Experimental Studies on the Bio-Mechanics of the Incudostapedial Joint in Human Temporal Bones

Abstract

Photographic recordings of the incudostapedial joint in human temporal bones were performed to analyse its movements as caused by a stapedius muscle contraction simulated by loading the muscle with weights. The purpose was to find the explanation of the outward or inward movement of the tympanic membrane caused by a stapedius muscle contraction. Using the double exposure photo technique, i.e. one exposure when the stapedius muscle was unloaded and the other when it was loaded, a sliding movement in the incudostapedial joint could be shown. Investigations of the articular surfaces of the head of the stapes showed that they were highly variable in shape, but from a functional point of view two different types could be identified. Thus, contraction of the stapedius muscle caused a sliding movement in the incudostapedial joint and as a result of the shape of the articular surfaces of the head of the stapes, the processus lenticularis was shown to slide upwards or downwards. For this reason the crus longum incudis was moved towards or away from the tympanic membrane, which was displaced outwards respectively inwards, as the tympanic membrane and the crus longum incudis had been shown to move in the same direction.