The passive elastic moment about the in vivo human knee joint

INTRODUCTION The literature contains numerous biomechanical models which attempt to determine how force is distributed amongst muscles crossing a joint during a movement (e.g., Davy and Audu, 1987). In order for a specific movement to be produced the muscles must interact with four types of stiffness: gravitational, inertial, viscous, and elastic. Gravity and inertia are usually always accounted for in a model, however viscosity and elasticity are often neglected. The effects of knee joint viscosity have been discussed in another abstract by the same authors in these proceedings. Various investigators (e.g. Smith, 1957; Hatze, 1975; Engin, 1985; and Mansour and Audu, 1986) have attempted to determine the passive elastic moments about the knee joint. Most of these studies differed in purpose and protocol and as a result much of the database remains incomplete and unclear. For example the moments measured at full extension ranged from about 2 N.m to 66 N.m. Regardless of the lack of data it is clear that the elastic moments rise sharply as the mechanical limits of the joint are approached. The purpose of the present investigation was to measure the passive elastic moments about the knee joint over the full range of flexion-extension for a normal subject sample.