AN ULTRASONIC-ATTENUATION PARAMETER FOR INVESTIGATING THE HOLDING POWER OF NON-THREADED FIXATION PINS IN CANINE FEMUR (IN-VITRO)

External skeletal fixation (ESF) is a widely used method of fracture t reatment but often produces medical complications in the patient. The most serious complication, pin loosening, may lead to pain, poor limb usage, pin tract infection, fracture instability and non-union. Studie s of pin loosening are based primarily on pin extraction force measure ments, which are destructive in nature. This paper will introduce a me thod for estimating the extraction force of non-threaded fixation pins based on three related parameters obtained from an ultrasonic pulse i ntroduced into the pin. The ultrasonic test takes advantage of the inh erent acoustic absorption across the bone-pin interface. A strong inte rlock between bone and pin results in increased transmission of ultras ound across the bone-pin interface. This is manifested as heavy signal attenuation, whereas a poor interlock results in considerably less at tenuation. The parameters proposed in this paper are intended to quant ify attenuation resulting from bone-pin interface interactions. One pr obe-parameter combination in particular showed considerable sensitivit y to the conditions of the bone-pin interface (R(2)=0.79). Further res earch is suggested and may lead to an operational process for non-inva sively evaluating pin security.