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tympanic membrane and middle ear implants and between the prosthesis
and the ossicular chain using model calculations and temporal bone ex-
periments.
The quality of the tympanic membrane, which can be considered as the “mo-
tor of the middle ear”, has the most important impact on the sound transfer
to the inner ear. Ventilation and mucosa problems can damp the tympanic
membrane vibrations as well as the reconstruction techniques or the me-
chanical properties of transplants. The coupling of the tympanic membrane
to either the surrounding bone or the cartilage transplants has an influence
on the stiffness. The contact of the tympanic membrane to the malleus han-
dle is of importance in order to allow good sound conduction to middle ear
prostheses in the high frequency range.

Furthermore the contact of prostheses to the stapes head or the footplate may
influence hearing results. In our investigations the angle of prostheses to-
wards the tympanic membrane and the stiffness of coupling plays an import-
ant role. Concerning the angle it is of importance to distinguish between the
x and y – direction. An absolutely stiff contact between malleus and stapes
can reduce the sound transfer and increase the risk of prosthesis dislocation
or even damage of the annular ligament. Even nowadays modern middle ear
reconstructions can only simulate the simple function of a columella. In fu-
ture it may be important to invent middle ear implants which will be able to
fulfill both required middle ear functions – the sound transfer and the com-
pensation of atmospheric pressure changes. It can be assumed that hearing
results may improve due to an unstressed coupling of middle ear prostheses
by taking the above mentioned techniques and findings into consideration.

VENTIL ATION TUBES

Infection frequency and type of bacteria after
tympanostomy tube drainage in childhood: gilded-silver
tubes versus silicone tubes
Schmäl F., Nieschalk M., Delank K.W., Stoll W.

Published: HNO 1999 Feb; 47 (2):107-111.
Otorrhea is the most common complication after tympanostomy tube in-
sertions. In Germany there are currently two commonly used types of tym-
panostomy tubes: silicon tubes (ST) and gilded silver tubes (GT). Previ-
ously published in vitro studies by Tajima uncovered a positive correlation
between the silicon concentration in culture fluid and the rate of growth
of Staphylococcus aureus. Our study retrospectively evaluates the types of
bacteria and rates of otorrhea after ST and GT insertions. The present study
was undertaken to determine which of these tubes had a higher incidence
of otorrhea and then whether silicon tubes stimulated the growth of certain
types of bacteria, such as Staphylococcus aureus. In all, 186 ST and 59 GT
were placed in 245 ears of 144 children. Both ST and GT were separated
into three groups: first insertion of a tympanostomy tube, second implanta-
tion and insertion of a tympanostomy tube in an infected ear in the course
of a mastoidectomy. No differences between ST and GT in causing otorrhea
were found in the three groups. Nevertheless, ST in comparison to GT was
associated with a higher incidence of infections with Pseudomonas aerugi-
nosa. In contrast, a higher incidence of Staphylococcus aureus related to ST
could not be proved. Twenty percent of the ears with mastoiditis were found
to have Pseudomonas aeruginosa, but none of these ears implanted with a
GT developed postoperative otorrhea. Our findings show that GT should be
used when a ventilation tube is used during a mastoidectomy. Further, it is
tenable to implant only GT because postoperative otorrhea in many cases is
caused by insufficient water protection and water is frequently polluted with
Pseudomonas aeruginosa.

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