Differential acoustic properties of early cartilage lesions in living human knee and ankle joints

Objective. Although numerous studies have been performed to determine whether there are histologic, biochemical, biomechanical, and metabolic differences between knee and ankle cartilage, none have investigated the presence of such differences in living human cartilage. We previously developed an ultrasonic evaluation system for articular cartilage that analyzes the A-mode echogram using wavelet transformation. The current study was undertaken to determine whether the acoustic properties of living human cartilage differ between knee and ankle joints. Methods. Twenty-eight patients were subjected to ultrasonic evaluation under arthroscopy. After arthroscopic grading, the cartilage was measured using an ultrasonic probe. Two quantitative parameters were used, i.e., the maximum magnitude and the echo duration at the 95% interval of the maximum magnitude. Results. In intact cartilage, the maximum magnitude and echo duration did not differ between the knee and the ankle. In lesional cartilage, in contrast, the maximum magnitude was higher, and the echo duration was shorter, in the ankle than in the knee. These differences were statistically significant. Conclusion. Ultrasound findings could be used to judge the degree of early cartilage degeneration in vivo on the basis of objective data such as the maximum magnitude and echo duration. Because we were unable to quantitatively analyze the biochemical and biomechanical properties of the cartilage in this study, our biochemical and biomechanical findings are based only on qualitative assessment. Nevertheless, the results indicate that this ultrasonic evaluation system may be useful for elucidating the processes of articular cartilage degeneration in osteoarthritis.