and tears
  • External lesions: direct trauma or impact
• Inadequate healing of muscle lesions can result in various complications including
  • Delayed healing time
  • Encysted hematoma
  • Fibrosis
  • Leads can all lead to myositis ossificans (MO)
• Precise pathophysiology is poorly understood, several proposed etiologies include
  • Inappropriate differentiation of fibroblasts into osteoblasts, chondroblasts following trauma
  • This is primarily due to bone morphogenic protein (BMP-2, BMP-4) and transforming growth factor (TGF)
  • Proinflammatory prostaglandin synthesis occurs following muscle damage can contribute
  • In the case of hematoma formation, subsequent necrosis and hemorrhage, followed by reparative fibroblastic and vascular proliferation
• Description
  • Liquefaction, formation of nonspecific sheets of cells in damaged muscle following injury
  • Cytokines recruit further inflammatory cells, macrophages into necrotic tissue
  • Mediators encourage the formation of heterotopic bone
  • Bone is laid down from outside to inside pattern (distinguishing it from neoplastic process)
• Natural history
  • Early stage: occurs within first 4 weeks of injury, calcifications can be seen on xray
  • Intermediate stage: between weeks 4 and 8
  • Mature stage: 8 weeks onward, potentially for months, marked calcifications visible on xray
• Location
  • Most commonly along diaphysis of long bones with larger muscle groups
  • Includes Brachialis, Quadriceps Femoris, Adductor Muscle Group
• Can be challenging to distinguish from other lesions, namely myosarcomas

Other Locations

• "Rider's Bone"
  • Occurs in the adductor muscle group among equestrian sports
• "Shooter's Bone"
  • Occurs in the deltoid muscle
• Occurs in the soleus muscle among ballet dancers

Associated Conditions

• Quadriceps Contusion

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Risk Factors

• For Quad MO
  • Quadriceps Contusion with knee flexion < 120°
  • Prior history of quadriceps contusion
  • Sympathetic knee effusion
  • Muscle injury with a delay of treatment of more than 3 days
• Sports
  • Football
  • Soccer

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Differential Diagnosis

Differential Diagnosis Thigh Pain

• Fractures
  • Femoral Shaft Fracture
  • Femoral Shaft Stress Fracture
  • Distal Femur Fracture
• Muscle and Tendon
  • Quadriceps Tendonitis
  • Quadriceps Contusion
  • Quadriceps Tendon Rupture
  • Hamstring Strain
  • Hamstring Tendonitis
  • Adductor Strain
  • Adductor Tendinopathy
• Neurological
  • Meralgia Paresthetica
• Other
  • Myositis Ossificans
  • Acute Compartment Syndrome
  • Osteitis Pubis

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Clinical Features

• History
  • Athletes will typically recall a specific injury or traumatic event
  • Often treated for muscle strain or contusion and treated conservatively
  • If pain or symptoms persist longer than anticipated, should suspect MO
  • Will report localized pain, joint stiffness
  • Will have difficult using muscle group, e.g. weight bearing if quad affected
• Physical Exam
  • Pain and tenderness at site of injury
  • Careful evaluation for any evidence of neurovascular compromise
• Special Tests

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Evaluation

Radiographs

• Standard initial imaging modality
  • Not ordered in the case of most suspected uncomplicated muscle injuries
  • Can rule out fracture
• Findings
  • 2-4 weeks: can see faint radiopacities or periosteal reactions
  • 4-8 weeks: sharply well-circumscribed mass with a peripheral radiopaque rim, radiolucent center
  • 8 weeks and on: becomes more radiopaque, well defined with radiolucent center
  • 6-12 months: lesion may spontaneously regress slightly, appear smaller
• Li et al describes 3 separate radiographic appearances
  • A) Periosteal, flat MO formation occurs adjacent to the long-bone shaft, damaging the periosteum
  • B) Stalk, where MO formation is attached to the long-bone shaft
  • C) Intramuscular disseminated, where intramuscular MO formation occurs without periosteal disruption

CT

• May be useful early on
  • Can detect calcifications that may not be detectable on radiographs initially
  • Greatest utility late-to-early-stage to intermediate-stages
  • Where classic zonal arrangement may be detected before the lesions become apparent on plain radiographs
• Findings
  • 2-4 weeks: soft tissue edema, mass, with or without calficiations
  • 4-8 weeks: mineralization with low attenuation center
  • 8 weeks and on: more diffuse ossification pattern

MRI

• General
  • Often considered gold standard for soft tissue masses
  • May not demonstrate early calcifications well
  • Contrast is not typically required
• Findings
  • 2-4 weeks: Hematoma which is isodense (T1), hyperintense (T2)
  • 4-8 weeks: Isointense/hypointense signal peripherally and centrally compared to surrounding skeletal muscle
  • 8 weeks and on: well defined mass, isodense to all fat sequences, resolution of surrounding edema

Ultrasound

• General
  • Helpful to distinguish between solid and fluid filled cystic structures
  • Abate et al suggests US is most suitable modality for MO due to low cost, ease of performance and favorable safety profile
• Findings
  • 2-4 weeks: Increased power Doppler signal with hyperechoic outer layer
  • 4-8 weeks: Increased power Doppler signal with increased peripheral hyperechogenicity
  • 8 weeks and on: Little to no power Doppler signal with more evident peripheral layer, hyperechogenicity

Laboratory

• No clear diagnostic test
• Acute phase
  • CRP, ESR elevated
• Alkaline Phosphatase
  • Begins to elevate around 3 weeks following acute injury
  • Peak around week 10, return to baseline at week 18
  • Can vary from 1.3x to 13.4x normal
  • Nonspecific to MO, however trending to ensure they return to baseline may help exclude neuplastic process
• Creatinine Phosphokinase
  • Role is not clearly defined in MO

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Classification

Radiographic Stages of Myositis Ossificans

• Early (0-4 weeks)
  • X-ray: Normal or faint calcification
  • CT: Soft tissue edema
  • MRI: Isodense on T1; hyperintense on T2
  • US: Increased power Doppler signal with hyperechoic outer layer
• Intermediate (4-8 weeks)
  • X-ray: Peripheral calcified rim, central lucency
  • CT: Peripheral mineralization with low attenuated center
  • MRI: Iso/hypodense to adjacent skeletal muscle on all images
  • US: Increased power Doppler signal with increased peripheral hyperechogenicity
• Mature (>8 weeks)
  • X-ray: Diffuse soft tissue calcification
  • CT: Diffuse ossification pattern
  • MRI: Well-defined mass, isodense to fat on all images
  • US: Little to no power Doppler signal with more evident peripheral layer, hyperechogenicity

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Management

Prognosis

• General
  • Self limited with most athletes able to return to sport
• Surgical management
  • Orava (2017) found 30/32 patients were able to return to preinjury level of competition

Nonoperative

• General
  • First line approach in virtually all cases
  • Goal is to minimize symptoms, restore function and range of motion
• Initial management
  • Relative rest
  • Ice Therapy or Cryotherapy can reduce blood flow to injury by up to 50% (need citation)
  • Brief period of immobilization, compression may reduce risk or size of hematoma formation
• NSAIDS
  • Consider avoiding in first 1-3 days due to antiplatelet effects
  • Then use of NSAIDs for 1-2 weeks is recommended
• Acetaminophen
  • Recommended by some experts for pain control
• Physical Therapy
  • Avoid aggressive rehab early on to prevent exacerbation of symptoms
  • Can begin gentle range of motion early
  • Role of static stretching in prevention or development of MO is not well defined
• Extracorporeal Shockwave Therapy (ECSWT)
  • One case report demonstrated full return to sport at 16 weeks
• Aspiration of hematoma
  • Case series among Vanderbilt football players demonstrated benefit of aspiration for recovery, return to sport (need citation)
  • No clear guidelines on when to utilize this procedure
• Bisphosphonates
  • Suppress bone turnover, slow down minieralize process
  • One case report describing an athlete receiving two doses of IV Pamidronate was associated with improvement in radiograph and clinical findings
  • Note should not be used in premenopausal women

Operative

• Indications
  • Not clearly established
  • Most lesions will regress when mature and become asymptomatic
  • Failure of conservative therapy by at least 6 months

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Rehab and Return to Play

Rehabilitation

• No clear guidelines for rehabilitation
  • Should not begin gradual progressive exercise or physical therapy until pain free range of motion

Return to Play

• No clear guidelines for RTP
• General
  • Symptoms start to subside between weeks 6-8
  • Competitive return to sport typically occurs between 4 and 6 months
• Simon et al
  • Found 90% of patients returned to light physical activity at 3 months
  • 90% of athletes returned to pre-injury level of sport at 6 months
  • 100% returned to sport by 1 year

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Complications

• Chronic pain
• Inability to return to sport

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See Also

• Muscle Pathology (Main)
• Osteology (Main)
• Thigh Pain (Main)

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