of Ear bones)
If the bones of hearing are eroded, then ossicular reconstruction (reconstruction of the bones of hearing) may be necessary at the time of tympanoplasty. In some cases, this can be determined before the surgery. In other cases, it only becomes obvious at the time that the ear is completely opened and examined under the microscope.
The ear surgeon must decide whether the bones of hearing can be reconstructed at the time of the reconstruction of the ear drum. In most cases, this is possible if the ear is dry and not infected. The most common bone erosion occurs at the tip of the incus (anvil). This bone normally connects to the stapes (stirrup bone) and the connection is normally only 1.5 mm (1/24th of an inch--lead pencil's lead width) in thickness. With prior infections, the circulation to the bone can become obstructed. Infection can gradually wear away the connection to the point where the bone is no longer in contact with the stapes bone. This is called ossicular discontinuity, a break in the bony connection. One can think of the incus as the player arm of a phonograph and the stapes as the needle. If the player arm is not in contact with the needle, sound will not be transmitted with the same force as it would with a good connection.
Reconstruction of this type of ossicular discontinuity can be performed at the time of tympanoplasty surgery. There are several options. If the gap is small, it can be bridged by inserting a small piece of bone or cartilage taken from the patient at another site (behind the ear or from the lobe of tissue called the tragus in front of the ear). If there is a larger gap, then the incus bone is removed and modeled into a tooth-like prosthesis,
using the operating microscope. This is then reinserted between the stapes and the malleus in order to reestablish continuity of the ossicular chain.
Other options include the insertion of a strut made out of an artificial bone, called hydroxl apatite. This artificial bone is porous and allows for the ingrowth of blood vessels and the complete assimilation of the artificial bone into the individual's middle ear. With the modern day use of hydroxl apatite, there has been a marked reduction in the rejection of ossicular reconstruction prostheses.
Prior prosthetic devices were made out of porous plastics which had a much higher rejection rate.
In other less common ossicular reconstructions, the malleus (hammer) can become fixated by scar tissue or bony ingrowth to the lateral wall of the ear. In this "malleus fixation," the bone must be separated from the canal wall and remodeled. Silastic or a plastic type of sheeting is often placed against the wall to prevent regrowth of new bone. Reconstruction in this instance often requires that the stapes and incus be separated from their connection to stop the transmission of the drill's vibration which would damage the inner ear.
SELECTION AND RESULTS
Tympanoplasty surgery is not always recommended. Chronic sinus or nasal problems such as severe allergies make the operation more difficult. They must be cleared up or controlled prior to tympanoplasty surgery.
The ear and nose are connected by the eustachian tube. If there is active infection in the sinuses or nose, infected materials may block the eustachian tube or even back up into the tube itself. Severe allergies may cause swelling of the tube which is normally lined with mucous membranes. Unless allergies are controlled, swelling will block the eustachian tube and surgical attempts to repair the eardrum will fail.
Tympanoplasty surgery may also not be recommended in very young children whose ears drain with every cold. However, this is a very controversial subject, because is perforations are neglected, they can form cholesteatomas.
Overall results of tympanoplasty surgery are very successful when precautions are observed. Prior to surgery, all infection should be cleared up. This may require antibiotics as well as weekly cleaning under the operating microscope in the office. Occasionally, clearing all infection may result in spontaneous healing of the perforation if it is not large or too long-standing. Once all infection is cleared, surgery should be scheduled. Ear surgeons generally expect that over 90 percent of tympanoplasty operations will be successful. Success includes closure of the perforation as well as improvement in hearing.
Results of tympanoplasty with ossicular reconstruction vary with the degree of prior damage to the bones of hearing. With an intact, normally mobile chain of ear bones, the restored hearing is generally very good once the hole is closed. Erosion of the incus is usually the most common bony problem and the easiest ossicular problem to repair. Good hearing results are obtained in a high percentage of operations.
Absence of both the stapes bone and the incus creates a much more difficult reconstructive problem. Artificial prostheses which extend from the footplate (diagram) (window of the inner ear) to the malleus (eardrum) are less reliable than other reconstructions, because they bypass the normal lever system of the ossicles. The reconstruction is less stable. During the healing process, it is more likely to become displaced. Even in this difficult situation, two-thirds of the operations bring significant hearing improvement.
If most of the eardrum is absent and the ossicles are destroyed by prior infection or disease, reconstruction will have to be staged into several operations. The first-stage operation reconstructs the eardrum. The second-stage operation, performed six months to one year later, addresses the reconstruction of the bones of hearing.
Mastoid infection, if present, may require that tympanoplasty surgery include mastoidectomy. The mastoid cavity may contain a reservoir of infection. If this material is not cleaned out, the new eardrum will break down after initial success. Thus, it is advisable to obtain a CT scan to visualize the mastoid cavity, if there is a history of prolonged and resistant infection. If the mastoid cavity appears diseased, the tympanoplasty with combined mastoidectomy is often recommended. This operation, termed tympano-mastoidectomy, not only involves repairing the eardrum, but during the same operation, the mastoid bone is opened with a drill and all diseased tissue is removed. This procedure may lengthen the operation by 45 minutes or more, but it will improve the chance of a successful result.