Cartilage mechanics in the guinea pig model of osteoarthritis studied with an osmotic loading method

Objective: To determine the material properties of articular cartilage in the Hartley guinea pig model of spontaneous osteoarthritis. Methods: Cartilage-bone samples from the medial femoral condyle and tibial plateau of 12 month-old guinea pig knees were subjected to osmotic loading. Site-matched swelling strains and fixed charge density values were used in a triphasic theoretical model for cartilage swelling to determine the modulus of the cartilage solid matrix. The degree of cartilage degeneration was assessed in adjacent tissue sections using a semi-quantitative histological grading scheme. Results: Decreased values for both moduli and surface zone fixed charge density were associated with increasing grades of cartilage degeneration. Decreases in moduli reflect damage to the collagen matrix, which give rise to greater swelling strains. Conclusion: Histological evidence of cartilage degeneration was associated with impaired cartilage mechanics in the aging Hartley guinea pig.