Detecting Subtle Meniscal Degeneration in Dogs: MTsat and T1 Mapping Show Promise

Magnetisation transfer, T1 and T2 relaxation in canine menisci of elderly dogs—an ex vivo study in stifle joints*

Lena Bunzendahl, Amir Moussavi, Martina Bleyer, Stephan Neumann, Susann Boretius

Background
Degenerative changes in the menisci contribute significantly to osteoarthritis (OA) of the canine stifle joint, particularly in elderly dogs. Although magnetic resonance imaging (MRI) is increasingly used for joint diagnostics, its application to early meniscal degeneration remains limited. This study expands on previous work evaluating T2 relaxation times by exploring additional quantitative MRI parameters—T1 relaxation time, T2* relaxation time, magnetisation transfer ratio (MTR), and magnetisation transfer saturation (MTsat)—to assess their sensitivity in detecting subtle microstructural changes in the canine meniscus.

Methods
This ex vivo study analysed 30 menisci (15 medial, 15 lateral) from 15 stifle joints of 8 elderly dogs (aged 10–17 years) without clinical signs of lameness or instability. MRI scans were performed at 3 Tesla, using multiple sequences to map T1, T2*, MTR, and MTsat. Histological scoring of menisci assessed cellularity, proteoglycan and collagen content, and organisation. Statistical comparisons, including ANOVA, Pearson correlation, and paired t-tests, evaluated the relationship between MRI parameters and histological findings.

Results
Most menisci exhibited only mild degenerative changes. T2* and MTR did not correlate significantly with any histological scores. However, MTsat values were significantly higher in menisci with elevated proteoglycan content, and apparent T1 relaxation time (T1app) was inversely correlated with proteoglycan content but positively associated with cellularity. A lower collagen-to-proteoglycan ratio also correlated with higher MTsat values. No statistically significant differences in MRI parameters were found between medial and lateral menisci, although medial menisci exhibited higher proteoglycan scores and a trend toward lower MTR.

Limitations
The study's findings are constrained by its ex vivo design using formalin-fixed tissues, which may affect relaxation times. The sample included only mildly degenerated menisci without healthy or severely diseased controls, and the histological scoring system offered limited resolution for subtle changes. Additionally, the study did not differentiate between meniscal subregions (e.g., horns vs. body), which could exhibit differing degeneration profiles.

Conclusions
MTsat and T1app demonstrated potential as non-invasive markers for early meniscal degeneration in elderly dogs, correlating with proteoglycan content and cellularity, respectively. These parameters could enhance early diagnosis of OA-related meniscal changes, though further in vivo studies including a wider range of degenerative severity are necessary to confirm their diagnostic value and establish clinical utility.

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