Acoustic trauma from the bone cutting burr By J. HELMS (Tubingen) INNER EAR hearing loss caused by middle ear surgery is a rare postoperative finding. It may occur when a burr has contacted the intact ossicular chain, e.g. in tympanoplasty, antrotomy, facial nerve decompression or in the surgery of malformations (Ziihlke, 1972). To prevent hair cell damage the continuity towards the inner ear must be disconnected before drilling manoeuvres on the ossicular chain are carried out (Wullstein, 1960, 1968; Scheer, 1967). Audiometric data, the demonstration of hair cell degeneration and the measurement of potentials of the cochlea and the VIHth nerve are indirect information on the trauma to the inner ear. Such data where obtained after the application of sound or by drilling temporal bones by Riiedi and Furrer (1946), Paparella (1962), Schuknecht and Tonndorf (1960) and others*. In these experiments the movements of the stapes footplate were not measured. This was done under physiological conditions by v. Bekesy (1941, i960). He found that the ear drum and the ossicles did not transmit sound waves above 2000-3000 Hz. Anderson (1962) and Cancura (1962, 1969) observed the transmission of higher frequencies too. The study of the literature indicates that lasting inner ear hearing loso will not occur by drilling the temporal bone, but that there exists a risk, especially for high frequency perception, when the ossicles are touched with a burr during a microsurgical procedure (Helms, 1972).
Clinical observation
In a 28-year-old female patient we had to admit to a severe inner ear hearing loss after a facial nerve decompression (Fig. 1). We assume, that during the surgical procedure—the ossicular chain rem.uned intact— the cutting or the diamond burr contacted the incus. This observation gave rise to an experimental analysis of the stapes footplate movements after touching the ossicles with a burr. Material and method
Human temporal bones removed within one day after death were . prepared. A calibrated magnetic pick-up of a record player (Dual, Shure M91MG-D) was placed on the inner ear surface of the stapes footplate with a pressure of 2 pond. Only vertical vibration generated * (Gunderson, 1971; Gottesberge, 1959; Montmollin, i960; Pellnitz, 1959; Ronke and Lullies, 1953)1143
J. Helms potential differences. The pick-up transformed the velocity of the footplate at a ratio of 3 mVolts/cm/sec. linearly within the frequency range of 30 to 10,000 Hz. Drilling was done with a cutting burr No. 9 and with a diamond burr No. 8 at 18,000 rpm on the handle of the malleus, head of the malleus, body of the incus, short process of the incus and head of the stapes. The electrical potentials were put on a real time third analyser 64
128
256
512
1024
2048
4096
dB 0
8192
bone conduction
10
preoperative
20
\
30
\
.postoperative
\
40 50 60
f
70 80 90
Pat ent: L A inelies I, 28 J.
100 110 120.
Inner ear hearing loss after facial nerve decompression FIG.
1.
Inner ear hearing loss after facial nerve decompression. The ossicular chain remained intact. No conductive hearing loss postoperatively.
(Briiel and Kjaer) with a tape—(Telefunken 28) and a paper recorder (Briiel and Kjaer) (Fig. 2). Determining the velocity of the footplate for each third, the amplitudes could be calculated in the following manner: ... , , . velocity (cm./sec.) amplitude (/A) = !-± '. ' v 27rXcps. . ., , , . registered mVolts velocity (cm./sec.) = —2 Results In all 32 experiments the velocity was found with a maximum in the range of 1,500 to 8,000 Hz. The cutting burr caused higher values than the diamond burr (Fig. 3). The curved black line was calculated from data of v. Bekesy (i960) (74 dB eardrum pressure) and represents a theoretical pressure on the 1144
Analysis of stapes movements site of
pick up
real time
tape
burr trauma
(Dual.Shure
third analyzer
recorder
M91MG-D)
(BriieloKjaer)
(Telefunken 28)
recorder
(BriieUKjaer)
Ritter-Kerr Tympano torque MD 5000 18000 rpm cutting burr No.9. diamond burr No. 8
FIG. 2. Experimental measurement of the vibration of the stapes footplate when the ossicles are drilled consecutively. The potential differences of a calibrated record player pick-up are analysed by a real time third analyser, recorded on tape and written out.
Velocity of the footplate during burr trauma
0.017J
200
300
Hz-
200
XXX)
2000 3000
5000
10000 dB(A)
5000
10000 dBIAI
third middle frequencies
300
Hz — t o -
1000
2000 3000
third middle frequencies
; 134 dB eardrum pressure (calculated from data of v Bekesy)
FIG. 3. Velocity (ordinate) plotted over the frequencies (abscissa). Above: burr contact with the short process of the incus (No. 25) Below: burr contact with the body of the incus (No. 26). Bent line: Values for 134 dB ear drum pressure calculated from data of v. Be'ke'sy. Superior burr symbol: cutting burr, inferior burr symbol: diamond burr (dotted). Right side: total noise values dB (A) curve.
J. Helms tympanic membrane of 134 dB. In the low frequency range peaks were; found in correspondence to the rotation of the burr. The shape of thej velocity curve resembles the dB (A) curve, that is the most traumatizing! frequencies show the highest sound pressure values. ) To control the time course of the footplate motion, the registered signals were reproduced from the tape recorder and analysed over the time (Fig. 4). Velocity of the footplate during the burr contact with the incus A: terz middle frequency 4000 Hz B: total sound pressure (dBIA))
A
B
w
— 1.7 211
- 2 - 1.7 21
033
053
f
0,17
0.053
0017
Ik
017
ft
0,053
1 11 1 1
0
1
2
»
3
••MM
4
5
6
0017
' sec.
0
1 2
3
4
5
6
7
duration of burr trauma
FIG. 4. Time course of the stapes motion when the ossicular chain is drilled (Nr.26) A: Analysis of the 4,000 Hz third. B: Total sound pressure in the dB(A) curve.
The velocity remains on a high level during the contact between the burr and the ossicle. The frequency of 4,000 Hz (Fig. 4), saw that with the highest level contributes most to the total velocity measured in the dB (A) curve (Fig. 4B). In contrast to an explosive trauma, where high sound pressure levels exist only for milliseconds, similar levels persist in burr trauma for the whole time of drilling contact. Discussion Plotting the calculated amplitudes in the ordinate against the frequencies in the abscissa (Fig. 5) the difference between normal sound pressure and the burr trauma becomes more evident. Ranke and Lullies (1953) found a 3A amplitude of the stapes footplate at a 74 dB eardrum pressure. V. Bekesy (i960) observed values below 100 A for the same sound pressure and measured it in the frequency range between 100 and 2,500 Hz. In our experimental conditions we found differ1146
Acoustic trauma from the bone cutting burr Amplitudes of stapes footplate at different freqencies 100000
burr t r a u m a 10000
\ 'slopes hflod.culting burr incus body.cutting burr incus body, diamond burr
1000
.incus snort procoss.dtamond burr incus short procsssjeutting burr
wo , v. Btktsy 1 dyn/cm* • 74 dB •ardrum pressure Rank*.
too
1 1 c c* Frequency
500 C2
WOO 1 c>
5000
1
Clinical observation
In a 28-year-old female patient we had to admit to a severe inner ear hearing loss after a facial nerve decompression (Fig. 1). We assume, that during the surgical procedure—the ossicular chain rem.uned intact— the cutting or the diamond burr contacted the incus. This observation gave rise to an experimental analysis of the stapes footplate movements after touching the ossicles with a burr. Material and method
Human temporal bones removed within one day after death were . prepared. A calibrated magnetic pick-up of a record player (Dual, Shure M91MG-D) was placed on the inner ear surface of the stapes footplate with a pressure of 2 pond. Only vertical vibration generated * (Gunderson, 1971; Gottesberge, 1959; Montmollin, i960; Pellnitz, 1959; Ronke and Lullies, 1953)1143
J. Helms potential differences. The pick-up transformed the velocity of the footplate at a ratio of 3 mVolts/cm/sec. linearly within the frequency range of 30 to 10,000 Hz. Drilling was done with a cutting burr No. 9 and with a diamond burr No. 8 at 18,000 rpm on the handle of the malleus, head of the malleus, body of the incus, short process of the incus and head of the stapes. The electrical potentials were put on a real time third analyser 64
128
256
512
1024
2048
4096
dB 0
8192
bone conduction
10
preoperative
20
\
30
\
.postoperative
\
40 50 60
f
70 80 90
Pat ent: L A inelies I, 28 J.
100 110 120.
Inner ear hearing loss after facial nerve decompression FIG.
1.
Inner ear hearing loss after facial nerve decompression. The ossicular chain remained intact. No conductive hearing loss postoperatively.
(Briiel and Kjaer) with a tape—(Telefunken 28) and a paper recorder (Briiel and Kjaer) (Fig. 2). Determining the velocity of the footplate for each third, the amplitudes could be calculated in the following manner: ... , , . velocity (cm./sec.) amplitude (/A) = !-± '. ' v 27rXcps. . ., , , . registered mVolts velocity (cm./sec.) = —2 Results In all 32 experiments the velocity was found with a maximum in the range of 1,500 to 8,000 Hz. The cutting burr caused higher values than the diamond burr (Fig. 3). The curved black line was calculated from data of v. Bekesy (i960) (74 dB eardrum pressure) and represents a theoretical pressure on the 1144
Analysis of stapes movements site of
pick up
real time
tape
burr trauma
(Dual.Shure
third analyzer
recorder
M91MG-D)
(BriieloKjaer)
(Telefunken 28)
recorder
(BriieUKjaer)
Ritter-Kerr Tympano torque MD 5000 18000 rpm cutting burr No.9. diamond burr No. 8
FIG. 2. Experimental measurement of the vibration of the stapes footplate when the ossicles are drilled consecutively. The potential differences of a calibrated record player pick-up are analysed by a real time third analyser, recorded on tape and written out.
Velocity of the footplate during burr trauma
0.017J
200
300
Hz-
200
XXX)
2000 3000
5000
10000 dB(A)
5000
10000 dBIAI
third middle frequencies
300
Hz — t o -
1000
2000 3000
third middle frequencies
; 134 dB eardrum pressure (calculated from data of v Bekesy)
FIG. 3. Velocity (ordinate) plotted over the frequencies (abscissa). Above: burr contact with the short process of the incus (No. 25) Below: burr contact with the body of the incus (No. 26). Bent line: Values for 134 dB ear drum pressure calculated from data of v. Be'ke'sy. Superior burr symbol: cutting burr, inferior burr symbol: diamond burr (dotted). Right side: total noise values dB (A) curve.
J. Helms tympanic membrane of 134 dB. In the low frequency range peaks were; found in correspondence to the rotation of the burr. The shape of thej velocity curve resembles the dB (A) curve, that is the most traumatizing! frequencies show the highest sound pressure values. ) To control the time course of the footplate motion, the registered signals were reproduced from the tape recorder and analysed over the time (Fig. 4). Velocity of the footplate during the burr contact with the incus A: terz middle frequency 4000 Hz B: total sound pressure (dBIA))
A
B
w
— 1.7 211
- 2 - 1.7 21
033
053
f
0,17
0.053
0017
Ik
017
ft
0,053
1 11 1 1
0
1
2
»
3
••MM
4
5
6
0017
' sec.
0
1 2
3
4
5
6
7
duration of burr trauma
FIG. 4. Time course of the stapes motion when the ossicular chain is drilled (Nr.26) A: Analysis of the 4,000 Hz third. B: Total sound pressure in the dB(A) curve.
The velocity remains on a high level during the contact between the burr and the ossicle. The frequency of 4,000 Hz (Fig. 4), saw that with the highest level contributes most to the total velocity measured in the dB (A) curve (Fig. 4B). In contrast to an explosive trauma, where high sound pressure levels exist only for milliseconds, similar levels persist in burr trauma for the whole time of drilling contact. Discussion Plotting the calculated amplitudes in the ordinate against the frequencies in the abscissa (Fig. 5) the difference between normal sound pressure and the burr trauma becomes more evident. Ranke and Lullies (1953) found a 3A amplitude of the stapes footplate at a 74 dB eardrum pressure. V. Bekesy (i960) observed values below 100 A for the same sound pressure and measured it in the frequency range between 100 and 2,500 Hz. In our experimental conditions we found differ1146
Acoustic trauma from the bone cutting burr Amplitudes of stapes footplate at different freqencies 100000
burr t r a u m a 10000
\ 'slopes hflod.culting burr incus body.cutting burr incus body, diamond burr
1000
.incus snort procoss.dtamond burr incus short procsssjeutting burr
wo , v. Btktsy 1 dyn/cm* • 74 dB •ardrum pressure Rank*.
too
1 1 c c* Frequency
500 C2
WOO 1 c>
5000
1
