Relationships Between Quantitative Pulse-Echo Ultrasound Parameters from the Superficial Zone of the Human Articular Cartilage and Changes in Surface Roughness,Collagen Content or Collagen Orientation Caused by Early Degeneration

We aimed to quantitatively investigate the relationship between amplitude-based pulse-echo ultrasound parameters and early degeneration of the knee articular cartilage. Twenty samples from six human femoral condyles judged as grade 0 or 1 according to International Cartilage Repair Society grading were assessed using a 15-MHz pulsed-ultrasound 3-D scanning system ex vivo. Surface roughness (R_q), average collagen content (A₁) and collagen orientation (A₁₂) in the superficial zone of the cartilage were measured via laser microscopy and Fourier transform infrared imaging spectroscopy. Multiple regression analysis with a linear mixed-effects model (LMM) revealed that a time-domain reflection coefficient at the cartilage surface (R_c) had a significant coefficient of determination with R_q and A₁₂ ($R_{\text{LMMm}}^2=0.79$); however, R_c did not correlate with A₁. Concerning the collagen characteristic in the superficial zone, R_c was found to be a sensitive indicator reflecting collagen disorganization, not collagen content, for the early degeneration samples.