Stapes (also called stirrup) is the name of the third bone of hearing (or ossicle) and could be affected by middle ear disease. The bone is made of 2 components which come from different embryologic structures. The top of the bone which looks like an inverted “U” is called the superstructure and has the anterior and posterior crura. The flat surface which superstructure is attached to is embedded in oval window through which sound energy is transmitted from the middle ear into the inner ear.
When the superstructure of stapes is affected but the footplate is mobile a total ossicular chain reconstruction (TORP) is used to communicate the sound into the inner ear. However, when the footplate is fixed by otosclerosis and rarely by tympanosclerosis, a very small hole or fenestra has to be created to convey the sound energy into the inner ear. This surgery is called stapedotomy. Before the advent of laser and microdrills the entire stapes along with the footplate was removed and replaced with a prostheses. This surgery is called stapedectomy. Although studies have not demonstrated major difference between the 2 methods, Dr. Monfared prefers the stapedotomy method since it might be less disturbing to the inner ear structures. However in select cases a stapedectomy has to be performed because of the anatomical or pathologic variations.
Except for very rare cases that the ear canal is incredibly small, stapedotomy is done through the ear canal without any external incisions. A small incision is made near the eardrum and middle ear is entered. The superstructure of stapes is removed with laser and a fenestra is made in the footplate. Next a prosthesis is placed in the fenestra and attached to the second bone of hearing thus creating ossicular chain continuity. The surgery is usually very well tolerated and performed as an outpatient.
This is a very common question for patients who have undergone stapes surgery. Studies have shown that virtually all stapes prostheses except for a particular lot of McGee stainless steel prostheses available in 1980s are nonferromagnetic and MRI compatible to 1.5 Tesla. Patients should refer to the implant card provided to them after surgery for further information. In cases of life-threatening emergencies obviously MRI could be performed considering little risk of implant being a ferromagnetic type.
The presence of prostheses connecting to the inner ear could theoretically interfere with certain activities that cause dramatic shift of middle ear pressure. Some of these activities such as a scuba diving are challenging to a normal ear and patients who are avid scuba divers should be cautious about undergoing stapedotomy. Also patients who use a CPAP machine at night may not be good candidates for the surgery. Many otosclerosis patients perform well with hearing aids and should certainly consider the alternative to surgery.
Images are courtesy of Dr. Robert Jackler and used with permission.