Measurement of the layered compressive properties of trypsin-treated articular cartilage: an ultrasound investigation

An ultrasound-compression system has been developed for the study of the la yered biomechanical properties of articular cartilage. Cartilage specimens harvested from the bovine patella groove, with and without trypsin digestio n, were tested using this system. It was noted that a large ultrasound refl ection can be detected in the interface of the trypsin digestion front, Thi s ultrasound reflection signal was used to differentiate the deformations o f different portions of the cartilage throughout its depth when a load was applied. The equilibrium compression moduli of the digested, undigested and entire portions of articular cartilage were measured. The modulus of the c artilage without any digestion was 660 +/- 230 kPa. After 1h digestion with 1 mg ml(-1) tryosin solution, the thickness of the digested portion was 0. 50 +/-0.06 mm, and the modulus of the entire cartilage layer changed to 125 +/- 42 kPa. The moduli of the digested and undigested portions were 58 +/- 24 kPa and 470 +/- 31 kPa, respectively. Similar results were obtained for the cartilage with trypsin digestion for 2h.