Ultrastructure of the sternocleidomastoid muscle in muscular torticollis.

The sternocleidomastoid muscles from five children with muscular torticollis--examined by transmission electron microscopy, exhibited a marked increase in interstitial collagen deposition, and scattered areas of amorphous ground substance with electron dense deposits. No vascular abnormalities were observed. Ultrastructural muscle abnormalities showed various stages of immobilization degeneration including nearly complete loss of myofibrils. The muscle abnormalities ultrastructurally are consistent with immobilization degeneration, probably secondary to the marked fibrosis in the sternocleidomastoid muscle.