Studies on the mechanics of the reconstructed human middle ear

Using a laser-Doppler interferometer the influence of different positions of an incus prosthesis on hearing performance was examined in human temporal bone preparations. The influence of position and tension of a malleus to footplate prosthesis (columella) was studied in the same way. It is concluded that an incus prosthesis should be placed along an imaginary line through the centre of the footplate and the head of the stapes. With a malleus to footplate prosthesis the position on the footplate is relatively unimportant. Tension between the malleus, prosthesis and footplate, however, is quite important and should be as low as possible, and compatible with a stable situation. The malleus to footplate prosthesis provides a columella type of prosthesis which for lower frequencies works better than an incus prosthesis, and occasionally even better than the normal ear.     

Reconstruction of the ossicular chain with hydroxyapatite prostheses

To achieve a lasting result in reconstruction of the ossicular chain, strict material and surgical criteria must be combined. The best biomaterial, apart from bone, is hydroxyapatite, the mineral matrix of living bone tissue. For the reconstruction, the assembly technique is used instead of a columella. Direct contact with the drum membrane is not reliable if a columella is used, and extrusion or lateralization may influence postoperative results. In the case of a missing incus, an assembly prosthesis of dense hydroxyapatite is placed on top of the stapes head and the handle of the malleus, in a pocket between drum membrane and the neck of the malleus. Long postoperative follow-up of 120 patients showed an air-bone gap closure within 20 dB for 83.3% of the patients, no extrusion was observed, and the hearing gain stayed constant. Reconstruction of a tympanic membrane perforation and posterior canal wall was performed in the same stage in sixty patients. In the case of a missing incus and stapes superstructure, an incus/stapes prosthesis of dense hydroxyapatite, as assembly between footplate and handle of the malleus, was used. Long postoperative follow-up of twenty-five patients showed an air-bone gap closure within 20 dB for 68% of the patients. Reconstruction of a tympanic membrane perforation and posterior canal wall was performed in sixteen patients. No extrusion was observed and the hearing gain stayed constant. Hydroxyapatite prostheses have proven to be a good alternative for autologous and homologous ossicles.     

A new L-shaped titanium prosthesis for total reconstruction of the ossicular chain.

OBJECTIVE: To describe the technique used for total ossiculoplasty with the Fisch titanium total prosthesis and evaluate the 1-year postoperative functional results in patients presenting with the stapes (or footplate) without the malleus handle. STUDY DESIGN: Prospective trial with preoperative and postoperative comparison. SETTING: Academic and private practice tertiary care center for otologic surgery. PATIENTS: Forty-nine consecutive patients operated on from September 1996 to December 2000. SURGERY:: Staged ossicular reconstruction with a Fisch titanium total prosthesis placed between the footplate and the tympanic membrane without regard to the presence or absence of the stapes arch. Coupling of the prosthesis to the footplate was achieved by various techniques, including perforation, foot and spike on the footplate without perforation, and shaft alone (without foot) with tragal cartilage fixation (disc or small wedges). There was no interposition of cartilage between the prosthesis head and the tympanic membrane. MAIN OUTCOME MEASURES: Pre- and postoperative air and bone-conduction thresholds and air-bone gaps for pure-tone averages of three and four frequencies and for single frequencies. RESULTS: Postoperative air-bone gap closures within 20 dB distributed equally (50%) between 0.5, 1, and 4 kHz and reached the highest rate (89%) at 2 kHz (p < 0.05). The postoperative air-bone gaps for pure-tone averages reached 0 to 20 dB in 57% and 0 to 30 dB in 87% of the cases. There were no dead ears and no partial or total extrusions of prostheses. The best functional results were achieved through perforation coupling of the spiked foot to the footplate in large oval windows and after fixation of the shaft (without foot) with tragal cartilage disc in narrow oval windows. CONCLUSION: The functional results of the L-shaped Fisch titanium total prosthesis implanted in ears with the stapes but no malleus handle are best at 2 kHz and better than those of comparable columellar titanium prostheses over the remaining tested frequencies.     

Experimental investigations on middle ear prostheses with an integrated micro joint

BACKGROUND: Quasi static pressure changes as they occur in altitude changes or Valsalva's manoeuvre are causing great tympanic membrane displacements. These can produce a prosthesis dislocation from the stapes footplate, in case of using a TORP for reconstruction. Additionally, prostheses extrusions can occur in the chronically poor ventilated middle ear. Anatomical studies on the ostrich demonstrate that the flexible columella in the avian middle ear provides a good sound transmission and features an effective inner ear protection in pressure changes. MATERIAL AND METHODS: Focusing on this bionic attempt, we designed a new micro joint TORP by interposing a silicone ball joint in the prosthesis shaft. This prototype was used for frequency response measurements with the laser Doppler vibrometer in the ventilated middle ear and under conditions of increased pressure in the external auditory canal. RESULTS: Frequency response measurements showed comparable results to those using a conventional TORP. Investigations on pressure changes in the external auditory canal demonstrated a significant decrease in footplate excursion after reconstruction with the new micro-joint prosthesis then compared to a common TORP. CONCLUSIONS: The insertion of the new silicone bordered micro joint into a TORP shaft provides an effective method to decrease the potentially damaging stapes footplate excursions after complete ossicular reconstruction. Limited deflections of the prosthesis shaft reduce the occurring forces on the stapes footplate as they partly bore the quasi static pressure changes. Thus, the micro joint can reduce the risk of prostheses dislocation and annular ligament damage and is additionally providing a proper sound transmission through the reconstructed middle ear. Moreover, the bionic modification of a TORP reflects the remaining possibilities for further improvements in prosthetic reconstruction.     

Evaluation of a cement incus replacement prosthesis in a temporal bone model.

In reconstruction of the ossicular chain for a damaged incus, it is important that the incus replacement prosthesis (IRP) length is ideal in order to provide optimal tension between the tympanic membrane or malleus and stapes head to achieve the best post-operative hearing result. Even though the length of commercially available IRPs can be adjusted, it still may be difficult to achieve clinically. We describe experiments in a human temporal bone model using dental cement as an IRP after removal of the incus. This cement IRP (CIRP) hardens in situ and becomes the length of the gap to be spanned so that tension should be ideal. Two different CIRPs were studied; one was a conventional rod-type CIRP connecting either the umbo or mid-malleus handle to the stapes head. The second was a Y-shaped CIRP (Y-CIRP), connecting two sites on the malleus to the stapes head. The wide Y-CIRP connected the malleus head and umbo to the stapes head, while the narrow Y-CIRP connected the malleus neck and mid-handle to the stapes head. The acoustic performance of these experimental CIRPs was studied using a laser Doppler vibrometer system in 12 fresh human temporal bones. The CIRP demonstrated better acoustic performance than conventional IRPs studied previously in the same model. While all the CIRPs showed similar function below 2.0 kHz, the narrow Y-CIRP appeared best above 3.0 kHz. A prosthesis of this type may have an acoustic advantage over conventional IRPs.     

Ossicular reconstruction in the absence of stapedial crura*

The reconstruction of the ossicular chain when the stapes crura are absent presents a difficult problem in achieving satisfactory functional results in the treatment of chronic oitis media by tympanoplasty. When the malleus handle is present, the cases have been treated mostly by repositioning part of an incus or a piece of cartilage between the malleus handle and the mobile footplate. The problem becomes more difficult in tympanoplastic management of old radical cavities with no ossicules apart from the stapes footplate. Apart of repositioning a part of incus or a cartilage strut between the fascial graft and the footplate, the author has tried, in the management of these cases during the last 3 years, a new ‘umbrella type’ of prosthesis made entirely of tragal cartilage. This prosthesis enables a good resting surface for the new tympanic membrane and the hearing improvement seems to be greater than that resulting from other types of ossicular reconstruction.     

Optimum tension for partial ossicular replacement prosthesis reconstruction in the human middle ear

OBJECTIVE: Hearing results from ossiculoplasty are unpredictable. There are many potentially modifiable parameters. One parameter that has not been adequately investigated in the past is the effect of tension on the mechanical functioning of the prosthesis. Our goal was to investigate this parameter further, with the hypothesis that the mechanical functioning of partial ossicular replacement prostheses (PORP) from the stapes head to the eardrum will be affected by the tension that they are placed under. METHODS: Fresh temporal bones were used to reconstruct a missing incus defect with a PORP-type prosthesis. Three different lengths of PORP were used, and the stapes vibrations were measured with a laser Doppler vibrometer using a calibrated standard sound in the ear canal. Eight temporal bones were used. RESULTS: Tension had a very significant effect on stapes vibration. In general, loose prostheses resulted in the best overall vibration transmission. The effects were most marked at the lower frequencies. There was a slight advantage to tight prostheses in the higher frequencies, but much less than the decrement in lower frequencies with tight prostheses. CONCLUSION: In ossicular reconstruction, best stapes vibration results in our model are achieved by shorter prostheses, which result in lower tension.     

Histological study of the binding of Polycel and Ceravital implants to the stapes footplate in rabbits

Five Polycel and five Ceravital implants were interposed between the stapedial footplate and the tympanic membrane in 10 rabbits. Four to 7 months later the connection of the prostheses to the stapes was histologically examined by temporal bone sections. The union of both types of prostheses to the stapedial footplate was achieved by remnants of crura, middle ear mucosa and connective tissue. Histology revealed a more stable connection of the Polycel prosthesis to the stapedial footplate.     

Titanium prosthesis with malleus notch: a study of its 'user-friendliness'

'User-friendliness' is an important factor in the choice of ossicular prosthesis. The current titanium prostheses have a flat, open head plate and are designed to sit under the tympanic membrane. Previously, the author had designed titanium prostheses with a malleus notch extension at the head plate. The present study aimed to assess whether these customized prostheses were user-friendly, compared with conventional prostheses. Fourteen surgeons were recruited to examine the user-friendliness of several ossicular prostheses. They performed ossiculoplasties on temporal bones and rated the user-friendliness of the malleus notch prosthesis against that of some of the more popular conventional ossicular prostheses. For malleus-stapes assembly, eight out of 13 surgeons preferred the malleus notch prosthesis to the Düsseldorf and Goldenberg designs. For malleus-footplate assembly, six out of 10 surgeons preferred the malleus notch prosthesis to the Düsseldorf and Richards designs. Most of the surgeons stated that the reconstruction was more stable using the malleus notch prosthesis.     

Ossicular reconstruction in ears with cholesteatoma

Ossicular reconstruction in ears with cholesteatoma is similar to ears without cholesteatoma involvement. The important difference is that all cholesteatoma must be meticulously and completely removed or the reconstruction will fail. Special prostheses of bone or hydroxyapatite are used to rebuild the conductive mechanism. If only the incus is absent, an incus replacement prosthesis is employed between the malleus and intact stapes. When the stapedial superstructure is also missing, the incus-stapes prosthesis is utilized. These prostheses are interlocking in that a notch created in the top of the body of the implant engages the malleus and a cup in the lower part slips over the stapedial head, or a shaft extends to the stapedial footplate when the stapedial crura are missing. In either case the patient hears by direct columellar pressure from the new tympanic membrane to the fluids of the inner ear. Care is taken to preserve the patient's tissues and anatomy for use in reconstruction. If the patient's malleus or posterior bony wall must be sacrificed to eradicate the disease, these structures are immediately rebuilt with homograft tissue so that an orderly rebuilding of the conductive components may proceed. If the cholesteatoma has been extensive or infected and the middle ear mucosa is of poor character, definitive reconstruction is delayed to a second stage.     

Experience with a polyethylene total ossicular replacement prosthesis.

Surgical reconstruction of ossicular defects in chronic middle ear disease is a difficult problem. We have reviewed our results with the use of the Plastipore total ossicular replacement prosthesis (TORP). Of 29 procedures that were analyzed, nine were considered successful. None of our patients had a stapes superstructure, and 13 had no malleus. Placement of the TORP under the malleus handle and use of extra tissue between the prosthesis and the tympanic membrane provided better hearing results, but extrusion of the prothesis still occurred. Positioning of the prosthesis and contraction of the middle ear space, which causes extrusion of the prosthesis, remain problems in this type of reconstruction.     

Ceramic prostheses used as a columella

Ceramic stems, their lateral end capped with a modelled ossicle, or ceramic prostheses manufactured with a cap-shaped head were used as a columella from the stapes footplate to the tympanic membrane or a fascia graft in 41 ears operated on during 1982-1985. Six ears had no membrane perforations and no severe disease of the tympanic mucosa. Twelve ears underwent primary operations for cholesteatoma and 23 ears had revision surgery. Good hearing improvement occurred in well-aerated ears while hearing in ears with extensive tympanic disease did not improve after surgery. No tissue reactions to the ceramic prosthesis were observed and no prosthesis was extruded. Ceramic can be regarded as an acceptable alternative to bone for columella grafts used in surgery for chronic middle ear disease when the stapes superstructure is missing.     

Effects of ossicular prosthesis mass and section of the stapes tendon on middle ear transmission

BACKGROUND: The effects of changing prosthesis mass on middle ear transmission have not been previously systematically studied. Neither has the effect of stapes tendon sectioning. These are important parameters that can be surgically varied. HYPOTHESIS: Because the middle ear is compliance dominated at low frequencies, prosthesis mass will affect transmission of higher frequencies in the middle ear. METHODS: Eight fresh cadaveric temporal bones, with the incus removed, were loaded with a replacement prosthesis from the tympanic membrane to the stapes head. Laser Doppler vibrometry was used to measure stapes footplate vibrations. Vibrations were measured in response to chirps from 250 to 8 kHz at 90 dB SPL in the ear canal. The unloaded prosthesis mass was approximately 16 mg. Loadings with masses of approximately 2, 12, and 30 mg were placed on the stem. Recordings were repeated after cutting the stapes tendon. RESULTS: Mass loading affected the higher frequencies only, with significant effects only above 4 kHz. There was little low-frequency effect. Stapes tendon section showed an improvement in the lower frequencies but did not reach statistical significance. CONCLUSIONS: Mass of prostheses affects mainly higher frequencies. There is no drop in lower frequencies from using lower masses, so lighter-mass prostheses may be preferred. Stapes tendon section does not have a detrimental effect on middle ear transmission after ossiculoplasty.     

Ossiculoplasty with intact stapes and absent malleus: the silastic banding technique.

OBJECTIVE: To report an original method of ossicular reconstruction with intact stapes and absent malleus. Ossiculoplasty is performed with a total ossicular replacement prosthesis positioned from the stapes footplate to the under-surface of the tympanic membrane, using a Silastic banding technique to stabilize the prosthesis. STUDY DESIGN: A prospective study of ossicular reconstruction using the Silastic banding technique. A consecutive series of cases with intact stapes superstructure and missing malleus handle (Austin-Kartush Group C) is presented. SETTING: One tertiary referral center. PATIENTS: Ninety-nine patients who underwent total ossicular reconstruction with Silastic banding technique were enrolled in the study from January 2000 to December 2002. INTERVENTIONS: Ossiculoplasty with total ossicular replacement prostheses with Silastic Rubber Band for chronic otitis media and non-inflammatory disease. MAIN OUTCOME MEASURES: Preoperative and postoperative audiometric evaluation using conventional audiometry. Air-bone gap, bone-conduction threshold, and air-conduction threshold were assessed. Postoperative audiometry was performed at the 6th, 9th, 12th, 18th, 24th, and 36th months. RESULTS: Overall, a postoperative air-bone gap closed to within 10 dB was achieved in 61.5% of cases. An air-bone gap smaller than 20 dB was obtained in 77% of cases. Postoperative improvement of air-conduction thresholds by at least 20 dB was found in 51% of cases. There was no case of postoperative sensorineural hearing loss. One case of extrusion of the prosthesis was seen (1%). CONCLUSION: Stabilizing the total ossicular replacement prosthesis with the Silastic banding technique when performing ossicular reconstruction is a safe, effective method when the stapes supra-structure is present and the malleus absent.     

三种类型鼓室成形术疗效分析

目的 探讨三种类型鼓室成形术的临床疗效。方法 Ⅰ型鼓膜修补术:外伤性穿孔,应用贴补法修补穿孔;陈旧性穿孔用内植法修补。Ⅱ型镫骨加高术:镫骨正常,镫骨以外的听骨腐损,在镫骨头上固定骨皮质,使镫骨加高与人工鼓膜相接。Ⅲ型镫骨小柱术:仅剩镫骨底板正常(或无镫骨底板)用骨皮质制成听小柱连接镫骨底板(或前庭窗的脂肪上)和人工鼓膜。结果 Ⅰ型完成597例,成功573例,Ⅱ型完成53例,成功49例。Ⅲ型完成15例,成功14例。手术成功率94.8％。结论 三种类型鼓室成形术临床疗效满意。     

Reconstruction of the ossicular chain using a multistrand wire spring prosthesis

A multistrand wire spring prosthesis is presented for ossicular reconstruction. This device offers a workable solution not only to the ossiculoplasty problems associated with lateralization of the tympanic graft and displacement of the prosthesis, but also to other problems such as fixation to middle ear wall, tissue reaction, resorption, degeneration, biodegradation, or poor sound conduction, which are obviated using a stainless steel wire for the ossicular prosthesis. The spring also protects the inner ear from external trauma. Long-term reconstruction results of 14 cases using first generation coil spring prosthesis are presented. A freely mobile prosthesis head composed of cartilage with perichondrium on a wire-mesh platform distributes pressure evenly to the undersurface of the tympanic membrane and further ensures the prevention of pressure necrosis and extrusion. When the handle of the malleus is present, the head-loop assembly of the spring prosthesis is designed to securely capture the handle. There is no practical loss of sound energy passing through the spring. Over a period of 14 years none of the wire prosthesis was found to have eroded through the stapedial footplate.     

A 3-D finite element analysis of the natural frequencies of vibration of a stapes prosthesis replacement reconstruction of the middle ear

In this work, the natural frequencies of vibration of two different stapes prosthesis replacement reconstructions have been analysed using the finite element method. Prosthesis 1 was constructed of fine stainless steel wire and a Teflon base, while prosthesis 2 was made entirely of Teflon. The results have indicated that generally, the first natural frequency of vibration falls as the prostheses become larger and more bulky. However, the fall in the first natural for prosthesis 1 was modest when compared with that of the isolated tympanic membrane. An important variable influencing frequencies and mode of vibration of the reconstruction was the tightness of fit of the prostheses within the remaining ossicular chain. The tightness of fit in this work was modelled as a range of spring constants applied at the stapes pseudo footplate, together with a series of joint elements at the incus tip/prosthesis head for the Teflon implant. When these spring constraints were below approximately 10 N/mm, the reconstruction exhibited normal mode 1 vibration behaviour, but at larger spring values, an abnormal mode 1 became established resembling the normal mode 2 vibration characteristics. The formation of new geometries and surfaces following reconstruction, introduces new constraints between umbo and stapes footplate particularly at the natural/artificial interfaces. These unnatural constraints may inhibit and modify the natural movements normally occurring at the stapes footplate leading to abnormal modes of vibration.     

Acoustomechanical properties of open TTP titanium middle ear prostheses

OBJECTIVE: The purpose of the study was to identify acoustcomechanical properties of various biostable and biocompatible materials to create a middle ear prosthesis with the following properties: (i) improved handling including a good view of the head of the stapes or footplate and adjustable length, (ii) improved acoustical characteristics that are adequate for ossiculoplastic. The identified material should serve to build CE and FDA approved prostheses for clinical use in patients. METHODS: Test models made of Teflon, polyetheretherketone, polyethylenterephtalate, polysulfone, gold, Al2O3 ceramics, carbon and titanium were investigated for their potential to fulfill the requirements. Acoustical properties were investigated by laser Doppler velocimetry (LDV) in mechanical middle ear models (MMM). Measured data were fed in to a recently created computer model of the middle ear (multibody systems approach, MBS). Using computer-aided design (CAD) measured and computed data allowed creation and fine precision of titanium prostheses (Tübingen Titanium Protheses, TTP). Their handling was tested in temporal bones. Acoustomechanical properties were investigated using the MBS and mechanical middle ear models. MAIN OUTCOME MEASURES: Input impedance, mass, stiffness, and geometry of test models and prostheses were determined. Furthermore, their influence on the intraprosthetic transfer functions and on coupling to either tympanic membrane or stapes was investigated. RESULTS: Final results were FDA- and CE-approved filigreed titanium prostheses with an open head that fulfilled the four requirements detailed above. The prostheses (TTP) were developed in defined lengths of between 1.75 and 3.5 mm (partial) and 3.0 and 6.5 mm (total) as well as in adjustable lengths (TTP-Vario). CONCLUSIONS: The results suggest acoustomechanical advantages of TTPs because they combine a significantly low mass with high stiffness. In contrast to closed prostheses, the open head and filigreed design allow an excellent view of the prosthesis foot during coupling to the head or footplate of stapes, contributing to an improved intraoperative reliability of prosthesis coupling.     

Experimental study of an adjustable-length prosthesis in a temporal bone model

CONCLUSIONS: This prosthesis has the advantage of rapid adjustment at the time of insertion in order to achieve optimal tension and, as a result, optimal sound transmission. OBJECTIVE: To test the acoustic performance of a new, adjustable incus replacement prosthesis in a human temporal bone model. MATERIAL AND METHODS: Experiments were performed in seven human temporal bones, before and after removal of the incus and insertion of the prosthesis. The input comprised 406 pure tones ranging in frequency between 0.1 and 10 kHz at an intensity of 80 dB SPL at the tympanic membrane. The output measurement was stapes footplate displacement, determined by means of a laser Doppler vibrometer. Three lengths of the prosthesis were investigated: optimal, optimal +0.2 mm and optimal +0.4 mm. RESULTS: The optimal-length prosthesis produced similar results to those of an intact middle ear. The slightly longer prostheses decreased middle ear sound transmission at all test frequencies, except those near 1.5 kHz.     

Middle-ear reconstruction: a review of 150 cases

This study is based on a retrospective analysis of 150 cases of tympanoplasty and ossicular chain reconstruction as a one-stage procedure. It was conducted at the Federal Government Services Hospital, Islamabad from 1983 to 1999. Temporalis fascia was used for myringoplasty and a sculptured autologous incus to bridge the malleus to stapes head and malleus to footplate gap. These interpositions have produced stable ossicular assemblies and provided satisfactory post-operative hearing gains. One hundred and twenty-six (84 per cent) patients achieved a healed tympanic membrane three months post-operatively. One year post-operatively, 121 (81 per cent) patients had an intact tympanic membrane and at five years 119 (79 per cent) had an intact tympanic membrane. The success rate was based on an intact tympanic membrane and an air-bone gap of less than 30 dB one-year post-operation. Accordingly, the overall success rate was 80 per cent (120 cases). Hearing gains in cases with an absent stapes arch were poorer than in cases with an intact arch. Early (one to three months) post-operative complications included tympanic membrane perforation, lateralization of the graft and persistence of infection. Late (one to five years) complications included the appearance of an anterior perforation and retraction and thinning of the tympanic membrane.