New Mechanics of Knee Joint Injury

The prediction and prevention of knee joint injury is an important aspect of preventive health science. This paper proposes a new coupled–loading–rate hypothesis, which states that the main cause of knee injury is a Euclidean jolt, or SE(3)−jolt, an impulsive loading that strikes knee in several coupled degrees-of-freedom simultaneously. Informally, it is a rate-of-change of acceleration in 6-degrees-of-freedom times the body mass, which happens when most of the body mass is on one leg with a semi-flexed knee – and then, caused by some external shock, the knee suddenly ‘jerks’. This can happen in running, skiing, sports games (e.g., soccer, rugby) and various crashes/impacts. To show this formally, based on the previously defined covariant force law, we formulate the coupled Newton–Euler dynamics of the knee motions and derive from it the corresponding coupled SE(3)−jolt dynamics. The SE(3)−jolt is the main cause of two forms of discontinuous knee injury: (i) mild rotational disclinations and (ii) severe translational dislocations. Both the knee disclinations and dislocations, as caused by the SE(3)−jolt, are described using the Cosserat multipolar viscoelastic continuum model.