ABSTRACT
I INTRODUCTION Deformation, both in its initiation and progression, requires the presence of at least one unstable motion segment. In addition, there must be a pathological stressor acting upon the spine. This may be absolute, resulting from the application of supraphysiological forces, or relative, whereby normally benign forces create pathological stresses when acting on an already deformed spine. The latter circumstance is summed up by the phase ‘‘deformity begets deformity.’’
