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Meniscal Motion

As the knee passes through a range of motion, the menisci move with respect to the tibial articular surface. A classic study demonstrated that from 0 degrees to 120 degrees of knee flexion the mean meniscal excursion (defined as the average anteroposterior displacement of the anterior and posterior meniscal horns along the tibial plateau in the midcondylar, parasagittal plane) of the medial meniscus was 5.1 (±0.96) mm while that of the lateral meniscus was 11.2 (±3.27) mm.

The lack of bony opposition (i.e., convex femoral condyle and tibial plateau), an unconstrained peripheral margin, and the close approximation of its central tibial attachment appear to allow the lateral meniscus a greater degree of movement.

Rotation of the knee joint also has an effect on meniscal motion with a greater effect being observed in the lateral meniscus. The posterior oblique fibers of the MCL appear to limit the movement of the medial meniscus in rotation, which may place it at increased risk of tear during tibiofemoral rotation.

In addition to their anterior-posterior translation, the menisci deform to remain in constant congruity with the tibial and femoral articular surfaces throughout the full range of joint motion. This allows the meniscus to provide additional joint stability.

The anterior horn segments of the medial and lateral menisci demonstrate differing mobility compared with posterior horn segments. This differential allows the menisci to assume a decreasing radius with flexion that correlates with a decreasing radius of curvature of the posterior femoral condyle.

The change in radius enables the menisci to maintain congruity with the articulating surfaces throughout flexion. The greatest deformation appears to occur at the anterior horn of the medial meniscus as it moves onto the tibial plateau with flexion and is manifested as an increase in the concavity of the superior articulating meniscal surface. This is probably due to the increasing load resulting from femoral flexion.

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