Ossicular Chain Reconstruction in Children

Ossicular Chain Reconstruction in Children (Ossiculoplasty)- technical

Synonyms: Appelbaum prosthesis; Incus interposition; Incus transposition; IS-joint prosthesis; Ossicular chain reconstruction (OCR); Ossiculoplasty; Partial ossicular replacement prosthesis (PORP); Total ossicular replacement prosthesis (TORP)

Definitions

Air-bone gap: A result on audiometric testing showing a difference in hearing responses from bone conduction of sound (testing that stimulates the inner ear directly, bypassing the middle ear) and air conduction (testing that sends the signal through the ear canal and middle ear to the inner ear).

Acquired cholesteatoma: Destructive and expanding growth or cyst of keratinizing squamous epithelium in the middle ear or mastoid space; can be the end result of middle ear atelectasis or a retraction pocket or other means of introduction of the squamous layer of the tympanic membrane into the middle ear; often arising in the posterior aspect of the tympanic membrane.

Conductive hearing loss: Hearing loss due to a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane, or ossicles.

Congenital cholesteatoma: Destructive or expanding growth or cyst of squamous epithelium present in the middle ear space from birth often occurring behind an intact tympanic membrane, the etiology of which is not known; usually located in the anterior superior aspect of the middle ear cavity.

Eustachian tube: The pharyngotympanic tube, tube connecting the middle ear to the nasopharynx, named for Bartolomeo Eustachi, the founder of human anatomy.

Eustachian tube dysfunction: The tube fails to open and close properly failing to clear fluid or normalize pressure in the middle ear, resulting in negative pressure, fluid collection, and other middle ear disease.

Middle ear atelectasis: End stage of severe negative pressure due to Eustachian tube dysfunction, with retraction of the tympanic membrane into the middle ear space and structures, often with adhesions forming between the tympanic membrane and these structures.

Ossicle: One of the three articulating bones in the middle ear that transmit sound from the tympanic membrane to the oval window.

Partial ossicular replacement prosthesis (PORP): An implantable middle ear device made of biocompatible materials used in the surgical treatment of conductive hearing loss by creating a bridge between the stapes suprastructure and the tympanic membrane with or without an arm placed medial to the manubrium of the malleus.

Sensorineural hearing loss: Hearing loss due to a problem with detection of sound in the inner ear for any reason or the transmission of the sound information along the cochlear nerve to the brainstem.

Total ossicular replacement prosthesis (TORP): An implantable middle ear device made of biocompatible materials used in the surgical treatment of conductive hearing loss by creating a bridge between the stapes footplate when the suprastructure is absent and the tympanic membrane with or without an arm placed medial to the manubrium of the malleus.

Tympanic membrane: Ear drum.

Tympanic membrane perforation: Hole in the ear drum usually due to trauma or middle ear disease, can occur as the result of tube placement and or Eustachian tube dysfunction.

Tympanoplasty: Repair or reconstruction of a defect, perforation, or retraction of the tympanic membrane.

Introduction

Sound is transformed into vibrations of the tympanic membrane that are then transmitted through the middle ear in the bones or “ossicles” of hearing to the inner ear. There are three bones of hearing, the malleus, incus, and stapes. The malleus is a long hammershaped bone that is connected across its manubrium or handle, to the tympanic membrane by a small process, the lateral process and a cartilaginous joint. It connects also to the smaller, broader bone, the incus in the area of the attic or epitympanum where another joint exists. At the end of the long process of the incus is a right angle, the lenticular process, which articulates by means of a third joint with the top or capitulum of the stapes. This last ossicle is shaped like a stirrup and its footplate sits on a membranous window to the inner ear, the oval window. Vibrations of the footplate transform the sound waves into fluid waves in the fluid filled inner ear where sound is detected. When the tympanic membrane is disconnected from the inner ear, there is a loss in the transmission of sound. This is usually the result of a hole in the tympanic membrane and/or loss of part or all one or more of the ossicles. The result is conductive hearing loss. On a hearing test one would see a difference in responses from bone conduction and air conduction, known as an “air-bone gap.”

When conductive hearing loss exists due to an ossicular chain discontinuity, a procedure done to reconnect the tympanic membrane to the inner ear by replacing or repositioning the middle ear bones is known as ossicular chain reconstruction. This is performed when a gap exists between the ossicles due to a missing or destroyed ossicle. This is often the result of destruction of the ossicles from chronic middle ear disease, infections, or cholesteatoma. The ossicle can be replaced using a reshaped ossicle that is repositioned or donor material from the patient, such as cartilage, or a prosthesis. There are hundreds of prostheses commercially available, the size and shape greatly dictated by the defect that needs to be bridged. Ideal prosthetic material consists of something lightweight, durable, and biocompatible to reduce the chance of extrusion. Titanium and hydroxyapatite are some of the more popular materials in the last 10 years.

Epidemiology

Middle ear infections are common in children. Treatment includes watchful-waiting, analgesia, and antibiotics in some instances. The Eustachian tube often does not function well in children leading to middle ear infection, effusion (fluid collection), or negative pressure. This Eustachian tube dysfunction can cause middle ear disease, recurrent or chronic ear infections or effusions or retraction of the tympanic membrane due to chronic negative middle ear pressure. Chronic retraction of the tympanic membrane can exert pressure on the ossicles causing erosion. This can often be treated by the placement of ear tubes. When ear tubes extrude they have a one percent chance of leaving a hole in the tympanic membrane. Untreated, chronic middle ear disease may also lead to perforation of the tympanic membrane, retraction of the middle ear, and destruction of the bones of hearing. If a child has a tympanic membrane perforation, it can cause conductive hearing loss. But there may also be damage to the bones of hearing contributing to the conductive hearing loss. It is often impossible to determine which problem is causing the hearing loss. Repair of the tympanic membrane must be performed to restore the hearing mechanism. The state of the ossicular chain can be assessed at the time of surgery with middle ear exploration. One can perform ossicular chain reconstruction at the time of the tympanoplasty or at a second surgery should the conductive hearing loss persist after closure of the tympanic membrane perforation.

The other common cause of ossicular destruction or discontinuity is cholesteatoma. This is a cyst in the middle ear that a child is either born with (congenital) or can acquire as a result of chronic ear disease (acquired). They are benign but can be destructive as they grow and exert pressure on middle and inner ear structures eroding bone. Complete removal is challenging and often the bones of hearing must be removed due to intimate involvement with the cholesteatoma or to obtain access to the recesses of the attic and middle ear to achieve complete excision. This is performed with either a tympanoplasty for a cholesteatoma confined to the middle ear or may include mastoidectomy if the cholesteatoma extends beyond the middle ear into the attic or mastoid bone. When ossicles are removed with or destroyed by the cholesteatoma, the patient is often left with conductive hearing loss. It is common to plan a second surgery to insure that there is no recurrent or residual cholesteatoma. If a defect in the ossicular chain is encountered at the time of surgery and the child has or is anticipated to develop conductive hearing loss, ossicular chain reconstruction can be performed to improve hearing.

Indications

When there is conductive hearing loss present and ossicular discontinuity is discovered at the time of middle ear surgery, ossicular chain reconstruction should be considered. The most common site of discontinuity is at the incudostapedial joint. The slender lenticular process of the incus that articulates with the capitulum of the stapes is vulnerable to pressure due to retraction of the tympanic membrane or ischemia during infection. This can result in erosion. This is also the site most vulnerable to separation due to blunt head trauma or temporal bone fracture, a less common cause of ossicular discontinuity. Sometimes the entire incus is destroyed. Further destruction can lead to erosion of the top of the stapes, the suprastructure, leaving only the footplate behind. In order to attempt an ossicular chain reconstruction, the child must have at a minimum, a stapes footplate or remnant of the footplate. If this does not exist, the type of ossicular chain reconstructions described here. The maleus can also be destroyed due to similar mechanisms often resulting in shortening of the manubrium or destruction of the malleus head. This is less common than incus and stapes erosion. One requirement for successful ossicular chain requirement is an intact, mobile stapes footplate. While reconstruction can be attempted without it, this is more involved and outside the scope of this discussion. When the suprastructure is intact, successful hearing results are more likely (Chandresekhar et al. 1995). A surgeon has multiple options to reconnect the ossicles, but the solution for the individual situation is dictated by the state of the remaining ossicles, middle ear and tympanic membrane, as well as the Eustachian tube function.

Pediatric Considerations

As awareness about the effects of bilateral and unilateral hearing loss on speech and language development and learning in general increases, parents are more likely to request surgical intervention for hearing loss due to middle ear disease (Tharpe 2008; Murphy 2000). Tympanoplasty to repair a tympanic membrane perforation can be successfully performed in children of any age and has been reported in children as young as 2 years (Koch et al. 1990). Eustachian tube dysfunction, the cause of many or most of middle ear problems necessitating surgery, is also the main cause of failure of such interventions. Eustachian tube dysfunction often resolves as children age, but it is difficult to determine when that occurs in the individual patient. On average it is improved in most children by age four, but not always.

Ongoing Eustachian tube dysfunction can complicate successful repair of the tympanic membrane. It can also result in retraction of the new tympanic membrane, which can put pressure on the newly reconstructed ossicular chain resulting in dislocation or extrusion of grafted bone or prosthesis (Mishiro et al. 2008). This is more common with prostheses made of foreign material. This can be minimized by covering the prosthesis with a cartilage graft at the time of placement. This stresses the importance of surgical planning in order to accommodate ongoing Eustachian tube dysfunction. Eustachian tube dysfunction in the opposite ear can be used to estimate risk of ongoing problems in the involved ear (Collins et al. 2003). Adenoidectomy can be performed to improve Eustachian tube dysfunction prior to middle ear surgery (McGrew et al. 2004).

When repairing the tympanic membrane in the presence of hearing loss, one must consider the amount of hearing loss prior to embarking on the ossiucloplasty or OCR. Also, if there is any connection remaining in partially eroded ossicles, it may be prudent to wait to attempt ossiculoplasty. In the presence of mild hearing loss and absence of speech delay, it might be reasonable to repair the tympanic membrane first then reassess the hearing. Sometimes repair of the tympanic membrane alone improves hearing. When there is an obvious defect or missing ossicle at the time of any middle ear surgery, OCR can be performed at the same time as a tympanoplasty for tympanic membrane perforation. In certain circumstances, the OCR can be done at the time of the initial excision of cholesteatoma.

Cholesteatoma does present some challenges. Given its high rate of recurrence, second-look procedures are regularly performed. When the canal wall remains intact after mastoidectomy, a second look is usually necessary. This does provide an opportunity for OCR if it was not attempted at the first surgery. The advantage of waiting until the second procedures is that one knows if the cholesteatoma is gone and will not likely interfere with the ossiculoplasty/OCR or hearing result (Kim et al. 2006). If there was good hearing at the time of the first surgery, one may want to wait and evaluate hearing postoperatively prior to performing OCR. One may attempt OCR at the time of the first surgery when there is already a significant hearing loss preoperatively or a maximal conductive hearing loss is anticipated, as in the case of removal or destruction of one or more of the ossicles. There is the lowest risk of complication in cases where the ossicles or oval window are not directly involved with cholesteatoma. Residual cholesteatoma can grow resulting in dislodgement of the prosthesis and destruction of hearing repair. Involvement of these areas with cholesteatoma is not an absolute contraindication one can proceed with immediate or primary repair with the first procedure in some circumstances (Chandresekhar et al. 1995). Even if the hearing result is not lasting, knowing that there will be an opportunity to correct it should the cholesteatoma return, is often enough for some surgeons to recommend OCR to their patients at the first surgery.

The second look usually follows the primary surgery around 6 months later. During that time, the patient, often a child suffers increased or maximal conductive hearing loss. A second look procedure does necessitate the need for a compliant, reliable family. In cases where this is in question, the canal wall is taken down opening the mastoid to the external ear canal, removing the hiding places for cholesteatoma to grow or redevelop. In cases where the canal wall is taken down and an open cavity is created, the second look may not be indicated. This also effectively reduces the middle ear space and permanently alters the meatus and external auditory canal. This reduces the chance for good hearing result by eliminating or reducing the amplification contributions made to sound transmission by the external auditory canal and to a lesser degree, the vibrations of the tympanic membrane. The height of the middle ear space is reduced in the creation of an open mastoid cavity, creating a shorter distance from tympanic membrane to the stapes footplate. This must be considered in performing the OCR.

Choice of Surgical Technique

This is generally dictated by the status of the ossicular chain. The minimum requirement for an ossicular chain reconstruction is the presence of a stapes footplate. A secondary requirement is ultimately the presence of a tympanic membrane and middle ear space. The ideal material to use to reconstruct the ossicular chain must be biocompatible, suitably rigid, durable, and easy to manipulate (Gardner et al. 2004). When available, nascent ossicles make the ideal graft material possessing all of these characteristics. In the past, cadaveric ossicles were used but this has been largely abandoned. Cartilage such as tragal or conchal cartilage also make good graft material and can often be obtained through the same or a very small regional incision. These can be used to augment defects in the ossicles. They are biocompatible, but can experience unpredictable amounts of resorption. The most popular materials for grafts of this type most recently include titanium and hydroxyapatite (Kobayashi et al. 2002; Gardner et al. 2004; Truy et al. 2007). The newest implants have open heads allowing better visualization of the stapes to ensure correct placement. When using foreign material for OCR, it is generally recommended to place a piece of cartilage, described above, between the graft and the tympanic membrane to prevent extrusion (Kobayashi et al. 2002). These grafts can also be incorporated into the tympanic membrane reconstruction.

The approach utilized is dictated by preference and other indications for surgery. Often in the absence of mastoid disease or cholesteatoma, a transcanal approach can be used. This often allows treatment of tympanic membrane defects and middle ear disease as well as provides adequate visualization of the ossicular chain for OCR. However, if there is concurrent chronic mastoiditis or suspected cholesteatoma, a tympanoplasty combined with a mastoidectomy is used. This does allow for opening of the facial recess which does give better visualization of the stapes and reconstruction. Sometimes a small ear canal in younger or syndromic children especially, negates the option of a transcanal repair and the mastoidectomy must be performed for that reason. Mastoidectomy may also improve aeration of the middle ear and combat ongoing Eustachian tube dysfunction (McGrew et al. 2004). A third option exists with a postauricular transfacial recess approach. This is best suited to a second procedure where the facial recess was previously opened and the tympanic membrane has healed successfully. It eliminates the need to raise a tympanomeatal flap and disrupt the intact tympanic membrane (Blevins 2004). It often requires placement of a cartilage graft in the posterior superior quadrant of the tympanic membrane at the first procedure to prevent extrusion of the prosthesis placed at the next surgery.

Autologous Grafts

In the instance where the incus is not directly involved with cholesteatoma or is not completely destroyed by middle ear disease, it can be used to reconstruct the ossicular chain. It can either be used immediately or “banked,” placed in the mastoid cavity for use in ossiculoplasty at the next surgery (Gyo et al. 2004). Most times, the incus will need to be modified to fit the gap between the malleus and stapes. In the case where the stapes suprastructure is intact, an excellent hearing result can be achieved with any method of OCR. However, when the incus is available, it makes a perfect source for graft material. It has identical weight and composition of the same material as the other ossicles, ideally suited for conduction of sound. Generally speaking, there is little absorption of the bone over time and it is well tolerated by the patient with low rates of extrusion due to absence of foreign material.

When the malleus is located more posterior and lateral to the stapes, the modified incus is used as an “ineterposition” graft. A groove is drilled along the joint facet of the incus remnant. A well is drilled at the base of the short process to fit on the capitulum of the stapes. The “neoincus” is then positioned between the manubrium of the malleus and on the capitulum of the stapes (Fig. 1, Pyle 2003). A similar technique is used when the malleus is in a more anterior and medial position. However, it is called an incus “transposition” as the stapes capitulum and manubrium are often closer in proximity with one another. This necessitates a different sculpting technique with the well placed on the incus to accommodate the stapes capitulum adjacent to the joint facet, and the groove for the malleus drilled at the junction of the short process and the body of the incus (Fig. 2, Pyle 2003). This creates a more favorable angle and better fit.

Prosthetic Grafts

More commonly, the incus has been removed or destroyed sufficiently that exogenous materials must be brought in to bridge the gap between the stapes remnant and tympanic membrane. Choice of the type of prosthesis chosen is largely dictated by the location of the defect, the location and status of the stapes, the presence or absence of the manubrium of the malleus, and the mobility of the malleus head. The most common form of discontinuity is erosion of the lenticular process of the incus, as noted in the discussion above. Rather than disrupt the intact malleolar-incus joint, a graft or “incudostapedial (IS)-joint prosthesis” can be used to extend the incus and connect it to the intact capitulum of the stapes. When the stapes suprastructure is intact, a “partial ossicular replacement prosthesis” can be used. When the suprastructure is absent, a “total ossicular replacement prosthesis” is necessary. These are more commonly referred to as a PORP or TORP, respectively. The distance of the capitulum or the stapes footplate from the tympanic membrane or malleus dictates the length of the prosthetic device necessary. Various surgical measuring devices commonly available can be used to estimate this length in all of the situations discussed here. Prosthesis made of hydroxyapatite are available in a variety of precut lengths, but adjustable devices are available in a variety of materials, the most popular more recently are comprised of titanium (Truy et al. 2007). Similar types are available from several manufacturers. It is often advantageous to interpose a local cartilage graft between the prosthesis and the tympanic membrane to prevent extrusion. There are a variety of cartilage knives available to thin the cartilage graft to maximize sound transmission.

In the situation, an alternative to an incus graft is an IS-joint reconstruction. When the defect is small or short, bone cement can be used to reconnect the ossicles. An IS joint prosthesis can be created with autologous material such as conchal cartilage or cartilage from the helix. The former is curved and can be placed directly on the capitulum of the stapes like a cap. The helix offers a more block-shaped graft that can be carved to suit the individual situation. A groove is created for the incus long process and a well for the capitulum. Several types of prosthetic devices are available in both HA and titanium. The most well known of the former is known as an “Applebaum prosthesis,” which is made of hydroxyapatite and available in several sizes. Severalmanufacturers of titanium prosthetics offer a titanium option. These can be used to span larger gaps in larger defects of the incus. These can also be secured using bone cement or other middle ear adhesives (Goebel and Jacob 2005).

Other situations that may influence the surgeon’s choice of device include erosion of the manubrium of the malleus, absence of the malleus, or fixation of the malleus head. In the instance where the manubrium is gone or the malleus head is fixed, the stapes suprastructure is intact and the incus is absent, a PORP may be used. It can be placed on the capitulum and make contact directly with the TM or cartilage, bypassing the malleus. When the malleus is mobile, intact and in a favorable location, a device may be positioned with an arm looped under the manubrium, increasing conduction and stabilization (Todd 2008). This can be more challenging to place and does require ideal circumstances with a more laterally positioned malleus. However, when the malleus is too anteriorly located, it can be repositioned using a special repositioning technique allowing it to be used to stabilize the prosthesis (Vincent et al. 2004). A similar approach should be used when the stapes suprastructure is absent and instead a TORP is used. When the malleus is present, intact, and mobile, a TORP with a side arm or cap can be used and secured medial to the manubrium to stabilize the device with the other end placed in the center of the footplate. More often, that ideal positioning of the malleus does not exist and a TORP needs to be connected directly to the TM. It is more challenging to stabilize the prosthesis, but it can be done successfully (Martin et al. 2004). A footplate “shoe” can be used to center the inferior aspect of the prosthesis squarely on the footplate and to prevent migration. This can be constructed from cartilage or a prosthesis can be used (Beutner et al. 2008).

Contraindications

Ongoing Eustachian tube dysfunction is the most common problem complicating middle ear surgery in general, and can pose challenges for successful ossiculoplasty or OCR. However, it is not necessarily a contraindication to the procedure (Martin et al. 2004). Presence of cholesteatoma is a relative contraindication for reconstruction of the ossicular chain at the time of the excision at the initial surgery if it involves the oval window or the stapes footplate integrity is in question. OCR should be avoided if other defects in the otic capsule exist, such as a dehiscent semicircular canal. Dehiscence of the facial nerve in the area of the oval window is also a relative contraindication to ossicular chain reconstruction. If the incus is intimately involved with cholesteatoma, it can be carefully debrided and banked for use at the second surgery, as noted above. It can be reexamined for any signs of cholesteatoma prior to use in reconstruction at the second-look procedure.

A perforation or defect in the tympanic membrane with some residual connectivity remaining between the ossicles might be reason to hold off on attempting ossiculoplasty. It might be prudent to allow healing and perform postoperative audiologic testing with an intact tympanic membrane to better assess hearing status. For mixed hearing loss with a significant sensorineural component, a conservative approach is warranted. If the baseline hearing loss is sufficient to warrant amplification, one may not want to risk further hearing loss with manipulation of the ossicular chain. The sensorineural component should be evaluated with imaging of the inner ear to rule out a congenital inner ear anomaly, some of which can also be associated with conductive loss of unclear etiology, not related to the ossicular chain (Zhou et al. 2008). Computed tomography or magnetic resonance imaging, or in some instances, both modalities may be necessary to fully delineate the anomalies and etiology of the hearing loss. It is important to remember that amplification with a hearing aid or other means is almost always an alternate option for most patients and should always be offered to the patient.

Complications

Early complications usually involve Eustachian tube dysfunction, recurrent middle ear disease, and otitis media. This can result in chronic middle ear effusion or perforation which can contribute to ongoing conductive hearing loss. Negative pressure can lead to atelectasis, retraction of the tympanic membrane, and dislocation or extrusion of the prosthesis or graft. This can often be prevented with tube placement. Mastoidectomy can improve successful repair of the tympanic membrane and provide better middle ear aeration (McGrew et al. 2004).

Adenoidectomy prior to undertaking the middle ear surgery can also improve Eustachian tube function. Extrusion is the most common complication of OCR (Vrabec et al. 2002). It is much more common when nonautologous material is used. Hydroxyapatite and titanium have similar extrusion rates (Truy et al. 2007). Persistent Eustachian tube dysfunction and recurrent middle ear disease significantly increase this risk of extrusion. With the development of middle ear atelectasis and persistent negative pressure, a prosthesis is more likely to extrude or erode the stapes footplate resulting in vestibular symptoms and even severe to profound sensorineural hearing loss (Mishiro et al. 2008). Cholesteatoma can occur as a consequence of any middle ear or mastoid surgery and can cause further destruction of the ossicles or disruption of the OCR.

References

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