Structural Quantification in Osteoarthritis of the Knee Using Power Spectral Analysis

An exact diagnosis of osteoarthritis is very important to prevent deterioration of ADL (activities of daily living) of the elderly. However, it is very difficult to diagnose the stage of osteoarthritis, and only a few indices for structural quantification of osteoarthritis have been reported. The purpose of this research is to investigate a new index for the bone structure in osteoarthritis. We examined right knees of 41 women aged from 34 to 85 years. Directivity index (DI) is a new index of bone structure calculated by directivity of the power spectrum from radiographs of tibial bone using fast Fourier transform (FFT). DI was obtained by subtracting the integral power value at 0 and 90 degree directions on the x-y plane of the two-dimensional power spectrum of tibial bone from the integral power value at a direction of 45 degrees. A significant relationship between the state of the knee joint by X-ray inspection and DI was indicated by evaluation of the correlation coefficient. However, no significant relationship was found between the state of the knee joint by X-ray inspection and the first moment of the Fourier power spectrum or the fractal dimension. There is a possibility that DI can estimate slight deformation of bone structure in osteoarthritis. In the future, we will apply DI to the prevention of osteoarthritis and a deterioration of ADL in the elderly.