The effects of intra-articular 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. Biochemical and morphologic analysis of treated cartilage has revealed conflicting results, but previous biomechanical assessment has not been undertaken. Objective: To compare the biomechanical properties of intra-articular methylprednisolone acetate (MPA) and diluent treated cartilage in treadmill exercised horses. Methods: Eight 2-year-old female horses had MPA or diluent administered into contralateral middle carpal joints at 14 day intervals for a total of four treatments per horse. Horses underwent a standard treadmill exercise protocol until euthanasia (day 70). Standard sites were tested on the third, radial and intermediate carpal bones using an automated indentation apparatus to obtain the creep and recovery behavior of the articular cartilage. Using previously validated biphasic creep indentation methodology, aggregate modulus, Poisson's ratio, permeability, shear modulus, thickness, creep and recovery equilibrium times and percent recovery were obtained at each 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 diluent 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% thicker (P=0.0001) than MPA treated articular cartilage. Conclusions: The findings indicate that repetitive intra-articular administration of MPA to exercising horses alters the mechanical integrity of articular cartilage, which could lead to early cartilage degeneration.