MR imaging methods to study meniscal position and mechanics.

Objective: Meniscal mechanics have been studied widely due to the high prevalence of meniscal injuries and their strong association with knee degeneration. Computational models and cadaver studies have contributed to our understanding of the menisci but require assumptions to extrapolate to living people. Imaging modalities provide the ability to make key measurements Design: A literature search was performed using PubMed and Google Scholar, with search terms including "meniscus" and "MRI" in combination with "mechanics", "position", "shape", "movement", "size", "loaded", and "unloaded". Articles were manually reviewed and selected by consensus between the authors as constituting the most important examples of work required to illustrate the breadth of measurement and imaging approaches used in research on meniscal function. Results: MRI has been used for quantitative 3D analyses of the morphology and position of the menisci. Morphological analyses included measurements of meniscal volume, thickness, width, and bulging. Positional analyses included measurements of the overlap between the meniscal surface and tibial joint surface, the amount of extrusion, and the percentage of joint surface area and meniscal area that were covered or uncovered. Open MR scanners have been used to measure the movement of the menisci from full extension to deep flexion. MR compatible loading devices have been used to study the effect of loading on meniscal morphology and extrusion. Studies using these methods have found that there are differences in meniscal morphology between healthy and osteoarthritic participants, that the lateral meniscus and anterior horns have greater movement throughout flexion, and that meniscal extrusion increases under load. Conclusions: MRI has improved our insight into meniscal mechanics. Simulated weightbearing, open imaging through the range of knee flexion, and image processing to yield 3D measurements have all contributed to this progress. These approaches have strong potential to explore clinically motivated research questions related to meniscal mechanics.