Paper 08: In Vitro Effects of Triamcinolone and Methylprednisolone on the Viability and Mechanics of Native Articular Cartilage

Abstract

Objectives: The chondrotoxic effects of methylprednisolone acetate (MP) and triamcinolone acetonide (TA) have been well described. Prior studies have demonstrated a dose-dependent chondrotoxic effect of intra articular (IA) steroids starting at 7 mg for MP and 18 mg for TA. However, the effects of these steroids on the mechanical properties of articular cartilage are largely unknown. The purpose of this study was to investigate the in vitro effects of a single one-hour MP or TA exposure on the viability, mechanics, and biochemical content of native articular cartilage explants. Methods: Articular cartilage explants (n=6 per group) were harvested from the femoral condyle of the bovine stifle. Explants were exposed to chondrogenic medium containing a clinical dose of MP or TA for one hour, followed by fresh medium wash and exchange. Explants in the negative control group underwent the same treatment with chondrogenic medium alone. At t=24 hours post-treatment, samples were assessed for viability (live/dead), mechanical properties (creep indentation and Instron tensile testing), biochemical (collagen and glycosaminoglycan) content, and pyridinoline cross linking via mass spectrometry. Results: Mean cell viability was significantly decreased in native explants exposed to MP (35.5%) compared to control (49.8%, p < 0.001) and TA (45.7%, p = 0.003) (Figure 1). There was significant weakening of mechanical properties of steroid-treated native explants when compared to control (Figure 2), with decreases in aggregate modulus (646.3 kPa vs 312.8 kPa [MP] and 257.0 kPa [TA), p < 0.001), shear modulus (370.1 kPa vs 191.2 kPa [MP] and 157.4 kPa [TA], p < 0.001), and ultimate tensile strength (UTS) (9.650 MPa vs 5.648 MPa [MP], p = 0.021 and 6.065 MPa [TA], p = 0.040). The Young’s modulus in TA-exposed native cartilage (7.924 MPa) was significantly lower than MP (12.35 MPa, p = 0.026) exposed explants but not significantly different compared to control (11.97 MPa, p =0.072). No significant differences in collagen and glycosaminoglycan content were found in the steroid-treated groups (Figure 3). Pyridinoline cross linking was significantly decreased in explants exposed to TA compared to control (p = 0.027). Conclusions: The results of this in vitro study suggest that a single clinical dose of MP is chondrotoxic and that a single clinical dose of MP or TA can lead to substantial early decreases in both the tensile and compressive properties of native articular cartilage. The shear modulus of steroid-exposed explants in this study dropped 48-57% compared to healthy control. In human knee cartilage, drops in shear modulus of this magnitude have been correlated with the progression from healthy knee cartilage to ICRS grade 1-2 osteoarthritis. Furthermore, decreases in Young’s modulus by 25-50% have been correlated with the same degree of osteoarthritis, and the Young’s modulus of steroid exposed cartilage dropped an average of 34% in this study. Although there were no detectable changes to the extracellular matrix composition or structure, a single one-hour steroid exposure was enough to cause chondrotoxicity and altered mechanics to native explants 24 hours after exposure, which raises the concern for risk of mechanical failure of the cartilage tissue. Clinicians should be judicious regarding use of intra-articular steroids, particularly in patients with intact healthy articular cartilage.