Myositis Ossificans of the Elbow

Myositis Ossificans is defined as the Ectopic ossification (formation of bone at odd places) in the muscle.

Types

Heterotrophic Ossifications

Formation of mature lamellar bone in non-osseous tissue (a dystrophic process involving ligaments and capsule; it can be metastatic)

Myositis Ossificans

Benign localized reactive proliferative lesion occurring with soft tissue (muscles)

Periarticular ossificans

Collection of calcium pyrophosphate in soft tissue (Lacks lamellar pattern)

Traumatic

• MO circumsripta, myo-osteosis, ossifying hematoma
• Contusion, tearing, post-operative

Neurogenic

• Injury to the neural axis

Myositis ossificans progressiva

• Inherited disorder
• More than 1/3 rd are inherited

Commonly involved in myositis ossificans in elbow= Brachialis; other: pronator teres, brachioradialis

Clinical features of MO

Depends upon phases

1. Acute/ Pseudoinflammatory phase ( 3^rd – 3^rd weeks)
   • Pain, swelling, and decreased ROM
2. Subacute/ Pseudotumor Phases (3-6 weeks)
   • Painless hard mass with raised temperature
3. Maturation (3-6 months)
4. Resolution (few cases only)

Classification of ectopic ossifications

Functional Classifications (Hasting and Graham)

Class I	Radiologically evident ectopic ossification with/without clinical limitations
Class II	Subtotal, functional, limitation of motion
A	In flexion and extension plane
B	In pronation and supination plane
C	In both planes
Class III	Ankylosis that eliminates motion
A	In flexion and extension plane
B	In pronation and supination plane
C	In both planes

Zonal Phenomena: Functional orientation of fibroblast to osteoblast in all ossifying masses. Myositis ossificans matures from inside to outside

Reverse zoning( Tumors): Matures from outside to inside. So, helps to differentiate between osteoid-forming tumors, typically osteosarcoma histologically.

Treatment of MO

Prophylactic measures

Acute phase

• Ice, compression
• Maintenance of ROM
• Support limb
• Avoid massage/ forceful passive mobilizations
• Bisphosphonates
• NSAIDS
• Calcitonin (? efficacy)
• Thalidomide

Radiation therapy: Low dose external beam radiation within 96 hr (20 Gy/ 10 fractions)

Surgery:

Delayed intervention (> 18 months) is recommended

• It helps to identify a metabolically quiescent bone in tissue in equilibrium

• Additional time for associated injuries to heal and stabilize

To assess the maturity of mass

• No local rise in temperature, no edema
• Normal ESR and ALP
• Bone Scintigraphy (> 2 bone scans show normal/decreased uptake)

Problems of delayed treatment

• Progressive and advanced contracture
• Potential articular cartilage destruction
• Prolonged infirmity

See also: The Stiff Elbow

See also: The Unstable Elbow