Stapedectomy

Anatomy and Physiology

The temporal bone is composed of four major subdivisions; the tympanic, squamous, petrous, mastoid, and styloid bones - it is the tympanic region where we find the external, middle, and inner ear. Working from the outside in, a surgeon would first find an external ear consisting of the pinnae, the external auditory canal, and the tympanic membrane. Beyond the tympanic membrane exists the middle ear space, which is defined as the air-containing space medial to the tympanic membrane and lateral to the promontory. It is in this space where most of the work of a stapedectomy will be performed and where we will be focusing most of our discussion. The oval window, on which the footplate of the stapes sits, is the tenuous boundary from which the inner ear begins. Encased in dense bone, the inner ear contains the membranous labyrinth of structures known as the cochlea, vestibule, saccule, utricle, and the three semicircular canals.

The middle ear space is sagittally oriented and traversed by the ossicular chain, which consists of the malleus, incus, and stapes. This space is lined by respiratory epithelium (cuboidal and goblet cells) as it is pneumatized by the eustachian tube and has been further subdivided into the mesotympanum, epitympanum, and the hypotympanum. Within the mesotympanum of a healthy ear, the surgeon will find the manubrium of the malleus, the stapes, the chorda tympani nerve, the long process of the incus, the pyramidal eminence giving rise to the stapes tendon, a suprapyramidal recess known as the facial recess and an infrapyramidal recess known as the sinus tympani, and the ponticulus running between the pyramidal eminence and the promontory. 

Above the mesotympanum is the epitympanum. The two are divided by a horizontal line drawn from the scutum to the tympanic segment of the facial nerve canal. The epitympanum is further divided into an anterior and posterior segment by a vertical crest of bone on its medial wall that extends from the tegmen to the cochleariform process. This piece of vertical bone is known as the “cog” and serves as a marker for identifying the facial nerve during surgery. The posterior partition contains the head of the malleus and the body of the incus.

Below, the mesotympanum is the hypotympanum. The two are divided by the inferior wall of the external auditory canal. It is essential to keep the varying size of this space in mind as it may rarely contain a dehiscent jugular bulb or an aberrant carotid artery.

The ossicular chain within the mesotympanum of a healthy individual serves to mechanically convey sound pressure from the tympanic membrane to the cochlea. The malleus lies most lateral of the ossicles, followed next by the largest ossicle -- the incus, and lastly by the stapes, which is the smallest of the ossicles and composed of a capitulum (head), anterior and posterior crura (the latter being where the stapedius tendon stretches from the pyramidal eminence to attach), and footplate. The footplate is the portion of the stapes that sits atop the oval window through the means of an annular ligament, which serves to create a joint between the two. It is the ossification of this ligament that results in otosclerosis.

Indications

While working up a patient for otosclerosis and a possible stapes procedure, it is ensured that the patient is not suffering from superior semicircular canal dehiscence (SSCD) or a dilated vestibular aqueduct, as these may also present with a low-frequency CHL. From a clinical standpoint, the presence of autophony, hyperacusis along with vertigo provocation with high volume or pressure changes (Tullio and Hennebert phenomena, respectively) should help point the provider down the path of SSCD.[21]

The utilization of the acoustic reflex arc is one method that may be used to help the provider differentiate between a third window disorder and ossicular chain pathology such as otosclerosis. In the presence of a third window disorder such as SSCD and a dilated vestibular aqueduct, one could expect a present and normal reflex. This differs from the workup of a surgical candidate for the correction of CHL as a result of otosclerosis, where the acoustic reflex is expected to be absent.[22][23]

A high-resolution computed tomography (CT) scan may also be useful in aiding the diagnosis and treatment of CHL pathologies. While not performed routinely due to the added costs and radiation exposure, high-resolution imaging of the temporal bone is more than 95% sensitive for diagnosing an osteosclerotic ear.[24] The typical CT findings associated with otosclerosis includes a radiolucent area over the fissula ante fenestram, just anterior to the stapes footplate, which follows more of a CHL pathology. However, otosclerosis may also result in sensorineural hearing loss (SNHL) and can be predicted by the presence of a “halo sign,” an area of hypodensity around the cochlea, or otic capsule in retrofenestral disease.[25]

This SNHL component to otosclerosis would be treated medically with sodium fluoride or bisphosphonates.[26] It should be mentioned that while a high-resolution CT scan serves as the gold standard for diagnosing SSCD, serving as a requirement in obtaining the diagnosis, the positive predictive value (PPV) is a mere 67%.[27][28] When progressing down the path of a suspected SSCD as a cause of CHL, low-threshold vestibular evoked myogenic potential (VEMP) testing and tone-evoked nystagmus have PPVs of 84% and 100%, respectively, but these testing measures are outside the scope of the current discussion.[29]

Before the procedure, the patient should have understood and consented to the details of the operation, including the operative procedure itself, along with its possible complications and all of the admission and discharge measures. Indications and considerations for stapes surgery are as follows:

• The patient should be healthy to endure the procedure proposed, particularly if general anesthesia is being considered.
• The poorer hearing ear should be operated on first. This should be based on the patient’s statement and not on audiometric data. Operating in the opposite ear can occur six months after, provided this ear is now the one with poorer hearing. In children, choosing the poorer performing ear to avoid the use of a hearing aid before the beginning of school may be important. Surgery for the opposite ear should be delayed until they are old enough to make their own decisions.
• Confirmed diagnosis of otosclerosis.[4]
• The patient has a 25 dB or greater CHL in the 250 and 1,000 Hz frequencies with a negative Rinne test at 512 Hz. A negative Rinne test at 1024 Hz shows an even greater CHL, making the patient a great candidate for surgery stapes surgery.
• Sheehy et al. in 1971 found that a Rinne test will exhibit a greater bone conduction response when compared to air while utilizing a 512 Hz tuning fork in the presence of a 15 dB or more conductive hearing impairment. A greater bone conduction response, when compared to air while utilizing a 1024 Hz tuning fork, signifies a conductive hearing deficit of 20 dB or more.[30] While close to the values of the CHL, Doyle et al. later reported that these deficits were greater than Sheehy had originally anticipated, with conductive losses ranging from 20 to 40 dB as one progressed from the 256 to 1024 Hz tuning fork.[31] This difference in conduction pathways while using the Rinne test is also known as “flipping the forks,” which is the result of a negative test.
• A mixed hearing loss that would require a CHL to be reduced for a hearing aid to be serviceable.

Contraindications

Stapes surgery is contraindicated in the following patients:

• Those patients who are in poor physical health and or cannot undergo anesthesia treatments.
• The patient has only one hearing ear.[4]
• There is an active infection of the external or middle ear space.
• If the patient has current balance issues, such as concomitant Meniere disease with a 45 dB or greater loss of hearing at 500 Hz and with a high-tone loss.[32]
• If the patient has an occupational requirement for intact vestibular function.

Equipment

Equipment required for stapes surgery and in particular, a stapedectomy includes but is not limited to:

• A full set of middle-ear instruments with a sickle knife and round knife, a fascia press, as well as multiple sizes of otologic specula.
• Depending on the surgeon, some may prefer to use a speculum holder for two-handed operation.
• An operative microscope is used for the entire procedure. Choosing one with a 200 to 250 mm objective lens is preferable, which is typically covered in a sterile drape.
• Surgeon preference plays a role in the method used for removing the stapes crura and footplate. Some may choose a microdrill, while others prefer to use a particular type of laser (usually argon, KTP, or CO2[33][34][35]) with hopes of minimizing vibratory acoustic trauma at the basal turn of the cochlea.[36]
• A stapes prosthesis in which the surgeon is comfortable and experienced with using.

Personnel

While working behind an operative microscope is primarily a single surgeon endeavor, the operating room scrub technician is an essential piece in creating a seamless working environment. The trained scrub technician affords the surgeon the luxury of never removing their eyes away from the microscope and, thus, the operative field. Depending on where a graft is obtained from, an assistant may be required to harvest a venous graft from the dorsum of the hand opposite the ear concurrently undergoing surgery. Alternatively, the single otologic surgeon may utilize a temporalis fascia graft, harvested before beginning the operation. In both cases, the scrub technician is capable of drying and caring for the graft until it is needed later in the procedure.

Preparation

Stapedectomy may be performed under local or general anesthesia. The surgeon should be in communication with the anesthesiologist regarding the use of a nerve monitor, thus discouraging the use of any long-acting paralytics should general anesthesia be chosen. When thinking of which local anesthetic to use for the canal skin incision, many choose to use lidocaine or bupivacaine with 1:100,000 epinephrine. There have been postulations that the use of diluted epinephrine alone may be the route of choice for fear of migration of the amide anesthetics to the facial nerve, resulting in the inability to monitor facial nerve function. The latter, however, has not been fully supported by the literature as of yet.[37]

Positioning the patient to achieve a comfortable procedural field for the surgeon is of utmost importance. The head of the operating table should be turned 180 degrees after proper anesthesia has been achieved, and the patient should be as close to the operating surgeon as possibly permitted by the table. In patients with short necks or large chests, placing the table in a very slight Trendelenburg position may be helpful. If a dorsal venous graft of the hand is planned, the arm opposite the ear being operated on should be positioned on an arm board. Patient comfort should be maintained with arm pads, knee elevation, and lumbar support as necessary.

Preparation of the field is carried out with alcohol or povidone-iodine (Betadine) solution, and the patient is draped for a transcanal procedure. The microscope being used is also draped before the case begins. The ear canal is suctioned of any remaining preparation, and cerumen is removed as necessary.

Technique or Treatment

 The patient's position is made so that the surgeon can see directly down the ear canal from a sitting position, local injections can begin with a 27- or 30-gauge needle starting at the posterior canal wall or the 6-o’clock position. Slow injection of anesthetic should be maintained, especially if performing under local anesthesia, as the skin is tightly adherent to bone or cartilage. An injection that is performed too rapidly can cause ballooning of the canal skin resulting in a subcutaneous collection of fluid, which should be punctured with a needle tip. Minimal injection volumes should be maintained as the surgeon progresses circumferentially around the canal to preserve exposure in such tight spaces. It is important to note that the tissue one anticipates using for an oval window graft, be it vein, fascia, perichondrium, or fat, can be procured before or after the canal surgery has started. The graft needs to be prepared before the opening of the stapes footplate, limiting the exposure time of the vestibule.

With many sizes of specula available to the surgeon, the largest one that can be seated into the ear canal should be used. Depending on the surgeon’s preference, a fixed speculum holder may be used. The technique described here will assume the role of a one-handed surgeon, or lack of the fixed speculum holder, providing flexibility in viewing the canal and allowing an awake, locally anesthetized patient to move their head if so desired. Plain metal specula and instruments are preferred, as black materials detract much-needed light from the operative field.

Proper exposure is essential in maximizing the success in every operation, and this principle is equally important when working in the middle ear space. As with all procedures, the anticipation of surgical challenges should be considered, and as such, a sufficient tympanomeatal flap should be created. Using a sickle knife, an incision beginning 1 mm from the tympanic membrane is extended superolaterally from the posteroinferior annulus to a point well superior to the pars flaccida. Several sweeps with the sickle knife may be required to ensure the periosteum has been cut. The length of the flap should be about 5-7 mm and is then dissected gently until the fibrous annulus is seen inferiorly, and the notch of Rivinus is seen superiorly. The surgeon will know the incision was sufficient when sectioning of the mallear fold allows the complete reflection of the tympanic membrane.

When performing a stapedectomy for suspected otosclerosis or working in the middle ear space to improve any conductive hearing impairment, adequate exposure is ensured when the following landmarks are visible: the neck and handle of the malleus, anteriorly; the round window, inferiorly; the pyramidal process, posteriorly; and the horizontal portion of the facial nerve, superiorly. These landmarks are visualized after the successful removal of the bony scutum, which typically begins with curettage at the notch of Rivinus, proceeding inferiorly. Care must be taken to avoid chorda tympani nerve damage during this process. 

After achieving good exposure, the ossicular chain must be palpated to determine the site of pathology. In the normal, non-diseased ear, palpation of the malleus will result in a round-window reflex, demonstrating an intact ossicular chain with the normal movement of fluid within the perilymph. In otosclerosis, however, this round-window reflex will be absent, as upon palpation of the malleus, the stapes is stuck and completely immobile. Once the degree and location of stapes fixation per the otosclerotic disease have been assessed, the incudostapedial joint is separated. The stapes footplate is then fenestrated, at its thinnest point, with a fine needle to decompress the vestibule and provide an area of instrumentation, should footplate floatation occur.

The next steps would be to section the stapedial tendon and fracture the stapes superstructure with the use of quick, downward pressure toward the promontory. A small, angled hook is then used to remove parts of the central footplate. How much footplate to be removed depends on how the bone fractures away, but typically amounts to approximately one-fourth of the footplates surface area. Careful use of the suction should be maintained so as not to inadvertently disturb perilymph fluid while suctioning blood around the oval window.

During footplate removal, any bone pieces or blood that enter into the vestibule are left alone. When measuring the appropriate length of the prosthesis to be used, the distance from the footplate to the top of the incus is often used. This often results in a prosthesis of about 4.5 mm, but the distance varies from 3.5 to 5.5 mm. Many types of prostheses may be used - categorized into buckets, wire loops, pistons, or even homemade.[38] This paper will not cover the selection process for each, but each surgeon must be proficient in more than one technique due to occasional unanticipated findings.

When the right prosthesis is selected and sized, the graft is gently placed over the oval window and pressed into the created fenestra to help identify the location where the medial end of the prosthesis will be placed. Care is taken to ensure that whatever prosthesis the surgeon chooses, it is placed carefully. When comfortable, the ossicular chain must be palpated to ensure continuity of the chain/prosthesis union. Finally, the transposed tympanomeatal skin flap can be returned to its original position and packed with small cotton balls that have been impregnated with antibiotic ointment.

Complications

When performing a stapedectomy or other middle ear surgery, the primary goal is to preserve auditory nerve function when possible. This holds even in those cases where complications may require the abandonment of the procedure. Having the option to fall-back to the use of a hearing aid is always more preferable than complete loss of a patient's cochlear reserve. According to Myer's Operative Otolaryngology, complications that might arise include tympanic membrane perforations, chorda tympani nerve damage, ossicular dislocation, floating stapedial footplate, perilymph gushers, round window otosclerosis, persistent stapedial artery, facial nerve abnormalities, intraoperative vertigo, reparative granuloma, and perilymphatic fistulas. Many of these can play a role in the risk of developing profound sensorineural hearing loss, or a "dead ear."

Tympanic membrane perforation may occur when raising the flap before the separation of the fibrous annulus from its sulcus. Small tears can be repaired with equally small planets of Gelfoam, while larger perforations may require the surgeon to reinforce the area with any additional harvested tissue that might not have been used for the oval window as an underlay graft. Preoperative evaluation of the tympanic membrane is essential, as highly atrophic and thinned tympanic membranes may require a myringoplasty at the time of surgery. These complications, however, rarely have an impact on the outcome of stapedectomy.

When bringing down the scutum to obtain good exposure for the stapedectomy, it is essential to do this carefully so as not to damage the chorda tympani nerve, which is often preserved (~90% of cases). Stretching of the nerve or partial sectioning can be remedied with reapproximation of the nerve fibers, as mentioned previously, but complete sectioning may be unavoidable in a small percentage of cases. It is interesting to note that those patients in whom chorda tympani nerve transection is required have experienced fewer symptoms of dysgeusia when compared to their stretch injury counterparts.[39]

Ossicular dislocation is an unusual complication and often involves the incudomalleal joint resulting from the lateral displacement of the long process of the incus. While this may result in some challenges when placing the prosthesis, moving the incus back to its original position will usually offer good hearing results.

When the stapes superstructure is down-fractured, there is a rare chance (<1%) that the entire footplate becomes avulsed from its surrounding annular attachment to the oval window. This complication may occur should the surgeon skip creating a small fenestration in the center of the footplate with a needle before bringing down the stapes superstructure. It is crucial to keep in mind that this may also occur while trying to create fenestrations in thickened footplates, so avoidance of excess pressure is vital. It will be necessary to gain a hold of the footplate, and when this is not possible, it may be achieved by drilling or curetting into the promontory side of the footplate until a small right-angled pick can grab beneath it, turning into a complete footplate extraction.

Large floating fragments may be extracted by placing a few drops of blood over the oval window, waiting for a clot to form, and removing them all en bloc. Do not, however, attempt to retrieve those pieces that have become subluxated into the vestibule, as this may cause inner ear damage. Displacements of large fragments may result in persistent postural vertigo, while small fragments should be left alone as they rarely result in a loss of hearing.

Perilymph gushers are a rare occurrence where a sudden flow of perilymph fluid occurs immediately upon accessing the vestibule. It is most common in children suffering from congenital stapes fixation but has been encountered in adults with otosclerotic disease processes on occasion. Sensorineural hearing loss occurs more often in those patients who experienced a perilymph gusher. The pathophysiology is usually due to a widening or enlargement of the cochlear aqueduct or communication between the medial internal auditory canal and the inner ear.

When considering a stapedectomy on a child, one might want to obtain a preoperative CT to identify abnormalities of the otic capsule. After encountering a gusher, control is best achieved by elevating the head while suctioning perilymphatic fluid, obtaining fat from the ear lobule to place into the oval window, and using a prosthesis to hold it in place. The head is to remain elevated, postoperatively, and insertion of a spinal drain may be a useful supplemental treatment.

While otosclerosis that results in complete obliteration of the round window is rare, if encountered, the procedure should be abandoned as drilling out the round window has been associated with increased risk of sensorineural hearing loss. Should there be a partial obliteration observed, the surgery may proceed as usual.

The occurrence of a persistent stapedial artery, a remnant of the second branchial arch vasculature, is an abnormality that can often be worked around - even larger arteries can be kept intact while using fenestrations of the footplate and placement of the prosthesis on whichever end of the footplate has the most space. If the artery obliterates the obturator foramen, the procedure should be terminated, and hearing amplification should be achieved with a hearing aid.

It is not uncommon to encounter a partial or total dehiscent facial nerve during middle ear surgery. The most important reason to be able to identify this anomaly is to avoid instrumentation that could damage the nerve. In sporadic cases, the facial nerve may overhang the oval window or travel directly across its surface. Gentle retraction of the nerve using the side of a suction tip often provides the surgeon with enough exposure to complete a fenestration and prosthesis placement. When overhang is more prominent, some metal crimp-on prostheses could be useful in curving around the nerve. Extreme displacement of the facial nerve that results in coverage of the footplate dictates abandonment of the surgery. 

Intraoperative vertigo occurs due to excessive manipulation of the stapes or an emptying of the fluid in the vestibule, which results in the stimulation of labyrinthine receptors. Under local anesthesia, the surgeon can use this symptom as a warning of impending inner ear damage, which, of course, is not the case regarding general anesthesia. In an awake patient, persistent vertigo can cause an obstacle to completing the surgery, which is partly the cause of many surgeons choosing general anesthesia, and rapid measures must be initiated to relieve these symptoms. Droperidol is the fastest acting drug in this emergency and is pushed intravenously, slowly. Patients should be monitored after the admission of droperidol, as there is potential for cardiac complication and hypotension. 

A terrible complication of stapes surgery is the formation of reactive granulation tissue in and around the oval window. There are many ideas on what causes such a reaction, but it is believed that the use of powderless gloves, the avoidance of Gelfoam, or washing the prosthesis before introducing it into the middle ear space has reduced granulomatous formations, postoperatively. These growths typically occur one week after surgery, as patients begin to complain of decreased hearing and dizziness. On otoscopic examination, a violaceous fullness in the posterosuperior quadrant of the tympanic membrane may be observed, and an audiometric evaluation will show sensorineural impairment with a reduction in speech-recognition thresholds.

Treatment for reparative granulomas involves an immediate surgical intervention to replace the original prosthesis and graft, along with the removal of the growth. Adjunctive therapy with high-dose steroids has been used, but if the disease process is not surgically corrected early enough, permanent sensorineural deficits persist.

Perilymphatic fistulas are a result of persistent or redevelopment of the temporary fistula made after footplate fenestration. This could be a result of imperfect tissue graft placement, a dislodging of the prosthesis, or a sudden leak of perilymphatic fluid from a cough or sneeze. Patients will usually complain of a fluctuant hearing loss and dizziness while an audiogram will exhibit deterioration of the cochlear function. Immediate surgical exploration is indicated to preserve hearing, and if a fistula is confirmed, replacement of the tissue graft and prosthesis is indicated.

Clinical Significance

Over the 40 years that John J. Shae had performed stapedectomy procedures, he had received good results from the very beginning. The success of stapes procedures showed improvement over the years as the quality of the microscopes, prostheses[40], and drills improved, and lasers were introduced. Having 90% and 70% success rates for primary and revision stapedectomy, respectively, there has always been the possibility of worsening the sensorineural hearing of a patient - Shae himself, finding that 1.8% of primary and 4% of revision stapedectomies resulted in worsening a patient’s sensorineural hearing.[10]

While stapedectomy and stapedotomy are considered state-of-the-art operations in treating the conductive hearing loss secondary to otosclerosis, most patients who opt for surgery these days undergo a small fenestra stapedotomy-type procedure performed with microdrill or laser. The reason is that perception of stapedotomy, affording greater improvements in hearing at the higher frequencies and lower complication rates.[4]

As many studies have alluded to, however, the experience of the surgeon will play a greater role in the success and safety of the stapes procedure [15][16][17][18][19][12][20], thus providing the surgeon the choice to perform that which he or she is most comfortable with. 

For otosclerosis to be effectively managed, detailed knowledge of the disease and the capacity to adapt to the surgical technique play essential roles. Stapedectomy is one of the most technically challenging operations, which is amplified in those cases requiring revision, as the risk of profound sensorineural hearing loss, or dead ear, is substantially higher. Considering this, it is best to use a conservative approach when addressing labyrinthine dysfunction in the postoperative period.[1]

Despite the risks involved and the expertise required for stapes surgery, there is currently no better treatment for improving bone conduction and closing the air-bone gap (ABG) associated with conductive hearing loss, especially those hearing losses resulting from otosclerosis.[41]

Enhancing Healthcare Team Outcomes

Only sufficiently trained surgeons who are comfortable with the anatomy involved and experienced in performing middle ear surgery for otosclerosis should proceed with stapedectomy. It is continually more evident that the procedure chosen to remedy a patient’s conductive hearing loss, whether it be complete or partial stapedectomy, stapedotomy, or stapes mobilization and the utilization of lasers versus drills versus plain instrumentation (handpick) is less critical than the proficiency of the surgeon performing them. If a surgeon is obtaining a 90% closure of the ABG and less than a 1% chance of worsening sensorineural hearing, then there is no need to change the technique being used.

Nursing, Allied Health, and Interprofessional Team Interventions

A knowledgeable scrub nurse trained in assisting and setting up cases involving the microscope and middle ear is an invaluable aspect of the surgical team. The scrub nurse's ability to dry and care for a procured graft as well as understand the steps of the procedure minimizes the amount of time a surgeon would spend away from the microscope, and thus, the operative field - a profoundly important aspect when working in such small confines.

Nursing, Allied Health, and Interprofessional Team Monitoring

The anesthesiologist plays an important role regardless of the type of anesthesia provided, whether the patient is awake or under general. Their assistance during such procedures could often serve as a challenge, as the bed may be turned 180-degrees away from the ventilator, resulting in the airway being the furthest possible distance from the anesthesiologist. Clear, respectful communication should any issues arise is imperative to a successful operation, mainly when operating in the head and neck region.

While performing middle ear surgery, the surgeon may find it essential to monitor facial nerve functioning. Considering the tympanic segment of the facial nerve crosses immediately superior to the stapes in its boney canal, active monitoring will alert the surgeon of their proximity to the nerve. Nerve monitoring may help to identify a dehiscent facial nerve. 

Skilled post-anesthesia care unit nurses are invaluable in the immediate postoperative period, as stapedectomy patients may experience pain, vertigo with nausea and vomiting (the latter posing a risk to prosthesis dislodgement), and facial nerve weakness. These nurses play a crucial role in notifying the surgeon of any early-onset complications associated with the procedure.