The influence of incudostapedial joint separation on the middle ear transfer function

Frequency-dependent hearing outcomes with or without preservation of intact ossicular articulations

Objective

To determine the frequency-specific benefits of ossicular chain preservation compared to performing disarticulations and reconstructions in transmastoid facial nerve decompression surgery in patients with an intact ossicular chain.

Methods

A retrospective chart review (January 2007 and June 2018) of patients undergoing transmastoid facial nerve decompression on the intact middle ear for severe facial palsy at a tertiary referral center. Surgery was performed with ossicular chain disarticulation on an as-needed basis using either ossicular chain preservation (without ossicular disarticulation), incudostapedial separation, or incus disarticulation technique. Hearing outcomes were assessed.

Results

The 108 patients were included in this study. Among these, 89 patients underwent ossicular chain preservation, 5 underwent incudostapedial separation and 14 underwent incus repositioning. The proportion of patients with a change in the 4-frequency air conduction pure-tone average of less than 10 dB was 91%, 60%, and 50%, respectively, for the three surgical techniques; these were significantly different (Fisher's exact test, p < .001). Frequency-specific analysis showed that air conduction was significantly better following the ossicular chain preservation technique compared with the incus repositioning technique at stimulation frequencies lower than 250 Hz and higher than 2000 Hz, and compared with the incudostapedial separation technique at 4000 Hz. Analysis of biometric measures determined on CT images suggested that the feasibility of the ossicular chain preservation technique correlates with incus body thickness on coronal CT images.

Conclusions

Ossicular chain preservation is an effective approach for hearing preservation in transmastoid facial nerve decompression or similar surgical procedures.

Long-Term Hearing Results of Endoskeletal Ossicular Reconstruction in Chronic Ears Using Titanium Prostheses Having a Helical Coil: Part 1-Kraus K-Helix Crown, Incus to Stapes

OBJECTIVES

1) To assess long-term hearing results after endoskeletal ossicular chain reconstruction (eOCR) using the titanium Kraus K-Helix Crown prosthesis, implanted incus to stapes, with glass-ionomer cement (GIC) in chronic ears and 2) to determine safety of the prosthesis and cement.

STUDY DESIGN

Prospective, nonrandomized, sequential, single center, single surgeon.

SETTING

Private practice, ambulatory surgical center.

PATIENTS

N = 15 males (42%) and 21 females (58%). Mean age was 40.4 years (range, 6-81 years); 38 ears (22 right ears [58%] and 16 left ears [42%]).

INTERVENTIONS

eOCR in chronic ears. Comprehensive preoperative and postoperative hearing measurements were performed for up to 9 years.

MAIN OUTCOME MEASURES

Postoperative hearing results at 1 year showed statistically significant improvement as compared with preoperative hearing. Long-term hearing results remained stable and showed no statistically significant change over 9 years.

RESULTS

Estimated mean pure-tone air conduction average improved by 14.5 dB (95% confidence interval = 10.3-18.7). Estimated mean speech reception thresholds improved by 15.5 dB (10.8-20.2). Word recognition scores improved by -2.2% (-5.3 to 1.0). The estimated mean postoperative air-bone gap was 10.5 dB (7.2-13.8). The estimated mean calculated air-bone gap was 11.3 dB (8.0-14.5). The estimated mean change in high-tone bone conduction (HTBC) average was +3.5 dB (0.9-6.0). Two prostheses extruded (5%). No patients experienced any unanticipated serious adverse effects or events.

CONCLUSION

eOCR using the K-Helix Crown prosthesis, incus to stapes, and GIC can significantly improve hearing at 1 year and maintain stable hearing over 9 years. Both prosthesis and cement are safe.

Measurement of Incus and Stapes Velocity Following Sound Stimulus in the Setting of Incudostapedial Joint Separation and Reconstruction

OBJECTIVE

Understand the biophysical property changes of incudostapedial joint (ISJ) separation and ossicular hydroxyapatite application on middle ear function.

STUDY DESIGN

Basic science.

SETTING

Cadaveric temporal bone research laboratory.

SUBJECTS AND METHODS

A complete mastoidectomy was performed on five human temporal bones. A Laser Doppler Vibrometer was utilized to obtain velocity transfer function measurements of the incus and stapes across a range of frequencies in response to an acoustic stimulus. Under binocular microscopy the ISJ was separated and subsequently repaired with bone cement. Measurements were taken prior to ISJ separation, following joint separation, 30 to 60 min postrepair of the joint, and again 24 to 48 h postrepair of the joint.

RESULTS

The stapes measurements taken from the intact ossicular chain and from the chains repaired with bone cement demonstrated a similar distribution of measurements. The ISJ separation showed dramatically reduced velocity transfer function stapes measurements but increased incus velocity transfer function measurements. In the early and delayed repaired chains, the mean velocity of the incus and stapes velocity peaked between 1.5 and 2 kHz, matching intact maximal velocity. Pure tone average at 0.5, 1, 2, and 3 kHz demonstrated no change in reconstructed stapes velocity at 24 to 48 h.

CONCLUSIONS

Isolated ISJ separation in fresh frozen and thawed temporal bones produces stapes velocity transfer function changes that corresponds with the clinically experienced conductive hearing loss. Repair with bone cement produced similar velocity curves to the intact ISJ curve with excellent recovery across mid-frequencies. This model would be useful for future ossicular mechanical studies.

Changes of incudostapedial joint angle in stapedotomy: does it impact hearing outcomes?

PURPOSE

The aims of this article are: (1) is there an ideal incudostapedial joint (ISJ) angle after stapedotomy? (2) is there any difference between pre- and postoperative ISJ angle? and (3) what is the significance of the ISJ angle in postoperative hearing outcomes?

METHODS

Forty six ears from 39 different adult patients (28 women and 11 men; 21 left and 25 right ears) with a mean age of 39 years with clinical otosclerosis who underwent stapedotomy between May 2017 and May 2019 were retrospectively registered, including seven bilateral surgery cases. ISJ angle and intravestibular depth of the stapes prosthesis were measured from multiple planar reconstruction-computed tomography images and the length of the prosthesis was measured during surgery. Relationships between the ISJ angle parameters and postoperative hearing outcomes and parameters of the prosthesis were analyzed.

RESULTS

The mean ISJ angle was 93.3° ± 8.8° preoperatively and 101.9° ± 6.3° postoperatively, increasing by 8.6° during stapedotomy (p < 0.01). There were weak and negative correlations between ISJ angle changes and postoperative air conduction gains at frequencies ≤1 kHz and bone conduction gains at 0.5 kHz. When the postoperative ISJ angle changed more than 20°, the success rate of the procedure decreased to 0%.

CONCLUSION

The stapedotomy operation increased the ISJ angle. The success of postoperative auditory outcomes had more to do with the ISJ angle change than the value of the angle itself, indicating there is no universal ideal ISJ angle that surgeons should aim for during stapedotomy.

High-resolution imaging of the human incudostapedial joint using synchrotron-radiation phase-contrast imaging

The incudostapedial joint (ISJ) of the middle ear is important for proper transmission of sound energy to the cochlea. Recently, the biomechanics of the ISJ have been investigated using finite-element (FE) modelling, using simplified geometry. The objective of the present study was to investigate the feasibility of synchrotron-radiation phase-contrast imaging (SR-PCI) in visualising the ISJ ultrastructure. Three human cadaveric ISJs were dissected and scanned using SR-PCI at 0.9 µm isotropic voxel size. One of the samples was previously scanned at 9 µm voxel size. The images were visually compared and contrast-to-noise ratios (CNRs) were calculated (of both bone and soft tissues) for quantitative comparisons. The ISJ ultrastructure as well as adjacent bone and soft tissues were clearly visible in images with a 0.9 µm voxel size. The CNRs of the 0.9 µm images were relatively lower than those of the 9 µm scans, while the ratio of bone to soft tissue CNRs were higher, indicating better discernibility of bone from soft tissue in the 0.9 µm scans. This study was the first known attempt to image the ISJ ultrastructure using an SR-PCI scanner at submicron voxel size and results suggest that this method was successful. Future studies are needed to optimise the contrast and test the feasibility of imaging the ISJ in situ. LAY DESCRIPTION: The human middle ear consists of the eardrum, three small bones (the malleus, incus and stapes) and two joints connecting the bones (the incudostapedial joint and the incudomallear joint). The role of the middle ear is to amplify and transfer sound energy to the cochlea, the end organ of hearing. The incudostapedial joint (ISJ) of the middle ear is a synovial joint which is important for proper transmission of sound energy to the cochlea. Similar to other synovial joints it consists of meniscus, fluid and articulating surfaces. Recently, the biomechanics of the ISJ have been investigated using computational models, using grossly simplified geometry. Synchrotron radiation phase contrast imaging (SR-PCI) is a high-resolution imaging technique used to visualise small structures in three dimensions. The objective of the present study was to investigate the feasibility of using SR-PCI in visualising the ISJ ultrastructure. Three human cadaveric ISJs were dissected and scanned using SR-PCI at 0.9 µm isotropic voxel size. One of the samples was previously scanned at 9 µm voxel size. The images were both qualitatively and quantitatively compared. This study was the first known attempt to image the ISJ ultrastructure using an SR-PCI scanner at submicron voxel size and results suggest that this method was successful. Future studies are needed to optimise the contrast and feasibility of imaging the ISJ in situ.