Discussion

Pease, A., Caron, J.

Aims: To determine if the molecular properties of articular cartilage can be evaluated using magnetic resonance imaging (MRI) when compared to histopathology. Methods: Horses with known arthritis that were to be subjected to euthanasia for humane reasons were used for this study. Prior to euthanasia, 20 ml of gadobenate dimeglumine (Bracco Diagnostics Inc. Singen, Germany) was administered intravenously. After euthanasia, 5 distal thoracic limbs were removed, 4 with osteoarthritis and one without, and were evaluated with radiographs and MRI. The metacarpophalangeal joints were examined using an 8-channel knee coil and T1, T2 and a delayed gadolinium enhanced MR imaging of cartilage (dGEMRIC) sequence, which creates a T1 colour map, were obtained. T1 colour map images were then imported and analysed using MatLab (MathWorks, Natick, Massachusetts). Limbs were then disarticulated and the medial and lateral aspects of the metacarpal condyles were sectioned and processed for histological sectioning. Alcian blue and Safranin O stains were used to evaluate proteoglycan content as well as haematoxylin and eosin stain. Results: Standard MR sequences and radiographs showed signs of degenerative joint disease in the 4 affected condyles, but no definitive evidence of articular cartilage damage was identified. Using dGEMRIC, a substantial increase in signal due to contrast medium enhancement was identified in the affected limbs compared to the normal limb. These lesions correlated with the lesions identified using histopathology as a loss of proteoglycan content without damage to the cartilage ultrastructure. Conclusions and practical significance: This method may provide an accurate assessment of joint cartilage health and can be performed in live horses. In addition to helping equine athletes by detecting articular cartilage damage before becoming irreversible, this method could also serve as a very useful research tool to monitor the effects of various anti-arthritis treatments over time, without requiring the sacrifice of horses to evaluate cartilage health.