An ossicular replacement prosthesis (ORP) (10) for coupling a first point to a second point in the middle ear of a patient, to replace all or part of the ossicular chain. The ORP includes a coupling having a variable configuration for accounting for pressure differentials. The coupling includes a fluid filled chamber (28, 14) having two relatively moveable portions (12, 22) for varying the configuration of the coupling. The coupling further includes unsealed portion constituting leak portion and flowpath portion for permitting displacement of the fluid (30). The relative movement of the relatively moveable portions is controlled by the movement of the fluid in said chamber. The chamber is configured to restrict the movement of the fluid such that relative movement of the moveable portions is permitted in response to quasi-static changes in pressure, and is substantially prevented in response to vibrational changes corresponding to sound frequencies.