Fig. 222. Stacke’s Protector.
In this connexion may be mentioned Stacke’s probe or ‘protector’ (Fig. 222). Although historically an instrument of importance, I do not make use of it. It is so large and of such sharp outline that, unless used with extreme care, it is itself very liable to injure the facial nerve. For this reason I prefer the seeker, a much finer and more delicate instrument, which will serve the purpose without the same risk ([Fig. 219]).
The ‘bridge’ is now carefully removed by the gouge or chisel, frequent use being made of the seeker meanwhile. As the roof of the antrum, aditus, and attic is a continuous one, the bone to be removed is necessarily at a higher level than the roof of the bony meatus. This is a point which must not be forgotten, as the great fault of the beginner is to remove the bone too low down.
Fig. 223. The ‘Radical’ Mastoid Operation. Showing removal of the remains of posterior wall of the auditory canal; the seeker acting as a protector.
As the aditus is approached, the strokes of the chisel must be very gentle. If too much force be used, the chisel, on breaking through the innermost portion of the ‘bridge’, may injure the deeper-lying parts, more especially the facial nerve.
Some authorities advocate removal of the ‘bridge’ by means of bone forceps. This, however, is not so sure a method as by the chisel or gouge.
After removal of the bridge, the tympanic cavity, antrum, and mastoid will form a continuous cavity. As a rule the outline of the external semicircular canal appears as a well-marked white eminence, and projecting beyond it are the remains of the posterior wall of the auditory canal. In removing this ridge good illumination is essential. The bone is removed in layers with the chisel, beginning at the tip of the mastoid process, and working parallel to the auditory canal and the underlying facial canal. If necessary the seeker may be used as a guide, its point being allowed to rest on the floor of the aditus, superficial to the semicircular canal (Fig. 223).