Acoustic properties of articular cartilage under mechanical stress

Issue title: Selected papers of the 4th International Symposium on Mechanobiology of Cartilage and Chondrocyte, Budapest, 20–22 May, 2006

Article type: Research Article

Authors: Nieminen, Heikki J.^{; ;} | Töyräs, Juha | Laasanen, Mikko S.^; | Jurvelin, Jukka S.^;

Affiliations: Department of Physics, University of Kuopio, POB 1627, 70211 Kuopio, Finland | Department of Anatomy, University of Kuopio, POB 1627, 70211 Kuopio, Finland | Department of Clinical Neurophysiology, Kuopio University Hospital and University of Kuopio, POB 1777, 70211 Kuopio, Finland | Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, POB 1777, 70211 Kuopio, Finland

Note: [] Address for correspondence: Heikki J. Nieminen, Department of Physics, University of Kuopio, POB 1627, 70211 Kuopio, Finland. Tel.: +358 17 162341; Fax: +358 17 162585; E-mail: heikki.nieminen@uku.fi; Web: www.luotain.uku.fi.

Abstract: Mechano-acoustic and elastographic techniques may provide quantitative means for the in vivo diagnostics of articular cartilage. These techniques assume that sound speed does not change during tissue loading. As articular cartilage shows volumetric changes during compression, acoustic properties of cartilage may change affecting the validity of mechano-acoustic measurements. In this study, we examined the ultrasound propagation through human, bovine and porcine articular cartilage during stress-relaxation in unconfined compression. The time of flight (TOF) technique with known cartilage thickness (true sound speed) as well as in situ calibration method [Suh, Youn, Fu, J. Biomech. 34 (2001), 1347–1353] were used for the determination of sound speed. Ultrasound speed and attenuation decreased in articular cartilage during ramp compression, but returned towards the level of original values during relaxation. Variations in ultrasound speed induced an error in strain and compressive moduli provided that constant ultrasound speed and time-of-flight data was used to determine the tissue thickness. Highest errors in strain (−11.8±12.0%) and dynamic modulus (15.4±17.9%) were recorded in bovine cartilage. TOF and in situ calibration methods yielded different results for changes in sound speed during compression. We speculate that the variations in acoustic properties in loaded cartilage are related to rearrangement of the interstitial matrix, especially to that of collagen fibers. In human cartilage the changes, are, however relatively small and, according to the numerical simulations, mechano-acoustic techniques that assume constant acoustic properties for the cartilage will not be significantly impaired by this phenomenon.

Keywords: Articular cartilage, osteoarthrosis, mechanical indentation, ultrasound speed, ultrasound attenuation

Journal: Biorheology, vol. 43, no. 3-4, pp. 523-535, 2006