Amianthoid fibres in ruptured human tendons.

So-called amianthoid fibres were identified in 17 of 460 tendons (3.7%) after spontaneous rupture. These tendons belonged to 10 men and 7 women with an age-range from 18 to 67 years. In 445 postmortem control tendons taken of accidentally killed previously healthy persons amianthoid fibres were not found. Ultrastructurally the tendineal amianthoid fibres differ from normal tendon collagen fibrils in many respects. Their diameter (600-1400 nm) is many times larger than that of native collagen fibrils (20-120 nm). The fibre profile is often irregular and the cross-sectioned fibres have a homogeneous granular appearance. In longitudinal sections, the amianthoid fibres are frequently disintegrated and outspread, and some of the fibres have lost their periodicity. In addition, some of the fibres are angulated and show nonparallel organization. Occasionally the amianthoid fibres are calcified.