Mechanisms Underlying the Knee Adduction Moment and its Regulation: Conducive to Explaining the Aetiologies of Medial Compartment Knee Osteoarthritis

The knee adduction moment (KAM) is considered to be closely related to the occurrence and progression of medial compartment knee osteoarthritis (OA); however, the mechanisms underlying the KAM remain unclear. The current understanding of the KAM does not explain some clinical phenomena well. In this study, the process underlying the KAM is expounded from a biomechanical perspective, which explains the KAM based on the elastic energy in the gait. In addition, a possible linkage regulation mechanism between the ankle-subtalar joint complex (ASTC) and knee joint is put forward, and an intrinsic connection between this linkage regulation mechanism and changes in KAM is established. These discussions cannot only reasonably explain the clinical phenomena identified by the author, but also contribute to the explanation of the aetiologies of medial compartment OA from a biomechanical perspective. The author believes that all the adjustment movements that occur in an individual’s gait are to maintain a stable centre of gravity (CG) and comfortable gait, and at the same time save energy consumption. A reasonable amount of KAM is conducive not only to the stability of CG in gait and comfortable advancement, but also to energy saving. Factors such as trunk inclination, pace, step width, toe-out angle, body weight, femorotibial angle, muscle strength, muscle mass, and tension of the iliotibial tract may all affect the KAM in gait, but the human body can also actively adjust KAM within a certain range through a specific regulation mechanism; the iliotibial tract plays an important role in this regulation mechanism because of its unique tension band effect. When some soft tissue structures in the human body degrade (mainly due to the decreased muscle strength of the vastus lateralis, biceps femoris, gluteus medius, and gluteus minimus, as well as the decreased muscle mass of the vastus lateralis, gluteus medius, and gluteus minimus, or the increased relaxation of the iliotibial tract), the tension band effect of the iliotibial tract does not fully manifest; therefore, the KAM will not be controlled reasonably. This causes continuously increased stress in the medial compartment of the knee joint, which may be the most important biomechanical aetiology of medial compartment knee OA