Implications of range of motion requirements for the laxity of ligaments in a lumbar finite element model.

Finite element models of the lumbar spine often adopt ligament properties from tensile tests without accounting for possible differences between testing and in situ initial ligament length. Such differences could result in laxities or preloads at the beginning of a simulation that would affect the ligament forces, tangent stiffness, and the posture at which they fail. In vivo and in vitro human experimental data reported laxities or preloads.