New Mechanics of Generic Musculo-Skeletal Injury

Prediction and prevention of musculo-skeletal injuries is an important aspect of preventive health science. Using as an example a human knee joint, this paper proposes a new coupled– loading–rate hypothesis, which states that a generic cause of any musculo-skeletal injury is a Euclidean jolt, or SE(3)−jolt, an impulsive loading that hits a joint in several coupled degreesof-freedom simultaneously. Informally, it is a rate-of-change of joint acceleration in all 6-degreesof-freedom simultaneously, times the corresponding portion of the body mass. In the case of a human knee, this 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 and its application to traumatic brain injury [Ivancevic 2008], we formulate the coupled Newton–Euler dynamics of human joint motions and derive from it the corresponding coupled SE(3)−jolt dynamics of the joint in case. The SE(3)−jolt is the main cause of two forms of discontinuous joint injury: (i) mild rotational disclinations and (ii) severe translational dislocations. Both the joint disclinations and dislocations, as caused by the SE(3)−jolt, are described using the Cosserat multipolar viscoelastic continuum joint model.