Myositis ossificans

myositis

1. Myositis Ossificans

2. Introduction What is Myositis Ossificans ? It is a reactive lesion occuring in the soft tissue characterised by fibrous, osseous and cartilagenous proliferation and by metaplasia . A form of heterotrophic ossification that is a result of trauma in the form of a single severe injury or a series of repeatitive minor trauma.

3. Types Of Myositis Ossificans 1) Traumatic Myositis Ossificans . 2) Myositis Ossificans Progressiva (Fibro-dysplasia ossificans progressiva )

4. Traumatic Myositis Ossificans

5. Epidemiology Occurs most commonly in young males Age group : 15 – 35 years Male:Female 2:1 Young athletic men are predisposed.

6. Sites involved commonly Most common site – Elbow Quadriceps of Thigh Adductor muscles of thigh Knee Hip

7. Pathogenesis Traumatic pathology Haematoma is a pre-requisite Peculiar alteration within the ground substance of the connective tissue. Striking Proliferation of undifferentiated mesenchymal cells.

8. Pathology Initially degeneration and necrosis of the involved tissue Disrupted muscles retract Histiocytic invasion for removal of necrotic debris Invasion of fibroblasts within 3-4 days in the affected region Rapid Formation of broad sheets of fibroblasts Proliferation of primitive mesenchymal cell within the injured connective tissue.

9. Pathology ( contd ) Simultaneous proliferation of sarcolemmic nuclei at the ends of the damaged muscle fibre . Chains and columns of polyhedral cells appear Production of sarcoplasm which extends as buds from pre-existing fibres . Sarcolemmic nuclei cluster within the centre of the sarcoplasmic mass. Ground substance of the proliferating mesenchyme becomes homogenous or glassy suggesting oedema .

10. The ground substance increases in amount and encloses the mesenchymal cells and attain morphological characteristics of osteoblasts . Mineralisation occurs Sequence of events take place first within the pereiphery and then progresses towards the centre. Central area : Extremely cellular Periphery : Mature and well deliniated bone.

11. Histology Zonal phenomenon :

12. Microscopy Centre : Highly cellular region of numerous cells with presence of occasional atypical mitotic figures Intermediate zone/ Middle zone : Zone of fibroblastic tissue showing osteoid formation with fibro-vascular background. Outer zone : Mature and well oriented peripheral bone. Zonal phenomenon is not present in soft tissue sarcomas (differentiating feature)

13. Clinical Picture Condition occurs as a result of single severe trauma or a series of repeatitive minor trauma. Brachialis is the most common site of myosistis ossiifcans following posterior elbow dislocation. Elbow is swollen and tender Active and passive motion is greatly restricted. Gradually pain and swelling subsides Circumscribed, indurated and hard mass is palpable over the anterior aspect of the elbow . Active extension of the joint is limited.

14. Elbow Myositis Ossificans .

15. Myositis ossificans occuring in deltoid is common among soldiers due to repetitive trauma caused by carrying a rifle. Constant pressure against the adductor muscles of the thigh in horse riders cause myositis ossificans of the adductor muscles. KNOWN AS PRUSSIAN DISEASE Disease is self limiting - Undergoes maturation and may persist as a hard ossified mass within the muscle or in some cases the mass completely regresses.

16. Diagnostic Modalities X-Rays : Plain radiographs donot show any chages in the ear;y stages of myositis ossificans ( 2-3 weeks after onset of pathology) X-Rays done at a later stage shows pathognomonic ossification surrounding a clear central area. CT – Scan: More sensitive in showing ossification at the early stages.

17. MRI: May show zone phenomenon before ossification appears. Hyperintense lesion in intra-muscular mass on T2W image. Gadolinium enhanced T2W image shows a hyperintense rim suggestive of zonal phenomenon.

18. USG : Sensitive imaging modality to depict zonal phenomenon Can show characteristic findings before before any other modality. 3 concentric zones : Most peripheral : Hypoechoic and hyperemia Middle zone : Thinner , hyperechoic Central zone : Hypoechoic ( central stromal fibroblastic component )

19. Treatment Conservative management : Rest Immobilisation initially NSAID Active mobilisation of the affected joint once pain and swelling subsides. Growth should not be removed in the pre-mature stage.

20. Myositis Ossificans Progressiva ( Fibrodysplasia Ossificans Progressiva ) Rare disorder. Autosomal dominant genetic disorder. Progressive heterotrophic ossification in humans. Characterised by congenital malformation of great toe. Usually within 1 st decade of life. Spontaneous or injury induced exacerbation.

21. Pathophysiology Autosomal dominant disorder. Mutation in ACTIVIN RECEPTOR 1A (ACVR1) or ACTIVIN LIKE KINASE (ALK2) – a BMP type 1 receptor. Inflammatory components of the immune system are affected. Lesions flare up

22. Clinical Picture Painful swellings seen in soft connective tissue including tendons and ligaments apart from skeletal muscle. Children with FOP have a malformed great toe ( hallux valgus ) Episodic painful inflammatory swellings in the first decade of life. Minor trauma such as intra-muscular injections , trivial fall, bruise can trigger painful flares leading to heterotrophic ossification. Most of the patients are confined to a wheel chair by the end of 3 rd decade.

23. Seen in dorsal axial and cranial proximal regions of the body. Later progresses to ventral appendicular , caudal and distal region. Cervical spine is involved early Large posterior element Tall narrow vertebrae Fusion of facet joints from c2-c7 Microdactyly Ankylosis of jaw – severe weight loss. Rigid chest wall – predisposes for pneumonia and right heart failure.

24. Labs ESR raised Serum alkaline phosphatase raised.

25. Diagnosis Mainly on the basis of clinical examination X-Rays Bone scan – Can detect heterotrophic ossification before it appears on x-rays.

26. Treatment Steroids within 24 hours of flare up reduces intense inflammation and tissue oedema . 2mg/Kg/day for 4 days. NSAID Leukotirene inhibitors Muscle relaxants Surgical removal and biopsy are not to be done. Median age of survival is 14 years. Death occurs due to thoracic insufficiency syndrome.

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