Changes in qMRI relaxation times and 3D pose of meniscus with load and flexion at 3T

Knee osteoarthritis (OA) is a degenerative joint disease that afflicts about 13% of the Canadian population. Unfortunately, there is no cure available for this progressive disease and affected individuals have to deal with the symptoms for the rest of their lives. Therefore, the best available course of action is to try preventing OA and diagnose the disease at early stages to prevent the progress; however, unfortunately, it is a clinical challenge to detect OA before gross-morphological alterations appear. OA is usually associated with injuries to the meniscus which is a tissue with a key role in load bearing and stability of the knee joint. Meniscal injuries are more common during knee flexion, however, research studying the behaviour of the meniscus under load and during flexion has been limited due to the challenges in non-invasive assessments of the meniscus. One of the most suitable techniques to study this tissue non-invasively is the quantitative magnetic resonance imaging technique (qMRI) since it provides images with superior soft tissue resolution as well as numerical values that represent the tissue’s health. Two of the most common qMRI techniques are T2 and T2* relaxation times which correlate with meniscal biochemical composition and structure. Thus, they are expected to be sensitive to the changes in the meniscal structure associated with knee loading and flexion. This project is exploratory research to determine if meniscus T2 and T2* relaxation times change in response to load and flexion. \nFor this project, six human cadaver knee specimens and five healthy participants were imaged using a 3T MRI scanner to obtain T2 and T2* images. Cadavers were scanned unloaded and under an axial load of 0.5 to 0.75 body weight stimulating prolonged standing. To consider the effect of the time-dependent viscoelastic nature of the meniscus, scans were performed after 110 minutes of loading. Healthy participants were scanned with knees in unloaded-fully extended and loaded-flexed of 0.25 body weight and a 30° flexion angle. The Wilcoxon-singed rank test was used to compare the mean value and texture features of the T2 and T2* relaxation time maps of the meniscus between the unloaded and loaded conditions and between the extended and flexed positions. In addition, the morphological images were used to assess the translation of the meniscus during knee flexion and under axial load. \nResults of this study showed significant changes in meniscal T2 and T2* mean values and some of the texture features in response to load and knee flexion. A significant reduction was found in mean T2 and T2* relaxation times from the unloaded and loaded conditions in cadavers. Also, significant changes were observed in texture features of T2 and T2* relaxation time maps between unloaded and loaded meniscus indicating a decrease in the overall heterogeneity of meniscal maps in response to load. A significant increase in mean T2 value and overall heterogeneity of the meniscal maps were found in response to loaded flexion in healthy participants. In addition, from the morphological images, a posterior translation of the meniscus was observed during knee flexion while this movement was negligible under axial loads. \nThese results indicate that T2 and T2* relaxation times are sensitive to changes in the meniscus with load. Further work needs to be done to determine how the changes in relaxation times can be used to detect diseases such as OA at early stages before the observation of degenerative morphological changes.

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