Menisci contribute to load distribution, damping and stabilization of the knee. Meniscal tears are a common injury in the young and active population during combined axial loading and twisting of the knee. The in situ effect of combined axial loading and knee rotation on hoop strain in the medial meniscus of human cadaveric specimens was examined.

Four fresh-frozen human cadaver knees were rigidly potted in base fixtures. Muscle tissue was removed, and the joint capsule and ligamentous structures were preserved. Through two arthrotomies, strain sensors (DVRTs) were placed in the peripheral border into the mid-substance of the medial meniscus. These DVRTs captured circumferential hoop strains e;AM, e;PM in the anteromedial and posteromedial medial meniscus. Each specimen was mounted in a knee loading simulator, driven by a biaxialmaterial test system and were axial loaded with 1,4 kN. While maintaining axial load, ± 10° tibial rotation (IR, ER) was subsequently applied at 1°/s. Tests were conducted for knees flexion between 10° and 60° in 10° intervals.

Strain reports e;AM and e;PM were highly similar for any given test. Therefore, they were averaged to express meniscal hoopstrain as e;AVG. At 30° flexion, 1.4 kN axial load yielded e;AVG =0.9%±0.4%. ER resulted in a significant strain increase (2.1%±0.8%) (p=0.003). IR caused a decrease (0.2%±0.7). At 60° knee flexion, 10° ER induced significantly less strain (1.3%±0.9%) as compared to the 10° flexed knee(2.8%±1.3). For knee flexion from 10° to 50°, combined ER and axial loading-caused significantly higher strain as compared to axial loading alone.

This study documents for the first time strain in the medial meniscus under combined axial and torsional loading. The finding that meniscal strain can increase over two-fold during 10°external rotation has implications for injury biomechanics and meniscal repair strategies.