When the clinical efficacy of spinal manipulative treatment for spinal pain has been assessed, high-velocity low-amplitude thrust (HVLAT) manipulation and mobilization have been regarded as clinical interventions giving identical and equivalent biologic effects. Hypotheses for lesions that respond to HVLAT manipulation were:
(1) Release of entrapped synovial folds or plica,
(2) Relaxation of hypertonic muscle by sudden stretching,
(3) Disruption of articular or periarticular adhesions, and
(4) Unbuckling of motion segments that have undergone disproportionate displacements.
Evans W (2002) reviewed is to critically discuss previous theories and research of spinal HVLAT manipulation, highlighting reported neurophysiologic effects that seem to be uniquely associated with cavitation of synovial fluid.
Evans W’s comments on 2 separate modes of action from zygapophyseal HVLAT manipulation:
1. Intra-articular "mechanical" effects of zygapophyseal HVLAT manipulation seem to be absolutely separate from and irrelevant to the occurrence of reported "neurophysiologic" effects.
2. Cavitation should not be an absolute requirement for the mechanical effects to occur but may be a reliable indicator for successful joint gapping.
So he concluded that, identification of these claimed unique neurophysiologic effects will provide enough theoretical reason for HVLAT manipulation. Thus manipulation & mobilization are to be assessed independently as individual clinical interventions.