[Scanning electron microscopy studies in arthritic changes in the malleus incus joint and reflections on the function of the middle ear muscles].

The surfaces of immobilised incus and malleus joints were studied with the scanning electron microscope. The hyaline cartilage showed arthritic changes similar to osteoarthritic big joints of the body. A direct radiologic magnification technique could likewise demonstrate typical arthritic signs. Comparing findings from histologic studies in the literature, we could demonstrate that the intact hyaline cartilage degenerates if the ossicles are immobilised. The minimal static friction of the intact smooth joint surface is a prerequisite for its assumed role namely protection of the inner ear against hazardous pressure changes. A hypothesis is developed to the effect that the movement of the ossicles, necessary for lubrification and nutrition of the hyaline cartilage, is maintained by the two middle-ear muscles. Their function, which had not been explained so far could thus be interpreted--besides a possible effect on sound transmission--as preserving the intact joint surfaces of the ossicles. Nature seems to set great store by the importance of the middle ear joints, as shown by the development of a new joint structure in an implanted homoio-incus.