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 treatment 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. Studies of pin loosening are based primarily on pin extraction force measurements, which are destructive in nature. This paper will introduce a method for estimating the extraction force of non-threaded fixation pins based on three related parameters obtained from an ultrasonic pulse introduced into the pin. The ultrasonic test takes advantage of the inherent acoustic absorption across the bone-pin interface. A strong interlock between bone and pin results in increased transmission of ultrasound across the bone-pin interface. This is manifested as heavy signal attenuation, whereas a poor interlock results in considerably less attenuation. The parameters proposed in this paper are intended to quantify attenuation resulting from bone-pin interface interactions. One probe-parameter combination in particular showed considerable sensitivity to the conditions of the bone-pin interface (R2 = 0.79). Further research is suggested and may lead to an operational process for non-invasively evaluating pin security.