Histological Findings and T2 Relaxation Time in Canine Menisci of Elderly Dogs—An Ex Vivo Study in Stifle Joints

SIMPLE SUMMARY: Osteoarthritis is a common disease in dogs, most often affecting the stifle joint and causing damage to all joint structures. Detecting early stages of osteoarthritis is important for an effective treatment. Conventional magnetic resonance imaging (MRI) is the golden standard imaging technique for diagnosing pathologies of soft tissues in the stifle joint. However, it is limited to the visualization of macroscopic tissue pathology. In contrast, quantitative MRI offers a more sensitive method for diagnosing early pathological changes, as it enables the detection of microstructural processes. The menisci play an important role in joint health. They undergo structural changes in osteoarthritis, including alterations in water content and collagen structures, as well as deviations in proteoglycan content. Different studies have shown the potential of special MRI sequences to identify these changes, e.g., T2 relaxation time. In this study, canine menisci of elderly dogs without clinical evidence of hindlimb lameness were examined histologically and using MRI. Our results showed that clinically healthy elderly dogs exhibited slight histological, probably age-related, degenerative changes in the menisci, but did not reveal significant radiological evidence of chronic inflammatory and degenerative changes, including no significant changes in T2 relaxation time. ABSTRACT: Osteoarthritis is a chronic disease that often affects the canine stifle joint. Due to their biomechanical function, the menisci in the canine stifle play an important role in osteoarthritis. They compensate for the incongruence in the joint and distribute and minimize compressive loads, protecting the hyaline articular cartilage from damage. Meniscal degeneration favors the development and progression of stifle joint osteoarthritis. Qualitative magnetic resonance imaging (MRI) is the current golden standard for detecting meniscal changes, but it has limitations in detecting early signs of meniscal degeneration. A quantitative MRI offers new options for detecting early structural changes. T2 mapping can especially visualize structural changes such as altered collagen structures and water content, as well as deviations in proteoglycan content. This study evaluated T2 mapping and performed a histological scoring of menisci in elderly dogs that had no or only low radiographic osteoarthritis grades. A total of 16 stifles from 8 older dogs of different sex and breed underwent ex vivo magnet resonance imaging, including a T2 mapping pulse sequence with multiple echoes. A histological analysis of corresponding menisci was performed using a modified scoring system. The mean T2 relaxation time was 18.2 ms and the mean histological score was 4.25. Descriptive statistics did not reveal a correlation between T2 relaxation time and histological score. Ex vivo T2 mapping of canine menisci did not demonstrate histological changes, suggesting that early meniscal degeneration can be present in the absence of radiological signs of osteoarthritis, including no significant changes in T2 relaxation time.