Ossicular Chain Dislocation
Ossicular chain dislocation may occur with a temporal bone fracture, traumatic tympanic membrane perforation, or barotrauma. The tympanic membrane may or may not be perforated. Ossicular chain dislocation with an intact eardrum will manifest as a maximal (60 dB) conductive hearing loss. Ossicular chain dislocation with a perforated eardrum will have lesser degrees of hearing loss. The most common form of ossicular discontinuity after temporal bone trauma is separation of the joint connecting the incus to the stapes. The second most common is separation of the joint connecting the malleus to the incus. Fracture of the arch stapes may also occur. Ossicular fixation may occur several months after the temporal bone fracture if exuberant growth of new bone at the fracture line fuses the ossicular chain.
Treatment in any case is middle ear exploration and ossicular chain reconstruction. This surgery is essentially the same as a tympanoplasty, however there is no hole in the tympanic membrane to fix. Sometimes, the surgery can be performed though the ear canal rather than having to make an incision behind the ear. The tympanic membrane is elevated and the ossicles inspected. Repair of the damaged ossicle is then performed. This may require removing the broken bone and replacing it with a prosthetic ossicle. Occasionally, a small cartilage graft is required. This can be taken from the tragus, the piece of cartilage in front of the ear canal. This is not usually noticeable.
The success rate of ossicular chain repair varies depending on the problem with the ossicular chain. If the stapes is intact, the rate of good hearing recovery is about 75 percent. If the stapes is not intact, the rate of good hearing recovery is about 50 percent. Although the surgeon always repairs the problem, the healing process can impact hearing outcomes. Scar tissue formation can pull on the delicate ossicles and/or ossicular prosthesis, moving them from their optimal position. If the hearing result is less than optimal, surgery can often be repeated in an effort to improve the outcome.
See Tympanic Membrane, Middle Ear and Mastoid Disease for more information.