Repair of subtotal tympanic membrane perforations: A temporal bone study of several tympanoplasty materials.

The aim of this project was to investigate the effects of different types of graft material, and different remaining segments of the native TM on its motion. In twelve human temporal bones, controlled TM perforations were made to simulate three different conditions. (1) Central perforation leaving both annular and umbo rims of native TM. (2) Central perforation leaving only a malleal rim of native TM. (3) Central perforation leaving only an annular rim of native TM. Five different graft materials (1) perichondrium (2) silastic (3) thin cartilage (4) thick cartilage (5) Lotriderm® cream were used to reconstruct each perforation condition. Umbo and stapes vibrations to acoustic stimuli from 250 to 6349 Hz were measured using a scanning laser Doppler vibrometer. Results showed that at low frequencies: in the Two Rims condition, all grafting materials except thick cartilage and Lotriderm cream showed no significant difference in umbo velocity from the Normal TM, while only Lotriderm cream showed a significant decrease in stapes velocity; in the Malleal Rim condition, all materials showed a significant decrease in both umbo and stapes velocities; in the Annular Rim condition, all grafting materials except Lotriderm and perichondrium showed no significant difference from the Normal TM in stapes velocity. Umbo data might not be reliable in some conditions because of coverage by the graft. At middle and high frequencies: all materials showed a significant difference from the Normal TM in both umbo and stapes velocities for all perforation conditions except in the Annular Rim condition, in which silastic and perichondrium showed no significant difference from the Normal TM at umbo velocity in the middle frequencies. In the low frequencies, the choice of repair material does not seem to have a large effect on sound transfer. Our data also suggests that the annular rim could be important for low frequency sound transfer.

Effects of Cartilage Overlay on the Tympanic Membrane: Lessons From a Temporal Bone Study for Cartilage Tympanoplasty.

HYPOTHESIS: Placing cartilage grafts on different tympanic membrane (TM) locations will affect sound transfer function, and the effects will differ according to the part of the TM modified. BACKGROUND: Cartilage tympanoplasty is increasingly popular because of lower reperforation rates, and better long-term stability. In this temporal bone study, we investigated the effect of placing cartilage grafts over different parts of the normal TM on sound transmission. METHODS: In 10 human fresh frozen temporal bones, umbo and stapes vibrations to acoustic stimuli from 250 to 8000 Hz were measured at multiple points using a scanning laser vibrometer. Four different cartilage arrangements were measured in each temporal bone. 1) Overlay condition leaving an umbo rim of normal TM (Umbo Rim). 2) Overlay condition leaving annular rim of normal TM (Annular Rim). 3) Overlay condition leaving both rims of normal TM (Two Rims). 4) Overlay condition leaving no normal TM exposed (No Rims). RESULTS: At low frequencies, there was a statistically significant decrease in velocity from baseline for the No Rims (umbo mean -4 dB; stapes -6 dB) and Umbo Rim (umbo -4 dB; stapes -3.7 dB) conditions. All conditions showed significant decreases for middle frequencies (umbo -4.0, -5.9, -7.4 and -6.3 dB; stapes -10.8, -6.6, -6.3 and -7.7 dB) and high frequencies (umbo -13.2, -3.0, -3.1 and -5.5 dB; stapes -4.6, -2.4, -2.6 and -3.5 dB). Results are in order for No Rims, Umbo Rim, Two Rims, and Annular Rim conditions. CONCLUSION: In the low frequencies, it seems to matter where the cartilage is placed, and in particular the annular rim of the TM seems to be important for the low-frequency acoustic transfer function. In the higher frequencies, all graft placements caused some drop at all frequencies. In all frequencies, effects were modest by clinical standards.

The Effect of Piston Diameter in Stapedotomy for Otosclerosis: A Temporal Bone Model.

HYPOTHESIS: The use of larger-diameter pistons in stapedotomy leads to better hearing outcomes compared with the use of smaller-diameter pistons. There is an interaction between stapes piston diameter and fenestration diameter. BACKGROUND: Otosclerosis can be treated surgically by removing part of the stapes and bypassing the stapes footplate with a prosthesis. Available piston shaft diameters range between 0.3 and 0.8 mm. There has been a tendency toward the use of smaller-diameter pistons, because of a suspected decreased risk of cochlear trauma and subsequent sensorineural hearing loss (SNHL) with smaller pistons. However, mathematical models, temporal bone studies, and clinical studies suggest that the use of larger-diameter pistons is associated with better hearing outcomes. METHODS: Three fresh-frozen, non-pathologic temporal bones were harvested from human cadaveric donors. Acoustic stimuli in the form of pure tones from 250 to 8000 Hz were generated at 110 dB sound pressure level. A total of 16 frequencies in a 1/3-octave series were used. Stapes and round window velocities in response to the acoustic stimuli were measured at multiple equally spaced points covering the stapes footplate and round window using a scanning laser Doppler interferometry system. Eight sets of measurements were performed in each temporal bone: 1) normal condition (mobile stapes), 2) stapes fixation and stapedotomy followed by insertion of 3) a 0.4-mm-diameter piston in a 0.5-mm-diameter fenestration, 4) a 0.4-mm-diameter piston in a 0.7-mm-diameter fenestration, 5) a 0.4-mm-diameter piston in a 0.9-mm-diameter fenestration, 6) a 0.6-mm-diameter piston in a 0.7-mm-diameter fenestration, 7) a 0.6-mm-diameter piston in a 0.9-mm-diameter fenestration, and 8) a 0.8-mm-diameter piston in a 0.9-mm-diameter fenestration. RESULTS: At midrange frequencies, between 500 and 4000 Hz, round window velocities increased by 2 to 3 dB when using a 0.6-mm-diameter piston compared with a 0.4-mm-diameter piston. Using a 0.8-mm-diameter piston led to a further increase in round window velocities by 2 to 4 dB. CONCLUSION: Our results suggest a modest effect of piston diameter on hearing results following stapedotomy.

Effect of Round Window Reinforcement on Hearing: A Temporal Bone Study With Clinical Implications for Surgical Reinforcement of the Round Window.

HYPOTHESIS: Round window reinforcement leads to conductive hearing loss. BACKGROUND: The round window is stiffened surgically as therapy for various conditions, including perilymphatic fistula and superior semicircular canal dehiscence. Round window reinforcement reduces symptoms in these patients. However, it also reduces fluid displacement in the cochlea and might therefore increase conductive hearing loss. METHODS: Perichondrium was applied to the round window membrane in nine fresh-frozen, nonpathologic temporal bones. In four temporal bones cartilage was applied subsequently. Acoustic stimuli in the form of frequency sweeps from 250 to 8000 Hz were generated at 110 dB sound pressure level. A total of 16 frequencies in a 1/3-octave series were used. Stapes velocities in response to the acoustic stimuli were measured at equally spaced multiple points covering the stapes footplate using a scanning laser Doppler interferometry system. Measurements were made at baseline, after applying perichondrium, and after applying cartilage. RESULTS: At frequencies up to 1000 Hz perichondrium reinforcement decreased stapes velocities by 1.5 to 2.9 dB compared with no reinforcement (p value = 0.003). Reinforcement with cartilage led to a further deterioration of stapes velocities by 2.6 to 4.2 dB at frequencies up to 1000 Hz (p value = 0.050). The higher frequencies were not affected by perichondrium reinforcement (p value = 0.774) or cartilage reinforcement (p value = 0.644). CONCLUSION: Our results seem to suggest a modest, clinically negligible effect of reinforcement with perichondrium. Placing cartilage on the round window resulted in a graded effect on stapes velocities in keeping with the increased stiffness of cartilage compared with perichondrium. Even so, the effect was relatively small.