P012 - Development of a Novel Quantitative Ultrasound Parameter to Measure Tidemark Remodeling
- C. Hoemann (Manassas, US)
- C. Hoemann (Manassas, US)
- J. Mutersbaugh (Manassas, US)
- A. Charan (Manassas, US)
- F. Pettrone (Arlington, US)
- P. Chitnis (Manassas, US)
Abstract
Purpose
Traumatic joint injury can initiate osteoarthritis and launch a slow process of creeping mineralization and tidemark advancement through unclear mechanisms. High-frequency ultrasound is a non-destructive approach that can be used to image the cartilage-bone interface. The purpose of this study was to develop a novel quantitative ultrasound (QUS) parameter that reflects alterations in tidemark structure due to changes in mineralization.
Methods and Materials
Osteochondral explants 3mm in diameter were extracted with 8G Jamshidi needles from an adult bovine shoulder (N=1) or intact human knee cartilage (N=3, de-identified arthroplasty surgical waste). Explants were cultured in vitro, fixed and decalcified in EDTA. Specimens were SAM scanned by raster-scanning a 15 MHz transducer (Olympus) at the optimal focal length of 50.8 in a 6x6mm grid at 100 µm steps. A log-compressed envelope signal (dB per mm) in a 1 mm2 area in the center of each explant was produced (MATLAB). The QUS alpha parameter was defined as the slope (dB/mm) between the maximal subchondral signal and 200 µm prior. Differences were evaluated by matched pair design (JMP-Pro, significance set at p˂0.05).
Results
Osteochondral SAM scans produced two prominent signals along the scanning axis at the articular cartilage surface and the tidemark (Fig. 1A), as previously reported by others. We report the novel finding that decalcification altered the echogenic backscatter at the tidemark, with increased echogenicity in subchondral bone (Fig. 1B). Compared to healthy bovine tissue, human OA articular cartilage was thicker, produced more backscatter inside the articular cartilage, showed higher alpha values, and required longer decalcification times to observe changes in alpha.
Conclusion
A high alpha indicates a rapid spatial increase in echogenicity that is expected for a well-developed and intact mature tidemark. Tidemark advancement produces a hypomineralized tissue suggesting that QUS could be useful for identifying longitudinal changes in the tidemark, in an explant model.