Fourier analysis of tibia acceleration in subjects with knee osteoarthritis: Preliminary results

Knee osteoarthritis (OA) can lead to pain and disability in the older population. Excessive loading has been suggested to contribute to the development of knee OA. In this paper, we investigated the frequency components in accelerometric signals of the tibia in the anterior-posterior (AP), medial-lateral (ML) and vertical (Vert) directions during walking between people with severe knee OA and asymptomatic control group. The Fast Fourier Transform (FFT) was applied to the tibia accelerations in the three directions for 3 trials. The FFT decomposes the acceleration signal into a series of signals at different frequencies to investigate the frequency components (harmonics) in a signal where the power spectrum graphs provide quantitative information of signal composition. The frequency components in the AP and ML accelerations appear at similar frequencies for both healthy and knee OA subjects. Frequency components in the vertical acceleration, however, were found to have larger frequency components in the higher frequencies (>5 Hz) for the knee OA subjects compared to the healthy group. The differences in power peaks corresponding to higher harmonics (>6 Hz) between the groups may indicate instability and altered attenuation of the impact during walking for people with knee OA. Further work, should be directed on investigating the position of occurrence of the high frequency during the gait cycle and understanding the biomechanical mechanism responsible for these differences.