![](bg4.png)
first eigen frequency of the oscillator was identified
at 67 Hz. The peak of the second harmonic was at
134 Hz. Comparison of different material layers
revealed decreased amplitudes with a thicker
gelatine layer.
Figure 7: Frequency spectrum of the oscillations of the
loosening sensor.
4 DISCUSSION
With respect to the standard application of total hip
replacements, unsatisfying results in loosening
diagnosis increase the demand for more precise in
vivo techniques. Inductive coupling based on radio
frequency powering to provide energy supply of in
vivo sensors causes problems, especially with regard
to the coupling factor between the two coils. To
circumvent this problem, our approach was to show
the capability of a novel sensor principle using basic
research models.
The trigger circuit to control the excitation and
detection coils allows the identification of the
highest velocity after impingement of the oscillator
on the membrane. This leads to promising
experimental results, which show the usability of the
described in vivo method for detecting total hip
replacement loosening with extracorporeal coils and
a passive internal sensor.
The robustness of the oscillators due to the
simplicity of the assembly guarantees functionality
during intraoperative impaction and sterilization of
the implant. Moreover, the oscillators can be used in
experimental applications to determine the quality of
osseointegration of new coated implant materials.
5 CONCLUSIONS
In the present study, a new measurement method for
in vivo diagnosis of total hip replacement loosening
without inductive coupling based radio frequency
powering was demonstrated. The described
loosening sensors with two coils and a custom
trigger circuit shows results with good prospects in
preliminary tests.
Future work will include the implementation of
the loosening sensor in real implants. Furthermore,
solutions for continuous excitation and therefore the
optimization of the trigger circuit are aspired.
Enhancements of the inductive unit are
designated with respect to air-core coils as detection
coils, which are switched as differential coils for
better erasure of the excitation field during
detection.
ACKNOWLEDGEMENTS
This research project is granted by the German
research foundation (DFG) under Reg.No. KL 2327.
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A NEW METHOD FOR DETECTION OF TOTAL HIP REPLACEMENT LOOSENING - Development and First Results
of a Novel Mechano-acoustical Sensor
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