The effects of osteoarthritis on the viscoelastic properties of human articular cartilage

Osteoarthritis (OA) is a disease that indiscriminately destroys the smooth, glassy surface of articular cartilage, compromising its integrity and causing pain for many individuals worldwide. The purpose of this study was to develop an understanding of the mechanical changes that OA causes on the viscoelastic properties of articular cartilage. This dissertation reports the results of incremental viscoelastic tensile and compression stress-strain testing of human osteoarthritic cartilage collected from patients undergoing total knee replacement surgery. The study population consisted of 109 patients, with 112 tissue specimens collected. A total of 73–2.5cm by 0.5cm cartilage specimens, cut in the direction of articulation, were used for incremental tensile stress-strain testing. The unconfined incremental compression stress-strain testing consisted of 39–13/16in diameter cartilage specimens that were removed parallel to the tensile specimens. The results of articular cartilage tested in tension showed a trend of increased viscous moduli with increasing strain rate (Fibrillated: 10% = 2.81 MPa, 10,000% = 10.89 MPa; Arthritic: 10% = 0.31 MPa, 10,000% = 1.67 MPa), however the viscous component was found not to be statistically strain rate dependent (p > 0.05). The elastic component was found to be strain rate dependent for strains up to 1,000% (p < 0.05), (Fibrillated: 10% = 6.63 MPa, 10,000% = 7.67 MPa; Arthritic: 10% = 0.62 MPa, 10,000% = 3.36 MPa). Both viscous and elastic properties were found to be dependent on the physical integrity of the tissue (which was visually noted at time of surgery and sample preparation). As the degree of OA increased the viscous moduli (“Normal”: 10% = 14.24 MPa, Arthritic: 10% = 0.31 MPa) and elastic moduli (“Normal”: 10% = 12.67 MPa, Arthritic: 10% = 0.62 MPa) were noted to decrease. Such trends were also found to exist in unconfined compression tests of similar samples (“Normal”: 10% viscous = 7.83 MPa, Arthritic: 10% viscous = 1.44 MPa; “Normal”: 10% elastic = 5.48 MPa, Arthritic: 10% elastic = 0.49 MPa). In summary, fibrillation and fissure formation seen in OA cartilage can directly be correlated through a grading scale to the viscous and elastic properties of the osteoarthritic tissue. In addition the decrease in moduli seen prior to visual alterations may be a result of impaired energy storage capabilities.