- See:
- Heterotopic Ossification
- Ossification of Soft Tissue:
- Discussion:
- extra-skeletal ossification that occurs in muscles & other soft tissues
- can be traumatic (75%), non traumatic, or progressive;
- severe blunt trauma causing an intra-muscular hematoma may result in delayed ossification;
- involved muscles: quadriceps, brachialis, and deltoid are involved most often;
- typically lesions are distant from joints, have decr pain w/ time;
- typically occurs in adolescents as a painless, enlarging mass in upper arm, thigh, or buttocks;
- associated with an intact cortex;
- demonstrate a zonal pattern;
- histology:
- microscopic, hypercellular spindle cells, peripheral woven bone, surrounding diseased & often trapped muscle, and normal osteoblasts making
bone are typical;
- zonation from central immature fibrous tissue to peripheral mature bone is characteristic, and helps distinguish myositis ossificans from osteosarcoma,
where the central bone is likely to be mature;
- diff dx:
- osteosarcoma:
- proliferative myositis
- Radiographs:
- soft tissue ossification not attached to bone is common;
- x-rays show round mass w/ distinct peripheral margin of mature ossification & a radiolucent center of immature osteoid & primative mesenchymal tissue;
- this peripheral maturation, reverse of that seen in a malignant tumor, is characteristic of myositis ossificans
- CT Scan:
- calcification of the herterotopic bone proceds from the outer margin and progresses centrally;
- Bone Scan:
- active myositis ossificans appears as intense para-osseous accumulation of tracer activity in acutely damaged muscle on delayed images;
- Prognosis:
- over time, the volume of heterotopic bone will diminish;
- Managment:
- indomethacin
Muscle contusion injury and myositis ossificans traumatica