Incudostapedial Joint Research Articles

Bilateral congenital ossicular chain disruption mimicking otosclerosis

A rare case of bilateral congenital ossicular chain disruption whose history and findings mimicked those of otosclerosis is reported. A 54-year-old male consulted us for slowly progressing hearing loss. Audiogram showed bilateral intermediate mixed hearing loss. The stapedial reflex was negative and the tympanogram was normal A-type. Based on the diagnosis of otosclerosis, stapes surgery was planned for the left side. Surgical findings revealed normal mobility of the stapes and a small disruption at the incudostapedial joint with connection of intact mucosa. The disruption was repaired with auto-bone columella. The patient's hearing improved after surgery. The surgery for the other side was performed successively, and similar ossicular disruption was observed. The mechanisms of findings that misled the preoperative diagnosis are discussed.

Middle Ear Admittance and Hearing Abnormalities in Individuals with Osteoarthritis

In osteoarthritis, the joint cartilage breaks down. Cartilage exists within the incudomalleolar and incudostapedial joints. In addition, the cartilage-covered base of the stapes footplate is bound to the cartilage-covered rim of the oval window by the annular ligament. Thus, higher prevalence of middle ear abnormalities and hearing loss can be expected in osteoarthritis due to degeneration of the cartilage and the subsequent abnormal repair response. In this study, tympanometric and audiometric data were obtained from 15 individuals diagnosed with osteoarthritis and 15 gender- and age-matched individuals without the diagnosis of arthritis. Results showed a significantly higher prevalence of middle ear abnormalities and hearing loss in ears with arthritis when compared to the control group. Interestingly, osteoarthritis and hearing loss are considered among the top chronic health concerns in older individuals although the connection between these two conditions has not been previously reported.

Magnetic Resonance Imaging Compatibility and Safety of the SOUNDTEC Direct System

The purpose of this study was to evaluate magnetic resonance imaging (MRI) compatibility and safety of an electromagnetic implanted hearing device (the SOUNDTEC Direct System; SOUNDTEC, Inc., Oklahoma City, OK) implant during a 0.3-Tesla open MRI imaging examination of the head and neck and to develop an MRI protocol that maximizes patient safety while minimizing the need for implant removal. The current literature regarding MRI compatibility of implantable hearing devices was reviewed. Linear and torsional forces, heating, and implant magnetization were evaluated in vitro. Implanted fresh-frozen human temporal bones were used to evaluate image distortion. A prospective study of 11 volunteers previously implanted with the SOUNDTEC Direct System was conducted to evaluate MRI compatibility and safety. A MEDLINE search of the literature between 1980 and July 2005 was reviewed to summarize MRI compatibility testing of implantable hearing devices. Torsional and linear forces experienced by eight implant magnets were measured using calibrated neurologic Von Frey Hairs and compared with finite element analysis predictions as well as forces required to separate the incudostapedial joints of 12 fresh-frozen human temporal bones. Implant heating was determined by measuring the temperature change of eight implant vials compared with saline controls immediately after a head MRI scan. Implant magnetization was evaluated after repeated exposure to a 0.3-Tesla magnetic field. An 11-patient prospective study was performed to evaluate MRI compatibility in a 0.3-Tesla open MRI environment using adult volunteers previously implanted with the SOUNDTEC Direct System. A modified MRI protocol was developed to maximize patient safety. Each individual underwent an audiometric and otologic examination immediately before and after MRI. Peak linear force at the MRI entry measured 0.5 g +/- 0.2 standard deviation (SD). Maximum torque occurred at isocenter and measured 11.4 g-cm +/- 1.2 SD. The mean torque required to separate the incudostapedial joint was 33.8 g-cm +/- 20.4 SD. The average increase in temperature of the eight implant vials was 0.45 degrees C +/- 0.11 SD, whereas the increase in temperature of the three saline controls measured 0.47 degrees C +/- 0.11 SD. The average change in magnetic flux density of the 14 implant magnets tested was 22.0 gauss. Maximum image distortion occurred during the gradient echo sequence and measured 8.6 cm in diameter with a volume of 5,096 mm. Eleven patients completed a total of 12 head, one shoulder, and three lumbar 0.3-Tesla open MRI scans without patient- or device-related complications other than degradation of the MR image. There was no report of discomfort, tinnitus, dizziness, change in hearing, or change in device performance. All post-MRI changes in pure-tone thresholds, speech discrimination, soundfield thresholds, and aided soundfield thresholds were within the range of test-retest variability. When considering MRI of implantable ferromagnetic hearing devices, issues related to mechanical forces, implant heating, current induction, implant demagnetization, image degradation, and acoustic trauma must be considered. The SOUNDTEC Direct System is both MRI-compatible and safe in a 0.3-Tesla open MRI environment when a modified protocol is used. Degradation of the head MRI image may impair visualization of the ipsilateral temporal bone and adjacent structures within a 2.5- to 4.3-cm radius of the implant and is minimized by using a fast spin echo sequence.

Practical Use of MESNA in Atelectatic Ears and Adhesive Otitis Media

Objective: MESNA is a synthetic sulfur compound that produces mucolysis by disrupting disulfide bonds. This study aimed to address indications and technique of MESNA application in otologic surgery, especially in retraction pockets and adhesive otitis media. Methods: MESNA application was performed in 42 ears of 39 patients. The diagnoses were retraction pockets fixed to incudostapedial joint, stapes or promontorium, and adhesive otitis media in 24 and 17 ears, respectively. Calculations were performed according to 24 ears of 23 patients with follow-up data. Results: One or more of the following surgical interventions were performed: MESNA application alone and ventilation tube insertion, reinforcement or mastoidectomy in addition to MESNA application. Sensorineural hearing loss was not encountered after MESNA application. The operation was successful in 79.2%. Overall revision surgery was needed in 20.8% of the ears. In 71.4% of the ears treated with MESNA alone, revision surgery was needed. Conclusion: In the light of our experience, we advocate the use of MESNA in atelectatic ears, because it makes the operation easy and safe by allowing elevation of the tympanic membrane by its mechanical and chemical actions.

Configurations of Incudostapedial Joint Surface, An SEM Study

There are few studies regarding the normal incudostapedial joint surface at the SEM level in dogs; therefore, in the present study we studied the normal morphology of the incudostapedial joint surface using SEM. The animals were anesthetized intravenously with Ketamine + Xylazine (5.2 mg/kg) and perfused with 2.5% glutaraldehyde in 0.1 M sodium phosphate buffer at pH 7.2 via left ventricle. Middle ear ossicles, the incus and stapes were processed using routine histological procedures for SEM studies and examined under a Philips 505 type SEM. The articular surfaces of incus and stapes had similar configuration and micromorphology. Articulation surface of the incus had small, spherical processes formed column-like structures lying in homogenously parallel fashion; the cartilage covering the articulation surface of the incus was present deep to these processes. The capsule of the incudostapedial joint was separated from the functional joint surface via a deeply lying sulcus. In contrast to incudomalleal (IM) joint, homogenously arranged and well formed controcytes and collagen fibers in the IS joint suggests that the ability of the IM joint to regulate the waves and strength of the sound arriving the IS joint. A comparative SEM studies of IM and IS joints will facilitate the understanding of the morphological changes during disease and aging.

The Evolution of Aural Acoustic-Immittance Measurements

The Evolution of Aural Acoustic-Immittance Measurements

On the coupling between the incus and the stapes in the cat.

The connection between the long process and the lenticular process of the incus is extremely fine, so much so that some authors have treated the lenticular process as a separate bone. We review descriptions of the lenticular process that have appeared in the literature, and present some new histological observations. We discuss the dimensions and composition of the lenticular process and of the incudostapedial joint, and present estimates of the material properties for the bone, cartilage, and ligament of which they are composed. We present a preliminary finite-element model which includes the lenticular plate, the bony pedicle connecting the lenticular plate to the long process, the head of the stapes, and the incudostapedial joint. The model has a much simplified geometry. We present simulation results for ranges of values for the material properties. We then present simulation results for this model when it is incorporated into an overall model of the middle ear of the cat. For the geometries and material properties used here, the bony pedicle is found to contribute significant flexibility to the coupling between the incus and the stapes.

The Effects of Mass Loading the Ossicles with a Floating Mass Transducer on Middle Ear Transfer Function

The aim of this study was to measure the mass loading effect of an active middle-ear implant (the Vibrant Soundbridge) in cadaver temporal bones. Implantable middle ear hearing devices such as Vibrant Soundbridge have been used as an alternative to conventional hearing aids for the rehabilitation of sensorineural hearing loss. Other than the obvious disadvantage of requiring implantation middle ear surgery, it also applies a direct weight on the ossicular chain which, in turn, may have an impact on residual hearing. Previous studies have shown that applying a mass directly on the ossicular chain has a damping effect on its response to sound. However, little has been done to investigate the magnitude and the frequency characteristics of the mass loading effect in devices such as the Vibrant Soundbridge. Five fresh cadaver temporal bones were used. The stapes displacement was measured using laser Doppler vibrometry before and after the placement of a Vibrant Soundbridge floating mass transducer. The effects of mass and attachment site were compared with the unloaded response. Measurements were obtained at frequencies between 0.1 and 10 kHz and at acoustic input levels of 100 dB sound pressure level. Each temporal bone acted as its own control. Placement of the floating mass transducer caused a reduction of the stapes displacement. There were variations between the bones. The change of the stapes displacement varied from 0 dB to 28 dB. The effect was more prominent at frequencies above 1,000 Hz. Placing the floating mass transducer close to the incudostapedial joint reduced the mass loading effect. The floating mass transducer produces a measurable reduction of the stapes displacement in the temporal bone model. The effect is more prominent at high frequencies.

Experience with the SOUNDTEC Implantable Hearing Aid

To assess the efficacy, morbidity, and patient satisfaction of the SOUNDTEC semi-implantable hearing aid. Retrospective case review. Two tertiary referral centers (the Silverstein Institute and the Atkins Institute). Sixty-four (four bilateral placements) patients with bilateral moderately severe sensorineural hearing loss: 47 patients had previously worn hearing aids. After separating the incudostapedial joint, a magnet encased in a titanium canister with a ring was introduced onto the stapes neck. Gelfoam or adipose tissue was used to stabilize the magnet. After 3 months, the external processor was fitted. At 1 month, audiometric testing was performed and functional gain was assessed. Patient acceptance and implant performance were measured by a visual analogue questionnaire. The device produced an average functional gain of 26 dB. Fifty-five percent of patients complained of magnet movement; this was eliminated in 80% of Silverstein Institute patients when the external processor was worn and fat was used to stabilize the magnet. The SOUNDTEC direct device is well tolerated in the majority of patients, with a significant increase in functional gain. Magnet instability and noise were the most frequent complaints and improved with processor placement and anchoring the magnet with fat. This electromagnetic semi-implantable hearing aid confers greater functional gain over conventional hearing aids and reduces occlusion effect and feedback.

Experimental ossicular fixations and the middle ear’s response to sound: Evidence for a flexible ossicular chain

A human temporal-bone preparation was used to determine the effects of various degrees of artificial ossicular fixation on the sound-induced velocity at the input-side (the umbo of the malleus) and the output-side (the stapes) of the ossicular chain. Construction of various degrees of attachment between an ossicle and the surrounding temporal bone provided a range of reduction in ossicular mobility or “fixations”. The results demonstrate different effects of the fixations on the umbo and stapes velocity: fixations of the stapes or incus produce larger reductions in sound-induced stapes velocity (as much as 40–50 dB with extensive stapes fixation), than reductions in umbo velocity (typically less than 10 dB). Fixations of the malleus produce similar-sized changes in both umbo and stapes velocity. These differential effects are consistent with significant flexibility in the ossicular joints (the incudo-malleolar joint and the incudo-stapedial joint) that permits relative motion between the coupled ossicles. The existence of flexibility in the ossicular joints indicates that joints in the ossicular chain can effect a loss of sound-induced mechanical energy between the umbo and the stapes, with a concomitant reduction in the sound-induced motion of the stapes. The introduction of such losses in sound transmission by the joints raises questions concerning the utility of three ossicles in the mammalian ear. The consequences of ossicular flexibility to ossicular-chain reconstruction is discussed. Also, as examined in a more clinically directed paper [Laryngoscope 115 (2005) 147], the different effects of the various ossicular fixations on the motion of the umbo and malleus may be useful in the diagnosis of the site of fixations in humans with conductive hearing losses caused by such pathologies.

Histochemical Characterization of the Rat Ossicular Joint Cartilage with a Special Reference to Stapediovestibular Joint

The stapes footplate articulates the vestibular window (stapediovestibular joint; SV joint). The SV joint is known as crucial region of otosclerosis. To shed a light on pathogenesis of otosclerosis, we have examined the histochemical characteristics of the rat ossicular joint cartilage. Interestingly, glycoconjugate histochemistry revealed that the cartilage matrix components of the SV joint were significantly different from those of the other ossicular joints, i.e. incudomalleolar (IM) and incudostapedial (IS) joints. Alcian blue, pH 2.5 and high-iron diamine procedures vividly stained the cartilage matrices of the IM and IS joints, while those of the SV joint were faintly stained. Chondroitin sulfate immunohistochemistry revealed intense labeling of the cartilage of the IM and IS joints, while the immunolabeling of the SV joint was negligible. On the contrary, keratan sulfate immunolabeling was discernible on the cartilage matrices of the SV joint, but not on those of the IM and IS joints. Type II collagen immunolabeling revealed that the marginal region of the IM and IS joint cartilage matrices was devoid of the immunostaining, while the SV joint cartilage matrices were uniformly labeled with this antibody. In this study, we have succeeded in demonstrating the histochemical characteristics of the rat SV joint cartilage matrices of which is quite different from those of the other ossicular joints.

耳小骨病変の画像診断

It has been widely pointed out that multislice CT (MSCT) is useful in middle ear disease. The evaluation of the pathological state of the middle ear using 3D CT imaging has been reported on up to now. It is well known that 3D CT imaging is susceptible to post-processing artifacts, whereas multiplanar reconstruction (MPR) is less susceptible to these artifacts. The usefulness of 2D CT imaging using MPR in the evaluation of ossicular lesions in middle ear diseases is discussed.MSCT imaging was performed by Aquilion® (Toshiba Medical Systems, Tokyo, Japan). The axial spiral scans were obtained. Dosimetric measurements using a head calibration phantom were performed for evaluating the radiation exposure of the lenses. The acquired high-resolution data were transferred to a workstation (ALATO VIEW, Toshiba).In approximately 90% of ears, MPR image findings of the malleus handle, the incus long process, incudostapedial joint and the superstructure of the stapes were compatible with their operative findings. Ninety-five to 100% of ears without soft tissue shadows around the ossicles showed agreement between the findings of MPR imaging and the operation. The footplate of the stapes in 7 of 48 ears showed a “sclerotic” finding. Five ears had an “erosive” finding. There was no correlation between MPR image findings and the mobility of the stapedial footplate. The results suggest that MPR imaging is valuable for providing information on the ossicles except the stapes footplate.MPR images showed abnormal findings in 29 of 32 ears (91%) with clinical otosclerosis, which showed demineralization located at the region anterior to the oval window corresponding to the fissula antefenestram, whereas the conventional axial images showed abnormal findings in 22 of 32 ears (69%). The results suggest that MPR imaging can detect small lesions in otosclerosis.

Effects of Individual Differences in Size and Mobility of the Middle Ear on Hearing

The size of the tympanic membrane and ossicles and the stiffness of the middle-ear ligaments and joint are different between individuals, and the effects of these differences on middle-ear transfer function have not been clarified. In this study, using finite-element middle-ear models, the effects of individual differences in the size and mobility of the middle ear on its transmission characteristics were analyzed. The individual differences in the size of the normal middle ear were found to affect the transfer function by up to 10dB. The effects of the Young’s moduli of the stapedial annular ligaments and the incudostapedial joint on the transfer function were large compared to the effects of the Young’s moduli of the other parts of the middle ear.

Mutation of the POU-domain gene Brn4/ Pou3f4 affects middle-ear sound conduction in the mouse

Mutagenesis of the POU-domain gene Brn4/ Pou3f4 causes defects in the cochlear duct, semicircular canal, temporal bone and stapes footplate. The footplate defect suggested a middle-ear conductive component to the hearing loss associated with this mutation. This was examined by measuring velocity transfer functions at the umbo of wild type and knockout mice during sound stimulation of the tympanic membrane. When the median umbo velocity of test frequencies in the two groups were compared, the mid-range frequencies of the knockout mice showed a statistically reliable reduction in velocity (maximum of 13 dB) and high variability among animals. These results indicated that mutation of the POU-domain gene, Brn4, changed middle-ear sound conduction when measured at the umbo. The origin of the abnormal velocity response was sought by puncturing a hole in the pars flaccida (PF), and subsequently, measuring movements at the umbo and the head of the long arm of the incus. This hole permitted us to measure velocity at the tip of the incus long arm, just above the incudostapedial joint. The comparison of umbo behavior in both groups with PF perforated showed a loss of sensitivity in the mid-range frequencies of the knockout animals. A comparison of incus velocity in the two groups also exhibited a velocity reduction in the mid-range frequencies of the knockout animals. The reduction at the incus, however, was milder than observed at the umbo. The effect of the perforation in, and variability of, the knockout incus responses may have masked a more potent mid-range frequency effect. Nevertheless, evaluation of the stapes and oval window in knockout mice showed variable pathology from ear to ear. The presence of this pathology, the mid-frequency loss in incus sensitivity and the variability in incus velocity among animals suggested that abnormal stapes behavior in Brn4 deficient mice may determine the response of the ossicles, and thus account for the abnormal mid-frequency umbo behavior seen in knockout animals.

Simultaneous measurement of middle-ear input impedance and forward/reverse transmission in cat

Reported here is a technique for measuring forward and reverse middle-ear transmission that exploits distortion-product otoacoustic emissions (DPOAEs) to drive the middle ear "in reverse" without opening the inner ear. The technique allows measurement of DPOAEs, middle-ear input impedance, and forward and reverse middle-ear transfer functions in the same animal. Intermodulation distortion in the cochlea generates a DPOAE at frequency 2f1-f2 measurable in both ear-canal pressure and the velocity of the stapes. The forward transfer function is computed from stapes velocities and corresponding ear-canal pressures measured at the two primary frequencies; the reverse transfer function is computed from velocity and pressure measurements at the DPOAE frequency. Middle-ear input impedance is computed from ear-canal pressure measurements and the measured Thévenin equivalent of the sound-delivery system. The technique was applied to measure middle-ear characteristics in anesthetized cats with widely opened middle-ear cavities (0.2-10 kHz). Stapes velocity was measured at the incudo-stapedial joint. Results on five animals are reported and compared with a published middle-ear model. The measured forward transfer functions and input impedances generally agree with previous measurements, and all measurements agree qualitatively with model predictions. The reverse transfer function is shown to depend on the acoustic load in the ear canal, and the measurements are used to compute the round-trip middle-ear gain and delay. Finally, the measurements are used to estimate the parameters of a two-port transfer-matrix description of the cat middle ear.

Management of incudostapedial congenital anomalies in stapes surgery

Objectives: The management of developmental anomalies of the ossicular chain and otic capsule in stapes surgery tests the otologist’s diagnositic skills and flexibility in technique and prosthesis choice. Although congenital malleus fixation and perilymph gusher are important clinical entities that have received considerable attention in the otolaryngology literature, congenital anomalies of the incus and stapes are less well described, can often be subtle, and have a distinct influence on management choice and hearing outcome. Methods: A review of over 200 stapes procedures yielded 8 cases of identified congenital anomalies of the stapes or incudo-stapedial complex including congenital absence of the footplate and malformed incus, columellar stapes, and incudo-stapedial joint fixation to the promontory. The developmental anatomy and surgical technique in each case is reviewed and hearing outcome presented. Results: The management technique for each case varied depending on the nuances of the ossicular anomaly and whether both the stapes and incus were affected. All 8 ears (7 patients) that underwent a stapes procedure for either an isolated congenital stapes anomaly or a combined incudo-stapedial anomaly experienced improvement to within 10 dB air-bone gap on postoperative audiometry. Conclusions: Despite unanticipated findings of congenital anomalies of the stapes and incus during middle ear exploration for conductive hearing loss, a flexible and creative management approach can lead to successful hearing outcomes.

Use of hydroxyapatite bone cement for difficult ossicular reconstruction

Objectives: Conventional ossiculoplasty relies on favorable anatomy, surface tension, and packing to hold the reconstruction in its desired position. This can be frustrating when faced with difficult ossicular chain abnormalities that need a more stable fixation. We describe the use of Mimix™, a rapidly setting, nontoxic hydroxyapatite bone cement for the repair of complex ossicular problems in patients undergoing tympanomastoidectomy or stapedotomy. Methods: Mimix™ was used to cement partial ossicular replacement prostheses into position, repair incudostapedial joint separation and incus necrosis, repair incus necrosis during revision stapedotomy, augment the tapered incus during primary stapedotomy, and rebuild a total tympanic membrane perforation with a tympanic membrane/malleus head homograft. Preoperative and serial postoperative audiograms were examined for 4-tone pure tone average (PTA), speech reception thresholds (SRT), and word recognition scores (WRS) in 14 patients with up to 18 months follow-up. Results: The average improvement for PTA, SRT, and WRS approximated 22dB, 23dB, and +6%. Most patients demonstrated a significant closure of their air-bone gap. There was 1 case of unexplained delayed mixed hearing loss 7 months after surgery following successful air-bone gap closure. Conclusions: Even experienced otologists have desired some way to better fixate an ossicular repair into place during difficult cases. Our experience with Mimix™ hydroxyapatite bone cement suggests that such rigid fixation may now be available. Its paste-like consistency, rapid setting time, osteoconductivity, and lack of neurotoxicity make it ideal for middle ear reconstruction. Prolonged stable fixation may translate into long term improvements in hearing.

Human middle ear transfer function measured by double laser interferometry system.

Simultaneous measurements of vibrations on the stapes footplate, incudostapedial (IS) joint, and tympanic membrane (TM) can be made in both normal and drained cochleae, and the stapes displacement transfer function (S-DTF) and TM displacement transfer function (TM-DTF) are derived. A single laser Doppler interferometer previously has been used for measuring movement of the stapes or TM in temporal bones. However, there may be a limitation to optimally describing acoustic-mechanical transmission when the interferometer and temporal bone are moved frequently during experimental recordings. Simultaneous measurements of vibrations of the TM and stapes footplate, or TM and IS joint may reveal different acoustic-mechanical characteristics of the middle ear. Dual laser interferometers simultaneously measured vibrations of the TM, IS joint, and stapes in 10 temporal bones with both intact and drained cochleae. From these measurements, the middle ear transfer function was expressed as the S-DTF, TM-DTF, and displacement transmission ratio (DTR). Simultaneous displacements of the TM, IS joint, and stapes footplate induced by sound pressure in the ear canal were recorded in both amplitude and phase. The middle ear transfer functions in terms of displacement ratio confirmed published single interferometer data but provided new information from drained cochlea. Stapes and TM displacement transfer functions were determined using dual interferometry, provided accurate amplitude and phase relationships from stapes footplate, IS joint, and TM, with new data from drained and normal cochlea.

３Ｄ‐ＣＴが有用であった耳小骨病変の２例

We experienced two cases of ossicular lesions in which three-dimensional (3D) images from multislice CT (MSCT) were useful in diagnosing the lesions. In the first case, the 3D images revealed an ossicular defect in the long process of the incus and the superstructure of the stapes in the middle ear. In the second case, discontinuity of the incudostapedial joint was revealed. The hearing level in both cases was improved by tympanoplasty. In the first case, besides the ossicular malformation, open-type congenital cholesteatoma was found in the middle ear during the operation. There is a possibility of residual recurrence of open-type cholesteatoma, so postoperative follow-up was necessary for the first case. Canal wall up tympanoplasty with posterior hypotympanotomy was performed in the second case. Since this procedure does not require managing the external auditory meatus or the tympanic membrane, it should be chosen in cases of normal tympanic membrane with traumatic ossicular chain discontinuity, such as the second case. In conclusion, reconstruction of 3D images by MSCT with 8 rows of detectors gave realistic and high-quality images of the ossicular lesions. The 3D images were useful for the surgeon's preoperative planning and for the patient's informed consent to the operation.

The incudostapedial joint angle: implications for stapes surgery prosthesis selection and crimping.

To evaluate the role of the incudostapedial joint (ISJ) angle in stapes prosthesis size selection and crimping. The ISJ of 13 cadaveric human temporal bones were photographed, then measured using computer-aided design software. The relationship of ISJ angle to prosthesis length was modeled. A literature review evaluated factors contributing to stapedectomy failure. The mean ISJ angle was 93.0 degrees (SD = 8.3 degrees ) (range, 75.0 degrees -104.0 degrees ). The mean ISJ angle deviation from 90 degrees was 7.35 degrees (SD = 4.45 degrees ) (range, 0.3 degrees -15.0 degrees ). The mean distance along the incus accessible for prosthesis placement was 3.21 mm (SD = 0.55 mm) (range, 2.00-4.00 mm). Significant deviation of the ISJ angle from 90 degrees was found (P <.0001). The length along the incus accessible for prosthesis placement was sufficient to result in errors in prosthesis size selection and crimping with only small variations in the ISJ angle. Incorrect prosthesis sizing and crimping are frequently associated with stapedectomy failure. Variations in ISJ anatomy should be considered when selecting stapes prostheses lengths and may affect crimping technique.