The prognostic influence of pre-surgery bone
conduction values on the improvement of
hearing in patients treated surgically
as a result of middle-ear conditions
Katarzyna Job
ABCDEF, Jacek Składzień
BDFGDepartment of Otolaryngology, Jagiellonian University Medical College in Krakow, Poland; prof. Jacek Składzień MD PhD Article history: Received: 14.12.2020 Accepted: 15.12.2020 Published: 16.12.2020
SUMMARY: Introduction: The influence of the mechanics of the middle ear on the function of the inner ear has been studied for many years. Among surgeries performed in the middle-ear area, those restoring full functionality of the system transmitting sound inside the middle ear may be pointed out as those fully restoring the mechanical influence of the middle ear on the function of the inner ear.
Aim: The aim of the performed analysis is to find the prognostic importance of measured pre-surgery values of bone conduction on the improvement of hearing in patients operated as a result of middle-ear disorders.
Material and methods: The analysis included 271 patients hospitalised and operated on due to otosclerosis or perforation of the tympanic membrane between 2016 and 2019. Only patients who had not had a surgical operation within the middle ear prior to the study were included. An audiological assessment was performed with the use of pure tone thresholds audiometry.
Results: A beneficial influence of the performed surgery on the improvement of bone conduction was observed in patients, in which the average threshold value of bone conduction measured before the surgery did not exceed 40 dB. In cases of the perceptive component of hearing impairment being higher than 40 dB, no statistically significant, beneficial influence of a performed stapedotomy or myringoplasty on the change of bone conduction thresholds was observed.
Conclusions: The perception component of hearing impairment up to 40 dB indicates bone conduction improvement after surgical restoration of the influence of middle-ear mechanics on the inner ear in patients treated as a result of otosclerosis, as well as of eardrum perforation.
KEYWORDS: bone conduction thresholds, hearing improvement, myringoplasty, stapedotomy
Authors’ Contribution:
A – Study Design B – Data Collection C – Statistical Analysis D – Data Interpretation E – Manuscript Preparation F – Literature Search G – Funds Collection
ABBREVIATIONS
ABG – air-bone gap BC – bone conduction COM – chronic otitis media
INTRODUCTION
The influence of the mechanics of the middle ear on the func- tion of the inner ear has been studied for many years. The bene- ficial impact of reconstruction performed inside the middle ear on the inner ear (also on the non-operated side) was discovered and documented by Prof. Jan Miodoński in 1956, in the work:
Fenestracja poza otosklerozą. Fenestracje nietypowe, drenaż cy- sterny. Phenomenon of Carhart’s notch is an audiometric con- firmation of the considered relationships. Carhart’s notch was described for the first time in 1950; it manifests in a depression of the threshold curve of bone conduction by approximately 10–20 dB at a frequency of 2000 Hz. This is a result of mechanical
immobilisation of the stapes base in the oval window and inter- ruptions of the resonance of the ossicle chain. Bone conduction improvement after a successful surgery (stapedotomy) changes the properties of the middle ear by changing the mass and rigi- dity of the ossicle chain and modifying the resonant frequency, and it results in improvement of the measured bone conduction thresholds [1–4].
Also, in cases of chronic otitis media, reconstruction of the sound- -transmitting system in the middle ear restores the relationship between the ossicle chain and the function of the sensorineural part of the hearing system. Post-surgery changes to the cochlear reserve are an audiometric reference to the performed tympano- plastic surgery. Changes to the bone conduction thresholds are also observed as a consequence of the influence of surgery per- formed on the conducting system of the middle ear. Total resto- ration of the influence of the middle ear on the function of the inner ear is possible if the amplifications characteristic for the middle ear are retained (the lever between the malleus and the in- cus, the eardrum surface to the oval window surface ratio) [5, 6].
In the group subjected to surgery because of otosclerosis, the youn- gest patient was 19 years old and the oldest was 62. The mean pa- tient age was 39.31 years. Most patients were in the age range of 41–50 years. A noticeably smaller number of surgeries was per- formed in patients aged over 60 years. The group with otosclerosis included 87 females (70.16%) and 37 males (29.84%).
Patients subjected to stapedectomy were not analysed because of the low group count.
The average values of bone conduction measured before surgery (as the average value for 500, 1000, 2000, and 4000 Hz) were used as a division criterion used to classify all patients into 3 groups (Tab. I.).
The hearing test was performed directly before surgery and 12 mon- ths after ear surgery. The analysis included observation of values of bone conduction (BC) and of the air-bone gap (ABG) changes as average values for speech frequencies (500, 1000, 2000, and 4000 Hz) for each of the groups of the initial bone conduction values.
Each of the operated patients provided consent for participation in the study. The local Bioethical Committee agreed to the analysis.
The obtained results were subjected to statistical analysis. Stati- stically significant results are provided for P < 0.05.
RESULTS
Audiometric data obtained from 147 patients with type I tympa- noplasty and from 124 patients after stapedotomy were analysed.
In the pre-surgery examination, all patients with chronic otitis media reported hearing impairment, and 30% reported tinnitus.
Almost 70% of patients reported the presence of continuous or intermittent exudate from the sick ear.
Each intervention in the ossicle system changing the aforemen- tioned relationships adequately to the performed ossicle plastic surgery also influences the inner ear.
Among surgeries performed in the middle-ear area, those re- storing full functionality of the system transmitting sound in- side the middle ear may be considered as those fully restoring the mechanical influence of the middle ear on the function of the inner ear [7–9]. These procedures include myringoplasty and stapedotomy – surgical procedures, after which one can expected total “closure” of the cochlea reserve in post-surgery tone pure audiometry.
AIM
The aim of the performed analysis is to find the prognostic im- portance of measured pre-surgery values of bone conduction re- garding the improvement of hearing in patients operated on as a result of middle-ear disorders.
MATERIAL AND METHODS
A prospective analysis of pure tone audiometry results obtained from 271 subsequent patients subjected to their first surgery du- ring the 2016–2019 period was performed. Surgical intervention types performed in the middle-ear area restoring the influence of the sound conduction system present in the middle ear on the inner ear were considered. Data were obtained from 147 patients after myringoplasty in the course of chronic otitis media and from 124 patients subjected to surgery because of otosclerosis.
The youngest of the patients with chronic otitis media was 18 years old and the oldest was 80. The mean patient age in this group was 42.84 years. The study included 80 female and 67 male patients.
Tab. I. Division of patients with chronic otitis media (COM) and with otosclerosis as a function of initial values of bone conduction, as the average value for 500, 1000, 2000, and 4000 Hz.
BONE CONDUCTION GROUPS N COM % COM N OTOSCLEROSIS % OTOSCLEROSIS
1 (0–20 dB) 45 31 23 19
2 (21–40 dB) 84 57 82 66
3 (> 40 dB) 18 12 19 15
Tab. II. Myringoplasty. Average values of cochlea reserves and average bone conduction at 500, 1000, 2000, and 4000 Hz in the created groups of bone conduction at the start of the treatment and after 12 months of observation.
BONE CONDUCTION
GROUPS ABG 0 SD 0 ABG 12 SD 12 BC 0 SD 0 BC 12 SD 12
1 (0–20 dB) 28.7* 12.15 19.28* 12.24 16.19 7.29 15.71 6.53
2 (21–40 dB) 30.60* 12.56 25.30* 12.01 23.50* 11.20 16.97* 10.31
3 (> 40 dB) 28.38 10.76 28.25 12.16 45.63 16.72 42.35 13.89
ABG – cochlea reserve (air-bone gap); COM – chronic otitis media; BC – bone conduction; SD – standard deviation
* statistically significant results (P < 0.05).
N – number of patients, COM – chronic otitis media
of bone conduction were found. The average value of bone con- duction observed 12 months later was significantly lower than the average bone conduction measured before surgery.
In group 3, in which deep impairment of bone conduction (> 40 dB) was observed during the pre-surgery period, the change to the average value of bone conduction 12 months after myringoplasty was not statistically significant. An improvement (decreased ave- rage values of bone conduction) was observed, but in follow-up audiometric examinations.
During the next stage of analysis, the average post-surgery thre- shold values of bone conduction and average post-surgery cochlea reserves were evaluated in patients with stapedotomy, within the initial groups of bone conduction values (Tab. III.).
On the basis of the obtained results, it was concluded that the change in the values of average cochlea reserves in the individu- al bone conduction groups was statistically significant 12 months after surgery. A simultaneous analysis of changes to the average value of cochlea reserve between individual groups did not show statistical difference.
A statistically significant improvement was observed in group 2 in the analysis of changes to the average threshold values of bone conduction after 12 months. The change of the average bone con- duction value in groups 1 and 3 was not statistically significant after this period of time.
DISCUSSION
Changes in cochlea reserve, in particular related to the speech fre- quency range, are taken into account in the assessment of hearing improvements after middle-ear surgeries. It should be remembered, however, that reconstruction of the conducting system of the mid- dle ear also results in an influence on the function of the inner ear.
Many researchers have looked for a relationship between a condi- tion in the middle ear and its influence on the inner ear, manife- sting in a higher bone conduction threshold. Numerous analyses show that such a relationship clearly exists. Significant observa- tions were made in patients with changes to the middle ear lining (advanced cholesteatoma, inflammatory granulation) or ossic- le destruction or immobilisation [10–12]. The aforementioned factors influencing the mechanics of ossicles seem to indirectly disrupt the function of the inner ear. An example illustrating In almost 60% of cases the loss of eardrum exceeded 30%, and in
more than 20% of patients the loss exceeded 70% of the eardrum surface.
Perichondrium was the material most frequently used in eardrum reconstruction. Temporal muscle fascia was used more rarely. In a few cases, perichondrium reinforced with cartilage obtained from a small part of the ear lobe was used.
In cases of otosclerosis, in the examination performed before sur- gery, all patients reported hearing impairment, and 81.42% repor- ted tinnitus. As many as 27.15% of patients reported subjective- ly perceived unilateral hearing impairment, and 72.85% reported bilateral impairment.
The values of average cochlea reserve and the average bone con- duction in the created groups of patients with chronic otitis me- dia are presented in Tab. II.
On the basis of the obtained data it was concluded that at 12 mon- ths after myringoplasty, the change to average cochlea reserve in group 1 was significantly smaller than the average values in groups 2 and 3 (P < 0.05). On the other hand, average cochlea reserves for groups 2 and 3 were statistically equal.
Next, changes to the average cochlea reserves were studied in pa- tients with eardrum perforation within each of the created initial groups for bone conduction values.
In patients with correct bone conduction (group 1: up to 20 dB) and in group 2 hearing improvement was observed, expressed as closure of the average cochlea reserve, present 12 months after surgery. The obtained results are statistically significant (P < 0.05).
In group 3, no statistically significant hearing improvement was observed 12 months after surgery (P > 0.05).
The next part of the study included evaluation of the change of bone conduction (BC) as the average value at 500, 1000, 2000, and 4000 Hz in the created bone conduction groups 12 months after type I tympanoplasty.
No statistically significant changes to the average value of bone conduction were found in group 1.
In group 2 (average value of pre-surgery bone conduction between 21 and 40 dB) statistically significant changes to the average value
Tab. III. Otosclerosis. Average values of cochlea reserves and average values of bone conduction at the beginning of the therapy and after 12 months of observation in bone conduction groups.
BONE CONDUCTION
GROUPS ABG 0 SD 0 ABG 12 SD 12 BC 0 SD 0 BC 12 SD 12
1 (0–20 dB) 27.31* 7.15 10,66* 9.75 19.18 9.24 17.08 8.25
2 (21–40 dB) 30.43* 8.94 12,14* 10.62 31.80* 7.15 26.91* 11.03
3 (> 40 dB) 32.16* 9.44 15,61* 15.47 46.50 4.61 45.96 18.96
ABG – cochlea reserve (air-bone gap); BC – bone conduction; SD – standard deviation
* statistically significant results (P < 0.05)
Another argument confirming the influence of the mechanism of the ossicle chain on the values of bone conduction is the best improvement of threshold values of bone conduction observed at 2000 Hz in patients in whom the cochlea reserve was decre- ased at 500, 1000, 2000, and 4000 Hz. The greatest disruption to values of bone conduction at 2000 Hz is caused by decreased or eliminated resonance of the ossicle chain. The ossicle chain resonance in humans occurs in the 1500–2000 Hz range. This effect is observed in the case of disturbances occurring in the ossicles [22, 23].
Maintenance of all ossicles once the comorbid irregularities of the tympanic cavity lining are removed provides the optimal con- ditions for hearing improvement. This stands in agreement with reports present in global literature, which state that a significant hearing improvement was observed after type I tympanoplasty in most patients with closure of the average cochlea reserve be- low 20 dB [24–26].
Considering the effectiveness of ear surgeries as a function of bone conduction values, it was concluded that significant improvement after myringoplasty is present in the group with correct bone conduction. Improvement was also observed at average values of bone conduction, in the range between 21 and 40 dB. A deeper perceptive hearing impairment (≥ 41 dB) was accompanied by the lack of significant hearing improvement after ear surgeries. This conclusion is original and extremely important from the practical point of view. This is because it raises a question about surgeries intended to improve hearing in patients with such a perceptive hearing loss. In this group of patients, the criterion used to refer them for surgery should include the need to remove the patholo- gy, for example cholesteatoma, or to close an eardrum loss resul- ting in separation of the middle ear space from the unfavourable influence of the environment.
CONCLUSIONS
The sensorineural component of hearing impairment up to 40 dB is a prospect of bone conduction thresholds’ improvement after surgical restoration of the influence of middle-ear mechanics on the inner ear in patients treated as a result of otosclerosis, as well as of eardrum perforation.
FINANCING
This research was supported by statutory funds of the Department of Otolaryngology of the Jagiellonian University, Krakow, Poland.
this statement is provided by the disruption of bone conduc- tion in response to stapes ankylosis in the course of otoscle- rosis [13, 14].
Bone conduction improvement after surgery is largely related to the previously described Carhart effect. According to the lite- rature, patients with otosclerosis experience apparent deterio- ration of bone conduction caused by disturbed sound transmis- sion in the middle ear. Surgery results in efficient functioning of the transmission system of the ossicle chain, thus restoring the physiological participation of middle-ear structures in sound conduction and improvement of threshold values for bone con- duction [15–17].
As a part of the considerations of changes to the threshold values of bone conduction 12 months after stapedotomy, a statistically significant improvement was observed in the group with initial va- lues of bone conduction in the 21–40 dB range. The post-surgery value of bone conduction thresholds in this group and its chan- ges were significantly greater than the average values in the other groups. The average post-surgery bone conduction value in the extreme groups: with initial bone conduction value in the range of 0–20 dB and the initial value of bone conduction > 40 dB, as well as its change, was not statistically significant.
In the studies performed by Vartiainen et al., in 181 patients sub- jected to surgery as a result of chronic otitis media, it was conc- luded that in the case of 92% of patients, bone conduction values did not change after surgery, 5% reported improvement, and 3%
reported deterioration of said values. Improvement in the range of 11–25 dB was noticeable once advanced pathological changes were removed from the tympanic cavity. Improvement of bone conduction values is observed, on average, in less than 10% of pa- tients subjected to surgery as a result of chronic otitis media. It is thought that impaired bone conduction in the course of chronic otitis media may be induced by chronic inflammation, may also be of iatrogenic nature as a result of manual intervention into the ossicle chain, but also may result from noise accompanying the opening of the temporal bone [18, 19].
There were also attempts to explain bone conduction disruptions by the toxic influence of inflammatory mediators present in the middle ear on the function of the inner ear. The possibility of bio- chemical changes in perilymph and endolymph caused by the in- fluence of substances penetrating from the middle ear through the round window is underlined [20, 21].
The aforementioned mechanical and biochemical factors often act simultaneously.
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Katarzyna Job MD; Department of Otolaryngology, Jagiellonian University Medical College in Krakow; Jakubowskiego street 2; 30-688 Krakow, Poland; Phone: +48 12 400 27 50; E-mail: kajob14@interia.pl
Job K., Skladzien J.: The prognostic influence of pre-surgery bone conduction values on the improvement of hearing in patients treated surgically as a result of middle-ear conditions; Otolaryngol Pol, 2021: 75 (3): 8-13
