The mechanical vibrations that are present in the air around us are disorganized; they function independent of direction, and there are great variations in the strengths of these vibrations. For the body to be able to digest and interpret this information, the multidirectional vibrations must first be organized into a simple linear vibration, and then this vibration must be calibrated to the proper strength to stimulate the hair cells of the inner ear. The majority of this process is performed through the function of the tympanic membrane and the bones of the middle ear. 

The tympanic membrane acts in the same manner as the vibrating surface of a drum (as both its Latin name and most common moniker, the "eardrum", would imply). Sound strikes this membranous structure from all directions; however, the resulting vibration that is passed along to the middle ear is unidirectional, and thus much better organized. 

The final step in conditioning this signal is to ensure that the amplitude of the mechanical vibrations is appropriate for sensorineural detection in the inner ear. The bones of the inner ear accomplish this task by acting as a system of levers, amplifying the vibrational signal much like the arm of a record player. Now that we have a better understanding of the basic functionality of the middle ear, we can derive the following guiding principles for surgical replacement of the bones of the middle ear:

1) The natural elasticity and impedance of the construct formed by the bones of the middle ear must be maintained for proper sound conduction. This is necessary not only to facilitate proper conduction of acoustic energy to the inner ear, but also to prevent the inner ear from subsequent damage due to excessive sound or barotrauma. In a normally functioning ear, the elasticity and impedance characteristics are a function of the action of the annular ligament; the use of a piston-style prosthesis in a surgically reconstructed middle ear necessitates the use of a vein graft in order to restore these mechanical properties.

2) The transmission of vibration through the linkage between the tympanic membrane and the stapes footplate must not be hindered, and the best surgical result is one that closely reproduces the original behavior of the system. Therefore, the prosthesis must be chosen on the basis of its mass and stiffness, in addition to biocompatibility and ease of surgical placement. The prosthesis should be placed such that it impinges upon the footplate in a perpendicular fashion to provide the maximum conduction of sound.

3) Since the natural system of levers used by the middle ear to amplify the signal is being partially obliterated and replaced by a straight prosthesis, it is necessary to use the principles of surface area and pressure to get the proper amplification. Exhaustive research has been conducted to determine the optimal gain relationship between the vibrating surfaces of the tympanic membrane and the footplate fenestration1,2; through finite-element modeling of the surgical construct, the following relationship has been established:
The surface area of the tympanic membrane should be 20 times the surface area that acts upon the inner ear fluids.¹

Stapedectomy- Surgical Technique Preparation of Vein Graft A vein is harvested from the forearm of the patient. The vein is threaded over the Curved Needle (MCO657), and using the Bishop Harmon Tissue Forceps (37-40052) and a #15 knife blade, the connective tissue is removed from the outer surface of the vein (Figure 1).		Figure 1
The connective tissue is kept in saline for later use as a sealant and adhesive in the oval window fenestration and for stapedius tendon reattachment. The smooth vein is then sectioned longitudinally using the Curved Iris Scissors (37-41027) and placed "sticky" (adventitial) side down over the 1.0mm hole in the Glass Plate (MCO660.10) (Figure 2). The center of the graft is gently pressed into the depression; the graft is then left to partially dry into this pre-formed shape during the next several steps of the surgery.		Figure 2
Elevation of Tympanomeatal Flap Using the Round Knife (MCO652), an incision is made at the distal edge of the ear speculum from the 11 o'clock to the 6 o'clock position in the left ear, or the 1 o'clock to the 6 o'clock position in the right ear. The incision is then deepened to the underlying bone using the V-Shaped Knife with Bent Shaft (MCO651) (Figure 3).		Figure 3
The bend in the shaft of the knife allows the tip to penetrate all the way down to the bony surface, even when the speculum is not closely approximated to the bone. The Flap Elevator (MCO667) is then used to elevate the tympanomeatal flap away from the bony surface (Figure 4).		Figure 4
The elevator is ergonomically angled to allow the most effective approach to the dissection, and the semi-sharp edge cleanly dissects the connective tissue without sticking on the bone. The 18 Gauge (1.2mm) Rosen Suction (37-24203) is used throughout to remove blood from the operative field and to manipulate the tympanic membrane. Once the flap has been completed, the chordae tympani is gently elevated using the Curved Needle (MCO657). In order to broaden the field of view into the middle ear and allow proper access for instruments, bone is removed from the posterior edge of the canal using the Curette (MCO655). The instrument has a downward bend at the handle that allows excellent visibility and hand strength, and has a durable design that remains consistently sharp after repeated use. The instrument should always be directed away from anatomical features such as the chordae tympani and the incus to eliminate the possibility of accidental damage. The bony rim of the canal is resected until the pyramidal process can be clearly viewed (Figure 5). Once the bony rim has been adequately reduced, the tympanic membrane is gently retracted from the long process of the Incus using the Curved Needle (MCO657).		Figure 5
Separation of Stapedius Tendon Using the Perpendicular Short Hook (MCO664), the stapedius tendon is deinserted from the posterior crus of the stapes process. In order to allow the tendon to be properly reattached to the piston prosthesis, every effort should be made to preserve its entire length by removing it at its insertion into the bone, and by progressively de-inserting its fibers instead of cleanly cutting the tendon (Figure 6).		Figure 6
Division of Incudostapedial Joint Using the Joint Knife (MCO656), the joint between the incus and stapes is carefully cut with a back and forth motion. In order to preserve the proper function of the incus, care should be taken not to elevate the incus during this maneuver. The angle at the tip of the knife has been carefully designed to allow this cut to be made without disturbing the incus (Figure 7).		Figure 7
Fracture/Obliteration of Crura  While separating the crura and removing the superstructure of the stapes, it is extremely important not to disturb the footplate of the stapes or the annular ligament. These structures must remain functional if hearing is to be properly restored. The least traumatic way to divide the crura of the stapes is to use the Skeeter Drill (30-55600) with the 0.8mm Carbide Bur (31-55638). The posterior crus is divided first, pressing the 20 Gauge (0.9mm) Rosen Suction (37-24205) against the medial side of the crus, opposite the drill, to minimize the lateral pressure applied to the footplate and annular ligament during drilling. (Figure 8) The same process is then used on the anterior crus to complete the detachment of the Stapes superstructure. The now-mobile superstructure is carefully removed from the surgical site using the Rosen suction.		Figure 8
Selection of Appropriate Prosthesis  The proper piston is chosen for the patient using the principles described in the introduction of this surgical technique. The mass of the piston should closely approximate that of the natural bones of the middle ear, and the diameter of the surface that interacts with the middle ear should be approximately 1/20th of the diameter of the tympanic membrane. It is important to note that this "interacting surface" is actually somewhat larger than the actual diameter of the shaft of the piston because of the use of a vein graft. The average thickness of a vein graft is 0.2mm. Therefore, the actual size of the interacting surface would be defined as: DI = DP + 0.4mm -where- DI is the diameter of the interacting surface DP is the diameter of the piston shaft For the vast majority of patients, the appropriate size of the interacting surface is 0.8mm; therefore, the proper prosthesis for most patients is the 0.4mm Causse Flouroplastic Prosthesis (11-31000). (Figure 9)		Figure 9
Fenestration of the Stapes Footplate  The footplate fenestration should be created to the size of the desired interacting surface. As mentioned above, the most appropriate fenestration size for most patients is 0.8mm. The fenestration should be located in the posterior half of the footplate so that the piston will not exert pressure on the saccule, which is located immediately beneath the anterior half of the footplate. The fenestration is created through the footplate using the Skeeter Drill with a diamond bur. This instrument allows the fenestration to be created accurately and safely, without the risk of thermal injury that other alternative fenestration methods may present. The footplate and annular ligament can be easily damaged, so great care must be taken not to apply excessive force to the footplate during the drilling process. In order to minimize the force applied to the footplate, the author uses a 0.6mm diamond bur (31-55646) to create the 0.8mm fenestration. The bur is used to drill a 0.6mm hole straight into the footplate, then several small circumferential motions are made to slightly enlarge the fenestration from 0.6mm to 0.8mm (Figure 10).		Figure 10
Vein Graft Positioning The vein graft is positioned "sticky" (adventitial) down over the fenestrated footplate using the 22 Gauge (0.7mm) Rosen Suction (37-24206) and the Curved Needle (MCO657) (Figure 11). The recess that has been pre-formed into the vein graft by the glass plate fits nicely into the fenestration. Using a large vein graft minimizes unwanted motion and penetration of the piston into the vestibule, and helps to develop normal function of the annular ligament, which is important to maintain the normal conductive impedance of the reconstructed ossicular chain.		Figure 11
Manipulation and Placement of the Causse  Flouroplastic Piston  The upper loop of the piston is opened in an asymmetric elliptical fashion to maximize its holding strength and contact area when closed on the incus (Figure 12).		Figure 12
The loop is opened by inserting the Micro Alligator Forceps (MC013) and deforming the loop until it maintains a 2mm gap at the opening. The piston is then inserted into the ear using the 20 Gauge (0.9mm) Rosen Suction (37-24205) and the Short Perpendicular Hook (MCO664). The distal tip of the piston is placed in the vein graft depression, and the upper loop is placed lateral to the long process of the incus. Now, using the long perpendicular hook (MCO665) on the lower surface of the loop opening and the short perpendicular hook (MCO664) on the upper surface of the loop opening, the prosthesis is rotated onto the long process of the incus with one slow, well-controlled motion. Finally, the prosthesis is crimped onto the incus with the Piston Closing Forceps (MCO658) in one motion (Figure 13).		Figure 13
The cupped forceps have been specifically designed to capture the loop of the piston and apply the closing forceps properly to achieve a snug fit between the prosthesis and the implant (Figure 14). To secure the tip of the piston in the fenestration following placement, some of the loose periveinous tissue can be used as an adhesive and sealant.		Figure 14
Stapedius Tendon Reattachment  For the best surgical outcome, stapedius tendon reattachment should be attempted. Clinical research has shown that the stapedius tendon reflex is used to aid in the discrimination of sound (i.e. separating a spoken voice from background noise) and to safeguard the inner ear from damage due to excessive sound3. The Causse 0.4mm Flouroplastic Piston (11-31000) has been designed with a PolyCel platform to provide an attachment point for the stapedius tendon. The tendon is reattached by grasping it with the tip of the 20 Gauge (0.9mm) Rosen Suction (37-24205) and stretching it to the PolyCel platform; the tendon will adhere to the platform enough to maintain its position temporarily. Finally, a small piece of the periveinous tissue that was collected while harvesting the vein at the beginning of the surgery is used as an adhesive to firmly reattach the end of the stapedius tendon to the PolyCel platform (Figure 15).		Figure 15

Reference List (with abstracts)

1. Blayney AW, Williams KR, Rice HJ
A dynamic and harmonic damped finite element analysis model of stapedotomy."
Acta Otolaryngol. 1997 Mar;117(2):269-73.
PMID: 9105464; UI: 97259344

This study was undertaken in an attempt to better understand the mechanics of sound transmission at the footplate following stapedotomy. The insertion of a Teflonฎ (polytetrafluoroethylene) stapes prosthesis introduces new constraints within the reconstructed ossicular chain which have an effect on the normal vibration patterns of the tympanic membrane. In a finite element model of the ear, constraints have been reproduced as a series of spring constants in the incus/prosthesis/footplate interfaces incorporating damping to simulate the impedance of the inner ear. At zero damping, the frequency response at the pseudo stapes footplate exhibit several maxima and minima between 800 Hz and 2.5 Hz. At higher damping values, these maxima and minima become smoothened out with two or three naturals occurring over the same frequency range. Severe ankylosis of a diseased footplate is reproduced by over-damped conditions. The umbo, incus and stapes footplate vibrate in phase with similar frequencies at light damping levels. The movement of the prosthesis at the pseudo-footplate can be large in the out of plane axis of the ossicular chain, unless sufficient support is provided at the reconstructed footplate. Clinically, this would suggest the vein graft interposed between the piston and stapedotomy hole should endow resistance and elasticity to the system.


2. Causse JB, Gherini S, Lopez A, Juberthie L, Olivier JC, Bastianelli G 
Impedance transfer: acoustic impedance of the annular ligament and stapedial 
tendon reconstruction in otosclerosis surgery.
Am J Otol. 1993 Nov;14(6):613-7.
PMID: 8296869; UI: 94127552

The resistance rebuilt around the lower tip of the piston must be the same as that created by the annular ligament of the stapes footplate. Otherwise, the threshold at which an acoustic or barotrauma is able to damage the membranes and hair cells of the inner ear will be lowered. The elasticity reestablished around the lower tip of the piston plays a part in the quality and quantity of hearing for the low frequencies up to 3 kHz. To protect the ear against acoustic traumas, an attempt to rebuild the stapedial reflex is proposed.

3. Causse JB, Michat M, Gherini S 
Stapedius tendon reconstruction during stapedotomy: technique and results.
Ear Nose Throat J. 1997 Apr;76(4):256-8, 260-9. Review.
PMID: 9127525; UI: 97272880

During surgery for otosclerosis, it is common for the surgeon to cut the stapedius tendon. Even without reconstruction of the tendon, the results of this kind of surgery are particularly satisfactory. The stapedial reflex is more important for improving intelligibility of speech in the presence of background noise than for protection against hazardous levels of noise. An intact stapedial reflex improves ones ability to follow speech in the presence of background noise. This report will present a technique to reconstruct the stapedius tendon, along with the results obtained when adding this procedure to stapedotomy surgery.

Ordering Information
Set Includes
MCO649 MicroFrance J.B. Causse Middle Ear Instrument Set MCO649SC Sterilization case only			MCO651 V-Shaped Canal Knife, Bent Shaft
MCO665 Perpendicular Hook, Long			MCO652 Round Canal Knife, Straight Shaft
MCO664 Perpendicular Hook, Short			MCO655 Bone Curette
MCO13C Micro Alligator Forceps			MCO656 Incudostapedial Joint Knife
MCO4A Micro Scissors			MCO657 Curved Needle
MCO658 Piston Closing Forceps			MCO660.10 Vein Preparation Plate
Available Instruments not shown: MCO12D Causse Measuring Instrument  MCO213.4 Graduated Prothesis Cutting Block  MCO27 Deiter Malleus Nipper  MCO666 Curved Needle, Dull  MCO667 Flap Elevator  MCO82O Fascia Press

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Nota Bene: The technique description herein and the use of instructions for the related procedures are made available by Medtronic Xomed, Inc. to the healthcare professional to illustrate the author's suggested treatment for the uncomplicated procedure. In the final analysis, the preferred treatment is that which, in the healthcare professional's judgment, addresses the needs of the individual patient.