Vibration Signal Analysis for Detecting Early-Stage Lumbar Spondylolysis Using Synthetic Bone

Abstract

Bone fractures can be detected by analyzing vibration signals following bone stimulation. This method can also be applied to detect stress fractures, such as spondylolysis. The aim of this study was to investigate whether vibration signal analysis can be used to detect lumbar spondylolysis in synthetic bone. Four synthetic spondylolysis models of the fifth lumbar vertebra (Sawbones, product No. SAW1352-10: Malmö, Sweden) were prepared, with the following conditions: intact, unilateral defect, and bilateral defect. Unilateral defects were created by making an incision of either half the diameter (50% incision) or the entire diameter (100% incision) in length through the pars interarticularis or pedicle. Bilateral defects were created by making an additional incision of half the diameter in length on the opposite side of the defected pars interarticularis or pedicle (50% + 100% incision). Hammering was performed five times on each spinous process of the fixed synthetic bones and vibration signals were measured using an accelerometer attached to the contralateral side of the hammer. Signals were analyzed using fast Fourier transform. The parameters analyzed included the mean power frequency, first power minimum frequency (the minimum value between the first and second peaks), spectral areas of low and high frequency bands, and the relative ratio between the spectral areas of low and high frequency bands. The relative ratio was significantly lower in the 50%, 100%, and 50% + 100% incision conditions compared to the intact condition (p < 0.01), suggesting the potential utility of vibration signal analysis in diagnosing lumbar spondylolysis.