THE EFFECTS OF INTRAARTICULAR METHYLPREDNISOLONE AND EXERCISE ON THE MECHANICAL-PROPERTIES OF ARTICULAR-CARTILAGE IN THE HORSE

Introduction: Intra-articular corticosteroids are widely used as anti- inflammatory agents for symptomatic management of arthritis, but their administration with concurrent exercise remains controversial. Bioche mical and morphologic analysis of treated cartilage has revealed confl icting results, but previous biomechanical assessment has not been und ertaken. Objective: To compare the biomechanical properties of intra-a rticular methylprednisolone acetate (MPA) and diluent treated cartilag e in treadmill exercised horses. Methods: Eight 2-year-old female hors es had MPA or diluent administered into contralateral middle carpal jo ints at 14 day intervals for a total of four treatments per horse. Hor ses underwent a standard treadmill exercise protocol until euthanasia (day 70). Standard sites were tested on the third, radial and intermed iate carpal bones using an automated indentation apparatus to obtain t he creep and recovery behavior of the articular cartilage. Using previ ously validated biphasic creep indentation methodology, aggregate modu lus, Poisson's ratio, permeability, shear modulus, thickness, creep an d recovery equilibrium times and percent recovery were obtained at eac h site. Results were analyzed using ANOVA and multiple comparisons of the means (P < 0.05). Results: Cartilage intrinsic material properties and thickness demonstrated significant differences between MPA and di luent treated joints. Diluent treated cartilage had a 97% increase in compressive stiffness modulus (P=0.0001), was 121% more permeable (P=0 .0001), had 88% increase in shear modulus (P=0.0001), and was 24% thic ker (P=0.0001) than MPA treated articular cartilage. Conclusions: The findings indicate that repetitive intra-articular administration of MP A to exercising horses alters the mechanical integrity of articular ca rtilage, which could lead to early cartilage degeneration.