Abstract: A medical instrument includes a lower plate, at least one upper plate opposite the lower plate, a spacer means which is disposed between the upper plate and the lower plate. The spacer means is used to permanently hold the upper plate in a substantially parallel position in relation to the lower plate and to move the upper plate away from the lower plate. The spacer means is fully contained between the upper and the lower plate. The minimal spacing between the outer surfaces of the upper plate and the lower plate is less than ten (10) millimeters. A flexible control means is connected to the spacing means.