Mw. Kay et al., AXIAL VIBRATION OF THREADED EXTERNAL FIXATION PINS - DETECTION OF PINLOOSENING, Annals of biomedical engineering, 26(3), 1998, pp. 361-368
The hypothesis of this study was that a nondestructive vibrational met
hod could detect bone lysis at the external fixation pin-bone interfac
e prior to current clinical and radiographic methods. In vitro models
were used to simulate changes observed during pin loosening in vivo. F
ixation pin axial natural frequency decreased with decreasing tensile
modulus of the material into which it was implanted. In a live animal
study the right tibia of 12 dogs was fractured and stabilized with a f
our-pin unilateral external fixation frame. The axial natural frequenc
y of each pin was measured and radiographs were taken at 0, 2, 4, 6, 8
, and 10 weeks after surgery. The natural frequency did not change whe
n the first radiographic changes around the interface were observed. P
ins were palpably stable at this point. As loosening progressed, the n
atural frequency did decrease. Frequency and quasistatic tests of diss
ected pin-bone structures revealed a good correlation between natural
frequency and pin-bone interface stiffness. In addition, the measureme
nt of natural frequency was more sensitive to bone structure changes a
t the pin-bone interface than low-load quasi-static stiffness. Therefo
re, a nondestructive vibration technique could be used instead of low-
load quasistatic tests for assessing the pin-bone interface ex vivo. (
C) 1998 Biomedical Engineering Society.