The mobility of the malleus and incus with varying middle ear pressures

The mobility of the malleus and incus was studied in two fresh human temporal bones. Various pressure gradients were applied across the intact tympanic membrane and the movement of the ossicles examined, firstly with the incus in situ and secondly, with the incus removed. The displacement of the long process of the incus was less than 100 microns at the extremes of pressure gradient. However, this mobility increased by over twofold when the posterior incudal ligament was divided. With removal of the incus, the mobility of the umbo with pressure changes was further increased and can be as much as half a millimetre. In all cases the maximal rate of ossicular excursion was noted with pressure gradients of less than 100 daPa (mmH2O) across the tympanic membrane.