The menisci are semi-lunar shaped fibrocartilages located between the femur and tibia of the knee joint. They are of decisive importance for the knee joints health since traumatic pathologies lead to degenerative cartilage changes and post-traumatic osteoarthritis (PTOA) in the long term.
In a healthy state, friction in the joint is extremely low. This is ensured by a very effective interplay between the articular cartilage, the menisci and the synovial fluid. In this context only very little is known, how meniscus injuries initiate tribological changes within the knee joint and how they possibly contribute to PTOA acceleration.
An in-vitro tribological study on six ovine stifle joints was performed at the Institute of Orthopaedic Research and Biomechanics in Ulm, while the influence of three different medial meniscus states (intact, simulation of a medial posterior root tear and medial total meniscectomy) on the whole knee joint friction was determined. The knee joints were tested in a passive pendulum friction setup under both, simulating the loading that occurs during the stance and swing phase of an ovine gait cycle. The three-dimensional kinematics of the joints was recorded using a motion capturing system and the joint motion in the sagittal plane (flexion-extension) was used to calculate the whole joint friction using two different constitutive mathematical models (boundary friction model from Stanton and viscous friction model from Crisco et al.).
This study indicated that neither a simulated posterior medial meniscus root tear nor the removal of the medial meniscus resulted in an initially increased whole joint friction. 
 de Roy et al., Meniscus injury and its surgical treatment does not increase initial whole knee joint friction, Frontiers in Bioengineering and Biotechnology (2021)
Find out more about this study here: https://www.frontiersin.org/articles/10.3389/fbioe.2021.779946/full