Marathon Running Transiently Causes Medial Meniscus Extrusion: Recovery Time Course and Factors Associated With Extrusion.

Meniscal recovery time following marathon running remains unknown, despite the need for practical recommendations on post-race return to training. We aimed (1) to characterize the time course of medial meniscus extrusion (MME) after a full marathon and (2) to identify baseline factors associated with the magnitude of the acute increase in MME. One hundred recreational runners (200 knees; mean age 47.2 years; 77 men, 23 women) from five marathons underwent weight-bearing, fully extended-knee portable ultrasonography at baseline and immediately post-race, and 90 runners (180 knees) were reassessed on post-race Days 1-5. Meniscus extrusion was measured as the distance from the medial tibial plateau to the outer meniscal edge. Baseline medial-to-lateral load distribution was quantified as walking knee adduction moment (KAM) impulse from a tibia-mounted inertial measurement unit, normalized to body mass and height. Linear mixed-effects models evaluated associations between acute extrusion change and candidate predictors. Mean baseline MME was 1.14 mm (95% CI 1.06-1.22) and increased to 1.57 mm (1.49-1.66) immediately post-race, a 38% increase (mean ΔMME 0.44 mm, 0.41-0.47; p < 0.001). MME remained significantly elevated through Day 3 (p < 0.01) but returned to baseline from Day 4 onward (p > 0.05). In multivariable analysis, a greater acute increase was independently associated with higher normalized KAM impulse (β = 0.24, 95% CI 0.10-0.37), higher BMI (β = 0.22, 0.09-0.36), and higher monthly running distance (β = 0.18, 0.04-0.31), with a borderline association for age (β = 0.15, -0.00 to 0.31). MME increased transiently after a marathon and returned to pre-race levels by approximately Day 4; whether this transient change has clinical consequences, or warrants a specific recovery interval, requires further study.