Hip Joint Replacement Wear Gauge

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Replacement hip joints typically use a dense plastic insert as a lubricant to avoid
metal-to-metal wear and associated particulate contamination in the bloodstream,
which can cause severe toxic reactions in some users. In this system, a resonant
module containing a quartz or ceramic resonator is installed across the joint ball and
socket components by electrically conductive leads. The metal hip replacement
parts become a functional radio frequency dipole antenna, resonant at nearly the
frequency of the inserted module, and responsive to near-field RF energy by
absorbing power at resonant frequency. A grid-dip meter or spectrum-sweep generator will show the actual resonant frequency.

Wear of the plastic insert, which acts as a capacitor between two conductors,
results in an increase of capacitance between the metal ball and socket as the distance
decreases with usage. This increase of capacitance causes a 'pulling' effect on the
resonant module by adding capacitance to the circuit, lowering its resonant frequency, and thus providing a non-invasive indication of thickness of the dense plastic insert.
A failure to absorb near-field energy will indicate a short-circuit between the replacement joint components and thus a need for replacement of the insert or of the entire joint system.


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    Jim Limber
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