Abstract
Introduction
Many surgeons are familiar with the audible change in the sound pitch while hammering a rasp in a long bone during surgeries like Hip Arthroplasty. We have developed a hypothesis indicating that there is a relationship between that sound change and the development of micro-fracture and subsequently full fracture.
Methods
An experiment using porcine femur bone performed by attaching a bone conduction microphone to the distal part of the bone while hammering a rasps of different sizes through the medullary canal till the point where a fracture developed. The transduce sound resonances created in the bone during rasping are converted to an analogue electrical signals that were sent to a Zoom H4n handheld recording device which recorded the signal to a disk.
The recorded signals subsequently were analysed using Matlab software and a spectrum analyzer using Fast Fourier Transforms (FFT).
Results
Our analysis of the sound frequency response (SFR) during hammering of a rasp in the medullary canal of a porcine bone proved that the (SFR) changes are influenced by the structural integrity of the Rasp-femur interface.
The pitch of the resonance increases as the rasp approaches optimal tension and grip in cortical bone. The SFR graph shifted to the right between successive hammer blows as the fixation stiffness increased and that was reflected by increasing resonance frequencies, Once bone fracture developed this structure was compromised leading to a change in the pitch and duration of the resonance. When the tension decreased due to the fracture The SFR graph shifted to the left as the structure no longer has the capacity to resonate to the same extent. SFR analysis can detect accurately the rasping end point where the risk of fracture increases if hammering continued beyond it.
Conclusion
There is a relationship between hammering sound frequency response during rasping and internal stress in the bone which could be used as an objective method to predict and prevent the development of intraoperative micro-fracture through the identification of insertion end point.
