Investigation of the coupling quality of partial prostheses at the stapes head

Abstract

Introduction: The success of partial ossicular chain reconstructions in cases of conductive hearing loss depends on many factors. One important factor is the coupling between the prosthesis and the stapes head, which has not been explicitly investigated previously. Prostheses with different forms of attachment to the stapes are available, namely clip and bell type PORP. We present a standardized method to assess the quality of the prosthesis-stapes connection. The coupling quality of different prostheses is compared using measurements on a specimen model.

Methods: This study delineated six groups categorized by prosthesis types, employing 12 temporal bones to create a reconstructed ossicular chain model. The model comprised stapes and inner ear of the specimen, various prostheses and a standardized mechanical excitation at the prosthesis head. Multiple-points measurements were conducted using laser Doppler vibrometry along the sound transfer direction. This methodology enabled the assessment of vibrational magnitude loss and sound distortion from the prosthesis to the stapes.

Results: All six groups showed uniformly good sound transmission, with low magnitude loss of < 10 dB and very low total harmonic distortion of < 1%.

Conclusion: The proposed measurement method enables an explicit and comparable examination of the prosthesis coupling to the stapes head. While the coupling mechanism may be important in terms of handling, stability or long-term robustness of the reconstruction, our results show no relevant differences between types in terms of sound transmission.

Keywords: Coupling; Laser doppler vibrometer (LDV); Middle ear reconstruction; Partial ossicular replacement prosthesis (PORP); Total harmony distortion (THD).

Fig. 1

A: Five Prostheses utilized in this study: Type1: Clip partial prosthesis Dresden type, Kurz, Germany. Type2: mCLIP Partial Prothesis, MED-EL, Austria. Type3: Centered alto byte partial, Grace medical, USA. Type4: Duesseldorf type prostheses, Kurz, Germany. Type5: mXACT Partial Prothesis, MED-EL, Austria. Type 3 was coupled using two methods, resulting in six groups from five prosthesis types. B: Schematic diagram of LDV measurement for each reconstruction with various prostheses, red points indicate the targets measured by laser (target a: magnet, b: prosthesis plate, c: prosthesis foot, d: stapes footplate center, e: stapes posterior foot, f: stapes anterior foot, g: middle point of lateral side of footplate, h: middle point of medial side of footplate)

Fig. 2

A: Rigid body motions of the stapes at its footplate center. The relevant components are marked red at the axes, the translational velocity and the rotational component and . They are derived from the data , and measured at targets 1(d), 2(f), 3(e), 4(h) and 5(g). B: The photos of one TB during one five-point measurement process, on which coordination axes are drawn in batch. The scale for pixel distances were respectively set to 2.83 mm for the long axis and 1.3 mm for the short axis within the photographs. The coordinates of the five designated points were measured from these images

Fig. 3

Mean magnitude loss and SD. across the coupling interface (cp. Figure 1B) at a range of frequencies (from 200 Hz to 10,000 Hz, with offset between groups along x-axis) for various types of clips and bells. (n = 12)

Fig. 4

The effect of prosthesis type on magnitude loss at each frequency band. (n = 12) Boxes show: mean, median, interquartile ranges, whisker with coef of 1.5, outliers

Fig. 5

The means and SD of THD values (n = 12) for various prostheses types labeled as Type1, Type2, Type3, Type4, Type5 and Type3 + crimp across a frequency range of 200 Hz to 10,000 Hz. A: the THD values at point c. B: the THD at point d

Fig. 6

Box plots for the THD values for each prosthesis type (n = 12) at A: point c and B: point d. Boxes show: mean, median, interquartile ranges, whisker with coef of 1.5, outliers. The underlining P value shows a significant ANOVA test at 500 Hz, but no significance in subsequent Tukey-HSD test

Fig. 7

The difference between measurement at point d and calculated translation of the footplate (measurement methods 1-point vs. 5-points) across frequencies. The data for each prosthesis group were separately displayed with the label of prosthesis name. (n = 12)